Transcutaneous carbon dioxide measurements and maternal pain scores in laboring parturients.

: 112 Transcutaneous carbon dioxide measurements and maternal pain scores in laboring parturients Presenting Author: Paloma Toledo M.D. Presenting Author's Institution: Northwestern University, Feinberg School of Medicine Chicago, IL Co-Authors: Renee C. Gora B.S.N. Northwestern University, Feinberg School of Medicine Chicago, IL Mary Jane Ebarvia B.S.N. Northwestern University, Feinberg School of Medicine Chicago, IL Cynthia A. Wong M.D. Northwestern University, Feinberg School of Medicine Chicago, IL Introduction: Pain during uterine contractions is associated with periods of hyperventilation, which causes a decrease in the maternal arterial carbon dioxide tension (pCO2). Transcutaneous carbon dioxide monitors generate estimations of arterial carbon dioxide partial pressure (PtcCO2). The PtcCO2 measurements have been shown to correlate well with arterial blood gas results. The purpose of this study was to evaluate the effect of neuraxial labor analgesia on maternal PtcCO2 levels, as well as the correlation with maternal reported pain levels. Methods: Laboring women who were requesting neuraxial labor analgesia were eligible to participate in this IRB-approved study. Exclusion criteria included patients who had received systemic opioid analgesia. A transcutaneous carbon dioxide probe was placed prior to the first request for analgesia. At the time of first request for labor analgesia, analgesia was initiated using a combined spinal-epidural technique. The intrathecal (IT) injection consisted of bupivacaine 2.5 mg and fentanyl 15 mcg. No additional epidural medications were administered until the second request for analgesia. At the second request for analgesia, bupivacaine 0.125% was incrementally administered until T10 sensory blockade was achieved. VAS pain scores (100 mm scale) and PtcCO2 levels were recorded at the first and second request for analgesia, and 15 minutes after IT and epidural analgesia administration. Groups were compared with a 2-tailed t-test. Results: 30 parturients participated. The mean ± SD for age was 30±4y, gravidity 2±2, parity 1±1, with a cervical dilation of 4±1cm at first request for analgesia. After initiation of IT analgesia, the PtcCO2 value increased and the VAS decreased (P<0.001). There was an increase in VAS between 15 min and the second request for analgesia (P<0.001), but there was no difference in the PtcCO2 values (P=0.23). After the initiation of epidural analgesia, the VAS score decreased (P<0.001), but the PtcCO2 values were not different (P=0.30). The correlation between the PtcCO2 values and maternal VAS are shown in the Table. Discussion: Although the PtcCO2 did increase after initiation of intrathecal labor analgesia, it correlated poorly with patient reported VAS scores at all time points. Possible explanations include poor sensitivity of transcutaneous carbon dioxide measurements in relation to pain scores, as well as the non-linear relationship of pain with VAS scores.