Evaluation of Ultrasound-Guided Erector Spinae Plane Block for Postoperative Analgesia in Adult Patients Undergoing Major Abdominal Surgery: A Prospective Randomized Controlled Clinical Trial

Introduction:Thoracic epidural analgesia is still considered the gold standard for postoperative analgesia in abdominal surgery; however, concerns regarding side effects such as hypotension and motor blockade, as well as the risk of major complications such as epidural hematoma and abscess, have led some to question its role. Abdominal wall blocks such as the transversus abdominis plane (TAP) block have been proposed as alternatives; nevertheless they have their own limitations: dermatomal coverage is limited, catheter techniques are cumbersome to perform given the proximity to the surgical field, and a recent meta-analysis found the TAP block to be marginally effective in this context. The erector spinae plane (ESP) block is a novel paraspinal plane block first described for thoracic analgesia when performed at the T5 level, but more recently has also been shown to be effective in providing extensive somatic and visceral abdominal analgesia when performed at the T7-9 level.

Morphine administration is the cornerstone of pain therapy, but acute tolerance after opioid exposure has been described as early as the immediate postoperative period.Enhanced recovery after surgery, which involves implementation of evidence-based multimodal procedure- specific perioperative care pathways, has been shown to improve postoperative outcome and reduce length of hospital stay. One of the major elements of a successful program for enhanced recovery after surgery is the provision of optimal postoperative analgesia to facilitate ambulation and rehabilitation therapy.

An ideal multimodal analgesic technique would include local/regional analgesic techniques (i.e., neuraxial blocks [epidural and paravertebral analgesia], field blocks [e.g., transversus abdominis plane blocks and rectus sheath block], and surgical site infiltration) combined with acetaminophen and either a nonsteroidal antiinflammatory drug or a cyclooxygenase-2 selective inhibitor and also analgesic adjuncts such as single intraoperative dose dexamethasone.

The origin of pain from abdominal surgery is multifactorial, including a parietal (or somatic) component originating from the surgical incision and a visceral component originating from the peritoneum and the manipulation of the intra-abdominal structures. The somatic innervation of the anterior abdominal wall arises from the thoracolumbar spinal nerves (i.e., T6-L1).A recent cadaveric study assessing the course of anterior abdominal wall nerves found that there is extensive branching and communications between the abdominal nerves.The communications occur at several sites, including the intercostal plexus, anterolateral large branch communication, the transversus abdominis plane plexus that lies between the internal oblique and the transversus abdominis muscles (T9-L1 segmental nerves adjacent to the deep circumflex iliac artery), and the rectus sheath plexus that comprises all the segmental nerves (i.e., T9-L1) adjacent to the deep inferior epigastric artery. In most cases, these nerves also pierce the posterior surface of the rectus abdominis muscle.The muscular and cutaneous branches of these segmental nerves enter the muscle and finally terminate in the skin. The skin above the umbilicus is supplied by the cutaneous nerves derived from T6 to T9, the area around the umbilicus is innervated by T10, and the skin below the umbilicus is derived from T11, T12, and L1.

It is now evident that the peritoneum is a metabolically active organ and responds to surgical insult by manifesting a local and systemic immunologic and inflammatory response.The peritoneum consists of "silent nociceptors" that are activated by surgical injury and intraperitoneal inflammation and contribute to visceral pain. The neuro-immuno-humoral pain pathways involved in abdominal surgery include somatic and autonomic nerves such as the afferent fibers of the abdominal vagus nerve. Parasympathetic activation has been shown to influence perioperative outcome, as reduced vagal tone augments inflammation and increases gastrointestinal dysfunction.