Constipation

1. THE 2-MINUTE PHYSIOLOGY (Rapid Pathophysiology)

• The Core Mechanism: Constipation is a symptom complex, not a specific disease, defined by delayed transit time, hard/infrequent stools, or a feeling of incomplete evacuation. The pathophysiology is broadly divided into functional (motility issues) and organic (mechanical or metabolic breakdown) causes.
• Cellular/Receptor Breakdown: Normal colonic peristalsis relies on the enteric nervous system and smooth muscle coordination. Medications (especially opioid analgesics and anticholinergics) bind to mu-receptors or block muscarinic receptors in the gut, directly paralyzing smooth muscle and prolonging transit time, which allows for excessive water reabsorption.
• Mechanical Failure (Obstipation): Obstipation represents the extreme end of the spectrum, progressing toward complete mechanical bowel obstruction. Massive fecal loading increases intraluminal pressure. If intraluminal pressure surpasses capillary perfusion pressure, the colonic mucosa becomes ischemic, leading to necrosis and catastrophic stercoral perforation.

2. THE BEDSIDE ACTION PLAN (Rapid ER Management)

• Immediate Stabilization: Assess ABCs and evaluate the patient to differentiate a "sick" (toxic/surgical abdomen) versus "well" (simple functional constipation) presentation. Ill-appearing patients require immediate IV access, isotonic fluid resuscitation, and surgical evaluation.
• The Disimpaction Protocol: For distal fecal impaction, enemas and oral laxatives provide little to no relief. You must perform manual digital disimpaction. Because this is a painful procedure, administer appropriate IV analgesia or procedural sedation prior to attempting.
• First-Line Medications (Post-Disimpaction or Mild Cases):
• Suppositories/Enemas: If soft stool is present in the rectal vault but the patient cannot evacuate, administer a Bisacodyl 10 mg suppository. If ineffective within 1 hour, administer a Fleet enema PR.
• Osmotic & Stimulant Laxatives: Polyethylene glycol (PEG) and lactulose are highly effective osmotic agents. Senna or bisacodyl act as stimulants.
• Ineffective Agents: Docusate sodium (a stool softener) is notoriously ineffective as a first-line monotherapy and should not be relied upon.
• Essential Monitoring: In patients with high spinal cord injuries (above T6), strictly monitor blood pressure, as fecal impaction is a primary trigger for life-threatening autonomic dysreflexia.

3. THE DIAGNOSTIC GRID (Differential Diagnosis & Workup)

• "Can't-Miss" Mimics & Organic Causes:
• Surgical Emergencies: Bowel obstruction, volvulus, and stercoral perforation.
• Malignancy: Slowly growing colon cancer or strictures.
• Neurologic/Spinal: Cauda equina syndrome, spinal cord injury, or Parkinson's disease.
• Endocrine/Metabolic Crises: Hypokalemia, hypercalcemia, hypomagnesemia, uremia, and hypothyroidism.
• Pediatric Specific: Hirschsprung's disease, cystic fibrosis, infant botulism, lead intoxication, and cow's milk intolerance.
• Prioritized Diagnostic Workup:
• Well-Appearing Patients: Routine laboratory testing and imaging are generally unnecessary for well-appearing patients with acute constipation and a normal physical exam.
• "Red Flag" Patients: Order a Comprehensive Metabolic Panel (CMP) to evaluate for hypercalcemia, hypokalemia, and uremia. Check a Complete Blood Count (CBC) to screen for occult anemia secondary to malignancy.
• Imaging: CT of the Abdomen and Pelvis with IV contrast is the gold standard if a tumor, stricture, obstruction, or perforation is suspected.

4. THE VISUAL BOARD (ECG / POCUS / Imaging)

• CT Abdomen/Pelvis: Look explicitly for a transition point indicating a mechanical bowel obstruction, colonic wall thickening/stranding indicating ischemic colitis, or free intraperitoneal air indicating a stercoral perforation.
• Plain Radiographs: While an abdominal X-ray can visualize a massive fecal load, it has notoriously low sensitivity and is generally not recommended for the routine ED evaluation of simple constipation.
• ECG: If the constipation is secondary to an underlying electrolyte derangement, scrutinize the ECG. (External EM knowledge: Look for shortened QT intervals in hypercalcemia, or flattened T-waves with prominent U-waves in hypokalemia).

