FRCA Notes

Nutrition in Intensive Care

Perioperative and critical care nutrition is a covertly behemoth topic.

It naturally has close ties to the pages on malnutrition (from the Perioperative Medicine section), parenteral nutrition and refeeding syndrome.

The material below focuses on covering the eight-point nutrition section in the FRCA curriculum, rather than the entirety of the near-thirty point nutrition tour de force in the FFICM curriculum.

Resources

  • NICE recommends screening all hospital admissions, and regularly reassessing inpatients, using the Malnutrition Universal Screening Tool (MUST)
  • This identifies higher-risk patients, such as those who are malnourished or obese

  • Although there are guidelines recommending further risk-scoring tools such as NRS-2002 or NUTRIC scoring, they are not validated in ICU nor does their use improve outcome
  • The ESPEN guidelines suggest using a general clinical assessment in critical care, and that those admitted for >48hrs should be deemed at high risk of malnutrition

  • Overall, an MDT approach is required, including Intensivists, Gastroenterologists, dieticians, pharmacists and dedicated nutritional support teams

Modes of assessing nutritional status

  • In line with the ESPEN recommendation for a 'general' assessment, there are a smorgasbord of measures one can make to assess and monitor a patient's nutritional status:

  • Anthropometry
    • Height
    • Body weight ± change in body weight
    • Adiposity | muscle mass | body water content | body composition

  • Biochemical
    • 24hr urinary urea (nitrogen balance) and creatinine (muscle mass lost)
    • Serum electrolytes
    • Plasma proteins
      • Albumin has a long half-life and is a poor marker of nutritional status
      • Pre-albumin has a short half-life (<2 days) and is a sensitive marker of response to nutritional support
      • Transferrin is affected by stress and iron status
      • Retinol binding protein is sensitive to protein depletion
    • Both WCC and CRP are affected by the acute phase

  • Clinical assessment
    • Physical appearance
    • Past medical history
    • Drug history
    • Current diagnosis

  • Dietary assessment

Methods of monitoring nutritional status

Parameter Rationale Frequency
Weight Mass and fluid balance Baseline → weekly
Fluid status Fluid balance Daily
Anthropometry E.g. mid-arm circumference Baseline → monthly
Medications For relevant interactions Every few days
Feed volume Adequacy and tolerance of feed Daily → twice weekly
Feed rate Adequacy and volume delivered Daily
GI tract Presence of nausea/vomiting/diarrhoea/distention/high aspirates Daily
Tube/catheter position Correct position, infection Daily
Renal and liver function Monitor urea, creatinine , albumin, CRP Daily until stable
Electrolytes Monitor risk of refeeding syndrome Daily until stable
Blood glucose To detect over- or under-feeding 4hrly → BD
Trace elements To detect deficiencies Baseline → PRN
Lipids To detect imbalance or overfeeding Baseline → PRN
Temperature Check presence of infection Daily


Total Daily Energy Expenditure (TDEE)

  • For maintenance nutritional therapy, the aim is to meet the patient's TDEE

  • Measuring a patient's actual TDEE necessitates indirect calorimetry, or failing that it requires a PA catheter
  • In lieu of these oft unavailable methods, there are various equations which purport to approximate a patient's energy requirements e.g. Harris-Benedict, Schofield
  • Unfortunately these are often inaccurate and/or inconsistent, so often requirements are estimated (see below) using a patients body weight (adjusted body weight if obese)

  • Using estimates rather than exact, individualised numbers doesn't appear to be harmful:
    • TICACOS study; using calculated energy expenditure (vs. a standard 25kcal/kg/day regimen) led to lower mortality but longer duration of mechanical ventilation and ICU stay
    • EAT-ICU study; early, indirect calorimetry-guided nutrition did not improve RRT rates or any clinical outcome at 6 months vs. standard care
      • Although it led to greater calorie and protein delivery, there was consequentially more hyperglycaemia, greater need for insulin and higher plasma urea levels

Nutritional requirements

Nutritional element 24hr requirement Proportion
Total energy 25kcal/kg
Carbohydrate 2g/kg (max 150g) 60-70%
Protein 0.8 - 1.2g/kg 10-20%
(Nitrogen) (0.13 - 0.24g/kg)
Lipid 1g/kg (max 1.5g) 20-30%
Water 30-35ml/kg
Sodium & chloride 1-2mmol/kg
Potassium 1mmol/kg
Calcium & magnesium 0.1mmol/kg
Phosphate 0.2-0.5mmol/kg
Vitamins Esp. thiamine
Micronutrients Inc. Zn, Cu and Se
  • There's some suggestion that the optimal calorie prescription is less than 100% recommended ('permissive underfeeding')
    • One study demonstrated patients receiving 33-66% of the recommended calories were more likely to be self-ventilating on discharge
    • Another showed receiving 80-85% of the recommended calories was associated with the greatest 60-day in-hospital mortality
    • Another study of permissive underfeeding did not demonstrate any difference in the rates of infections, vomiting or mortality
    • The PERMIT trial showed no difference in outcomes inc. 90-day mortality in those who were given 40-60% vs. 70-100% of daily calorie requirements, regardless of nutritional risk

  • The recent EFFORT trial did not demonstrate any outcome benefit if higher rates of protein (2.2g/kg vs. 1.2g/kg) were provided
  • The PROTINVENT trial found initial low (<0.8g/kg) protein for 72hrs then high (>0.8g/kg) protein thereafter was associated with better 6-month mortality than either pure low or high protein feeds

