Aortocaval compression in the sitting and lateral decubitus positions during extradural catheter placement in the parturient

We prospectively studied the incidence of concealed aortocaval compression in parturients at term during identification of the extradural space. Forty ASA I or II parturients, at term and in active labour, who requested extradural analgesia were randomly allocated to one of two groups. Parturients in the first group (n = 22) were positioned in the left lateral decubitus position and those in the second group (n = 18) were in the sitting position. Cardiac output (CO) was recorded at one-minute intervals for five minutes before extradural catheter placement (supine position with a 15° wedge under the right side), and during and thereafter for five minutes (in the supine wedged position), using the BoMED NCCOM3-R7 thoracic electrical bioimpedance (TEB) monitor. The average of five CO_TEB recordings before positioning the patient were compared with the average of five CO_TEB measurements during and after extradural space identification. A change of >25% CO_TEB was considered beyond machine variability. Upper limb arterial pressure was recorded at one-minute intervals. In the left lateral decubitus position, 17 of 22 patients demonstrated a >25% reduction in CO_TEB compared with five of 18 patients in the sitting position (X²,P <0.01). The percentage change in CO_TEB in the lateral decubitus position (?29.8%, 95% CI ?17% to ?44%) was greater than the sitting position (?9.8%, 95% CI +36% to ?32%) (P <0.01). A decreased incidence of aortocaval compression during identification of the extradural space was demonstrated in the sitting position when compared with the left lateral decubitus position.