T
T-piece breathing systems, see Anaesthetic breathing systems
t tests, see Statistical tests
T wave, Wave on the ECG representing ventricular repolarisation (see Fig. 59b; Electrocardiography). Normally upright in leads I, II and V3–6; the upper height limit is 5 mm in the standard leads and 10 mm in the chest leads.
may be inverted in myocardial ischaemia, ventricular hypertrophy, mitral valve prolapse, bundle branch block and digoxin toxicity.
Tachycardias, see Sinus tachycardia; Supraventricular tachycardia; Ventricular tachycardia
Tachykinins. Group of neuropeptides involved in cardiovascular, respiratory, endocrine and behavioural responses. Include substance P, neurokinin A and neurokinin B, which are natural agonists at NK1, NK2 and NK3 receptors, respectively. Particular interest has focused on NK1 and NK2 receptor activation, which results in bronchoconstriction, and on development of neurokinin-1 receptor antagonists as antiemetic drugs.
Tachyphylaxis. Term usually referring to acute drug tolerance, usually due to depletion of receptors (or for indirectly acting drugs, depletion of neurotransmitter/signalling molecule) following repeated exposure.
Tacrine, see Tetrahydroaminocrine
Tacrolimus. Immunosuppressive drug; acts by inhibiting cytotoxic lymphocyte proliferation and cytokine expression. Used to prevent graft rejection after liver and renal transplantation. A topical preparation is available for treatment of dermatitis. Extensively bound to red blood cells and plasma proteins. Achieves steady-state concentrations after about 3 days’ administration; half-life varies from 3 to 40 h with mainly hepatic metabolism and biliary excretion.
Tamponade, see Cardiac tamponade
TAP block, see Transversus abdominis plane block
Tapentadol hydrochloride. Opioid analgesic drug, similar in structure to tramadol, used to treat moderate-to-severe pain. Acts via agonism at mu opioid receptors and inhibition of reuptake of noradrenaline. Rapidly absorbed via the oral route; undergoes extensive first-pass metabolism. Cleared by hepatic metabolism to inactive metabolites, followed by renal excretion; used with caution in patients with hepatic failure.
• Dosage: 50 mg orally 4–6-hourly, adjusted to response, maximum 600 mg daily.
• Side effects: nausea, vomiting, dizziness, dry mouth, sweating, confusion, hallucinations, seizures, respiratory depression, sedation (the latter two less commonly than with morphine). Drug dependence and withdrawal have been reported, especially following prolonged treatment.
Target-controlled infusion (TCI). Technique utilising a computer-controlled intravenous infusion device to achieve and maintain a desired target drug concentration (in plasma, or at the ‘effect site’). May be used for sedation or total intravenous anaesthesia. Requires:
a computer programmed with an algorithm based on a model of the drug’s pharmacokinetics. Familiarity with the specific model incorporated into the TCI system being used is important; the clinical effect associated with a given target concentration for one model may be different for another.
The first licensed TCI system was for propofol, using a proprietary microprocessor that could only be used with electronically tagged pre-filled syringes. Since the expiry of the patent on propofol, several ‘open-label’ pharmacokinetic protocols have been developed and incorporated into a range of TCI devices. TCI systems for other drugs (e.g. remifentanil and sufentanil) are also available and widely used.
Absalom AR, Mani V, De Smet T, Struys MM (2009). Br J Anaesth; 103: 26–37
TB, see Tuberculosis
Teeth. Composed of the crown (consisting of enamel, dentine and pulp from outside inwards) and root. All parts may be damaged during anaesthesia; the deeper the damage, the more extensive is the treatment required. Traumatic damage is involved in about 30% of malpractice claims against anaesthetists, with a rough incidence of 1:1000 general anaesthetics and, because of its frequency, claims are rarely contested. Damage most commonly occurs during intubation or postoperatively when the patient bites on an oral airway. Preoperative assessment of the teeth is essential, noting any loose, chipped or false teeth. Patients with caries, prostheses and periodontal disease, and those in whom tracheal intubation is difficult, are at particular risk. Appropriate warnings should be given and noted on the anaesthetic chart preoperatively.
