Nutrition in ICU

Introduction

Nutrition plays a vital role in the management of critically ill patients, influencing outcomes, recovery, immune function, and mortality. Malnutrition in ICU patients is associated with increased infection rates, prolonged mechanical ventilation, delayed wound healing, and higher mortality. A well-structured nutrition strategy is essential for optimizing patient recovery.

1. Physiological Changes in Critical Illness and Nutrition Requirements

Critically ill patients experience catabolic stress, leading to:

• Hypermetabolism → Increased energy demand
• Muscle protein breakdown → Loss of lean body mass
• Insulin resistance → Altered glucose metabolism
• Immune suppression → Increased infection risk

Energy and Macronutrient Requirements

•  
• Initiate feeding early at a reduced rate (approximately 25-50% of the caloric goal)-Providing full nutritional support during the early catabolic phase can lead to overfeeding, as the combination of exogenous nutrition and endogenous energy from catabolism may exceed the patient’s actual metabolic needs. To avoid this, full caloric targets should not be met immediately, and nutrition should be gradually increased based on the patient’s metabolic state and tolerance
• Gradually increase to 100% of target calories over 3-7 days, based on patient tolerance. Priority should be given to meeting full protein requirements(1.2 grams/kg/day ) whenever possible.

2. Nutritional Assessment in ICU

A common pitfall in nutritional assessment is misinterpreting the effects of acute illness (e.g., albumin shifts in septic shock) as indicators of underlying malnutrition.

• Acute disease effects: Conditions like sepsis, trauma, or inflammation can cause fluid shifts, hypoalbuminemia, and weight fluctuations, which may not reflect true nutritional status.

How to Assess Nutritional Risk?

Nutritional risk assessment requires clinical judgment, considering multiple factors that indicate malnutrition or inadequate intake:

• Oral intake history: Has the patient been NPO for several days or had restricted access to food?
• BMI (Body Mass Index): Low BMI may indicate chronic undernutrition, while high BMI does not necessarily rule out malnutrition (obesity-related sarcopenia).
• Recent weight loss: Unintentional weight loss over weeks to months suggests catabolic stress and malnutrition.
• Physical signs of cachexia: Temporal wasting, loss of muscle mass, and subcutaneous fat depletion(check by USG)indicate severe malnutrition.

Key Assessment Tools

1. Subjective Global Assessment (SGA) – Evaluates weight loss, dietary intake, functional status.
2. Nutritional Risk Screening (NRS-2002) – Identifies malnutrition risk in hospitalized patients.
3. Nutrition Risk in Critically Ill (NUTRIC) Score – ICU-specific scoring system incorporating APACHE II and SOFA scores.
4. Indirect Calorimetry – Gold standard for measuring energy expenditure.

NUTRIC Score Interpretation

3. Enteral vs. Parenteral Nutrition

A. Enteral Nutrition (EN)

• Preferred over parenteral nutrition as it preserves gut integrity and reduces infections,reduction in bacterial translocation, and stress ulcer prophylaxis.
• Initiated within 24-48 hours of ICU admission if no contraindications.
• Common enteral formulas:
  • Standard polymeric (normal digestion)
  • Peptide-based (malabsorption)
  • Immune-modulating (arginine, glutamine, omega-3)

Indications for Enteral Nutrition

✔️ Functioning GI tract
✔️ Unable to meet needs orally
✔️ Expected to need support >48 hours

Contraindications to Enteral Nutrition

❌ Bowel obstruction,Abdominal compartment syndrome.
❌ Ischemic gut
❌ major gastrointestinal bleeding
❌ Uncontrolled vomiting or high-output fistula

Enteral nutrition is contraindicated among patients with refractory shock or patients on high doses of vasopressors (e.g., greater than ~0.3-0.5 mcg/kg/min norepinephrine).

The following conditions are not contraindications to enteral nutrition:

• Absence of bowel sounds: This may simply indicate a lack of air in the intestines rather than dysfunction. The clinical significance of bowel sounds in decision-making has never been validated.(normal bowel sounds 5-30/min)
• Therapeutic paralysis: Paralytic agents only affect skeletal muscles, not smooth muscles like those in the intestines or pupils, meaning gut motility remains intact.
• Requirement to lie flat: While a semi-recumbent position is preferable to reduce aspiration risk, the evidence supporting this practice is weak, and feeding can still be initiated if the patient must remain supine.
• Use of vasopressors: Concerns about intestinal ischemia during shock have not been substantiated. Enteral feeding may actually enhance gut perfusion and maintain intestinal integrity. Once fluid resuscitation is complete and the patient is stable on vasopressors, enteral nutrition can be cautiously initiated at low rates.
• Open abdomen: If no bowel injury is present, enteral feeding is recommended, even in patients with an open abdomen.
• Pancreatitis: Early enteral nutrition is beneficial in severe pancreatitis, similar to its role in other critically ill patients, as supported by current evidence.

