What are the causes of postoperative abdominal distension?

Causes of Postoperative Abdominal Distension

Postoperative abdominal distension results primarily from postoperative ileus (POI), which is a temporary inhibition of gastrointestinal motility due to non-mechanical causes that prevents sufficient oral intake. 1

Primary Pathophysiological Mechanisms

The development of postoperative distension involves three main pathways that work simultaneously 2:

Neurogenic Mechanisms

• Acute phase: Spinal and supraspinal adrenergic and non-adrenergic pathways become activated immediately after surgery, disrupting sympathetic/parasympathetic balance to the GI tract 3, 2
• This autonomic dysfunction occurs both primarily from surgical manipulation and secondarily as part of the surgical stress response 4

Inflammatory Mechanisms

• Prolonged phase: An enteric molecular inflammatory response develops in the intestinal segments manipulated during surgery 2
• Recruitment of leukocytes into the muscularis layer impairs local neuromuscular function 2
• Cytokine release associated with the surgical stress response contributes significantly 5
• This inflammation activates neurogenic inhibitory pathways that suppress motility throughout the entire gastrointestinal tract 2

Pharmacological Mechanisms

• Opioid analgesics are the most significant pharmacological contributor, causing dose-dependent reduction in propulsive GI motility 6, 3, 2
• Opioids can induce hyperalgesia at high doses and exacerbate ileus, particularly problematic in patients with pre-existing intestinal overdistension 6
• Certain antiemetic medications and inhaled anesthetics also contribute 5

Secondary Contributing Factors

Fluid Management Issues

• Fluid overload causes splanchnic edema, increased abdominal pressure, ascites, and potentially abdominal compartment syndrome 6
• Excess fluid decreases mesenteric blood flow and causes ileus with delayed recovery of GI function 6
• Hyperchloremic acidosis from excessive 0.9% saline reduces gastric blood flow and impairs gastric motility 6
• Even fluid deficit of as little as 2.5 L can cause adverse effects 6

Gastric Distention from Anesthetic Management

• Mask ventilation during induction significantly increases intragastric pressure, especially with excessive ventilation pressures or cricoid pressure application 7
• This is particularly problematic in emergency surgery with full stomach or bowel obstruction where gastric distention is already present 7

Gastrointestinal Smooth Muscle Dysfunction

• Patients may develop gastroparesis, intestinal dysmotility, and constipation postoperatively 6
• Pain medications exacerbate these conditions 6
• GI dysfunction impairs breathing when abdominal distention and increased intra-abdominal pressure hamper diaphragmatic excursion 6

High-Risk Clinical Scenarios

Bariatric Surgery Patients

• Internal hernia after LRYGB presents with abdominal distension (60% of cases), pain, nausea, and vomiting 6
• Small bowel obstruction in post-RYGB pregnant patients presents with symptoms commonly found in normal pregnancy, leading to delayed diagnosis 6

Emergency Abdominal Surgery

• Emergency procedures create a higher inflammatory background compared to elective surgery 6
• Patients with bowel obstruction have pre-existing intestinal overdistension that makes recovery of intestinal motility more difficult 6

Critical Preventive Considerations

To minimize postoperative distension risk 6, 5:

• Minimize opioid use through multimodal analgesia with thoracic epidural anesthesia using local anesthetics 6, 5
• Maintain near-zero fluid balance to avoid splanchnic edema 6
• Insert nasogastric tube for gastric decompression in high-risk patients (bowel obstruction, gastroparesis) before induction 6, 7
• Use gentle mask ventilation with pressures <15 cm H₂O to avoid gastric inflation 7
• Implement bowel regimens preoperatively and postoperatively to prevent constipation 6
• Consider prokinetic GI medications in selected patients with known dysmotility 6