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Sonoanatomic Predictors of Difficult Epidural Insertion in Term Pregnant Women: A Prospective Observational Study
Abstract Number: S 22
Abstract Type: Original Research
Ultrasound (US) has been shown to improve efficacy and decrease complications of neuraxial anesthesia (1). There is a need to study whether specific sonoanatomic features can predict difficult placement of neuraxial blocks. While 2 studies have identified some predictors in geriatric patients (2,3), no data is available for the obstetric population. The purpose of this study was to identify sonoanatomic features of the L3-L4 interspace that may predict difficult epidural placement in pregnant women.
We conducted a pilot study in 20 laboring women who requested epidural analgesia. The most common sonoanatomic features of the L3-L4 interspace in the paramedian saggital oblique (PSO) and transverse medial (TM) planes were identified. The US assessment was performed with a 5-2 MHz curvilinear transducer. The landmarks assessed in the pilot study are presented in Table 1. Following the pre-procedural US assessment, the attending anesthesiologist was informed of the puncture site and estimated depth to the epidural space. The following outcomes were assessed: the number of needle redirections, the need to change interspace and the patient’s comfort during the procedure. The primary outcome was the number of needle redirections at L3-L4, which served to allocate patients into 2 groups - easy (<4 redirections) or difficult (≥4 redirections) punctures. The 2 groups were compared for differences in the sonoanatomical features of the L3-4 interspace using Fisher's exact test and Wilcoxon Rank Sum test as appropriate.
The results are presented in Table 1. Variables that showed a difference between the 2 groups with a p value <0.15 or a magnitude >40% were selected. Three variables were identified according to those criteria (all in TM plane): visualization of the ligamentum flavum-dura mater (LF/DM) unit, symmetry of the articular processes, and the distance from the skin to the LF/DM unit. The sample size calculation for the final study (103 patients for 80% power at a significance level of 0.05) was based on this pilot study.
Although we have identified the sonoanatomic features that may be related to difficult placement of epidurals at L3-L4, our hypothesis has to be confirmed in the final study. We are currently recruiting patients and the final results will be discussed during the conference.
References: 1) Anesthesiol Clin 2008; 26: 145-58; 2)Anaesthesia 2011;66:925: 3) Reg Anesth Pain Med 2013;38 :34-8.