t_1/2,  see Half-life

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 V_3–6; the upper height limit is 5 mm in the standard leads and 10 mm in the chest leads.

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.

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:

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

TCD,  see Transcranial Doppler ultrasound

TCI,  Target-controlled infusion, see Propofol

TEE,  Transesophageal echocardiography, see Transoesophageal echocardiography

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.

Dentures and removable bridges are traditionally removed before anaesthesia, in case they become dislodged and obstruct or pass into the airway. However, the need for routine preoperative removal of dentures has been questioned since this may cause distress to patients. If damage to teeth does occur, avulsed or broken teeth should be retrieved and stored in saline for possible reimplantation (up to 90% success rate if performed within 30 min); the extent of damage should be documented and the patient referred as soon as possible to a dentist (ideally in the same hospital) who can carry out necessary emergency treatment.

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.

10–30 mg orally, 45–60 min preoperatively, is usually an effective anxiolytic. For children, 0.5 mg/kg may be given. Gel-filled capsules were withdrawn from NHS use in 1995 because of abuse by iv drug users, the liquefied gel causing marked vascular damage on injection. Temazepam became a Schedule 3 Controlled Drug in 1996, although without special prescription requirements.

See also, Misuse of Drugs Act

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.

[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.

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.

Pitoni S, Sinclair HL, Andrews PJD (2011). Curr Opin Crit Care; 17: 115–21

See also, Heat loss during anaesthesia

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.

See also, Intubation, difficult; Trismus

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.

TENS,  see Transcutaneous electrical nerve stimulation

Tensilon test,  see Edrophonium

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.

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.

Camorcia M (2009). Curr Opin Anesthesiol; 22: 336–40

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

Tetanus.  Disease caused by infection with Clostridium tetani, a prevalent spore-forming Gram-positive bacillus found in soil, dust and faeces. Inoculation may be via minor injury. Rare in developed countries following immunisation programmes, but accounts for up to 1 million deaths annually worldwide. Recently reported in drug abusers ‘skin-popping’ contaminated heroin.

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.

Mortality is 15% in those treated in modern ICUs (greater in previously unvaccinated individuals, if age exceeds 50, and if generalised spasms rapidly follow initial symptoms).

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

See also, Clostridial infections

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.

Maximal safe dose: 1.5 mg/kg.

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).

Peters M, Heijboer H, Smiers F, Giordano PC (2012). Br Med J; 344: e228

[Thomas B Cooley (1871–1945), US paediatrician]

THAM,  tris-(hydroxymethyl)-aminomethane, see 2-Amino-2-hydroxymethyl-1,3-propanediol

Theophylline.  Bronchodilator drug, used alone or in combination with ethylenediamine as aminophylline.

Actions and effects: as for aminophylline.

Therapeutic intervention scoring system (TISS).  Scoring system for assessing the severity of critical illness according to the number of interventions a patient receives. Originally comprising over 70 interventions that were scored 1–4 according to complexity and invasiveness; more recent modifications have reduced this number to < 30. Although of value in an individual clinician’s practice, the score for a particular patient may vary between clinicians and units according to differences in treatment strategies. Has been used as a means of assessing the need for ICU resources.

Miranda DR (1997). Intensive Care Med; 23: 615–17

Therapeutic ratio/index.  Relationship between the doses of a drug required to produce toxic and therapeutic effects. A drug with a high therapeutic ratio has a greater margin of safety than one with low therapeutic ratio. Defined experimentally as the ratio of median lethal dose to median effective dose:

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. pK_a 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).

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.

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.

See also, Stress response to surgery

Thoracic inlet.  Kidney-shaped superior (cranial) opening of the thorax, bounded by the superior border of the manubrium sternum anteriorly, first thoracic vertebra posteriorly, and the first ribs laterally. Anteroposterior diameter is about 5 cm; transverse diameter about 10 cm. Its plane slopes downward (60° to the horizontal) and forward.

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.

Specific procedures and conditions include removal of inhaled foreign body, repair of bronchopleural fistula, chest trauma and bronchopulmonary lavage.

Similar considerations apply to oesophageal surgery. Ivor Lewis oesophagectomy (performed for carcinoma of the middle third of the oesophagus) involves laparotomy to mobilise the stomach and duodenum, followed by turning of the patient and right thoracotomy. Patients are often malnourished.

[Arthur I Parry Brown (1908–2007), London anaesthetist; Ivor Lewis (1895–1982), London surgeon]

See also, Pneumothorax

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.

Lee CJ, Ansell JE (2011). Br J Clin Pharmacol; 72: 581–92

Thrombin time,  see Coagulation studies

Thrombocytopenia.  Defined as a platelet count below 100 × 10⁹/l. Common in critically ill patients.

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.

Arnold DM, Lim W (2011). Semin Hematol; 48: 251–8

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.

Ganter MT, Hofer CK (2008). Anesth Analg; 106: 1366–75

Thromboembolism,  see Coagulation; Deep vein thrombosis

Thrombolytic drugs,  see Fibrinolytic drugs

Thrombophlebitis,  see Intravenous fluid administration

Thromboplastin time,  see Coagulation studies

Thrombotic thrombocytopenic purpura (TTP).  Rare disorder characterised by intravascular thrombosis, consumptive thrombocytopenia and haemolytic anaemia (due to mechanical damage to red cells). May be difficult to distinguish from haemolytic–uraemic syndrome (with which it is thought to overlap) and DIC. Often associated with increased plasma levels of large von Willebrand factor multimers and a congenital deficiency of a specific metalloprotease that cleaves it, ADAMTS13. Clinical episodes are often preceded by triggering events (e.g. surgery, infection, pregnancy) in susceptible individuals.

Typically presents with abdominal pain, nausea/vomiting and weakness. Neurological symptoms (e.g. CVA, convulsions) may also occur. Diagnosed largely clinically.

Treated by plasmapheresis, for which there is good evidence of efficacy. Immunosuppressive drugs have also been used, e.g. corticosteroids. Refractory disease has been treated with intravenous immunoglobulins. Untreated, may rapidly progress to death in ~80% of cases; mortality with treatment is ~20%.

