Gastrointestinal (GI) System


Constipation is broadly defined as an unsatisfactory defecation characterized by infrequent stools, difficult stool passage or both

Constipation is broadly defined as an unsatisfactory defecation characterized by infrequent stools, difficult stool passage or both

  • Constipation is a symptom, not a disease.


Primary or functional constipation (M/C)

Risk factors for functional constipation include advanced age, low fiber diet, low socioeconomic status, immobility, abdominal or pelvic surgery and polypharmacy.
  • Slow transit constipation: Delayed passage of fecal contents through the colon and is more common in women.
    • Opioid-induced constipation is a common cause of slow transit constipations
  • Outlet dysfunction: Impaired rectal evacuation from inadequate rectal propulsive forces or increased resistance to evacuation or both
  • Dyssynergic defecation: Form of outlet dysfunction, and is defined by inadequate relaxation or paradoxical contraction of anorectal muscles while attempting to pass a bowel movement.
    • Risk factors: Anxiety, psychological stress, and chronicity of constipation
Normal anatomy and physiology of the pelvic floor in the sagittal plane at rest, during normal defecation and during dyssynergic defecation
Normal anatomy and physiology of the pelvic floor in the sagittal plane at rest, during normal defecation and during dyssynergic defecation: The resting profile shows the arrangement of the internal and external anal sphincters (IAS and EAS, respectively), as well as the puborectalis muscle. During defecation, the anal sphincters and the puborectalis relax and the abdominal and rectal contraction generate a push force to empty the rectum of stool. In patients with dyssynergia, the push effort or anal relaxation may be impaired, or the anal sphincters and puborectalis may not relax during attempted defecation, leading to incoordination (ie, dyssynergia) and stool retention. | Rao SS. Advances in diagnostic assessment of fecal incontinence and dyssynergic defecation. Clin Gastroenterol Hepatol. 2010;8:910–9.

Secondary constipation

When evaluating patients with constipation, secondary causes should be considered first and after secondary causes of constipation have been ruled out, the patient should be evaluated for primary or functional constipation.
  • Metabolic disturbances: Diabetes, hypothyroidism, hypercalcemia, panhypopituitarism and pheochromocytoma
  • Neurological disorders: Parkinson’s disease, multiple sclerosis, dementia, Hirschprung’s disease and spinal cord lesions
  • Myopathic diseases: Scleroderma, myotonic dystrophy and amyloidosis
  • Structural disorder: Colon cancer, strictures and a large rectocele
  • Medications:
    • Analgesics: Opioids and NSAIDs
    • Anticholinergics: Antidepressants and antipsychotics
    • Anti-hypertensives: CCBs & diuretics
    • Iron supplementation
The Calgary Guide |


Rome IV Criteria for functional constipation

At least 2 of the 6 criteria required. In addition to the above, the following three criteria should also be met to diagnose functional constipation: (1) Loose stools should rarely be present without the use of laxatives (2) Insufficient criteria for IBS (3) Present for at least 3 months during a period of 6 months.
  • < 3 bowel movement per week
  • Straining during > 25% of the time
  • Lumpy or hard stools > 25% of the time
  • Sensation of anorectal obstruction > 25% of the time
  • Sensation of incomplete evacuation > 25% of the time
  • Manual maneuvers required to aid defecation > 25% of the time
Diagnostic algorithm for constipation
Diagnostic algorithm for constipation | Jani, B., & Marsicano, E. (2018). Constipation: Evaluation and Management. Missouri medicine, 115(3), 236–240.

Anorectal manometry:

Measures the rectal and anal pressure at rest and during attempted defecation. It is also able to assess rectal sensation, recto-anal reflexes and rectal compliance. During the maneuver, when a patient mimics defecation, or tries to bear down, there should be a rise in the rectal pressure along with relaxation of the internal and external anal sphincters.
  • Inability to relax the external anal sphincter and/or the puborectalis, along with inability to expel a 50cc water-filled balloon within one minute, is diagnostic of dyssynergic defecation
High resolution anorectal manometry
High resolution anorectal manometry: A catheter with multiple pressure transducers is introduced through the anal canal and into the rectum and provides real-time pressure measurements at the external anal sphincter, internal anal sphincter and within the rectum. The patient is asked to try to expel the catheter by increasing intraabdominal pressure and relaxing the external sphincter. as shown in this example, two attempts to expel the catheter (from 3 to 11 seconds and 34 to 42 seconds) resulted in appropriately increased intraabdominal pressure but dyssynergic contraction of the external sphincter and no relaxation of the internal sphincter. The color pressure scale is shown on the right from low pressure (blue) to high pressure (red). | Jani, B., & Marsicano, E. (2018). Constipation: Evaluation and Management. Missouri medicine, 115(3), 236–240.

