Perioperative nutrition support

1. Nutrition
. . . and the surgical patient
Carli Schwartz, RD,LDN

2. Nutrition and Surgery
 Malnutrition may compound the severity of
complications related to a surgical procedure
 A well-nourished patient usually tolerates
major surgery better than a severely
malnourished patient
 Malnutrition is associated with a high incidence of
operative complications and death.

3. Normal Nutrition (EatRight.org)

4. The Newest Food Guide
Pyramid
 Balancing Calories ● Enjoy your food, but eat less. ● Avoid oversized portions.
 Foods to Increase ● Make half your plate fruits and vegetables. ● Make at least half
your grains whole grains. ● Switch to fat-free or low-fat (1%) milk.
 Foods to Reduce ● Compare sodium in foods like soup, bread, and frozen meals ―
and choose the foods with lower numbers. ● Drink water instead of sugary drinks.
 Website: http://www.choosemyplate.gov/
 Includes interactive tools including a personalized daily food plan and food tracker

5. Macronutrients
 Carbohydrates
 Main sources include grains, fruits and beans
 Limited storage capacity, needed for CNS (glucose) function
 Yields 3.4 kcal/gm
 Recommended 45-65% total daily calories.
 Fats
 Main sources include oil, nuts, butter, milk and cheese
 Major endogenous fuel source in healthy adults
 Yields 9 kcal/gm
 Too little can lead to essential fatty acid (linoleic acid) deficiency and
increased risk of infections
 Recommended 20-30% of total caloric intake
 Protein
 Main sources include fish, beef, poultry and dairy products
 Needed to maintain anabolic state (match catabolism)
 Yields 4 kcal/gm
 Must adjust in patients with renal and hepatic failure
 Recommended 10-35% of total caloric intake.

6. Normal Nutrition
 Requirements
HEALTHLY male/female
(weight maintenance)
• Caloric intake=25-30 kcal/kg/day
• Protein intake=0.8-1gm/kg/day
(max=150gm/day)
• Fluid intake=~ 30 ml/kg/day

7. Nutritional Needs for the
Surgery Patient

8. Comparison of Protein/Energy
Demands
SURGERY PATIENT
Caloric intake
*Mild stress, inpatient
25-30 kcal/kg/day
*Moderate stress, ICU patient
30-35 kcal/kg/day
*Severe stress, burn patient
30-40 kcal/kg/day
Protein intake
1-2 gm/kg/day
Fluid intake
INDIVIDUALIZED
HEALTHLY 70 kg MALE
Caloric intake
25-30 kcal/kg/day
Protein intake
0.8-1gm/kg/day
(max=150gm/day)
Fluid intake
30 ml/kg/day

9.  The surgical patient . . . .
 Nutrient depletion occurs in the surgical patient due to
decreased intake, increased metabolic expenditure and altered
nutrient use.
 Increased risk of malnutrition due to:
 Inadequate nutritional intake
 Metabolic response (hypermetabolism from long term
inflammation or infectious conditions)
 Nutrient losses without proper replenishment
 Protein /energy store depletion
 Diminished nutrient intake (pre/post operative)
 Prevalence of GI obstruction, anorexia, malabsorption
 Extraordinary stressors (surgical stress, hypovolemia, sepsis,
bacteremia, medications)
 Wound healing
 Anabolic state, higher demand for nutrients (amino acids,
zinc, vitamin A & C, arginine)

10. Perioperative Nutritional
Assessment
 Individuals are generally classified as well nourished or mildly,
moderately, or severely malnourished
 1: well nourished: no significant weight change; preoperative serum
albumin > 3.5 g/dL
 2. Mildly malnourished: <10% wt loss; preoperative serum albumin
3.2-3.5 g/dL
 3. Moderately malnourished: 10-20% wt loss; preoperative serum
albumin 2.5-32 g/dL
 4. Severely malnourished: >20% wt loss; preoperative serum
albumin < 2.5 g/dL
 Nutritional assessment parameters also include a complete medical
history, surgical history, social history, diet history, physical exam,
anthropometric and laboratory evaluations.

