1. Clinical Assessment

A focused history and physical examination are the cornerstones of initial evaluation. They help identify red flags, differentiate mechanical from functional causes, and significantly narrow the differential diagnosis.

A. Detailed History and Symptom Characterization

• Timing & Pattern:
  • Sudden onset suggests an obstructive or acute inflammatory etiology.
  • Insidious onset points toward dysmotility, metabolic, or central causes.
  • Postprandial vomiting can be early (gastroparesis) or delayed (distal obstruction).
• Vomit Characteristics: Bilious (proximal obstruction), feculent (distal obstruction, fistula), or bloody (upper GI bleed) vomit provides crucial clues.
• Associated Symptoms: Abdominal pain (colicky vs. constant), hematemesis, weight loss, fever, and neurologic signs (vertigo, headache) help pinpoint the underlying system.
• Triggers & Alleviators: Note medications (chemotherapy, opioids), metabolic states (uremia), fasting, and response to antiemetics.
• Comorbidities: A history of diabetes (autonomic neuropathy), CNS disease, or prior abdominal surgery is highly relevant.

B. Physical Examination: Hydration & Abdominal Findings

• Vital Signs: Tachycardia, hypotension, and orthostatic changes are key indicators of significant volume depletion.
• Hydration Status: Assess for poor skin turgor, dry mucous membranes, and delayed capillary refill.
• Abdominal Exam:
  • Inspection: Look for distension or surgical scars.
  • Auscultation: Hyperactive or high-pitched bowel sounds suggest obstruction; hypoactive or absent sounds suggest ileus.
  • Percussion: Tympany may indicate gaseous distension from obstruction, while shifting dullness suggests ascites.
  • Palpation: Identify focal tenderness, rebound tenderness, guarding, or a positive Murphy’s sign (cholecystitis).
• Additional Exam: Always inspect for hernias (inguinal, femoral, incisional) and surgical stomas.

2. Laboratory Evaluation

Early laboratory testing is crucial to identify metabolic contributors and correctable derangements that can either mimic or exacerbate gastrointestinal symptoms.

A. Electrolyte Disturbances

• Hypokalemia: Common with repetitive vomiting and can worsen gastric atony.
• Hypochloremic Metabolic Alkalosis: A classic finding in patients with projectile or vigorous vomiting due to loss of gastric acid.
• Hyponatremia: May result from volume depletion or the syndrome of inappropriate antidiuretic hormone (SIADH) in patients with central nervous system causes.

B. Renal Function

• Elevated BUN/Creatinine Ratio: Suggests prerenal azotemia from dehydration. Uremia itself is a potent cause of nausea.
• Chronic Kidney Disease: Can cause gastroparesis through associated autonomic neuropathy.

C. Liver Function

• Cholestatic Pattern: Elevations in alkaline phosphatase (ALP) and gamma-glutamyl transferase (GGT) suggest biliary obstruction or cholangitis.
• Synthetic Function: Low albumin or an elevated INR may indicate portal hypertension and an increased risk of variceal bleeding.

3. Imaging Studies

Radiologic studies are essential to distinguish mechanical obstruction from functional ileus and to detect complications like perforation or ischemia that require urgent intervention.

A. Abdominal X-Ray (Supine & Upright)

• Obstruction: Look for multiple air-fluid levels on the upright film, dilated small bowel loops (>3 cm), and a paucity of gas in the colon.
• Ileus: Characterized by uniform dilation of both the small and large bowel without a clear transition point.
• Perforation: Free air (pneumoperitoneum) under the diaphragm is a surgical emergency.

B. Abdominal CT Scan (with IV contrast if renal function allows)

• Vascular Causes: Can reveal bowel wall thickening, pneumatosis (air in the bowel wall), or mesenteric vessel occlusion.
• Inflammatory Conditions: The gold standard for diagnosing pancreatitis, appendicitis, and diverticulitis.
• Neoplastic Disease: Identifies obstructing masses and associated lymphadenopathy.

4. Classification Systems

Standardized tools help quantify symptom severity, guide risk stratification, and inform the urgency of intervention, particularly in oncology and critical care settings.

A. MASCC Antiemesis Tool (MAT)

The MAT is an eight-item patient-reported scale designed to assess control of chemotherapy-induced nausea and vomiting (CINV). A higher score indicates fewer symptoms. While validated for CINV, its use in general ICU patients is not established.

B. CTCAE Grading (Version 5.0)

The Common Terminology Criteria for Adverse Events (CTCAE) provides clinician-assessed grading for nausea and vomiting, which is widely used across clinical trials and practice.

5. Integration into Management

Evidence-based algorithms that integrate clinical findings, lab results, imaging, and severity grading can streamline triage, guide antiemetic selection, and establish clear thresholds for escalating care.

A. Diagnostic–Therapeutic Algorithm

B. Urgency Stratification & Escalation Triggers

• CTCAE Grade 3–4: Consider total parenteral nutrition (TPN), ICU-level care, and a surgical consultation.
• Persistent Hemodynamic Instability: Requires aggressive fluid resuscitation and potential vasopressor support.
• Refractory CINV: If first-line therapy fails, add an agent from a different class, such as an NK₁ receptor antagonist (e.g., aprepitant).
• Refractory Gastroparesis: In select, severe cases, gastric electrical stimulation may be an option.