Ultrasound evaluation of inferior vena cava compression in tilted and supine term parturients.

Abstract

Hypotension is common following spinal anesthesia (SA) during elective Cesarean delivery (CD). Although common practice is to alleviate inferior vena cava (IVC) compression, limited evidence supports a 15° tilt for CD. We measured collapsibility of the IVC in supine and 15° left lateral tilt positions with ultrasound before and after SA and phenylephrine infusion in term parturients. Twenty term parturients scheduled for CD were recruited for this prospective study. Ultrasound measurements of the IVC were taken 1) supine before SA, 2) tilted 15° before SA, 3) supine after SA, and 4) tilted 15° after SA. A phenylephrine infusion was begun after injection of SA. The primary outcome was to evaluate the impact of position on the IVC collapsibility index (IVCCI): a measure of the difference between the maximum and minimum IVC diameter with respiration. The mean (standard deviation) IVCCI (%) before SA was higher in the supine 19.5 (8.0) than in the tilted 15.0 (6.4) position (mean difference, 4.5; 95% confidence interval [CI], 0.1 to 8.9; P = 0.04). After SA, there was no significant difference between IVCCI (%) in the supine 17.8 (8.3) and tilted 14.2 (6.9) position (mean difference, 3.5; 95% CI, -0.9 to 7.9; P = 0.13). There was no correlation between the pre-spinal IVVCI measurements and the quantity of phenylephrine used during the surgery. The IVCCI was lower in the 15° tilt position than in the supine position, but not after SA with a phenylephrine infusion. Ultrasound imaging can help identify IVC compression. www.clinicaltrials.gov (NCT03410199); registered 18 January 2018.