E.E.G. monitoring for the control of anaesthesia produced by the infusion of althesin in primates.

The continuous infusion of Althesin under electroencephalographic (e.e.g.) control provided a constant level of light anaesthesia for periods of 1--5.5 h during experimental brain hypoxia in spontaneously breathing baboons and Rhesus monkeys. Polygraphic records (respiration, heart rate, arterial pressure, cerebral venous sinus pressure, end-tidal gas concentrations) and also estimation of blood-gas tensions, pH, and concentrations of pyruvate and lactate demonstrated a steady physiological state. Various methods of e.e.g. monitoring were tested to establish an optimal assessment of depth of anaesthesia as a guide to the control of the rate of infusion of Althesin. A purpose-built modification of the Cerebral Function Monitor was found to give unequivocal recognition of changing depths of anaesthesia.