Kiss JE (2010). Int J Hematol; 91: 36–45

Thromboxanes.  Substances related to prostaglandins, synthesised by the action of cyclo-oxygenase on arachidonic acid. Thromboxane A₂ is released by platelets at sites of injury, causing vasoconstriction and platelet aggregation, and is opposed by prostacyclin. It is metabolised to thromboxane B₂, which has little activity.

Thymol.  Aromatic hydrocarbon used as an antioxidant in halothane and trichloroethylene. May build up inside vaporisers unless cleaned regularly. Also used as a disinfectant and deodorant, e.g. in mouthwashes.

Thyroid crisis (Thyroid storm).  Rare manifestation of severe hyperthyroidism. May be triggered by stress, including surgery and infection. Features include tachycardia, arrhythmias (including VT, VF and AF), cardiac failure, fever, diarrhoea, sweating, hyperventilation, confusion and coma.

Thyroid gland.  Largest endocrine gland, extending from the attachment of sternothyroid muscle to the thyroid cartilage superiorly, to the sixth tracheal ring inferiorly. The two lateral lobes lie lateral to the oesophagus and pharynx, with the isthmus overlying the second to fourth tracheal rings anteriorly. Arterial supply is via the superior and inferior thyroid arteries (branches of the external carotid arteries and thyrocervical trunk of the subclavian artery respectively). The external and recurrent laryngeal nerves are closely related to the superior and inferior thyroid arteries respectively.

Produces thyroxine (T₄) and triiodothyronine (T₃), which increase tissue metabolism and growth. They also increase the effects of catecholamines by increasing the number and sensitivity of β-adrenergic receptors. Iodine is absorbed from the GIT as iodide and actively transported into the thyroid gland, where it is oxidised by a peroxidase and bound to thyroglobulin. Iodination of tyrosine residues of thyroglobulin produces T₃ and T₄, which are cleaved from the parent molecule. Both hormones are more than 99% bound to plasma proteins, including thyroxine binding globulin (TBG) and albumin. T₃ is secreted in smaller amounts than T₄, is 3–5 times as potent, is faster acting, and has a shorter half-life. T₄ is converted to T₃ peripherally.

Control of T₃ and T₄ production is by thyroid stimulating hormone (TSH), secreted by the pituitary gland. Secretion is inhibited by T₃, T₄ and stress, and stimulated by thyrotrophin releasing hormone (TRH), secreted by the hypothalamus. TRH secretion is also inhibited by T₃ and T₄.

The gland also secretes calcitonin, important in calcium homeostasis, from parafollicular (C) cells.

Anaesthetic considerations of thyroid surgery: as for hyper-/hypothyroidism.

See also, Neck, cross-sectional anatomy; Sick euthyroid syndrome

Thyroidectomy,  see Hyperthyroidism; Thyroid gland

Thyrotoxicosis,  see Hyperthyroidism; Thyroid crisis

Tibial nerve block,  see Ankle, nerve blocks; Knee, nerve blocks

Ticagrelor.  Nucleoside analogue antiplatelet drug, used in combination with aspirin in patients with acute coronary syndromes. More effective than clopidogrel at reducing ischaemic events and all-cause mortality, but with a higher risk of minor bleeding.

Antagonises platelet P2Y₁₂ ADP receptors, thereby inhibiting ADP-mediated platelet aggregation by blocking the glycoprotein IIb/IIIa pathway. Oral bioavailability is 35%, with peak clinical effect occurring within 2–4 h. Eliminated via hepatic metabolism, with a half-life of 7–8 h. As with clopidogrel, cessation 7 days before surgery is recommended.

Ticarcillin.  Carboxypenicillin antibacterial drug, used primarily for pseudomonas infections, although also active against other Gram-negative organisms. Available in the UK only in combination with clavulanic acid.

Tick-borne diseases.  Common worldwide, although uncommon in the UK; soft ticks cause a variety of skin lesions and transmit spirochaetal relapsing fevers whilst hard ticks are the vectors for arboviral haemorrhagic fevers, encephalitis, typhus and Lyme disease. Rarely, tick bites may result in ascending flaccid paralysis, leading to respiratory and bulbar involvement within a few days unless the tick is removed. The causative agent is unknown. Treatment is supportive, with appropriate antibacterial drugs (e.g. tetracyclines or aminoglycosides).

Graham J, Stockley K, Goldman RD (2011). Pediatr Emerg Care; 27: 141–7

Tidal volume.  Volume of gas inspired and expired with each breath. Normally 7 ml/kg. Measured using spirometers or respirometers. ‘Effective’ tidal volume equals tidal volume minus dead space volume.

See also, Lung volumes

Tigecycline.  Antibacterial drug related to tetracycline; active against Gram-positive and -negative organisms and some anaerobic bacteria. Reserved for complicated soft tissue and abdominal infections.

Time constant (τ).  Expression used to describe an exponential process. Equals the time in which the process would be completed if the rate of change were maintained at its initial value. May also be described as the ratio of quantity present to the rate of change of quantity at that moment. At 1τ the process is 63% complete (i.e. 37% of the initial quantity remains), at 2τ it is 86.5% complete, and at 3τ it is 95% complete. After 6τ the process is 99.75% complete.

When used to refer to passive expiration of air from the lungs, τ equals compliance × resistance; thus stiff alveoli served by narrow airways empty at similar rates to compliant alveoli served by wide airways. May also be applied to the washout of nitrogen from the lungs during preoxygenation; τ equals FRC divided by alveolar ventilation.

See also, Half-life

Time to sustained respiration.  Time for adequate regular respiration to occur in the neonate after delivery, without stimulation. Related to fetal wellbeing and respiratory depression caused by drugs administered to the mother before delivery.

See also, Fetus, effects of anaesthetic drugs on; Obstetric analgesia and anaesthesia

Tinzaparin sodium,  see Heparin

Tirofiban.  Antiplatelet drug, used in acute coronary syndromes, within 12 h of the last episode of chest pain. Acts by reversibly inhibiting activation of the glycoprotein IIb/IIIa complex on the surface of platelets.

