Haemodynamic effects from aortocaval compression at different angles of lateral tilt in non-labouring term pregnant women†‡

Aortocaval compression (ACC) can result in haemodynamic disturbances and uteroplacental hypoperfusion in parturients. Its detection is difficult because in most patients, sympathetic compensation results in no signs or symptoms. However, profound hypotension may develop after sympathectomy during regional anaesthesia. In this prospective observational study, we aimed to detect ACC by analysing haemodynamic changes in term parturients who were positioned sequentially at different angles of lateral tilt. We studied haemodynamic changes in 157 non-labouring term parturients who were positioned in random order at 0, 7.5, 15, and full left lateral tilt. Cardiac output (CO), stroke volume, and systemic vascular resistance were derived using suprasternal Doppler. Non-invasive arterial pressure (AP) measured in the upper and lower limbs was analysed to detect aortic compression. CO was on average 5 higher when patients were tilted at epsilon 15 compared with 15. In a subgroup of patients (n11), CO decreased by more than 20, without changes in systolic AP, when they were tilted to 15 which was considered attributable to severe inferior vena caval compression. Only one patient in the supine position had aortic compression with the systolic AP in the upper limb 25 mm Hg higher than the lower limb. Patients with ACC can be identified by the CO changes from serial measurements between supine, 15, or full lateral tilt. Our findings suggest that in non-labouring parturients, ACC is asymptomatic and can be effectively minimized by the use of a left lateral tilt of 15 or greater.