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Enteral and Parenteral Nutrition

Chapter 346 | Part 10: Disorders of the Gastrointestinal System · Part 10 – Gastrointestinal Disorders · Chapter 346

Key Clinical Points

  1. Three types of Specialized Nutritional Support (SNS): (1) Optimized voluntary nutritional support; (2) Instrumental enteral nutrition (EN); and (3) Parenteral nutrition (PN).
  2. Starvation-Related Malnutrition (SRM) is distinguished from Chronic Disease-Related Malnutrition (CDM) by the presence or absence of systemic inflammation.
  3. Acute Disease-Related Malnutrition (ADM) is an injury-induced metabolic condition characterized by rapid muscle loss and increased resting energy expenditure.
  4. BMI thresholds: <19–20 indicates reduced muscle/fat; <15 indicates severe starvation; <13 is thermodynamically incompatible with life.
  5. Protein requirements: Minimum 0.65 g/kg; recommended 0.80 g/kg; critically ill patients often require 1.2–2.0 g/kg.
  6. Nitrogen (N) loss calculation: N loss (g) = N in urinary urea / 0.85 + 2.
  7. Insulin dosing for PN: Non-diabetic ≈ 10 units/100g glucose; Non-insulin dependent diabetes ≈ 20 units/100g glucose; Insulin-dependent diabetes ≈ 2x at-home dose.
  8. EN contraindications: intestinal ischemia, mechanical obstruction, peritonitis, and gastrointestinal hemorrhage.
  9. Visual BMI allows estimation of normalized dry body weight in obese or edematous patients (e.g., a 1.75m adult with visual BMI 17 = 52 kg).
  10. Systemic inflammation reduces serum albumin (negative acute-phase reactant) and increases C-reactive protein (CRP).

1. DEFINITION & OVERVIEW

Management of in-hospital nutritional disorders follows a three-step process:

  1. Screening and diagnosis of the nutritional disorder.
  2. Determination of severity and urgency of the treatment within the overall clinical context.
  3. Selection of specialized nutritional support (SNS), including its composition and administration details.

Note: Collaboration with clinical dietitians and specialized pharmacists is recommended due to the complexity of these requirements.

1.1 Specialized Nutritional Support (SNS) Types

There are three categories of SNS:

  1. Optimized voluntary nutritional support
  2. Instrumental enteral nutrition (EN)
  3. Parenteral nutrition (PN)

2. EPIDEMIOLOGY

• Prevalence: Malnutrition is common in hospitalized patients. • Causes of In-Hospital Malnutrition: Often a combination of factors including: ◦ Inadvertent or physician-ordered food deprivation ◦ Psychological distress, depression, or anxiety ◦ Anorexia nervosa ◦ Poorly controlled pain or nausea ◦ Unappealing/poorly presented food ◦ Communication barriers ◦ Physical or sensory disability ◦ Dysphagia and other mechanical difficulties ◦ Gastrointestinal issues (partial obstruction, thrush, intestinal angina) • Micronutrient Deficiencies: Common but less investigated; includes zinc, vitamin C, and vitamin D. ◦ Clinical Note: Hospital diets do not automatically protect against these if the patient is already deficient upon admission.

3. ETIOLOGY & PATHOPHYYSOLOGY

• Macronutrient Malnutrition Syndromes: ◦ SRM (Starvation-Related Malnutrition): Also known as "starvation disease." Result of prolonged semi-starvation. ◦ CDM (Chronic Disease-Related Malnutrition): SRM combined with moderately severe systemic inflammation. Common in chronic infection, inflammatory autoimmune disease, and organ failure (hepatic, renal, cardiac, pulmonary) or neoplasm. ◦ ADM (Acute Disease-Related Malnutrition): Also known as "injury-induced malnutrition" or "protein-catabolic critical illness." An injury-induced metabolic condition causing rapid muscle loss and increased energy expenditure. Often occurs without prior SRM/CDM.

3.1 Systemic Inflammation

• Distinction: The primary differentiator between SRM and CDM. • Laboratory Markers: ◦ Serum Albumin: Decreased (negative acute-phase reactant). Reduced due to increased capillary permeability, redistribution into ECF, increased catabolism, and reduced liver synthesis. ◦ C-reactive Protein (CRP): Increased; useful for determining the intensity of inflammation. • Impact on Micronutrients: Inflammation can sequester nutrients (iron, selenium, zinc) into tissue stores, making standard laboratory tests less reliable. Assessment should include a review of prior intake and potential routes of loss.

3.2 Protein-Catabolic Intensity

• Measurement: Tracked via body Nitrogen (N) loss. ◦ Formula: N loss (g) = N in urinary urea / 0.85 + 2. ◦ Tissue Loss Calculation: 1. 1 g N lost = 6.25 g protein lost. 2. 15 g N/day → 94 g protein/day loss. 3. Since body cell mass is ≈ 20% protein, 94 g protein/day loss → ≈ 470 g (1 lb) of active tissue mass lost per day. • Clinical Risk: Patients with high-catabolic disease but preserved muscle stores are at greater risk than those with already depleted stores because they are closer to the threshold of lethal depletion.

