PATTERN OF RESPIRATION AND RESPONSES TO CARBON DIOXIDE DURING TRICHLOROETHYLENE ANAESTHESIA IN THE CAT

Tidal volume (KT), minute ventilation (KE), the duration of inspiration and expiration, and Paco, were measured via a tracheostomy in adult cats anaesthetized with 0.7%, 1 % and 1.5 % (inspired) trichloroethylene (TCE). The tracheal cannula was occluded at intervals at the start of inspiration and the tracheal pressure was measured to assess the force of contraction of the respiratory muscles. Anaesthesia with TCE 0.7 % was associated with an increase in VE, a reduction in VT, and a marked increase in respiratory frequency and mean inspiratory flow rate, but Pacot values did not differ significantly from those in conscious animals. Ventilation was also greater than in conscious animals during anaesthesia with TCE 1%. TCE 1.5 % caused a significantly greater Paco, than in conscious animals. All concentrations of TCE caused a reduction in the ventilatory response to carbon dioxide, measured by the steady-state method. Cervical vagal section did not abolish the tachypnoea caused by TCE. The characteristic pattern of breathing during anaes-thesia with trichloroethylene (TCE) is a reduction in tidal volume (FT) and an increase in respiratory frequency (/). Although this pattern has been known for many years (Hewer and Hadfield, 1941; Dundee, 1953), information about the effect of TCE on the pattern of respiration and the ventilatory response to carbon dioxide is sparse and often conflicting. Whitteridge and Biilbring (1944) suggested that TCE caused a persistent sensitization of the inflation and deflation receptors in the cat lung and this could account for the reduction in tidal volume and tachy-pnoea seen during TCE anaesthesia. However, section of the vagi did not prevent the onset of tachypnoea after inhalation of TCE in decerebrate cats (Ngai, Katz and Farhie, 1965), suggesting that TCE causes this effect by a central action. Talcott, Larson and Buechel (1965) reported that TCE did not influence the ventilatory response to carbon dioxide in man, but the response was severely depressed in cats (Ngai