Anaphylaxis in the monkey: respiratory mechanics, acid-base status and blood gases.

Aggregate anaphylaxis was induced by intravenous injection of the specific antigen in eight ovalbumin-sensitized monkeys. Changes in respiratory mechanics, acid-base status and blood gases were studied during the following half hour. Within 1 minute after challenge, a short period of respiratory depression, probably reflex-mediated, was observed. This was followed by hyperventilation, and arterial PCO2 decreased. There was a rapid increase in pulmonary resistance (Rpulm) and a concomitant decrease in pulmonary dynamic compliance (Cdyn), suggesting constriction of smooth muscles in the lung. Rpulm returned to the control value but Cdyn remained depressed, as a result of constriction of small airways and pulmonary congestion. Oxygen saturation in arterial blood decreased slightly due to a marked desaturation of mixed venous blood and increased venous admixture. Progressive metabolic acidosis developed, indicating poor tissue oxygenation and perfusion. The changes observed in this study were not severe enough to cause any major disturbance of the gas exchange in the lungs, despite a severe anaphylactic shock.