  • Nutritional supplementation may improve a variety of outcomes in various patient groups

  • In elderly patients, high-protein oral nutritional support can improve grip strength, reduce hospital admission rates and overall complication rates

  • In malnourished patients:
    • Medical: an individualised approach to nutritional support will reduce complications, antibiotic use and re-admission rate
    • Surgical: immunonutrient enteral feeds may reduce length of stay, infection rates, morbidity and mortality

  • In those undergoing major surgery, nutritional support forms a key component of prehabilitation
    • Use of immune-modulating feeds may reduce length of stay and infection rates

  • In cancer patients undergoing surgery, NG feeding reduces length of stay, rate of infective complications and sepsis (but not mortality)

  • In those at risk of pressure ulcer formation
    • 25% reduction in pressure ulcer development if high-protein oral nutritional supplements (250 - 500kcal for up to 26 weeks) are used vs. routine care
    • Use of higher-protein enteral feed shows a trend towards better healing of existing ulcers

Critical care

  • Use of nutritional support attenuates the catabolic effects of critical illness
  • There is conflicting/inconsistent evidence about the use of immune-enhancing feeds and infectious complications

  • Increased energy and protein intake may be associated with an increased number of ventilator-free days
  • Conversely, a higher cumulative energy debt is associated with an increased duration of ventilation & increased incidence of complications
  • Nutritional support may reduce mean length of hospital stay, but not necessarily length of ICU stay
  • Early, individualised, evidence-based nutrition may reduce ICU and in-hospital mortality

  • Nutritional support may be oral, enteral (EN) or parenteral (PN)
  • Artificial nutritional support should be considered for patients who:
    • Are already suffering from malnutrition
    • Are at risk of malnutrition owing to:
      • Poor oral intake for ≥5 days (and expected to continue to be so)
      • Poor absorptive capacity and/or high nutrient losses
      • Increased demands from catabolic or hypermetabolic states

  • ESPEN and ASPEN guidelines suggest enteral nutrition should be started within 48hrs of ICU admission, preferably once haemodynamic stability is achieved
  • If the oral route unavailable → enteral nutrition → parenteral nutrition

Early vs. late enteral feeding

  • Early, aggressive feeding in a cohort of head-injured patients led to fewer infections, a trend towards improved neurological outcome at 3 months but no mortality benefit
  • In the EDEN trial, trophic feed (10-20ml/hr of 1kcal/ml feed) for up to 6 days led to less GI intolerance, and no other outcome differences, vs. full rate feed
  • Conversely, the EPaNIC trial showed late (>day 8) feeding was associated with:
    • Fewer infections
    • Less RRT
    • Fewer ventilated days
    • Increased likelihood of ICU survival & hospital discharge
    • Decreased healthcare costs

  • For PN, the optimal timing of initiation is not known
  • There seems to be no additional benefit to PN in those who could tolerate EN (CALORIES, EPaNIC, NUTRIREA-2)
  • ESPEN recommend starting PN after 3-7 days only if EN is not tolerated

  • Overall, early nutritional support (EN or PN) does not appear to improve ICU mortality

  • Enteral nutrition should be used in those for whom:
    • The oral route is inadequate or not possible e.g. intubated, unsafe swallow
    • Requirements are increased due to a disease process

Benefits

  • Maintenance of gut flora, important for synthesis of B-vitamins and vitamin K and the metabolism of bile acids & sterols
  • Maintains physiological gut barrier (and reduced gram negative bacteraemia)
  • Those of nutritional support in general (see above)

Routes of enteral feeding

  • Nasogastric tube: up to 4 weeks

  • Orogastric tube: for patients with facial trauma or base-of-skull fracture where NGT cannot be safely passed

  • Post-pyloric tube: e.g. duodenal or jejunal tube to bypass upper GI obstruction/dysfunction
    • Lower rates of pneumonia
    • Potentially more calories received
    • No improvement in ventilator-free days or mortality
    • No increased complications associated with tube insertion (although increased cost)

  • Gastrostomy: for longer-term enteral feeding >4 weeks e.g. post-oesophagectomy
    • Surgically placed e.g. intra-operatively
    • Endoscopically placed (PEG; percutaneous endoscopic gastroscopy)
    • Radiologically placed (RIG; radiologically inserted gastrostomy) e.g. head and neck cancer patients

Administration

  • NG tubes should be checked after placement, before use, with CXR ± pH paper (pH <5.5)
  • Enteral nutrition can be delivered either as a bolus or continuously (over 16-24hrs)

  • Feeds may be:
    • Whole protein feeds, further sub-categorised into an array of different types including:
      • Standard feed (1kcal/ml)
      • High-energy (1.2 - 2kcal/ml)
      • High-protein
      • Disease-specific e.g. low sodium, immune formulae, renal, respiratory
    • Peptide-based (semi-elemental) feeds, which are mostly used in patients with severe gut impairment

Complications

  • Aspiration and ventilator-associated pneumonia
  • NG tube in wrong place (a never event)
  • Hyper-osmolar diarrhoea
  • Failure to achieve expected calorie delivery (although possibly not exquisitely detrimental)
  • Possible insulin resistance
  • Over-feeding
    • Hypermetabolism and insulin resistance
    • High lipid load: acute pancreatitis, increased blood viscosity
    • Hyperglycaemia
    • Increased CO2 production
    • Hepatic steatosis

  • Metoclopramide 10mg QDS
  • Erythromycin 60mg QDS

  • Improve gastric motility
  • Limited evidence they enhance absorption
  • Do not necessarily improve nutrition