4. Specialized Nutritional Strategies in ICU

A. Immunonutrition

• Special nutrients (arginine, glutamine, omega-3, nucleotides) to enhance immune function.
• Beneficial in trauma, burns, major surgery, but controversial in sepsis.

B. Early vs. Late Feeding

• Early enteral feeding (within 24-48 hours) is associated with better outcomes.
• Late feeding (>5 days) increases infection risk and mortality.

C. Continuous vs. Bolus Feeding vs. Intermittent Tube Feeding

Benefits of Intermittent Feeding in the ICU

Intermittent feeding offers several advantages over continuous feeding, supported by research:

1. Improved insulin sensitivity – Periodic fasting may enhance insulin sensitivity, thereby reducing insulin requirements 
2. Enhanced muscle protein synthesis – The pulsatile release of insulin and amino acids following meals stimulates muscle growth and repair.
3. Better achievement of nutritional targets – Even if a patient is NPO for part of the day, intermittent feeding allows for flexible meal rescheduling, making it easier to meet daily caloric and protein goals.
4. Higher success in reaching nutritional targets – RCTs have demonstrated that intermittent feeding is more effective than continuous feeding in achieving prescribed nutritional targets .

Implementing Intermittent Tube Feeding in the ICU

1. Determine Total Volume:
   • Calculate the total daily volume of tube feeding needed.
   • Divide it into 4-6 meals, with each meal typically 240-720 mL 

2. Optimize Meal Timing:

1. • Spacing meals during daylight hours may help maintain circadian rhythm and improve metabolic regulation.

3. Administration Methods:

1. • Gravity infusion: Simple and effective, though rate control is limited.
   • Infusion pump: Modern pumps can be programmed for automatic intermittent feeding, reducing nursing workload and improving precision.

Benefits of Continous Feeding in the ICU

Despite being aphysiological, continuous feeding has benefits in specific ICU scenarios:

✅ Hemodynamically unstable or critically ill patients (reduces metabolic stress).

✅ Patients with poor gastric emptying, severe gastroparesis, or high aspiration risk (gentler on the stomach).

✅ Early enteral nutrition in sepsis or shock (better tolerated at slow infusion rates).

D. Trophic vs. Full Feeding

• Trophic feeding (minimal calorie intake, ~10-20 kcal/hr) is used in hemodynamically unstable patients.
• Full feeding (meeting 100% of energy needs) is started once stable.

E. There is little justification for stopping tube feeds before most procedures (e.g., interventional radiology), as proper sedation and analgesia minimize the risk of vomiting. Additionally, intubated patients have a protected airway, further reducing aspiration risk.

A common practice is to discontinue tube feeds at midnight if extubation is anticipated the next morning. However, in the absence of strong evidence, it may be preferable to continue feeding until a definite extubation decision is made. Before extubation, if the patient is receiving nasogastric or orogastric feeds, the stomach should be suctioned empty to minimize aspiration risk.

F. Post-pyloric feeding generally yields similar outcomes to gastric feeding in terms of mortality, ICU length of stay, and duration of mechanical ventilation. Gastric feeding is typically the first-line approach for intubated patients due to its ease of administration. However, if a patient has difficulty tolerating gastric feeding, post-pyloric feeding serves as a reasonable alternative.

5. Nutrition in Specific ICU Conditions

Feeding patients with renal or hepatic failure has long been a topic of debate. Concerns include whether protein intake worsens uremia in renal failure or exacerbates hepatic encephalopathy in cirrhosis, as well as how to approach nutrition in pancreatitis.

According to SCCM/ASPEN guidelines, these patients should be fed similarly to other ICU patients, and protein restriction is not recommended as a means to avoid dialysis or hepatic encephalopathy. Key considerations include:

• Renal failure: Standard tube feeds can be used initially. If significant electrolyte imbalances (e.g., hyperkalemia, hyperphosphatemia) occur, switching to a renal-specific formula is advised.
• Patients on dialysis: Protein requirements are higher due to losses during dialysis, with intake increased up to 2.5 g/kg/day in critically ill patients.

A. Sepsis and Critical Illness

• Early enteral nutrition is preferred.
• Avoid overfeeding (increased CO₂ production worsens respiratory failure).
• Glutamine supplementation is controversial in septic shock.

B. Acute Respiratory Distress Syndrome (ARDS)

• Avoid excessive carbohydrate intake (reduces CO₂ production).
• Omega-3 fatty acids may reduce inflammation.

C. Acute Kidney Injury (AKI)

• Protein intake:
  • No dialysis: 0.8-1.0 g/kg/day
  • On dialysis: 1.5-2.0 g/kg/day
• Fluid restriction may be necessary.

D. Liver Failure

• Use branched-chain amino acids (BCAA) to prevent hepatic encephalopathy.
• Restrict sodium and fluids to prevent ascites.

E. Burns and Trauma

• Very high protein requirements (2.0-2.5 g/kg/day).
• Increased calorie needs (30-40 kcal/kg/day).

F.According to SCCM/ASPEN guidelines, nutritional targets for critically ill obese patients are as follows:

• BMI 30-50:
  • Calories: 11-14 kcal/kg (based on actual body weight)
  • Protein: 2 g/kg (based on ideal body weight)
• BMI >50:
  • Calories: 22-25 kcal/kg (based on ideal body weight)
  • Protein: 2.5 g/kg (based on ideal body weight)

Adjusted weight = IBW + (1/3)[Actual wt – IBW]

These recommendations help ensure adequate protein intake while avoiding excessive caloric provision, which can contribute to complications like hyperglycemia and fat accumulation.

G. It is important to note that sodium content, rather than the volume of tube feeds, is the key factor affecting edema and fluid balance. Managing sodium intake is crucial in patients with fluid overload, as excessive sodium can exacerbate edema and third-spacing, regardless of total fluid volume administered.

6. Monitoring and Adjusting Nutrition

7. Complications of ICU Nutrition

Parental Nutrition

Indications 

• intestinal failure (IF) due to disease or treatment 
• (short bowel syndrome, inflammatory bowel diseases, intestinal pseudo-obstruction, radiation enteritis), 
• high-output fistulas, 
• severe intestinal obstruction
• supplemental PN is also indicated to achieve estimated nutritional requirements.
• In post surgery patient-The ESPEN guidelines on clinical nutrition in surgery recommend that if oral and enteral intake cannot cover >50% of requirements for more than 7 days, a combination of enteral nutrition and PN is recommended 

—IF has been defined as a reduction in gut functions below the minimum necessary for the absorption of nutrients from the gastrointestinal tract to maintain health and growth.

Timing

• In well-nourished patients who are not able to achieve necessary nutritional requirements after 7 days 
• In patients at risk of malnutrition, within 3–6 days, if they are unlikely to achieve satisfactory oral nutrition or EN.

Vascular Access and Administration

• Most of the Peripheral PN formulations are between 750 and 900 mOsm/L. These formulations are based on a decreased dextrose concentration and osmolarity (by increasing final volume). Therefore, patients with fluid restriction should not be candidates for PPN due to the risk of fluid overload to achieve their energy requirements. 
• Peripheral PN is recommended for short-term therapies (≤10–14 days) because of the low reliability of peripheral VADs(Vascular Access Devices).
• peripheral PN < 900 mOsm/L for pediatric patients and <800–850 mOsm/L for adults 

• For administration of hyperosmolar PN admixtures, a central VAD is needed.
• The most common insertion sites include the subclavian, internal jugular, femoral, cephalic and basilic veins.
• Central VADs four categories: peripherally inserted central catheters (PICCs), nontunneled (inserted into jugular, subclavian or femoral vein), tunneled and implanted.

Administration

• Continuous infusion-Administration over 24h enables less manipulation and a lower infusion rate, limiting the overloading of glucose as well as fluids. 
• cyclic (discontinuous) schedule-during a portion of the day or night allows the patient freedom from the intravenous tubing and pump apparatus .Cyclic PN administration has also been used as a strategy against liver impairment associated with PN. When cyclic administration is proposed, glycemia should be monitored to avoid hypoglycemia after discontinuation, as well as hyperglycemia due to the increased rate of infusion.
• Risk of infusing particulates, recommendations to use in-line filters.
• PN admixtures should be protected from light.

Composition of PN Admixtures

• In an all-in-one system, also called total PN (TPN) or total parenteral admixture (TNA), all nutrients are mixed in a single bag and infused simultaneously. 
• To reduce osmolarity, PPN should have an increased total volume as well as reduced solutes (mainly macronutrients).
• General recommendations for PPN macronutrient content are as follows: amino acids < 4%, glucose < 10%. Consequently, a lower load of amino acids and glucose is often compensated for by an increased lipid load to achieve caloric goals due to the lower osmolarity of the lipids.

Proteins

• energy (4 kal/g) 
• 6.25 g of protein = 1 g of nitrogen
• Non-protein calories per nitrogen ratio range from 125 to 225 kcal/g N for non-stressed PN patients.if non protein calories are inadequate then protein will be used as sole source of energy 
• American Society for Parenteral and Enteral Nutrition (ASPEN) guidelines, the best non-protein calories/nitrogen ratio is from 70:1 to 100:1 for critically ill .patients, reduced to 30:1 to 50:1 for obese critically ill patients 
• the usual dose of protein is 1 g/kg of body weight for unstressed healthy patients 
• The recommended dose of protein in patients with acute renal failure is 0.6–0.8 g/kg/day 
• 0.8–1 g/kg/day in chronic renal failure. 
• renal replacement therapy is implemented (1.2–1.5 g/kg/day with hemodialysis and 1.3–2 g/kg/day with continuous renal replacement therapy).
• current European Society for Clinical Nutrition and Metabolism (ESPEN) guidelines recommend BCAA-enriched formulas in patients with hepatic encephalopathy in need of EN.

Carbohydrates

• most commonly used carbohydrate substrate is dextrose
• 4 kcal/g 
• 50–60% of total daily calories.
• minimum of 130 g of carbohydrates must be provided in healthy patients. 
• Continuous dextrose infusion rates in adult patients should be kept at ≤4–7 mg/kg/min

Lipids

• Each gram of fat provides 10kcal
• 20–30% of total daily calories
• 1 g/kg body weight/day 
• The currently available IVFEs are derived from soybean, safflower, coconut, olive or fish oil. 
• Commercially available IVFEs for PN have a 20% concentration
• Coconut oil is the source of medium-chain triglycerides (MCT) in IVFE. 

Micronutrients: Electrolytes, Vitamins and Trace Elements

• Baseline serum electrolyte measurements are recommended before ordering a PN solution and then electrolytes are added accordingly. 
• vitamins and trace elements should be administered daily, and therefore routinely added to PN solutions,

Complications and Monitoring

• Hyperglycemia -the most common complication of PN.
• Lipid overload has been associated with hypertriglyceridemia and liver dysfunction.
• In stressed patients, as well as in renal impairment, lipoprotein lipase activity is decreased leading to an accumulation of lipids in blood 
• Acceptable serum triglyceride concentrations for those receiving PN are <400 mg/dL 
• a lowering of dextrose has also been suggested if hypertriglyceridemia is thought to be associated with dextrose overfeeding. 
• Refeeding Syndrome-starting with a low caloric intake (10–20 kcal/kg/day or less in extreme cases) in patients at risk of RS, increasing slowly over 4–7 days to meet requirements
• Catheter-Related Complications
• vol-overload(if weight gain>1kg/day)

Hepatobiliary Complications

• Parenteral nutrition-associated liver disease (PNALD) is a spectrum of diseases that can range from mild liver enzyme abnormalities to steatosis to eventual fibrosis or cirrhosis. 
• There are three primary types of PNALD: steatosis, cholestasis, and gallbladder sludge/stones. Patients may have one of these disorders or a combination of the three. 
• Other terms for PNALD, intestinal failure-associated liver disease (IFALD) and parenteral nutrition-associated cholestasis (PNAC).
• occurs within 2 weeks of PN initiation.  

defined biochemically as 1.5 times the upper limit of normal elevation of two out of the following liver test: gamma-glutamyl transferase or alkaline phosphatase and/or serum conjugated bilirubin ≥2 mg/dL.

Monitoring

Rbs- 3times/daily

Na,k,Cl,Hco3,bun-daily until stable then 2/weekly

Cbs,creat,albumin,ca,mg,po4-baseline then 2/week

INR-baseline then weekly

Discontinuation of TPN

• When pt meets 75% of energy or protein requirement by enteral route
• Infusion rate halved for 1 hour, then again halved then stopped(tapered tp prevent hypoglycaemia)

Total Volume Required

• 25-35ml/kg/day add  insensible loss exp 10% increase with 1 degree celsius.
• Increase or decrease acc to I/O chart

Total calorie requirement

Total energy expenditure=REE x stress factor  x Activity factor