"improving intensive care in Scotland"

Nutrition in ICU

5. Nutritional assessment in ICU

Malnutrition is common in patients admitted to hospital (a recent study estimated that 40% of inpatients are malnourished on admission, and more worryingly, in many cases their nutritional status continues to deteriorate in hospital).

Nutritional assessment is poorly done in many hospitals, and BAPEN, the British Association for Parenteral and Enteral Nutrition, is trying to remedy this by the widespread introduction of MUST (Malnutrition Universal Screening Tool) for nutritional assessment in all hospital departments (see box below).


MUST defines malnourished patients as those with any one of the following:

BMI less than 18.5 kg/m2

Unintentional weight loss greater than 10% within the last 3-6 months

BMI < 20 kg/m2 and unintentional weight loss > 5% within the last 3-6 months


Patients at risk of malnutrition have any one of the following

Eaten little or nothing for > 5 days and/or likely to eat little or nothing for the next 5 days or longer (i.e. most critically ill patients)

Poor absorptive capacity, and/or high nutrient losses and/or increased nutritional needs from causes such as catabolism (i.e. most critically ill patients)


Difficulties with assessment in ICU:

• methods of weighing the patient may not be available
• weight may be influenced by fluid resuscitation, and
• accurate measurement of height is difficult in a supine patient.
• history of weight loss or poor oral intake from family may be inaccurate
• records of feeding given on the wards are often sketchy
• need to combine MUST assessment with refeeding assessment

Particular effort should be made within 24-48 hours to feed ICU patients who are deemed on admission to be malnourished or at risk of malnutrition and to ensure their requirements are met with as few interruptions to feeding as possible, taking into account any refeeding risk.

NICE recommend that the nutritional prescription of total intake for non-critically ill and well-nourished patients, or for patients established on feeding regimes should provide all of the following:

  • 25-35 kcal/kg/day total energy (including that derived from protein)
  • 0.8-1.5g protein (0.13-0.24 g nitrogen)/kg/day
  • 30-35ml fluid/kg/24hours (basic maintenance requirement).
  • Add 2.5ml/kg/24 hours for each degree of temperature above 37ºC
  • Adequate electrolytes, minerals and micronutrients (allowing for any pre-existing deficits, excessive losses or increased demands)
  • Fibre if appropriate.

Calculations of fluid intake in the critically ill should account for feed volume and any IV fluids including fluid given with drugs. The basic maintenance requirement should be administered with replacement for extra losses from drains, fistulae, bleeding, excessive urine output, excessive diarrhoea and gastric losses.

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