A Nonlinear Model for the Uptake and Distribution of Halothane in Man

An analog computer simulation of the uptake and distribution of halothane in man which incorporates the effect of halothane on cardiac output is presented. The computed partial pressures in each tissue compartment in response to a constant inspired partial pressure of 1.0 per cent atm are given. A theoretical derivation of the inspired partial pressure necessary to achieve instantaneously a constant anesthetic depth is also included. Based on this information, a program for the induction of halothane anesthesia in man utilizing a nonrebreathing anesthesia circuit is developed. With a maximum inspired partial pressure of 4.0 per cent atm, this program achieves a partial pressure of 0.75 per cent atm in the well perfused tissues in six minutes without overshoot, and will maintain this partial pressure indefinitely. Comparing the nonlinear model with a linear model having fixed cardiac output, the authors have shown that the difference between these two models is insignificant for the first five minutes; however, the effect of the nonlinearity is to elevate the partial pressures in the well-perfused tissues and the lung by 6 per cent after one hour of anesthesia with an inspired partial pressure of 1.0 per cent atm.