Suxamethonium Nitrous oxide

In 113 patients undergoing general anesthesia, intravenous midazolam 15 mg slowed recovery of the twitch height after vecuronium and atracurium compared with diazepam. The recovery index was not altered (162). However, in another study in 20 patients, midazolam 0.3 mg/kg did not affect the duration of blockade, recovery time, intensity of fasciculations, or adequacy of relaxation for tracheal intubation produced by suxamethonium 1 mg/kg, nor the duration of blockade and adequacy of relaxation for tracheal intubation produced by pancuronium 0.025 mg/kg in incremental doses until 99% depression of muscle-twitch tension was obtained (161). Furthermore, in 60 patients undergoing maintenance anesthesia randomly assigned to one of six regimens (etomidate, fentanyl, midazolam, propofol, thiopental plus nitrous oxide, or isoflurane plus nitrous oxide), midazolam did not alter rocuronium dosage requirements (165). 

A 6-year-old boy sustained pelvic injuries and a femoral fracture. The first anesthetic he received consisted of thiopental, suxamethonium, isoflurane, and nitrous oxide. He also received two units of blood. He subsequently underwent four halothane anesthetics over 6 weeks for dilatation of a urethral stricture. Two days after the last anesthetic he was noted to be jaundiced. He had a negative viral screen but was positive for antitrifluoroacetyl IgG antibodies. He developed fulminant hepatic failure with grade 2 hepatic encephalopathy and underwent an auxiliary Uver transplantation 24 days after his last exposure to halothane. He died of septicemia 18 days later. Both at autopsy and on a previous hepatobiliary scan he was noted to have had extensive native Uver regeneration. 

Isoflurane in nitrous oxide inhibited suxamethonium-induced muscle fasciculation in children (26). 

Caldwell JE, Heier T, Kitts JB, Lynam DP, Fahey MR, Miller RD. Comparison of the neuromuscular block induced by mivacurium, suxamethonium or atracurium during nitrous oxide entanyl anaesthesia. Br J Anaesth 1989 63(4) 393-9. 

The inhalational anaesthetics increase the effects of the neuromuscular blockers to differing extents, but nitrous oxide appears not to interact significantly. Ketamine has been reported to potentiate the effects of atracurium. Propofol does not appear to interact with mivacurium or vecuronium. Xenon is reported not to interact with mivacurium or rocuronium, and has less effect than sevoflurane on vecuronium neuromuscular blockade. Bradycardia has been seen in patients given vecuronium with eto-midate or thiopental. Propofol can cause serious bradycardia if it is given with suxamethonium (succinylcholine) without adequate antimuscarinic premedication, and asystole has been seen when fentanyl, propofol and suxamethonium were given sequentially. 

Although it is generally assumed that nitrous oxide does not affect the potency of neuromuscular blockers, one study found that the administration of nitrous oxide increased suxamethonium (succinylcholine) neuromuscular blockade. 

A patient anaesthetised with fluroxene and nitrous oxide demonstrated 100% blockade with suxamethonium (succinylcholine) and tubocurar-ine. About 50 minutes later when twitch height had fully returned and tidal volume was 400 mL, she was given lidocaine 50 mg intravenously for premature ventricular contractions. She immediately stopped breathing and the twitch disappeared. About 45 minutes later the tidal volume was 450 mL. Later it was found that the patient had a dibucaine number (a measure of cholinesterase activity) of 23%. ... 

Eight out of 17 digitalised patients (anaesthetised with thiamylal and then maintained with nitrous oxide and oxygen) developed serious ventricular arrhythmias following the intravenous injection of suxamethonium (suc-cinylcholine)40 to 100 mg. Four out of the 8 patients reverted to their previous rhythm when they were given tubocurarine 15 to 30 mg, with one patient returning to a regular nodal rhythm from ventricular tachycardia. ... 

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