Page 532 - ACCCN's Critical Care Nursing

Gastrointestinal, Liver and Nutritional Alterations 509

increased, characterised by a rise in resting energy expen-
diture and oxygen consumption, which in some critically TABLE 19.3 Nutritional indices
26
ill patients can be increased by over 50%. Depletion of
body energy stores result from alterations in protein, car- Assessment Limitations in critical illness
27
bohydrate and fat metabolism. In addition to the rise 40,43
in metabolic demands, patients who are critically ill often Subjective global Not validated in the critically ill
assessment
experience a concomitant fall in nutritional intake. The
metabolic and nutrition alterations vary with the stress Biochemical
markers:
level, severity of illness, type of injury, organ dysfunction ● albumin Decreased sensitivity because of 20-day
and nutrition status. 25 half-life; influenced by fluid balance/shifts 42
● transferrin Half-life of 8 days but lacks the sensitivity and
To maintain normal cellular function, body cells require specificity for determining nitrogen
adequate amounts of the six basic nutrients: carbohy- balance; influenced by fluid balance/shifts
43
drates, fats and proteins to provide energy, vitamins, min- ● prealbumin Most sensitive with a half-life of 2 days, but
44
erals and water to catalyse metabolic processes. Unlike changes may result from the metabolic
normal metabolism, which preferentially uses carbohy- response to illness rather than change in
drates and fats for energy, the hypermetabolic state asso- nutritional status; influenced by fluid
balance/shifts
ciated with critical illness consumes proportionally more
fats and proteins than carbohydrates to generate energy. Delayed Used to assess the patient’s immune status,
28
As a consequence of the gluconeogenesis and the synthe- hypersensitivity but alterations can be related to underlying
42
disease rather than nutritional status
sis of acute-phase proteins, there is a decrease in lean
body mass and negative nitrogen balance. Skeletal muscle Mechanical characteristics of skeletal muscle
function influenced by energy stores rather than
loss of muscle mass 42
CONSEQUENCES OF MALNUTRITION
When adequate and timely nutrition support is not pro-
vided, body energy and protein depletion can occur with importance of nutritional assessment and the impact of
negative consequences on patient outcome. Critically ill malnutrition in the critically ill informs management and
29
30
patients require adequate nutrition to limit muscle is likely to improve outcomes.
wasting, respiratory and gastrointestinal dysfunction and Determining Nutritional Requirements
alterations in immunity, all of which are associated with
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malnutrition. Respiratory support is often necessary Determining caloric requirements is largely dependent
during critical illness, and changes in respiratory muscle on energy expenditure, influenced by patient activity,
function and ventilatory drive may contribute to an stage of illness, type of injury and previous nutritional
42
increase in the number of ventilator days. Furthermore, status. Indirect calorimetry is the ‘gold standard’ and
infection rates may be increased in malnourished criti- most precise way of determining the nutritional require-
45
cally ill patients. The decrease in lean body mass and ments in critical illness. Energy expenditure is measured
negative nitrogen balance is associated with delayed using the oxygen consumption obtained from carbon
wound healing and a higher risk of infection. 28 dioxide levels (PaCO 2 ), or using a metabolic monitor. It
is infrequently used in critical care settings, possibly
These complications contribute to increased length of because of the high equipment costs and unreliability in
31
stay, cost, morbidity and mortality. The degree of critical the critically ill. 46
illness and hypercatabolism varies between patients and
is often difficult to accurately determine. For this reason Calculating basal energy expenditure using the Harris-
it is necessary to assess, as accurately as possible, the Benedict equation is a common, but less precise, method
42,47,48
nutritional requirements of each individual patient. of determining nutritional requirements. The Harris-
Benedict equation, and others, takes into account the age,
NUTRITIONAL ASSESSMENT height, weight and gender of the patient, with adjust-
ments made for treatment, disease process and metabolic
The majority of studies report cumulative energy deficit state. Importantly, these equations fail to find any signifi-
or caloric debt is associated with worse clinical cant benefits in outcomes, most likely because they do
36
outcomes. 32-35 Krishnan and colleagues, however, not measure energy requirement. 49
describe better clinical outcomes for patients fed fewer
than the target nutrition goals when compared to those The Prognostic Inflammatory Nutrition Index (PINI) uses
who received near target goals. Nutritional assessment the elevations in acute phase proteins (alpha-1-acid gly-
includes patient history, physical examination and assess- coprotein and C-reactive protein [CRP]) that occur with
ment of nutritional indices (see Table 19.3), but is often simultaneous reductions in transport proteins (albumin
unreliable in the critically ill patient. 37,38 Clinical judge- and pre-albumin) in a simple formula to stratify critically
50
ment remains the most common way of assessing a ill patients by risk of complications or death.
patient’s nutritional status, and is shown to be as reliable NUTRITION SUPPORT
as biochemical tests. 39-41 Clinical judgement takes into
consideration recent weight loss, reduced dietary intake, For patients in ICU who are unable to take oral nutrition,
anorexia, vomiting, diarrhoea, muscle wasting and enteral nutrition (EN), parenteral nutrition (PN) or com-
42
signs of nutritional deficiency. Appreciation of the bined EN and PN is available. The best method of