Drug reference
Induction of anaesthesia (in oxygen or nitrous oxide– oxygen) ▶BY INHALATION ▶Adult: Initially 0.5–1 %, then increased to up to 8 %, increased gradually, according to response, to be administered using specifically calibrated vaporiser Maintenance of anaesthesia (in oxygen or nitrous oxide– oxygen) ▶BY INHALATION ▶Adult: 0.5–3 %, adjusted according to response, to be administered using specifically calibrated vaporiser
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Susceptibility to QT-interval prolongation
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→Appendix 1: volatile halogenated anaesthetics Anaesthesia
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▶Common or very common Drowsiness. fever. hypothermia ▶Uncommon Asthma. atrioventricular block. confusion ▶Frequency not known Dystonia. intracranial pressure increased. muscle rigidity. nephritis tubulointerstitial. oedema. pancreatitis
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May depress neonatal respiration if used during delivery.
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Breast-feeding can be resumed as soon as mother has recovered sufficiently from anaesthesia.
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Use with caution.
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There can be variation in the licensing of different medicines containing the same drug. Inhalation vapour ▶Sevoflurane (Non-proprietary) Sevoflurane 1 ml per 1 ml Sevoflurane volatile liquid | 250 ml P £123.00 (Hospital only) Anaesthesia adjuvants Pre-medication and peri-operative drugs Drugs that affect gastric pH Regurgitation and aspiration of gastric contents (Mendelson’s syndrome) can be an important complication of general anaesthesia, particularly in obstetrics and during emergency surgery, and requires prophylaxis against acid aspiration. Prophylaxis is also needed in those with gastro- oesophageal reflux disease and in circumstances where gastric emptying may be delayed. A H2-receptor antagonist can be used before surgery to increase the pH and reduce the volume of gastric fluid. It does not affect the pH of fluid already in the stomach and this limits its value in emergency procedures; an oral H2- receptor antagonist can be given 1–2 hours before the procedure. Antacids are frequently used to neutralise the acidity of the fluid already in the stomach; ‘clear’ (non- particulate) antacids such as sodium citrate p. 832 are preferred. Antimuscarinic drugs Antimuscarinic drugs are used (less commonly nowadays) as premedicants to dry bronchial and salivary secretions which are increased by intubation, upper airway surgery, or some inhalational anaesthetics. They are also used before or with neostigmine p. 1188 to prevent bradycardia, excessive salivation, and other muscarinic actions of neostigmine. They also prevent bradycardia and hypotension associated with drugs such as propofol p. 1400 and suxamethonium chloride p. 1407. Atropine sulfate p. 1404 is now rarely used for premedication but still has an emergency role in the treatment of vagotonic side-effects. Atropine sulfate may have a role in acute arrhythmias after myocardial infarction. Hyoscine hydrobromide p. 458 reduces secretions and also provides a degree of amnesia, sedation, and anti-emesis. Unlike atropine sulfate it may produce bradycardia rather than tachycardia. Glycopyrronium bromide p. 1405 reduces salivary secretions. When given intravenously it produces less tachycardia than atropine sulfate. It is widely used with neostigmine for reversal of non-depolarising neuromuscular blocking drugs. Phenothiazines do not effectively reduce secretions when used alone. Sedative drugs Anaesthesia Fear and anxiety before a procedure (including the night before) can be minimised by using a sedative drug, usually a benzodiazepine. Premedication may also augment the action of anaesthetics and provide some degree of pre- operative amnesia. The choice of drug depends on the individual, the nature of the procedure, the anaesthetic to be used, and other prevailing circumstances such as outpatients, obstetrics, and availability of recovery facilities. The choice also varies between elective and emergency procedures. Premedicants can be given the night before major surgery; a further, smaller dose may be required before surgery. Alternatively, the first dose may be given on the day of the procedure. Benzodiazepines Benzodiazepines possess useful properties for premedication including relief of anxiety, sedation, and amnesia; short- acting benzodiazepines taken by mouth are the most common premedicants. Benzodiazepines are also used in intensive care units for sedation, particularly in those receiving assisted ventilation. Flumazenil p. 1439 is used to antagonise the effects of benzodiazepines. Diazepam p. 360 is used to produce mild sedation with amnesia. It is a long-acting drug with active metabolites and a second period of drowsiness can occur several hours after its administration. Peri-operative use of diazepam in children is not recommended; its effect and timing of response are unreliable and paradoxical effects may occur. Diazepam is relatively insoluble in water and preparations formulated in organic solvents are painful on intravenous injection and give rise to a high incidence of venous thrombosis (which may not be noticed for several days after the injection). Intramuscular injection of diazepam is painful and absorption is erratic. An emulsion formulated for intravenous injection is less irritant and reduces the risk of venous thrombosis; it is not suitable for intramuscular injection. Temazepam p. 509 is given by mouth for premedication and has a shorter duration of action and a more rapid onset than oral diazepam; anxiolytic and sedative effects last about 90 minutes although there may be residual drowsiness. Lorazepam p. 355 produces more prolonged sedation than temazepam and it has marked amnesic effects. Midazolam p. 356 is a water-soluble benzodiazepine that is often used in preference to intravenous diazepam; recovery is faster than from diazepam, but may be significantly longer in the elderly, in patients with a low cardiac output, or after repeated dosing. Midazolam is associated with profound sedation when high doses are given intravenously or when it is used with certain other drugs. Other drugs for sedation Dexmedetomidine p. 1416 and clonidine hydrochloride p. 156 are alpha2-adrenergic agonists with sedative properties. Dexmedetomidine is licensed for the sedation of patients receiving intensive care who need to remain responsive to verbal stimulation. Clonidine hydrochloride [unlicensed indication] can be used by mouth or by intravenous injection as a sedative agent when adequate sedation cannot be achieved with standard treatment. Antagonists for central and respiratory depression Respiratory depression is a major concern with opioid analgesics and it may be treated by artificial ventilation or be reversed by naloxone hydrochloride p. 1440. Naloxone hydrochloride will immediately reverse opioid-induced respiratory depression but the dose may have to be repeated because of the short duration of action of naloxone hydrochloride; however, naloxone hydrochloride will also antagonise the analgesic effect. Flumazenil is a benzodiazepine antagonist for the reversal of the central sedative effects of benzodiazepines after anaesthetic and similar procedures. Flumazenil has a shorter half-life and duration of action than diazepam or midazolam so patients may become resedated. Doxapram hydrochloride p. 314 is a central and respiratory stimulant but is of limited value in anaesthesia. ANTIMUSCARINICS eiiii F 820
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Initially 0.5–1 %, then increased to up to 8 %,
First-line fragment. Read the complete Indications and Dose section above.
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0.5–3 %, adjusted according to response, to be
First-line fragment. Read the complete Indications and Dose section above.
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