TISS,  see Therapeutic intervention scoring system

Tissue oxygen tension,  see Oxygen, tissue tension

TIVA,  see Total intravenous anaesthesia

TMJ,  see Temporomandibular joint

TNS,  Transcutaneous nerve stimulation, see Transcutaneous electrical nerve stimulation

Tobramycin.  Aminoglycoside and antibacterial drug with similar activity to gentamicin but more active against pseudomonas, although less active against other Gram-negative organisms.

Tocainide hydrochloride.  Class Ib antiarrhythmic drug previously used for life-threatening ventricular arrhythmias. Withdrawn from use in the UK and USA due to severely toxic side effects, including life-threatening agranulocytosis, thrombocytopenia, hepatitis, pneumonitis and an SLE-like syndrome.

Tocolytic drugs.  Used to inhibit uterine contractions when premature delivery of the fetus is threatened, to prevent uterine activity during/after incidental maternal surgery or fetal surgery, and to relax the uterus acutely, e.g. in fetal distress, obstructed delivery or uterine inversion. Drugs traditionally used are β₂–adrenergic receptor agonists and include ritodrine, salbutamol and terbutaline. Side effects may persist after discontinuation of the infusion; these include tachycardia, arrhythmias, hypotension and occasionally pulmonary oedema (unclear mechanism, but thought to involve increased pulmonary hydrostatic pressure; fluid administration and concomitant corticosteroids may also contribute). Arrhythmias may occur if halothane is subsequently used.

Other tocolytic drugs include atosiban (an oxytocin antagonist), which is more expensive but has fewer side effects than β₂-agonists in preterm labour (although it may cause nausea, vomiting, tachycardia and hypotension). Nifedipine, magnesium sulphate and inhibitors of prostaglandin synthesis (e.g. indometacin) also cause tocolysis but are not widely used in the UK. GTN patches have also been used. Acutely, GTN 100–400 µg iv or sublingually is also used.

See also, Obstetric analgesia and anaesthesia

TOE,  see Transoesophageal echocardiography

Tolazoline hydrochloride.  α-Adrenergic receptor antagonist, structurally related to phentolamine. Traditionally used by iv infusion to relieve arterial spasm following accidental intra-arterial injection of thiopental. Also used to reduce pulmonary vascular resistance, e.g. in congenital diaphragmatic hernia.

Tolerance.  Progressively decreasing response to repeated administration of a drug. May result from altered number of receptors, altered response to receptor activation, altered pharmacokinetics (e.g. enzyme induction) or development of physiological compensatory mechanisms. Classically occurs with morphine.

See also, Tachyphylaxis

Tongue.  Muscular organ attached to the hyoid bone and mandible. Covered by mucous membrane and divided into anterior two-thirds and posterior one-third by a V-shaped groove, the sulcus terminalis. At the latter’s apex is a small depression, the foramen caecum. The lower surface is attached to the floor of the mouth by the frenulum.

The tone of genioglossus is important in preventing approximation of the tongue and posterior pharyngeal wall, which results in airway obstruction. Genioglossus tone varies with respiration and is maximal in inspiration. It also decreases during sleep; this may contribute to the development of sleep apnoea. Anaesthetic and sedative agents decrease this tone and thus predispose to obstruction, which may be relieved by elevating the jaw, placing the patient in the lateral position, and use of pharyngeal airways.

Macroglossia predisposes to respiratory obstruction and may hinder tracheal intubation, e.g. in acromegaly, Down’s syndrome and light chain amyloidosis. It may also occur after posterior fossa neurosurgery. Tongue piercing studs should be removed preoperatively.

Tongue forceps,  see Forceps

Tonicity.  Refers to the effective osmotic pressure of solutions in relation to that of plasma. Thus a urea solution may be isosmotic with plasma but its effective osmotic pressure (and thus tonicity) falls after infusion because urea distributes evenly across cell membranes. Similarly, 5% dextrose solution is isosmotic with plasma but hypotonic when infused since the dextrose is metabolised by red blood cells leaving water.

See also, Intravenous fluids

Tonometry, gastric,  see Gastric tonometry

Tonsil, bleeding.  Haemorrhage usually occurs within a few hours postoperatively, but may be delayed.

See also, Ear, nose and throat surgery; Induction, rapid sequence

Topical anaesthesia.  Application of local anaesthetic agent (e.g. cocaine, lidocaine, tetracaine) to skin or mucous membranes to produce anaesthesia. Used on the skin, conjunctiva, nasal passages, larynx and pharynx, tracheobronchial tree, rectum and urethra. Local anaesthetic has also been instilled into the bladder, pleural cavity, peritoneal cavity and synovial fluid of joints.

May be applied via direct instillation, soaked swabs, pastes/ointments or sprays. Systemic absorption may be rapid and the maximal safe doses should not be exceeded.

See also, EMLA cream; Iontophoresis

Torr.  Non-SI unit of pressure; 1 torr = 1/760 atmosphere = 1 mmHg.

[Evangelista Torricelli (1608–1647), Italian physicist]

Torsade de pointes.  Atypical VT characterised by polymorphic QRS complexes with repeated fluctuations of QRS axis, the complexes appearing to twist about the baseline (Fig. 156). Often associated with a prolonged Q–T interval. Initiated by a ventricular ectopic beat occurring during a prolonged pause after a previous ectopic.

Class I antiarrhythmic drugs should be avoided.

Total intravenous anaesthesia (TIVA).  Anaesthetic technique employing iv agents alone, and avoiding the use of inhalational agents. The patient breathes O₂, air, or a mixture of the two. Drugs are given usually by infusion to achieve anaesthesia and appropriate analgesia. The drugs chosen are usually of short action and half-life to prevent accumulation and prolonged recovery. Examples include propofol, together with alfentanil, fentanyl or remifentanil. Ketamine has been used for its analgesic properties, e.g. together with midazolam. Neuroleptanaesthesia has also been used.

Total lung capacity.  Volume of gas in the lungs after maximal inspiration. Normally approximately 6 litres. Determined by helium dilution (does not measure gas in poorly ventilated regions) or with the body plethysmograph.

