Conclusion
The isoflurane concentrations used in this study during maintenance are very close to the predicted values and to the values demonstrated in the NDA study10 (Table 17). A range of concentrations from 0.4 to 3.2 per cent delivered in 50–70 per cent nitrous oxide induced and maintained anaesthesia in most patients. When low flow or closed systems were used, extensive rebreathing required delivery of much higher concentrations.
Age, premedication druqgs (particularly narcotics), and higher ASA status all were associ ated with lower delivered isoflurane concentrations. Patients who received barbiturates during induction received lower isoflurane doses. Patients undergoing EENT surgery received more isoflurane than most other patients, particularly those undergoing intracranial surgery who had the lowest requirements. The use of nondepolarizing relaxants was also associated with lower concentrations of isoflurane.
Surprisingly, males consistently received more isoflurane than females, a finding not previously demonstrated for inhalational anaesthetics. However the difference is too small to be of clinical significance.
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Cahalan, M.K. Dose requirements. Canad. Anaesth. Soc. J. 29 (Suppl 1), S11–S14 (1982). https://doi.org/10.1007/BF03009427
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DOI: https://doi.org/10.1007/BF03009427