Ear, nose and throat surgery (ENT surgery).  Procedures vary from minor day-case surgery (e.g. myringotomy) to major head and neck dissections. Anaesthetic considerations:

See also, Intubation, difficult; Mandibular nerve blocks; Maxillary nerve blocks

Early warning scores.  Simple scoring systems used to aid identification of critically ill patients or those at risk of further clinical deterioration. Several different systems have been described, employing different groups of physiological parameters (e.g. systolic BP, heart rate, respiratory rate, temperature, neurological status and urine output) that are weighted on the basis of their deviation from a ‘normal’ range. Early warning schemes may be used to ‘trigger’ calls for assistance from the patient’s primary team, a medical emergency team, an outreach team or others. In the UK, the modified early warning score is most commonly used.

Cuthbertson BH, Smith GB (2007). Br J Anaesth; 98: 704–6

See also, Acute life-threatening events – recognition and treatment

Earth-leakage circuit-breaker,  see Current-operated earth-leakage circuit-breaker

East–Freeman automatic vent,  see Ventilators

Eaton–Lambert syndrome,  see Myasthenic syndrome

Ebstein’s anomaly.  Congenital heart defect characterised by apical displacement of the posterior and septal leaflets of the tricuspid valve, causing ‘atrialisation’ of the right ventricle. Results in:

May lead to arrhythmias, conduction defects (especially the Wolff–Parkinson–White syndrome) and sudden death. Surgery may be indicated in severe cases.

[Wilhelm Ebstein (1836–1912), German physician]

Paranon S, Acar P (2008). Heart; 97: 237–43

See also, Congenital heart disease; Tricuspid valve lesions

ECCO₂R,  see Extracorporeal carbon dioxide removal

ECF,  see Extracellular fluid

ECG,  see Electrocardiography

Echocardiography.  Cardiac imaging using reflection of ultrasound pulses from interfaces between tissue planes. A single beam may be studied as it passes through the heart, displaying movement of tissue planes over time, usually recorded on moving paper (M mode). Alternatively, beams are directed in different directions from the same point, covering a sector of tissue; a moving cross-section may then be displayed on a screen. Analysis of the frequencies of reflected pulses may provide information about the velocity of moving structures and blood flow (Doppler effect); flow characteristics may be colour-coded and superimposed on sector images. The passage of injected saline may be studied as it travels through the heart, probably due to entrainment of small air bubbles.

Useful in diagnosing and quantifying valvular heart disease, congenital heart disease, patent foramen ovale, myocardial and pericardial disease, and in assessing myocardial function. Techniques for the latter involve measurement of left ventricular dimensions and provide information about ejection fraction and cardiac output. Doppler techniques may be used to estimate pressure gradients across valves, as the gradient is related to the difference in velocities across the stenosis. Abnormalities of ventricular wall movement may occur in the early stages of myocardial ischaemia, before ECG changes occur.

‘Focused’ echocardiography consists of an abbreviated examination using limited views; increasingly performed by non-cardiologists to guide immediate management in emergency or critical care environments.

Transoesophageal echocardiography gives a good view of much of the heart, and has been used perioperatively and in ICU.

Eclampsia.  Convulsions caused by hypertensive disease of pregnancy (pre-eclampsia).

Incidence is 2–3 cases per 10 000 births in the UK. Occurs antepartum in 45% of cases, intrapartum in 20% and postpartum in 35% (usually under 2–4 days postpartum but eclampsia has been reported up to 2–3 weeks afterwards). Only 40% of cases have hypertension and proteinuria in the preceding week, and in many cases premonitory signs of headache, photophobia and hyperreflexia do not precede convulsions, which may recur if untreated. Mortality is almost 2% in the UK, usually from CVA; perinatal mortality is 5–6%. Maternal mortality is up to 25% mortality in developing countries.

Sibai BM (2005). Obstet Gynecol; 105: 402–10

ECMO,  see Extracorporeal membrane oxygenation

Ecothiopate iodide.  Organophosphorus compound, used as eye drops to treat severe glaucoma. Plasma cholinesterase levels may be reduced for 3–4 weeks following its use, prolonging the action of suxamethonium.

Ecstasy,  see Methylenedioxymethylamphetamine

ECT,  see Electroconvulsive therapy

Ectopic beats,  see Atrial ectopic beats; Junctional arrhythmias; Ventricular ectopic beats

ED₅₀,  see Therapeutic ratio/index

Edema,  see Oedema

Edetate,  see Cyanide poisoning; Sodium calcium edetate

EDRF,  Endothelium-derived relaxing factor, see Nitric oxide

Edrophonium chloride.  Acetylcholinesterase inhibitor, used to reverse non-depolarising neuromuscular blockade, and in the diagnosis of myasthenia gravis and dual block. Has also been used to treat SVT. Binds reversibly to acetylcholinesterase, with onset of action 30 s and duration of about 5 min. Of faster onset than neostigmine, and with fewer muscarinic side effects.

EEG,  see Electroencephalography

Efficacy.  Maximal effect attainable by a drug; e.g. morphine is more efficacious than codeine. A pure antagonist has an efficacy of zero.

See also, Dose–response curves; Potency

EGTA,  Esophageal gastric tube airway, see Oesophageal obturators and airways

Eicosanoids.  Collective term used for products of arachidonic acid metabolism involved in inflammation, immunity and cell signalling. Include:

Eisenmenger’s syndrome.  Right-to-left cardiac shunt developing after long-standing left-to-right shunt; shunt reversal occurs because increased pulmonary blood flow results in increased pulmonary vascular resistance and pulmonary hypertension. Prognosis is poor, since pulmonary hypertension is not affected by surgical correction of the shunt. May follow any left-to-right shunt, although the original description referred to VSD. May occur late in ASD and patent ductus arteriosus.

Anaesthesia is tolerated poorly; reduction in peripheral resistance increases the shunt with worsening hypoxaemia, that in turn further increases pulmonary vascular resistance. Factors that decrease pulmonary blood flow also exacerbate the right-to-left shunt, e.g. IPPV. Risk of systemic air embolism following iv injection of bubbles is high.

Pregnancy is also tolerated badly; maternal mortality is 30–50%. Very cautious epidural anaesthesia has been suggested if pregnancy progresses to term.

Heart–lung transplantation is the only definitive treatment.

[Victor Eisenmenger (1864–1932), German physician]

Ejection fraction.  Left ventricular stroke volume as a fraction of end-diastolic volume.

Useful as an indication of the heart’s ability to eject stroke volume. Measured using nuclear cardiology, echocardiography, pulmonary artery catheterisation or contrast angiography. Normally greater than 60%. May also be determined for the right ventricle.

Ejector flowmeter.  Device used for scavenging from anaesthetic breathing systems. O₂ or air passing through the ejector causes entrainment of waste gases by the Venturi principle. The rate of removal is adjusted using a flowmeter until it equals the rate of fresh gas supply. Several litres of driving gas may be required per minute, at a pressure of at least 1 bar.

EKG,  see Electrocardiography

Elastance.  Reciprocal of compliance. Total elastance for lungs + chest wall is approximately 10 cmH₂O/l.

Elbow, nerve blocks.  Used for surgery to the hand and wrist; useful for supplementation of a brachial plexus block. May be performed using surface anatomy landmarks, a peripheral nerve stimulator and/or ultrasound guidance.

See also, Brachial plexus block; Wrist, nerve blocks

Elderly, anaesthesia for.  Increasingly common as the population ages. Mortality and morbidity are higher in older patients.

In general, patients are frailer, with greater likelihood of perioperative complications and slower healing. Attention to detail (e.g. fluid balance) is more important than with younger patients, since physiological reserves are less. Smaller doses of most agents are required, and arm–brain circulation time is prolonged.

Warming blankets, adequate humidification and appropriate monitoring (e.g. of urine output) should be provided. Postoperative O₂ therapy should be instituted immediately and possibly continued for 1–3 days, since hypoxia may readily occur.

The ‘physiological age’ of the patient is usually more relevant than the chronological age: e.g. fit 90-year-olds may present less risk than frail 70-year-olds.

Electrical symbols.  Used to denote components of electrical circuits. Specific symbols are also used on electrical equipment to indicate the safety features or other characteristics or instructions (Fig. 58).

See also, Electrocution and electrical burns

Electroacupuncture,  see Acupuncture

Electrocardiography (ECG).  Recording and display of cardiac electrical activity. First performed through the intact chest in 1887 by Waller. Used for investigation of cardiac disease, particularly ischaemic heart disease and arrhythmias, also for monitoring cardiac rhythm.

