Differential retrograde epidural block has been advocated as a diagnostic tool to distinguish visceral and non-visceral sources of pain and, by extension, the associated nausea and vomiting. To this date, a few reports with small patient cohorts have argued in the favor of retrograde differential epidural block as a predictor of future chronic abdominal pain treatment response [12–15]. This technique involves placing an epidural catheter with subsequent injection of saline (placebo) twice followed by incremental doses of local anesthetic. The diagnostic value of this procedure relies on the differential sensitivity of different nerve fibers of varying size and myelination. Sympathetic fibers and visceral afferent nerves (C fibers) are relatively more sensitive to local anesthetic blockade compared to large sensory or motor fibers (A δ fibers) by a tenfold margin [15]. It must be recognized that the retrograde differential nerve block has not been validated. Drawbacks of this method include difficulties in isolating subgroups of nerve fibers in the desired size range using a single local anesthetic, the long time interval needed to complete the procedure (frequently 2–3 h), and the neuro-axial placement of the catheter [3, 15].

Transversus abdominis plane (TAP) block is a newer diagnostic and therapeutic block that may help differentiate somatosensory pain from that of visceral origin [16]. The TAP block was first described back in 2001, detailing injection of local anesthetic into the transversus abdominal plane situated between the internal oblique and transversus abdominis muscles [17, 18]. The TAP block delivers the analgesia to the entire anterolateral abdominal wall between the costal margin and inguinal ligament [19]. More recent introduction of ultrasound guidance for TAP blockade allows precise installation of local anesthetics around the anterior branches of the thoracolumbar ventral rami blocking most of the somatic nerves of the anterior abdominal wall [20]. Using a posterior approach, ultrasound visualizes the three muscular layers of the lateral abdominal wall in order from superficial to deep including the external oblique, internal oblique, and transverse abdominis muscles (Fig. 5.2). The value of a single TAP block in distinguishing a source of abdominal pain originating from the abdominal wall is still debatable, but initial data are encouraging [16–20]. When it comes to treatment of CAWP using TAP block, a single guided anesthetic injection or even a continuous infusion can be used [17].

Other advanced therapies to treat CAWP and (perhaps) its associated nausea include peripheral nerve blockade, neurolysis, cryoablation, alcohol or phenol injection, radiofrequency ablation, or surgical neurectomy [22–24] (Fig. 5.3). All these modalities have been used to treat abdominal wall pain, nerve entrapment syndromes (ilioinguinal, iliohypogastric, genitofemoral nerves), neuropathic pains, and neuralgia from direct abdominal wall injuries or surgeries [25]. It is important to note that ilioinguinal, iliohypogastric, or genitofemoral neuralgia is difficult to distinguish from true ACNES in the lower abdomen [2]. All peripheral nerve blocks can be used for diagnostic, therapeutic, or even preoperative analgesia. Traditionally, such blocks were conducted using an electrical stimulator or paresthesia guidance. More recently, ultrasound-guided techniques have provided real-time, precise delivery of the block [26]. The approach to abdominal wall pain is summarized in Fig. 5.3. The abdominal wall is innervated by the spinal nerves exiting at T7-T12. Irritation of a nerve root due to disc herniation or degeneration typically produces neurogenic pain in a radicular pattern and presents as unexplained abdominal pain. Similarly, patients with long-standing diabetes mellitus can infrequently experience abdominal neuropathic pain originating from the thoracic nerves [27]. Thoracic nerves (T7-12) are also commonly affected by shingles and herpes simplex producing neuropathic abdominal pain that may be accompanied by nausea and vomiting [28]. Thoracic disc herniation causes myelopathy, sensory deficits, and thoracic radicular pain, but on occasion can present as nausea, vomiting, and abdominal pain [29, 30]. Epidural injection of corticosteroids can be an initial therapeutic step, if surgery is not indicated based on the lack of motor deficits. Thoracic epidural anesthetic and analgesic techniques provide visceral and somatosensory analgesia as well as sympathectomy which promotes intestinal motility and increases visceral blood perfusion [31–34]. When required, a temporary epidural catheter can be placed in the mid thoracic dermatomal regions to deliver local anesthetics and opioids to provide rescue analgesia.

Pediatric chronic abdominal pain syndromes frequently present with associated nausea and vomiting. Peripheral nerve blockade has become an important therapeutic approach in children to control pain and facilitate responses to physical therapy [35]. Ultrasound-guided techniques provide safer approaches to anesthesia delivery with improved success rates [36, 37]. TAP and ilioinguinal/iliohypogastric nerve blocks are commonly used in children suffering from CAWP; the rectus sheath block is used frequently in children with periumbilical abdominal wall pain and also for single incision laparoscopic surgery and umbilical hernia repairs [37–39]. Under ultrasound guidance, local anesthetic is injected in the potential space between the rectus abdominis muscle and its posterior sheath.

Chronic opiate use is a common cause of nausea and vomiting among patients with CAWP, with an incidence of 10–50 % [40]. Affected patients commonly also report associated bloating, abdominal distension, and constipation. Some use the term narcotic bowel syndrome to describe the centrally mediated dysfunction in opioid receptor activity which presents with severe abdominal pain accompanied by distension, nausea, and vomiting [41]. Treatment includes a program of opioid weaning, complemented with treatment membrane stabilizers and neuromodulatory antidepressants to decrease pain and limit depression, anxiety, and withdrawal symptoms [41].

Peripheral nerve stimulation (PNS) is an emerging subcategory of neuromodulation and has been used to treat severe CAWP. Indications for PNS include neuralgias and neuropathic damage of the genitofemoral, ilioinguinal, and iliohypogastric nerves [42]. In the past, surgical electrode implantation was required for PNS. However, newer ultrasound guided percutaneous protocols have been developed for lead placement to avoid operative intervention. PNS with subcutaneous or peripheral field stimulation may be combined with spinal cord stimulation (SCS) for improved long-term analgesia for CAWP [42].

Spinal cord stimulation is mainly intended for cases of refractory neuropathic, chronic truncal pain. Traditional low-frequency SCS also has demonstrated safety and efficacy in treating chronic abdominal pain [31, 32, 43]. Advantages of this therapy include its minimally invasive nature, superior patient control of stimulation, reduced opioid intake, and, consequently, fewer side effects. Despite its frequent use in chronic abdominal pain syndromes, there is little high quality evidence in the clinical literature to support such therapy in these patients. SCS may relieve chronic abdominal pain by several possible mechanisms [33]. Suppression of lumbosacral spinal neuron responses to the noxious colorectal stimuli by SCS is produced by placing the electrical lead either near the lumbar or cervical dorsal columns. Antidromic activation of primary afferent fibers within the dorsal column at high intensities, spinal gating mechanisms, and suppression of sympathetic tone also might play roles in controlling chronic abdominal pain from both visceral and somatic sites [33, 34].