Respiratory monitoring during postoperative analgesia.

Respiratory monitoring, using a novel flow sensor based on an acoustic principle, has been investigated in 30 patients during postoperative analgesia. Each patient was subjected to monitoring and human observation for 8 hr. The study was performed by independent observers at three clinics. Significant correlation was noted between respiratory rate (RR) determined by the sensor and the observers. Recordings of respiratory duration index (RDI), breathing time intervals (BTIs) indicated high sensitivity of the instrument to respiratory depression and perturbations in the breathing rhythm. More than 800 apnea alarms were noted, using an alarm setting of 30 sec; 61% of the categorized alarms were noted by the observers as true apneas. From the recordings it was shown that the number of alarms can be reduced by a factor of four if the alarm setting is changed to 45 sec. We conclude that the suggested technique, with slight modifications, provides adequate respiratory monitoring of patients during postoperative analgesia.