Variations in hemodynamic and stress hormonal responses in open heart surgery with buprenorphine/diazepam anesthesia

Random Forest Segregation of Drug Responses May Define Regions of Biological Significance

The ability to assess brain responses in unsupervised manner based on fMRI measure has remained a challenge. Here we have applied the Random Forest (RF) method to detect differences in the pharmacological MRI (phMRI) response in rats to treatment with an analgesic drug (buprenorphine) as compared to control (saline). Three groups of animals were studied: two groups treated with different doses of the opioid buprenorphine, low (LD), and high dose (HD), and one receiving saline. PhMRI responses were evaluated in 45 brain regions and RF analysis was applied to allocate rats to the individual treatment groups. RF analysis was able to identify drug effects based on differential phMRI responses in the hippocampus, amygdala, nucleus accumbens, superior colliculus, and the lateral and posterior thalamus for drug vs. saline. These structures have high levels of mu opioid receptors. In addition these regions are involved in aversive signaling, which is inhibited by mu opioids. The results demonstrate that buprenorphine mediated phMRI responses comprise characteristic features that allow a supervised differentiation from placebo treated rats as well as the proper allocation to the respective drug dose group using the RF method, a method that has been successfully applied in clinical studies.

The effect of increasing the dose of buprenorphine on the haemodynamic response associated with tracheal intubation

The effect of buprenorphine on the haemodynamic response to tracheal intubation was studied at two dose levels, 2.5 micrograms.kg-1 and 5 micrograms.kg-1, in a placebo-controlled double-blind trial in 75 patients undergoing laparoscopic cholecystectomy. The study drugs were administered intravenously 8 min before induction of anaesthesia with thiopentone 5 mg.kg-1 and vecuronium 0.1 mg/kg-1. Buprenorphine 2.5 micrograms.kg-1 caused 50% attenuation of the blood pressure response whereas 5 micrograms/kg-1 caused 70% attenuation compared to the saline placebo. The maximum increase in heart rate was 14% of the control value after 2.5 micrograms.kg-1 and 11% after 5 micrograms/kg-1 of buprenorphine. A significant difference in heart rate was also observed between the two buprenorphine groups at 5 and 10 min after intubation. Blood pressure and heart rate both showed a significant fall from baseline values 10 min after intubation in both buprenorphine groups, with the changes being greater in the 5 micrograms.kg-1 group. We recommend the use of 2.5 micrograms.kg-1 buprenorphine for attenuation of the hypertensive response to intubation in major abdominal surgery.