BACKGROUND: The cardiovascular responses following the insertion of oropharyngeal airways in anaesthetized patients have been found to be of little consequence. However, those following the insertion of nasopharyngeal airways have not been studied. The aim of this investigation was to compare the cardiovascular responses to the insertion of oropharyngeal and nasopharyngeal airways in anaesthetized patients. METHODS: Twenty-four ASA I or II patients aged 16-65 yr, requiring nasotracheal intubation as part of their anaesthetic management, received a standardized general anaesthetic and were randomly allocated to receive either a nasopharyngeal or an oropharyngeal airway. RESULTS: The two groups were similar with respect to age, weight and gender. There was a significant decrease in systolic pressure following the induction of anaesthesia in both groups. Following nasopharyngeal airway insertion, there was a significant rise in systolic pressure above pre-insertion levels (P<or =0.001), though not above pre-induction levels (P=0.808). There was no significant change in the oropharyngeal airway insertion group (P=0.619). At 1 min post-insertion, the mean (sd) systolic pressure in the nasopharyngeal insertion group, 122 (21.6) mm Hg, was significantly greater than that in the oropharyngeal insertion group, 103 (15.3) mm Hg (P=0.017). Diastolic pressure followed a similar pattern. In both groups, heart rate fell after induction and fell further after insertion, and at 4 min post-insertion was significantly lower than pre-induction and pre-insertion levels. There was no significant difference in heart rates between the two groups (P=0.372). CONCLUSIONS: The pressor response following the insertion of nasopharyngeal airways in anaesthetized patients is significantly greater than that following the insertion of oropharyngeal airways. However, the mean rise in arterial pressure does not exceed pre-induction level, and thus the response is less severe than that likely to be associated with orotracheal or nasotracheal intubation.