Chapter 073. Enteral and Parenteral Nutrition (Part 2) pdf

Chapter 073. Enteral and
Parenteral Nutrition
(Part 2)

Decision-making for the implementation of specialized nutrition
support (SNS). CVC, central venous catheter; PICC, peripherally inserted central
catheter. (Adapted from previous chapter by Lyn Howard, MD.)
The first step in deciding to administer SNS is to consider the nutritional
implications of the disease process. Is the condition or its treatment likely to
impair food intake and absorption for a prolonged period of time? For example, a
well-nourished individual can tolerate approximately 7 days of starvation while
experiencing a systemic response to inflammation (SRI). The second step is to
determine if the patient is already significantly malnourished to the degree that
critical functions such as wound healing, immune function, or ventilatory function
are impaired (Chap. 72). An unintentional weight loss of >10% during the
previous 6 months or a weight/height <90% of standard, when associated with
physiologic impairment, represents significant PCM. Weight loss >20% of usual
or <80% of standard reflects severe PCM. The presence or absence of SRI should
be noted, since inflammation, injury, and infection increase the rate of lean tissue
loss. SRI also has pathophysiologic effects that influence nutritional responses
such as fluid retention and hyperglycemia, as well as impairment of anabolic
responses to nutritional support.
Once it is determined that a patient is already or at risk of becoming
malnourished, the next step is to decide whether SNS will impact positively on the
patient's response to disease. In the end stages of many chronic illnesses with
accompanying PCM, particularly those due to cancer or terminal neurologic
disorders, nutrition may not reverse the PCM or improve quality of life. While the
provision of food and water is part of basic medical care, nutrition delivered by
tube or catheter, either enterally or parenterally, is associated with risk and
discomfort. Thus, SNS should be recommended only when potential benefits
exceed risks, and should be undertaken with the consent of the patient. Like other

life support measures, enteral or parenteral therapy is difficult to withdraw once
started. Initiating nutrition support may be appropriate before a final prognosis can
be determined, but this should not preclude its subsequent withdrawal. If
preventing or treating PCM with SNS is appropriate, nutritional requirements and
the method of delivery should be determined. The optimal route depends on the
degree of gut function and somewhat on the available technical resources.
The timing of nutritional support is based on evaluation of the preexisting
nutritional status, the presence and extent of SRI, and the anticipated clinical
course. SRI is identified by the standard clinical signs of leukocytosis, tachycardia,
tachypnea, and/or temperature elevation or depression. Although the degree of
hypoalbuminemia provides an estimate of SRI severity, normal serum albumin
levels will not be restored by adequate nutritional support until the SRI remits,
even though nutritional benefits can be achieved by adequate feeding.
The SRI can be graded as severe, moderate, or mild. Examples of severe
SRI include sepsis or other inflammatory conditions like pancreatitis requiring
ICU care, multiple trauma with an Injury Severity Score > 20–25 or APACHE II >
25, closed head injury with a Glasgow Coma Scale < 8, or major third-degree
burns of >40% of body surface area. Moderate SRI includes less severe infections,
injuries, or inflammatory conditions like pneumonia, major surgery, acute hepatic
or renal insufficiency, and exacerbations of ulcerative colitis or regional enteritis
requiring hospitalization. PCM should also be defined as severe, moderate, or
minimal as assessed by weight/height, percent recent weight loss, and body mass
index. The body mass index in relation to nutritional status is listed in Table 73-1.
A patient with a severe SRI requires early feeding within the first several days of
care because the condition is likely to produce inadequate spontaneous intake over
the next 7 days. A moderate SRI, as commonly seen during a postoperative period
without oral intake that exceeds 5 days, benefits from adequate feeding by day 5–7
if the patient was initially well nourished. If severely malnourished, candidates for
elective major surgery benefit from preoperative nutritional repletion for 5–7 days.
However, this is not often possible. Thus, early postoperative feeding is indicated.

Patients with a moderate SRI and moderate PCM also benefit from earlier feeding
within the first several days.
Table 73-1 Body Mass Index (BMI) and Nutritional Status
BMI Nutritional Status
>30 kg/m
2


Obese
>25–30 kg/m
2


Overweight
20–25 kg/m
2


Normal
<18.5 kg/m
2


Moderate malnutrition
<16 kg/m
2


Severe malnutrition
<13 kg/m

2


Lethal in males
<11 kg/m
2


Lethal in females
From D Driscoll, B Bistrian: Parenteral and enteral nutrition in the
intensive care unit, in Intensive Care Medicine , R Irwin, J Rippe (eds). Lippincott
Williams & Wilkins, Philadelphia, 2003.