DEPRESSION OF VENTILATION BY DESFLURANE IN HUMANS

We studied the ventilatory effects of desflurane (formerly I-653) with and without N2O in healthy male volunteers. After insertion of venous and arterial (radial and pulmonary) catheters, baseline measurements of tidal volume (V(T)), respiratory rate (RR), ventilatory response to CO2, and arterial and mixed venous blood gases were made. Subjects were randomly assigned to receive either desflurane with O2 (n = 6) or with O2 and 60% N2O (n = 6). Anesthesia was induced by inhalation of desflurane followed by tracheal intubation without muscle relaxants. In each volunteer, at end-tidal concentrations totaling 0.83, 1.24, and 1.66 MAC, we repeated measurements of V(T), RR, response to CO2, and arterial and mixed venous blood gases. As depth of anesthesia increased, V(T) significantly (P < 0.05) decreased from 363 +/- 22 ml awake to 76 +/- 22 ml at 1.66 MAC without N2O and from 473 +/- 70 ml awake to 128 +/- 6 ml at 1.66 MAC with N2O (mean +/- SE). Similarly, RR increased from 15 +/- 0.5 breaths per min awake to 32 +/- 2 breaths per min at 1.66 MAC without N2O and from 14 +/- 0.5 breaths per min awake to 40 +/- 3 breaths per min at 1.66 MAC with N2O. Desflurance without N2O depressed the ventilatory response to CO2 to 45 +/- 9, 31 +/- 5, and 11 +/- 4% of the awake values at 0.83, 1.24, and 1.66 MAC, respectively. With N2O, values were 52 +/- 14, 23 +/- 5, and 26 +/- 9% of the awake value at 0.83, 1.24, and 1.66 MAC, respectively. With or without N2O, arterial CO2 tension (PaCO2) increased, not always significantly, with depth of anesthesia. At 1.24 and 1.66 MAC, Pa(CO2) was significantly higher in the group that received desflurance in O2 (58 +/- 2 and 84 +/- 5 mm, respectively) than in the group that received desflurance with N2O (50 +/- 2 and 59 +/- 2 mm, respectively). We conclude that desflurane is a ventilatory depressant in humans. At anesthetic concentrations up to 1.24 MAC, with or without N2O, the depression observed is comparable to that found in previous studies with isoflurane. At deeper levels (up to 1.66 MAC), depression of ventilation with desflurane is comparable to that previously reported with enflurane.