Standard modern ECG recordings are obtained from different combinations of chest and limb electrodes, each set recording along a different vector, thus providing information about a different part of the heart. A ‘lead’ refers to the recorded voltage difference between two electrodes; one acts as the positive electrode, the other as the negative (or reference) electrode. The limb leads (I–III, aVR, aVL, aVF) record in the frontal plane, the chest leads (V_1–6) in the transverse plane. The leads may be represented on the chest and heart as in Figure 59a. Thus abnormalities of the inferior portion of the heart will be demonstrated in the ‘inferior’ leads (i.e. aVF, II and III), and abnormalities of the anterolateral heart in aVL, I, II, etc. V_1–2 demonstrate electrical activity from the right side of the heart, V_3–4 from the septum and front, and V_5–6 from the left side. Depolarisation towards a positive electrode (or repolarisation away) results in a positive deflection; depolarisation away (or repolarisation towards) causes negative deflection.

Output is displayed on an oscilloscope or recorded on moving paper. Frequency range is 0.5–80 Hz. Magnitude of deflection is proportional to the amount of heart muscle, but reduced by passage through the chest. Skin resistance is reduced by cleaning with alcohol and skin abrasion. Electrodes are usually silver/silver chloride with chloride conducting gel, to reduce generation of potentials in the electrode by the recorded potential, and reduce impedance variability. Electrodes of differing compounds may generate potential by a battery-like effect. Interference may result from muscle activity, radiofrequency waves from diathermy and other equipment and inductance by electrical equipment. Differential amplifiers with common-mode rejection (elimination of signals affecting both input terminals of a recording system) are used to reduce interference.

During anaesthesia/intensive care, a three-electrode system (allowing recording of the three standard limb leads) is often used and lead II is selected for continuous rhythm monitoring. A five-electrode system incorporating a right leg and precordial electrode (in addition to the right arm/left arm/left leg electrodes) enables recording of an anterior chest lead; useful when monitoring left ventricular myocardial ischaemia. The CM₅ lead configuration (central manubrium V₅) also ‘looks at’ the left ventricle:

Other lead configurations are also used, e.g. CH₅, CC₅ and CS₅, with right arm electrode on the patient’s head, right side of chest and subscapular regions respectively. The CB₅ configuration with electrode over the right scapula is better for demonstrating arrhythmias.

24-hour ambulatory ECG monitoring is performed for assessing arrhythmias and their therapy, and detecting myocardial ischaemia. Some devices run continuously whilst others are activated by the patient when he or she experiences symptoms. 24-hour tapes have been used to investigate arrhythmias and ischaemia perioperatively.

[Augustus Desiré Waller (1856–1922), French-born British physiologist; Willem Einthoven (1860–1927), Dutch physician and physiologist]

See also, Cardiac cycle; Heart block: His bundle electrography; Myocardial infarction

Electroconvulsive therapy (ECT).  Passage of electric current, usually alternating, across the skull to produce convulsions; used to treat severe depressive psychosis. 30–45 J is usually given over 0.5–1.5 s; it may also be given as repeated ultra-short bursts. Usually given in courses over a few weeks. First used in the late 1930s.

Brief general anaesthesia is required; partial muscle relaxation is usually provided, to allow assessment of resultant convulsions whilst reducing the risk of vertebral fractures and other trauma.

Ding Z, White PF (2002). Anesth Analg; 94: 1351–64

Electrocution and electrical burns.  Hazard of using electrical equipment; during anaesthesia, malfunction or improper use of diathermy, monitoring equipment or infusion devices may cause sudden cardiac arrest or burns.

Current flows between opposite poles for direct current, or from live wire to earth for alternating current, e.g. mains power. Mains voltage is 240 V at 50 Hz in the UK and 110 V at 60 Hz in the USA. Current flows via the path of least resistance; if this path includes a person, e.g. patient or doctor via earthed equipment, ECG lead or floor, electrocution occurs.

Medical electrical equipment is marked with the appropriate electrical symbols to indicate its level of safety features (see Fig. 58).

Electroencephalography (EEG).  Recording of electrical activity of the brain. Signals from different combinations of 20–22 scalp electrodes are presented as 16 continuous traces on paper sheets. Shape, distribution, incidence and symmetry of waves are analysed to give information about underlying brain activity, in conjunction with clinical details. Concealed abnormalities may be revealed during voluntary hyperventilation.

As age increases, infantile beta activity is slowly replaced by adult alpha activity. Characteristic patterns occur in normal sleep. During anaesthesia, alpha rhythms become depressed, and are replaced by theta and delta rhythms. Slow rhythms may reappear at deeper levels of anaesthesia, followed by periods of little or no activity separated by bursts of activity (burst suppression). The pattern differs with different agents used. Perioperative use is limited by electrical interference, difficult interpretation and production of large amounts of paper. Modified forms of EEG have therefore been developed, e.g. cerebral function monitor, cerebral function analysing monitor, power spectral analysis, bispectral index monitor. Used to investigate intracranial activity in, e.g., head injury, epilepsy, cerebrovascular disease, coma, encephalopathies, surgery. Similar principles are involved in measuring evoked potentials.

See also, Anaesthesia, depth of

Electrolyte.  Compound that dissociates in solution to produce ions, allowing conduction of electricity; also refers to the ions themselves. Sodium, potassium, calcium, magnesium and hydrogen ions are the most important cations in the body; chloride and bicarbonate ions the most important anions.

See also, Fluids, body; Intravenous fluids

Electrolyte imbalance,  see individual disorders

Electrolyte solutions,  see Intravenous fluids

Electromagnetic flow measurement.  Relies on the principle that a moving conductor within a magnetic field induces current that is proportional to the rate of movement (Faraday’s law). Relationship of movement, field and current is described by Fleming’s right-hand rule, with thumb, forefinger and middle finger of the right hand extended at mutual right angles (e.g. forefinger pointing forward, thumb upward and middle finger medially). If the forefinger points in the direction of the field, and thumb in the direction of movement, the middle finger will point in the direction of the induced current.

Electromagnets within a semicircular probe are placed around an artery, and the moving blood is the conductor. The potential difference between the walls of the vessel is measured and average velocity of blood flow determined. Alternating current is used for magnetic field generation, to avoid the effect of induction of current in the detector electrode circuit.

[Michael Faraday (1791–1867), English chemist; Sir John Fleming (1849–1945), English electrical engineer]

Electromechanical dissociation (EMD).  Term used to describe a cardiac state in which organised electrical depolarisation occurs throughout the myocardium, but there is no synchronous shortening of the myocardial fibres and mechanical contractions are absent. Part of the spectrum of pulseless electrical activity, though the latter also includes mechanical contractions too weak to produce a detectable cardiac output.

See also, Cardiac arrest

Electromyography (EMG).  Recording of spontaneous or evoked electrical activity from skeletal muscle; usually combined with nerve conduction studies that measure the velocity of nerve conduction following stimulation at different sites along a nerve pathway. Thus useful in distinguishing between disorders of muscle, isolated or generalised nerve disease or lesions, and disorders affecting the neuromuscular junction.

In anaesthesia, it has been used to determine frontalis muscle tone to monitor depth of anaesthesia. Also used in neuromuscular blockade monitoring; nerve stimulation and muscle action potential recording are achieved using surface skin electrodes, although needle electrodes have been used. Less convenient than devices measuring mechanical muscle response, it may detect electrical activity when mechanical contraction is undetectable.

Is also used to investigate critical illness polyneuropathy and the neuromuscular function of the eye, bladder, GIT, etc.

See also, Anaesthesia, depth of

Electron capture detector.  Device used in the analysis of gas mixtures that have been separated by, for example, gas chromatography; particularly useful in detecting halogenated compounds. Electrons within an ionisation chamber pass from cathode to anode, but are ‘captured’ by the halogenated substance blown through the chamber. The current passing across the chamber is therefore reduced, depending on how many electrons are captured. Used to quantify the amount of known substances, not to identify unknown ones.

See also, Gas analysis

Embryo,  see Environmental safety of anaesthetists; Fetus, effect of anaesthetic agents on

EMD,  see Electromechanical dissociation

Emergence phenomena.  Usually consist of agitation and confusion, with laryngospasm, breath-holding, etc.; may be equivalent to the second stage of anaesthesia seen on induction, or be due to other causes of confusion, including the central anticholinergic syndrome and dystonic reactions. Hallucinations and frightening dreams are common after ketamine.

Emergency surgery.  Usually refers to surgery occurring within 24 h of admission or diagnosis; i.e. includes those cases where surgery follows resuscitation, and those where surgery and resuscitation proceed simultaneously (e.g. ruptured aortic aneurysm).

