Increasing body mass index predicts increasing difficulty, failure rate, and time to discovery of failure of epidural anesthesia in laboring patients

Abstract

Study objective: Obese parturients both greatly benefit from neuraxial techniques, and may represent a technical challenge to obstetric anesthesiologists. Several studies address the topic of obesity and neuraxial analgesia in general, but few offer well described definitions or rates of "difficulty" and "failure" of labor epidural analgesia. Providing those definitions, we hypothesized that increasing body mass index (BMI) is associated with negative outcomes in both categories and increased time needed for epidural placement.

Design: Single center retrospective chart review.

Setting: Labor and Delivery Unit of an inner city academic teaching hospital.

Patients: 2485 parturients, ASA status 2 to 4, receiving labor epidural analgesia for anticipated vaginal delivery.

Interventions: None.

Measurements: We reviewed quality assurance and anesthesia records over a 12-month period. "Failure" was defined as either inadequate analgesia or a positive test dose, requiring replacement, and/or when the anesthesia record stated they failed. "Difficulty" was defined as six or more needle redirections or a note indicating difficulty in the anesthesia record.

Main results: Overall epidural failure and difficulty rates were 4.3% and 3.0%, respectively. Patients with a BMI of 30kg/m² or higher had a higher chance of both failure and difficulty with two and almost three fold increases, respectively. Regression analysis indicated that failure was best predicted by BMI and less provider training while difficulty was best predicted by BMI. Additionally, increased BMI was associated with increased time of discovery of epidural catheter failure.

Conclusions: Obesity is associated with increasing technical difficulty and failure of neuraxial analgesia for labor. Practitioners should consider allotting extra time for obese parturients in order to manage potential problems.

Keywords: BMI; Cesarean section; Dural puncture; Inadequate analgesia; Labor epidural; Morbid obesity; Neuraxial; Quality assurance.

Figure 1:

The rate (in %) of difficulty (white circles, dotted line) and failure (black diamonds, continuous line) of epidural catheter placement as a function of body mass index (BMI, in kg/m²). Regression analysis of binned data in BMI intervals of 5 revealed a significant linear relationship and correlations of BMI vs. difficulty and failure, respectively. All values are given ± standard error. For easier visibility, standard errors are displayed as capped horizontal bars slightly above the mean symbols. * P < 0.05 (two-tailed).

Figure 2:

Duration of epidural placement (in min; white triangles, continuous line) is plotted against body mass index (BMI, in kg/m²). Regression analysis of binned data in BMI intervals of 5 revealed a significant linear relation and correlation of BMI vs. duration. Values are given ± standard errors. For easier visibility BMI standard errors are displayed as capped horizontal bars slightly above the mean symbols. * P < 0.05 (two-tailed).

Figure 3:

Time between epidural placement and the decision that the catheter has failed. Every unit of BMI increases the average time to decision regarding failure by almost 6 min while decreasing its predictability as indicated by increasing heteroscedasticity and a low correlation coefficient. Values are given ± standard error; * P < 0.05 (two-tailed).