Continuous transcutaneous PCO2 monitoring during epidural morphine analgesia

We evaluated the transcutaneous PCO2 (PtcCO2) sensor as a ventilation monitor for patients receiving epidural morphine analgesia during interstitial radiation therapy for carcinoma of the cervix. The sensor was heated to 42 degrees C. Ten patients were monitored for 18 +/- 7 h after 2.9 +/- 0.5 mg of morphine was injected epidurally. Baseline respiratory rate (RR) and PtcCO2 were 21 +/- 3 breath/min and 37 +/- 8 torr, respectively. Peak PtcCO2 was 43 +/- 7 torr, corresponding to a RR of 19 +/- 3 breath/min. The increase of PtcCO2 from baseline was statistically significant. PtcCO2 peaked from 1 to 19 h after epidural morphine, and 90% of patients showed peak values between 11 PM and 4:30 AM. The prolonged monitoring caused no complications. Although there was no clinically significant respiratory depression in these patients, the PtcCO2 sensor may be a useful monitor of ventilation during epidural morphine administration.