See also, Lung volumes

Total parenteral nutrition,  see Nutrition, total parenteral

Tourniquets.  Used to reduce bleeding during limb surgery, and to allow IVRA. Inflated following exsanguination of the limb, e.g. by raising it for 2–3 min with the artery compressed, or by using a rubber Esmarch bandage. The latter increases CVP and may provoke cardiac failure in susceptible patients. It may also dislodge emboli from DVTs. Complications from tourniquets include: direct skin, muscle, nerve or vascular injury; reperfusion hyperaemia and limb oedema; and hypertension and tachycardia due to pain.

Equipment should be checked before use. Tourniquets should not be used in sickle cell anaemia (avoidance in sickle trait has also been suggested). Protective padding is required under the tourniquet. Skin preparation solutions may cause chemical burns if allowed to soak into the padding.

[Johann FA von Esmarch (1823–1908), German surgeon]

Estebe JP, Davies JM, Richebe P (2011). Eur J Anaesthesiol; 28: 404–11

See also, Compartment syndromes

Toxic epidermal necrolysis,  see Stevens–Johnson syndrome

Toxic shock syndrome.  Systemic illness associated with certain Staphylococcus aureus strains, thought to be caused by exotoxins (possibly with concurrent Gram-negative endotoxin production). Streptococci have also been implicated.

First described in 1978; the reported incidence increased around 1980, especially associated with menstruation and use of tampons. Features typically occur rapidly and include fever, hypotension, GIT upset, headache and myalgia. Generalised rash and/or oedema lead to desquamation 10–20 days later. MODS may occur. Treatment is supportive, with antibacterial drug therapy.

TPN,  Total parenteral nutrition, see Nutrition, total parenteral

TPR,  Total peripheral resistance, see Systemic vascular resistance

Trachea,  see Tracheobronchial tree

Tracheal administration of drugs.  Previously used when iv administration was not possible, e.g. cardiac arrest. Superseded by the intraosseous route in the emergency setting. Previously advocated at 2–3 times the iv dose, diluted in 10 ml saline; atropine, adrenaline and lidocaine were the drugs most commonly administered in this way. Many respiratory drugs are administered using inhalers and nebulisers.

Tracheal extubation,  see Extubation, tracheal

Tracheal intubation,  see Intubation, tracheal

Tracheal tubes.  Developed along with techniques for tracheal intubation. O’Dwyer described his intubating tube in 1885, although various tubes had been used previously, e.g. for CPR. The modern wide-bore tracheal tube was developed by Magill and Rowbotham after World War I, following the use of thin gum-elastic tubes for insufflation techniques. Separate tubes were placed into the trachea for delivery and removal of gases; these were eventually replaced by a single rubber (‘Magill’) tube. Cuffs were introduced by Guedel in 1928. Red rubber tracheal tubes have largely been replaced by sterile disposable polyvinyl chloride tubes, since the former deteriorate on repeated sterilisation, are more costly to use, and are irritant to the respiratory mucosa. Plastic tubes soften as they warm, e.g. in the trachea, and may be vulnerable to kinking.

Size 9 mm and 8 mm internal diameter orotracheal tubes are often employed for men and women respectively; smaller tubes (e.g. 7 mm and 6 mm) are often used in the elective surgical setting since they are associated with a lower incidence of sore throat and hoarse voice. However, for emergency intubation and ICU admission, larger-bore tubes are preferred to facilitate tracheobronchial suctioning and fibreoptic bronchoscopy. Average suitable length is 22–25 cm for oral tubes, and 25–28 cm for nasal tubes (for sizes of tubes for children, see Paediatric anaesthesia).

Tubes may bear an extra channel for sampling of distal gases or for jet ventilation. A directional tube has also been described, in which traction on a ring at the proximal end flexes the distal end, aiding placement during tracheal intubation. Laser-protected tubes include tubes made totally out of metal and those coated with ‘laser-proof’ substances.

[Francis J Murphy (1900–1972), Detroit anaesthetist; Frank Cole (1918–1977), US anaesthetist; RAE: Wallace H Ring, John C Adair, Richard A Elwyn, Salt Lake City anaesthetists]

See also, Endobronchial tubes; Intubation, tracheal; Tracheostomy

Tracheobronchial suctioning.  Required in patients who have a tracheal tube in place because of inability to mobilise secretions effectively. Also useful for diagnostic purposes, e.g. for obtaining sputum samples. The catheter should be inserted gently until resistance is felt, withdrawn slightly and suction applied whilst withdrawing. ‘Closed’ suction systems are used in the ICU setting to reduce the risk of bacterial contamination of the airway.

See also, Ciliary activity

Tracheobronchial tree.  Branching system consisting of 23 generations of passages from trachea to alveoli, comprising:

[Pierre CA Louis (1787–1872), French physician]

See also, Alveolus; Ciliary activity; Lung

Tracheo-oesophageal fistula (TOF).  Oesophageal atresia occurs in 1:3000 births, with TOF in 25% of cases. Different forms exist (Fig. 159). Babies may be premature and have other congenital abnormalities. TOF may present with choking during feeds, production of copious frothy mucus from the mouth or repeated chest infections following pulmonary aspiration. It is diagnosed by passing a radio-opaque nasogastric tube into the blind pouch; contrast medium is avoided because of risk of aspiration. Treated by surgery, performed thorascopically or via right thoracotomy. Primary anastomosis of the oesophagus is performed if possible.

After repair, a blind passage may remain at the site of the fistula, making subsequent tracheal intubation difficult. Tracheomalacia may also occur.

Broemling N, Campbell F (2011). Pediatr Anesth; 21: 1092–9

Tracheostomy.  First performed in the 1700s for upper airway obstruction. Modern indications:

The traditional open procedure may be performed under general or local anaesthesia. The patient lies supine with the neck hyperextended, and a horizontal incision is made 1.5 cm below the level of the cricoid cartilage. After location of the trachea, a vertical incision is made through the second, third and fourth tracheal rings. A slit or circular opening is made in the trachea (creation of a tracheal flap has been implicated in causing tracheal stenosis). During general anaesthesia, ventilation with 100% O₂ should precede withdrawal of the tracheal tube (which is withdrawn into the larynx only, in case readvancement is required). The tracheostomy tube is then inserted. Stay sutures may be brought out on to the skin from the trachea, to aid subsequent tube reinsertion.

