Metabolic Abnormalities

Question 1

What is metabolism

Answer 1

Anabolism + catabolism

Question 2

What are anabolism and catabolism

Answer 2

Anabolism
- constructive mechanism where small, precursor molecules use ATP to synthesise larger organic molecules
Catabolism
- destructive mechanism where large organic molecules are broken down to provide material for synthesis and ATP release

Question 3

Give examples of stress that can provoke a metabolic response

Answer 3

Injury
Surgery
Sepsis
Dehydration
Starvation
Anaesthesia
Hypothermia
Severe psychological stress

Question 4

What affects the nature, severity and duration of the metabolic response

Answer 4

Nature and degree of trauma
Co-exisiting systemic disease
Gender (decreased in young women)
Drugs
Age (decreased in young children and the elderly)
Nutritional status (decreased in malnutrition)

Question 5

What are the two main metabolic responses to injury

Answer 5

1) local - inflammation and wound healing
2) general
- conserves fluid and provided energy for the repair process
- includes the ebb and flow phases

Question 6

What is the ebb phase of metabolic response to trauma

Answer 6

The initial response (<24 hours)

Protective - conserves the circulating volume and minimises energy demands

Question 7

What are the effects of the ebb phase, and what are they modulated by

Answer 7

Effects
- decreased oxygen consumption
- decreased enzyme activity 
- decreased cardiac output 
- decreased basal metabolic rate
- decreased body temperature 
- increased production of acute phase proteins 
Modulated by catecholamines, cortisol and aldosterone

Question 8

What is the flow phase of the metabolic response to trauma

Answer 8

A hypermetabolic state (>24 hours)

• initially is catabolic (3-10 days) to allow mobilisation for the building blocks of repair
• subsequently becomes anabolic (10-60 days) to allow repair of tissue, weight gain, and repletion of fat and protein stores

Question 9

What are the effects of the flow phase, and what are they modulated by

Answer 9

Effects
- increased oxygen consumption
- increased glucose production
- increased cardiac output 
- increased basal metabolic rate
- increased body temperature 
- decreased weight loss
Catabolic part modulated by glucagon, cortisol and catecholamines
Anabolic part modulated by growth hormones, androgens and ketosteroids.

Question 10

What are the main energy sources in catabolism

Answer 10

Glucose
Fat
Protein

Question 11

How is glucose produced in catabolism

Answer 11

Released from the liver by glycolysis of glycogen stores
- causes high BMs
Critically ill patients may develop a glucose intolerance , so have very high glucose nutritional support needs

Question 12

How is fat utilised in catabolism

Answer 12

Interleukins and TNF control the breakdown of adipose tissue

Lipases release glycerol (used in gluconeogenesis) and fatty acids (oxidised for energy) from triglycerides

Question 13

How is protein utilised in catabolism

Answer 13

Proteolysis-inducing factor (PIF) increased rate of skeletal muscle breakdown after trauma
- releases alanine and glutamine (amino acids used for gluconeogensis and acute phase protein synthesis)
A loss of muscle mass causes immunocompromise and lack of amino acids (especially glutamine) risks gut integrity

Question 14

How can the metabolic response be managed

Answer 14

Minimise initial insult if possible
Fluid and electrolyte management - prevents decreased tissue perfusion
Provide sufficient oxygen (ventilation and respiratory support)
Control glucose levels
Control pain - causes hormone release and increases basal metabolic rate
Manage body temperature
Prevent and control sepsis
Optimise nutrition - 70% glucose and 30% emulsified fat
Support for any failing organs

Question 15

What is the energy from food catabolism used for

Answer 15

Heat
Storage
External work
Necessary synthesis/analbolism

Question 16

How is energy from food measured

Answer 16

1kCal is amount of heat needed to rise the temperature of one litre of water by one degree

Question 17

What is the energy of different types of food

Answer 17

1g carbohydrate - 4.1kCal
1g protein - 5.3kCal
1g fat - 9.3kCal

Question 18

How is energy production by the body measured

Answer 18

Direct calorimetry - heat released by body (experimental)
Indirect calorimetry
- measures bodily processes associated with consumption and production of energy
- respiratory quotient (RQ) is ratio of oxygen consumption to volume of CO2 produced per unit time
- reflects fuel used to produce energy

Question 19

What is the basal metabolic rate (BMR)

Answer 19

Minimal calorific requirement to sustain life
- (35-40 kcal/m2 per hour)
Affected by factors such as age, temperature, catabolic state (e.g. burns)

Question 20

How is the BMR measured

Answer 20

Estimate is BMR = body mass(kg) x 20kcal

• 20kcal is the average energy required to maintain 1kg of body mass
• increased in catabolic state (e.g. burns)