Ilioinguinal/Iliohypogastric Blocks: Where Is the Anesthetic Injected?

To the Editor: We wish to complement the results of Wientraud et al.1 studying the results of ilioinguinal/iliohypogastric blocks in children with our own obtained in an adult population. Although we agree that the best results for ultrasound nerve block include nerve visualization, this might be equipment and operator dependent.2 In an attempt to develop an ilioinguinal/iliohypogastric echographic aided block, without nerve identification, a pilot study to determine the anatomic site of local anesthetic placement was completed. We studied (IRB approved) 19 adult patients, scheduled for primary inguinal hernia repair under general anesthesia. Before surgery, abdominal wall anatomy was scanned (Figs. 1a and b; Philips EnVisor C, L12-3 transducer) in a transverse view medial to the anterior superior iliac spine (ASIS), immediately before and after an iliohypogastric block. This was performed as usually done at our institution, injecting after one loss of resistance or “pop”3 (Figs. 2a and b). No attempt to redo the block was done, if ultrasound scanning suggested an incorrect location of local anesthetic. In the recovery room, the extent of cutaneous anesthesia area was measured using insensitivity to pinprick. Successful block was defined as an anesthesia area >25 cm2. Three observers determined the extent of local anesthetic distribution. Results included 1 subcutaneous injection resulting in failed block, 4 external oblique injections of which 3 resulted in failed blocks, and 14 internal oblique injections yielding 12 successful blocks. Overall success rate was 68%. Thus, in our experience, one fascial click sensation (pop) does not consistently result in the same location of injection. We hypothesize that in adults, an internal oblique plane injection using ultrasound, medial to the ASIS, regardless of nerve visualization should improve the success compared with usual blind procedure.Figure 1.: (a, b) Pre- and postilioinguinal block images of the abdominal wall, in a patient with a successful block.Figure 2.: (a, b) Pre- and postilioinguinal block images, in a patient with a failed result. Notice in left image, strong Scarpa’s fascia, that probably induced a premature sense of loss of resistance or pop.Denise Thibaut, MD Juan Carlos de la Cuadra-Fontaine, MD María Pía Bravo, MD René de la Fuente, MD Departamento de Anestesiología Facultad de Medicina Pontificia Universidad Católica de Chile Santiago, Chile [email protected]