The balance between the need for preoperative treatment and urgency of surgery is sometimes difficult, but inadequate preoperative correction of fluid and electrolyte disturbance is consistently associated with increased perioperative mortality. Treatment of cardiac failure is also important whenever possible. Careful preoperative assessment and discussion with the surgeon are vital. Anaesthetic management is as for routine surgery but with the above considerations. Thus smaller doses of drugs than usual are given initially. Rapid sequence induction is usually employed. Measures against heat loss are important. Invasive monitoring and postoperative HDU/ICU and IPPV should be considered.

Regional techniques are particularly useful for limb surgery, but epidural/spinal anaesthesia is hazardous if hypovolaemia is present.

Special Issue (2013). Anaesthesia; 68 s1: 1–124

See also, specific procedures; Anaesthetic morbidity and mortality

Emesis,  see Vomiting

Emetic drugs.  Given to empty the stomach, e.g. following poisoning, or preoperatively to reduce risk of aspiration pneumonitis. Now rarely used, because of poor efficacy and the risk of causing aspiration; particularly dangerous after ingestion of corrosive or petroleum derivatives, or in unconscious patients. Include apomorphine and ipecacuanha; copper sulphate and sodium chloride are no longer used.

EMG,  see Electromyography

EMLA cream (Eutectic mixture of local anaesthetics).  Mixture of prilocaine base 2.5% and lidocaine base 2.5% as an oil–water emulsion. The melting point of each local anaesthetic agent is lowered by the presence of the other; the resultant mixture has a melting point of 18°C and is effective in providing analgesia of the skin 60–90 min after topical application and covering with an occlusive dressing. May continue to be released from skin depots even after removal of surface cream. Particularly useful in children. May produce blanching of the skin; increases in methaemoglobin have been reported several hours after application.

Uses described include analgesia for venepuncture, venous and arterial cannulation, lumbar puncture, epidural injection, superficial skin surgery and relief of tourniquet pain during IVRA.

EMMV,  Extended mandatory minute ventilation, see Mandatory minute ventilation

EMO inhaler,  see Vaporisers

Emphysema,  see Chronic obstructive pulmonary disease

Emphysema, subcutaneous.  Presence of gas in subcutaneous tissues.

Often palpable under the skin, and may be visible on X-ray. The gas is slowly absorbed once the cause is treated. Multiple skin puncture has been performed to allow escape of gas, and high F_IO₂ suggested to increase absorption (O₂ being more soluble than nitrogen), but the value of these measures is unknown.

Empyema.  Collection of pus within the pleural cavity. A complication of chest trauma (especially if haemothorax was present), pneumonia, chest drainage, thoracic surgery and subdiaphragmatic abscess. Clinical features include pyrexia, chest pain and productive cough. CXR features are those of a pleural effusion; if encapsulated it may resemble a pulmonary cyst. Diagnosis is confirmed by imaging and aspiration of pus. Treatment depends on aetiology but includes antibacterial drugs, chest drainage (sometimes requiring ultrasound or CT scan guidance) and surgery. May rarely lead to bronchopleural fistula.

Enalapril maleate.  Angiotensin converting enzyme inhibitor, used to treat hypertension and cardiac failure (including following MI). A prodrug, it is converted to enalaprilat by hepatic metabolism. Longer acting than captopril, with onset of action within 2 h; half-life is up to 35 h via active metabolites.

Encephalitis.  Acute infection of the brain parenchyma, usually caused by a virus, that results in diffuse inflammation affecting the meninges. Usually presents with the triad of fever, headache and altered mental status. Other clinical features include neck stiffness, lethargy, confusion, coma, encephalopathy, focal neurological signs and epilepsy.

Differential diagnosis includes meningitis and cerebral abscess. Investigations include CSF examination (mild increase in protein, lymphocytosis, normal glucose in viral encephalitis), CT and MRI scanning, EEG and viral titres/cultures from blood and CSF. Treatment is largely supportive, with tracheal intubation and IPPV for patients with depressed consciousness. Aciclovir should be given to all cases of suspected viral encephalitis whilst a definitive diagnosis is sought.

Long SS (2011). Adv Exp Med Biol; 697; 153–73

Encephalopathy.  Diffuse disorder of cerebral function with or without focal neurological deficit. Usually results in delirium, stupor and coma. Aetiology is as for coma.

Endobronchial blockers (Bronchial blockers).  Used in thoracic surgery to isolate a portion of lung, e.g. to avoid air leaks during IPPV or prevent contamination of normal lung with secretions, pus or blood. Less often used now, except for paediatric surgery, endobronchial tubes being more popular and versatile. Previous versions were made of red rubber; modern versions are thin plastic catheters with an inflatable distal cuff, usually inserted under direct vision via a bronchoscope, either before tracheal intubation with a standard tracheal tube or after intubation with a specific tube–blocker combination.

Endobronchial tubes.  Used in thoracic surgery to allow sleeve resection of the bronchus, or to isolate infected lung or potential air leak, e.g. in bronchopleural fistula or emphysematous lung cysts. Other pulmonary surgery (e.g. pneumonectomy/lobectomy, pleural, aortic, oesophageal and mediastinal surgery) is possible with conventional tracheal tubes, although surgery may be made easier by collapsing one lung. Also used in ICU in patients with severe, unilateral lung injury or bronchopleural fistula. Risks of one-lung anaesthesia should be considered before use.

Different tubes, usually made of red rubber, were developed in the 1930s–1950s, and included single-lumen and double-lumen designs, for insertion into the left (most commonly) or right main bronchus. Modern double-lumen tubes are usually plastic, with thinner walls and low-pressure cuffs, and have the following features (Fig. 60):

Complications are as for tracheal intubation (see Intubation, complications of). Bronchial rupture may occur if excessive volumes are used for cuff inflation. Incorrect positioning, or movement during positioning of the patient, may result in uneven ventilation and impaired gas exchange.

See also, Tracheobronchial tree

Endocardial viability ratio (EVR).  Ratio of diastolic pressure time index to tension time index, obtained by recording left ventricular and aortic root pressure tracings (Fig. 61). May indicate myocardial O₂ supply/demand ratio and likelihood of myocardial ischaemia (thought to be likely when the ratio is under 0.7).

Endocarditis, infective.  Infective inflammation of the endocardial lining of the heart and valves, most commonly the aortic valve (previously the mitral valve). Commonly associated with abnormal valves (e.g. rheumatic, degenerative or prosthetic valves) or congenital heart disease, but approximately 50% of cases involve normal valves. Men are twice as commonly affected. Nosocomial endocarditis may result from catheter-related sepsis or invasive procedures (e.g. endoscopy, dental extractions). Results in tissue destruction and vegetations of platelets, macrophages and organisms, with systemic embolisation. Systemic immune complex deposition may also occur. Overall mortality is ~40%.

Treatment is supportive with antimicrobial therapy depending on the infecting organism. Treatment usually lasts 4–6 weeks. Cardiac valve replacement is necessary in ~50%; indications include CVS instability associated with valve destruction, persistent fever despite prolonged antimicrobial therapy, presence of highly resistant organisms, prosthetic valve involvement and large vegetations with embolic potential. Prophylaxis in structural disease is as for congenital heart disease.

[Moritz Roth (1849–1914), Swiss physician; Sir William Osler (1849–1919), Canadian-born US and English physician; Theodore Caldwell Janeway (1872–1917), US physician]

European Society of Cardiology Task Force (2009). Eur Heart J; 30: 2369–413

Endocrine disorders,  see individual diseases

Endomorphins.  Endogenous opioid peptides for µ opioid receptors. Produce spinal and supraspinal analgesia experimentally; have been found in the human brain, although their role is uncertain.

Endorphins.  Endogenous opioid peptides derived from β-lipotropin, secreted by the anterior pituitary and hypothalamus. β-Endorphin (31 amino acids) is the most potent endogenous opioid, active mainly at µ and δ opioid receptors. Also inhibits GABA and promotes dopamine secretion. Derived from pro-opiomelanocortin (99 amino acids), from which ACTH is derived. Thought to be involved in central pain pathways, emotion, etc. May also be involved in haemorrhagic and septic shock; thought to reduce SVR, cardiac output and BP, while decreasing GIT motility and sympathetic activity and enhancing parasympathetic activity. This may explain why naloxone sometimes improves cardiovascular variables in shock.

Endothelin.  Vasoconstrictor peptide derived from vascular endothelium, involved in regulation of basal vascular tone and BP. Produced from an inactive precursor, it acts at specific endothelin receptors to cause vasoconstriction (type A receptors). Type B receptor activation may also result in production of nitric oxide and prostacyclin. May be involved in local blood flow and in various cardiovascular disorders, notably cardiac failure and pulmonary hypertension. Endothelin receptor antagonists such as bosentan (which antagonises both A and B receptors) have been investigated as possible treatments for these.