Yasny JS (2009). Anesth Analg; 108: 1564–73
See also, Dental surgery; Mandibular nerve blocks; Maxillary nerve blocks
Teicoplanin. Glycopeptide and antibacterial drug, related to vancomycin but longer acting, allowing once-daily dosing. Active against most Gram-positive organisms, as for vancomycin. 90% protein-bound, with a half-life of 7 days. Excreted unchanged in urine.
Temazepam. Benzodiazepine used in insomnia, and commonly used for premedication. Shorter acting than diazepam, with faster onset of action. Half-life is 8 h.
Temperature. Property of a system that determines whether heat is transferred to or from other systems. Related to the mean kinetic energy of its constituent particles. Three temperature scales are recognised: Kelvin (formerly Absolute) scale, Celsius (formerly Centigrade) scale and Fahrenheit scale (Table 42). The SI unit of temperature is the kelvin.
[Anders Celsius (1701–1744), Swedish scientist; Gabriel D Fahrenheit (1686–1736), German scientist]
Temperature measurement. Performed routinely as part of basic monitoring in ICUs. Used perioperatively to monitor heat loss during anaesthesia and detect hyperthermia.
– thermocouple: relies on the Seebeck effect; i.e. the production of voltage at the junction of two different conductors joined in a loop; the magnitude of the voltage generated is proportional to the temperature difference between the two junctions. The circuit thus consists of a measuring junction and a reference junction, with measurement of the voltage difference between the two. Because voltage is also produced at the reference junction, electrical manipulation is required to compensate for changes in temperature at the latter.
– gas expansion thermometers, e.g. an anaeroid gauge used for pressure measurement is calibrated in units of temperature. Accuracy is poor and calibration may be difficult.
nasopharyngeal and bladder: similar to oesophageal.
blood: thermistors incorporated into pulmonary artery catheters allow continuous measurement.
[Thomas J Seebeck (1770–1831), Russian-born German physicist]
Temperature regulation. Humans are homeothermic, maintaining body core temperature at 37 ± 1°C. The core usually includes cranial, thoracic, abdominal and pelvic contents, and variable amounts of the deep portions of the limbs. Temperature is lowest at night and highest in mid-afternoon, also varying with the menstrual cycle.
Constant temperature is required for optimal enzyme activity. Denaturation of proteins occurs at 42°C. Loss of consciousness occurs at hypothermia below 30°C.
• Mechanisms of heat loss/gain:
– from metabolism (mainly in the brain, liver and kidneys): approximately 80 W is produced in an average man under resting conditions. This would raise body temperature by about 1°C/h if totally insulated. Vigorous muscular activity may increase heat production by up to 20 times. In babies, brown fat produces much heat.
– radiation from the skin. May account for 40% of total loss.
– convection: related to airflow (e.g. ‘wind chill’). Accounts for up to 40% of total loss.
– conduction: of little importance in air, but significant in water.
Temperature-sensitive cells are present in the anterior hypothalamus (thought to be the most important site), brainstem, spinal cord, skin, skeletal muscle and abdominal viscera. Peripheral temperature receptors are primary afferent nerve endings and respond to cold and hot stimuli via Aδ and C fibres respectively. Central control of thermoregulation is by the hypothalamus. Efferents pass via the sympathetic nervous system to blood vessels, sweat glands and piloerector muscles. Local reflexes are also involved. Efferents also pass to somatic motor centres in the lower brainstem to cause shivering, and to higher centres.
behavioural, e.g. curling up in the cold, wearing appropriate clothing.
skin blood flow: may be altered by vasodilatation or vasoconstriction of skin vessels, and by opening or closing of arteriovenous anastomoses in the skin. Affects all routes of heat loss. Alteration alone is sufficient to maintain constant body temperature in environments of 20–28°C in adults and 35–37°C in neonates (thermoneutral range).
shivering and piloerection (reduced or absent in babies, brown fat metabolism occurring instead). Reflex shivering can hinder induced hypothermia; measures to inhibit shivering include use of neuromuscular blocking drugs, α2-adrenergic receptor agonists and skin surface warming (with core cooling).
