Scottish Intensive Care Society

ICM Induction programme ©

Nutrition in ICU

1 Nutritional challenges in the critically ill

Critically ill patients present nutritional challenges as a consequence of their pre-existing ill-health, their critical illness and their management in Intensive Care.

Pre-existing ill-health

Causes of malnutrition in ICU patients:

• poor oral intake due to the acute illness before admission
• alcohol and drug abuse
• inadequate social circumstances
• malignancy
• inflammatory bowel disease
• chronic respiratory or cardiac failure

Many of these conditions result in immuno-suppression.

Critical illness

Critical illness places an increased metabolic burden on the human body.

Sepsis and the Systemic Inflammatory Response Syndrome (SIRS) lead to:

• an increase in basal metabolic rate
• increased oxygen consumption and carbon dioxide production
• an overall increase in resting energy expenditure

After glycogen stores are used up, protein breakdown, initially from skeletal muscle, and after several days from the viscera, leads to loss of lean body mass. This occurs even with full nutritional provision. The reduction of muscle fibre cross-sectional area is 3% to 4% per day.

Gastroparesis, and intestinal oedema and ileus are very common in all types of critical illness, especially after emergency gastro-intestinal surgery, and result in reduced absorption of feed. Large nutritional deficits build up quickly.

Management of critical illness

• Acid-suppressing drugs result in a rise in intra-gastric pH, which contributes to altered gut flora; these bacteria may rapidly become pathogenic.
• Antibiotics and other drugs may result in diarrhoea which can result in malabsorption.
• Difficulties with access can lead to long gaps in feeding.
• Opioids, immobility and lack of a normal diet cause constipation, which may contribute to failure to wean from ventilation.
• Opioids also reduce gastric motility, reducing absorption of enteral feed.

Adequacy of nutritional support must be one of the daily considerations in ICU care.

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