The autonomic nervous system . Ed-Westphal Edinger-Westphal nucleus, Sup Saliv superior salivatory nucleus, Inf Saliv inferior salivatory nucleus, Dorsal Motor and Nucl Ambig dorsal motor nucleus of the vagus nerve and nucleus ambiguus. Visceral ganglia refer to ganglia located near or on the respective organs, such as the cardiac, pulmonary, celiac, myenteric, and submucosal plexuses
The celiac plexus receives parasympathetic innervation from the vagus nerve , sympathetic input from three splanchnic nerves [7, 8], and visceral sensation via both the vagus and the splanchnic nerves. In terms of the three splanchnic nerves, the first is the greater splanchnic nerve, which receives inputs from the T5–T10 levels of the sympathetic paravertebral chain (the T5–T10 thoracic ganglia) but may also involve T4 or T11. The second is the lesser splanchnic nerve, which receives inputs from T10–T11 but may also involve T8 and T9. The third is the least splanchnic nerve, which receives inputs from T12 but may also involve T10 and T11; the least splanchnic nerve is occasionally absent [8, 9], with its nerves presumably incorporated into the other splanchnic nerves. The most common pattern is for all three nerves to pass through the diaphragm at a single hiatus, making this a favorable location for blockade in what has been referred to as a splanchnic or retrocrural celiac block. In rare cases, however, the three nerves can go through three separate hiatuses . Visceral sensation, including nociception, is derived from spinal and vagal visceral afferents that pass through the celiac ganglion; while the spinal afferents have traditionally been thought to be responsible for nociception and pass through the splanchnic nerves, some evidence suggests that vagal visceral afferents may also play a role .
The exact organs innervated by the celiac plexus are a matter of some debate but generally include sympathetic, parasympathetic, and visceral sensory innervation of the stomach, liver, gallbladder, bile ducts, pancreas, small intestine, ascending colon, distal esophagus, and possibly kidneys and adrenals [2, 11]. Thus, the celiac plexus is a favorable single target to provide a dense visceral sensory block of the upper abdomen, but a block at this location invariably affects autonomic nerves as well as visceral sensation.
There are several approaches to the celiac plexus, and thus there is often confusion about the rationale and the risks/benefits of each technique. In performing a percutaneous needle-based procedure, the goal is simply to have the needle tip at the location or in a plane contiguous with the celiac plexus or splanchnic nerves. In some situations, an open technique can be performed in conjunction with surgeons performing a laparotomy; this allows for direct application of solution to the nerves under direct visualization. Given the central location of these nerves, multiple needle trajectories have been described.
22.214.171.124 Posterior Percutaneous Retrocrural/Splanchnic Approach
The most common trajectories currently are the posterior approaches . The first posterior approach is commonly referred to as a retrocrural celiac plexus block and is similar in injectate spread to a splanchnic nerve block. The term splanchnic nerve block is often used because it specifies that these are the nerves that are blocked on their way to the celiac plexus. This block, as the name describes, is performed with the final needle position near the anterior border of the T12 or L1 vertebral body and posterior to the diaphragm; it targets the greater, lesser, and least splanchnic nerves as they all come in close proximity. This technique avoids piercing the aorta, but it does require two needles on each side of the vertebral bodies. This is also a potential target for thermal neurolysis, which can be done with radiofrequency ablation. One does not generally attempt chemical neurolysis with these blocks given the potential for nerve root neurolysis.
126.96.36.199 Posterior Percutaneous Antecrural Approach
The antecrural approach is, as the name implies, where the needle’s final position is anterior to the crus of the diaphragm. With this technique, there are several potential locations for the needle to reside in relation to the aorta, generally a distance 10 mm anterior to the anterior border of the vertebral body. The purpose is to be in a plane where the injectate can reach the celiac plexus without diffusing into the aorta. It can lie posterior to it in the retro-aortic space or lateral to it without piercing it. This latter approach, with the needle positioned lateral and adjacent to the aorta, is often described as the transcrural approach. On occasion with this approach, the needle is within the aorta as noted by blood return or contrast injection revealing an aortogram; in this situation, one can proceed with the transaortic approach.