Pitoni S, Sinclair HL, Andrews PJD (2011). Curr Opin Crit Care; 17: 115–21
Temporomandibular joint (TMJ). Synovial joint between the mandibular condyle and the articular surface of the squamous temporal bone. Protrusion, retraction and grinding movements of the lower jaw occur by a gliding mechanism whereas mouth opening and closing involve gliding and hinging movements. Joint stability is least when the mouth is fully open (e.g. during laryngoscopy) and forward dislocation may occur. Affected by rheumatoid arthritis, degenerative disease, ankylosing spondylitis and systemic sclerosis. Mouth opening may be severely limited, hindering laryngoscopy.
Tenecteplase. Fibrinolytic drug, used in acute management of acute coronary syndromes. Binds to fibrin, the resultant complex converting plasminogen to plasmin, which dissolves the fibrin.
Tension. In physics, another word for force, implying stretching (cf. compression). Also refers to the partial pressure of a gas in solution.
Tension time index, Area between tracings of left ventricular pressure and aortic root pressure during systole, multiplied by heart rate (see Fig. 61; Endocardial viability ratio). Represents myocardial workload and hence O2 demand; when taken in conjunction with diastolic pressure time index, it may indicate the myocardial O2 supply/demand ratio and the likelihood of myocardial ischaemia.
Terbutaline sulphate. β-Adrenergic receptor agonist, used as a bronchodilator drug and tocolytic drug. Has similar effects to salbutamol, but possibly has less cardiac effect.
• Dosage:
250–500 µg im/sc qds as required.
250–500 µg iv slowly, repeated as required. 1–5 µg/min infusion may be used (containing 3–5 µg/ml). Up to 25 µg/min may be required in premature labour (see Ritodrine).
1–2 puffs by aerosol (250–500 µg) tds/qds.
Terlipressin, see Vasopressin
Terminal care, see Palliative care; Withdrawal of treatment in ICU
Test dose, epidural. In epidural anaesthesia, injection of a small amount of local anaesthetic agent through the catheter before injection of the main dose, in order to identify accidental subarachnoid or iv placement of the catheter. Less commonly performed before ‘through the needle’ epidural block, since leakage of CSF or blood should be more easily noticeable.
Controversial, since it is not always reliable. The volume and strength of the test solution are also controversial. 3 ml 2% lidocaine with adrenaline 1:200 000 has been suggested as the ideal solution; subarachnoid injection produces spinal anaesthesia within 2–3 min, and iv injection produces tachycardia within 90 s. Injection of fentanyl 50–100 µg or 1 ml air (with Doppler monitoring) has also been used. In modern ‘low-dose’ techniques (e.g. epidural analgesia for labour), each dose ‘acts as its own test’ since a standard dose of e.g. 10 ml bupivacaine 0.1% with 20 µg fentanyl would be expected to produce noticeable effects were it to be injected subarachnoid or iv without causing a dangerously high block or severe systemic toxicity.
Tetanic contraction. Sustained muscle contraction caused by repetitive electrical stimulation of a motor nerve. About 25 Hz stimulation is required for frequent enough action potentials to produce it, although the necessary rate varies according to the muscle studied. The force produced exceeds that of single muscle twitches. During tetanic contraction, acetylcholine is mobilised from reserve stores to the readily available pool.
Produced during neuromuscular blockade monitoring.
