A novel methodology for identifying the sciatic nerve before blockade has been developed. That task is often challenging, particularly in morbidly obese patients.
Blockade of the sciatic nerve, necessary for complete analgesia of the lower extremity using peripheral nerve blocks, usually relies on ultrasound to identify the sciatic nerve; however, ultrasound is technically difficult in obese patients, particularly in deep blocks. The new research, from the University of Louisville, Kentucky, is a follow-up to a previously published study (Anesth Analg 2010;110:958-963), which assessed the methodology in patients in the prone position. The new study, presented at the Euroanaesthesia 2015 conference (abstract 3AP1-6), demonstrated that the technique, which uses the ischial tuberosity as a landmark, also works well when patients are in the lateral Sims’ position.
“Sciatic nerve blocks are the most dreaded within the field of anesthesiology,” said co-author Anu Wadhwa, MD, associate professor of anesthesiology and director of resident education and curriculum at the University of Louisville. “I have seen anesthesiologists struggling for 45 minutes or more to find the sciatic nerve. Our approach is much faster. We can identify the sciatic nerve literally in seconds. We see this as a revolution in the procedure.”
Fewer Needle Passes
Dr. Wadhwa and her colleagues sought to develop a landmark-based technique that could be performed quickly, an important consideration given the pressures of turnover time in many surgery centers. She and her team randomly assigned 40 patients undergoing lower limb surgery to receive sciatic nerve blockade either via their novel approach, which positions the blockade 3 cm lateral from the ischial tuberosity, or using the conventional approach via ultrasound; all patients were in the lateral Sims’ position. The time taken to obtain the first sciatic nerve twitch and the number of needle passes needed to obtain the sciatic nerve twitch were the primary and secondary outcomes, respectively.
In all, successful placement of the blockade occurred in 15 of 19 (79%) patients in the conventional group and 13 of 17 (77%) patients in the experimental group. However, 41% of patients in the experimental group had a sciatic nerve response in the first pass of the needle compared with 15% of the patients in the conventional group. The average numbers of needle passes needed to obtain the first twitch in the experimental and conventional groups were 3.5 and five, respectively. In addition, the number of patients with twitch stimulating the tibial nerve was substantially higher in the experimental group (87.5% vs. 66%).
Jiabin (JB) Liu, MD, PhD, assistant professor in the Department of Anesthesiology and Critical Care and anesthesia director in the Ambulatory Surgery Facility at Penn Medicine University City in Philadelphia, said the approach developed by Dr. Wadhwa and her colleagues is “viable,” even though he has not used it himself in clinical practice.
“It makes sense anatomically,” explained Dr. Liu, who was not part of the study. “I foresee this approach being adopted for future clinical practice. It is fairly simple, with one landmark, which should be palpable even in the high body mass index patient population.”
Nathan Clendenen, MD, a resident in the Department of Anesthesiology at Yale School of Medicine in New Haven, Conn., who has worked in other research projects involving sciatic nerve blockade, added, “The study has not provided overwhelming evidence in favor of the new technique, but the authors have shown at least that the approach is possibly noninferior to the control approach in the hands of a single operator. The single most important aspect in the practice of regional anesthesia is the skill and experience of the clinician performing the block. A more illuminating study would be to take inexperienced operators and compare the techniques based on time to proficiency with the block.”