High Success Rates Using Ultrasound for Neuraxial Block in Obese Patients

Successful neuraxial block performance relies on assessment and palpation of surface landmarks, potentially challenging in patients with a high body mass index (BMI).

To evaluate the use of ultrasound-assisted neuraxial bock in a non-obstetric population with BMI above versus below 30 kg/m2.

Healthy adult patients undergoing extracorporeal shock wave lithotripsy (ESWL) under neuraxial block were observed in this quality assurance study. Prior to the neuraxial block, an ultrasound examination was performed to identify the puncture site. Neuraxial anesthesia block was performed under aseptic surgical conditions with the patient in the sitting position. Following block placement, external landmarks were palpated. Our primary study outcome was the number of attempts (skin insertions with the needle) after pre-puncture ultrasound identification of the insertion point, comparing patients with BMI above versus below 30 kg/m2. Our secondary outcome was assessment by palpation of external anatomical landmarks.

Our study group included 63 consecutive patients undergoing neuraxial block for ESWL. Data were assessed according to BMI (above versus below 30 kg/m2). An overall success rate at the first attempt of 90.5% (CI 0.8-0.95) was achieved using ultrasound-guided neuraxial block. This block placement success rate was similar for all patients, regardless of BMI above versus below 30 kg/m2. In contrast, the ease of palpation of anatomic landmarks, P = 0.001, and the ease of palpation of iliac crest, P < 0.001, differed significantly between the patients above versus below 30 kg/m2. The reported verbal pain scores (VPS) due to block insertion was similar among all patients regardless of BMI category (above versus below 30 kg/m2).

We observed high success rates when ultrasound-assisted neuraxial block is performed, regardless of BMI above versus below 30 kg/m2, despite expected differences in surface landmark palpation.