See also, Neuromuscular junction; Neuromuscular transmission; Post-tetanic potentiation
Clinical features are caused by a potent exotoxin, tetanospasmin, which moves along peripheral nerves to the spinal cord, where it blocks release of neurotransmitters at inhibitory neurons, causing muscle spasm and autonomic disturbance. Incubation period is 3–21 days (average 7 days). Local infection may cause muscle spasm around the site of injury; generalised tetanus is characterised by trismus, irritability, rigidity and opisthotonos. Cardiac arrhythmias/arrest and hypertension may occur due to sympathetic hyperactivity. As binding of tetanospasmin is irreversible, recovery depends on formation of new nerve terminals. The diagnosis is based on clinical findings but the spatula test (touching the oropharynx with a wooden spatula; in tetanus this results in spasm of the masseter muscles causing biting of the spatula) is highly sensitive and specific for tetanus.
human antitetanus immunoglobulin (5000–10 000 units): neutralises circulating toxin.
surgical excision and debridement of the wound.
metronidazole to eradicate existing organisms.
sedation, neuromuscular blocking drugs and IPPV may be required. Dantrolene and magnesium sulphate have been used. The latter reduces sympathetic overactivity and reduces spasm by decreasing presynaptic activity.
Active immunisation with tetanus vaccine should always be performed in trauma and burns unless within 5–10 years of previous administration. Antitetanus immunoglobulin is given to non-immune patients with heavily contaminated or old wounds.
Gibson K, Bonaventure Uwineza J, Kiviri W, Parlow J (2009). Can J Anaesth; 56: 307–15
Tetany. Increased sensitivity of excitable cells, manifested as peripheral muscle spasm. Usually facial and carpopedal, the shape of the hand in the latter termed main d’accoucheur (French: obstetrician’s hand). Usually caused by hypocalcaemia; it also occurs in hypomagnesaemia and may be hereditary.
Tetracaine hydrochloride (Amethocaine). Ester local anaesthetic agent, introduced in 1931. Widely used in the USA for spinal anaesthesia; in the UK, used only for topical anaesthesia, e.g. in ophthalmology. More potent and longer lasting than lidocaine, but more toxic. Toxicity resembles that of cocaine. Weak base with a pK of 8.5. Rapidly absorbed from mucous membranes. Hydrolysed completely by plasma cholinesterase to form butylaminobenzoic acid and dimethylaminoethanol. Administration: 0.5–1% solution for spinal anaesthesia; 0.4–0.5% for epidural anaesthesia; 0.1–0.2% solution for infiltration, usually with adrenaline; 0.5–1% solutions for surface analgesia.
Available in a 4% gel (available over the counter without prescription) for topical anaesthesia of the skin, e.g. before venepuncture. The melting point of the drug is lowered by the formation of specific hydrates within the gel. The resultant oil globules penetrate the skin readily with onset of action about 30–45 min; effects last 4–6 h. Skin blistering may occur. Has been combined with lidocaine and a heating compound in a plaster, for topical anaesthesia before venepuncture.
Tetracycline. Broad-spectrum antibacterial drug, used mainly for chlamydia, rickettsia, spirochaete and brucella infections, certain mycoplasma infections, acne, acute exacerbations of COPD and leptospirosis. Several tetracyclines exist, with tetracycline itself the only one administered iv. Has also been instilled into the pleural cavity to treat recurrent pleural effusions.
Tetrahydroaminocrine hydrochloride (Tacrine). Acetylcholinesterase inhibitor formerly used to prolong the action of suxamethonium. Also used prophylactically to reduce muscle pains following suxamethonium, and as a central stimulant. Used as a treatment for Alzheimer’s disease.
[Alois Alzheimer (1864–1915), German neurologist and pathologist]
Tetrodotoxin. Toxin obtained from puffer fish, that selectively blocks neuronal voltage-gated fast sodium channels. Used experimentally, e.g. for investigating neuromuscular transmission.
Thalassaemia. Group of autosomally inherited disorders involving decreased production of the α or β chains of haemoglobin (Hb). More common in Mediterranean, African and Asian areas. Severity is related to the pattern of inheritance of the Hb genes (normally, one β gene and two α genes are inherited from each parent).
– not apparent immediately as fetal haemoglobin does not contain β chains.
