Medical Nutrition Therapy for
Metabolic Stress and Critical Care
Objectives
• Describe the metabolic response to
critical illness
• Describe role of nutrition therapy for
critically ill patients
• Describe how to assess nutrient
needs for a critically ill patient
Metabolic Stress
• Stressors:
– Sepsis
– Surgery
– Trauma (includes burns)
• These stressors activate a particular
systemic response, leading to a
number of physiologic and metabolic
changes
What happens during metabolic stress?
• Metabolic alterations to meet the body’s
needs for survival
– hypermetabolism
– hypercatabolism
– hyperglycemia
– sodium & water retention
– increased heart rate & cardiac output
– hypercoagulability & increased platelet
aggregation
– increased sympathetic tone
• controls “fight or flight” response
Metabolic Response to Stress
• Involves most metabolic pathways
• Accelerated metabolism of lean body
mass
• Negative nitrogen balance
• Muscle wasting
Hypercatabolism!
Ebb Phase
• Usually restricted to the first 24-48 hours
• Immediate response
–
–
–
–
–
Hypovolemia and tissue hypoxia
Decreased cardiac output
Decreased oxygen consumption
Lowered body temperature
Decreased insulin and increased glucacon
levels
Flow Phase
• Follows fluid resuscitation and improved
O2 transport
• Increased cardiac output begins
• Increased body temperature
• Increased energy expenditure
• Total body protein catabolism begins
• glucose production, free fatty acids,
circulating insulin, catecholamines,
glucagon, & cortisol
Figure 89.2. Neuroendocrine and metabolic consequences of
injury. ACTH, adrenocorticotropic hormone. From: Lowry SF &
Perez JM. The hypercatabolic state. In Shils ME, et al. (eds) Modern
Nutrition in Health & Disease. Lippincott, Williams & Wilkins, 2006.
Metabolic Responses During Sepsis
Organ
Liver
Response
Glucose production
Amino acid uptake
Acute-phase protein
synthesis
Trace metal sequestration
Central nervous system
Circulation
Anorexia, fever
Glucose
Triglycerides
Amino acids
Urea
Iron
Zinc
Metabolic Responses During Sepsis
(continued)
Skeletal
muscle
Amino acid efflux (especially glutamine),
Intestine
Amino acid uptake from both luminal and
leading to loss of muscle mass
circulating sources, leading to gut mucosal
atrophy
Endocrine
Adrenocorticotropic hormone
Cortisol
Growth hormone
Epinephrine
Norepinephrine
Glucagon
Insulin initially, then levels & insulin resistance
From Michie HR: Metabolism of sepsis and multiple organ failure, World J Surg 20:461, 1996.
Hormonal and Cell-Mediated Response
• Causes energy metabolism to shift to protein
as a primary fuel
–The body needs glucose, so protein is used for
gluconeogenesis
• Increase in hepatic amino acid uptake for
protein synthesis
–“Acute phase proteins” are made instead of visceral
proteins
• Lean body mass may be mobilized as a
protein source
Skeletal Muscle Proteolysis
Hormonal Stress Response Specifics
• Conserve fluid & sodium to maintain
blood volume:
– Aldosterone
• Corticosteroid that causes the kidney to retain
sodium
– Antidiuretic hormone
• Stimulates renal tubular water absorption
Hormonal Stress Response Specifics
(continued)
• Simulate metabolism:
– Adrenocorticotropic hormone (ACTH)
• Acts on adrenal cortex to release cortisol
• Mobilize amino acids from skeletal muscle
– Catecholamines
• Epinephrine & norepinephrine from renal medulla
• Stimulate hepatic glycogenolysis, fat
mobilization, gluconeogenesis
From: accessed 2/28/09
Acute Phase Response
• Occurs when a patient is very stressed
• See increased production of cytokines
– Protein mediators secreted by
macrophages in response to tissue
damage, infection, inflammation, and some
drugs and chemicals
– Hormone regulators of the immune system
– Stimulate production of inflammatory
mediators associated with shock & sepsis
Actions of Specific Cytokines
• Tumor necrosis factor (TNF)
– Increased catabolism of lean body mass
– Causes anorexia
– Activates the hypothalamic-pituitaryadrenal axis
• Interleukin-1
– Mediates the acute phase response
– Associated with fever, hypotension,
inflammation, protein catabolism
• Interleukin-6
– Release of hepatic acute phase proteins
Response at the Cellular Level
• Eicosanoids are produced in response
to this stress
– These are lipid mediators of inflammation
– Three major types:
• Prostaglandins
• Leukotrienes
• Thromboxanes
Immune Cell Saturated with
omega-6 Fat
AA
Phospholipid
Membrane
AA
AA
AA
AA
AA
AA
AA
AA
Slide courtesy Abbott Nutrition
Proinflammatory
compounds
Prostaglandins
• Prostaglandins
– Modulate intensity & duration of inflammatory &
immune responses
– 2 series derived from arachidonic acid (n-6)
– PGE2 has significant pro-inflammatory function
•
•
•
•
Induction of fever & erythema
Increased vascular permeability
Vasodilation
Enhancement of pain & edema in response to
histamine
• Inhibition of B-cell & T-cell proliferation
Prostaglandins
(continued)
• The 3 series is less inflammatory
– Derived from omega-3 fatty acids:
eicosapentaenoic acid (EPA) and
docosahexaenoic acid (DHA)
– Thromboxanes are derived from PGH
• These are similar to PG in that
– 2 series is pro-inflammatory
– 3 series is much less active
Leukotrienes
• Primary mediators of inflammation &
allergic reactions
• Also increase microvascular permeability
• Promote arteriolar constriction
• Promote bronchoconstriction and
increase bronchial mucous production
Leukotrienes
(continued)
• The 4 series, derived from AA, is
proinflammatory
• LTB4 has the most significant action
– Potent chemoattractant & chemokinetic action
toward leukocytes
– Inhibition of T-cell mitogenesis
– Stimulation of PMN cells to aggregate & adhere to
endothelial cells
– Promote secretion of inflammatory products by
neutrophils
– Synergy with other mediators to increase vascular
permeability
• The 5 series, made from EPA & DHA, is less
active
Thromboxanes
•
•
•
•
Similar function to leukotrienes
Derived from PGH
Involved in platelet aggregation
TXA2 stimulates formation of plateletderived growth factor
– Stimulates blood clotting
• 2-series is inflammatory & 3-series is
less so
Influencing Eicosanoid Production
• Arachidonic acid comes from omega-6 fatty
acids
– Example: corn oil is high in omega-6 fatty acids
• Feeding more omega-3 fats may help push
production of the anti-inflammatory (or less
active) eicosanoids
– Example: enteral formulas with fish oil are
promoted as “immune modulating”
Metabolic Response in
Starvation vs. Stressed
State