Physiologic Response to Surgery Flashcards
Describe the HPA axis and ACTH levels in response to stress.
CRH released from hypothalamus causes release of ACTH from anterior pituitary, ACTH causes adrenals to release cortisol. Normal mech is that increasing levels of cortisol cause the ACTH production to slow down or stop, in stress response you have failure of that feedback mechanism. Will have elevated cortisol and ACTH.
What is the sympathetic nervous systems response to stress on the adrenal medulla?
Sympathetic nervous system releases catecholamines from adrenal medulla. NE increases from presynaptic nerve terminals leading to tachycardia and hypertension.
Describe the effects stress has on renal function.
Renal:
-renin release causes conversion of angiotensin I to II, angiotensin II cause a release of aldosterone leading to Na+ retention and therefore fluid retention. Likely to have edema. Also K+ loss.
Describe the effects stress has on pancreatic and hepatic function.
Pancreatic: glucagon release.
Increased Glucagon stimulates glycogen breakdown in the liver to be released as glucose.
Decreased insulin release and little development of insulin resistance leading to hyperglycemia.
Hepatic:
-mobilization of free fatty acids from lipid stores to be used as fuel.
During a stress response which hormones from the Anterior Pituitary are being released? Posterior pituitary?
Describe the effects each hormone has during a stress response.
AP:
-ACTH, GH, Prolactin
PP:
-ADH
EFFECTS:
-ACTH: increased ACTH leads to increase in cortisol and glucocorticoids from the adrenal cortex.
- GH: increased GH leads to increased blood sugar as it antagonizes insulin. May also have positive role in wound healing.
- Prolactin: Increased prolactin d/t decreased prolactin inhibiting factor.
- ADH: increased ADH leads to further increase in ACTH. Increased ADH promotes water retention and concentrated urine.
What does cortisol do?
- promotes protein breakdown and gluconeogenesis
- inhibits glucose use by the cells and increases blood glucose
- promotes lipolysis leading to further increase in blood glucose
- has glucocorticoid anti-inflamm effects
- has mineralocorticoid effects causing fluid retention and K+ loss.
Why do insulin levels decrease with stress response?
Concentration of insulin decreases after induction of anesthesia and during trauma by inhibition of Beta cells in the pancreas by the alpha-2 adrenergic effects of catecholamines.
How are the thyroid hormones affected by stress?
May be unaltered or decreased during surgery, total and free T3 decrease after surgery and return to normal after several days.
TSH concentrations decrease after the first 2 hrs and then return to normal.
Changes are related to catecholamines and cortisol.
Describe carbohydrate metabolism during a stress response.
Catabolic hormones promote glucose production, there is lack of insulin and peripheral insulin resistance d/t cortisol, Catecholamines, and GH.
What are some SE of perioperative hyperglycemia?
Wound infection
Impaired wound healing
Describe the effects of increased cortisol and cytokine concentration on protein metabolism under stress.
What are the consequences of this?
Increased cortisol and cytokine concentration promote:
- catabolism of proteins and skeletal muscle
- these may be used by the liver for energy or to make new proteins like acute phase proteins.
*Albumin production is reduced and alters extracellular volume.
Consequences:
-weight loss and muscle wasting.
Describe what happens to lipid metabolism during stress response.
Lipolysis and ketone production.
Cytokines:
- examples
- produced from?
- function
- most important cytokine associated with surgery?
Examples:
- IL1-17
- interferons
- TNF
Produced from activated Mfs, fibroblasts, endothelial and glial cells.
Function: mediators of immunity and inflammation.
Most important cytokine associated with surgery is IL-6.
Effects of IL-6
Causes teh acute phase response;
-produces acute phase proteins such as fibrinogen, CRP, complement, ceruloplasmin
These acute phase proteins cause:
-fever, granulocytosis, hemostasis, tissue damage limitation, and promotion of healing
Cytokine production is limited by?
Cortisol.