– heterozygous β thalassaemia (thalassaemia minor) produces mild (often asymptomatic) anaemia, but may be associated with other types of Hb (e.g. HbC, HbE, HbS); resultant anaemia may vary from mild to severe.
– homozygous β thalassaemia (Cooley’s anaemia; thalassaemia major) results in severe anaemia in infancy, with no production of HbA. Features include craniofacial bone hyperplasia, hepatosplenomegaly and cardiac failure. Haemosiderosis may occur due to repeated blood transfusion. Usually fatal before adulthood, although bone marrow transplantation may offer a cure. Some genetic subtypes are associated with a milder clinical course (thalassaemia intermedia).
Peters M, Heijboer H, Smiers F, Giordano PC (2012). Br Med J; 344: e228
Theophylline. Bronchodilator drug, used alone or in combination with ethylenediamine as aminophylline.
Thermal conductivity detector, see Katharometer
Thermistor, see Temperature measurement
Thermocouple, see Temperature measurement
Thermodilution cardiac output measurement, see Cardiac output measurement
Thermoneutral range. Temperature range in which temperature regulation may be maintained by changes in skin blood flow alone. Corresponds to the temperature that feels ‘comfortable’. About 20–28°C in adults and 35–37°C in neonates. Neonatal metabolic rate and mortality are reduced if body temperature is kept within the thermoneutral range.
Thiamylal sodium. IV anaesthetic agent, with similar properties to thiopental. Unavailable in the UK.
Thiazide diuretics. Group of diuretics used to treat mild hypertension, oedema caused by cardiac failure and nephrogenic diabetes insipidus. Chlorothiazide was the first to be studied but many now exist, e.g. bendroflumethiazide (bendrofluazide). Act mainly at the proximal part of the distal convoluted tubule of the nephron, where they inhibit sodium reabsorption. They also act at the proximal tubule, causing weak inhibition of carbonic anhydrase and increasing bicarbonate and potassium excretion, and have a direct vasodilator action. Their antihypertensive action increases only slightly as dosage is increased. Rapidly absorbed from the GIT with onset of action within 1–2 h, lasting 12–24 h. Some non-thiazide drugs have thiazide-like properties (e.g. chlortalidone, metolazone).
Side effects include hypokalaemia, hyponatraemia, hyperuricaemia, hypomagnesaemia, hypochloraemic alkalosis, hyperglycaemia, hypercholesterolaemia, exacerbation of renal and hepatic impairment, impotence, and, rarely, rashes and thrombocytopenia.
Thiazolidinediones. Oral hypoglycaemic drugs used in management of type II diabetes mellitus. Bind to a nuclear receptor, PPARγ, in adipose cells, liver and skeletal muscle, increasing sensitivity to insulin. Not indicated for monotherapy; usually used in combination with a biguanide or sulphonylurea. Agents include pioglitazone (restricted in some countries because of the risk of bladder cancer), rosiglitazone (restricted in the USA and unavailable in Europe because of the risk of cardiovascular events) and troglitazone (withdrawn because of the risk of hepatitis).
Thigh, lateral cutaneous nerve block. Provides analgesia of the anterolateral thigh/knee, e.g. for leg surgery (especially skin graft harvesting) and diagnosis of meralgia paraesthetica (numbness and paraesthesia caused by lateral cutaneous nerve compression by the inguinal ligament, under which it passes).
With the patient supine, a needle is introduced perpendicular to the skin, 2 cm medial and caudal to the anterior superior iliac spine. A click is felt as the fascia lata is pierced. 10–15 ml local anaesthetic agent is injected in a fan shape laterally.
Thiopental sodium (Thiopentone; 5-ethyl-5-(1-methylbutyl)-2-thiobarbiturate). IV anaesthetic agent, synthesised in 1932 and first used in 1934 by Lundy and Waters. Also used in refractory status epilepticus. The sulphur analogue of pentobarbitone (Fig. 154). Stored as the sodium salt, a yellow powder with a faint garlic smell, with 6% anhydrous sodium carbonate added to prevent formation of (insoluble) free acid when exposed to atmospheric CO2 and presented in an atmosphere of nitrogen. Most commonly used as a 2.5% solution, with pH of 10.5. pKa is 7.6; at a pH of 7.4 about 60% is non-ionised. The solution is stable for 24–36 h after mixing, although the manufacturers recommend discarding after 7 h.