Increasingly, surgical tracheostomy is being replaced by the percutaneous procedure, especially in critically ill patients receiving IPPV (see Tracheostomy, percutaneous).

The initial tube is usually left in situ for at least a week, to allow formation of a tract. The tube may be changed over a thin catheter or guide-wire. Once decannulated, the stoma usually closes spontaneously within a few days, but surgical closure may be required.

Mallick A, Bodenham AR (2010). Eur J Anaesthesiol; 27: 676–82

See also, Minitracheotomy

Tracheostomy, percutaneous.  Increasingly used in critically ill patients requiring tracheostomy instead of the traditional open procedure because of the following advantages:

Avoided in children and in the presence of coagulopathy, localised infection and difficult anatomy.

Complications are as for open surgery; initial studies suggest their incidence is low. Tracheal tears and oesophageal perforation may occur with all the above methods.

[Pasquale Ciaglia (1912–2000), US thoracic surgeon; Bill Griggs, Australian intensivist]

Cabrini L, Monti G, Landoni G, et al (2012). Acta Anaesthesiol Scand; 56: 270–81

Train-of-four nerve stimulation,  see Neuromuscular blockade monitoring

TRALI,  Transfusion-related acute lung injury, see Blood transfusion

Tramadol hydrochloride.  Opioid analgesic drug, introduced in the UK in 1994. A pure agonist at mu opioid receptors, it is also a delta and kappa receptor agonist; it also inhibits noradrenaline uptake and enhances 5-HT release. Undergoes hepatic and renal elimination; contraindicated in patients with end-stage renal failure. Half-life is about 6 h. Administration with morphine was previously suggested to reduce the efficacy of both (i.e. an infra-additive effect); however, this is disputed, and several studies demonstrate that tramadol improves analgesia and reduces morphine requirements after major surgery.

Tranexamic acid.  Antifibrinolytic drug, used to reduce bleeding, e.g. in trauma, cardiac surgery, prostatectomy, menorrhagia or dental extraction in haemophiliacs; it has also been used in streptokinase overdose and hereditary angioneurotic oedema.

Transcranial Doppler ultrasound (TCD).  Application of ultrasound to demonstrate cerebral vessels. A low-frequency (2 MHz) pulse range-gated ultrasound beam is directed through the thin-boned transtemporal window; this allows assessment of the middle and anterior cerebral arteries of the cerebral circulation. Using the Doppler effect, flow velocities within these vessels can be determined. Uses include the detection of cerebral vasospasm following subarachnoid haemorrhage, assessment of cerebral blood flow (e.g. in head injury, carotid endarterectomy) and the detection of air embolism. Has also been used to assess cerebral autoregulation.

Kincaid MS (2008). Curr Opin Anaesthesiol; 21: 552–9

Transcutaneous electrical nerve stimulation (TENS).  Stimulation of peripheral nerves via cutaneous electrodes, to relieve pain. Based on the gate control theory of pain transmission; i.e. stimulation of Aβ fibres (by high-frequency TENS) and Aδ fibres (by low-frequency TENS) inhibits pain transmission by C fibres. Current is provided by a battery-powered pulse generator, which typically delivers a range of currents (0–50 mA), frequencies (0–200 Hz) and pulse widths (0.1–0.5 ms). Rectangular pulses are usually employed. Surface electrodes are usually carbon-impregnated silicone rubber.

The electrodes are placed either side of the painful area or its supplying nerves, and the current increased until tingling is felt. Experimentation with timing and duration is usually required to achieve maximal effects.

Has been used successfully in acute pain (e.g. for fractured ribs, labour, postoperatively), but is usually employed for chronic pain management (peripheral nerve disorders, spinal cord and root disorders, muscle pain and joint pain). Efficacy is difficult to assess as there is significant placebo effect, but TENS may reduce analgesic requirements.

Allergic dermatitis at electrode sites may occur. Contraindicated in patients with pacemakers.

Transducers.  Devices that convert one form of energy to another, usually to electricity in monitoring systems.

See also, Arterial blood pressure measurement; Damping; pH measurement; Pressure measurement; Temperature measurement

Transfer factor,  see Diffusing capacity

Transfusion,  see Blood transfusion

Transfusion-related acute lung injury,  see Blood transfusion

Transient radicular irritation syndrome (Transient neurologic syndrome).  Pain and dysaesthesia in the buttock, thighs or calves following spinal anaesthesia; usually occurs within 24 h of the block and typically resolves within 72 h. Particularly associated with the use of lidocaine in hyperbaric solutions of higher concentrations (2.5–5%), and very narrow-gauge needles or microcatheters, which result in pooling of the drug around nerve roots. The lithotomy position has also been implicated, via stretching of the lumbosacral nerve roots and increasing their vulnerability. The syndrome may reflect a transient form of cauda equina syndrome following continuous spinal anaesthesia.

Zaric D, Pace NL (2009). Cochrane Database Syst Rev; 2: CD003006

Transoesophageal echocardiography (TOE).  Form of echocardiography allowing imaging of the heart in a variety of different planes without requiring access to the chest. Increasingly used to assess cardiac function in awake, anaesthetised and critically ill patients. Basic principles are as for echocardiography and ultrasound, combined with the ability to manipulate the probe’s tip and place it under the heart within the stomach, behind the heart in the oesophagus or anywhere in between. Views may be obtained of the left and right atria and ventricles (both transversely and longitudinally), all valves and outflow tracts, and proximal aorta and pulmonary vessels.

Can be used to detect structural abnormalities, myocardial ischaemia or MI (manifest by changes in segmental wall motion), presence of valve vegetations, pericarditis and aortic abnormalities. Doppler analysis allows estimation of blood flows and cardiac output. Commonly used perioperatively during cardiac surgery, especially for:

Also used in high-risk patients undergoing non-cardiac surgery, and in ICU and emergency departments.

Complications include dental, pharyngeal and oesophageal trauma and cardiovascular disturbances. Contraindicated in oesophageal disease and upper GIT bleeding.

Greenhalgh DL, Patrick MR (2012). Anaesthesia; 67: 343–6

Transplantation.  Use of cadaveric or live donor tissues has increased with improved techniques and introduction of immunosuppressive drugs such as ciclosporin.