5. THE SCORING MATRIX (Risk Stratification & Guidelines)

• While there is no single universally mandated scoring system for ED constipation, clinical guidelines dictate strict "Red Flag" criteria to stratify patients into functional versus organic (high-risk) etiologies.
• Red Flag Criteria for Organic Constipation:
• Acute onset in an older patient
• Unintentional weight loss
• Rectal bleeding or melena
• Nausea and vomiting
• Fever or severe rectal pain
• Change in stool caliber (e.g., "pencil-thin" stools suggesting an obstructing mass)
• Disposition Cutoffs: Patients with a normal examination and no red flags can be safely discharged with empiric treatment and lifestyle modification advice. Patients with red flags, unstable vital signs, or intractable vomiting require advanced imaging and surgical/GI consultation.

6. THE DANGER ZONE (Pitfalls & Critical Actions)

• Cognitive Trap (The "Diarrhea" Decoy): Assuming that a patient presenting with diarrhea cannot be constipated. Correction: Diarrhea does not rule out fecal impaction. Elderly or debilitated patients frequently present with "overflow diarrhea" (liquid stool leaking around a massive, rock-hard fecal impaction).
• Cognitive Trap (Avoiding the DRE): Failure to perform a Digital Rectal Examination (DRE). Correction: Physician resistance to performing a manual rectal exam and disimpaction does the patient a massive disservice and is a primary cause of misdiagnosis.
• Critical Action (Diagnostic Anchoring): A patient's self-reported "normal" stooling history should never be taken at face value. Furthermore, constipation must always be treated as a diagnosis of exclusion in any patient presenting with acute abdominal pain.
• Critical Action (Oral Meds in Impaction): Never prescribe oral laxatives (like milk of magnesia) to a patient with a distal fecal impaction or suspected obstruction, as this will worsen cramping and risks perforation.

7. MCQ MASTERCLASS (Written Exam Tips)

• Classic Distractor: A question describes an elderly bedbound patient or a patient with a previous CVA who presents with paradoxical diarrhea and lower abdominal pain. The options will include ordering a C. diff toxin assay, prescribing docusate, or inserting a glycerin suppository. Correction: The patient has a denervated rectum and a distal fecal impaction. A glycerin suppository is useless. The correct answer is to perform manual disimpaction with analgesia.
• Buzzwords:
• "Spinal cord injury above T6 + headache, hypertension, diaphoresis + constipation" = Autonomic Dysreflexia triggered by fecal impaction.
• "Change in stool caliber" or "pencil-thin stools" = Organic constipation / Colorectal Carcinoma.
• Pharmacology Trap: If asked for the best first-line oral medical treatment for functional constipation, avoid docusate sodium. Look for osmotic laxatives (Polyethylene glycol) or stimulant laxatives (bisacodyl, senna).

8. THE BOARDROOM SCRIPT (OSCE & Oral Board Tips)

• The Mandatory Exam Phrase: "Because constipation is a diagnosis of exclusion and a common mimic for surgical emergencies, I will perform a comprehensive abdominal examination to look for peritonitis or masses, and I will strictly perform a Digital Rectal Examination (DRE) to evaluate for fecal impaction, occult bleeding, or rectal tumors."
• The Risk Stratification: "I am specifically asking the patient about red flags: any recent weight loss, fever, vomiting, blood in the stool, or a change in stool caliber that would raise my suspicion for an organic cause like colon cancer."
• The Disposition/Management Plan: "The patient is well-appearing, hemodynamically stable, and my rectal exam shows no hard impaction. Therefore, advanced imaging and lab work are unnecessary. I will discharge the patient with an osmotic laxative like polyethylene glycol, counsel them on increasing fluid and fiber intake, and provide strict return precautions for intractable pain, vomiting, or inability to pass gas."