Oxyhemoglobin Saturation following Cesarean Section in Patients Receiving Epidural Morphine, PCA, or im Meperidine Analgesia

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Abstract
The frequency and severity of oxyhemoglobin desaturation was compared in 49 patients receiving epidural morphine, 5 mg (n = 21); patient-controlled analgesia (PCA) using meperidine (n = 20); or intramuscular (im) meperidine (n = 8) for psotoperative analgesia following elective cesarean section performed with epidural anesthesia. Oxygen saturation (SpO2) was monitored for 24 h using a pulse oximeter; data were continuously collected and stored every 30 s via an interface connected to a computer. For analysis purposes, SpO2 was divided into five categories: 96-100%, 91-95%, 86-90%, 81-85%, and .ltoreq. 80%. Although SpO2 remained above 95% for the majority of the monitored period, patients in all groups experienced periods of desaturation. PCA patients spent the longest cumulative time with SpO2 between 91 and 95%, 231 .+-. 49 min (mean .+-. SEM), compared with only 112 .+-. 30 min and 152 .+-. 42 min for the epidural and im groups, respectively (P < 0.05 vs. epidural group). PCA patients also spent longest with SpO2 at 86-90% (19 .+-. 10 min, vs. 6 .+-. 3 and 0.5 .+-. 0.3 min for the epidural and im groups, respectively), although this difference was not statistically significant. Severe desaturation episodes, defined as SpO2 .ltoreq. 85% for more than 30 s, occurred in 71% of patients in the epidural group, 30% in the PCA group, and 63% in the im group (P < 0.05 PCA vs. epidural and im). Mean minimum SpO2 was lowest in the epidural group (83 .+-. 2%, vs 88 .+-. 1% in the PCA, and 85 .+-. 2% in the im group; P < 0.05 epidural vs. PCA). In a group of ten women (not receiving opiates) studied in a similar fashion for 24 h following vaginal delivery, no severe desaturations occurred and SpO2 decreased to 91-95% for only a bried period. The authors conclude that, following cesarean section, patients receiving all three opioid analgesic techniques potentially are at risk from respiratory depression. This is manifested by prolonged periods of mild desaturation following PCA, and a high incidence of brief periods of severe desaturation following epidural and im opioids.

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