Effect of five human anesthetics on respiratory control in cats

The effect of halothane, fentanyl, Innovar, thiopental, and ketamine on inspiratory output, vagal influence, and chest wall reflex was assessed in seven cats lightly anesthetized with pentobarbital, using the method of airway occlusion with and without rapid vagal cooling. All anesthetics depressed inspiratory output, as expressed by deltaP/deltat, of the first occluded inspiration. However, only halothane depressed peak inspiratory output (Pmax). Phasic vagal influence was markedly depressed by 2% halothane but was preserved under other anesthetics. The ability to induce tonic vagal influence (expiratory muscle recruitment) was lost under halothane. Inspiratory inhibitory chest wall reflex was evident in two cats during airway occlusion. Addition of any test anesthetic abolished the reflex. It is concluded that halothane should be avoided in studies dealing with assessment of vagal influence.