Ultrasound Decreases the Failed Labor Epidural Rate in Resident Trainees

Abstract

A lthough epidural analgesia is used widely for pain relief during labor, the failure rate ranges from 1.5% to 20%. This prospective, randomized, nonblinded study investigated whether ultrasound measurement of the depth from the skin to the epidural space before epidural placement decreases the failure rate of labor analgesia. The second objective of the study was to correlate the ultrasoundmeasured depth to the epidural space with the actual depth of the needle when the epidural space is reached.A total of 370 laboring parturients were randomized to undergo epidural placement by first-year anesthesia residents with or without prior ultrasound measurement of the depth to the epidural space. Patients in the ultrasound group underwent ultrasound visualization of the epidural space in the longitudinal median and transverse planes while in the sitting position. The ultrasound measurements were used to estimate the distance from the skin to the ligamentum flavum before the epidural catheter was inserted. The epidural was performed in both groups using the midline approach at the L3-4 or L4-5 vertebral interspace using a loss of resistance to saline technique. All patients received a 10 mL bolus of ropivacaine 0.1% + 100 mcg fentanyl and were then placed on a continuous maintenance epidural infusion of ropivacaine 0.1% and fentanyl 2 mcg/ mL. Outcomes measured included the incidence of epidural catheter replacement for failed analgesia, the number of epidural attempts, and the number of accidental dural punctures.The 189 patients in the ultrasound group and 181 in the control group did not differ significantly in age, height, weight, body mass index, gestation, or parity. The groups did not differ in cervical dilation, station at epidural placement, and initial visual analog score for pain. The use of ultrasound, undertaken by an investigator skilled in ultrasound epidural placement (not the learner), added 60 ± 15 seconds to the mean preparation time. The epidural block failed in 3 and 10 patients in the ultrasound and control groups, respectively, with one in the ultrasound and 6 in the control group considered early failures (within the first 90 min after placement), P = NS. Patients in the control group had more initial placement attempts (2 vs. 1), but the need for staff intervention was not significantly different. The ultrasoundestimated mean epidural depth was 4.6 ± 0.9 cm when measured in the longitudinal plane and 4.7 ± 1.0 cm as measured in the transverse plane showed a strong correlation with the actual clinical depth of the epidural space. No significant differences in staff interventions, need for additional top-ups, or delivery outcomes were determined.In conclusion, the investigators determined that the use of ultrasound to measure the depth of the epidural space before an epidural catheter is inserted for labor analgesia is an excellent teaching tool for neophyte learners of the clinical skill set necessary to locate the epidural space.

Pre-Procedure Neuraxial Ultrasound in Obstetric Anesthesia

“…Several clinical studies have reported that neuraxial pre-procedural imaging decreases the number of attempts required for epidural placement, determines the optimal puncture site and needle angulation, and accurately predicts the depth from the skin to the epidural space (2,5). Superior epidural catheter function and fewer replacement rates are other reported benefits of ultrasoundguided epidural placement (Table 2) (2, 5).…”

“…It has been shown to improve the epidural placement learning curve by increasing the epidural success rate, and reducing the number of epidural attempts and catheter replacement for failed labor analgesia (4,5,8).…”

“…A low-frequency (2 -5 MHz) curved array transducer (the same transducer used by obstetricians for fetal scanning of the uterus) is used for the procedure (5,9,10). This low-frequency probe allows deeper penetration of tissues to target the structures of interest, but sacrifices resolution and precision of the image.…”

“…Furthermore, obese patients are more likely to experience longer procedure times, a higher incidence of accidental dural puncture, a higher incidence of epidural venous puncture, and higher overall failure and complication rates during neuraxial anesthesia placement (2,17,18). In non-obese parturients with BMI ' s ranging from 25.1 to 39.9, Vallejo et al (5) found that the Pearson correlation coefficients comparing the actual needle depth (ND) versus ultrasound depth (UD) to the epidural space in the longitudinal median and transverse planes were (0.914 and 0.909, respectively). In comparing the distance from the skin to the epidural space at the level of L3 -4 in obese women (BMI at delivery of 33-86 kg/m2), Balki et al (18) found that the Pearson correlation coefficient between the ultrasound depth (UD) and the actual needle depth (ND) was 0.85 (95% confidence interval: 0.75-0.91), with a concordance correlation coefficient of 0.79 (95% confidence interval: 0.71 -0.88).…”

“…Multiple clinical studies have determined that neuraxial ultrasound imaging can be used to identify the intervertebral space(s), the midline for insertion, determine the depth from the skin to the epidural space, the best needle insertion point, and the best angle for needle insertion (Table 1) (1)(2)(3)(4)(5). In 2013, a meta-analysis of multiple clinical studies involving neuraxial ultrasound concluded that ultrasound imaging can reduce the risk of failed or traumatic lumbar punctures and epidural catheterizations, as well as the number of insertion attempts and needle redirections (1).…”