CPB (Neuro/Endo) Flashcards
What is the incidence of stroke during surgery?
2-8%
Does CPB alone increase the risk of minor post-op neurologic dysfunction?
Yes, especially during the early post-op period
What are the sources of microemboli while on CPB?
Air (from oxygenator, heart, temperature gradients, IV solutions, arterial line filter) + Oxygen + Lipid globules (from cardiotomy suction) + muscle/connective tissue fragments + platelet/leukocyte fibrin aggregates + plastic + calcific particles (from aorta, cannulation sites)
What are the major sources of macroemboli during cardiac surgery?
Large air bubbles or atheromatous/calcific debris from valvular lesions or plaques on the aorta; most often occurs during clamping and cannulation of the aorta
What is an air embolus made primarily of?
Nitrogen (doesn’t desolve rapidly); this is why a CPB circuit is flushed with highly disssolvable CO2
What are signs of an air embolus?
Seizures, arrhythmias, and ventricular dysfunction
How can you decrease the risk of air embolism while on CPB?
Arterial filters/pre-bypass filters (decreases pump debris and gas/particular matter)
What are common sources of air embolisms?
Aorta, pulmonary vessels, and intracardiac negative pressure vents + unexpected, open contracting heart + pressured cardiotomy circuit + reversal of vents
Where does most air end up in the heart?
LAA + ventricular apex + spaces between chordae tendinae, pap muscles, and trabeculae carinae + cardiac chamber cul-de-sacs + aortic root
What are independent risk factors for neurologic dysfunction after cardiac surgery?
Advanced age (>75yo are 2x more likely to have a neurologic event) + duration of CPB (>2 hrs) + DM, history of CVA, and calcified aorta
What are ways to monitor the CNS during cardiac surgery?
EEG + transcranial doppler (measures blood flow velocity through MCA - can detect embolic events) + jugular venous O2 sat (measures cerebral O2 delivery)
What is the formula for cerebral perfusion pressure and what is the normal range?
CPP = MAP - ICP (or CVP); normal is 60-80 mmHg
What does pH stat generally do to the CNS during hypothermia?
Keeps patients more acidotic (adding CO2 to preserve pH of 7.4 and PCO2 of 40) which leads to cerebral vasodilation and increased CBF; loss of cerebral autoregulation and mismatch of CBF and CMRO2
Which method of acid-base management has been associated with improved neurologic outcomes in adults?
Alpha stat; possibly due to decreased risk of microemboli (since there is hypocarbia and cerebral vasoconstriction) while pH stat adds CO2 so increased CBF and higher risk of emboli
Which method of acid-base management has been associated with improved neurologic outcomes in children?
pH stat; less risk of emboli so you get better balanced brain cooling with cerebral vasodilation (CBF and CMRO2 are dissociated) + right-shift of oxy-hemoglobin dissociation curve
How much of your CO does the splanchnic circulation receive and why is it at risk during CPB?
20% of CO and is unable to autoregulate at extremes of blood pressure so it is more vulnerable to flow changes while on CPB
What are factors that contribute to splanchnic ischemia?
Systemic inflammation from the CPB machine + non-pulsatile blood flow + hypothermia
What is the minimum flow needed for hepatic O2 consumption to be maintained?
2.2 L/m2/min
What can you see after bypass with the hepatic system?
Transient increased LFTs + jaundice (from hepatic injury, excessive bilirubin 2/2 blood transfusions or trauma from the pump itself and hemolysis)
What can you to do reduce the risk of GI complications while on CPB?
Avoid hemodilution and severe anemia + use pulsatile flow + use filters to reduce emboli + use echo for aortic cannulation (decrease atheroemboli) + avoid IABP in patients with significant plaque
How does CPB affect the catecholamine release?
Increases catecholamine release during CPB likely due to hypothermia, hypovolemia, hemodilution, hypotension, non-pulsatile flow and decreased perfusion of endocrine glands
What can decrease the endocrine response to CPB?
Dexmedetomidine and neuraxial anesthesia has been shown to decrease the neuroendocrine response to CPB
What is secreted from the posterior pituitary gland? When are these released?
ADH or vasopressin: released if increased plasma osmolality, decreased blood volume, hypoglycemia, stress and pain
What happens to ADH levels while on CPB?
Increased ADH levels in the first 30 minutes of CPB independent of anesthetic technique
What is secreted from the anterior pituitary gland?
ACTH, TSH, growth hormone, LH, FSH, and and prolactin
What does ACTH do and what happens to ACTH levels while on CPB?
ACTH stimulates adrenal gland secretion of flucocorticoid and androgen hormones; levels increase with incision and fall during non-pulsatile CPB and increase again after bypass
What does growth hormone do and what happens to GH levels while on CPB?
GH decreases protein catabolism and promotes protein synthesis (increases fat mobilization and glycogen deposition); GH increases with skin incision and CPB (peaks at 120 mins of CPB) and it rapidly decreases to preop levels 6 hours post CPB
What is secreted from the adrenal cortex?
Cortisol and aldosterone
What happens to cortisol levels during CPB?
Like all surgeries, cortisol increases with incision, it then decreases at the initiation of CPB (hemodilution and hypothermia) and then increases again post-op
What is the role of aldosterone?
Helps regulate renal sodium reabsorption
What happens to aldosterone levels during CPB?
Aldosterone levels increase with incision, then decreases with the start of CPB but increases 15 mins later
How does hypothermia and CPB affect catecholamines released from the adrenal medulla?
Hypothermia delays metabolism of catecholamines while being on CPB decreases perfusion to the lungs, liver, and kidney which delays plasma clearance
What happens to glucose and insulin levels on CPB for nondiabetic patients?
Glucose utilization decreases from hypothermia, cortisol/catechoaline release and suppression of insulin secretion; glucose levels increase during CPB due to decreased glucose utilization as above and increased hepatic glycogenolysis and gluconeogenesis from increased stress hormones
When do glucose levels return to normal after cardiac surgery?
Usually post-op day 2
What happens to glucose and insulin levels on CPB for diabetic patients?
During CPB, decrease in insulin and increase in glucose levels similar to nondiabetic patients; however, when rewarming, insulin requirements increase more for diabetic patients
What does thyroid hormone do?
TSH from the anterior pituitary causes T4 (thryoxine) rleease from the thyroid gland which increases O2 consumption, cardiac output, contractility, and renal blood flow; T3 (thriiodothyonine) is more active and responsible for the hormonal effects
What happens to thyroid hormone levels during CPB?
T3 levels decrease with the start of CPB, then increase slightly after CPB but still remain significantly lower than normal postoperatively
What is euthryoid sick syndrome?
Low T3, low to normal T4, and normal TSH; can be seen in post CPB patients
What happens to parathyroid hormone with CPB?
With CPB, there is a decrease in ionized Ca as well as a decrease in PTH; PTH initially decreases with CPB, then increases and peaks 60 min after the start of bypass
Endocrine Effects Summary Table
See Excel Sheet
