459: Sonographically measured inferior vena caval diameter in response to different maternal positions in pregnancy

Abstract

Placing pregnant patients in left lateral tilt (LLT) position to avoid compression of the inferior vena cava (IVC) has long been standard obstetric practice. The American Heart Association recommends continuous manual left uterine displacement (LUD) instead of LLT position during a maternal cardiac arrest. The relationship between maternal position and proximal filling of the IVC is unknown. The hypothesis is that the maternal IVC diameter would increase in response to LLT and LUD compared to supine position. A pilot prospective observational study was performed on 60 healthy gravidas. 30 patients at 20-24 weeks and 30 patients at 37-41 weeks were recruited. Patients were placed in supine, 30 degree left lateral tilt and supine with left uterine displacement positions. The IVC was visualized by ultrasound using the subxiphoid technique. The primary outcome was IVC diameter at end expiration. Descriptive analysis and student's paired t-test were performed. In the 20-24 weeks cohort, patients in LLT position (77.5 +/- 9.8, p=0.03) and LUD position (77.3 +/-9.5, p=0.04) had a significant decrease in heart rate (bpm) compared to supine position (80.5 +/-8.5). Patients in the LUD position (80.7 +/-7.6, p<0.001) had a significant decrease in MAP compared to supine position (83.7 +/- 7.4). No significant differences were seen in the IVC diameter between all 3 positions.In the 37-41 weeks cohort, there were no significant differences in the MAP, heart rate, and IVC measurement between all 3 positions.In the 20-24 weeks cohort, 48.3%, 30%, 18.3% of patients had their largest IVC diameter in the LUD, LLT, and supine position, respectively. In the 37-41 weeks cohort, 33.3%, 28.3%, 30% of patients had their largest IVC diameter in the LUD, LLT, and supine position, respectively. 1 subject in each cohort experienced symptoms consistent with supine hypotension syndrome in the supine position (3.33%). Sonographically the IVC diameters were not statistically different between all 3 positions. Furthermore, 18% in the 20-24 weeks cohort and 30% in the 37-41 weeks cohort had their largest IVC diameter in the supine position. This observation challenges the universal belief of uterine IVC compression with associating decrease in proximal IVC filling among pregnant cohort. This study suggests that LLT or LUD may not be universally beneficial.