In Reply:-Dr. Ramsay and his colleagues question the measurement of the adequacy of respiratory function in the above two studies. They state that adequacy of respiratory function cannot be ascertained by measuring the respiratory rate and O2saturation alone. I agree. That is why the studies were performed with anesthesia personnel in attendance at all times during spontaneous ventilation with concomitant remifentanil infusion. Respiratory pattern and wakefulness were noted, and verbal contact (no less than once per 5-min interval) was also maintained at all times.
The Gold et al. paper compared intraoperative analgesic doses of remifentanil with and without midazolam. Spontaneous ventilation was maintained, and end-tidal CO2was measured. The Yarmush et al. paper compared analgesic doses of remifentanil with intravenous morphine in the post-anesthesia care unit (PACU). Spontaneous ventilation was maintained, but end-tidal CO2was not measured. This was consistent with standard PACU monitoring techniques.
These same concerns were obviously on the mind of the Food and Drug Administration (FDA). The indication for postoperative analgesic infusion of remifentanil stipulates that it must be administered under the direct supervision of an anesthesia practitioner.
To measure PCO2in the PACU with arterial blood gases would have required a far more invasive technique than was warranted for these patients. Future investigations could include end-tidal CO2and a more detailed analysis of respiratory pattern.
Joel Mann Yarmush, M.D.
Department of Anesthesiology; New Jersey Medical School; 185 South Orange Avenue; University Heights; Newark, New Jersey 07103–2714.
(Accepted for publication December 2, 1997.)