New intravenous anaesthetics and neuromuscular blocking drugs. A review of their properties and clinical use.

The newer neuromuscular blocking drugs include vecuronium and atracurium. Vecuronium is a competitive neuromuscular blocking drug with a steroid nucleus. A dose of 0.1 mg/kg has an onset time of 2 minutes and provides surgical paralysis for 20 minutes. Recovery to 90% twitch height occurs in 40 to 50 minutes. Vecuronium has few adverse effects and its use is associated with cardiovascular stability. Atracurium is a competitive neuromuscular blocking drug which undergoes Hofmann degradation and ester hydrolysis in plasma. A dose of 0.6 mg/kg has an onset time of around 2 minutes and provides surgical paralysis for 20 to 30 minutes. Recovery to 90% twitch height occurs in 60 to 80 minutes. Histamine release, usually only localised, has been reported in association with the use of atracurium. The organ-independent metabolism of atracurium allows its use in standard dosage in patients with renal or hepatic disease. Edrophonium, although not a new drug, has recently been re-evaluated for reversal of neuromuscular blockade. In a dose of 0.5 mg/kg it has been shown to be as effective as neostigmine at reversing neuromuscular blockade after recovery has started (greater than 25% twitch height recovery). However, if blockade is profound (less than 10% recovery), edrophonium is less effective. Among the newer intravenous anaesthetics are propofol (disoprofol) and midazolam. In a dose of 1.5 to 2.5 mg/kg, propofol produces sleep rapidly with a prompt recovery in 4 to 6 minutes. Induction of anaesthesia may be associated with a transient apnoea and a fall in systolic pressure. The rapid recovery has led to its use for maintenance of anaesthesia. Midazolam is a water-soluble benzodiazepine which has been used as an anaesthetic agent. The dose needed to induce sleep varies widely (0.15 to 0.5 mg/kg); onset is slow (1.5 to 5 minutes), and recovery may be prolonged. Midazolam is also used in lower doses as a sedative. Ketamine, an intravenous induction agent, has recently been used intrathecally and extradurally to provide analgesia.