Acute Constipation

Name: Acute Constipation
Creator: MedVellum Editorial Team

1. Clinical Overview

Summary

Acute constipation is defined as a sudden change in bowel habit characterized by decreased stool frequency (fewer than 3 bowel movements per week) and/or increased difficulty in defecation, lasting less than three months. [1] While chronic constipation is highly prevalent (10–15% of adults), acute constipation represents a distinct "alarm" presentation that requires immediate evaluation to exclude serious underlying pathology such as colorectal malignancy, mechanical bowel obstruction, or neurological emergencies (e.g., Cauda Equina Syndrome). [2,3]

Management follows a stepwise "Laxative Ladder" approach, prioritizing lifestyle modification and osmotic laxatives (Macrogol) over stimulants. Identifying Opioid-Induced Constipation (OIC) is critical in acute medical admissions, as this condition requires specific prophylactic management. [4]

Key Facts

Definition: less than 3 stools/week, straining, lumpy/hard stools (Bristol 1–2), or sensation of incomplete evacuation.
Red Flag Threshold: New onset constipation in patients > 50 years is a red flag for colorectal cancer until proven otherwise. [5]
Faecal Impaction: A common cause of "overflow diarrhoea" (spurious diarrhoea) in the elderly. Always perform a digital rectal examination (PR).
Opioid Rule: Prophylactic laxatives are omitted in ~40% of patients prescribed strong opioids; they should be prescribed for every patient starting opioids. [6]
Emergency Signs: Absolute constipation (no flatus) + distension + vomiting = Mechanical Bowel Obstruction.

Clinical Pearls

The "Overflow" Pearl: In elderly patients presenting with watery diarrhoea and faecal incontinence, the most common cause is severe constipation with overflow. Anti-diarrhoeals (Loperamide) will worsen the impaction and may precipitate perforation. ALWAYS perform a PR exam to exclude impaction.

The "Opioid" Pearl: Tolerance develops to the analgesic and sedative effects of opioids, but never to the constipating effects. Every patient started on regular opioids must have a prophylactic laxative prescribed (usually a stimulant + osmotic).

The "Laxative Ladder" Pearl: Start low and go slow. Bulk-forming agents (Ispaghula) require 2L of fluid daily; if the patient is dehydrated, these can form a "cement" obstruction. In acute/dehydrated patients, start with Osmotics (Macrogol).

2. Epidemiology & Risk Factors

Incidence & Distribution

Prevalence: Point prevalence of constipation in the general population is 12–19%. [7]
Hospitalization: Up to 50% of hospitalized patients develop constipation due to immobility, opioids, and dietary changes.
Demographics: Bimodal distribution; peaks in young women (functional/slow transit) and the elderly (secondary causes/polypharmacy).

Risk Factors

Category	Factor	Impact
Iatrogenic	Opioids	μ-receptor agonism inhibits propulsive contractions (OIC).
Metabolic	Hypercalcaemia	Reduces smooth muscle excitability and gut motility.
Metabolic	Hypothyroidism	Slows general metabolic rate and colonic transit.
Mechanical	Anal Fissure	Pain leads to stool withholding and a "vicious cycle" of hardening.
Lifestyle	Low Fibre/Fluids	Reduces stool bulk and increases transit time.

3. Pathophysiology

1. Colonic Motility

Normal motility involves haustral churning (mixing) and mass movements (propulsion). Mass movements are high-amplitude propagating contractions (HAPCs) triggered by the gastrocolic reflex after meals.

2. The Defaecation Reflex

Rectal distension stimulates stretch receptors, triggering the Recto-anal Inhibitory Reflex (RAIR), where the internal anal sphincter relaxes. If the setting is appropriate, the external anal sphincter and puborectalis muscle relax, and abdominal pressure increases (Valsalva) to expel stool. [8]

3. Opioid-Induced Constipation (OIC)

Opioids bind to μ-receptors in the myenteric plexus, inhibiting the release of excitatory neurotransmitters (Acetylcholine). This leads to:

Decreased propulsive contractions.
Increased anal sphincter tone.
Decreased fluid secretion into the lumen. [4,9]

4. Clinical Presentation

Symptoms

Infrequent Stools: less than 3 per week.
Stool Consistency: Hard, lumpy, "rabbit droppings" (Bristol 1–2).
Straining: Excessive effort required for evacuation.
Incomplete Evacuation: Persistent feeling of stool remaining.
Manual Manoeuvres: Need to support the perineum or use digital evacuation.

