Impact of morbid obesity on epidural anesthesia complications in labor.
Am J Obstet Gynecol. 2011 Oct; 205(4):370.e1-6
This is the first study to evaluate the association between the initiation of epidural analgesia in morbidly obese women and the incidence of maternal hypotension and fetal heart rate (FHR) abnormalities. The authors concluded that morbidly obese women had more frequent hypotension and a higher incidence of prolonged FHR abnormalities following epidural analgesia.
In the first retrospective study of its kind, the authors sought <= 25kg/m2) following a standardized epidural analgesia protocol and concluded that morbidly obese women had more frequent hypotension and a higher incidence of prolonged FHR abnormalities following institution of epidural analgesia. With the rising prevalence of morbid obesity, the significance of this study is obvious.
The authors surmise that one of the reasons for the increased incidence of hypotension was likely due to a combination of decreased epidural space volumes and increased epidural pressures in morbidly obese women causing a greater cephalad spread of local anesthetic. However, this did not bear out in the reported results; the sensory level was undistinguishable between the groups (T9 vs. T8, normal weight and morbidly obese, respectively). In addition, it is unclear how effective the left uterine tilt was in morbidly obese women compared to normal-weight women (a practical difficulty often realized when taking care of morbidly obese women), raising the specter of undetected supine hypotension syndrome as a potential factor responsible for the reported findings. Furthermore, there are significant concerns that question the external validity of the study. For example, the standardized epidural protocol in the study will be considered non-standard elsewhere; all epidural bolus doses were manually administered by the anesthesiologist (without an automated pump, and as a consequence, no background infusion), had a higher concentration of fentanyl (7.5µg/ml than the more common 2µg/ml) and contained epinephrine (5µg/ml). The measurement of blood pressure (a primary outcome) and the use of vasopressor (phenylephrine) were not standardized, which are the other understandable limitations of this retrospective study.
Notwithstanding these limitations, this study behooves us to be diligent in dosing up epidural catheters in morbidly obese women. Prospective, randomized studies will be required to confirm or refute these findings and to stratify risk according to BMI (women with BMI>...
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