188.8.131.52 Posterior Percutaneous Posterior Transaortic Approach
The transaortic approach is performed with the needle positioned through the aorta at the T12 or L1 vertebral level until the needle is placed through and anterior to the aortic adventitia. This can be accomplished with one needle from the left side and is the preferred choice for chemical neurolysis. This particular approach is done with the provider using aortic pulsations to determine progress through the vessel. Practitioners can feel resonance through the needle, or they can attach low dead-space Luer-locking tubing with a length greater than the recorded blood pressure with conversion from mmHg to cmH2O, and the column of blood can be seen pulsating until needle position is into the anterior aortic wall. At least another 2–4 mm of advancement is required to ensure that the needle does not remain in the intima, media, or adventitia, or any plane between; care must be taken to ensure that the needle is through the aortic wall to avoid the potential for aortic dissection during injection. The use of contrast and plunger pressure monitoring of injection can aid in reducing this complication.
In spite of the seeming danger, puncture of the aorta is actually relatively safe, and overall, major complications from celiac plexus block occur in less than 1% of patients . Nonetheless, aortic dissection is one of the most concerning complications and has been reported to arise from use of the transaortic approach. Kaplan et al. described a fatal case of needle puncture in the anterior aortic intima between the superior mesenteric artery (SMA) and celiac artery causing dissection and vascular thrombosis that resulted in bowel and liver infarction . Additionally, Naveira et al. reported an atheromatous aortic plaque presenting as a loss of resistance that also resulted in aortic dissection . Because of the puncture of the aorta and the proximity of other vascular structures like the SMA and celiac and renal arteries, the transaortic approach is contraindicated in patients receiving anticoagulant medication and in patients with coagulopathy secondary to antiblastic chemotherapy or liver abnormalities, as they are at increased risk for retroperitoneal hemorrhage, a complication which is discussed in the previous chapter [16–18].
184.108.40.206 Posterior Percutaneous Transdiscal Approach
The posterior transdiscal approach involves passage of the needle directly through the T12–L1 or L1–L2 intervertebral disk via fluoroscopic or CT guidance. The needle is inserted 5–7 cm from the midline and directed to reach the paraaortic region at the level of the celiac trunk . By traversing the intervertebral disk, this approach theoretically minimizes hazards of injury to the arteries and spinal cord, and potential damage to the liver, kidney, and pancreas as with other approaches can be avoided [20, 21]. It can also be used when the paravertebral needle path is obstructed by transverse processes or ribs or for improved access to the anterolateral wall of the aorta in patients with abnormal anatomy [16, 18, 19]. Although this procedure offers the possibility of avoiding vascular or organ trauma, it is not routinely used. There is increased risk for disk trauma that could lead to diskitis, herniation, meningeal puncture, and spinal cord puncture; this approach should be avoided in patients with degenerative disk disease in the thoracolumbar spine [16, 18, 19].
220.127.116.11 Anterior Percutaneous Approach
The celiac plexus can be approached from the ventral surface of the abdomen using CT guidance, MRI guidance, or ultrasound guidance. This approach can be more comfortable for patients who cannot lie prone with their pain or because they have a colostomy/ileostomy. In the anterior approach, the patient lies supine. The needle is inserted through the epigastrium at an entry site 1.5 cm below and 1.5 cm to the left of the xiphoid process . The needle is advanced to a depth anterior to the aorta and the diaphragmatic crura between the roots of the celiac trunk and the SMA and most commonly traverses the stomach, liver, or pancreas before reaching the plexus [21, 22]. Although the anterior approach minimizes the risk of injury to the kidney and spinal cord, steps should be taken to prevent other complications . It is essential to avoid major blood vessels, dilated biliary ducts, and portal hilum, and multiple punctures to the liver capsule can increase the risk of bleeding [21, 23]. Vascular structures in the neck of the pancreas must be avoided to prevent unnecessary bleeding . Additionally, there have been reports of gastric perforation, pancreatic fistula, hepatic hematoma, retroperitoneal hematoma, paraplegia, and abscess with this approach [24–26]. While there is concern about contamination and potential infectious seeding, this approach, when done with a styleted and small needle (e.g., Chiba or Quincke), has been reported to be safe .
18.104.22.168 Endoscopic Ultrasound-Guided Approach
An endoscopic ultrasound-guided approach can be performed by endoscopists and generally is well-tolerated by patients. In a prospective randomized comparison of endoscopic ultrasound (EUS) and CT-guided celiac plexus block in 22 patients, the authors concluded that EUS-guided block provided more persistent pain relief than CT-guided block . Advantages include a lack of radiation with EUS as compared to CT and costs. Challenges include visualization of deeper structures as intestinal air can impede sonographic imaging. Gastric perforation and infectious complications appear to be the most common complications associated with this approach. It can be more comfortable for patients and can also be combined with diagnostic endoscopic procedures [28, 29].