Endothelium-derived relaxing factor,  see Nitric oxide

Endotoxins.  Lipopolysaccharides (LPS) present on the surface of Gram-negative bacteria. LPS consist of: a lipid chain (lipid A), responsible for the biological effects; a core polysaccharide; and oligosaccharide side chains specific to each strain. Released when the bacteria die, and extremely toxic, probably via release and activation of many inflammatory substances, including cytokines. Endotoxaemia may be involved in the aetiology of sepsis, although it may occur in the absence of infection, and proven Gram-negative sepsis may not be accompanied by endotoxaemia. Translocation of GIT organisms or their endotoxins into the bloodstream across the gut wall has been suggested to occur in critical illness. Attempts have been made to prevent endotoxaemia by killing GIT organisms (selective decontamination of the digestive tract), and to treat established endotoxaemia with anti-endotoxin antibodies.

Wendel M, Paul R, Heller AR (2007). Intensive Care Med; 33: 25–35

See also, Bacterial translocation

Endotracheal tubes,  see Tracheal tubes

End-plate potentials.  Depolarisation potentials produced at the postsynaptic motor end-plate of the neuromuscular junction by binding of acetylcholine (ACh) to receptors. Their size and duration depend on the amount of ACh released, the number of ACh receptors free and the activity of acetylcholinesterase. Miniature end-plate potentials (under 1 mV) are thought to be produced by random release of ACh from single vesicles (quantal theory), and are too small to initiate muscle contraction. Simultaneous release of ACh from many vesicles follows depolarisation of the pre-synaptic membrane; the resultant large end-plate potential causes depolarisation of adjacent muscle membrane, and muscle contraction.

See also, Neuromuscular transmission

End-tidal gas sampling.  Gives the approximate composition of alveolar gas, unless major mismatch exists or tidal volume is very small. Useful for estimating alveolar and hence arterial PCO₂, e.g. for monitoring adequacy of ventilation. Alveolar concentrations of inhalational anaesthetic agents may also be monitored. May also indicate extent and rate of uptake of inhalational agents, if expired and inspired concentrations are compared, and the state of O₂ supply/demand. On-line multiple gas monitors are now routine, providing breath-by-breath measurements. Since the gas sampled by these is not strictly end-tidal, the sampling line being placed some distance away from the patient’s airway, the term ‘end-expiratory’ is more accurately applied. Mixing of end-expiratory gas with fresh gas may lead to inaccuracy, especially if samples are taken between the breathing system filter and the anaesthetic machine.

See also, Carbon dioxide, end-tidal; Gas analysis

Energy.  Capacity to perform work, whether mechanical, chemical or electrical. Kinetic energy is the energy of a body due to its motion; potential energy is the energy of a body due to its state or position. Thus a body on a table has potential energy due to the effect of gravity; when it falls, this is converted to kinetic energy. Similarly, the potential energy of a stretched spring is converted to kinetic energy as it recoils. The law of conservation of energy states that energy cannot be destroyed or created, but only converted to other forms of energy, e.g. heat, light, sound. Molecules within a body have potential energy due to their chemical composition and forces between them, and kinetic energy due to their movement. SI unit is the joule, although the Calorie (Cal; equals 1000 cal) is widely used for dietary energy estimations.

Energy is liberated in the body by breakdown of metabolic substrates, e.g. approximately 4 Cal/g carbohydrate and protein, 9 Cal/g fat, 7 Cal/g alcohol. It may be stored in high phosphate bonds, e.g. in ATP, and in other compounds, e.g. glycogen.

See also, Basal metabolic rate; Energy balance; Metabolism

Energy balance.  Difference between Calorie intake and energy output. If intake is less than expenditure, energy balance is negative and endogenous energy stores are utilised; if it is greater, balance is positive and the individual gains weight. Many critically ill patients (e.g. those with trauma, sepsis) have increased catabolism and glycogenolysis, insulin resistance with resultant lipolysis and increased basal metabolic rate. In order to provide adequate nutrition in these patients, it is possible to estimate energy expenditure, e.g. with indirect calorimetry using bedside devices (‘metabolic carts’). This allows measurement of O₂ and CO₂ exchange and thus respiratory exchange ratio; however such techniques are not widely used because of inaccuracies related to gas leaks from the patient/ventilator circuit and the effect of water vapour.

Normal subjects require about 25 Cal/kg/day; most critically ill patients require about 25–40 Cal/kg/day.

See also, Nitrogen balance

Enflurane.  2-Chloro-1,1,2-trifluoroethyl difluoromethyl ether (Fig. 62). Inhalational anaesthetic agent, introduced in 1966.

About 2% metabolised, the rest excreted via the lungs. Although fluoride ions may be produced by metabolism, toxic levels are usually not reached, although they have been reported in obese patients after prolonged anaesthesia. Patients with pre-existing renal impairment or receiving other nephrotoxic drugs or enzyme-inducing drugs, e.g. isoniazid, are also thought to be at risk.

Hepatitis has been reported following enflurane; cross-sensitivity with halothane has been suggested, but this is disputed.

Inspired concentrations of 1–3% are usually adequate for anaesthesia, with higher concentrations for induction.

Enkephalins.  Endogenous opioid peptides found in the CNS, especially:

Methionine enkephalin and leucine enkephalin (each 5 amino acids) are derived from proenkephalin; they are thought to be involved in the modulation of pain pathways, e.g. gate control theory of pain. Active mainly at δ opioid receptors.

See also, Endorphins

Enoxaparin,  see Heparin

Enoximone.  Selective (PDE III) phosphodiesterase inhibitor unrelated to catecholamines or cardiac glycosides. Used as an inotropic drug, particularly in cardiogenic or other types of shock, in which there is an element of heart failure (e.g. after cardiac surgery, and in patients awaiting heart transplants). Increases cardiac contractility and stroke volume with minimal tachycardia, and without increasing myocardial O₂ demand. Also causes vasodilatation (reducing both preload and afterload), thereby decreasing ventricular filling pressures. BP may fall.

Acts directly on cardiac muscle rather than adrenergic (or other) receptors.

Preparation contains alcohol, propylene glycol and sodium hydroxide (pH 12). Crystal formation may occur with glass syringes, etc., and if mixed with other drugs and dextrose solutions.

Undergoes hepatic metabolism to partially active metabolites, excreted renally.

ENT surgery,  see Ear, nose and throat surgery

Enteral nutrition,  see Nutrition, enteral

Entonox.  Trade name for gaseous N₂O/O₂ 50 : 50 mixture, supplied in cylinders at a pressure of 137 bar. Invented by Tunstall in 1962. Cylinders are coloured blue with blue/white quartered shoulders. May also be supplied by pipeline. Formed by bubbling O₂ through liquid N₂O (Poynting effect).

Cylinders must be kept above –7°C (pseudocritical temperature) to prevent liquefaction of the N₂O (a process called lamination). If this occurs and gas is drawn from the top of the cylinder, O₂ will be delivered first, followed by almost pure N₂O. In the large cylinders used for connection to a pipeline system via a manifold, gas is therefore drawn first from the bottom of the cylinder by a tube; should liquefaction of N₂O now occur, N₂O containing about 20% O₂ is delivered first. Warming and repeated inversion of the cylinders will reconstitute the gaseous mixture.

Widely used for inhalational analgesia for trauma and minor procedures, e.g. physiotherapy or change of dressings; most commonly used with a demand valve for self-administration. Onset of analgesia is rapid, with minimal cardiovascular, respiratory or neurological side effects. Should sedation occur, the patient reduces the intake and recovery rapidly occurs. Caution is required if the patient has an undrained pneumothorax, as N₂O may increase its size.

Also widely used in the UK for inhalational analgesia during labour, although there is little evidence that pain scores are reduced.

Continuous use (e.g. in ICU) has declined because of interaction of N₂O with the methionine synthase system.

[Michael Tunstall (1928–2011), Scottish anaesthetist]

See also, Obstetric analgesia and anaesthesia

Envenomation,  see Bites and stings

Environmental impact of anaesthesia.  Has attracted increasing attention through two main areas:

Suggested measures to minimise the above include:

Sneyd JR, Montgomery H, Pencheon D (2010). Anaesthesia; 65; 435–7

Environmental safety of anaesthetists.  Hazards faced may be due to:

Similar concerns exist for staff on the ICU.

Andersen MP, Nielsen OJ, Wallington TJ (2012). Anesth Analg; 114: 1081–5

See also, Contamination of anaesthetic equipment; COSHH regulations

Enzyme.  Protein accelerating a specific chemical reaction, i.e. a biological catalyst. Sensitive to pH and temperature.

Reactions involve formation of intermediate structures, with formation of reaction products and reformation of enzyme.

