Gastroenterology & Nutrition | Parenteral Nutrition

Specific Clinical Situations Underlying Special Needs

Provided below are problems (and possible solutions for those problems) associated with each of the following:

• High Body Mass Index
• Extra fluid requirements
• Fluid restrictions
• Higher energy needs
• Lower energy needs
• Minor biochemical alterations
• Specific disease states

High Body Mass Index

Problems

Body Mass Index is a recently employed methodology for evaluating body composition. Body mass index is determined by the formula: weight(kg)/ height(m) x height(m). Graphs of BMI versus age are readily available to determine where an individual patient plots at any particular age. A BMI above expected normals indicates that a patient's body composition is not normal, usually because weight exceeds what is expected for height at a particular age. Excessive weight may be caused by:

• excess body fat
• edema
• comparmentalized fluid such as ascites or effusion

These excesses contribute to body weight, but not to metabolic activity. Calculations with body weight assume that body composition is normal, consisting of 70 to 75% lean body mass and 25 to 30% fat mass. Lean body mass is the energy-consuming compartment of the body. Thus, using excess weight to calculate energy expenditures results in an overestimation of energy needs since the increased weight is assumed to contain 70 to 75% metabolically active tissue.

Solutions

To estimate energy expenditure accurately when BMI is high, calculations of energy expenditure should employ ideal body weight for height or length rather than actual body weight. Ideal body weight(IBW) can be determined by:

• Employing the BMI formula: Ideal body weight(kg) = BMI (50%tile for age) x height(m) x height (m)
  BMI for Girls [chart]
  BMI for Boys [chart]
  
• Using normal growth charts: Ideal body weight(kg) = weight at the 50%tile for the actual height or length at the patient's age
  Girls 0-36 Months Growth Chart [growth chart]
  Girls 2-20 Years Growth Chart [growth chart]
  Boys 0-36 Months Growth Chart [growth chart]
  Boys 2-20 Years Growth Chart [growth chart]
  
• Another location to access BMI and Growth Charts: CDC compilation of BMI and Growth Charts [clinical charts]
  

The use of ideal body weight results in a more accurate determination of actual resting and total daily energy expenditures. Thus, when the BMI exceeds the expected value for age, the IBW should be substituted for the actual body weight when performing calculations of energy expenditure and nutritional needs.

Extra Fluid Requirements

Problems

• extremely LBW infant
• significant nasogastric tube drainage
• severe diarrhea
• wound or chest tube drainage
• post-obstructive or post-ATN diuresis
• diabetes insipidus

Solutions

Additional fluid and/or electrolyte administered as a separate IV solution through a Y-connector with TPN. As fluid and salt needs change, these supplemental fluids can be altered in amount and type without interruption of nutritional support.

Fluid Restrictions

Problems

• pre- or post-operative congenital heart disease
• renal failure
• severe lung disease with cor pulmonale

Solutions

PN is provided via central access. Peripheral PN cannot be designed to provide sufficient energy intake to justify use. Special solutions with high concentrations of dextrose (> 30%) and amino acids (AAM > 30 gm/L) may be needed.

Higher Energy Needs

The nutrition literature is replete with various recommendations for increasing energy intake in patients with underlying disease. Documentation of increased energy needs has accumulated for only a few specific conditions:

Problems

• burns [reference]
• congenital heart disease [references]
• chronic lung disease: cystic fibrosis [reference] and lung disease of prematurity [PDF reference]
• fever
• catch-up growth
• cachexia [reference], e.g. cancer

Infection without fever, post-operative status, or trauma may not necessitate any calorie increase above the usual requirements. Even with extra needs, TDEE does not usually exceed 2.0 x REE.

Solutions

Carefully considered inceases in energy intake are achievable. Generally, glucose infusion rates should not exceed 20 mg/kg/min, and IL infusion rates should not exceed 0.1 gm/kg/hour.

Lower Energy Needs

(See also Nutrition Literature Resource)

Many patients with severe underlying disease actually consume less energy than would be expected.

Problems

• mechanically ventilated patients
• paralyzed patients
• comatose patients
• patients with markedly altered body composition, e.g. obese children with profound neurological impairment

Solutions

When estimating energy requirements, begin with measured, calculated, or estimated REE and do not assume extra needs for underlying illness.

Minor Biochemical Alterations

Mild alterations is serum concentrations of sodium, potassium, calcium, phosphorus, magnesium, and albumin are common in ill patients. Often, these abnormalities will improve with remission of the basic illness and routine TPN support. Special adjustments of PN solutions are not necessary.

Specific Disease States