The results of this study indicate that simulation-based training for ultrasound-guided TAP block using an anesthetized porcine model reduced the anxiety and improved the knowledge and confidence of anesthesiology trainees for performing the procedure. The three basic requirements for ultrasound-guided regional block training are (i) pattern recognition, (ii) probe handling and scanning, and (iii) manual dexterity to align the needle with the ultrasound beam [9], the latter two of which are challenging for residents with no experience with regional block using ultrasound [10]. Correct identification of the needle tip on ultrasound during regional block, particularly as the tip proceeds to abdominal muscle layers without a bony landmark, is important for patient safety and determines block success.
For effective analgesia, the needle should be placed between the internal oblique and transversus abdominis muscles. Previously, TAP blocks were performed in a blind manner, but current clinical trends show a reliance on ultrasound for checking the needle tip to prevent possible damage to internal organs [4]. Although needle handling and optimal positioning may still be difficult after a single training session, residents gain realistic practice and confidence with this hydrodissection technique. To strengthen resident training, simulation training programs should be further incorporated for both skill retention and familiarity for trainees.
For ultrasound training, water, gelatin, meat, cadavers, and animals carcasses have been used [11-13]. However, water and gelatin are more suitable for spine models, and fascial plane blocks are difficult to reproduce with these. A meat phantom provides tactile feedback from the needle, with echogenicity resembling that of human tissue [14], as with cadaver phantoms, though these are expensive and not readily available. These models are fixed and do not incorporate movement, such as that of the abdominal wall caused by respiration of the patient, which can interfere with the TAP block. For this reason and because of their similar anatomy, live pigs are superior for practicing TAP block. Indeed, most (87%) of the residents surveyed for this study reported that the experience was closer to that with real patients.
In our institution, the anesthetized porcine model has been incorporated for educating residents about other regional anesthesia techniques and anatomy. Notably, this model provides vivid sonoanatomies of the ribs, intercostal muscle layers, and most importantly, the sliding pleura sign, for performing intercostal nerve blocks. As the sonoanatomy of the porcine lumbar spine is similar to that of humans, this model can be used for practicing block techniques, including facet joint injection, medial branch block, and psoas compartment block. Blocks in the thoracic region, such as paravertebral blocks, have a risk of pneumothorax, and a living porcine model with breathing patterns can provide an opportunity for practice to avoid such complications. Nevertheless, the use of live pigs for nerve blocks involves general anesthesia requiring veterinarian assistance and equipment. In addition, training can only occur while the pigs are anesthetized, which limits training time and space. Regardless of the extra effort, a live porcine model provides a clinical and anatomical environment similar to that of real patients as a desirable option for training various ultrasound-guided regional block techniques.
This study has some limitations. First, we surveyed a relatively small sample of residents from a single institution. Second, the residents had no opportunity to perform the TAP block on actual patients, and so we could not directly assess the outcome of nerve block training. Finally, the efficacy of the training performed in this study was not compared with that of other simulation-based training models.