Physical Signs

Abdominal Palpation: Faecal loading may be felt as a "doughy" mass in the Left Iliac Fossa.
Digital Rectal Exam (PR): Mandatory. Assess for:
- Empty Rectum: Suggests slow transit or proximal obstruction.
- Hard Stool: Confirms impaction.
- Soft Stool: Suggests an evacuation disorder (dyssynergia).
- Masses: Ruling out rectal cancer. [10]

5. Investigations

1. Laboratory Assessment

FBC: To rule out anaemia (malignancy).
U&Es: To check for dehydration or electrolyte causes.
Calcium: To exclude hypercalcaemia.
TFTs: To exclude hypothyroidism.

2. Imaging

Abdominal X-ray (AXR): Not routine. Reserved for suspected obstruction or to confirm faecal loading in patients with "spurious diarrhoea." [11]
CT Abdomen/Pelvis: Indicated if red flags (weight loss, mass) are present to rule out malignancy or obstruction.

6. Management: The Acute Algorithm

Management Flowchart (ASCII)

                  [ACUTE CONSTIPATION ASSESSMENT]
                               |
                +--------------v--------------+
                |   RULE OUT RED FLAGS        |
                | (Weight loss, Bleeding, Mass)|
                +--------------+--------------+
                               |
                +--------------v--------------+
                |    PERFORM PR EXAMINATION   |
                +--------------+--------------+
                /              |               \
       [IMPACTION]        [NO IMPACTION]       [RED FLAGS]
          |                    |                     |
  +-------v-------+    +-------v-------+     +-------v-------+
  | DISIMPACTION  |    | LIFESTYLE     |     | URGENT 2WW    |
  | 1. High-dose  |    | 1. Fluids/Fib.|     | REFERRAL      |
  |    Macrogol   |    | 2. Osmotic    |     |               |
  | 2. Suppos./   |    |    Laxative   |     | (Colonoscopy) |
  |    Enemas     |    +---------------+     +---------------+
  +---------------+

1. Lifestyle and First-line Medical

Fluids/Fibre: 2L fluid daily and 30g fibre.
Osmotic Laxatives: Macrogol (PEG 3350) is first-line. It retains water in the stool and is superior to lactulose (which causes more bloating). [12]

2. Escalation

Stimulant Laxatives: Senna or Bisacodyl. Used if osmotics are insufficient.
Prokinetics: Prucalopride (5-HT4 agonist) for refractory cases.

3. Management of Impaction

NICE Regimen: Macrogol up to 8 sachets/day for disimpaction.
Rectal: Glycerin suppositories (soften) followed by Phosphate enemas (empty). [13]

4. Single Best Answer (SBA) Questions

Question 1

An 82-year-old female presents with watery diarrhoea and faecal incontinence for 3 days. She has a history of chronic constipation and takes codeine for back pain. Abdominal palpation reveals a doughy mass in the LIF. What is the most appropriate next step?

A) Start Loperamide 2mg
B) Order stool culture for C. difficile
C) Perform a digital rectal examination
D) Prescribe high-dose Prednisolone
E) Arrange urgent colonoscopy
Answer: C. The presentation is classic for spurious (overflow) diarrhoea due to faecal impaction. A PR is mandatory to confirm the diagnosis before starting treatment.

Question 2

A 55-year-old male presents with a 4-week history of new-onset constipation and 6kg unintentional weight loss. He has no previous history of bowel issues. What is the most appropriate management?

A) Start Macrogol 1 sachet daily
B) Advise increasing dietary fibre to 30g/day
C) Refer via the 2-week wait (2WW) colorectal pathway
D) Perform an abdominal X-ray
E) Start a 5-day course of Senna
Answer: C. New-onset constipation in a patient > 50 years associated with weight loss is a red flag for malignancy requiring urgent referral.

Question 3

Which of the following electrolyte abnormalities is a known metabolic cause of acute constipation?

A) Hypocalcaemia
B) Hyperkalaemia
C) Hypercalcaemia
D) Hyponatraemia
E) Hypophosphataemia
Answer: C. Hypercalcaemia reduces the excitability of gastrointestinal smooth muscle, leading to decreased motility.

Question 4

A patient is started on Morphine for cancer-related pain. According to guidelines, what should be prescribed alongside the opioid to prevent constipation?

A) Bulk-forming laxative (e.g., Ispaghula)
B) Prophylactic osmotic and stimulant laxative
C) Loperamide as needed
D) No treatment until constipation develops
E) High-dose vitamin C
Answer: B. Patients starting opioids should be prescribed a combination of an osmotic and a stimulant laxative prophylactically, as tolerance to OIC does not occur.

Question 5

What is the mechanism of action of Prucalopride in the treatment of chronic or refractory constipation?

