• P J Andrews, W E Ackerman, and M M Juneja.
• Department of Anesthesiology, University of Louisville, School of Medicine, Kentucky 40292.
• Can J Anaesth. 1993 Apr 1;40(4):320-4.

AbstractWe 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 degrees 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 COTEB recordings before positioning the patient were compared with the average of five COTEB measurements during and after extradural space identification. A change of > 25% COTEB 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 COTEB compared with five of 18 patients in the sitting position (chi 2, P < 0.01). The percentage change in COTEB 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.

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