Enteral and Parenteral Nutrition¶

Chapter 346 | Part 12: Endocrinology

KEY CLINICAL POINTS¶

Enteral nutrition (EN) is preferred over parenteral nutrition (PN) when the gastrointestinal tract is functional and accessible.
Starvation-related malnutrition (SRM) and chronic disease-related malnutrition (CDM) are common treatable causes of muscle loss.
Refeeding syndrome is a critical complication of nutritional resumption in malnourished patients, requiring close monitoring of electrolytes.

1. DEFINITION & OVERVIEW¶

Enteral and parenteral nutrition are specialized nutritional support strategies. Enteral nutrition (EN) delivers nutrients via the gastrointestinal tract, while parenteral nutrition (PN) provides nutrients intravenously. These methods are indicated when patients cannot meet their nutritional needs through oral intake.

Table 345-2: Common Body Composition Studies, Laboratories, and Other Studies Used in Nutrition Assessment¶

TEST	NOTES
Clinical Frailty Scale	Measures frailty via self-reported factors (physical mobility, cognitive function, daily activities). Patients scoring ‡5 are considered frail.
Sit-to-Stand Test	Assesses lower limb strength, balance, and functional mobility by measuring time to stand and sit five times.
Handgrip Strength	Evaluates upper body strength; low grip strength correlates with poorer clinical outcomes.
SARC-F	Screening tool for sarcopenia using self-reported deficiencies in strength, walking, rising from a chair, climbing stairs, and falls.
6-Meter Walk Test	Measures walking speed over 6 meters to assess functional mobility and gait.

1.1 Types of Specialized Nutritional Support¶

Optimized voluntary nutritional support: Enhances patient autonomy and dietary intake.
Instrumental enteral nutrition (EN): Delivers liquid formulas via tubes to the stomach or intestines.
Parenteral nutrition (PN): Provides nutrients intravenously for patients with gastrointestinal dysfunction.

1.2 Nutritional Assessment Tools¶

Functional tests like the Clinical Frailty Scale, Sit-to-Stand Test, and SARC-F are used to assess frailty and sarcopenia risk. These tools help identify patients at risk of malnutrition.

2. EPIDEMIOLOGY¶

SRM is the leading cause of malnutrition globally, driven by involuntary food deprivation. Hospitalized patients with conditions like cancer, chronic infections, or severe inflammation are at high risk. CDM is common in patients with chronic diseases, while ADM occurs in acute critical illnesses.

2.1 Risk Factors¶

Inadequate food intake, systemic inflammation, malabsorption, and prolonged fasting increase risk. Elderly patients, those with cancer, and post-surgical patients are particularly vulnerable.

2.2 Demographics¶

SRM is prevalent in hospitalized patients with prolonged semi-starvation. CDM is common in patients with chronic diseases, while ADM is associated with acute critical illnesses.

3. ETIOLOGY & PATHOPHYSIOLOGY¶

Malnutrition arises from energy deficiency, systemic inflammation, or protein catabolism. SRM results from prolonged starvation, while CDM is driven by chronic inflammation and organ dysfunction. ADM occurs due to acute tissue injury and systemic inflammation.

3.1 Protein-Catabolic States¶

Systemic inflammation and critical illness increase protein catabolism. Patients may excrete 15 g N/day in urine, leading to significant muscle and tissue loss.

3.2 Role of Inflammation¶

Inflammation increases amino acid demand, reduces albumin synthesis, and alters nutrient metabolism. It exacerbates muscle wasting and impairs nutrient utilization.

4. CLINICAL FEATURES¶

Key features include generalized muscle loss, weakness, fatigue, and impaired functional mobility. Patients may present with weight loss, edema, and frailty. Systemic inflammation worsens outcomes and complicates diagnosis.

4.1 Physical Findings¶

Muscle atrophy, subcutaneous fat depletion, and edema are common. Visual BMI assessment helps estimate dry body weight in obese or edematous patients.

4.2 Laboratory Findings¶

Low serum albumin, elevated C-reactive protein, and hypoalbuminemia indicate systemic inflammation. Urinary urea nitrogen and nitrogen balance assessments help quantify protein loss.

5. DIFFERENTIAL DIAGNOSIS¶

Distinguish SRM, CDM, and ADM based on etiology and clinical context. SRM is due to prolonged starvation, CDM from chronic inflammation, and ADM from acute critical illness.

5.1 SRM vs. CDM¶

SRM is caused by food deprivation, while CDM results from chronic inflammation and organ dysfunction. Both involve muscle loss but differ in etiology and metabolic responses.

5.2 ADM vs. SRM¶

ADM is an acute metabolic response to injury, whereas SRM is a chronic starvation state. ADM is associated with higher energy expenditure and rapid muscle loss.

6. INVESTIGATIONS & DIAGNOSIS¶

Diagnosis involves clinical assessment, laboratory tests, and imaging. Key indicators include BMI, serum albumin, C-reactive protein, and nitrogen balance. Visual BMI and bedside ultrasound aid in assessing muscle mass.

6.1 Laboratory Tests¶

Serum albumin, prealbumin, C-reactive protein, and electrolytes are critical. Urinary urea nitrogen and nitrogen balance help quantify protein loss.

6.2 Imaging and Biomarkers¶

Computed tomography (CT) and ultrasound assess body composition. Biomarkers like serum ferritin and transferrin saturation help identify micronutrient deficiencies.

7. MANAGEMENT & TREATMENT¶

EN is preferred for functional gastrointestinal tracts. PN is used when EN is not feasible. Nutritional formulas must balance protein, carbohydrates, and lipids to meet metabolic demands.

7.1 Enteral Nutrition¶

Standard polymeric formulas provide 1000–2000 kcal/L with 50–70 g protein/L. Elemental formulas are used for malabsorption. Protein-enriched formulas increase amino acid delivery.

7.2 Parenteral Nutrition¶

PN solutions include amino acids, glucose, lipids, electrolytes, and micronutrients. Lipid infusion rates should not exceed 50 g/day in ADM. Insulin management is critical to prevent hyperglycemia.

8. PROGNOSIS & COMPLICATIONS¶

Prognosis depends on underlying disease and nutritional intervention. Complications include refeeding syndrome, infections, and metabolic derangements. Early EN reduces mortality in critical illness.

8.1 Refeeding Syndrome¶

Rapid carbohydrate reintroduction in malnourished patients causes hypophosphatemia, hypokalemia, and cardiac arrhythmias. Monitoring electrolytes and gradual refeeding are essential.

8.2 Complications of PN¶

Infections, metabolic derangements, and liver dysfunction are risks. PN should be avoided in patients with severe hepatic or renal failure unless necessary.

9. SPECIAL CONSIDERATIONS¶

Special populations require tailored approaches. Elderly patients, cancer patients, and those with advanced dementia benefit from early nutritional intervention. Postoperative patients may require EN to reduce complications.

9.1 Elderly Patients¶

Sarcopenia and frailty increase risk of malnutrition. Early EN and physical rehabilitation improve outcomes. Nutritional support should address both protein and micronutrient deficiencies.

9.2 Cancer Patients¶

Cancer-related inflammation and catabolism require high-protein, high-calorie nutrition. EN is preferred over PN to minimize complications and improve tolerance.

10. KEY POINTS & CLINICAL PEARLS¶

EN is preferred over PN for functional gastrointestinal tracts.
SRM, CDM, and ADM require distinct management strategies based on etiology.
Refeeding syndrome is a critical complication requiring close electrolyte monitoring.
Early nutritional intervention improves outcomes in critical illness and chronic disease.
Micronutrient deficiencies (iron, zinc) are common and require targeted supplementation.