Interaction of nitrous oxide and propofol to reduce hypertensive response to stimulation

Purpose: To evaluate the interaction between nitrous oxide and propofol for the suppression of hypertension following electrical stimulation of the me ntal nerve in the rabbit. Methods: Male Japan White rabbits were tracheostomized, cannulated and mech anically ventilated under isoflurane anesthesia. Square wave pulses (5 V, 0 .5 msec, 50 Hz for 5 sec) were delivered to-the left mental nerve. Animals received nitrous oxide 20, 40, 60 and 80% (Group 1); propofol 200, 400; 600 and 800 mu g(.)kg(-1.)min(-1) (Group 2); or combinations of nitrous oxide and propofol at 10 + 100, 20 + 200, 30 + 300 and 40 % + 400 mu g(.)kg(-1.)m in(-1) (Group 3). Systolic blood pressure was recorded from immediately bef ore to maximal increase following nerve stimulation. Probit analysis was us ed to obtain ED50 values for 50 % suppression of blood pressure elevation. Isobolographic analysis was used to evaluate the interaction between nitrou s oxide and propofol. Results: ED50 values are 52.9% for nitrous oxide (Group 1), 464.1 mu g(.)kg (-1.)min(-1) for propofol (Group 2), 21.7 % + 217.1 mu g(.)kg(-1.)min(-1) f or nitrous oxide and propofol combination (Group 3) and 24.7 % + 247.1 mu g (.)kg(-1.)min(-1) for the theoretically additive combination of nitrous oxi de and propofol, respectively. Conclusion: The interaction between nitrous oxide and propofol for the supp ression of blood pressure elevation following electrical stimulation of the mental nerve is additive.