The influence of alfentanil pre-treatment on ventilatory effects of doxapram following induction of anaesthesia with propofol

Background: Hypoventilation may occur following induction of anaesthesia with propofol and is potentiated by concurrent use of opioid drugs. This effect is undesirable in patients who will continue to maintain spontaneous respiration during anaesthesia and surgery. The analeptic drug doxapram is known to have selective respiratory stimulatory effects but its action during induction of anaesthesia has been inconsistent. Method: In a double-blind, placebo-controlled study, the influence of alfentanil pre-treatment on the ventilatory effects of doxapram given during induction of anaesthesia with propofol was studied in 40 patients. Four groups of ten patients (two groups pre-treated with 7 mu g.kg(-1) of alfentanil and two groups with saline) were randomly allocated to receive either 0.5 mg.kg(-1) doxapram or saline following infusion of propofol to loss of verbal contact. Results: In the groups that received doxapram, minute volumes were significantly increased and end-tidal carbon dioxide concentrations were significantly reduced compared to control groups, although the duration and extent of these effects were less in the group that received alfentanil. Doxapram also reversed an alfentanil-induced reduction in respiratory rate. No adverse cardiovascular or neurological stimulatory effects of doxapram were evident at any time. Conclusion: We conclude that doxapram 0.5 mg.kg(-1)is effective in augmenting ventilation that has been obtunded following induction of anaesthesia with propofol in patients pre-treated with alfentanil.