E
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:
– airway obstruction may be present (often worse on lying flat), particularly in adults presenting with known or suspected tumours. Flexible nasendoscopy performed in clinic can be a useful source of information regarding the patient’s upper airway anatomy. Potential difficulty with intubation/mask ventilation should be assessed.
– obstructive sleep apnoea (with features of chronic hypoxaemia) may be present.
– specific emergencies include bleeding tonsil, inhaled foreign body, epiglottitis and peritonsillar abscess.
– anxiolytic, analgesic or antisialagogue premedication may be useful depending on the clinical context and intended anaesthetic technique.
– induction appropriate to the patient’s age, co-morbidities, anticipated airway difficulty, etc.
– techniques for securing the airway in potentially difficult cases include:
– direct laryngoscopy under deep inhalational anaesthesia.
– fibreoptic intubation (awake or anaesthetised).
– tracheostomy or cricothyrotomy performed under local anaesthesia.
– options for airway maintenance:
– tracheal tube: traditionally used for most procedures, with a throat pack if bleeding or debris is anticipated. Preformed tubes are useful. Oral intubation is suitable for many procedures, including laryngectomy and tonsillectomy. Nasal intubation provides better surgical access to the oral cavity; topical local anaesthetic agents and vasopressor drugs (e.g. cocaine) are used to reduce nasal bleeding (see Nose). A small-diameter (5 mm) tube, passed orally or nasally, is usually suitable for microlaryngoscopy.
– LMA (flexible/reinforced): avoids problems associated with intubation/extubation but may impair surgical access and be more prone to displacement.
– facemask anaesthesia: suitable for minor ear operations (e.g. myringotomy/grommets).
– injector techniques: often used for bronchoscopy, laryngoscopy, tracheal surgery.
– access to the airway during surgery is restricted, therefore monitoring is particularly important. Obstruction of the airway is possible, especially during tonsillectomy if a mouth gag is used.
– N2O is usually avoided in middle ear surgery, because of expansion of gas-filled cavities.
– surgery involving the face and neck may damage the facial and laryngeal nerves respectively (see Hyperthryoidism). Absence of neuromuscular blockade may be requested by the surgeon in order to allow identification of nerves by electrical stimulation. Spontaneous ventilation, or IPPV using opioids (e.g. remifentanil), a volatile agent and induced hypocapnia, may be employed.
– thoracotomy is occasionally required, e.g. mobilisation of the stomach for anastomosis.
– laser surgery is common, especially for laryngeal surgery.
– adrenaline solutions are often used by the surgeon.
– tracheal extubation is performed with the patient deeply anaesthetised or awake (but not in between, because of the risk of laryngospasm) and in the head-down, lateral position to reduce airway soiling.
postoperatively: as for any surgery. Major procedures may require ICU/IPPV postoperatively.
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
East–Freeman automatic vent, see Ventilators
Eaton–Lambert syndrome, see Myasthenic syndrome
right heart failure and cyanosis (due to right-to-left shunting).
tricuspid valve regurgitation.
ASD is often present.
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]
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.
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).
complications of pre-eclampsia, especially coagulopathy.
cerebral oedema/haemorrhage, coma, death.
aspiration of gastric contents, cardiac failure, pulmonary oedema.
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.
anticonvulsant drugs; magnesium sulphate is the drug of choice for treating eclamptic seizures, superseding diazepam and phenytoin that were traditionally used in the UK; it reduces the incidence of recurrent convulsions and of fetal/maternal complications. Thiopental is suitable in resistant cases; tracheal intubation is required.
head-down, left lateral position, if the trachea is unprotected.
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.
Ectopic beats, see Atrial ectopic beats; Junctional arrhythmias; Ventricular ectopic beats
ED50, see Therapeutic ratio/index
Edetate, see Cyanide poisoning; Sodium calcium edetate
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.
• Dosage:
reversal of neuromuscular blockade: 0.5–0.7 mg/kg iv with atropine.
differentiation between myasthenic and cholinergic crises: 2 mg iv, 1 h after the last dose of cholinergic drug. Increased muscle strength occurs in myasthenic crisis; worsening of weakness in cholinergic crisis.
diagnosis of dual block: 10 mg iv; causes transient improvement in muscle power.
• Side effects: bradycardia, hypotension, nausea, vomiting, diarrhoea, abdominal cramps, increased salivation, muscle fasciculation. Convulsions and bronchospasm may also occur. The ECG should always be monitored when edrophonium is administered, and atropine must always be available.
Efficacy. Maximal effect attainable by a drug; e.g. morphine is more efficacious than codeine. A pure antagonist has an efficacy of zero.
