Echocardiographic determination of resting haemodynamics and optimal positioning in term pregnant women

Abstract

Optimal positioning for anaesthesia in pregnant women involves balancing the need for ideal tracheal intubation conditions (achieved by the head elevated ramped position), with the prevention of reduced cardiac output from aortocaval compression (achieved by left lateral pelvic tilt). No studies have examined the effect on cardiac output of left lateral pelvic tilt in the ramped position. We studied non-labouring, non-anaesthetised healthy term pregnant women who underwent baseline (left lateral decubitus) cardiac assessment using transthoracic echocardiography. We then compared cardiac output, maternal physiological variables, fetal heart rate and comfort scores in three positions: left lateral decubitus; ramped position with wedge; and ramped position alone. Thirty women completed the study. Mean (SD) age, gestation and body mass index were 33.5 (3.93) years, 38.5 (0.94) weeks and 29.0 (4.0) kg.m , respectively. Mean ejection fraction, left ventricular internal diameter and mitral valve E/e' were 55.2 (6.8) %, 4.70 (0.43) cm and 7.50 (1.82), respectively. There were no differences in cardiac output between the positions (p = 0.503). There were no differences in systolic (p = 0.955) or diastolic (p = 0.987) blood pressure, maternal heart rate (p = 0.133), oxygen saturation, respiratory rate (p = 0.964) or fetal heart rate (p = 0.361) between ramped with wedge and ramped alone positions. Left lateral decubitus was most comfortable (p = 0.001), however, there were no differences in comfort levels between ramped with wedge and ramped alone positions. The ramped position without left lateral tilt is safe and acceptable in non-labouring, non-anaesthetised, healthy term pregnant women. Left lateral pelvic tilt may be unnecessary in the head elevated ramped position in term pregnant women.

Supine hypotensive syndrome of pregnancy

“…Rawles et al 32 demonstrated that even the sequence of shifting position might influence measurements. In addition, the various noninvasive methods of functional haemodynamic monitoring used to estimate stroke volume, cardiac output or even peripheral vascular resistance, include echocardiography, 30 bioimpedance cardiography, 15 acetylene rebreathing technique, 21 suprasternal Doppler ultrasound, 26 MRI phase-contrast images of the aorta, 17,18 cardiovascular magnetic resonance, 24 electrical cardiometry (ICON) 29 and noninvasive cardiac output monitoring (NICOM). 33 The comparability of such a wide range of techniques is limited.…”

“…However, several studies have failed to prove that in different maternal positions that the baseline foetal heart rate varies significantly. 23,28,30,41,42 In the 1970 and 1980s, radionuclide studies were used in the assessment of foetal wellbeing, but in recent times have been superseded by Doppler ultrasonography, all with inconsistent results.…”

Doctor, why are you driving a wedge between us? Calculating sample size in multiple testing and the need for Geisser‐Greenhouse correction

“…Logically then, we would extrapolate use of a wedge even in the ramped position to gain the marginal benefit of an improved venous return compared with the fully supine position, in addition to the gain in terms of airway management. In a recent issue of Anaesthesia , Dennis et al examined whether this is indeed the case . In a prospective observational study of 30 pregnant women > 37 weeks gestation, the investigators evaluated the haemodynamic effects of different positions by means of transthoracic echocardiography, in particular, the effect of adding a wedge in the ramped position.…”

“…The ANOVA test makes three main assumptions. Firstly, the dependent variable (see Table 3 ), is normally distributed. Secondly, there should be independence of observations.…”

“…intra‐observer agreement), which can be calculated as 1.96 times the standard deviation of the differences between the two measurements. To better illustrate the inter‐ or intra‐observer agreement, the investigators in the current study could have included the Bland–Altman plot. The authors chose not to include the plots as the intra‐ and inter‐observer biases were negligible.…”