Prospective observational study of serial cardiac output by transthoracic echocardiography in healthy pregnant women undergoing elective caesarean delivery.

BACKGROUND

An understanding of cardiovascular changes in parturients is crucial for their anaesthetic management, but few studies have examined the effect of posture on cardiac output in the peripartum period.

METHOD

Cardiac output was measured in four different positions by transthoracic echocardiography (Doppler) in 30 term women undergoing elective caesarean delivery. These positions were left lateral level (P1), left lateral with 20 degrees head up (P2), left lateral with 10 degrees head down (P3) measured preoperatively and supine (P4) measured postoperatively.

RESULTS

Mean +/- SD cardiac output was 4407+/-1109 mL/min (P1), 4182+/-825 mL/min (P2), 4031+/-798 mL/min (P3) and 4641+/-1064 mL/min (P4). Cardiac output was significantly less in P3 than in P1 (P = 0.049) due to a lower P3 velocity time integral compared with P1 (P = 0.020). Postoperatively, in the supine position, there was no difference in cardiac output, although there was a lower heart rate (P = <0.001) and increased velocity time integral (P = <0.001) compared with P1. The mean differences in interobserver measurements were 0.02 cm (left ventricular outflow tract) and -1.06 cm (velocity time integral). The mean differences in intraobserver measurements were 0.00 cm (left ventricular outflow tract) and -0.22 cm (velocity time integral). Echocardiography was well accepted by all women. Eight women found the left lateral 10 degrees head-down position (P3) uncomfortable due to dizziness, headache, or increased abdominal pressure.

CONCLUSIONS

Cardiac output showed large variability and was lower than previously reported. Cardiac output decreased with the left lateral 10 degrees head-down position due to a reduction in stroke volume that has not previously been reported. The transthoracic examination was acceptable to all women.