A dose-response study of remifentanil for attenuation of the hypertensive response to laryngoscopy and tracheal intubation in severely preeclamptic women undergoing caesarean delivery under general anaesthesia.

BACKGROUND

Remifentanil is known to attenuate the cardiovascular responses to tracheal intubation. We determined effective doses (ED(50)/ED(95)) of remifentanil to prevent the pressor response to tracheal intubation in patients with severe preeclampsia.

METHODS

Seventy-five women with severe preeclampsia were randomly allocated to one of five remifentanil dose groups (0.25, 0.50, 0.75, 1.0, or 1.25 μg/kg) given before induction of anaesthesia using thiopental 5 mg/kg and suxamethonium 1.5 mg/kg. Systolic arterial pressure, heart rate and plasma catecholamine concentrations were measured. Neonatal effects were assessed by Apgar scores and umbilical cord blood gas analysis. A dose was considered effective when systolic arterial pressure did not exceed 160 mmHg for more than 1 min following tracheal intubation.

RESULTS

Baseline systolic blood pressure and heart rate did not differ among the groups. The intubation-induced increases of heart rate and blood pressure were attenuated in a dose-dependent manner by remifentanil. ED(50) and ED(95) were 0.59 (95% CI 0.47-0.70) μg/kg and 1.34 (1.04-2.19)μg/kg, respectively. Norepinephrine concentrations remained unaltered following intubation but increased significantly at delivery, with no differences between the groups. Apgar scores and umbilical arterial and venous pH and blood gas values were comparable among the groups. Two women each in the 1.0 and 1.25 μg/kg groups received ephedrine for hypotension defined as systolic arterial pressure <90 mmHg.

CONCLUSIONS

The ED(95) of remifentanil for attenuating the hypertensive response to tracheal intubation during induction of anaesthesia in severely preeclamptic patients undergoing caesarean delivery under general anaesthesia was 1.34 μg/kg.