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Accuracy of Intervertebral Level Determination for Obstetric Neuraxial Anesthetic Procedures
Abstract Number: T-44
Abstract Type: Original Research
BACKGROUND:Using palpation of the iliac crest for identification of Tuffier’s line may result in inaccurate level determination for neuraxial anesthetic procedures.1 Anatomic changes associated with pregnancy may further distort the anatomy.2 Improper identification of interspaces has safety concerns given the variability of conus medullaris ending often beyond the level of L1.3 Ultrasound (US) use may increase accuracy,2 yet routine use of US to identify level is not the standard of care. Previous investigators have documented poor accuracy of level determination by palpation in an experimental environment.1 We undertook this study to determine accuracy of vertebral level identification in the obstetric anesthesia clinical environment.
METHODS: In this IRB-approved study we identified and consented patients who had neuraxial labor analgesia and performed US examination of their back on postpartum day 1 or 2. We determined level of neuraxial anesthetic placement by noting the US-determined level of the puncture mark on the skin and after US was completed, compared that to the level documented in the electronic medical record (EMR). We noted BMI and relevant details of the anesthetic procedure, including whether placement had been US-guided. The examiner recorded ease of visualization of US (easy, moderate, difficult) based on time spent and image quality.
RESULTS: Of 95 patients studied, level could not be determined by US in 1 and level was not documented in the EMR in 2. US-determined level correlated with EMR-documented level in 32/92 (35%) of cases, was 2 segments higher in 8/92 (9%), was 1 segment higher in 34/92 (37%), and was 1 segment lower in 18/92 (21%) of patients. BMI was 33 SD±7.4. 79/95 (83%) of anesthetics were CSE or IT procedures, and only 4/95 (4%) of procedures were US-guided. 68/95 (72%) of US exams were judged to be easy.
CONCLUSIONS: Consistent with studies under experimental conditions1 accuracy of identification of intervertebral level by palpation in clinical settings is poor and most errors result in placement of neuraxial anesthetic higher than estimated. A large portion of our blocks intentionally entered the IT space arguing for a greater need for accuracy. Visualization of intervertebral level using US is easy in most parturients, including in an obese population of patients, and may improve accuracy.
1.Broadbent Anesthesia 2000; 55:1106
2.Grau Brit J Anesthesia 2001; 86:798
3.Reynolds Anesthesia 2000; 55:1045