Isoflurane 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). 

In man, potentiation and prolongation of the action of atracurium by halothane (62-64) have been reported, as has potentiation after 30 minutes of isoflurane anesthesia (65). Whether the dose of atracurium should be reduced from that used during balanced anesthesia by 20, 30, or 50% when patients are anesthetized with inhalational anesthetics can only be decided in the case of an individual patient if neuromuscular monitoring is available, since many other variables, such as the tissue concentrations of the volatile anesthetic and the response of the individual patient to the neuromuscular blocking drug, will influence the overall blocking effect. 

A synergistic interaction between isoflurane and atracurium (high doses) has been incriminated in the causation of an increased incidence of generalized tonic-clonic seizures after neurosurgical operations (SEDA-15,125) (66). 

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. 

Beemer GH, Dawson PJ, Bjorksten AR, Edwards NE. Early postoperative seizures in neurosurgical patients administered atracurium and isoflurane. Anaesth Intensive Care 1989 17(4) 504-9. 

The potency and duration of the drug is affected by the type of anesthetic used—if either en-flurane or isoflurane are used in conjunction with the drug, the potency of atracurium is increased, and the duration of neuromuscular blockade is increased by 35 percent. 

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. ... 

Vanlimhout LEH, Booij LHDJ, van Egmond J, Robertson EN Effect of isoflurane and sevoflurane on the magnitude and time courae of neuromuscular block produced by vecuronium, pancuronium and atracurium. BrJAnaesth (1996) 76, 389-95. 

Sokoll MD, Geigis SD, Mehta M, Ali NN Lineberry C. Safety and efficacy of atracurium (BW33A) in suigical patients receiving balanced or isoflurane anesthesia. Anesthesiology (1983) 58,450-5. 

Smiley RM, Omstein E, Mathews D, Matteo RS. A cemparison of the effects of desflurane and isoflurane on the action of atracurium in man. Anesthesiology (1990) 73, A882. 

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