4. CLINICAL FEATURES

• Body Mass Index (BMI): ◦ Definition: weight (kg) / height (m^2). ◦ Normal range: 20–25 kg/m^2. ◦ Clinical Thresholds: ◦ <19–20: Reduced muscle/fat. ◦ <15: Severe starvation. ◦ <13: Thermodynamically incompatible with life. ◦ Note: BMI may be misleading in obese or edematous patients due to expanded ECF volume.

• Visual BMI: ◦ Technique: Assess muscle groups while discounting subcutaneous fat and edema. ◦ Example: A 1.75-m adult with a visual BMI of 17 has a normalized dry weight of 52 kg (calculated as 1.75^2 imes 17).

• Muscle Mass: ◦ Composition: ≈ 80% of an adult's active tissue mass. ◦ Causes of loss: ◦ Age-related (sarcopenia) ◦ Disuse atrophy ◦ High-dose glucocorticoids ◦ Endocrine diseases (uncontrolled DM, adrenocortical insufficiency, hyperthyroidism, androgen deficiency, hypopituitarism) ◦ Primary muscle or neuromuscular diseases. ◦ Clinical Rule: SRM and CDM are common treatable causes of muscle loss; these should be identified and addressed first.

• Extracellular Fluid (ECF): ◦ Normal: ≈ 20% of body weight. ◦ Effect: SRM increases ECF; CDM adds edema due to hypoalbuminemia from inflammation.

Assessment Tools

• Sarcopenia: A progressive and generalized loss of skeletal muscle mass and strength. ◦ Screening: SARC-F score ≥ 4 indicates risk. • Frailty: A state of increased vulnerability to adverse health outcomes due to reduced physiologic reserves. ◦ Assessment: Clinical Frailty Scale; Score ≥ 5 is considered frail.

DIAGNOSTIC APPROACH

  1. Screening and Diagnosis: Identify the presence of nutritional disorders (SRM, CDM, or ADM) based on clinical presentation and history.
  2. Severity and Urgency Assessment: Determine the severity of the identified disorder within the context of the patient's overall clinical condition.
  3. Selection of Support: Choose the appropriate type of Specialized Nutritional Support (SNS) based on the diagnosis and goals.
  4. Options include:
  5. Optimized voluntary
  6. Instrumental enteral (EN)
  7. Parenteral (PN)

MANAGEMENT & TREATMENT

  1. Establish Goals: Define clear therapeutic goals based on the specific diagnosis (e.g., reversing muscle loss in ADM vs. managing anorexia in CDM).
  2. Select Nutritional Route:
  3. Optimized Voluntary: For patients with no physical barriers to intake.
  4. Instrumental Enteral Nutrition (EN): For patients with impaired intake but viable GI tract.
  5. Contraindications: intestinal ischemia, mechanical obstruction, peritonitis, and gastrointestinal hemorrhage.
  6. Parenteral Nutrition (PN): For patients with non-functional GI tracts or severe malabsorption.
  7. Determine Protein Requirements:
  8. Standard: 0.80 g/kg.
  9. Critically Ill: 1.2–2.0 g protein/kg of normal body weight.
  10. Calculate Insulin for PN:
  11. Non-diabetic: ≈ 10 units/100g glucose.
  12. Non-insulin dependent diabetes: ≈ 20 units/100g glucose.
  13. Insulin-dependent diabetes: ≈ 2x at-home dose.
  14. Monitor Progress: Assess muscle mass, functional status (e.g., Handgrip strength), and inflammatory markers (CRP, Albumin).

KEY PEARLS & HIGH-YIELD POINTS

• Differentiation Rule: The presence of systemic inflammation (High CRP, Low Albumin) is the primary differentiator between CDM and SRM. • Nitrogen Calculation: Use $N ext{ loss (g)} = N ext{ in urinary urea} / 0.85 + 2$ to quantify daily protein loss; 15 g N/day → ≈ 470 g tissue mass lost per day. • BMI Interpretation: A patient with a normal BMI may still have severe muscle wasting due to increased ECF volume (starvation edema). • Sarcopenia & Frailty: SARC-F score ≥ 4 indicates risk of sarcopenia; Clinical Frailty Scale ≥ 5 indicates frailty. • Clinical Rule: Always treat identifiable causes of muscle loss (e.g., glucocorticoid use, endocrine issues) in addition to nutritional support.

Reference Tables

TABLE 345-2 Common Body Composition Studies, Laboratories, and Other Studies Used in Nutrition Assessment TEST…

Harrison's 22e, p.2619

TEST NOTES
Functional tests (Recommended)
Clinical Frailty Scale A tool that measures frailty, which is defined as a state of increased vulnerability to adverse health outcomes due to reduced
physiologic reserves. It uses various self-reported factors (e.g., physical mobility, cognitive function, and the ability to perform
daily activities) to classify frailty into nine classifications, ranging from very fit (level 1) to severely frail (level 9). Patients who
score ≥5 are considered frail.
Handgrip strength A measure of muscular strength generated by one’s forearm muscles to screen for upper body strength. Low grip strength
is associated with poorer clinical outcomes. Patients with low grip strength may benefit most from personalized nutritional
support.
6-Meter Walk Test Assesses walking speed (meter/sec) over a 6-m distance to determine functional mobility, gait, and vestibular function.
346 Enteral and Parenteral
Nutrition
L. John Hoffer, Bruce R. Bistrian