See also, Enzyme induction/inhibition; Michaelis–Menten kinetics

Enzyme induction/inhibition.  Certain drugs may alter the activity of enzymes involved in their metabolism, most importantly, in the liver. Induction is an increase in the amount of enzyme, caused by increased synthesis or decreased breakdown. It is usually related to the duration and extent of drug exposure. The cytochrome P₄₅₀ system is often involved. Inhibition is a reduction in the amount of enzyme or impairment of its activity.

Sweeney BP, Bromilow J (2006). Anaesthesia; 61: 159–77

EOA,  Esophageal obturator airway, see Oesophageal obturators and airways

Ephedrine hydrochloride.  Sympathomimetic and vasopressor drug, mainly used to treat hypotension (especially in spinal and epidural anaesthesia). Sometimes used in the treatment of bronchospasm and autonomic neuropathy.

Tachyphylaxis occurs with repeated administration. May cause restlessness and palpitations in overdose.

Epidural anaesthesia.  Introduction of local anaesthetic agent into the epidural space in order to induce loss of sensation adequate for surgery (the term ‘epidural analgesia’ refers to provision of pain relief, e.g. during labour). Can be divided anatomically into cervical, thoracic, lumbar and caudal. Caudal analgesia was first performed in 1901; lumbar blockade was performed by Pages in 1921 and popularised by Dogliotti in the 1920s–1930s, although it was probably introduced by Corning following his initial experiments. Continuous catheter techniques were introduced in the late 1940s.

Following injection, local anaesthetic may act at epidural, paravertebral or subarachnoid nerve roots, or directly at the spinal cord. Systemic effects may also occur.

Indications are as for spinal anaesthesia; main advantages are avoidance of dural puncture, and those related to catheter technique, i.e. allows control over onset, extent and duration of blockade. Thus used for peri- and postoperative analgesia, analgesia following chest trauma, obstetric analgesia and anaesthesia, and treatment of chronic pain. However, blockade is less intense than spinal anaesthesia, with greater chance of missed segments, and the dose of drug injected is potentially dangerous if incorrectly placed.

Opioid analgesic drugs may be injected into the epidural space to provide analgesia.

(For anatomy, path taken by needle, etc., see Epidural space.)

[Fidel Pages (1886–1923), Spanish surgeon; Achilles Dogliotti (1897–1966), Italian surgeon; Edward B Tuohy (1908–1959), US anaesthetist; John Alfred Lee (1906–1989), Southend anaesthetist; Oral B Crawford, US anaesthetist]

Epidural opioids,  see Spinal opioids

Epidural space.  Continuous space within the vertebral column, extending from the foramen magnum to the sacrococcygeal membrane of the sacral canal. The vertebral canal becomes triangular in cross-section in the lumbar region, its base anterior; the epidural space is that part external to the spinal dura. It is very narrow anteriorly, and up to 5 mm wide posteriorly.

Contains epidural fat, epidural veins (Batson’s plexus), lymphatics and spinal nerve roots. Connective tissue layers have been demonstrated by radiology and endoscopy within the epidural space, in some cases (rarely) dividing it into right and left portions.

The normal distance between the skin and the epidural space varies between 2 and 9 cm.

For the lateral approach: 1, 2, 5, 6.

See also, Epidural anaesthesia; Vertebrae; Vertebral ligaments

Epidural volume expansion,  see Combined spinal–epidural anaesthesia

Epiglottis,  see Larynx

Epiglottitis.  Infective inflammation of the epiglottis, often resulting in upper airway obstruction. Caused by Haemophilus influenzae type b in over 50% of cases. Most common in children aged 2–5 years but may also occur in adults (usually aged 20–40 years); the incidence in the UK has fallen since a specific vaccine was introduced. Classically follows an acute course, with fever, marked systemic upset, stridor and adoption of the sitting position with the jaw thrust forward and an open drooling mouth. These features, plus absence of cough, help distinguish it from croup. Epiglottitis may progress to complete airway obstruction, which may be provoked by pharyngeal examination and anxiety (e.g. due to iv cannulation). Although lateral X-rays of the neck may reveal epiglottic enlargement, they may also provoke obstruction, and clinical assessment is sufficient in severe cases. Pulmonary oedema may occur if obstruction is severe.

See also, Paediatric anaesthesia

Epilepsy.  Tendency to epileptic seizures, associated with abnormal or excessive hypersynchronous neuronal activity within the brain.

Definition of disease is difficult because certain stimuli will induce convulsions in normal subjects, e.g. hypoxia, hypo/hyperglycaemia. Usually idiopathic, especially in childhood; intracranial lesions and infections (e.g. encephalitis) must be excluded in adults presenting with a single seizure. Pyrexia is a common cause in children; other causes are as for convulsions.

Treatment is with anticonvulsant drugs, and is directed at any underlying cause.

[John Hughlings Jackson (1835–1911), English neurologist]

Perks A, Cheema S, Mohanraj R (2012). Br J Anaesth; 108: 562–71

Epinephrine,  see Adrenaline

Epistaxis.  Nasal bleeding. May occur from:

Usually follows trauma, but predisposing conditions include bleeding disorders, hereditary telangiectasia and raised venous pressure. Bleeding may be caused by nasal intubation or passage of a nasal airway, especially if a vasoconstrictor (e.g. cocaine) is not used first.

Usually managed by nasal packing but may require ligation of the maxillary or anterior ethmoidal arteries, the former via the neck or oral route, the latter from the front of the nose.

Anaesthetic management is similar to that of the bleeding tonsil (see Tonsil, bleeding).

[James L Little (1836–1885), US surgeon]

EPLS,  see European Paediatric Life Support

Epoprostenol,  see Prostacyclin

EPSP,  Excitatory postsynaptic potential, see Synaptic transmission

Eptacog alfa.  Recombinant activated coagulation factor VIIa. Prohaemostatic agent that activates the coagulation cascade mainly via factors IX and X. Used for patients with complicated coagulation disorders, both pre-existing (e.g. certain types of haemophilia) and acquired, e.g. after major surgery or trauma. Because of the difficulty studying the latter group, most experience is limited to case series and anecdotal reports and this, along with the high cost of the preparation (~£500 per mg), makes its use controversial. Associated with a 1–2% incidence of thrombotic complications, adding to the controversy. Requires functioning platelets and normal fibrinogen levels for maximal clinical effect.

Levi M, Peters M, Buller HR (2005). Crit Care Med; 33: 883–90

Eptifibatide.  Antiplatelet drug, used in some acute coronary syndromes. Acts by reversibly inhibiting activation of the glycoprotein IIb/IIIa complex on the surface of platelets.

Equivalence.  Amount of a substance divided by its valence. Equivalent weight (gram equivalent) is the weight of substance combining with or chemically equivalent to 8 g O₂, or 1 g hydrogen.

Electrical equivalence is the number of moles of ionised substance divided by valence.

Erg.  Unit of work in the cgs system. 1 erg = work done by a force of 1 dyne acting through a distance of 1 centimetre.

Ergometrine maleate.  Smooth muscle constrictor, with potent effects on uterine and vascular tone; used to reduce postpartum or post-termination uterine bleeding. Uterine contraction occurs 5 min after im injection and 1 min after iv injection; it lasts up to an hour. Slowly being replaced by synthetic oxytocin because of its adverse effects (nausea, vomiting and vasoconstriction causing a marked rise in BP and CVP; the latter is exacerbated by autotransfusion of blood from the uterus, and lasts up to several hours). Therefore hazardous in patients with cardiovascular disease, particularly pre-eclampsia. Despite this, it is often given routinely combined with oxytocin at the end of the second stage of labour. An aggravating role of ergometrine-induced vasoconstriction has been suggested in aspiration pneumonitis. Has been used as a vasopressor, e.g. in spinal anaesthesia.

See also, Uterus

Error, fixation,  see Fixation error

Errors, statistical.  In statistics, may lead to incorrect conclusions because of inadequate test design and analysis, too small a sample size or inaccurate data collection. Include:

It is thus ‘easier’ to demonstrate a non-significant result than a significant one. As the required P value is made smaller, the risk of rejecting a real result (i.e. type II error) increases (assuming a constant sample size). Errors may limit the usefulness of an investigation described by its sensitivity, specificity and predictive value.

Ertapenem.  Broad-spectum carbapenem and antibacterial drug, active against Gram-positive organisms and anaerobes, but not against pseudomonas or acinetobacter species, unlike imipenem or meropenem.

Erythrocytes (Red blood cells).  Biconcave discs, about 2 µm thick and 8 µm in diameter and without nuclei. Produced by red bone marrow. Contain haemoglobin, maintained in an appropriate state for O₂ transport (i.e. containing iron in the reduced state, in the presence of 2,3-DPG). Also have an integral role in carbon dioxide transport. Maintenance of structural integrity and osmotic stability is via membrane pumps; the main energy source is aerobic glycolysis.