22.214.171.124 Summary of Techniques
Based on the approach, the needle may pass near the nerve roots (posterior approaches) and kidney (posterior approaches), near or through the aorta (posterior approaches), through a disk (transdiscal), or through the bowel (endoscopic and anterior approaches). Structures nearby the celiac plexus that may be affected by all the approaches include other autonomic plexuses such as the cardiothoracic, superior hypogastric, and inferior hypogastric plexuses, as well as the artery of Adamkiewicz which supplies the spinal cord. Blockade of these structures can cause additional autonomic symptoms such as hypotension, sexual dysfunction, and bowel/bladder dysfunction.
There are few reports comparing the autonomic side effects of the different approaches to celiac plexus block [18, 21, 28, 29]. The differences are also varied based on volumes and doses of drugs used as well as the drugs themselves.
In addition to local anesthetics, adjuvants such as clonidine, while off-label, are used to prolong the duration of analgesia. Symptoms of bradycardia and hypotension may be augmented with the addition of clonidine. There is insufficient data to compare the different forms of denervation, such as alcohol or phenol neurolysis, or radiofrequency ablation. There are some limited data to suggest that, when comparing the two posterior approaches, hypotension is more common with a retrocrural approach and diarrhea is more common with the anterocrural approach . Celiac plexus blocks are often repeated, and hypotension and diarrhea still appear to be the most common symptoms with repeat procedures .
22.2.3 Adverse Effects
The autonomic side effects from a celiac plexus block are presented in Table 22.1, with the two most common side effects being transient hypotension and diarrhea. The exact incidence of hypotension is unclear: some studies have reported it in 1–3% of patients [32, 33] and others between 30 and 38% [2, 34]. It was such a well-known side effect that, in the 1940s, surgical splanchiectomy of the greater, lesser, and least splanchnic nerves was proposed as a treatment for hypertension . After a celiac plexus block, autonomic symptoms usually subside within 1–3 days . Risk factors include advanced age, arteriosclerosis, and hypovolemia [12, 36]. It should be noted that many patients receive sedation for the procedure and are asked not to eat or drink for several hours prior to the procedure, so many patients have some degree of hypovolemia before the block. Furthermore, patients selected for this procedure often have poor nutritional intake and have a lower threshold for compensation to insult.
Autonomic effects of splanchnic nerve and celiac plexus block
Common side effects
Transient hypotension (1–3 days)
Transient diarrhea (1–3 days)
Uncommon side effects
Increased gastric acid secretion
Bowel dysfunction (most commonly in a setting of spinal artery stroke)
Bladder dysfunction (most commonly in a setting of spinal artery stroke)
Sexual dysfunction (most commonly in a setting of spinal artery stroke)
Side effects observed in animal studies
Temperature dysregulation (heat intolerance)
Altered glucose uptake
Pancreatic polypeptide release
Two major mechanisms have been proposed for hypotension. The first is inhibition of splanchnic vasoconstriction, which lowers blood pressure through pooling of blood in the visceral circulation . Visceral vasoconstriction is a noradrenergically mediated and unopposed function of the sympathetic nervous system. While parasympathetic nerves cause vasodilation of the skin and mucosa of the face, the parasympathetic nervous system has no effect on the visceral vasculature . Thus, blockade of the visceral autonomic system at the celiac ganglia inhibits vasoconstriction. In support of this mechanism, norepinephrine concentrations in all splanchnic-innervated organs are decreased after splanchnic nerve blocks , and in a histologic study in rats, most sympathetic nerves are not visible on mesenteric arteries and veins 2 weeks after surgical celiac ganglionectomy . The second proposed mechanism is cephalad spread of the injectate, presumably involving blockade of the cardiac sympathetic nerves. In a study where contrast was injected prior to injection of bupivacaine or alcohol, cephalad spread extended to the T8–T10 levels in six of seven cases and up to T4 in one case . None of these patients had hypotension.
The treatment and prevention of hypotension are done with liberal intravenous fluid administration, given the relative hypovolemia from fasting prior to sedation. Typically, patients are instructed to be nil per os (NPO) after midnight prior to their procedure. Further consideration should be given according to the American Society of Anesthesiology Preoperative Fasting Guidelines  which does allow patients to have clear fluids up to 2 h prior to the administration of anesthetic or sedating agents. The concern is that patients may not abide correctly (e.g., cream in the coffee), thus resulting in cancelation of procedures. In patients who are able to drink, with proper education, this allowance can mitigate the risk of post-procedural hypotension. Other preventative strategies that have previously been employed include recommending 12 h of bed rest after the procedure  or admitting patients for blood pressure monitoring until they are normotensive (usually overnight) .