Effect of naloxone reversal on CO2 output, oxygen uptake and cardiac index during recovery from fentanyl-supplemented anaesthesia.

Abstract

For reversal of contingent residual narcotic depression after fentanyl administration during balanced anaesthesia, the effect of 0.08 mg of naloxone on CO2 output, O2 uptake and cardiac index was studied immediately after extubation. This dose maintained normocapnia (5.7 kPa) during early recovery, while in the control group slight hypercapnia was present (6.0 kPa). No significant differences, however, could be detected between the groups in CO2 output, O2 uptake or cardiac index. When 0.16 mg of naloxone was given to six other patients 10 min after the anaesthesia, when spontaneous respiration had stabilized on the same level as in the control group, significant increases in respiratory minute volume and rate and CO2 output were recorded as compared with the respective prenaloxone levels. O2 uptake increased with simultaneous improvement of PaO2 and the cardiac index also increased significantly. A slight but highly significant increase in CO2 output was detected after 0.16 mg of naloxone in six patients during anaesthesia and volume‐controlled IPPV. A significant increase in PacO2 was also measured. These findings indicate that if naloxone is used postoperatively, a significant metabolic increase may take place due to increased muscular work, restlessness and shivering. Ventilation and cardiac output were adequate for demand under present conditions using 2 μg/kg of naloxone, but careful titration of naloxone is recommended in order to avoid harmful metabolic changes.