Nitrous oxide Atracurium

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). 

Rupp SM, Fahey MR, Miller RD. Neuromuscular and cardiovascular effects of atracurium during nitrous oxide-fentanyl and nitrous oxide-isoflurane anaesthesia. Br J Anaesth 1983 55(Suppl l) S67-70. 

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. 

The dosage of the neuromuscular blocker may need to be adjusted according to the anaesthetic in use. For example, the dosage of atracurium can be reduced by 25 to 30% if, instead of balanced anaesthesia (with thiopental, fentanyl and nitrous oxide/oxygen)," enflurane is used, and by up to 50% if isoflurane or desflurane are used. Another study recommended reduced doses of neuromuscular blockers such as atracurium and tubocurarine in children undergoing anaesthesia with enflurane or isoflurane. In one study, enflurane and isoflurane reduced the vecuronium infusion rate requirements by as much as 70%, when compared with fentanyl anaesthesia. Another study demonstrated that although halothane and isoflurane could both increase the neuromuscular potency of vecuronium, only isoflurane prolonged the recovery from neuromuscular blockade. ... 

Eight out of 42 patients taking unnamed beta blockers given atracurium developed bradycardia (less than 50 bpm) and hypotension (systolic pressure less than 80 mniHg). Most of them had been premedicated with diazepam, induced with methohexital, and maintained with droperidol, fentanyl and nitrous oxide/oxygen. A further 24 showed bradycardia, associated with hypotension on 9 oeeasions. All responded promptly to 300 to 600 micrograms of intravenous atropine. ... 

---