40. ICU Nutrition Flashcards
(35 cards)
Why is nutritional support important in ICU patient
A significant number of patients admitted to hospital are malnourished, up to 40% according to McWhirter.
The majority of patients that are admitted to intensive care are catabolic and will have had a preceding period of starvation due to their surgery or underlying pathology
Complications of poor nutritional support
Impaired wound healing
Reduced muscle bulk/strength and delayed mobilisation
Increased incidence of respiratory infection
Problems with weaning from mechanical ventilation
How can you make an assessment of a patient’s nutritional status
on ICU?
There are objective markers that can be used in the assessment of
malnutrition, but many of these are flawed when faced with a patient with
multiorgan failure on intensive care. There are other methods that are more clinically orientated.
Traditional objective assessment tools
Triceps skinfold thickness
Hand grip tests
Serum albumin (t1/2 14–20 days)
Serum prealbumin (t1/2 24–48 hours)
Serum transferrin
Total iron-binding capacity
Lymphocyte count
These are relatively insensitive and non-specific markers, e.g. albumin affected
by trauma, sepsis and excess extracellular water.
Other methods
Subjective global assessment (SGA) – history and physical factors
Hill and Windsor (bedside nutritional assessment)
Lean body mass assessment – experimental methods
Lean body mass assessment – experimental methods
Bioimpedence
Measuring total body water or potassium
Neutron activation
Muscle biopsy to measure muscle fibre area
These methods are similarly difficult to interpret in a critical care setting.
A nutritional history should be elicited (including normal weight and recent food intake) and there are formulae to derive ideal body mass and daily calorific requirements.
This question initially seems difficult to answer (as rarely formally done
on ICU).
Your answer should emphasise that a detailed history and examination
are still the mainstay of nutritional assessment.
However, you will need to be aware of the tests available.
Be wary of starting your answer with a negative comment about how
difficult it is to assess nutritional status on ICU – perhaps mention this at
the end, with the reasons why
What routes can be used for nutritional support?
Enteral feeding Can be given by nasogastric, nasojejunal or
percutaneous gastrostomy/jejunostomy tubes.
Post-pyloric feeding is becoming more popular as
gastric atony can be a problem in critically ill patients
Side effects: diarrhoea, aspiration.
Parenteral feeding Often through a dedicated central venous catheter,
although peripheral polyurethane catheters or
peripherally inserted central catheters (PICC) can be
used.
Some enteral feeding guidance
‘Underfeeding’ may provide a protective safety barrier (33%–65% of
calculated feed received led to less mortality than >65% of feed
received).
NICE recommend that, for the first 48 hours, parental nutrition should
be <50% of calculated requirement.
Nurse head-up 45%.
Accept gastric residual volumes of 200–250 ml.
Early use of prokinetics
Some enteral feeding guidance
‘Underfeeding’ may provide a protective safety barrier (33%–65% of
calculated feed received led to less mortality than >65% of feed
received).
NICE recommend that, for the first 48 hours, parental nutrition should
be <50% of calculated requirement.
Nurse head-up 45%.
Accept gastric residual volumes of 200–250 ml.
Early use of prokinetics
What problems are associated with parenteral nutrition?
Central venous catheter
Complications related to insertion
Catheter-related sepsis
Displacement
Occlusion / thrombosis
Metabolic
Hypo/hyperglycaemia
Metabolic acidosis
Potassium, sodium and phosphate imbalance
Excess CO2 production
Hypercholesterolaemia/hypertriglyceridemia
Essential fatty acid/vitamins / trace element
deficiencies
Intestinal
TPN fails to reverse intestinal villous atrophy
and bacterial translocation can occur
Hepatobiliary
Abnormal liver function tests.
This is multifactorial
Refeeding syndrome
↑Glu, ↓MgSO4, ↓K+, ↓PO4 seen when
refeeding malnourished patients
What are the advantages of enteral nutrition?
More physiological route for digestion and absorption
Prevents mucosal atrophy – intestinal enterocytes receive a proportion of
their own nutrition directly from the gut lumen and enteral nutrition helps
maintain mucosal blood flow
Supports the normal gut flora
Reduction of bacterial translocation→↓risk of sepsis
Fewer metabolic complications
No catheter-associated complications of TPN – in particular, the risk of
central line sepsis.