See also, Heart–lung transplantation; Heart transplantation; Liver transplantation; Lung transplantation; Renal transplantation

Transportation of critically ill patients.  May be primary (from site of injury or illness to hospital, e.g. by ambulance) or secondary (from one ICU to another). Up to 10 000 interhospital transfers of critically ill patients occur per year in the UK.

Ideally, transfer and retrieval systems should be planned and coordinated at local, regional and national levels, with adequate funding, clear guidelines and communication channels, and a transport coordinator (consultant) identified in each hospital. Considerable stabilisation may be required before transfer, avoiding transfer of unstable patients. All relevant notes and radiographs should accompany the patient.

Other aspects include audit of transfers (there should be documentation of patient observations, transfer events and any critical incidents) and team insurance. Although, in general, patients’ relatives should not travel with the patient, arrangements should be made for them to travel and be received at the receiving hospital. Patients may also require transfer between departments in a single hospital, e.g. from ICU to the radiology department. Similar considerations apply to those above.

See also, Safe transport and retrieval

Handy JM (2011). Anaesthesia; 66: 337–40

Transposition of the great arteries.  Accounts for 5% of congenital heart disease. Caused by failure of the truncus arteriosus to rotate during embryological development. The aorta arises from the right ventricle and the pulmonary artery from the left ventricle. Thus the pulmonary and systemic circulations work independently, resulting in severe hypoxaemia. Survival is only possible if a connection exists between the two circulations, e.g. ASD, VSD or patent ductus arteriosus. Other malpositions of the great arteries may occur.

Features include cyanosis, early cardiac failure and right ventricular hypertrophy, with normal pulmonary and systemic pressures. 85–90% of infants die within a year without treatment.

[William T Mustard (1914–1987), Toronto surgeon]

Sommer RJ, Hijazi ZM, Rhodes JF (2008). Circulation; 117: 1140–50

Transpulmonary thermodilution cardiac output measurement,  see Cardiac output measurement

Transurethral resection of the prostate (TURP).  Cystoscopic procedure for the removal of hypertrophied prostatic tissue.

General or regional techniques may be used. Postoperative course is generally considered to be better with the latter (spinal or epidural anaesthesia), which also allows monitoring of CNS function during the procedure.

Transversus abdominis plane block (TAP block).  Block of the nerves supplying the anterior abdominal wall by deposition of local anaesthetic agent in the fascial plane between the internal oblique and transversus abdominis muscles. Useful as part of a multimodal postoperative analgesia strategy, reducing requirements for opioid analgesic drugs after major abdominal surgery.

With the patient supine, a blunt needle is inserted perpendicular to the skin just cranial to the iliac crest and just anterior to the edge of the latissimus dorsi muscle. A resistance is felt as the external oblique aponeurosis is encountered, followed by a ‘give’ as it is pierced and a second ‘give’ as the needle passes through the internal oblique aponeurosis. After aspiration, 20 ml solution (e.g. 0.25–0.5% bupivacaine) is injected.

An in-plane ultrasound-guided technique may also be used, allowing visual confirmation of accurate placement of local anaesthetic; the ultrasound probe is placed in the mid-axillary line midway between the iliac crest and the costal margin.

Petersen PL, Mathieson O, Torup H, Dahl JB (2010). Acta Anaesthesiol Scand; 54: 529–35

See also, Abdominal field block, Rectus sheath block

Trauma.  Most common cause of death in young adults in the UK and USA, and the third commonest cause overall.

Management has been consistently shown to be inadequate in many cases, exacerbated by poor coordination of resources. Care in some countries (e.g. USA, Germany and Australia) is better organised than in the UK (e.g. 20% of deaths were considered preventable in recent Royal College of Surgeons of England reports).

Adequate resuscitation is required first unless surgery is life-saving. For surgery, regional techniques may be useful if no contraindications exist. Sedation should be avoided in head injury. Postoperative care should be on ICU/HDU unless injury is minor.

Recommendations now exist for the uniform reporting of data following major trauma using an Utstein style system.

See also, Emergency surgery; Transportation of critically ill patients

Trauma revised injury severity score (TRISS).  Trauma scale combining the revised trauma score (RTS), injury severity score (ISS), age and type of injury in an attempt to improve the individual scoring systems’ usefulness. Used primarily in audit since it provides a probability of survival and thus comparison against actual survival rates. Revised trauma and injury severity scores are each weighted by a coefficient depending on whether injury was blunt or penetrating, and the result adjusted again by a factor accounting for the patient’s age.

Trauma scales.  Scoring systems developed to aid assessment and triage of trauma cases, prediction of outcome, comparison between centres/countries. Several have been described:

See also, Audit; Mortality/survival prediction on intensive care unit

Trauma score.  Scoring system based on the Glasgow coma score, systolic BP, respiratory rate and effort, and capillary refill. Each is awarded points between 0–1 and 1–5, giving a total of 1–16, with 16 the best possible. Originally presented as a means of triage, with transfer of patients scoring under 12 to a trauma centre. Since capillary refill and respiratory effort may be difficult to assess in the field, they have been removed in the revised trauma score.

Traumatic neurotic syndrome.  Obsolete psychological diagnosis applied to patients whose claims of awareness during anaesthesia were met with professional denial, before the possibility of awareness was fully appreciated by anaesthetists. Sharing features with a general post-traumatic stress syndrome, it was characterised by recurrent nightmares, anxiety, irritability, preoccupation with death and fear of insanity. An excellent prognosis was possible once the patient’s experience was accepted by health workers.

Treacher Collins syndrome,  see Facial deformities, congenital

TREM-1 (Triggering receptor expressed on myeloid cells-1).  Immunoglobulin molecule thought to be involved in, and to amplify, the inflammatory pathway that is activated in sepsis.

Klesney Tait J, Turnbull IR, Colonna M (2006). Nat Immunol; 7: 1266–73

Triage.  Sorting of patients according to severity of injury in order to maximise total number of survivors. Usually refers to trauma cases in battles or major incidents, although similar approaches have been used in other fields of acute medicine, e.g. chest pain. First used during Napoleon’s Russian campaign by Larrey, who scored soldiers according to their need for medical treatment, treating the most severely injured first. Modern triage systems give first priority to those patients who might survive only if treated, leaving until later those expected to die even if treated, and those expected to survive even without treatment.

