Constipation in critically ill adults

Table 4 Enterally-administered laxatives used in management of constipation in the intensive care unit

Parameter	Osmotic laxatives		Stimulant laxatives	Stool softeners	Bulk-forming laxatives
	Saline	Non-saline
Examples	Milk of magnesia; magnesium citrate; sodium phosphate	Lactulose; macrogol/PEG	Senna; bisacodyl	Docusate	Psyllium; methylcellulose; polycarbophil
Mecha-nism of action	Increase intestinal osmotic pressure and water retention; promotes intestinal motility by stimulating cholecysto-kinin secretion	Poorly absorbed by the gut and act as hyperosmolar agents	Increase intestinal motility, water and electrolyte secretions; stimulates peristalsis	Act as a surfactant which emulsifies stool with fat and water	Increase stool bulk and frequency
Onset	0.5-6 hours (rapid)	Lactulose: 24-72 hours; PEG: 24-96 hours	6-12 hours	24-72 hours (slow)	12-72 hours (slow)
Clinical use	Rescue treatment for acute constipation. May cause electrolyte disturbances; caution in renal or cardiac dysfunction	Common use in ICU. Lactulose may result in shorter ICU length of stay; PEG may be more effective in opioid-induced constipation and has lower risk of acute intestinal pseudo-obstruction	Common use in ICU. Often combined with osmotic laxatives	Prophylactic use only. Often adjunctive, limited efficacy when used alone	Rarely used in ICU. Requires adequate hydration. Contraindicated in presence of bowel obstruction, ileus or megacolon

PEG: Poly-ethylene glycol; ICU: Intensive care unit.