Flashcards in Perioperative Managment and Complications, pt 2 Deck (37)
describe the important factors in myocardial ischemia
-management of oxygen supply and demand
describe myocardial oxygen supply and demand imbalance
-increase in myocardial oxygen demand is of greater significance than a decrease in myocardial O2 supply
-simultaneous tachycardia and hypotension present greatest risk to pts. with a h/o IHD as it causes increased demand and decreased supply
what populations are at risk for MI?
-MI within the past 6 months
-previous h/o perioperative myocardial ischemia
-all cardiac pts. (40% ischemia postop; 60% intraop)
what are major perioperative CV risk factors?
-unstable coronary syndromes: acute/recent MI, unstable angina
-decompensated heart failure
-significant dysrhythmias: high-grade AV block, symptomatic ventricular dysrhythmias in presence of heart disease; supraventricular dysrhythmias w/ uncontrolled ventricular rate
-severe valve disease
what are intermediate perioperative CV risk factors?
-mild angina pectoris
-previous MI by h/o Q waves on ECG
-compensated or previous heart failure
-DM (esp. insulin dependent)
what are minor perioperative CV risk factors?
-advanced aged (> 70)
-abnormal ECG: LVH, LBBB, ST-T abnormalities
-rhythm other than sinus
-low functional capacity
-uncontrolled systemic HTN
what contributes to myocardial ischemia?
-increased myocardial oxygen demand
-decreased myocardial oxygen supply
what causes an increased myocardial O2 demand?
-increased HR (tachycardia)
-increased wall tension (afterload)
what causes a decrease in myocardial O2 supply?
-decreased coronary blood flow (vasoconstriction, thrombosis, decreased diastolic time, decreased aortic diastolic pressure, increased ventricular end-diastolic pressure)
-decreased blood oxygen content: decrease Hct, anemia, decreased O2 sat
-hypocapnia (coronary artery vasoconstriction)
-coronary artery spasm
-shift of oxyhgb curve to the left
describe TEE use in detecting ischemia
*abnormal regional wall motion via TEE is most reliable and most accepted standard for detection of intraoperative myocardial ischemia
-abnormal regional wall motion occurs prior to ECG changes
describe PA catheters use in detecting ischemia
-acute increase in PAWP indicative of decreased LV compliance and performance
-V waves in PAWP tracing may indicate ischemia
-limited use b/c PAWP are only taken intermittently
describe EKG ischemia detection
-most commonly utilized modality for detection of ischemia
-most perioperative myocardial ischemia and infarctions are subendocardial
*ST depression > 1mm or T wave inversion = subendocardial ischemia
*ST elevation indicates transmural ischemia
what leads are best for ischemia detection?
-V5 is most sensitive lead for ischemia (detects 75%)
-combining V4 and V5 results in 85% detection
what is important with leads for early detection of myocardial ischemia?
*proper 5 lead ECG placement
-three leads important to improve detection (Lead II, V4, V5)
what area of the heart does Lead II detect ischemia?
RCA ischemia: inferior wall supplied 90% of time by RCA
what are of the heart does Leads V4 and V5 detect ischemia?
LV ischemia: bulk of left ventricle is supplied by LAD
in what ways can myocardial ischemia be prevented?
-minimize hypotension and HTN (maintain BP within 20% of baseline)
-continue beta blockers therapy
-avoid hyperventilation (hypocarbia may lead to coronary vasoconstriction)
-minimize SNS stimulation (pain, hypercarbia, hypovolemia)
-maintain normal blood oxygen content w/ CAD pts. (monitor excessive blood loss causing dec. hgb)
-early extubation if criteria met
-avoid intraoperative hypothermia
-utilize muscle relaxants that don't effect HR (no Pavulon)
-reversal of NMB w/ anti-muscarinic w/ less chronotropic effect (use glycopyrrolate over atropine)
-short duration direct laryngoscopy (less than 15 sec)
what should be considered with chronic HTN pts.
-usually volume depleted d/t meds and their autoregulation curve is shifted to the right (used to a higher BP)
why is early extubation better with pts. at risk for cardiac ischemia?
deeper extubation to prevent increase in HR and BP on emergence which can lead to increased ischemia
why should intraop hypothermia be avoided?
-postop shivering can increase oxygen consumption > 600%
-maintaining normothermia has been shown to reduce perioperative ischemia and subsequent cardiac mortality
what NMB are good when you do not want an effect on HR?
what can be utilized to blunt the SNS response and increased HR associated with intubation?
-LTA: lidocaine topical anesthesia
what are the effects of ketamine that should be avoided?
-increased myocardial O2 requirements
how can myocardial O2 supply and demand be optimized?
-decrease myocardial oxygen requirements
-precondition myocardium to tolerate ischemic events in presence of decreased SBP and CPP (cardioprotectant)
-decreased coronary vascular resistance w/ iso
-coronary steal (no evidence w/ iso): dilates only normal vessels, stealing blood flow from stenotic vessels
*avoid tachycardia HR > 80 (use esmolol)
describe sympathomimetic use for ischemia
-treat hypotension: restores coronary perfusion pressure (CPP)
-inotropic support when hemodynamically instable (ischemia reduces CO and causes hypotension)
-beta adrenergic agonist
*beneficial: decrease LVEDV and increase aortic diastolic pressure
*harmful: increase HR and contractility, decreased diastolic time
describe alpha agonist use for ischemia
alpha adrenergic agonists...
-increased myocardial oxygen supply by increasing aortic diastolic pressure
-detrimental effects: increased myocardial O2 demand (arterial pressure increase associated with 60% increase in myocardial O2 consumption); coronary artery vasoconstriction
-alpha 2 agonists can decrease SNS outflow and decrease HR and BP (dexmetatomidine)
describe nitrate use for ischemia
-nitroglycerin (NTG): utilized when ischemia by increased BP; coronary vasodilation (increases supply); decreases preload improving subendocardial blood flow
-nipride: much like NTG but with afterload reduction; controversial use in myocardial ischemia (possible coronary steal)
describe beta blocker use for ischemia
-mixed research regarding reduction in post of cardiac mortality
-decrease myocardial demand and increase supply
-decrease HR and contractility but may cause cardiac depression
describe calcium channel blocker use for ischemia
-decrease myocardial O2 demand and increase supply
-shown to reduce coronary artery vasospasm