About 85% bound to plasma proteins after injection. Follows a multicompartmental pharmacokinetic model after a single iv injection, with redistribution from vessel-rich tissues (e.g. brain) to lean body tissues (e.g. muscle), with return of consciousness. Slower redistribution then occurs to vessel-poor tissues (e.g. fat: see Fig. 88; Intravenous anaesthetic agents).
• Effects:
– smooth, occurring within one arm–brain circulation time. Involuntary movements and painful injection are rare.
– recovery within 5–10 min after a single dose.
– causes dose-related direct myocardial depression, decreasing cardiac output and causing compensatory tachycardia with increased myocardial O2 demand. Cardiovascular depression is related to speed of injection and is exacerbated by hypovolaemia.
– has little effect on SVR but may decrease venous vascular tone, reducing venous return.
– causes dose-related depression of the respiratory centre, decreasing the responsiveness to CO2 and hypoxia. Apnoea is common after induction.
– laryngospasm readily occurs following laryngeal stimulation.
– has been implicated in causing bronchospasm, but this is disputed.
– decreases pain threshold (antanalgesia).
– reduces cerebral perfusion pressure, ICP and cerebral metabolism.
– causes brief skeletal muscle relaxation at peak CNS effect.
– reduces renal and hepatic blood flow secondary to reduced cardiac output. Causes hepatic enzyme induction.
Metabolised by oxidation in the liver (10–15% per hour), with < 1% appearing unchanged in the urine. Desulphuration to pentobarbitone may also occur following prolonged administration. Elimination half-life is 5–10 h. Up to 30% may remain in the body after 24 h. Accumulation may occur on repeated dosage.
extravenous injection causes pain and erythema.
intra-arterial injection causes intense pain, and may cause distal blistering, oedema and gangrene, attributed to crystallisation of thiopental within arterioles and capillaries, with local noradrenaline release and vasospasm. Endothelial damage and subsequent inflammatory reaction have been suggested as being more likely. Particularly hazardous with the 5% solution, now rarely used. Treatment: leaving the needle/cannula in the artery, the following may be injected:
– vasodilators, traditionally papaverine 40 mg, tolazoline 40 mg, phentolamine 2–5 mg, to reduce arterial spasm.
– local anaesthetic, traditionally procaine 50–100 mg (also a vasodilator), to reduce pain.
– heparin, to reduce subsequent thrombosis.
Brachial plexus block and stellate ganglion block have been used to encourage vasodilatation (before heparinisation). Postponement of surgery has been suggested.
respiratory/cardiovascular depression as above.
adverse drug reactions. Severe anaphylaxis is rare (1:14 000–35 000), typically occurring after several previous exposures.
• Dosage:
3–6 mg/kg iv. Requirements are reduced in hypoproteinaemia, hypovolaemia, the elderly and critically ill patients. Injection should be over 10–15 s, with a pause after the expected adequate dose before further administration.
has also been given rectally: 40–50 mg/kg as 5–10% solution.
Fig. 154 Structure of thiopental
Thiosulphate, see Cyanide poisoning
Third gas effect, see Fink effect
Third space. ‘Non-functional’ interstitial fluid compartment, to which fluid is transferred following trauma, burns, surgery and other conditions, including infection, pancreatitis. Most of the fluid originates from the ECF, but some movement from intracellular fluid also occurs. Includes fluid lost to the transcellular fluid compartment, e.g. ascites, bowel contents. Although not lost from the body, fluid shifts to the third space are equivalent to functional ECF losses and must be accounted for when estimating fluid balance. Losses may exceed 10 ml/kg/h during abdominal surgery, and should be replaced initially with 0.9% saline or Hartmann’s solution, although colloids may also be used.
