Cessation of Nitrous Oxide: A Possible Risk after Open Heart Surgery

Summary

Hypertension is still a major problem at the end of open heart surgery despite improvements in anesthetic and surgical techniques. Hundred two adult patients undergoing coronary bypass or valve replacement were studied for 30 minutes after termination of nitrous oxide anesthesia and hemodynamic changes were measured.

Anesthesia was induced with etomidate and maintained with nitrous oxide (FIO₂ = 0.5), opiate analgesia, dehydrobenzperidol (0.2 ± 0.1 mg/kg) and pancuronium bromide. Group I received morphine; Group II received pethidine; Group III fentanyl; Group IV fentanyl plus an additional dose of 0.25 mg/kg droperidol at sternal closure and in Group V patients had fentanyl as in Group III, but were placed on a heating blanket for reduction of heat loss. Results: In the fentanyl groups slightly higher values for cardiac index, systemic blood pressure and rate pressure product were found than in the other 2 groups. Apart from these small differences the hemodynamic behavior after open heart surgery, when nitrous oxide administration had been terminated, was nearly the same in all groups. The possible etiology of hypertension and vasoconstriction at the end of open heart surgery is still unknown, but it quite definitely is initiated by the withdrawal of nitrous oxide. We suggest a change in the anesthetic technique either by avoiding nitrous oxide in the post-bypass period or by continuation of this anesthetic. When nitrous oxide administration has to be discontinued close monitoring is mandatory.

Key words

Nitrous oxide - Neuroleptanesthesia - Hypertension - Open heart surgery