How to manage a post-operative patient with recurrent vomiting, tachycardia, and metabolic acidosis (low HCO3), as indicated by an arterial blood gas (ABG) report showing acidosis (pH 7.35, HCO3 14.7, pCO2 28.7)?

Management of Post-Operative Day 15 Patient with Vomiting, Tachycardia, and Metabolic Acidosis

This patient requires immediate aggressive fluid resuscitation with balanced crystalloids, urgent surgical evaluation to rule out bowel obstruction or mesenteric ischemia, and multimodal antiemetic therapy—the metabolic acidosis with low bicarbonate (14.7 mEq/L) despite vomiting suggests a mixed disorder or underlying surgical complication rather than simple gastric fluid loss.

Critical Initial Assessment

The ABG shows metabolic acidosis (pH 7.35, HCO3 14.7, pCO2 28.7) with appropriate respiratory compensation, which is paradoxical for a patient with persistent vomiting. Vomiting typically causes metabolic alkalosis from gastric acid loss, not acidosis 1, 2. This discordance indicates either:

• Bowel obstruction with ischemia or perforation (most concerning at POD 15)
• Severe dehydration with lactic acidosis overwhelming any alkalotic tendency
• Starvation ketoacidosis from prolonged poor oral intake 3
• Hyperchloremic acidosis from prior aggressive normal saline resuscitation 4

The tachycardia combined with acidosis suggests inadequate tissue perfusion and possible evolving shock 4, 5.

Immediate Resuscitation (First 1-2 Hours)

Fluid Management

• Administer balanced crystalloids (lactated Ringer's or Plasma-Lyte) rather than normal saline to avoid worsening hyperchloremic acidosis 4, 5, 6
• Begin with 20 mL/kg crystalloid boluses if signs of shock are present 6
• Establish large-bore IV access for rapid fluid administration 6
• Target mean arterial pressure ≥65 mmHg and urine output >0.5 mL/kg/h 4, 5, 6
• Use frequent small-volume crystalloid boluses rather than high-rate continuous infusions to avoid fluid overload and bowel edema 7

Monitoring

• Insert urinary catheter to monitor hourly urine output 6
• Obtain serial lactate measurements every 2-4 hours to assess tissue perfusion and guide resuscitation 4, 5, 6
• Perform serial arterial blood gases every 2-4 hours initially to monitor acid-base status 5, 6
• Implement early hemodynamic monitoring with goal-directed fluid therapy targeting physiologic oxygen delivery 4, 5

Urgent Diagnostic Evaluation

Imaging

• Obtain CT angiography of abdomen/pelvis immediately to assess for bowel obstruction, ischemia, perforation, pneumatosis, portal venous gas, or lack of bowel wall enhancement 7, 6
• Look specifically for closed-loop obstruction or signs suggesting mesenteric ischemia 7

Laboratory Studies

• Check serum lactate, electrolytes (especially potassium), and calculate anion gap 4, 5, 8, 9
• Elevated lactate and D-dimer may assist in diagnosing mesenteric ischemia 6
• Severe hyperkalemia may accompany acidosis in bowel ischemia due to tissue necrosis 4, 5

Supportive Medical Management

Gastrointestinal Decompression

• Insert nasogastric tube for decompression to reduce aspiration risk and improve intestinal perfusion 4, 6

Antiemetic Therapy

• Administer at least 2 antiemetic drugs such as ondansetron 4 mg IV and dexamethasone 4, 10
• Ondansetron 4 mg IV given over 2-5 minutes is effective for postoperative nausea and vomiting 10
• Use caution with dexamethasone if patient is diabetic as it can transiently worsen glycemic control 4

Antibiotic Coverage

• Administer broad-spectrum antibiotics immediately covering gram-negative and anaerobic organisms 4, 7, 6
• Continue antibiotics for at least 4 days in immunocompetent stable patients 4

Bicarbonate Therapy Considerations

• Bicarbonate administration is NOT routinely recommended for metabolic acidosis unless pH <7.15 5, 11, 9
• If pH <7.15, consider sodium bicarbonate 44.6-100 mEq (one to two 50 mL vials) IV, but prioritize treating the underlying cause 5, 11
• Treatment of underlying disease or removal of toxin is more important than normalizing pH 8, 9
• Bicarbonate therapy should be planned stepwise since the degree of response is not precisely predictable 11

Surgical Decision-Making

Indications for Urgent Surgery

• Proceed to prompt laparotomy if signs of peritonitis are present 4, 6
• Do not delay surgical consultation while attempting prolonged conservative management in a patient with persistent symptoms at POD 15 7
• Delayed laparotomy increases mortality by 1% every 3 minutes in patients with hemodynamic instability 5, 6

Surgical Approach

• Consider damage control surgery if patient develops physiologic derangement (pH ≤7.2, lactate ≥5 mmol/L, core temperature ≤34°C) 4, 7, 5
• Resect non-viable bowel and leave abdomen open if patient is physiologically deranged 7
• Plan for second-look laparotomy within 24-48 hours to reassess bowel viability 7
• Use negative pressure wound therapy (NPWT) with fascial traction for temporary abdominal closure if open abdomen required 7

Critical Pitfalls to Avoid

• Do not delay fluid resuscitation while waiting for laboratory results or imaging 6
• Avoid excessive crystalloid overload which can worsen bowel edema and perfusion 7, 6
• Do not rely on clinical examination alone to detect intra-abdominal hypertension/abdominal compartment syndrome—requires bladder pressure measurement 7
• Do not assume vomiting alone explains the acidosis—the metabolic acidosis is paradoxical and demands investigation for surgical complications 1, 2
• Avoid normal saline as it causes hyperchloremic acidosis, decreased renal blood flow, and impaired gastric motility 4, 5

Specific Considerations for Non-Occlusive Mesenteric Ischemia (NOMI)

• Suspect NOMI in any critically ill patient with abdominal pain, distension, or unexplained clinical deterioration 7
• Reduce vasopressor doses if hemodynamically tolerable and consider intra-arterial vasodilator therapy if available 7

Prognosis and Monitoring Endpoints

• Lactate clearance is a key endpoint—persistent or rising lactate despite resuscitation suggests ongoing tissue hypoperfusion or unrecognized pathology 5
• Mortality is significantly higher in hemodynamically unstable patients requiring vasopressors 7
• Early surgical intervention before development of perforation or extensive necrosis is critical for survival 7