• Contents (see Fig. 26; Brachial plexus and Fig. 104; Mediastinum):
– right side: brachiocephalic vessels; vagus; phrenic nerve.
– left side: common carotid/subclavian arteries; vagus; brachiocephalic vein; phrenic nerve.
Thoracic inlet X-ray views may be useful if tracheal compression or displacement is suspected.
Thoracic surgery. The first pneumonectomy was performed in 1895 by Macewan. Surgical and anaesthetic techniques improved with experience of treating chest injuries during World War II. The commonest indication for thoracic surgery was formerly TB and empyema but is now malignancy, especially bronchial carcinoma.
• Main anaesthetic principles:
– preoperative assessment of exercise tolerance, cough and haemoptysis. Ischaemic heart disease secondary to smoking is common. Cyanosis, tracheal deviation, stridor, abnormal chest wall movement, pleural effusion and systemic features of malignancy may be present.
– investigations include CXR, CT scanning and MRI. Distortion of the trachea/bronchi should be noted as this may hinder endobronchial intubation. Rarely, bronchography is performed, e.g. in bronchiectasis. Arterial blood gas interpretation and lung function tests are routinely performed, e.g. spirometry, flow–volume loops. A poor postoperative course following pneumonectomy is suggested if any of FVC, FEV1, maximal voluntary ventilation, residual volume : total lung capacity ratio or diffusing capacity is < 50% of predicted. Pulmonary hypertension is also associated with poor outcome.
– cardiopulmonary exercise testing may be employed; a maximum O2 uptake of < 15 ml/kg/min is cited as predictive of poorer outcomes.
– preparation includes antibiotic therapy, physiotherapy and use of bronchodilator drugs as appropriate.
– premedication commonly includes anticholinergic drugs to reduce secretions.
– specific diagnostic procedures include bronchoscopy, mediastinoscopy, bronchography and oesophagoscopy.
– preoxygenation is usually employed. IV induction of anaesthesia is usually suitable; difficulties may include cardiovascular instability, airway obstruction, difficult tracheal intubation, risk of aspiration of gastric contents in oesophageal disease and problems of lesions affecting the mediastinum.
– endobronchial tubes are often used, although standard tracheal tubes are usually acceptable unless isolation of lung segments is required. Endobronchial blockers may also be used.
– large-bore iv cannulae are vital, since blood loss may be severe.
– standard monitoring is used; arterial and central venous cannulation is often employed.
– maintenance of anaesthesia is usually with standard agents and techniques. Pendelluft, 
mismatch and decreased venous return secondary to mediastinal shift may also occur. Hypoxaemia is common during one-lung anaesthesia. Injector techniques and high-frequency ventilation have been used for tracheal resection.
– positioning of the patient: the lateral position with the operative lung uppermost is usual. The arm is placed over the head, displacing the scapula upwards. Drainage of secretions from the affected lung without soiling the unaffected lung may be achieved using the Parry Brown position (prone, with a pillow under the pelvis and a 10 cm rest under the chest; the arm on the operated side overhangs the table’s edge with the head turned to the opposite side, and the table is tipped head-down so that the trachea slopes downwards).
– at closure of the chest, the lung is re-expanded after endobronchial suction. Up to 40 cmH2O airway pressure may be requested by the surgeon to test bronchial sutures. Tubes are placed for chest drainage. After pneumonectomy, chest drains are often not used; air is introduced or removed to equalise the intrapleural pressures on both sides and centralise the mediastinum. The pleural space slowly fills with fluid postoperatively, with eventual fibrosis.
– postoperative analgesia is vital to ensure adequate ventilation. Standard techniques are used, including patient-controlled analgesia, thoracic epidural anaesthesia and use of spinal opioids. Cryoanalgesia and intercostal nerve block may be performed by the surgeon whilst the chest is open.
Specific procedures and conditions include removal of inhaled foreign body, repair of bronchopleural fistula, chest trauma and bronchopulmonary lavage.
