AORTOCAVAL COMPRESSION IN THE SITTING AND LATERAL DECUBITUS POSITIONSDURING EXTRADURAL CATHETER PLACEMENT IN THE PARTURIENT

We prospectively studied the incidence of concealed aortocaval compres sion in parturients at term during identification of the extradural sp ace. Forty ASAI or II parturients, at term and in active labour, who r equested extradural analgesia were randomly allocated to one of two gr oups. Parturients in the first group (n = 22) were positioned in the l eft 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 d uring and thereafter for five minutes (in the supine wedged position), using the BoMED NCCOM3-R7 thoracic electrical bioimpedance (TEB) moni tor. The average of five CO(TEB) recordings before positioning the pat ient were compared with the average of five CO(TEB) measurements durin g and after extradural space identification. A change of >25% CO(TEB) was considered beyond machine variability. Upper limb arterial pressur e was recorded at one-minute intervals. In the left lateral decubitus position, 17 of 22 patients demonstrated a >25% reduction in CO(TEB) c ompared 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 co mpression during identification of the extradural space was demonstrat ed in the sitting position when compared with the left lateral decubit us position.