The Basic Principles of Nutritional Support in the Intensive Care Unit
Dominic J. Nompleggi
I. GENERAL PRINCIPLES
A. Severe protein-calorie malnutrition, unfortunately, is common in critically ill patients.
B. In all patients with serious illness, appropriate measures to avoid substrate deficiency and to replete nutrient deficiency are best recognized promptly, and appropriate therapy is instituted without delay.
II. PATHOGENESIS
A. Malnutrition can be present on admission or develop as a result of the metabolic response to injury.
B. Changes in metabolic response are difficult to assess.
C. Assessment includes evaluation of clinical, anthropometric, chemical, and immunologic parameters reflecting altered body composition.
III. DIAGNOSIS
A. General assessment.
1. The purpose of nutritional assessment is to identify the type and degree of malnutrition in order to devise a rational approach to treatment.
2. Percentage weight loss in the last 6 months, serum albumin level, and total lymphocyte count are the commonly used measures to assess nutritional status.
3. Weight loss of 20% to 30% suggests moderate caloric malnutrition, while 30% or greater indicates severe protein-calorie malnutrition; loss of 10% or more over a short period of time is also considered clinically important.
4. The general appearance of the patient, with emphasis on evidence of temporal, upper body, and upper extremity wasting of skeletal muscle mass, provides a quick, inexpensive, and clinically useful measure of nutritional status.
B. Laboratory assessment.
1. Serum albumin measures visceral protein stores; it is a useful and readily available indicator of kwashiorkor (protein malnutrition).
2. Serum albumin is not a sensitive indicator of malnutrition in ICU patients because its synthesis is influenced by numerous factors other
than nutritional status (e.g., protein-losing states, hepatic function, and acute infection or inflammation).
than nutritional status (e.g., protein-losing states, hepatic function, and acute infection or inflammation).
3. Malnutrition is closely correlated with alterations in immune response as measured by skin test reactivity and total lymphocyte count.
4. A total lymphocyte count <1,000/mm3 is indicative of altered immune function and is associated with decreased skin test reactivity.
5. Loss of skin test reactivity is a measure of impaired cellular immunity, which consistently has been found to be associated with malnutrition.
C. Subjective global assessment.
1. Subjective global assessment (SGA) evaluates nutritional status using clinical parameters such as history, physical findings, and symptoms.
2. The SGA determines whether
a. nutritional assimilation has been restricted because of decreased food intake, maldigestion, or malabsorption;
b. any effects of malnutrition on organ function and body composition have occurred; and
c. the patient’s disease process influences nutrient requirements.
3. In hospitalized patients, SGA has been shown to provide reliable and reproducible results with more than 80% agreement when blinded observers assessed the same patient.
IV. TREATMENT