Eicosanoids. Collective term used for products of arachidonic acid metabolism involved in inflammation, immunity and cell signalling. Include:
prostanoids: produced by the cyclo-oxygenase pathway, i.e. prostaglandins, prostacyclin and thromboxanes.
leukotrienes produced by the lipoxygenase pathways.
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.
dyspnoea, effort syncope, angina, haemoptysis.
supraventricular arrhythmias, right ventricular failure, features of pulmonary hypertension.
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.
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.
• The following nerves are blocked (Fig. 57):
median (C5–T1): lies immediately medial to the brachial artery in the antecubital fossa. A needle is inserted with the elbow extended, level with the epicondyles, to approximately 5 mm, and 5 ml local anaesthetic agent injected. Subcutaneous infiltration blocks cutaneous branches.
radial (C5–T1): lies in the antecubital fossa in the groove between biceps tendon medially and brachioradialis muscle laterally. A needle is inserted level with the epicondyles with the elbow extended, and directed proximally and laterally to contact the lateral epicondyle. 2–4 ml solution is injected, and a further 5 ml during withdrawal to skin. This is repeated with the needle directed more proximally.
lateral cutaneous nerve of the forearm (C5–7): lies alongside the radial nerve. It is a continuation of the musculoskeletal nerve of the brachial plexus. May be blocked by subcutaneous infiltration between biceps and brachioradialis, using the same puncture site as for the radial nerve.
ulnar (C6–T1): passes through the ulnar groove behind the medial humeral epicondyle. With the elbow flexed to 90°, a fine needle is inserted 1–2 cm proximal to the groove, pointing distally. At 1–2 cm depth, 2–5 ml solution is injected. Neuritis may follow injection into the nerve, or block within the ulnar groove.
Elderly, anaesthesia for. Increasingly common as the population ages. Mortality and morbidity are higher in older patients.
• Anaesthetic considerations, compared with younger patients:
– ischaemic heart disease is more likely, with reduced ventricular compliance and contractility, and cardiac output.
– decreased blood flow to vital organs.
– cerebrovascular insufficiency is common.
– widespread atherosclerosis with a less compliant arterial system. Hypertension is common.
– veins are more tortuous, thickened and fragile.
– DVT is more common.
– decreased lung compliance and alveolar surface area.
– increased closing capacity, therefore more airway collapse with resultant increase in alveolar–arterial O2 difference. Normal alveolar PO2 is approximately:
– decreased response to hypercapnia and hypoxaemia.
– higher incidence of postoperative atelectasis, PE and chest infection.
– increased sensitivity to many drugs, especially CNS depressants.
– half-lives of many drugs are increased.
– fluid balance is more critical with reduction in total body water; dehydration is common following trauma and illness.
– diabetes mellitus and malnutrition are more common.
– cerebrovascular disease is common.
– confusion and postoperative cognitive dysfunction are more likely, and may be caused by hypoxia, hyperventilation, drugs, hospitalisation and any illness.
– autonomic nervous system dysfunction is common.
– impaired hearing, vision and memory loss are common.
– heat loss during anaesthesia is more likely due to impairment of both central control and compensatory mechanisms.
– hiatus hernia is more common, with risk of regurgitation and aspiration.
– systemic diseases and multiple drug therapy are more common.
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.
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
Fig. 58 Electrical symbols
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 (V1–6) 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. V1–2 demonstrate electrical activity from the right side of the heart, V3–4 from the septum and front, and V5–6 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.
– I: between left arm (positive electrode) and right arm (negative).
– II: between left leg (positive electrode) and right arm (negative).
– III: between left leg (positive electrode) and left arm.
– V1: fourth intercostal space, right sternal edge.
– V2: fourth intercostal space, left sternal edge.
– V3: midway between V2 and V4.
– V4: fifth intercostal space, left midclavicular line.
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.
• Plan for the interpretation of standard ECG, with normal values (Fig. 59b):
patient’s name, clinical context, date.
rate: heart rate in beats/min is calculated by dividing the number of 5 mm squares between successive QRS complexes into 300, assuming a recording speed of 25 mm/s.
– regular or irregular. An irregular rhythm may be regularly (e.g. missing every third QRS) or irregularly irregular (e.g. completely random in AF).
– presence/absence of P waves, flutter waves in atrial flutter, ventricular ectopic beats, pacing spikes, etc.
axis: summation of electrical potentials from the standard and aV leads, plotted as vectors. The normal axis lies between –30° and +90° (Fig. 59c).
Left axis deviation (< −30°) may occur in:
– normal subjects (especially if pregnant), ascites, etc.
– left bundle branch block, left anterior hemiblock.
– left ventricular hypertrophy.