Circulating lifespan is about 120 days; they are removed by the reticuloendothelial system and broken down, with salvage and reuse of iron and amino acids from haemoglobin.

Examination of the peripheral blood film gives information about haematological disease, e.g. abnormally shaped erythrocytes (sickle cell anaemia, hereditary spherocytosis, target cells in impaired haemoglobin production or liver disease).

See also, Erythropoiesis

Erythromycin.  Macrolide-type antibacterial drug with similar spectrum to penicillin; thus a useful alternative in penicillin allergy. Especially useful in respiratory infections (including Legionnaires’ disease and Mycoplasma infections) and staphylococcal infections. Also promotes GIT activity via stimulation of GIT motilin receptors; used as a prokinetic drug in ileus (given iv or via nasogastric tube).

Erythropoiesis.  Formation of erythrocytes, usually restricted to the vertebrae, sternum, ribs, upper long bones and iliac crests in adults. Requires iron, vitamin B₁₂ and folate, and possibly other vitamins and minerals. Stepwise differentiation from stem cells includes haemoglobin synthesis and nuclear extrusion to form reticulocytes, taking about 7 days. Regulated by erythropoietin.

Erythropoietin.  Glycoprotein hormone secreted mainly by the kidneys, but also by the liver. Secretion is increased by haemorrhage and hypoxia (possibly via prostaglandin synthesis), and inhibited by increased numbers of circulating erythrocytes. Causes increased erythropoiesis. Erythropoietin receptors are present in erythrocytes, bone marrow and on central and peripheral neurones; the latter are involved in neuronal development and repair. Infusion of erythropoietin produced by recombinant genetic engineering has been used to treat anaemia in renal failure, but treatment is very expensive. It has also been used to increase the yield of blood collected for autologous blood transfusion, e.g. 300 U/kg thrice weekly, reducing to 100 U/kg after 2 weeks. The first dose given iv produces higher levels; subsequent sc dosage produces a more sustained effect. Red cell aplasia has been reported following its sc use in renal failure.

Escape beats.  On the ECG, complexes arising from sites other than the sinoatrial node, when the latter does not discharge (i.e. sinus arrest or severe bradycardia). Distinct from ectopic beats, which arise prematurely in the cardiac cycle.

Esmolol hydrochloride.  Cardioselective β-adrenergic receptor antagonist, with no intrinsic sympathomimetic activity. Hydrolysed by red blood and other esterases, with a half-life of 9 min. Used to treat AF, atrial flutter and SVT, and during anaesthesia to prevent/treat tachycardia and hypertension, e.g. associated with tracheal intubation. Has been used in hypotensive anaesthesia.

Esophagus,  see Oesophagus

ESR,  Erythrocyte sedimentation rate, see Erythrocytes

Etamsylate (Ethamsylate).  Haemostatic drug, thought to reduce bleeding by correcting abnormal platelet adhesion. Does not affect fibrinolysis. Has been used to prevent and treat periventricular haemorrhage in premature babies (12.5 mg/kg im/iv qds).

Ethambutol hydrochloride.  Antituberculous drug added to triple therapy (isoniazid, rifampicin, pyrazinamide) if resistance is suspected.

Ethamsylate,  see Etamsylate

Ethanol,  see Alcohols

Ethanol poisoning,  see Alcohol poisoning

Ether,  see Diethyl ether

Ethics.  Principles of moral behaviour; often translated into medical practice by reference to four basic concepts:

The principles underlying ethical practice are not mutually exclusive and may even oppose one another, e.g. withholding blood from a Jehovah’s Witness respects his/her autonomy whilst not practising beneficence/non-maleficence.

The above approach (‘principlism’) is favoured by many because it is relatively simple and easy to understand, though there are many other systems for judging the moral value of medical decisions, such as consequentialism (judgement according to the outcomes of decisions) and rights-based approaches.

Waisel DB, Truog RD (1997). Anesthesiology; 87: 411–17

Ethmoidal nerve block, anterior,  see Ophthalmic nerve blocks

Ethoheptazine citrate.  Analgesic drug, used for mild/moderate pain. Combined with meprobamate, a sedative muscular antispasmodic, and aspirin. Not available in the UK.

Ethosuximide.  Anticonvulsant drug used in petit mal epilepsy and myoclonic seizures. Thought to block T-type calcium channels in thalamic neurones.

Ethyl alcohol,  see Alcohol poisoning; Alcohol withdrawal syndromes; Alcoholism; Alcohols

Ethyl chloride.  Inhalational anaesthetic agent, first described in 1848; popular in the 1920s particularly for induction of anaesthesia because of its rapid action. Extremely volatile (boiling point 13°C) and difficult to control; also inflammable. Now used solely for its cooling action when sprayed on to skin, to cause anaesthesia before minor procedures or to test the extent of regional blockade.

Ethylene.  Inhalational anaesthetic agent, used clinically in 1923. A gas of similar blood/gas solubility to N₂O, but more potent. Also extremely explosive and unpleasant to inhale. Cylinder body and shoulder are coloured violet.

Ethylene glycol poisoning,  see Alcohol poisoning

Ethylene oxide,  see Contamination of anaesthetic equipment

Etidocaine hydrochloride.  Local anaesthetic agent introduced in 1972, derived from lidocaine. Onset is rapid, and duration of action is similar to that of bupivacaine. Produces motor blockade that may exceed sensory blockade. Used in 1–1.5% solutions. Maximal safe dose is 2 mg/kg. Not available in the UK.

Etomidate.  IV anaesthetic agent, introduced in 1973. A carboxylated imidazole (five-membered ring containing three carbon atoms and two nitrogen atoms) compound (Fig. 64), presented in 35% propylene glycol; pH is 8.1. 75% bound to plasma proteins after injection. Methoxycarbonyl-etomidate (MOC-etomidate) is a new etomidate analogue that is rapidly metabolised and does not cause adrenocortical suppression (see below).

Etorphine hydrochloride.  Analogue of thebaine, a naturally occurring opioid. 1000–3000 times as potent as morphine. Used to immobilise large animals.

European Academy of Anaesthesiology (EAA).  Founded in 1978 to improve standards, training and research in anaesthesia. Organises the European Diploma in Anaesthesiology and Intensive Care. Amalgamated with the European Society of Anaesthesiologists and the Confederation of European National Societies of Anaesthesiologists to form the European Society of Anaesthesiology in 2005.

Thomson D (1995). Acta Anaesth Scand; 39: 442–4

See also, European Federation of Anaesthesiologists

European Board of Anaesthesiology (EBA).  Governing body for specialist anaesthetic training within the European Union, under the auspices of the European Union of Medical Specialties, which was founded in 1958. Works with the various anaesthetic bodies in member states.

Scherpereel P (1995). Acta Anaesth Scand; 39: 438–9

European Diploma in Intensive Care Medicine (EDIC).  Organised by the European Society of Intensive Care Medicine since 1989. Consists of an English written (multiple choice) examination and an oral/clinical one (usually in the country and language of the examinee), together with a requirement for a basic medical specialty and 2 years’ intensive care medicine training.

European Diploma in Anaesthesiology and Intensive Care (EDAIC).  Examination held since 2005 by the European Society of Anaesthesiology, having taken over this function from the European Academy of Anaesthesiology, which ran it from 1984. Available in multiple languages; consists of two parts (written and oral), each covering basic science and clinical topics. Pass rates are in the order of 60% and 80% respectively. There is also an optional in-training assessment part.

Zorab JSM (1995). Acta Anaesth Scand; 39: 579–81

European Federation of Anaesthesiologists (EFA).  Umbrella organisation formed in 2001 to coordinate the activities of and encourage cooperation between the European Academy of Anaesthesiology, European Society of Anaesthesiologists and Confederation of European National Societies of Anaesthesiology. Adopted the European Journal of Anaesthesiology as its official journal.

European Journal of Anaesthesiology.  Established in 1984. The official journal of the European Society of Anaesthesiology, having been the official journal of the European Academy of Anaesthesiology, the European Society of Anaesthesiologists, the Confederation of European National Societies of Anaesthesiology, Fondation Européenne d’Enseignement en Anaesthésiologie and European Union of Medical Specialties (since 1999) and the European Federation of Anaesthesiologists (since 2001).

European Medicines Evaluation Agency (EMEA).  Body established in 1995 to regulate the introduction and investigation of new drugs throughout Europe, and to ease communication between the various national regulatory bodies. Thus acts as a link between the Committee on Safety of Medicines in the UK and similar bodies in other countries.