Assisted by trauma scales, with attention also paid to the mechanism of injury. Some systems include colour-coded labels with details of injuries, treatments, to be attached to patients. Triage may be repeated at different stages of retrieval and treatment, e.g. at the scene of accident, at the receiving hospital, on wards; thus patients may change in priority as circumstances change.

Trials, clinical,  see Clinical trials

Tribavirin,  see Ribavirin

Tricarboxylic acid cycle (Citric acid cycle; Krebs cycle).  Final common pathway for oxidation of carbohydrate, fat and some amino acids to CO₂ and water. Consists of a sequence of reactions that occur within mitochondria and require O₂. Acetyl coenzyme A (containing two carbon atoms) enters the cycle, having been formed from fat metabolism or glycolysis via pyruvate (Fig. 160). At each step where a carbon atom is lost, CO₂ is produced. For each turn of the cycle, 15 ATP molecules are formed via transfer of hydrogen atoms to the cytochrome oxidase system or formation of guanosine triphosphate (including the two ATP molecules generated by conversion of pyruvate to acetyl coenzyme A).

[Hans A Krebs (1900–1981), German-born English biochemist]

Trichloroethylene.  CCl₂CHCl. Inhalational anaesthetic agent, synthesised in 1864 and used clinically in 1935; withdrawn from use in the UK in 1988. Similar smell and properties to chloroform (hence coloured with waxoline blue to distinguish them). Decomposed by light, and stabilised by thymol 0.01%. Interacts with soda lime at 60°C to form dichloroacetylene (C₂Cl₂), a potent neurotoxin that may cause temporary or permanent damage to the cranial nerves, especially V and VII. Very soluble in blood (blood/gas partition coefficient of 9); induction and recovery are thus slow. Extremely potent (MAC 0.17) and a powerful analgesic. Previously popular in obstetrics as an analgesic agent, and for providing analgesia during IPPV; traditionally used instead of N₂O by the Armed Forces (e.g. in the triservice apparatus).

Triclofos.  Related drug to chloral hydrate. Metabolised to trichloroethanol, as is chloral hydrate. Discontinued in the UK in 2010.

Tricuspid valve lesions.  Tricuspid stenosis is usually associated with mitral stenosis and aortic valve disease resulting from rheumatic fever; may also coexist with pulmonary stenosis in the carcinoid syndrome. Isolated tricuspid stenosis is very rare.

Tricuspid regurgitation usually results from right ventricular enlargement, e.g. in right-sided cardiac failure. Usually causes little functional impairment.

See also, Ebstein’s anomaly

Tricyclic antidepressant drug poisoning.  Accounts for about 10% of cases of poisoning. Newer drugs (e.g. selective serotonin reuptake inhibitors) have better safety profiles.

See also, Tricyclic antidepressant drugs

Tricyclic antidepressant drugs.  Group of antidepressant drugs; the term includes several newer one-, two- and four-ring structured drugs with similar actions. Competitively block neuronal reuptake of noradrenaline and 5-HT. Also have CNS anticholinergic properties. Used in depression and pain management; analgesic properties are thought to be associated with impairment of 5-HT reuptake (e.g. especially by amitriptyline and clomipramine). Many cause sedation, e.g. amitriptyline, dosulepin (dothiepin), mianserin, trazodone and trimipramine. Sedation is less likely with clomipramine, nortriptyline, imipramine and desipramine.

2–4 weeks’ therapy is required before their effect is apparent. Half-lives may be up to 48 h. Metabolised in the liver and excreted renally.

See also, Tricyclic antidepressant drug poisoning

Trigeminal nerve blocks,  see Gasserian ganglion block; Mandibular nerve blocks; Maxillary nerve blocks; Nose; Ophthalmic nerve blocks

Trigeminal neuralgia (Tic douloureux).  Chronic pain state characterised by brief, severe lancinating pain involving the trigeminal nerve distribution. Usually involves the mandibular division; may also involve the glossopharyngeal nerve. Pain tends to be unilateral during the acute attack, which may be triggered by non-noxious stimulation of the ipsilateral nasal or perioral region (sometimes restricted to one specific zone). There is minimal or no sensory loss in the trigeminal distribution. Pain-free intervals typically separate attacks, which may be so severe as to cause suicide. Aetiology is uncertain, although it may be associated with an aberrant blood vessel loop abutting the trigeminal root in the pons.

Zakrzewska JM, McMillan R (2011). Postgrad Med J; 87: 410–16

See also, Gasserian ganglion block

Trigger points.  Areas in muscle or fascia in which mechanical stimulation may cause muscle pain, weakness and/or local twitching. May be latent (tender when palpated) or active (painful at rest or on exertion or stretching). Pain is often referred, giving rise to myofascial pain syndromes. Examination may reveal tender nodules within taut bands of muscle, felt especially if the fingertips are moved perpendicular to the direction of muscle fibres. May be numerous, and may correspond to traditional acupuncture points. Local anaesthetic injection and acupuncture may relieve symptoms.

Trimeprazine,  see Alimemazine

Trimetaphan camsylate.  Ganglion blocking drug, no longer generally available in the UK, used to lower BP during hypotensive anaesthesia. Its hypotensive effect is enhanced by a direct relaxant action on vascular smooth muscle and by histamine release from mast cells. Rapid onset and offset, thus usually given by iv infusion. Compensatory tachycardia is common. Tachyphylaxis may occur. Partially broken down by plasma cholinesterase and may have prolonged action in patients with decreased activity of this enzyme.

Trimethoprim.  Antibacterial drug used especially in urinary tract infections, exacerbations of COPD and in combination with the sulphonamide sulfamethoxazole (co-trimoxazole). Reversibly inhibits bacterial dihydrofolate dehydrogenase.

Triple point.  Temperature and pressure at which the solid, liquid and gas phases of a substance exist in equilibrium. The kelvin is defined according to the triple point of water (273.16 K at 611.2 Pa).

