CONSTIPATION / FECAL IMPACTION

<3 BM/week or hard/straining stools — extremely common inpatient due to opioids, immobility, dehydration; fecal impaction can cause overflow diarrhea, delirium, and urinary retention

SYMPTOMS / ASSOCIATED SX

• Infrequent or hard stools; straining; incomplete evacuation; bloating, crampy abdominal pain

• Fecal impaction: firm stool in rectal vault on exam; paradoxical diarrhea (liquid stool around impaction)

• Nausea, decreased appetite (autonomic response to distention)

• Delirium, urinary retention in elderly (autonomic effects of fecal impaction)

• Opioid-induced constipation (OIC): extremely common; begin bowel regimen at opioid initiation

DENIES

• New constipation with weight loss/rectal bleeding (colorectal malignancy — urgent colonoscopy)

• Hypothyroid symptoms (TSH elevated — constipation common presentation)

• Complete obstipation + dilated colon on XR (Ogilvie's, LBO)

• AMS/abdominal distension + no bowel sounds (ileus)

SOCIAL HISTORY

• Dietary fiber intake; fluid intake; activity level; baseline bowel habits; laxative use history

• Opioid, anticholinergic, calcium channel blocker, iron supplement use

MAIN ETIOLOGY

• Medications (most common inpatient): opioids, anticholinergics, calcium channel blockers, iron supplements, antidepressants, aluminum/calcium-based antacids

• Immobility and dehydration (universal in hospitalized patients)

• Structural: colorectal malignancy, sigmoid volvulus, stricture, anorectal dysfunction

• Systemic: hypothyroidism, hypercalcemia, hypokalemia, Parkinson's, DM autonomic neuropathy

MOST COMMON DDX

• Fecal impaction (rectal exam — hard stool in rectal vault)

• LBO (CT abdomen — dilated colon, transition point; no gas beyond obstruction)

• Ileus (distended bowel, no bowel sounds, post-operative or metabolic)

• Ogilvie's syndrome (acute colonic pseudo-obstruction; severe dilation without mechanical obstruction)

• Volvulus (sigmoid or cecal; abdominal XR + CT)

• Colorectal cancer (new constipation + rectal bleeding + weight loss + age >45 → colonoscopy)

DATA

• Rectal exam (mandatory if impaction suspected — clinical/bedside diagnosis)

• Abdominal XR (stool burden, free air, dilation, obstruction)

• BMP (K, Ca — metabolic causes); TSH (hypothyroidism)

• CT abdomen/pelvis (if obstruction suspected or new unexplained constipation)

• Colonoscopy for new constipation >45 years with no recent scope

HOME MEDS

• Opioids — reduce dose; schedule bowel regimen at opioid initiation; methylnaltrexone for refractory OIC

• Anticholinergics — hold/switch if contributing

• Calcium channel blockers, iron supplements — continue with adequate bowel regimen

PLAN

• Step 1 — Fecal impaction (treat BEFORE laxatives if present):

  • Manual disimpaction (digital if low; warm water enema for higher)

  • PEG (MiraLAX) 17 g PO in 8 oz water daily–BID for residual stool

  • Bisacodyl suppository 10 mg rectally; or phosphate enema

• Step 2 — Bowel regimen for prevention and treatment:

  • PEG (MiraLAX) 17 g PO daily (most evidence; well-tolerated; first-line)

  • Senna 2 tablets PO BID (stimulant; preferred for OIC)

  • Combination PEG + senna (often used together for opioid-induced constipation)

  • Docusate (Colace) 100 mg PO BID (stool softener; minimal evidence alone — inadequate as monotherapy)

  • Lactulose 15–30 mL PO BID–TID (osmotic; effective but flatulence/cramping common)

  • Bisacodyl 10 mg PO/PR (stimulant; for acute relief)

• OIC prophylaxis — START AT OPIOID INITIATION:

  • Senna 2 tablets PO BID ± PEG 17 g daily — dose up as opioid increases

  • Methylnaltrexone (Relistor) 0.15 mg/kg SC q other day OR naloxegol 25 mg PO daily — for refractory OIC (peripheral opioid antagonists; do not reverse analgesia)

• Increase hydration (≥2 L/day), mobility, dietary fiber if tolerated

• Ogilvie's syndrome (acute colonic pseudo-obstruction, cecum >12 cm):

  • Neostigmine 2 mg IV slow push (have atropine 0.5–1 mg IV ready for bradycardia); GI consult

  • Colonoscopic decompression if refractory; surgery if perforation imminent

• DISCHARGE:

  • Document bowel regimen on ALL patients discharged on opioids

  • PEG ± senna at home; reassess at PCP follow-up

  • Colonoscopy referral if new constipation ≥45 years without recent scope

RED FLAGS

• Obstipation + dilated cecum >12 cm on XR → perforation risk; surgery consult; neostigmine

• Absent bowel sounds + abdominal rigidity + fever → peritonitis/perforation; emergent surgery

• New constipation + rectal bleeding + weight loss ≥45 years → colorectal cancer; urgent colonoscopy

• Fecal impaction + AMS or urinary retention in elderly → disimpact urgently; delirium precipitant

SENIOR IM RESIDENT PEARLS

• Start bowel regimen at opioid initiation — OIC is universal; do not wait for patient to complain

• Docusate is nearly useless as monotherapy (Tarumi et al., JGIM) — use senna or PEG instead

• Paradoxical diarrhea = liquid stool oozing around a fecal impaction — rectal exam is mandatory

• PEG (MiraLAX) is the most evidence-based osmotic laxative — well-tolerated; preferred for chronic constipation and OIC

• Common mistake: prescribing docusate alone without a stimulant or osmotic agent

• Neostigmine: 80–90% effective for Ogilvie's; have atropine at bedside; contraindicated in mechanical obstruction

• Naloxegol and methylnaltrexone: peripheral opioid antagonists — treat OIC without reversing central analgesia