Lateral thinking - Positioning for obstetric anesthesia and its effects on maternal cardiac output and fetal well-being
Abstract Number: 86
Abstract Type: Original Research
Introduction: There are concerns regarding aortocaval compression effects on maternal hemodynamics(1) and fetal well-being in various positions. There has been much debate regarding the optimal position particularly when performing regional blockade for labour analgesia(2) and cesarean section. We aimed to establish the effects of position on maternal cardiovascular response and blood flow to the fetus Previous studies have relied on thoracic bioimpedence the results of which may be significantly affected by position whereas we used a suprasternal Doppler.
Methods: With ethical approval a prospective, randomised observational cross-over study was conducted in 25 ASA I/II women (target 15) with uncomplicated pregnancies presenting for elective cesarean section at term. The women were recruited and sequentially randomised to four different positions - supine with a 15 degree left tilt (Sup), sitting with neck and hips flexed (Sit), flexed left lateral (LL) and flexed right lateral (RL) positions. Maternal cardiac indices were measured and averaged over three readings using a non-invasive suprasternal Doppler device and upper arm non-invasive blood pressure. Umbilical Dopplers were performed simultaneously to measure the fetal heart rate (FHR) and umbilical artery pulsativity (PI) and resistivity (RI) indices. . Sample size was determined to demonstrate a 20% difference in cardiac index (0.85L/min/m2) between positions (α=0.05, power=90%). Variables were compared using a Tukey-Kramer multiple-comparison test in conjunction with Repeated Measures ANOVA and a P-value less than 0.05 was chosen as significant.
Results: We found maternal hemodynamics were significantly improved in the lateral positions as compared to the sitting position with respect to maternal cardiac index (CI), stroke volume index (SVI), heart rate and systolic blood pressure (SBP). We found no significant differences in FHR, PI or RI between positions.
Conclusion: Positioning for regional anaesthesia significantly influences maternal hemodynamic parameters and our results suggest the lateral position may be preferable for induction of regional blockade. Although we found no effect of position on blood flow to the healthy fetus we postulate that there may be implications for those fetuses who are subsequently compromised by reduced umbilical blood flow resulting in urgent or emergency cesarean sections.
1. Br J Anaesthesia 1968;40:120-124
2. Int J Obstet Anest 2008;17:146-152