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Echocardiography has demonstrated uterine contractions increase cardiac preload and stroke volume through auto-transfusion. These hemodynamic changes may be associated with a compensatory decrease in maternal heart rate. Our objective was to evaluate a visual maternal Contraction-Associated Heart Rate Deceleration (CAHD) pattern as a potential marker of relative hypovolemia.
We performed a pre-specified secondary analysis of a prospectively collected cohort from a RCT of maternal admission pulse pressure (PP), epidural coload volume, and post-epidural complications. Participants were healthy laboring women with non-anomalous singleton gestations ≥35 weeks and a category 1 FHR pattern from admission to epidural placement. Those without continuous maternal pulse oximetry data were excluded. Maternal heart rate tracings were evaluated for the presence of CAHD (Figure 1) in the hour prior to epidural placement. Women with and without CAHD were compared. Evaluated study outcomes were: post-epidural category 2/3 FHR abnormalities, maternal hypotension, and obstetric interventions.
Of 414 participants, 388 (93.7%) met inclusion criteria; of these 124 (32.0%) had CAHD before epidural placement. On admission, women with CAHD had lower systolic (116.6 vs 119.5, p=.002) and higher diastolic (75.3 vs 73.6, p=.03) blood pressures and a narrower PP (41.3 vs 46.0, p<.001) than women without CAHD. Demographic and clinical characteristics were otherwise similar between groups. CAHD was associated with more frequent post-epidural FHR abnormalities, diastolic hypotension, and obstetric interventions (Table 1). Among women with CAHD, a larger initial epidural bolus (1500 vs 500 mL) was associated with less frequent systolic hypotension (9.8 vs 32.8%, p=.003) and obstetric interventions (21.6 vs 42.5%, p=.02). Among women with CAHD and narrow PP, post-epidural FHR abnormalities were less frequent with a 1500 mL bolus (37.3 vs 58.2%, p=.03), but this finding was not significant for those without CAHD.
Maternal CAHD pattern is a pragmatic visual marker of intrapartum maternal volume status. CAHD is associated with more frequent post-epidural FHR abnormalities and need for obstetric interventions. Additional maternal volume loading with epidural placement should be considered for women with CAHD.