Diarrhea is the passage of loose, watery stools, typically in increased frequency and volume relative to a patient’s normal pattern. It can be acute (lasting <14 days), persistent (14–30 days), or chronic (>30 days), and may range from mild to life-threatening. It often presents with abdominal cramps, urgency, tenesmus, and may be associated with systemic signs such as fever or dehydration.

Pathophysiology and Mechanisms

The underlying pathophysiologic processes that contribute to diarrhea include:

• Secretory diarrhea: Excessive secretion of electrolytes and water (e.g., cholera, carcinoid syndrome).

• Osmotic diarrhea: Osmotically active particles draw water into the bowel (e.g., lactose intolerance, laxative abuse).

• Exudative/inflammatory diarrhea: Mucosal damage leads to mucus, pus, and blood in stool (e.g., ulcerative colitis, C. difficile).

• Malabsorptive diarrhea: Impaired absorption of nutrients and water (e.g., celiac disease, post-surgical states).

• Motility disorders: Accelerated transit prevents absorption (e.g., irritable bowel syndrome).

Emergency diagnostic and Therapeutic considerations

1. Immediate Stabilization

If signs of shock are present:

• Lay the patient supine and elevate legs 20 degrees.

• Insert IV access; begin fluid resuscitation (normal saline or Ringer's lactate).

• Monitor for:

  • Tachycardia, hypotension, cool clammy skin

  • Electrolyte imbalances (K⁺, Na⁺, HCO₃⁻)

  • Signs of sepsis or toxic megacolon

2. Assessment and Monitoring

• Perform full abdominal and systemic examination.

• Evaluate stool frequency, character (bloody, mucoid, foul-smelling), and volume.

• Monitor vital signs, hydration status, and mental status.

• Order:

  • Stool analysis (WBC, RBC, ova, and parasites, C. difficile toxin)

  • CBC, urea/electrolytes, blood cultures

  • Imaging if obstruction or ischemia is suspected

Medical causes of diarrhea

Special populations and situational considerations

Pediatrics

• Commonly caused by viral gastroenteritis.

• Rapid fluid loss may cause severe dehydration or hypovolemic shock.

• Assess for malabsorption, milk protein allergy, or CF in chronic cases.

Geriatrics

• New-onset bloody diarrhea: rule out ischemic colitis.

• Dehydration may present subtly (falls, confusion).

• Polypharmacy (e.g., laxatives, antibiotics) is a common cause.

Surgical and cancer patients

• Post-gastrectomy diarrhea (dumping syndrome).

• Radiation enteritis after abdominal/pelvic therapy.

Clinical management strategies

immediate interventions

• Rehydration: Oral rehydration salts (ORS) for mild/moderate cases; IV fluids if severe.

• Empirical antimicrobials only in suspected bacterial or protozoal causes.

• Antimotility agents (e.g., loperamide) only if no fever or bloody stool.

Monitoring and support

• Electrolyte replacement: especially K⁺, Mg²⁺.

• Monitor urine output and serial weight.

• Nutritional support in chronic cases.

Patient education and prognosis

• Advise hydration, rest, and safe food practices.

• Avoid milk, caffeine, and high-fat foods during acute illness.

• Educate on early signs of dehydration or deterioration.

• For IBD or chronic infections, stress importance of follow-up.

References

1. Guerrant RL, Van Gilder T, Steiner TS, et al. Practice guidelines for the management of infectious diarrhea. Clin Infect Dis. 2001;32(3):331–51.

2. Thielman NM, Guerrant RL. Clinical practice. Acute infectious diarrhea. N Engl J Med. 2004;350(1):38–47.

3. Bartlett JG. Clinical practice. Antibiotic-associated diarrhea. N Engl J Med. 2002;346(5):334–9.

4. DuPont HL. Persistent diarrhea: a clinical review. JAMA. 2016;315(24):2712–23.

5. Shen B, et al. Diagnosis and management of Crohn’s disease. Gastroenterol Clin North Am. 2009;38(4):705–17.

6. Parry CM, et al. Typhoid fever. N Engl J Med. 2002;347(22):1770–82.

7. Bhutta ZA. Current concepts in the diagnosis and treatment of acute diarrhea. J Infect. 2000;40(2):104–10.