11. Visceral Proteins
 Albumin
 Normal range: 3.5-5 g/dL.
 Synthesized in and catabolized by the liver
 Pro: often ranked as the strongest predictor of surgical
outcomes- inverse relationship between postoperative
morbidity and mortality compared with preoperative
serum albumin levels
 Con: lack of specificity due to long half-life
(approximately 20 days). Not accurate in pt’s with liver
disease or during inflammatory response

12. Visceral proteins
 Prealbumin (transthyretin) - transport protein for thyroid
hormone, synthesized by the liver and partly catabolized by
the kidneys.
 Normal range:16 to 40 mg/dL; values of <16 mg/dL are associated
with malnutrition.
 Pro: Shorter half life (two to three days) making it a more favorable
marker of acute change in nutritional status. A baseline
prealbumin is useful as part of the initial nutritional assessment if
routine monitoring is planned.
 Cons: More expensive than albumin. Levels may be increased in
the setting of renal dysfunction, corticosteroid therapy, or
dehydration, whereas physiological stress, infection, liver
dysfunction, and over-hydration can decrease prealbumin levels.

13. Visceral proteins
 Transferrin: acute-phase reactant and a
transport protein for iron
 normal range: 200 to 360 mg/dL.
 Medium half-life (8-10 days)
 Smaller body pool than albumin, reflects more acute
changes.
 influenced by several factors, including liver disease,
fluid status, inflammation, iron status and illness.
 Cons: not studied extensively as albumin and pre-
albumin in relation to nutritional status, may indicator
more about iron metabolism
 Levels decrease in the setting of severe malnutrition,
however unreliable in the assessment of mild
malnutrition

14. Other measures of nutrition
status
 Nitrogen balance: the relationship between the amount of
nitrogen taken into the body, usually as food, and that excreted
from the body in urine and feces. Most of the body's nitrogen is
incorporated into protein.
 Protein ~ 16% nitrogen
 Protein intake (gm)/6.25 - (UUN +4)= balance in
grams
 Positive value: found during periods of growth, tissue repair or pregnancy. This means
that the intake of nitrogen into the body is greater than the loss of nitrogen from the body,
so there is an increase in the total body pool of protein.
 Negative value: can be associated with burns, fevers, wasting diseases and other serious
injuries and during periods of fasting. This means that the amount of nitrogen excreted
from the body is greater than the amount of nitrogen ingested.
 Healthy Humans= Nitrogen Equilibrium
 Cons: Complex determination of balance, measures
of losses difficult and limited utility in clinical setting

15. Feeding the patient: Post-
operative Nutrient Provision

16. Traditional Method: Diet
advancement
 Introduction of solid food depends on the
condition of the GI tract.
 Oral feeding delayed for 24-48 hours after surgery
 Wait for return of bowel sounds or passage of flatus.
 Start clear liquids when signs of bowel function
returns
 Rationale
 Clear liquid diets supply fluid and electrolytes that
require minimal digestion and little stimulation of the
GI tract
 Clear liquids are intended for short-term use due
to inadequacy

17. Things to Consider…
 For liquid diets, patients must have adequate
swallowing functions
 Even patients with mild dysphagia often require
thickened liquids.
 Must be specific in writing liquid diet orders for
patients with dysphagia
 There is no physiological reason for solid foods not to be
introduced as soon as the GI tract is functioning and a few
liquids are being tolerated. Multiple studies show patients
can be fed a regular solid-food diet after surgery without
initiation of liquid diets.

18. Diet Advancement
 Advance diet to full liquids followed by solid
foods, depending on patient’s tolerance.
 Consider the patient’s disease state and any
complications that may have come about since
surgery.
 Ex: steroid-induced diabetes in a post-kidney
transplant patient.

19. Patients who cannot eat . . . ?
Consider Nutrition Support!

20. Perioperative Nutritional
Support
 Length of time a patient can remain NPO
after surgery without complications is
unknown, however depends on:
 Severity of operative stress
 Patient’s preexisting nutritional status
 Nature and severity of illness
 “In uncomplicated cases, well nourished patients tolerate up to 10
days of starvation with no medical complications. Moderately or
severely malnourished patients usually require nutritional support
earlier.” (A.S.P.E.N Nutrition Support Practice Manual 2nd
Ed)

21. Goals of perioperative
Nutrition Support
 Decrease surgical mortality
 Decrease surgical complications and infection
 Reduce the catabolic state and restore anabolism
 Support the depleted patient throughout the catabolic
phase of recovery
 Decrease hospital LOS
 Speed the healing/recovery process
 Ensure the prompt return of GI function to resume
standard oral intake as soon as possible

