Nutrition and Metabolism

Question 1

Baseline human calorie requirements

Answer 1

20-25 kcal/kg/day

Question 2

Baseline human protein requirement

How man kcal/g protein?

Answer 2

1g/kg/d

20% of caloric intake - 4 kcal/g of protein

Question 3

Baseline human fat requirement?

How many kcal/g fat?

Answer 3

30% of caloric intake

9 kcal/g fat (most calorie dense)

Question 4

Baseline carbohydrate requirement?

How man kcal/g carbs

Answer 4

50% of caloric intake (biggest need)

4 kcal/g carb (same as protein)

Question 5

What is the Harris-Benedict equation needed to calculate BMR?

Answer 5

• Men: BMR = (10 × weight in kg) + (6.25 × height in cm) – (5 × age) + 5
• Women: BMR = (10 × weight in kg) + (6.25 × height in cm) – (5 × age) – 161

Question 6

What is the percentage increase in nutritional requirements during multisystem trauma, surgery, or sepsis?

In kcal/kg/day, what nutritional guidelines are recommended for these patients?

Answer 6

20% - 40%

25-30 kcal/kg/d

Question 7

What is the calorie and protein nutritional requirement in a burn patient?

Answer 7

• Calories: 25 kcal/kg/d + (30 kcal/d × % burn)
• Protein: 1 g/kg/d + (3 g/d × % burn)

Question 8

Predicted increase in caloric requirements as a function of a stressor?

• Elective surgery
• Multisystem trauma
• Sepsis
• Burns

Answer 8

• Elective surgery: 1.2 times higher
• Multisystem trauma: 1.3 to 1.5 times higher
• Sepsis: 1.5 to 1.8 times higher
• Burns: 1.5 to 2.0 times higher

Question 9

Biochemical changes in the critically ill/postop patient?

• Metabolic state?
• Protein requirement?

Answer 9

• catabolic - continued proteolysis, protein requirements taken from endogenous sources if not inadequate otherwise
• protein - 1 g/kg/d to 1.5 g/kg/d in critical illness; 2 g/kg/d

Question 10

What can be given to patients to possibly decrease proteolysis?

Answer 10

small amount of carbs/fat (400 kcal/d) - protein-sparing effect

Question 11

In the setting of starvation, patients can develop resistance to insulin. This is caused by?

Answer 11

Inhibition of glucose oxidation. The body also shifts into a state of gluconeogenesis, contributing to hyperglycemia.

Question 12

How can you lessen the insulin resistance in the setting of starvation?

Answer 12

• adequate pain control, high-carb beverage 2-3 hrs before surgery
• monitor for hyperglycemia
• keep glucose 140-180 mg/dL

Question 13

When is feeding recommended in a normotensive patient with intact GI tract?

Answer 13

early enteral feeding - 24-48 hrs

NG, OG, NJ if necessary

Question 14

When is parenteral nutrition indicated?

Answer 14

• some recommend TPN at 7 days w/o ability to start enteral nutrition
• can supplement enteral if unable to tolerate full support
  
  • trophic feeds (10-30 ml/h) can help maintain GI health
• little benefit to TPN before 7 days
• TPN before 3 days increases infectious M&M compared to 8 days

Question 15

What are the negative effects of overfeeding a patient?

Answer 15

• hyperglycemia
• hypertriglyceridemia
• increased RQ - weaning failure d/t increased CO2 needing to be expired causing more work for lungs

Question 16

Pathophysiology of refeeding syndrome

Answer 16

• sudden introduction of nutrition in a malnourished patient
• stimulation of insulin release
• intracellular shift of already depleted levels of PO4, K, Mg
• decreased ATP stores cause muscle weakness
• electrolyte abnormalities can cause neuro/cardiac sx

Question 17

What are associated side effects of parenteral nutrition?

Answer 17

• electrolyte disturbances 2/2 inability of body to naturally regulate what is absorbed in gut - monitor lytes until stable formula found
• refeeding syndrome - slowly introduce nutrition
• liver dysfunction - steatosis 2/2 excess calories, micronutrient deficiency, lack of GI stimulation
• line infection - requires sterile placement, place peripherally if required long-term
• GI dysfunction - mucosal atrophy leads to loss of brush border enzymes, bacterial overgrowth, and decreased gut immunity

Question 18

What equation is used to analyze the balance of anabolism and catabolism?

Answer 18

nitrogen balance - positive balance means requirements met

(protein intake/6.25) - (UUN+4)

UUN is 24hr urine urea nitrogen

“4” is an estimate of insensible nitrogen loss

Question 19

What is the RQ and what is it used for?

Answer 19

respiratory quotient - measures nutrition adequacy by measuring energy expenditure

• RQ = CO2 produced/oxygen consumed
• RQ = 0.7 is fat utilization - ketosis and fat oxidation (starvation)
• RQ = 0.8 is protein utilization
• RQ = 1.0 is carb utilization - lipogenesis (overfeeding)

Question 20

What lab values can be used to help assess adequate nutrition?

Answer 20

• albumin - 20d t1/2
• transferrin - 10d t1/2
• prealbumin - 2d t1/2
• RBP - 12hr t1/2

Question 21

A 48-year-old man with a long-standing history of alcoholism and malnutrition is brought to the intensive care unit after having sustained a severe traumatic brain injury. The initial computed tomography scan of the head is consistent with diffuse axonal injury, and a neurosurgical consult leads to insertion of a ventriculostomy for monitoring intracranial pressure. Once the patient is stabilized, how do you assess and subsequently provide for the daily caloric needs?

Answer 21

• calculate daily caloric requirements w/ Harris-Benedict equation
• high caloric need 2/2 brain injury
• early enteral feeds
• watch for refeeding syndrome d/t malnutrition
• watch for folate and other nutritional deficits d/t chronic alcoholism
• watch for alcohol withdrawal
• NGT postpyloric for enteral feeds
• depending on neuro status, may need PEG

Question 22

A 45-year-old man has sustained full-thickness burns involving 40% of his total body surface area. After appropriate resuscitation with fluids and administration of analgesia, how would you assess and provide for his nutritional requirements? What other complications can affect the general nutritional status in this patient?

Answer 22

• hypermetabolic state 2/2 burns
• will need 1.5-2x calories
• calories: 25 kcal/kg/d + (30 kcal/d × % burn)
• protein: 1 g/kg/d + (3 g/d × % burn)
• adequate nutrition will decrease risk of wound infection/sepsis

Question 23

After 2 weeks on total parenteral nutrition (TPN), a trauma patient is now diagnosed with respiratory failure and is deemed to be difficult to wean from mechanical ventilation. What nutritional parameters can account for this respiratory deterioration? What adjustments can be made that can potentially benefit this patient?

Answer 23

• overfeeding can cause difficulty with weaning from mechanical ventilation
• measure resting energy expenditure w/ RQ by indirect calorimetry; if >1.0, then the patient is being overfed, subsequently producing too much CO2, and creating more work for his lungs
• reduce calorits in TPN, and ideally transition to enteral

Question 24

A 75-year-old man was brought to the emergency department from a nursing home after he was noticed to have altered mental status. After initial evaluation, it was determined that the patient was severely malnourished and was started on enteral nutrition. In 24 hours, the man had a rapid deterioration in the respiratory status, and he was intubated and brought to the surgical intensive care unit for further workup. His chest x-ray was normal. What aspects of his nutritional status might account for the deterioration of clinical status?

Answer 24

• refeeding syndrome
• prevent by assessing nutritional status and starting slowly
• hypophosphatemia can cause respiratory weakness/failure
• another possibility in a mentally altered patient is silent aspiration - CXR helps rule this out