Triservice apparatus.  Anaesthetic apparatus adopted by the Armed Forces for battle use. Consists of (in order, starting at the patient):

For spontaneous ventilation, a draw-over technique is employed. Controlled ventilation may be performed by squeezing the bag, or replacing it with a suitable ventilator. A variety of volatile agents may be used in the vaporisers, the calibration scales of which may be changed accordingly. They are specially adapted to contain more liquid (50 ml), and are fitted with extendable feet. Halothane, enflurane or isoflurane is traditionally used in the upstream vaporiser, and trichloroethylene (to compensate for the absence of N₂O) in the downstream one.

Trismus.  Spasm of the masseter muscles, resulting in impaired mouth opening (lockjaw).

May occur after administration of suxamethonium (e.g. masseter spasm or in dystrophia myotonica).

Anaesthesia in the presence of trismus is as for airway obstruction and difficult intubation. Injection of local anaesthetic into the masseter muscle may relieve the spasm.

See also, Intubation, difficult

Trisodium edetate.  Chelating agent used in severe hypercalcaemia. Rarely used because of the risk of renal damage.

TRISS,  see Trauma revised injury severity score

Tropical diseases.  Many diseases are restricted to tropical and subtropical regions. Several are considered ‘tropical’ because they have been largely eradicated in developed countries, but may be imported by travellers. Anaemia and malnutrition are common features. Anaesthetic involvement may be related to ICU management or perioperative care.

[Carlos Chagas (1879–1934), Brazilian physician]

Tropisetron hydrochloride.  5-HT₃ receptor antagonist, licensed as an antiemetic drug in chemotherapy-induced nausea and vomiting. Similar to ondansetron but with longer duration of action.

Trypanosomiasis,  see Tropical diseases

TS,  see Trauma score

TSR,  see Time to sustained respiration

TT,  Thrombin time, see Coagulation studies

TTP,  see Thrombotic thrombocytopenic purpura

Tuberculosis (TB).  Infection with the acid- and alcohol-fast bacillus Mycobacterium tuberculosis that most commonly affects the lungs and lymph nodes, although any tissues may be affected. Declined in incidence through much of the twentieth century until an increase in the 1980s/90s, thought to be related to increases in world population, population movement, resistance to antituberculous drugs (itself related to poor compliance with treatment) and HIV infection, with which it is often associated. It has been estimated that one-third of the world’s population is infected with TB. In the UK, it is still largely restricted to migrants from developing countries, immunosuppressed patients and the homeless.

Ideally, single-use anaesthetic and respiratory equipment should be used for patients with active TB. Cases of spread to other patients have been reported in the ICUs of UK hospitals.

Lawn SD, Zumla AI (2011). Lancet; 378: 57–72

See also, Contamination of anaesthetic equipment

Tubocurarine chloride (D-tubocurarine chloride).  Non-depolarising neuromuscular blocking drug, isolated from curare in 1935. Its name is derived from the early classification of curare according to the means of storage (‘tubes’ refers to tubular bamboo canes). Commonly caused histamine release and ganglion blockade, with vasodilatation and hypotension. Severe anaphylaxis is rare. Excreted mainly in the urine, but 30% via the liver. Discontinued in the UK since 1996.

Tumescent anaesthesia.  Method of infiltrating large volumes of dilute local anaesthetic agent into tissues until they become swollen, used mainly for plastic surgery, e.g. liposuction. Typical solutions contain 0.05–0.1% lidocaine ± 1:1 000 000–1:2 000 000 adrenaline; bicarbonate, steroids and antibiotics have also been added. The volumes may exceed several litres, leading to the risk of local anaesthetic toxicity and fluid overload. PE and surgical complications have also been reported. May be used alone or in combination with sedation or general anaesthesia.

Tumour lysis syndrome.  Condition in which medical treatment of an aggressive malignancy (typically haematological) causes sudden release of intracellular contents, resulting in severe and potentially life-threatening hyperkalaemia, hypocalcaemia, hyperphosphataemia, lactic acidosis and hyperuricaemia. May occasionally occur spontaneously. Individual electrolyte abnormalities are managed along standard lines. Good hydration and prevention of renal uric acid precipitation by alkalisation of the urine (e.g. with bicarbonate or acetazolamide) and allopurinol administration may prevent acute kidney injury from developing.

Howard SC, Jones DP, Pui CH (2011). N Engl J Med; 364: 1844–54

Tumour necrosis factor,  see Cytokines

Turbulence,  see Flow

Turner’s syndrome (Gonadal dysgenesis).  Congenital absence of the second X chromosome. Sufferers are female in appearance, but with primary amenorrhoea and immature genitalia. Other features include short stature, short webbed neck and high palate; thus tracheal intubation may be difficult. Renal abnormalities, hypertension and coarctation of the aorta may occur.

[Henry H Turner (1892–1970), US physician]

TURP,  see Transurethral resection of the prostate

TURP syndrome.  Syndrome following TURP, thought to occur in a mild form in up to 8% of cases but severe in only 1–2%. Caused by absorption of irrigating fluid (usually hypotonic glycine 1.5%) through open prostatic vessels or from the extraprostatic tissues. Has also been reported following other procedures involving irrigation with electrolyte-free solutions, e.g. percutaneous lithotripsy and hysteroscopic endometrial resection.

Symptoms are caused by intravascular volume overload, dilutional hyponatraemia and intracellular oedema. Additional effects are caused by glycine and its metabolites, e.g. ammonia.

Features include bradycardia, hypotension (often preceded by hypertension), angina, dyspnoea, visual and mental changes, convulsions and coma. Severity depends on the volume of irrigant absorbed (e.g. lethargy and nausea after 1–2 litres glycine; severe symptoms after > 2 litres) and the rate of absorption (faster onset if absorbed via prostatic veins; slower if absorbed from the extravascular tissues). Features may occur during surgery, or postoperatively.

Hahn RG (2006). Br J Anaesth; 96: 8–20

Twilight sleep.  Obsolete technique formerly popular in obstetrics as a means of easing labour pain and reducing subsequent recall. Injection of morphine and hyoscine was followed by hyoscine alone. Apart from causing maternal restlessness, it often caused neonatal respiratory depression.

See also, Obstetric analgesia and anaesthesia