Herxheimer A (1996). Br Med J; 312: 394

European Paediatric Life Support (EPLS).  Collaboration between the European Resuscitation Council and the Resuscitation Council (UK). The EPLS course provides training for healthcare professionals in the early recognition of the child in respiratory or circulatory failure and the prevention of respiratory or cardiorespiratory arrest.

European Resuscitation Council (ERC).  Formed in 1989 with a mandate to produce guidelines and recommendations appropriate to Europe for the practice of basic and advanced cardiopulmonary and cerebral resuscitation. Composed of elected representatives from the participating European countries. Held its first major international conference in 1992. Regularly produces guidelines regarding basic and advanced CPR. Resuscitation is its official journal.

See also, Resuscitation Council (UK); International Liaison Committee on Resuscitation

European Society of Anaesthesiology (ESA).  Formed in 2005 by the amalgamation of the European Society of Anaesthesiologists, the European Academy of Anaesthesiology and the Confederation of European National Societies of Anaesthesiologists. Seeks to provide all the educational and regulatory activities of the three component organisations. Adopted the European Journal of Anaesthesiology as its official journal. Representation of different nationalities within the organisation is via individual members (who are all eligible to join the ESA’s various committees) and the National Anaesthesia Societies Committee (NASC).

Priebe HJ (2005). Eur J Anaesth; 22: 1–3

European Society of Intensive Care Medicine (ESICM).  Founded in 1982 in Geneva to advance knowledge, research and education in intensive care medicine, and subsequently to improve facilities for intensive care medicine in Europe. Holds an annual congress, organises the European Diploma in Intensive Care Medicine and administers several multicentre and multinational surveys, e.g. the European Consortium for Intensive Care Data (ECICD). Also administers the educational programme PACT. Intensive Care Medicine is its official journal.

European Society of Paediatric and Neonatal Intensive Care (ESPNIC).  Founded and based in Brussels to advance and promote paediatric and neonatal intensive care. Has medical and nursing branches. Holds an annual congress and has Intensive Care Medicine as its official journal.

European Union of Medical Specialties (Union Européenne des Médecins Spécialistes; UEMS),  see European Board of Anaesthesiology

Euthanasia.  Intentional ending of a patient’s life for his or her benefit, e.g. to relieve intolerable and incurable suffering. May be voluntary if administered to a competent person in response to his or her informed request, or non-voluntary if administered to an incompetent person. Distinction is also made between active euthanasia, in which medical intervention hastens death, and passive euthanasia, in which life-sustaining treatment is withheld or withdrawn (e.g. enteral feeding). Assisted suicide differs in that the physician provides the mechanism for death but the patient administers the lethal agent. Euthanasia remains illegal throughout the world except in the Netherlands, where it was legalised in 2000, Belgium (2002) and Luxembourg (2009), all with formal guidelines laid down for its use. Assisted suicide is legal in Switzerland (since 1941) and the states of Montana, Oregon and Washington in the USA.

Emanuel EJ (2002). Arch Intern Med; 162: 142–52

EVE,  Epidural volume expansion, see Combined spinal–epidural anaesthesia

Evoked potentials (EPs).  Electrical activity recorded from the CNS or peripherally following peripheral or central stimulation. Used to investigate demyelinating disease, neuropathies and brain tumours, and in monitoring of head injury and coma. Also used to monitor and investigate depth of anaesthesia or CNS integrity during surgery.

Requires complex equipment to increase recording sensitivity and reduce interference. Recorded potentials are small (usually 1–2 µV) compared with background electrical activity (over 100 µV); the signal is amplified and (random) background activity averaged out using computer averaging. Filters reduce noise. Displayed as a plot of voltage against time; a stimulation spike occurs within 1 ms, followed by a composite pattern representing potentials from near and distant structures along the conduction pathway, depending on the sites of stimulation and recording. Upward peaks represent negative potentials by convention. Latency is the time between the stimulation spike and the first major peak; amplitude is the height from this peak to the following trough.

Kumar A, Bhattacharya A, Makhija N (2000). Anaesthesia; 55: 225–41

See also, Anaesthesia, depth of

Exercise.  Produces physiological changes that increase oxygen flux and removal of waste products from active tissues:

If extreme exercise continues, exhaustion follows; BP falls, cutaneous vasoconstriction occurs, body temperature rises and accumulation of lactic acid and CO₂ results in increasing acidosis. Muscle cramps and fatigue occur. Exertional myoglobinuria may be seen.

Exercise testing.  Most commonly, involves ECG recording while performing exercise, e.g. using a treadmill or bicycle, with workload increased in steps.

Testing is used to help diagnose chest pain or breathlessness, and to indicate prognosis in ischaemic heart disease, especially following MI. S–T depression is the most significant sign during exercise, but other changes, e.g. S–T elevation, Q waves, may occur. Chest pain, hypotension and arrhythmias may also be provoked. Testing may be combined with other measurements, e.g. arterial BP, respiratory rate, tidal volume, O₂ consumption, CO₂ output, arterial blood gases and cardiac output. Reduced ejection fraction (e.g. demonstrated by echocardiography) or cardiac output may suggest reversible ischaemia that may persist after cessation of exercise (myocardial stunning).

Inotropic drugs, e.g. dobutamine, may also be used to provoke similar changes to those caused by exercise (dobutamine stress test).

Traditionally, the patient’s own exercise tolerance (e.g. maximum walking distance or stairs climbed) has been used as a general indicator of cardiorespiratory function. More recently, formal cardiopulmonary exercise testing has been used to predict outcomes after major surgery, using the work at which maximal O₂ consumption is reached, or the work at which anaerobic energy metabolism (anaerobic threshold) starts, as markers of cardiopulmonary reserve.

Albouaini K, Egred M, Alahmar A, Wright DJ (2007). Heart; 93: 1285–92

Exomphalos,  see Gastroschisis and exomphalos

Exotoxins.  High-molecular-weight, heat-labile and antigenic proteins produced by micro-organisms. Although some bacteria produce only one significant kind of exotoxin (e.g. clostridia), others produce several (e.g. streptococci and staphylococci). Exotoxins and endotoxins contribute to the pathogenesis of SIRS. Some are used clinically, e.g. botulinum toxins.

Expert systems.  Computerised systems consisting of databases of knowledge and rules that are connected to the user via an interface. The latter takes data from the database and delivers inferences to the user. A facility for adding knowledge to the database allows the system to ‘learn’ continually. Expert systems may be:

Expiratory flow rate,  see Forced expiratory flow rate

Expiratory pause,  see Inspiratory: expiratory ratio

Expiratory reserve volume (ERV).  FRC minus residual volume. Normally 1–1.2 litres. Reduced ERV is usually the cause of reduced FRC. See also, Lung volumes

Expiratory valve,  see Adjustable pressure-limiting valve

Expired air ventilation.  Component of CPR said to be referred to in the Bible (2 Kings 4: 34–5). Reported in the 1700s and 1800s, but only became medically accepted practice in the 1950s, following demonstration that it was effective in apnoea during anaesthesia. Adequate oxygenation may be maintained with expired air of O₂ concentration 15–16%.

Having cleared the airway of debris, and with the patient supine, the neck is extended and the jaw held forward. In adults, the nose is pinched closed and the operator’s mouth placed firmly over that of the patient (mouth-to-mouth respiration). Slow deep exhalations are made whilst observing the patient’s chest for expansion. Exhalation is passive. May also be performed through the patient’s nose (mouth-to-nose respiration). In children, the operator’s mouth is placed over the patient’s nose and mouth.

Regurgitation of gastric contents may occur during expired air ventilation; this may be reduced by application of cricoid pressure if another person is available.

Various devices, some with valves, are available for avoidance of direct mouth-to-mouth contact, to improve aesthetic acceptability and reduce risk of cross-contamination; most hinder efficient ventilation. An anaesthetic facemask is suitable. Expired air ventilation may be performed through a correctly placed tracheal tube or LMA.

Explosions,  see Burns; Chest trauma; Explosions and fires; Incident, major; Smoke inhalation; Trauma

Explosions and fires.  Occur when a substance combines with O₂ or another oxidising agent, with release of energy. Activation energy is required to start the process, with utilisation of energy produced to maintain combustion. If the reaction proceeds very fast, large amounts of heat, light and sound are given out, i.e. an explosion occurs. Speed of reaction is greatest for stoichiometric mixtures.

May result in burns, direct trauma and smoke inhalation. Although uncommon now with modern techniques, explosions and fires continue to be reported.

Fire-fighting equipment should be present in every operating department.

Non-combustion explosions may occur if cylinders are faulty or internal pressure excessively high.

Macdonald AG (1994). Br J Anaesth; 72: 710–22; 73: 847–56

See also, Ignition temperature

Exponential process.  A process in which the rate of change of a quantity at a given time is in constant proportion to the amount of the quantity at that time.

