RESPIRATORY EFFECTS OF TRICHLORETHYLENE, HALOTHANE AND METHOXYFLURANE IN THE CAT

¹ Departments of Anesthesiology and Pharmacology, College of Physicians and Surgeons, Columbia University, and the Anesthesiology Service, The Presbyterian Hospital, New York, N. Y.

Respiratory effects of trichlorethylene, halothance and methoxyflurane were studied in midcollicular decerebrate cats. One per cent trichlorethylene increased the respiratory frequency and decreased the tidal volume. Changes in minute volume and arterial blood pH and P_co2 were inconsistent. Two per cent trichlorethylene consistently increased the minute volume, markedly increased the respiratory frequency and decreased the tidal volume. One and 2% halothane decreased minute volume and tidal volume. Respiratory frequency also increased with 2% halothane, although not to the same extent as with trichlorethylene. One half and 1% methoxyflurane decreased minute volume, tidal volume and respiratory frequency. Significant hypercarbia and acidosis developed regularly with 2% trichlorethylene, 1% halothane and 0.5% methoxyflurane. In addition, all three agents depressed the ventilatory response to inhaled CO₂, elevated the electrical stimulus threshold of the medullary inspiratory center, but not the maximal inspiratory response to supramaximal stimuli. The results indicate that these anesthetics are primarily respiratory depressants through their action on the central regulatory and integratory mechanisms.

Tachypnea during trichlorethylene anesthesia was not prevented by bilateral vagotomy and carotid denervation. It was exaggerated by an increase in arterial P_co2 but still occurred when the arterial P_co2 was kept at control levels by artificial respiration. Thus, trichlorethylene caused tachypnea through its action on vagal efferents, central mechanisms and CO₂ retention. This action appears different from that of diethyl ether. The basis for tachypnea during halothane anesthesia was not determined with certainty because of concomitant circulatory depression, but is probably similar to that during trichlorethylene or diethyl ether anesthesia. Methoxyflurane is distinct in its respiratory effect in that it decreased the respiratory frequency.