Balloon expulsion test:

Can be done during anorectal manometry or as an independent test. It involves filling a balloon with 50cc of saline and asking the patient to expel it. Patients with normal defecation are able to expel the balloon within 1 minute. If the patient has difficulty expelling the balloon in this time frame, dyssynergic defecation should be suspected.
Balloon expulsion test
Balloon expulsion test | J Neurogastroenterol Motil 2014;20:407~409

Colonic transit study “Sitz Marker Study”:

After excluding outlet dysfunction with anorectal manometry and balloon expulsion, colonic transit should be evaluated using radiopaque markers (sitzmark study) or a wireless motility capsule. A sitzmark study can measure colonic transit time by administering 24 radiopaque markers and obtaining a plain abdominal x-ray on day 5.
  • Prolonged colonic transit time: > 20% markers or > 5 markers remaining in the colon on day 5

Wireless motility capsule:

It is a wireless capsule which measures pH, temperature and pressure throughout the entirety of the gastrointestinal tract, therefore providing gastric, small bowel and colonic transit time without radiation exposure.
Investigation of Colonic and Whole-Gut Transit With Wireless Motility Capsule and Radiopaque Markers in Constipation
This shows examples of the SmartPill and ROMs recording in a (A) healthy and (B) constipated subject. The healthy subject shows normal GET at 2.5 hours, normal SBTT at 5.3 hours, and normal CTT at 15.5 hours, and 4 ROMs on the day 2 radiograph. The constipated subject shows a delayed GET at 5.8 hours, normal SBTT at 4.3 hours, and delayed CTT at 80.25 hours. The day 2 radiograph shows the SmartPill and 24 ROMs and the day 5 radiograph shows that the SmartPill has been expelled but 10 ROMs remain. | Rao, S. S. C., Kuo, B., McCallum, R. W., Chey, W. D., DiBaise, J. K., Hasler, W. L., Koch, K. L., Lackner, J. M., Miller, C., Saad, R., Semler, J. R., Sitrin, M. D., Wilding, G. E., & Parkman, H. P. (2009). Investigation of Colonic and Whole-Gut Transit With Wireless Motility Capsule and Radiopaque Markers in Constipation. Clinical Gastroenterology and Hepatology, 7(5), 537–544.

Additional tests:

These record the pelvic anatomy of the patient during attempted defecation and are useful for evaluating conditions like rectocele or sigmoidocele, intussusception, rectal prolapse, and megarectum.
  • Defecography
  • Magnetic Resonance Defecography


Lifestyle Modifications:

The initial management of constipation should involve lifestyle modifications, reassurance of their concept of a healthy or “regular” bowel movement, and biofeedback. Identification of patients that need psychological support should be undertaken because constipation may be aggravated by stress or may be a manifestation of emotional disturbance. Patients should be encouraged to set aside a regular time for defecation, to use proper sitting positions, and to monitor their bowel habits by using a diary of the characteristics of their stools to assess and direct treatment interventions.
  • Dietary modifications: High-fiber diet, water intake, and fruits.

Once secondary causes of constipation are excluded, patients should be advised to increase their fiber and fluid intake, engage in regular physical activity and conduct timed toilet training.18

Treatment algorithm for functional constipation
Treatment algorithm for functional constipation: Once secondary constipation has been excluded and functional constipation has been characterized, treatment can be focused on the underlying disorders. | Jani, B., & Marsicano, E. (2018). Constipation: Evaluation and Management. Missouri medicine, 115(3), 236–240.


Most patients with constipation require the use of laxatives at some point in their course.
  • Bulk laxatives (fiber): Psyllium (Metamucil) and methylcellulose (Citrucel)
  • Stimulant laxatives: Senna and bisacodyl (Dulcolax)
  • Emollient stool softeners: Docusate (e.g., Colace)
  • Osmotic agents: Polyethylene glycol (PEG)-based solutions, magnesium citrate–based products, sodium phosphate–based products (e.g., Fleets), and non-absorbable carbohydrates (e.g., sorbitol)

Newer medications:

  • Lubiprostone: Activates chloride channels (like cholera toxin) and increases luminal fluid secretion and has been been shown to decrease stool transit time and improve symptoms of chronic idiopathic constipation
  • Linaclotide (guanylin analog): Stimulates guanylyl cyclase-C receptor to increase chloride secretion (like E. coli enterotoxin), and has been shown in studies to have neuromodulatory benefits in patients with IBS-C as well as decrease stool transit time
  • Plecanatide: Stimulates guanylyl cyclase inhibitor and causes increased chloride and bicarbonate entry into the lumen via the activation of the cystic fibrosis transmembrane conductance regulator (CFTR) ion channel
  • Tegaserod: Serotonin type 4 (5-HT4) receptor partial agonist that is thought to trigger a peristaltic reflex via 5-HT4 activation, which enhances motor activity and normalizes impaired GI motility

Opioid-induced constipation

First-line treatment for opioid-induced constipation typically involves a combination of pharmacological and non-pharmacological interventions such as laxatives and increased dietary fiber. Alternatively, targeted treatment can be used.
  • Peripherally acting μ-opioid receptor antagonists (PAMORAs): Targeted treatment to reverse opioid-induced constipation by selectively blocking opioid actions at peripheral μ-opioid receptors, including those in the enteric nervous system, without affecting analgesia in the CNS
    • Aloxegol, methylnaltrexone, alvimopan and naldemidine

Surgical management:

Surgical options, such as colectomy, should be a last resort for those patients who have failed medical management.

Easier to prevent than to treat.


  • Adequate exercise
  • Fluid intake
  • High-fibre diet

The National Institute of Health and Care Excellence (NICE) guidelines

  • Chronic constipation of unknown cause:
    • ↑ intake of water and fiber (either dietary or as supplements)
    • The routine use of laxatives is discouraged (as having bowel movements may come to be dependent upon their use)
    • Enemas can be used to provide a form of mechanical stimulation.
  • Constipation due to opiates
Chronic constipation
Chronic constipation is a prevalent condition characterized by hard stools, excessive straining, infrequent bowel movements, bloating and abdominal pain. | Chronic constipation. Nat Rev Dis Primers 3, 17096 (2017).

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