A) μ-opioid receptor antagonist
B) Guanylate cyclase-C agonist
C) 5-HT4 receptor agonist
D) Dopamine D2 antagonist
E) Chloride channel activator
Answer: C. Prucalopride is a high-affinity 5-HT4 agonist that stimulates colonic mass movements.

Question 6

An abdominal X-ray is performed on an elderly patient with suspected constipation. It shows a "mottled" appearance in the sigmoid colon but no dilated loops of bowel. What does this "mottled" appearance indicate?

A) Small bowel obstruction
B) Colonic volvulus
C) Faecal loading
D) Pneumoperitoneum
E) Toxic megacolon
Answer: C. A mottled appearance on AXR is characteristic of gas trapped within a faecal mass, indicating loading.

Question 7

In the management of faecal impaction, which agent is recommended by NICE as the first-line oral treatment?

A) Senna
B) Lactulose
C) Macrogol (Polyethylene Glycol)
D) Docusate Sodium
E) Liquid Paraffin
Answer: C. Macrogol (high-dose regimen) is the first-line oral treatment for disimpaction.

Question 8

A 30-year-old female presents with constipation, cold intolerance, and weight gain. Which investigation is most likely to identify the cause?

A) Colonoscopy
B) Thyroid Function Tests (TFTs)
C) Serum Calcium
D) Abdominal CT
E) Coeliac Serology
Answer: B. The symptoms (constipation, cold intolerance, weight gain) are classic for hypothyroidism, a common secondary cause of constipation.

Question 9

Why should bulk-forming laxatives (e.g., Ispaghula husk) be avoided in patients with faecal impaction?

A) They cause severe hypokalaemia
B) They can worsen the obstruction by forming a hard mass
C) They interfere with opioid absorption
D) They cause melanosis coli
E) They increase the risk of bowel cancer
Answer: B. In the presence of impaction, adding bulk without resolving the distal blockage can lead to further distension and potential perforation.

Question 10

Which of the following is a "near-fatal" complication of chronic severe constipation, typically involving pressure necrosis of the colonic wall?

A) Haemorrhoids
B) Anal fissure
C) Stercoral perforation
D) Rectal prolapse
E) Diverticulosis
Answer: C. Stercoral perforation occurs when a hard faecolith causes pressure necrosis and subsequent perforation of the colonic wall.

10. Patient Explanation

"Constipation is when your bowel movements become less frequent or harder to pass than usual. It’s very common and often happens when the bowel slows down. Think of it like a conveyor belt that isn't moving fast enough—the longer the waste sits there, the harder and drier it becomes.

For most people, we can get things moving again by drinking more water, eating more fibre (like fruit and oats), and staying active. We also recommend using a small footstool to raise your knees when you’re on the toilet, which helps the bowel straighten out. If these don't work, we use 'osmotic' medicines like Macrogol, which act like a sponge to pull water back into the bowel and soften the stool. If you ever notice blood, lose weight without trying, or have severe tummy pain where you can't even pass wind, you must see a doctor immediately."

11. References

Aziz I, et al. Managing constipation in adults. BMJ. 2015. [PMID: 25573413]
NICE CKS. Constipation. National Institute for Health and Care Excellence. 2021.
Ford AC, et al. American Gastroenterological Association medical position statement on constipation. Gastroenterology. 2013. [PMID: 23261064]
Camilleri M, et al. Opioid-induced constipation: challenges and therapeutic opportunities. Nat Rev Gastroenterol Hepatol. 2014. [PMID: 25048123]
NICE NG12. Suspected cancer: recognition and referral. National Institute for Health and Care Excellence. 2015.
Larkin PJ, et al. The management of constipation in palliative care: clinical practice recommendations. Palliat Med. 2008. [PMID: 18715971]
Suares NC, et al. Prevalence of, and risk factors for, chronic idiopathic constipation in the community: systematic review and meta-analysis. Am J Gastroenterol. 2011. [PMID: 21606976]
Heitmann PT, et al. Pathophysiology of constipation. J Gastroenterol Hepatol. 2021. [PMID: 33507613]
Farmer AD, et al. Opioid-induced gastrointestinal dysfunction: from pathophysiology to clinical practice. Neurogastroenterol Motil. 2019. [PMID: 30456817]
Trowbridge RL, et al. Does this patient have acute constipation? JAMA. 2003.
Rao SS, et al. American Gastroenterological Association technical review on constipation. Gastroenterology. 2013. [PMID: 23261065]
Lee-Robichaud H, et al. Lactulose versus Polyethylene Glycol for Chronic Constipation. Cochrane Database Syst Rev. 2010. [PMID: 20614462]
NICE. Constipation in adults: management. NICE Guideline. 2010.

Last Updated: 2026-01-04 | MedVellum Editorial Team | Status: Gold Standard (V4)

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