22. Perioperative Nutrition
Support Guidelines
 The American Society for Parenteral and
Enteral Nutrition evidence-based practice
guidelines
 1. preoperative specialized nutrition support should be
administered for 7-14 days to moderately or severely
malnourished pts undergoing major surgery
 2. PN should not be routinely given in the immediate post-op
period to pts undergoing major GI procedures
 3. Postoperative nutrition support should be administered to
patients who are expected to be unable to meet their nutrient
needs orally for 7-10 days

23. Nutrition support: Clinical
Decision Algorithm
AAFP.org

24. Nutrition Support
 Enteral Nutrition Support
 Parenteral Nutrition support

25. What is enteral nutrition?
 Enteral Nutrition
 Also called "tube feeding," enteral nutrition is a
liquid mixture of all the needed nutrients.
 Consistency is sometimes similar to a milkshake.
 It is given through a tube in the stomach or small
intestine.
 If oral feeding is not possible, or an extended
NPO period is anticipated, an access devise for
enteral feeding should be inserted at the time of
surgery.
 Feeds can meet 100% of patient’s needs or can
be used to supplement poor po intake.

26. Indications for Enteral
Nutrition
When the GI tract is functional or partially
functional and…..
 Patient has inability to consume or absorb
adequate nutrients.
 Patient is not meeting > 75% of needs with
po intake.
 Malnourished patient expected to be unable
to eat adequately for > 5-7 days
 Adequately nourished patient expected to be
unable to eat > 10 days

27. Contraindications to Enteral
Nutrition Support
 Expected need less than 5-7 days if malnourished or 7-9
days if normally nourished
 Severe acute pancreatitis
 Small bowel obstruction, ileus or high output enteric
fistula distal to feeding tube
 Inability to gain access
 Hemodynamic instability
 Need for high dose pressors/vasoactives
 MAP consistently < 60 mmHg
 Intractable vomiting or diarrhea
 Those requiring massive fluid resuscitation

28. Enteral Access Devices
 Nasogastric
 Nasoenteric
 Gastrostomy
 PEG (percutaneous endoscopic gastrostomy)
 Surgical or open gastrostomy
 Jejunostomy
 PEJ (percutaneous endoscopic jejunostomy)
 Surgical or open jejunostomy
 Transgastric Jejunostomy
 PEG-J (percutaneous endoscopic gastro-jejunostomy)
 Surgical or open gastro-jejunostomy

29. Feeding Tube Selection
1) Can the patient be fed into the stomach, or
is small bowel access required?
2) How long will the patient need tube
feedings?

30. Gastric vs. Small Bowel
Access
 Gastric access: “If the stomach empties, use it.”
 Indications to consider small bowel access:
 Gastroparesis / gastric ileus
 Recent abdominal surgery
 Sepsis
 Significant gastroesophageal reflux
 Pancreatitis
 Aspiration
 Ileus
 Proximal enteric fistula or obstruction

31. Short-Term vs. Long-Term
Tube Feeding Access
 No standard of care for cut-off time between
short-term and long-term access
 However, if patient is expected to require
nutrition support longer than 6-8 weeks, long-
term access should be considered

32. Choosing Appropriate
Formulas
 Categories of enteral formulas:
 Polymeric
 Whole protein nitrogen source, for use in patients with normal or near
normal GI function. Examples include Ensure and Jevity.
 Monomeric or elemental
 Predigested nutrients; most have a low fat content or high % of MCT;
for use in patients with severely impaired GI function. Examples
include Peptamen and Optimental
 Disease specific
 Formulas designed for feeding patients with specific disease states
 Formulas are available for respiratory disease, diabetes, renal failure,
hepatic failure, and immune compromise. Examples include Glucerna
and Nepro
*well-designed clinical trials may or may not be available

33. Tulane Enteral Nutrition
Product Formulary

34. Complications of Enteral
Nutrition Support
 Issues with access, administration, GI
complications, metabolic complications.
These include:
 Nausea, vomitting, diarrhea, constipation, delayed
gastric emptying, malabsorption, refeeding
syndrome, hyponatremia, microbial
contamination, tube obstruction, leakage from
ostomy/stoma site, micronutrient deficiencies.

