[Blocking effect of remifentanil on sympathetic response to tracheal intubation during sevoflurane anesthesia]

We examined the hemodynamic responses to tracheal intubation during anesthetic induction by inhalational sevoflurane with continuous administration of remifentanil.

This study enrolled 30 ASA physical status 1-2 patients, aged 20-65 undergoing elective surgical procedure. Anesthesia was induced with 5% sevoflurane in all patients, and then adjusted to maintain BIS values ranging from 40 to 60. Remifentanil at the rate of 0.5 microg x kg(-1) x min(-1) was administrated continuously, and tracheal intubation was performed by each anesthesiologist, at various times after administration of remifentanil. We recorded blood pressure (BP), heart rate (HR) and the duration between the initiation of an administration of remifentanil and a tracheal intubation (DRI). Sympathetic response to tracheal intubation was defined as more than 20% increase in either BP or HR at the intubation compared with that at preintubation. We analyzed the P50, representing the duration of remifentanil infusion with 50% probability of blocking sympathetic response to tracheal intubation.

DRI for individual patients varied from 77 sec up to 660 sec. According to the present data, P50 was calculated as 210 +/- 16.4 sec (mean +/- SD).

During sevoflurane anesthesia, remifentanil infusion at 0.5 microg x kg(-1) x min(-1) for more than 210 sec could provide the effective blocking of the sympathetic response to tracheal intubation with more than 50% probability.