cardiac anesthesia Flashcards
what cardiac history should be included in the pre anesthetic assessment for cardiac anesthesia?
- cardiac medications
- history of myocardial infarction
- history of hospitalizations
- exercise tolerance
- cardiac catheterization report
- myocardial wall movement
- coronary angiography
what does MI history determine?
if within less than a month, an increase in morbidity and mortality rates
what does exercise tolerance determine?
disease severity
- angina at rest or w/ major exertion?
- angina accompanied by dyspnea? (indicates ventricular dysfunction)
- ask specifically how are they active daily and how they tolerate activity
- need to know their reserve
what does the cardiac cath report provide?
- hemodynamic information: CO, CI, SVR, PVR, intracardiac shunts (right heart), degree of coronary stenosis, EF, myocardial wall motion abnormalities, LVEDP
- EF of 40% or greater have best outcomes
- desirable: low filling pressures and good EF (wedge less than 15)
- poor: elevated filling pressures, low CO, and low BPs (high risk w/ anesthesia)
what else should be determined in the pre anesthetic assessment outside of cardiac hx?
- airway assessment
- aspiration risk
- hiatal hernia (relative contraindication to TEE)
- cerebrovascular disease (Doppler studies for carotid disease; stroke cause of increased morbidity post pump)
- equal BP in both arms (for placement of art line)
- aortic and femoral disease (for arterial cannula or intra aortic balloon pump insertion)
- renal disease
- HTN
why are most cardiac pts. intubated post op?
difficult to allow to wake up w/ high dose opioids and muscle relaxants
why are cardiac pts. usually at a higher risk for aspiration?
- emergency cases (non adequate NPO time)
- diabetic
- obese
- narcotics
- stress and anxiety
what should be done w/ cardiac pts. for aspiration risk?
- premedicate w/ metoclopramide and H2 antagonist
- RSI w/ induction agent and different muscle relaxant (SCh, Rocuronium)
why is renal function a concern w/ cardiac anesthesia?
- insufficiency: dye, decrease perfusion, vasopressors
- acetyl cysteine can help w/ reaction to dye
- ESRD: anemia, dialysis site care, platelet dysfunction, hypovolemia, fluid overload post-op, hyperkalemia
- usu. dialyze prior to surgery so hypovolemic
- may have to pace post-op until dialysis is done since may remain asystole d/t hyperkalemia
how does HTN affect anesthesia?
- alters autoregulation (normal 50-150 mm Hg)
- may be elevated (shifted right) d/t higher pressures to perfuse the coronaries, cerebral circulation (may need to run BP higher)
- if hypertrophic ventricle, needs the atrial kick (harder to empty and harder to open and allow filling)
- if rhythm other than sinus, will have a decrease in pressure (no atrial kick)
- expect HTN post-pump
- vasodilator to keep pressure down and decrease post-op bleeding
describe abnormalities in myocardial wall movement
- hypokinetic: region contracts during systole, but w/ less force than neighboring regions (ischemic wall motion)
- akinetic: region doesn’t contract during systole (infarcted myocardium)
- dyskinetic: region bulges outward during systole, thus moving in the opposite of surrounding regions (severely ischemic [necrotic] or aneurysmic)
what information can coronary angiography provide?
- severity of blockage of each coronary artery
- collateral blood flow (younger/healthier pts. don’t have)
- right or left dominant
- right: RCA continues to posterior wall as a posterior descending coronary artery; AV node also (85%)- blockage causes dysrhythmias
- left: circumflex continues to posterior wall as posterior descending coronary artery (8%)
- left main: branches into left anterior descending and left circumflex (most of left ventricular wall)
- blockage results in significant ventricular dysfunction- widow maker
- left main equivalent
describe the hemodynamic subsets of acute myocardial infarction
- Class I: no pulmonary congestion or systemic hypoperfusion (CI more than 2.2; PCWP less than 18)
- mortality 3%
- Class II: pulmonary congestion only (CI more than 2.2; PCWP more than 18) *mortality 9%
- Class III: reduced perfusion only (CI less than 2.2, PCWP less than 18) *mortality 23%
- Class IV: both pulmonary edema and hypoperfusion (shock) (CI less than 2.2; PCWP more than 18)
- mortality 51%
what is considered when controlling myocardial oxygen demand?
- myocardial wall tension
- heart rate
- blood pressure
- goal: prevent excessive myocardial oxygen demand
what can done to avoid increased myocardial oxygen demand?
- avoid inotropes pre-op (increases O2 consumption)
- transfuse pre-op for anemia (improve O2 carrying capacity)
- beta blockers (decrease HR w/o too much drop in BP)
- not beneficial for low risk pts.
what can be done to optimize myocardial oxygen supply?
