Hypercapnia does not shorten emergence time from propofol anesthesia: a pilot randomized clinical study

BACKGROUND: The elimination of anesthetic agents is a decisive factor in the emergence from general anesthesia. In this pilot study, we hypothesized that hypercapnia would decrease the emergence time from propofol anesthesia by increasing cardiac output and cerebral blood flow. METHODS: A total of 32 patients were randomly divided into two groups based on the end-tidal carbon dioxide values: 30 mmHg (the hypocapnia group) and 50 mmHg (the hypercapnia group). Propofol and remifentanil were infused to maintain a bispectral index of 40–50. Remifentanil infusion was stopped 10 min before the discontinuation of propofol. After cessation of propofol infusion, ventilation settings in the hypocapnia group were maintained constant; a rebreathing tube was connected to the respiratory circuit in the hypercapnia group. The time to spontaneous respiration, eye opening (primary endpoint), mouth opening, and tracheal extubation was recorded and analyzed. RESULTS: Time to eye opening was 9.7 (1.3) min in the hypocapnia group and 9.0 (1.0) min in the hypercapnia group. The difference in the mean times to eye opening between groups was −0.7 min (95% CI, −4.0 to 2.7, P = 0.688). On multiple regression analysis, there was a significant difference in the mean time to eye opening between males and females. Females recovered about 3.6 min faster than males (95% CI, −6.1 to −1.1, P = 0.009). CONCLUSIONS: We could not detect a beneficial effect of hypercapnia on propofol emergence time. Irrespective of hypercapnia, females seemed to recover faster than males.