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Maternal Cardiac Output is Improved with Lateral Tilt Positioning Only in a Subset of Term Parturients
Abstract Number: S 16
Abstract Type: Original Research
Introduction: Aortocaval compression by the gravid uterus is a recognized contributor to decreased cardiac output (CO), especially after neuraxial block placement (1). It is common clinical practice to tilt the operating room (OR) table to mitigate the effects of this compression. Recent meta-analysis (2) suggests there is no conclusive evidence as to the utility of this positioning in the OR. The goal of our controlled prospective study was to primarily evaluate hemodynamic changes and secondarily factors predictive of improvement of CO associated with differing degrees of lateral tilt in term non-laboring parturients.
Methods: After IRB approval and informed consent, enrolled patients were placed on an OR table positioned sequentially for hemodynamic measurements: sitting (beach chair), supine, Left tilt (LT) 5 º, LT 10 º, sitting, supine, right tilt (RT) 5 º , RT 10 º. Positioning was confirmed using an inclinometer. Each position was maintained for 3 min, then CO, cardiac index, stroke volume, systemic vascular resistance, heart rate, blood pressure, and EKG were assessed continuously for 1 min via transthoracic bioimpedance (PhysioFlow CO Monitor, NeuMedx, Bristol, PA). Priori power analysis suggested a sample size of 30 was needed to detect a 20% improvement in CO between supine and any other position with power of 0.80 and α= 0.05. P<0.05 was considered significant.
Results: 29 of 30 planned subjects were enrolled. Overall changes in CO, CI, SV, BP and HR between supine position and each tilt position were minimal and not statistically significant. Tilting from supine positions did not always result in an increase in CO. With 10 º LT, only 62% showed an average of 7.2% increase in CO from the supine position. With 10 º RT, only 35% showed an average 5% increase in CO from the supine position. Changes in CO in the LT position did not correlate with changes in the RT position (R= -0.2, P>0.05). Fetal weight and maternal BMI also did not correlate with changes in CO.
Discussion: Consistent with the findings of Cyna, et al (2), our preliminary findings showed that there was no consistent hemodynamic benefit with lateral tilt of the parturients. However, a subset of patients did show modest increases in CO with this change in positioning. This may be explained by the varied adequacy of existing collateral circulation in providing venous return. Further study is needed to identify subgroups of parturients who may benefit from this modest increase in CO (e.g. patients with uteroplacental insufficiency, preeclampsia or morbid obesity).
1. Danilenko-Dixon - Am J Obstet Gynecol 1996
2. Cyna – Cochrane Rev. 2006