35. Implementation of Enteral
Nutrition
 Gastric feeding
 Pump assisted: Continuous feeding and cyclic feeding
 Allows for max nutrient absoroption and improved tolerance
 best in sicker/hospitalized patients
 Start at rate 30 mL/hour and advance in increments of 20 mL q 8
hours to goal. Check gastric residuals q 4 hours for tolerance
 Gravity Controlled: Bolus feeding
 Infusion of a predetermined volume of formula at specified
intervals. Example: 1 can Glucerna (240 ml) via PEG tube q 4
hours.
 Easiest, least expensive, more physiologic (mimic normal eating
pattern)
 Small bowel feeding
 Continuous feeding only; do not bolus due to risk of dumping
syndrome
 Start at low volume to assess tolerance (20 mL/hour)
 Advance in increments of 20 mL q 8 hours to goal
 Do not check gastric residuals

36. Determining Your Enteral
Nutrition Prescription
1. Estimate energy, protein, and fluid needs
2. Select most appropriate enteral formula
3. Determine continuous vs. bolus feeding
4. Determine goal rate to meet estimated
needs
5. Write/recommend the enteral nutrition
prescription

37. Enteral Nutrition Case Study
 78-year-old woman admitted with new CVA
 Significant aspiration detected on bedside
swallow evaluation and confirmed with modified
barium swallow study; speech language
pathologist recommended strict NPO with
alternate means of nutrition
 PEG placed for long-term feeding access
 Plan of care is to stabilize the patient and
transfer her to a long-term care facility for
rehabilitation

38. Enteral Nutrition Case Study
(continued)
 Height: 5’4” IBW: 120# +/- 10%
 Weight: 130# / 59kg 100% IBW
 BMI: 22
 Usual weight: ~130# no weight change
 Estimated needs:
 1475-1770 kcal (25-30 kcal/kg)
 59-71g protein (1-1.2 g/kg)
 1770 mL fluid (30 mL/kg)

39. Enteral Nutrition Prescription
 Tube feeding via PEG with full strength
Jevity 1.2
 Initiate at 30 mL/hour, advance by 20 mL q 8
hours to goal
 Goal rate = 55 mL/hour continuous infusion
 Above goal will provide 1584 kcal, 73g protein, 1069
mL free H2O
 Give additional free H2O 175 mL QID to meet
hydration needs and keep tube patent
 Check gastric residuals q 4 hours; hold feeds for
residual > 200 mL
 Keep HOB > 30° at all times

40. What is parenteral nutrition?
 Parenteral Nutrition
 also called "total parenteral nutrition," "TPN," or
"hyperalimentation."
 Defined as nutrients provided intravenously.
 Components of a PN mixture include:
 Protein (Amino Acids) , carboydrates (dextrose) , Fats
(Long-chain fatty acids), sterile water, electrolytes,
vitamins and trace minerals
 For use in nutritionally compromised patients
when enteral nutrition is contra-indicated.

41. Indications for Parenteral
Nutrition Support
 Malnourished patient expected to be unable
to eat > 5-7 days AND enteral nutrition is
contraindicated
 Patient failed enteral nutrition trial with
appropriate tube placement (post-pyloric)
 Enteral nutrition is contraindicated or severe
GI dysfunction is present
 Paralytic ileus, mesenteric ischemia, small bowel
obstruction, enteric fistula distal to enteral access
sites

42. PPN vs. TPN
 TPN (total parenteral nutrition)
 High glucose concentration (15%-25% final dextrose
concentration)
 Provides a hyperosmolar formulation (1300-1800
mOsm/L)
 Must be delivered into a large-diameter vein
 PPN (peripheral parenteral nutrition)
 Similar nutrient components as TPN, but lower
glucose concentration (5%-10% final dextrose
concentration)
 Osmolarity < 900 mOsm/L (maximum tolerated by a
peripheral vein)
 May be delivered into a peripheral vein
 Because of lower concentration, large fluid volumes
are needed to provide a comparable calorie and
protein dose as TPN

43. Parenteral Access Devices
 Peripheral venous access
 Catheter placed percutaneously into a peripheral
vessel
 Central venous access (catheter tip in SVC)
 Percutaneous jugular, femoral, or subclavian
catheter
 Implanted ports (surgically placed)
 PICC (peripherally inserted central catheter)