- must maintain arterial pressure (coronary autoregulation 50-120 w/ disease; maximized to maintain resting flow to myocardium)
- must avoid tachycardia (coronary perfusion during diastole which is shortened)
- coronary perfusion pressure is improved by raising diastolic arterial BP and decreasing LVEDP
- CPP equals DBP-LVEDP
- pressure distal to the stenosis minus LVEDP
- Hgb: correct anemia
- high concentrations of O2 inspired (keep well oxygenated, even while awake place on NC)
what are normal physiologic parameters of determinants of myocardium supply and demand?
- coronary blood flow: 225-250 ml/min or 4-7% or CO
- myocardial O2 consumption: 65-70% extraction or 8-10 ml O2/100 gm per min
- normal autoregulation: 50-120 mmHg (MAP)
- coronary filling: 80-90% during diastole
what are goals of anesthetic for cardiac?
- producing analgesia, amnesia, and muscle relaxation
- abolishing autonomic reflexes
- maintaining physiologic homeostasis
- providing myocardial and cerebral protection
what is needed for the physical set-up for cardiac surgery?
- large ETT (f: 7.5-8.0; m: 8.5-9.0)
- nasal cannula
- NS 500 on microdrip extra port of PA cath
- one or two large gauge IVs (14-16g)
- PA catheter and CO monitor
- art line
- pharmacologic agents
- atrial-ventricular sequential pacer
- gel pads for arms and heels and gel donut for headrest
- esophageal stethoscope (monitor temp)
- BIS or cerebral oximetry monitor
what fluids should be hung during set-up for cardiac surgery?
- 1 L LR or plasmalyte-A
- 1 L NS on blood set through warmer
- *avoid dextrose d/t neurologic problems
what pharmacologic agents should you get during set up?
- infusions: NTG, epinephrine, phenylephrine, nitroprusside, dopamine
- opioid (fentanyl, sufentanil)
- benzo (versed; some use lorazepam on younger pts. or pre op and versed intra op)
- lidocaine 2% (2, 1 on induction and 1 when re-warming)
- muscle relaxant (pavulon, rocuronium, SCh)
- heparin 1000u/ml- 30 ml
- ancef (1 g for less than 80 kg; 2g over 80 kg)
- calcium chloride
- atropine
- ephedrine
- protamine (NEVER draw up before giving)
why is positioning so important w/ cardiac surgery?
cardiac surgery on pump causes NON PULSATILE flow
describe premedication for cardiac surgery
- midazolam 1-5 mg IV in OR or Ativan 1 mg po (best amnestic)
- morphine 0.1 mg/kg (decreases pre-load) and scopolamine 0.2-0.4 mg IM (IV) on call (good amnestic w/o hemodynamic effects)
- sorbitrate 5 mg PO on call (nitrate to dilate coronary arteries, decrease preload; also effects venous so beneficial w/ saphenous vein harvest)
- goals: want to avoid tachycardia and HTN during insertion of invasive lines and PIV so minimize anxiety 1st
- individualized based on pt.
describe pt. prep in the OR for cardiac surgery
- nasal O2 2-3 L/min
- start L arm PIV (14-16g; atleast 18g) *anticipate transfusion
- start R arm radial arterial line (18 g)
- insert IJ cordis introducer
- insert PA cath and connect to cardiac output monitor
what monitoring is including w/ cardiac surgery?
- electrocardiography
- arterial blood pressure
- PA catheters
- TEE
- Urinary output
- computer-process EEG (BIS)
- cerebral oximetry
- esophageal temperature
- surgical field
- peripheral nerve stimulator (check adequate muscle relaxation)
what should be monitored w/ PA cath?
- CVP for all
- PA cath if compromised ventricular function (EF less 40-50%)
- routinely pull back 2-3 cm during bypass to avoid incidental wedging of cath (heart emptied, distance shorter)
what is closely monitored on the ECG?
- II and V5 or site of MI
- rhythm
- rate
- changes in ST segments
what should be remembered when monitoring the arterial BP?
- radial site effected by sternal retraction and brachial artery cutdown form cath
- have automated BP cuff in place on r. arm to compare measurements
what is TEE useful for during monitoring?
-best detection of myocardial ischemia looking at wall motion abnormalities
assesses:
-ventricular function
-valvular function
-residual air
-other structures: ascending aorta, coronary sinus
what should be monitored w/ urine output?
- hourly output
- bladder temperature
- watch for hemolysis
why is BIS monitoring important for cardiac surgery?
- major concern for awareness since mostly narcotic anesthesia is used
- no inhalation agent unless perfusionist has own vaporizer on bypass machine
- if circulatory arrest, ensure complete silence
what should be closely watched in the surgical field?
- lung expansion
- ventricular function, rhythm, volume
- blood loss
- watch and anticipate surgical steps
- esp. important when preparing to come off pump
describe the purpose of cardiopulmonary bypass (CPB)
allows the heart to rest (quiet field) by serving as the lungs and pump for the body
*decreased metabolic needs w/ heart at rest and also via cooling
