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An observational study of post-cesarean delivery respiratory patterns using a non-invasive minute ventilation monitor
Abstract Number: F-28
Abstract Type: Original Research
Background: Morphine is commonly injected neuraxially for post-cesarean delivery (CD) analgesia. We previously reported no respiratory depression (RD) in 5036 parturients who received neuraxial morphine (NM) despite a high incidence of obesity1. However, conventional intermittent monitoring could not exclude episodes of minor hypoventilation and the incidence of RD in high-risk parturients remains unknown. This has led some centers to withhold NM in some high-risk parturients. In this study, we monitor parturients who received NM using a non-invasive, continuous respiratory volume monitor (RVM) that measures respiratory rate, tidal volume, and minute ventilation (MV)
Methods: Continuous RVM (ExSpiron, Respiratory Motion, Waltham, MA) and opioid administration data were collected prior to and for 24 h following elective CD under neuraxial anesthesia with 150 mcg intrathecal or 3-mg epidural morphine. Demographics and co-morbidities were collected, and obstructive sleep apnea (OSA) screening tools were administered. Predicted MV (MVPRED, based on BSA) was calculated and Low MV (LMVe) was defined as MV < 40% MVPRED for > 1-min. LMVes were plotted over 24 h along with NM, intravenous and oral narcotics. Clinicians were blinded to the RVM measurements and followed routine care protocols.
Results: 13 parturients (mean (range) age, 32 yrs (18-81); BMI, 40.7 kg/m2 (26-57)) were included in this ongoing study. Only 2 patients (Figure 1, BMI 55 and 57 kg/m2) experienced repeated LMVe in the first 24 h following NM administration. Although neither had an OSA diagnosis, patient12 had numerous risk factors for OSA on screening questions. No abnormal vital signs were documented in either subject’s chart surrounding these LMVe. Of note, 2 subjects in this sample with diagnosed OSA had no LMVe.
Conclusions: In this small observational study, only 2 parturients experienced repeated LMVe, but this did not result in adverse outcomes. Larger studies might identify clinically relevant adverse respiratory events. Current clinical practices, based on intermittent vital signs monitoring, may be incapable of identifying such events. Continuous RVM monitoring may prove useful for monitoring high-risk parturients receiving NM. More data are needed to quantify the true incidence of post-operative hypoventilation among parturients with NM and to identify patients who may benefit from additional monitoring.
1. Crowgey TR. Anesth Analg 2013; 117: 1368-1370