Hypoxic ventilatory drive in the dog under Althesin anaesthesia

Althesin was administered i.v. to eight dogs, using two different rates of infusion (6.55 +/- 2.13 microliter kg-1 min and 12.80 +/- 2.00 microliter kg-1 min). Ventilation (TI, TE, RR, TI/Ttot, VT, VE, VT/TI) and arterial blood-gas tensions were measured in air and during a 10-min period of 100% oxygen breathing. For both rates of Althesin infusion the ventilatory response to oxygen was identical: there was significant depression of ventilation (decrease in VE and of the ventilatory drive, VT/TI) from the 1st min of inhalation lasting up to the 10th min. This decrease in ventilation was more marked and persistent than the decrease noticed in the unanaesthetized dog. We conclude that the hypoxic ventilatory drive persists in the dog under Althesin anaesthesia.