Dr. Danilenkodixon et al., POSITIONAL EFFECTS ON MATERNAL CARDIAC-OUTPUT DURING LABOR WITH EPIDURAL ANALGESIA, American journal of obstetrics and gynecology, 175(4), 1996, pp. 867-872
OBJECTIVE: Our purpose was to test the hypothesis that the supine vers
us the lateral position is associated with a greater decrement in card
iac output after epidural analgesia in labor. STUDY DESIGN: Twenty-one
normal term subjects were randomized to the left lateral or supine po
sition in early labor. Cardiac output measured by the acetylene rebrea
thing method, stroke volume, heart rate, mean arterial pressure, and s
ystemic vascular resistance were obtained at 5-minute intervals, begin
ning before a 500 ml intravenous fluid bolus (baseline) and ending 45
minutes after epidural injection. RESULTS: Mean baseline supine versus
lateral group differences were significant for 21% lower cardiac outp
ut, 21% lower stroke volume, 19% higher mean arterial pressure, 50% hi
gher systemic vascular resistance, and equivalent heart rate. In the s
upine group fluid bolus resulted in significantly increased cardiac ou
tput and stroke volume, decreased mean arterial pressure and systemic
vascular resistance, and unchanged heart rate. In the supine group car
diac output and stroke volume decreased significantly after epidural i
njection. The lateral position group exhibited no hemodynamic alterati
ons after fluid bolus or epidural. CONCLUSIONS: In contrast to the lat
eral position, the supine position is associated with a significant po
stepidural decrement in cardiac output, not identified by a change in
heart rate. This likely reflects an inability to maintain stable prelo
ad volume in the supine position.