Cardiovascular responses to asphyxial challenge in chronically hypokalemic dogs.

To study the physiological tolerance to asphyxia and hypokalemia during anesthesia, the cardiovascular responses to clamping of the endotracheal tube during mechanical ventilation were evaluated in ten anesthetized mongrel dogs before and after they had been made hypokalemic by administration of furosemide, 10 mg X kg-1 X day-1 for 3-4 weeks. Furosemide reduced the serum potassium to 2.93 +/- 0.03 from 4.16 +/- 0.07 mEq/L. The animals were anesthetized with halothane in N2O-O2 (60/40) and mechanically ventilated to a PaCO2 of approximately 30 torr during continuous monitoring of heart rate, mean arterial pressure, ECG, and periodic determinations of serum electrolyte levels and arterial blood-gas tensions. The endpoint for unclamping of the endotracheal tube and reestablishing ventilation of the lungs was when mean arterial pressure decreased to levels present before clamping the trachea, approximately 100 torr, after an initial response of hypertension and tachycardia. The duration of clamping was not significantly different in normokalemic (8.41 +/- 1.47 min) and hypokalemic (9.01 +/- 0.47 min) dogs, but the time required to regain circulatory stability and normal ECG rhythm was longer for the hypokalemic group (2.95 +/- 0.44 min vs 2.17 +/- 0.47). In addition, while all normokalemic dogs survived, three of the hypokalemic dogs could not be resuscitated. The results suggest that chronic hypokalemia reduces the tolerance of the cardiovascular system to severe physiologic trespass.