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Nutritional Support in the ICU

Nutritional Support in the ICU. Reasons for Support. Limit catabolism Substrate for healing Increase survival. Baseline Patient Assessment. History of weight loss % ideal body weight Immune studies anergy, total lymphocyte count Serum proteins albumin, transferrin, prealbumin

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Nutritional Support in the ICU

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  1. Nutritional Support in the ICU

  2. Reasons for Support • Limit catabolism • Substrate for healing • Increase survival

  3. Baseline 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

  4. Surgery: Scientific Principles and Practice

  5. Stimuli for Stress Response • Blood volume • pH/pCO2/pO2 • Emotion/pain/fear • Substrate availability • Temperature • Infection • Tissue injury

  6. Goals of Stress Response • Maintain energy substrates (GLUCOSE) • Maintain oxygen delivery • Minimize further injury

  7. Greenfield 1997

  8. Response to Stress/Injury • Neurohormonal - “Counterregulatory Hormones” • Glucagon • Epinephrine • Glucocorticoids • Inflammatory Mediators • IL-1, IL-2, IL-6 • TNF-a • IFN-g

  9. Glucose Dependent Organs • Brain(ketoadaptive) • RBC, WBC • Healing tissue • Renal medulla

  10. Glucose Precursors • Pyruvate/lactate • Alanine/glutamine • Glycerol • Glycogen

  11. Energy Substrates: Carbohydrates • Glucose - parallels degree of injury • Increased hepatic production of 3 - carbon precursors (fat/AAs) • Breakdown of liver glycogen

  12. Energy 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

  13. Greenfield 1997

  14. Energy 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?)

  15. Metabolic Needs • Formulae: (starting point for feeding) • Harris-Benedict Equation • Ireton Jones Equation • Nitrogen Balance • Resting Energy Expenditure

  16. Goal Calculations: Ireton 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)

  17. Harris-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

  18. Harris-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

  19. Nitrogen Balance • Measure/estimate all sources of nitrogen output • stool, urine, skin, fistulae, wounds, etc. • Measure all sources of nitrogen input • enteral or parenteral nutrition

  20. Greenfield 1997

  21. Calculating Nitrogen Balance

  22. Problems with Nutritional Parameters • UUN will be invalid if creatinine clearance is 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.

  23. Metabolic CartIndirect Calorimetry: Theory • 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!

  24. Metabolic Cart - Indirect Calorimetry: Results • 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

  25. Wound healing Measured proteins Albumin (t½ = weeks) Prealbumin (t½ = days) Non-water weight gain Other Clinical Parameters

  26. 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

  27. Starting 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

  28. Nutrients • 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)

  29. Nutrients • Trace Minerals • Chromium, copper, zinc, manganese, selenium, iron • Vitamins • Thiamine • Folate • Vitamin C

  30. Rules 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

  31. TPN 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

  32. TPN vs. Enteral: Advantages? • Many prospective, randomized studies • TPN group had much higher infection rates - pneumonia, intraabdominal abscess, line sepsis

  33. TPN increases blood glucose if not strictly controlled numerous studies now show hyperglycemia increases mortality and infectious complications Does not contain glutamine Potential Reasons for TPN Failure

  34. 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

  35. 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) Timing of Enteral Feeds

  36. Reflux • 80% reflux with NG in supine position • 50% reflux without NG in supine position • 12.5% reflux without NG if semi-recumbent

  37. Gastric 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.

  38. 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

  39. Refeeding 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

  40. Theoretical Advantages of Early Enteral Nutrition 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.

  41. Energy Requirement in Critical Illness: Different Conditions Greenfield 1997

  42. Total 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

  43. Total 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

  44. Lipid 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

  45. Nutritional Algorithm Greenfield 1997

  46. Consequences 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).

  47. Consequences 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.

  48. Consequences 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.

  49. Nutritional 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.

  50. Clinical 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

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