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Cardiac Output at Term Pregnancy as it Relates to Maternal Position and Body Mass Index
Abstract Number: SA-20
Abstract Type: Original Research
Background: It is well documented that supine hypotensive syndrome occurs in term parturients in the supine position due to aortocaval compression by the gravid uterus. Cardiac output can also be affected by patient positioning for epidural placement. Currently, there is no study that addresses the effect that body mass index (BMI) has on maternal cardiac output in the two common epidural positions – flexed sitting and lateral decubitus. The aim of this study is to determine if increasing BMI will negatively affect cardiac output (CO) in patients placed in traditional epidural positions. We hypothesize that the cardiac output will be the lowest in the flexed sitting position when compared to lateral tilt and lateral decubitus and that patients with a greater BMI will have a significantly decreased CO when compared to normal weight patients.
Methods: A total of 32 out of 40 patients have been recruited to this prospective, observational study. Two out of the 32 have been excluded from the analysis – one due to equipment error and the other due to initiation of oxytocin during hemodynamic measurements. Measurements were taken noninvasively using the ClearSight System (Edwards Lifesciences). Using left lateral tilt as our hemodynamic baseline, measurements were taken in the following order: left lateral tilt, flexed sitting, left lateral tilt then finally full left lateral. Hemodynamic measurements investigated were CO, stroke volume (SV), heart rate (HR) and fetal heart tones (FHT).
Results: Position and BMI have a significant effect on CO. Positioning from left lateral tilt (LLT) up to flexed sitting (FS) is positively correlated to an increase in CO. Of the CO components, HR was more profoundly altered than stroke volume. The FS position was associated with a 0.38 L/min (p< 0.0001) increase in CO compared to the left lateral tilt position. In regards to BMI, there was a highly significant (p<0.0001) positive correlation between BMI and CO. An increase in BMI from 30 to 40 correlated to a 0.6 L/min increase in CO. Notably, this positive correlation does not change with position. There was no significant change in FHT with change in maternal position or in relation to maternal BMI.
Conclusion: We found an elevation in CO with FS position and an elevation in CO with increasing BMI. This would suggest that parturients with marginal placental perfusion and/or non-reassuring FHT would benefit from the sitting epidural position.