44. Writing TPN prescriptions
1. Determine total volume of formulation based on
individual patient fluid needs
2. Determine amino acid (protein) content
Adequate to meet patient’s estimated needs
1. Determine dextrose (carbohydrate) content
~70-80% of non-protein calories or ~50% calorie needs
1. Determine lipid (fat) content
~20-30% non-protein calories
1. Determine electrolyte needs
2. Determine acid/base status based on chloride and co2
levels
3. Check to make sure desired formulation will fit in the
total volume indicated

45. Parenteral Nutrition
Prescription
 Important items to consider:
 Glucose infusion rate should be < 5 mg/kg/minute
(maximum tolerated by the liver) to prevent
hepatic steatosis
 Lipid infusion should be < 0.1 g/kg/hour (ideally <
0.4 g/kg/day to minimize/prevent TPN-induced
liver dysfunction)
 Initiate TPN at ~½ of goal rate/concentration and
gradually increase to goal over 2-3 days to
optimize serum glucose control

46. Tulane Daily Parenteral
Nutrition Order Form

47. Parenteral Nutrition Monitoring
 Electrolytes -adjust TPN/PPN electrolyte additives daily according to labs
 Check accu-check glucose q 6 hours
 Regular insulin may be added to TPN/PPN bag for glucose control as needed
 Check triglyceride level within 24 hours of starting TPN/PPN
 If TG >250-400 mg/dL, lipid infusion should be significantly reduced or
discontinued
 Daily addition of Carnitine to TPN/PPN may improve lipid metabolism
 ~100 grams fat per week is needed to prevent essential fatty acid deficiency
 Check LFT’s weekly
 If LFT’s significantly elevated as a result of TPN, then minimize lipids to < 1
g/kd/day and cycle TPN/PPN over 12 hours to rest the liver
 If Bilirubin > 5-10 mg/dL due to hepatic dysfunction, then discontinue trace
elements due to potential for toxicity of manganese and copper
 Check pre-albumin weekly
 Adjust amino acid content of TPN/PPN to reach normal pre-albumin 18-35 mg/dL
 Adequate amino acids provided when there is an increase in pre-albumin of ~1
mg/dL per day
 Acid/base balance
 Adjust TPN/PPN anion concentration to maintain proper acid/base balance
 Increase/decrease chloride content as needed
 Since bicarbonate is unstable in TPN/PPN preparations, the precursor—acetate
—is used; adjust acetate content as needed

48. Complications of Parenteral
Nutrition
 Hepatic steatosis
 May occur within 1-2 weeks after starting PN
 May be associated with fatty liver infiltration
 Usually is benign, transient, and reversible in patients on short-term PN and
typically resolves in 10-15 days
 Limiting fat content of PN and cycling PN over 12 hours is needed to control
steatosis in long-term PN patients
 Cholestasis
 Occurs because there are no intestinal nutrients to stimulate hepatic bile flow
 May occur 2-6 weeks after starting PN
 Indicated by progressive increase in TBili and an elevated serum alkaline
phosphatase
 *Trophic enteral feeding to stimulate the gallbladder can be helpful in
reducing/preventing cholestasis
 Gastrointestinal atrophy
 Lack of enteral stimulation is associated with villus hypoplasia, colonic mucosal
atrophy, decreased gastric function, impaired GI immunity, bacterial overgrowth,
and bacterial translocation
 *Trophic enteral feeding to minimize/prevent GI atrophy

49. Parenteral Nutrition Case
Study
 55-year-old male admitted with small bowel
obstruction
 History of complicated cholecystecomy 1 month
ago. Since then patient has had poor appetite
and 20-pound weight loss
 Patient has been NPO for 3 days since admit
 Right subclavian central line was placed and
plan noted to start TPN since patient is expected
to be NPO for at least 1-2 weeks

50. Parenteral Nutrition Case
Study
(continued)
 Height: 6’0” IBW: 178# +/- 10%
 Weight: 155# / 70kg 87% IBW
 BMI: 21
 Usual wt: 175# 11% wt loss x 1 mo.
 Estimated needs:
 2100-2450 kcal (30-35 kcal/kg)
 84-98g protein (1.2-1.4 g/kg)
 2100-2450 mL fluid (30-35 mL/kg)

