Pupillary diameter and ventilatory CO2 sensitivity after epidural morphine and buprenorphine in volunteers

The aim of this study was to correlate pupillary diameter with respiratory depression for 20 hr after epidural administration of morphine or buprenorphine. Pupillary diameter and the ventilatory sensitivity to CO2 were measured in six healthy volunteers at various times (0, 0.5, 1, 2, 3, 4, 6, 8, 10, 12, and 20 hr) in two sessions, separated by at least 1 week, at which either epidural morphine, 4 mg, or epidural buprenorphine, 0.15 mg, was administered randomly in a double-blind manner. Three of the six volunteers received 0.3 mg buprenorphine epidurally in a third session. Pupillary diameter was measured with a modified Essilor pupillometer. The ventilatory CO2 sensitivity was measured by a modified Read rebreathing technique. The ventilatory parameters measured were mouth occlusion pressure during the first 0.1 sec of inspiration (P0.1), end-tidal CO2 (PETCO2), tidal volume (VT) and respiratory rate (RR). Slopes of the linear regression lines (P0.1/CO2, VT/CO2, VE/CO2, and RR/CO2) and the intercept values of the regression lines and PETCO2 = 7.2 kPa (P0.1:7.2, VT:7.2, VE:7.2, and RR:7.2) were calculated. Pupillary diameter after epidural morphine was smallest at the second hour and had returned to normal after eight hours. After epidural buprenorphine there were two periods of miosis, one at 1-3 hr, the other at 10 hr. With epidural morphine, a statistically significant correlation (P less than 0.05) was found between pupillary diameter and VE/CO2, VE:7.2, P0.1:7.2, and VT:7.2. With epidural buprenorphine 0.15 mg a significant correlation was found between pupillary diameter and VE:7.2 and P0.1:7.2. With epidural buprenorphine 0.3 mg the correlations between pupillary diameter and VE:CO2, VE:7.2, and P0.1:7.2 were significant.(ABSTRACT TRUNCATED AT 250 WORDS)