[Arthur I Parry Brown (1908–2007), London anaesthetist; Ivor Lewis (1895–1982), London surgeon]
Thoracocardiography, see Inductance cardiography
Three-in-one block, see Femoral nerve block; Lumbar plexus
Thrombin inhibitors. Group of compounds that bind to various sites on the thrombin molecule, investigated as alternatives to heparin. Includes hirudin and related substances. Ximelagatran, a prodrug for melagatran, was extensively investigated as an oral anticoagulant but withdrawn in 2006 following reports of hepatic impairment. Rivaroxaban and dabigatran are licensed for the prevention of DVT in adults undergoing elective hip or knee replacement; the latter is also used for prevention of CVA in high-risk patients with atrial fibrillation.
Thrombin time, see Coagulation studies
Thrombocytopenia. Defined as a platelet count below 100 × 109/l. Common in critically ill patients.
decreased production: e.g. bone marrow depression (by drugs, infection, etc.), vitamin B12/folate deficiency, hereditary defects, paroxysmal nocturnal haemoglobinuria, thiazide diuretics, alcoholism.
– immune: autoantibodies (e.g. idiopathic thrombocytopaenic purpura, SLE, rheumatoid arthritis, malignancy, drugs (e.g. quinine, heparin, α-methyldopa), infection (e.g. HIV), alloantibodies (e.g. post-transfusion).
– non-immune: DIC, thrombotic thrombocytopenic purpura, cardiopulmonary bypass, haemolytic–uraemic syndrome.
Patients with platelet counts above 50 × 109/l are usually asymptomatic. Bleeding time increases progressively as the count falls below 100 × 109/l. Counts below 20–30 × 109/l may be associated with spontaneous bleeding, e.g. mucocutaneous, gastrointestinal, cerebral. Diagnosis of the underlying condition requires examination of the blood film and bone marrow and coagulation studies.
Regional anaesthesia in the presence of thrombocytopenia (e.g. in obstetric analgesia and anaesthesia) is controversial, with any benefits weighed against the potential risk of spinal haematoma. Many anaesthetists would consider a platelet count above 70–80 × 109/l acceptable if there is no clinical evidence of impaired function (e.g. bruising or noticeably prolonged bleeding), coagulation studies are normal, the count has been stable for at least several days and regional anaesthesia would be particularly advantageous.
Thromboelastography (TEG). Point-of-care coagulation monitoring technique that assesses the speed and quality of clot formation (and resolution). A pin is suspended via a torsion wire in a sample of whole fresh blood held in a rotating cuvette (usually combined with a coagulation activator); as the clot forms, the rotation of the cuvette is transmitted to the pin, the movement of which thus reflects the viscoelastic properties of the clot as it forms and resolves. This movement is transduced to an electrical signal and displayed, giving the characteristic TEG trace (Fig. 155). A related technique uses an optical detector system to measure the movement of the pin (termed ROTEM or rotational thromboelastometry). Initially used mainly during liver transplantation and cardiac surgery, it is increasingly being used to guide administration of blood products in other situations involving major haemorrhage, e.g. obstetrics and trauma.
• TEG parameters and normal ranges:
clot formation/‘K’ time (time for clot firmness to reach 20 mm): 1–4 min. Prolonged by thrombocytopenia, hypofibrinogenaemia and anticoagulants.
maximum amplitude (MA; maximum clot strength): 55–73 mm. Parameter most influenced by platelet number and function; reduced by thrombocytopenia and antiplatelet drugs.
LY30 (per cent clot lysis at 30 s): < 7.5%. Increased in early DIC.
• Advantages over standard laboratory studies:
faster acquisition of results.
incorporates assessment of platelet function.
analysis can be performed at the patient’s body temperature (thus taking into account the effect of hypothermia if present).
ability to add activators/inhibitors to analyse specific aspects of coagulation (e.g. heparinase to assess the effect of administered heparin)
Thromboembolism, see Coagulation; Deep vein thrombosis
