Postsurgical gastroparesis

Introduction

Postsurgical gastroparesis (PSG) is a syndrome of objectively delayed gastric emptying without mechanical obstruction following a surgical intervention on the stomach or esophagus. It most commonly results from a surgical disruption of the vagal pathways innervating the stomach and pylorus. The symptoms most commonly associated with the syndrome are early satiety, nausea, vomiting, abdominal pain and bloating occurring early after a foregut operation. Classically, PSG developed as a result of a vagotomy for peptic ulcer disease, however in the current era it is more commonly associated with a variety of foregut and thoracic operations. Interestingly, not all patients who undergo truncal vagotomy without a gastric resection or drainage procedure will develop gastroparesis and likewise, some patients with intact vagus nerves can have PSG. It is estimated that 5–10% of patients who undergo intentional or inadvertent vagotomy, and 50% who undergo resection for gastric outlet obstruction, will develop gastroparesis . Although diabetic and idiopathic gastroparesis are more common, cases of PSG present a unique challenge in diagnosis and management. This chapter will review the epidemiology of PSG, clinical characteristics of the disease, and suggest strategies for diagnosis and management.

Epidemiology of PSG

The true incidence of postsurgical gastroparesis is difficult determine given that the majority of the literature on the subject is limited to retrospective case series. Additionally, much of the research on PSG comes from tertiary academic centers which likely treat only the most severe or complex cases of PSG . Many cases of PSG may be mild with symptoms controlled with dietary modification or medications. One of the best estimates of the incidence of PSG comes from a population-based study of Olmsted County, Minnesota. Over a ten year period the investigators identified 83 confirmed cases of gastroparesis of any cause with an incidence rate of 6.3 cases per 100,000 person-years, of which 7.2% of cases were related to a prior foregut operation . In one series of cases of gastroparesis referred to a tertiary center, PSG was the third most common cause accounting for 13% of all cases, compared with 29% of cases caused by diabetes and 36% which were idiopathic . The exact relation to surgery is further complicated by the fact that many patients operated on for foregut disorder, primarily GERD, may have had preexisting gastroparesis that was either subclinical or missed as the underlying cause of the reflux (so called “overflow reflux”).

Mechanism and pathophysiology

Post-surgical gastroparesis is most commonly the result of entrapment or division of the vagal nerves after a surgical procedure. Historically, vagotomy for peptic ulcer disease was the most common procedure associated with the development of PSG, however this operation is now performed rarely in the era of proton pump inhibitor therapy and treatment of Helicobacter pylori . Gastro/pyloric dysmotility is the end common pathway for PSG. Normal gastric empty relies on the vagal inputs to control gastric relaxation, stimulate contraction of the antrum and induce pyloric relaxation. Truncal vagotomy results in loss of gastric receptive relaxation which sometimes leads to rapid transit of a food bolus from the proximal to distal stomach causing early satiety and bloating. Loss of antral contraction and pyloric relaxation can cause food retention in the stomach . Ironically, the other common physiologic complication following vagotomy is dumping, which is characterized by too rapid emptying of the stomach. Recent studies using endoscopic impedance planimetry to measure the mechanical characteristics of the pylorus in patients with gastroparesis have found that pyloric diameter is inversely correlated with symptom intensity and that decreased pyloric compliance was associated with worse symptoms and quality of life suggesting that vagal inputs to the pylorus are critical in the development of PSG .

One theory regarding patients who experience vagal nerve injury and develop either delayed gastric emptying or dumping is that there are different vagal nerve injury patterns that impacts the innervation to the body and fundus differently than innervation to the antrum and pylorus. When the antrum and pylorus are spared, the loss of gastric reception/storage results in rapid transit of food into the duodenum and the development of dumping syndrome. In contrast, when inputs to both the antrum and body are disrupted the stomach is unable to emptying properly and gastroparesis develops. These findings are the basis for the highly selective vagotomy procedure which aims to reduce parietal cell innervation in the body to reduce acid secretion while maintaining pyloric innervation to preserve normal gastric emptying.

Other rarer causes of PSG are mechanical obstruction due to gastric outlet stricturing, which if chronic enough can result in progressive gastric motility failure or dysmotility caused by extensive perigastric adhesions, the so called “frozen stomach”. or post-gastric disruption of GI motility such as following duodenal resections.

Clinical characteristics and diagnosis

The symptoms of gastroparesis are similar regardless of the etiology . The diagnosis of PSG relies on a high index of suspicion. PSG should be suspected in any patient who has undergone an upper abdominal or thoracic operation and presents with symptoms of early satiety, postprandial bloating, abdominal pain, nausea or vomiting. In one study of 146 patient with objectively confirmed delayed gastric emptying nausea was present in 92%, vomiting in 84%, abdominal bloating in 75%, and early satiety in 60% . In many patients these symptoms are mild or transient however persistent or progressive symptoms warrant further investigation. The first step in the diagnostic evaluation of a patient with suspected gastroparesis is to rule out gastric outlet obstruction either endoscopically or fluoroscopically and to rule out exogenous causes of delayed gastric emptying such as medications or opioid use. Additionally, other diagnoses such as peptic ulcer disease, gastric cancer, bowel obstruction and biliary dysfunction should be considered as there is significant overlap in the symptoms of these diagnoses .

Gastric emptying can be objectively tested using either scintigraphy or a wireless motility capsule . For either of these tests, the patient should discontinue any medication which might impact gastric emptying including opioid medications or prokinetic agents. Scintigraphy is the conventional means of measuring gastric emptying. This test is performed by having the patient ingest a sulfur colloid labeled test meal and obtained serial images at the 0, 1, 2, 3 and 4-hour time points. Gastric retention of the radiotracer is measured; delayed retention is defined as >90% at 1 hour, >60% at 2 hours, and >10% gastric retention at 4 hours. The 4-hour parameter being the most reliable predictor of delayed gastric emptying . Wireless motility capsule testing is a newer technology in which the patient ingests a capsule which measure pH, pressure and temperature. These variables are used to determine the location of the capsule within the GI tract. The findings of this study have been shown to correlate well with traditional scintigraphy. The wireless motility capsule also provides information regarding small bowel and colonic transit times which, if abnormal, may influence the decision to proceed with surgical intervention .

Interpretation of objective gastric emptying studies can be challenging in the post-surgical patient as gastric emptying is likely significantly different from normal controls. Unfortunately, there are no standardized normal values for gastric emptying after gastroesophageal surgery and little information regarding expected values for symptomatic patients. After gastric resection the expected gastric function is a delay in the emptying of solids with rapid emptying of liquids, however the degree to which this occurs likely varies with the extent of gastric resection and method of reconstruction (Bilroth I or II vs Roux-en-y) . Additionally, fundoplication alone can result in accelerated emptying of both solids and liquids compared to normal controls . Inadvetant injury to the vagus nerves during fundoplication can however, lead to a different outcome,

Operations commonly associated with post-surgical gastroparesis