What can you tell me about immunomodulation and feeding?
…
Typical daily nutritional requirements
Water 30 ml/kg
Na+ 1.2 mmol/kg
K+ 0.8 mmol/kg
Calories 30 kcal/kg
Protein 0.25 g nitrogen/kg
(10 g nitrogen ∼ 60 g protein)
Fat 2 g/kg
Glucose 2 g/kg
Indications for nutritional support
cachectic patients with a preoperative
weight loss of 15% or more, or who have effectively been starved for more than
10 days (for example, because of dysphagia), have improved outcomes if they
receive nutritional support before surgery. There are numerous other indications,
including malabsorption owing to small bowel resection, small bowel fistulas,
radiation enteritis, intractable diarrhoea and vomiting, and hyperemesis
gravidarum.
Starvation
: this can be defined as the result of a severe or total lack of nutrients
needed for the maintenance of life. In the absence of adequate intake, hepatic
glycogen stores are depleted within 24–48 hours, after which adipose tissue becomes
the source of fatty acids for use as an energy substrate
A small number of cell types,
amongst which are erythrocytes and cells in the renal medulla, can utilize only
glucose, and this has to be provided via amino acids that are produced from protein
breakdown. The CNS normally depends on glucose but can function using ketones as
an energy substrate.
Nutritional requirements energy
– : basal expenditure can be judged from the Harris–Benedict equation
(which links weight, height and age)
or from nomograms.
Kilocalorie needs range from around
30 kcal kg1 in the non-stressed ambulatory state to
60 kcal kg1 in sepsis or following major trauma
After severe thermal injury,
which exemplifies an accelerated catabolic state, patients may require 80 kcal kg
Nutritional requirements - protein
– protein: this can be estimated empirically.
Demands may range from 0.5–1.0 g kg1 in the non-stressed state
to 2.5 g kg1 under conditions of extreme stress.
Assessment of nitrogen balance
: each gram of nitrogen is equivalent to 6.2 g of
protein or 30 g of muscle. In catabolic states patients are in negative balance. Losses
can be determined over each 24-hour period by measuring urinary urea and incorporating
the value into a formula, a typical example of which is 24-hour nitrogen
loss
Nutritional requirements – fluids:
a simple formula for basal requirements in a
temperate climate is 100 ml kg1 for the first 10 kg body weight, 50 ml kg1 for the
next 10 kg and then 20 ml kg1 thereafter. To this total must be added the various
losses as appropriate. (This formula can also be used to approximate normal kilocalorie
requirements.)
Calorie sources:
carbohydrate (glucose) and protein (amino acids) provide 4 kcal of
energy per gram, fat provides 9 kcal
Glucose-rich solutions are associated with hyperglycaemia and fatty infiltration of the liver,
with excess CO2 production which increases the respiratory quotient (RQ) to unity,
with hyperinsulinaemia and fluid retention, with hypophosphataemia
causing reduced tissue oxygenation, and with decreased immune function.
Lipid administration (10% or 20% emulsion) reduces reliance on glucose as a calorie source with its attendant problems and provides essential fatty acids.
Hyperlipidaemia can complicate its administration.
Protein is given in the form of crystalline amino acids
Additives:
these include extra electrolytes, where appropriate, together with phosphate
and magnesium; trace elements, including zinc, copper, manganese, chromium
and selenium; and the full range of fat-soluble and water-soluble vitamins.
Other supplements
Glutamine appears to improve energy utilization and protein
synthesis in skeletal muscle as well as enhancing both gut immunity and lymphocyte
function.
The Refeeding Syndrome
severe metabolic derangements that can occur when nutrition
is reintroduced to individuals who have been starved or severely malnourished,
to patients with severe illness who are profoundly catabolic
presents typically within 4 days of the start of replenishment and is characterized by
metabolic derangement and acidosis, together with variable symptoms and signs.
Symptoms + Signs
These include gastrointestinal symptoms,
muscle weakness and myalgia,
impaired cerebration,
cardiac arrhythmias
myocardial dysfunction.
It is because these are relatively non-specific that the condition may go unrecognized
