By Will Boggs, MD
NEW YORK (Reuters Health) Jul 26 - Maternal pulse pressure may predict changes in the fetal heart rate after administration of epidural anesthesia for labor, a retrospective study suggests.
"There is a simple vital sign parameter-pulse pressure-that can give us a crude estimation of intravascular volume in a way that can be clinically relevant to how we care for women in labor requesting an epidural for pain management," Dr. Nathaniel R. Miller from Darnall Army Medical Center, Fort Hood, Texas, told Reuters Health.
"Many factors influence maternal health and tissue perfusion and fetal oxygenation and perceived fetal well-being during labor and during the initial bolus of a labor epidural," Dr. Miller said. "Some are in our control, others are foreseeable, and yet others very elusive."
Dr. Miller, with colleagues at Madigan Army Medical Center, Tacoma, Washington, investigated whether a low admission pulse pressure increased the risk of post-epidural fetal heart rate abnormalities by comparing 95 women with an admission pulse pressure below 45 mm Hg to 95 matched control women with an admission pulse pressure of at least 45 mm Hg.
As reported online June 14 in the American Journal of Obstetrics & Gynecology, fetal heart rate abnormalities were defined as recurrent late decelerations and/or prolonged decelerations in the first 60 minutes after initial dosing of labor epidural.
Both groups of women received a similar total volume of intravenous fluid from admission and a similar epidural preload IV bolus.
Although vital signs did not differ between the low and normal pulse pressure groups at the time of the epidural request, women in the low pulse pressure group had significantly lower systolic blood pressure and pulse pressure during the 60 minutes after their initial epidural dosing, as well as significantly lower average mean arterial pressure at 20-40 minutes after initial dosing.
New onset fetal heart rate abnormalities occurred in 27% of women in the low pulse pressure group, compared with only 6% of women in the normal pulse pressure group (p<0.001).
After controlling for numerous other variables, the risk of fetal heart rate abnormalities was 29-fold higher in the low pulse pressure group than in the normal pulse pressure group (p<0.001).
The rate of new onset maternal hypotension, however, did not differ significantly between the groups.
The differences in fetal heart rate abnormalities between the groups was not accompanied by significant differences in overall length of labor, length of each stage of labor, time from epidural placement to delivery, mode of delivery, or delivery outcomes.
"Studies using noninvasive assessments of intravascular volume in a prospective manner would be helpful to confirm our findings and validate pulse pressure as a surrogate for intravascular volume in the laboring parturient by describing the relation of pulse pressure to stroke volume and cardiac output," the researchers note.
"Women with reduced pulse pressure at admission should be evaluated for other potential causes of intravascular volume reduction (e.g. bleeding) and (their) medical history reviewed for any renal or cardiovascular diseases," Dr. Miller said.
"One should consider then in the otherwise healthy patient to increase the maintenance IV fluids above 125 mL (designed to replace losses in a resting patient, not someone as metabolically and physiologically active as a woman in labor) and also to pretreat with a vasoconstricting agent at the time of initial epidural dosing," he added.
"Basic physiology and fluid management may be taken for granted, especially in an obstetric population that is otherwise healthy," Dr. Miller continued. "Remembering and using some of these basic principles may help providers identify patients at risk and use treatments targeted to maximize maternal and fetal tissue perfusion throughout pregnancy and the course of labor and birth."
Am J Obstet Gynecol 2013.
Reuters Health Information © 2013