Plotted on semi-logarithmic paper, exponential processes assume straight lines, e.g. used in the analysis of washout curves.

Extended mandatory minute ventilation,  see Mandatory minute ventilation

External jugular venous cannulation,  The external jugular vein passes posteriorly over the sternomastoid muscle from the angle of the jaw and joins the subclavian vein behind the midpoint of the clavicle (see Fig. 86; Internal jugular venous cannulation). It is often visible and thus easier to locate than the internal jugular vein, although valves may hinder cannulation and misplacement is common. In some individuals the vessel is not a distinct structure but is replaced by a venous plexus. The technique of cannulation involves placing the patient slightly head down with the arms by the side and the head turned to the contralateral side. After cleansing the skin, the skin is punctured well above the clavicle and the needle advanced immediately over the vein at about 20° to the frontal plane. A J-wire may help the catheter negotiate the valves at the junction with the subclavian vein.

Extracellular fluid (ECF).  Body fluid compartment; volume is about 14 litres (20% of body weight). Consists of interstitial fluid and plasma. Transcellular fluid (approximately 1 litre, composed of CSF, synovial fluid, etc.) and fluid within dense connective tissue, bone, etc., are usually excluded from the definition since these fluids are not readily exchangeable.

Measurement by dilution techniques is difficult because of eventual exchange with the above compartments, and because the substance used must remain extracellular. Substances used include inulin labelled with carbon-14, mannitol, sucrose, chloride-36 ions, bromide-82 ions, sulphate and thiosulphate. Slightly different values are obtained for each.

Compositions of plasma and interstitial fluid are different (see Fluids, body).

See also, Dehydration; Fluid balance

Extracorporeal carbon dioxide removal (ECCO₂R).  Method of respiratory support in which CO₂ is removed via a venovenous extracorporeal circuit and oxygenation is maintained by either apnoeic oxygenation or IPPV at very slow rates (1–4 breaths/min). Facilitates lung-protective ventilation strategies by preventing respiratory acidosis. The extracorporeal circuit runs at only 1–2 l/min; thus lung ischaemia is less likely than with extracorporeal membrane oxygenation. Initial human studies showed improved survival rates compared with conventional IPPV.

Practical considerations and complications are as for cardiopulmonary bypass.

Extracorporeal circulation,  see Cardiopulmonary bypass; Extracorporeal carbon dioxide removal; Extracorporeal membrane oxygenation; Haemodiafiltration; Haemodialysis; Haemofiltration; Haemoperfusion; Plasmapheresis; Ultrafiltration

Extracorporeal membrane oxygenation (ECMO).  Method of respiratory support for extremely hypoxaemic patients despite optimum mechanical ventilation. An arteriovenous extracorporeal circuit provides oxygenation and removal of CO₂ from anticoagulated blood. Very successful in neonates (e.g. with respiratory distress syndrome) but results are less clear in adults, in whom it is used mainly for temporary support before lung transplantation. Removal of a large proportion of the cardiac output by the arteriovenous circuit may exacerbate lung ischaemia. Simpler external oxygenators include the Novolung interventional lung assist device, a pumpless alternative that uses an arteriovenous shunt.

Practical considerations and complications are as for cardiopulmonary bypass.

Brodie D, Bacchetta M (2011). N Engl J Med; 365: 1905–14

Extracorporeal shock wave lithotripsy.  Non-invasive treatment of renal and biliary calculi using an acoustic pulse. Shock waves generated by the underwater discharge of a spark plug (18–24 000 V) are focused on the calculus by a computer-controlled reflector, with the patient suspended in a water bath on a hydraulic supportive cradle. At the interface between tissue fluid and calculus, energy released from the shock wave fragments the stone. Approximately 1000–2000 shocks are required to disintegrate an average stone, taking about 30–60 min. Shocks are triggered by the ECG R wave to avoid arrhythmias. Contraindications include cardiac pacemakers unless reprogrammed (timing may be modified), aortic calcification, pregnancy and presence of orthopaedic prostheses.

Energy may be released at any interface and cause pain, e.g. at water/skin interfaces; therefore anaesthesia is required. General and regional techniques have been used. High-frequency ventilation has been used, since diaphragmatic movement is reduced. Other anaesthetic considerations are related to positioning, temperature control, inaccessibility of the patient and monitoring, effects of immersion (increased CVP and pulmonary artery pressure) and requests for pharmacological intervention to increase heart rate and thus rate of discharge. IV fluid administration is usually required to produce a good diuresis, to wash away calculi fragments. Renal bleeding may occur if coagulation is impaired.

Plasma lactate dehydrogenase concentrations may be increased postoperatively. PONV is common.

The newest lithotriptors do not require immersion of the patient in water; the pain produced is less and sedation ± local anaesthesia may be suitable.

Extraction ratio (ER).  Measure of the amount of removal of drug by an organ, e.g. liver:

where C_i = drug concentration in blood entering the organ,

C_o = drug concentration in blood leaving the organ.

Factors affecting ER include enzyme activity and drug protein-binding.

Drugs with high ER (e.g. lidocaine and propranolol) undergo significant first-pass metabolism in the liver after oral administration. The rate of elimination is thus more dependent on hepatic blood flow than hepatic function; clearance of drugs with a low ER is more sensitive to changes in hepatic function (e.g. enzyme induction/inhibition) than blood flow.

Drugs with low ER include diazepam, digoxin and phenytoin.

Extradural (epidural) haemorrhage.  Haemorrhage between the periosteum and dura.

Extravascular lung water (EVLW).  Volume of water contained within the pulmonary interstitium and alveolar space. Usually 4–5 ml/kg. Measurement of EVLW has attracted attention as a possible means of detecting pulmonary oedema before it becomes apparent, although its usefulness in clinical practice is controversial. Determined by Starling forces and integrity of the pulmonary capillary and alveolar epithelium. Disruption of the former (e.g. by left ventricular failure) or the latter (e.g. in acute lung injury) may result in increased EVLW.

Measured by the double indicator dilution technique in which cold indocyanine dye is injected into the right atrium. The dye is contained within the intravascular space and its dilution curve allows calculation of the intravascular compartment. In contrast, the heat (measured by a thermistor placed in the aorta) from the solution is dissipated into the surrounding lung tissue and its dilution curve represents the sum of the intravascular and extravascular compartments. Subtraction of the curves allows calculation of the EVLW. Other methods of assessing EVLW include CXR, CT and MRI scanning and positron emission tomography techniques.

See also, Cardiac output measurement; Dilution techniques

Extubation, tracheal.  Problems that may occur include the following:

At the end of anaesthesia, tracheal extubation is performed with the patient either deeply anaesthetised or awake. Whilst the former avoids complications such as coughing and hypertension, the latter option allows return of the patient’s respiratory and laryngeal reflexes and is therefore recommended in patients particularly at risk of complications. These include those in whom access to the airway is impaired and those at risk of airway obstruction or aspiration (in whom extubation may be performed in the lateral position).

In patients in whom deep extubation is unsuitable but when smooth emergence from anaesthesia is particularly important (e.g. neurosurgery, maxillofacial surgery), alternative techniques include exchanging the tracheal tube for an LMA, or use of a remifentanil infusion.

Extubation should be preceded by suction to the pharynx and larynx, preferably under direct vision, to remove secretions and blood that might otherwise be inhaled. Secretions are particularly marked in unpremedicated patients and following neostigmine. Inflation of the lungs with O₂ immediately before and during extubation provides an O₂ reserve in case of laryngospasm and helps expel sputum from the upper airway. Facilities for reintubation should be available.

In patients in whom reintubation is predicted to be difficult, a bougie, fibrescope or airway exchange catheter may be placed into the trachea before extubation. In this group of patients high-dose corticosteroids may be considered to prevent post-extubation laryngeal oedema. After extubation, adequate ventilation should be confirmed and supplemental oxygen administered during transfer to a recovery room.

Similar considerations apply to patients in ICU after successful weaning from ventilators.

Popat M, Mitchell V, Dravid R, et al (2012). Anaesthesia; 67: 318–40

Eye, anatomy,  see Cranial nerves; Orbit; Skull

Eye care.  Important during both anaesthesia and intensive care since the eye is at risk for a number of reasons:

Paraffin-based ointments reduce the incidence of abrasions but may impair vision for up to several hours. Methylcellulose or saline drops may also be efficacious but require regular administration (e.g. hourly). Routine taping of the eyes is the simplest method of preventing corneal abrasions.

Suresh P, Mercieca F, Morton A, Tullo AB (2000). Intensive Care Med; 26: 162–6

Eye, penetrating injury.  Anaesthetic considerations: