Nutritional Support in the ICUNutritional Support in the ICU

Reasons for SupportReasons for Support

Limit catabolism

Substrate for healing

Increase survival

Baseline Patient AssessmentBaseline Patient Assessment

History of weight loss

% ideal body weight

Immune studies• anergy, total lymphocyte count

Serum proteins• albumin, transferrin, prealbumin

Measurement of lean body mass

Surgery: Scientific Principles and PracticeSurgery: Scientific Principles and Practice

Stimuli for Stress ResponseStimuli for Stress Response

Blood volume

pH/pCO2/pO2

Emotion/pain/fear

Substrate availability

Temperature

Infection

Tissue injury

Goals of Stress ResponseGoals of Stress Response

Maintain energy substrates (GLUCOSE)

Maintain oxygen delivery

Minimize further injury

Greenfield 1997

Response to Stress/InjuryResponse to Stress/Injury

Neurohormonal - “Counterregulatory Hormones”• Glucagon

• Epinephrine

• Glucocorticoids

Inflammatory Mediators• IL-1, IL-2, IL-6

• TNF-a

• IFN-g

Glucose Dependent OrgansGlucose Dependent Organs

Brain(ketoadaptive)

RBC, WBC

Healing tissue

Renal medulla

Glucose PrecursorsGlucose Precursors

Pyruvate/lactate

Alanine/glutamine

Glycerol

Glycogen

Energy Substrates: CarbohydratesEnergy Substrates: Carbohydrates

Glucose - parallels degree of injury

Increased hepatic production of 3 - carbon precursors (fat/AAs)

Breakdown of liver glycogen

Energy Substrates: Amino AcidsEnergy Substrates: Amino Acids

Skeletal muscle breakdown skewed toward alanine and glutamine

Muscle nitrogen transferred to visceral organs• Glutamine major source for enterocyte oxidation• Glutamine transfers ammonia groups in kidney• Alanine in liver leads to gluconeogenesis

Greenfield 1997

Energy Substrates: FatEnergy Substrates: Fat

Lipolysis under catecholamine regulation

Provides 3-carbon fragments to the liver

Major provider of energy substrates in early sepsis and trauma (regulated through leptin?)

Metabolic NeedsMetabolic Needs

Formulae: (starting point for feeding)• Harris-Benedict Equation• Ireton Jones Equation

Nitrogen Balance

Resting Energy Expenditure

Goal Calculations: Goal Calculations: Ireton JonesIreton Jones

Developed for intubated patients

1784 - 11(A) + 5(W) + 244(S) + 239(T) + 804(B) for total calorie prescription

A = age W = wt in kg S = sex (1 = male, 0 = female) T = trauma (1 = yes, 0 = no) B = burns (1 = yes, 0 = no)

Harris-Benedict EquationHarris-Benedict Equation

Estimates Basal Metabolic Rate (BMR):• Male BMR kcal/day =

66.47 + 13.7 (kg) + 5 (cm) - 6.76 (yrs)

• Female BMR kcal/day =

665.1 + 9.56 (kg) + 1.85 (cm) - 4.68 (yrs)

Harris-Benedict Equationhttp://www-users.med.cornell.edu/~spon/picu/calc/beecalc.htm

Harris-Benedict EquationHarris-Benedict Equation

Factors to add to the BMR:• 25%

- mild peritonitis, long bone fracture or mild/moderate trauma

• 50%- severe infection, MSOD, severe trauma

• 100%- burn of 40 to 100% TBSA

Nitrogen BalanceNitrogen Balance

Measure/estimate all sources of nitrogen output• stool, urine, skin, fistulae, wounds, etc.

Measure all sources of nitrogen input• enteral or parenteral nutrition

Greenfield 1997

Calculating Nitrogen BalanceCalculating Nitrogen Balance

Problems with Nutritional ParametersProblems with Nutritional Parameters

UUN will be invalid if creatinine clearance is

less than 50.less than 50.

UUN and prealbumin are not helpful if the patient has not

received goal volumes of feeding consistently for three

to four days prior to the test.

Metabolic CartMetabolic CartIndirect Calorimetry: Indirect Calorimetry: TheoryTheory

Measures O2 absorbed in lungs

Assumptions of Fick equation, at steady state O2 absorbed equals O2 consumed

Metabolic rate in cc of O2 per minute

Conversion 5kcal/liter O2

24 hour steady state measurement recommended

Theory - start with a formula, tune it up long-term with the metabolic cart!

Metabolic Cart - Indirect Calorimetry: Metabolic Cart - Indirect Calorimetry: ResultsResults

RQ or respiratory quotient (CO2 expired/O2 inspired)

0.6 - 0.7 starvation/underfeeding

0.84 - 0.86 desired range/mixed fuel utilization

0.9 - 1.0 carbohydrate metabolism

1.0 + overfeeding/lipogenesis

Other Clinical ParametersOther Clinical Parameters

Wound healing

Measured proteins• Albumin (t½ = weeks)

• Prealbumin (t½ = days)

Non-water weight gain

Enteral vs. Parenteral?Enteral vs. Parenteral?

Use the GI tract whenever possible

Contraindications to GI feeds• large output fistula

• SBO

• severe pancreatitis

• short gut, severe diarrhea, enteritis

• non-functional GI tract

Starting EstimatesStarting Estimates

Determine number of calories needed

Determine normal or increased protein needs

Determine if contraindication to fats

Determine fluid restrictions

USE THE GI TRACT IF POSSIBLE

NutrientsNutrients

Fat - essential linolenic, linoleic, arachidonic acids• 9 kcal/gm

Protein - essential and branched chain AA in TPN• 4 kcal/gm - not to be included in calorie estimates

• no glutamine in TPN due to instability

Carbohydrates - converted to glucose• 3.4 kcal/gm (4.0 kcal from endogenous source)

NutrientsNutrients

Trace Minerals• Chromium, copper, zinc, manganese, selenium, iron

Vitamins• Thiamine

• Folate

• Vitamin C

Rules of Thumb: TPNRules of Thumb: TPN

Want 25 - 35% solution of dextrose

Want 4.25 - 6% AA solution• normal 0.8 gm/kg/day up to 2.0 gm/kg/day

Kcal/nitrogen ratio• normal 300:1

• post-op 150:1

• trauma/sepsis 100:1

Lipids 10 - 20% at least twice per week

TPN ExampleTPN Example

2 liters of 25% dextrose• 500 gm dextrose X 3.4 Kcal/gm = 1700 Kcal

500 cc of 20% lipids• 100 gm lipids X 9 Kcal/gm = 900 Kcal

TPN vs. Enteral: Advantages?TPN vs. Enteral: Advantages?

Many prospective, randomized studies• TPN group had much higher infection rates

- pneumonia, intraabdominal abscess, line sepsis

Potential Reasons for TPN FailurePotential Reasons for TPN Failure

TPN increases blood glucose if not strictly controlled• numerous studies now show hyperglycemia increases mortality and

infectious complications

Does not contain glutamine

Why Enteral?Why Enteral?

Preservation of villous architecture• may prevent translocation

• role of translocation unclear in humans

• good study in BMT patients

Ability to give glutamine• major fuel of enterocytes

• major nitrogen transfer agent to viscera

• in catabolic stress may be an essential AA

Timing of Enteral FeedsTiming of Enteral Feeds

Many studies claim benefits to early EN

Meta-analysis (Marik and Zaloga Crit Care Med. 2001)

• looked at 27 randomized,prospective studies

• early EN had lower infections (RR 0.45)

• early EN had shorter LOS (2.2 days)

RefluxReflux

80% reflux with NG in supine position

50% reflux without NG in supine position

12.5% reflux without NG if semi-recumbent

Gastric vs. Post-pyloric FeedsGastric vs. Post-pyloric Feeds

Route probably not important if patient tolerating feeds

If gastric ileus, recent surgery, or need for frequent procedures where feeds would be stopped if gastric, post-pyloric may be better.

Anabolic Steroids (Oxandrolone)Anabolic Steroids (Oxandrolone)

Hart et al. Annals of Surgery. 2001 • increases muscle protein net balance

Wolf et al. Annals of Surgery. 2003• improves net protein balance

Demling. J Trauma. 1997 • increases weight gain in recovery phase post burns

NO data that LOS different

Physical therapy assessments were better

Refeeding SyndromeRefeeding Syndrome

In severely malnourished

Development of severe electrolyte abnormalities:• phosphorous, potassium, magnesium

As muscle mass, cell mass, and ATP repleted:• may reach critically low values, cardiac arrest

Theoretical Advantages of Early Enteral Theoretical Advantages of Early Enteral NutritionNutrition

1. Ameliorate the stress response, hypermetabolism, and hypercatabolism.

2. Provide gut stimulation to prevent atrophy and the loss of immunologic and barrier functions of the gut.

3. Minimize rapid onset of acute malnutrition.

4. Decrease LOS and complication rates.

Energy Requirement in Critical Illness: Energy Requirement in Critical Illness: Different ConditionsDifferent Conditions

Greenfield 1997

Total Kcal GoalsTotal Kcal Goals

25 - 35 kcal/kg is suitable for most hospitalized patients and is a good rule of thumb

21 kcal/kg is appropriate for obese patients

30 - 40 kcal/kg may be necessary for highly stressed patients

Total Protein GoalsTotal Protein Goals

1.0 g/kg for healthy individuals

1.2 - 1.5 g/kg for mildly stressed

1.5 - 2.0 severely stressed/multiple trauma/head injury/burns

Lipid GoalsLipid Goals

High calorie, low volume

Suggested max calories - no more than 50% of non-protein Kcal, or < 1 cal/Kg/hr

Minimum to prevent EFAD is 2 x 500 cc bottles/week

Diprivan (propofol) = 1calorie/ml

Nutritional AlgorithmNutritional Algorithm

Greenfield 1997

Consequences of OverfeedingConsequences of Overfeeding

1. Azotemia - patients > 65 years and patients given > 2g/kg protein are at risk.

2. Fat-overload syndrome - recommended maximum is 1g lipid/kg/d. Infuse IV lipid slowly over 16 - 24 hours.

3. Hepatic steatosis - patients receiving high carbohydrate, very low fat TPN are at risk.

4. Hypercapnia - makes weaning difficult.

5. Hyperglycemia - increases risk of infection. Glucose should not exceed 5 mg/kg/min (4 mg/kg/min for diabetics).

Consequences of OverfeedingConsequences of Overfeeding

6. Hypertonic dehydration - can be caused by high-protein formula with inadequate fluid provision.

7. Hypertriglyceridemia - propofol, high TPN lipid loads, and sepsis increase the risk. If the patient is hypertriglyceridemic, decrease lipid to an amount to prevent EFAD (500 cc 10% lipid twice weekly) and monitor.

Consequences of OverfeedingConsequences of Overfeeding

8. Metabolic acidosis - patients receiving low ratios of energy to nitrogen are at risk. Acidosis can cause muscle catabolism and negative nitrogen balance.

9. Refeeding syndrome - common in malnourished patients or those held NPO prior to initiation of feeding. Start feedings conservatively, advance gradually, and monitor Mg, Ph, and K closely.

Nutritional GoalsNutritional Goals

Feed as soon as hemodynamically stable, after adequate resuscitation.

No disease state improves with starvation.

Poor gut perfusion may contraindicate enteral feeds, but enteral feeds are always preferred when possible.

Clinical Scenario 1Clinical Scenario 1

42-year-old 80-kg man with 40% burn needs approximately how many calories?

Harris Benedict Equation• Male BMR kcal/day =

– 66.47 + 13.7 (kg) + 5 (cm) - 6.76 (yrs)

BEE = 1793 kcal/day

Calorie requirement (adding stress factor of 2.2 for burn > 40%) = 3,945 kcal/day

Scenario 1 Scenario 1 (cont.)

Ireton Jones Equation• 1784 - 11(A) + 5(W) + 244(S) + 239(T) + 804(B) for total calorie

prescription

• A = age W = wt in kg S = sex (1 = male, 0 = female) T = trauma (1 = yes, 0 = no) B = burns

1,910 kcal/day - This does not take into account specific stress factors based on size of wounds, activity, fever, etc.

Scenario 2Scenario 2

A 65-year-old female patient develops pneumonia and respiratory failure.

She is known to have COPD and diabetes mellitus.

You are unsuccessful in initial weaning attempts.

What are the main nutritional issues as they relate to this patient?

Scenario 2Scenario 2

What are the caloric needs?

What means of nutrition would you use?

When discussing nutrition:• What are the issues relating to COPD? Diabetes? Difficult to wean

patients?

ReferencesReferences

1. Marik PE. Zaloga GP. Early enteral nutrition in acutely ill patients: a systematic review. Crit Care Med. 2001;29(12):2264-70.

2. McClave SA, et al. Poor validity of residual volumes as a marker for risk of aspiration in critically ill patients. Crit Care Med. 2005;33(2);449-50.

3. Souba WW, Austen WG. Nutrition and Metabolism. In Mulholland MW, Oldham KT, et al (eds). Surgery: Scientific Principles and Practice. 2nd ed. Greenfield LJ, Lippincott-Raven, New York, 1997.

ReferencesReferences

4. Hart DW, et al. Anabolic effects of oxandrolone after severe burn. Annals of Surgery. 2001;233(4):556-64.

5. Wolf SE, et al. Improved net protein balance, lean mass, and gene expression changes with oxandrolone treatment in the severely burned. Annals of Surgery. 2003;237(6):801-10; discussion 810-1.

6. Demling RH. DeSanti L. Oxandrolone, an anabolic steroid, significantly increases the rate of weight gain in the recovery phase after major burns. J Trauma-Inj Inf Crit Care. 1997;43(1):47-51.