51. Parenteral Nutrition
Prescription
 TPN via right-SC line
 2 L total volume x 24 hours
 Amino acid 4.5% (or 45 g/liter)
 Dextrose 17.5% (or 175 g/liter)
 Lipid 20% 285 mL over 24 hours
 Above will provide 2120 kcal, 90g protein,
glucose infusion rate 3.5 mg/kg/minute, lipid
0.9 g/kg/day

52. Benefits of Enteral Nutrition
over parenteral nutrition
 Cost
 Tube feeding cost ~ $10-20 per day
 TPN cost ~ $100 or more per day!
 Maintains integrity of the gut
 Tube feeding preserves intestinal function; it is more
physiologic
 TPN may be associated with gut atrophy
 Less infection
 Tube feeding—very small risk of infection and may
prevent bacterial translocation across the gut wall
 TPN—high risk/incidence of infection and sepsis

53. Transitional Feedings
 Parenteral to enteral feedings
 Introduce a minimal amount of enteral feeding at a low
rate (30-40 ml/hr) to establish tolerance.
 Decrease PN level slowly to keep nutrient levels at
same prescribed amount
 As enteral rate is increased by 25-30 ml/hr increments
every 8-24 hrs, parenteral can be reduced
 Discontinue PN solution if 75% of nutrient needs met
by enteral route.
 Parenteral/Enteral to oral feedings
 Ideally accomplished by monitoring oral intake and
concomitantly decreasing rate of nutrition support until
75% of needs are met.
 Oral supplements are useful if needs not met 100% by
diet. Ex (Nepro, Glucerna, Boost, Ensure).

54. Dangers of Over and Under
Feeding
 Risks associated with over-feeding:
 Hyperglycemia
 Hepatic dysfunction from fatty infiltration
 Respiratory acidosis from increased CO2 production
 Difficulty weaning from the ventilator
 Refeeding syndrome
 Risks associated with under-feeding:
 Depressed ventilatory drive
 Decreased respiratory muscle function
 Impaired immune function
 Increased infection
 Weight loss and malnutrition

55. Refeeding Syndrome
 “the metabolic and physiologic consequences of
depletion, repletion, compartmental shifts, and
interrelationships of phosphorus, potassium, and
magnesium…”
 Severe drop in serum electrolyte levels resulting from
intracellular electrolyte movement when energy is
provided after a period of starvation (usually > 7-10
days)
 Physiologic and metabolic sequelae may include:
 EKG changes, hypotension, arrhythmia, cardiac arrest
 Weakness, paralysis
 Respiratory depression
 Ketoacidosis / metabolic acidosis

56. Refeeding Syndrome
(continued)
 Prevention and Therapy
 Correct electrolyte abnormalities before starting
nutrition support
 Continue to monitor serum electrolytes after
nutrition support begins and replete aggressively
 Initiate nutrition support at low rate/concentration (~
50% of estimated needs) and advance to goal
slowly in patients who are at high risk

57. Questions
Contact Information:
Carli Schwartz, RD,LDN
Clinical Dietitian, Tulane Abdominal Transplant Institute
(504) 988-1176
Carli.Schwartz@hcahealthcare.com

58. References
 American Society for Parenteral and Enteral Nutrition. The Science and
Practice of Nutrition Support. 2001.
 Han-Geurts, I.J, Jeekel,J.,Tilanus H.W, Brouwer,K.J., Randomized
clinical trial of patient-controlled versus fixed regimen feeding after
elective abdominal surgery. British Journal of Surgery. 2001,
Dec;88(12):1578-82
 Jeffery K.M., Harkins B., Cresci, G.A., Marindale, R.G., The clear liquid
diet is no longer a necessity in the routine postoperative management of
surgical patients. American Journal of Surgery.1996 Mar; 62(3):167-70
 Reissman.P., Teoh, T.A., Cohen S.M., Weiss, E.G., Nogueras, J.J.,
Wexner, S.D. Is early oral feeding safe after elective colorectal surgery?
A prospective randomized trial. Annals of Surgery. 1995 July;222(1):73-
7.
 Ross, R. Micronutrient recommendations for wound healing. Support
Line. 2004(4): 4.
 Krause’s Food, Nutrition & Diet Therapy, 11th
Ed. Mahan, K., Stump, S.
Saunders, 2004.
 American Society for Parenteral and Enteral Nutrition. The Science and
Practice of Nutrition Support. 2001.