Right axis deviation (> 90°) may occur in:
– right ventricular hypertrophy.
– right bundle branch block, left posterior hemiblock.
P wave (atrial depolarisation):
– positive in I, II, and V4–6; negative in aVR, since depolarisation moves downwards and to the left.
– shape.
P–R interval: normally 0.12–0.2 s (3–5 mm squares).
QRS complex (ventricular depolarisation):
– duration is 0.04–0.12 s (1–3 mm squares).
– amplitude in I + II + III > 5 mm. Left ventricular hypertrophy exists if the R wave in V6 + S wave in V1 > 35 mm. In right ventricular hypertrophy the R : S ratio > 1 in V1–2.
– abnormal waves, e.g. J and δ waves in hypothermia and Wolff–Parkinson–White syndrome respectively.
– level within 1 mm of baseline.
– shape.
T wave (ventricular repolarisation):
– orientation as for QRS complexes.
– shape.
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:
right arm electrode in suprasternal notch.
left arm electrode over apex of heart (V5 position).
left leg electrode on left shoulder or leg serves as ground.
See also, Cardiac cycle; Heart block: His bundle electrography; Myocardial infarction
– concurrent drug therapy may include antidepressant drugs, including monoamine oxidase inhibitors, lithium.
– premedication is usually omitted.
– monitoring is required as for any procedure.
– a single induction dose of iv agent is usually given. Methohexital was traditionally used because of its short action and pro-convulsant properties. Propofol (at 1 mg/kg) provides greater haemodynamic stability and more rapid post-ictal recovery whilst having the same therapeutic benefit as methohexital and has become the induction agent of choice.
– suxamethonium 0.5 mg/kg is commonly given, although smaller doses have been used.
– a soft mouth guard is inserted to protect the teeth and gums.
– intense parasympathetic discharge may follow passage of current, and may be followed by increased sympathetic activity. Atropine should always be available; routine administration has been suggested.
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.
• Effects:
heat production due to high resistance of tissues. Amount of heat is related to current density. May produce burns at sites of current entry/departure.
nerve and muscle stimulation; e.g. effect of current across chest (approximate values):
– 15 mA: tonic muscle contraction, i.e. ‘can’t let go’ threshold.
– > 5 A: tonic contraction of the myocardium (utilised in defibrillation).
– frequency of alternating current: 50–60 Hz is particularly dangerous but cheap to provide.
– timing of shock (e.g. R on T phenomenon).
regular checking and maintenance of electrical equipment.
use of batteries only (impractical).
double insulation of all conducting wires within equipment (class II).
reduction of stray leakage currents, e.g. due to drops in potential along the length of conductors, caused by capacitance between casing and innards or inductance. Leakage currents may be sufficient to produce microshock. Earth conductors are connected to each other to reduce differences between them. Current-operated earth-leakage circuit breakers may be used. Standards for leakage currents are defined, e.g. 10 µA maximum from the casing or delivered to the patient for intracardiac equipment; 100–500 µA for other equipment, depending on usage.
Medical electrical equipment is marked with the appropriate electrical symbols to indicate its level of safety features (see Fig. 58).
beta: normal 13–30 Hz waves. Prominent over the frontal area during the awake and active state.
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.
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.
Electrolyte imbalance, see individual disorders
Electrolyte solutions, see Intravenous fluids
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.
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.
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.
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.
inadequate preparation of patients for surgery:
full stomach, i.e. risk of aspiration of gastric contents.
untreated pre-existing disease, electrolyte imbalance, etc.
appropriate investigations and cross-matching of blood not performed or not ready.
– haemorrhage and hypovolaemia.
– intestinal obstruction/intra-abdominal pathology: dehydration and hypovolaemia, electrolyte imbalance, etc. Further risk of aspiration due to delayed gastric emptying and vomiting/haematemesis.
– trauma: haemorrhage, head injury, chest trauma, etc.
– airway obstruction/inhaled foreign body.
– related to specialist surgery, e.g. cardiac surgery, neurosurgery.
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
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.
EMO inhaler, see Vaporisers
Emphysema, see Chronic obstructive pulmonary disease
Emphysema, subcutaneous. Presence of gas in subcutaneous tissues.
pneumothorax or rupture of a viscus, e.g. oesophagus.
infection with gas-producing organisms, e.g. gas gangrene.
rarely, deliberate self-injection of subcutaneous air in disordered mental states.
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.
• Causes:
autoimmune encephalitis (including anti-NMDA receptor encephalitis and anti-voltage-gated potassium channel encephalitis) is being increasingly recognised; presents with psychiatric, epileptic and movement disorder features.
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.
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):
