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
describe the path of the cardiopulmonary bypass
- removes blood via venous return form r. atrium (SVC/IVC) by gravity to the venous reservoir
- blood then moved by mechanical pump (roller or centrifugal)
- creates non-pulsatile flow
- blood goes to the oxygenator where O2 is added and CO2 is eliminated
- blood enter the heat exchanger where it is either cooled or warmed (by conduction w/ water flowing through)
- blood goes through an arterial filter to clean out thrombi, tissue debris, fat, and calcium
- blood pumped back through the arterial cannula into ascending aorta (most common)
- blood from suction and from l. ventricular vent are directed to the venous reservoir also
- while on bypass, arterial pressure is below normal and blood flow is non-pulsatile
how is the CPB circuit primed?
w/ more than 2000 ml of crystalloid which causes 30-50% hemodilution of pt.’s blood
*counteracts the viscosity caused by cooling
what is utilized to protect organs from damage during CPB?
systemic hypothermia (20-32 degrees C)
how does systemic hypothermia protect organs from damage during CPB?
- systemic oxygen demand decreases 9% for every degree of temp drop
- hemodilution counteracts the 5% increase in blood viscosity for every 1 degree C decrease in core temp
what are used to protect the myocardium during CPB?
- cardioplegia caused arrest
- hypothermia
- decompression of the ventricles
what is cardioplegia and its purpose?
- crystalloid solution w/ high potassium
- used to cause rapid cardiac arrest to reduce consumption of energy
how should cardioplegia be administered?
- can be either cold or normothermic
- can be delivered either antegrade via the aorta before the cross clamp or retrograde via the coronary sinus
what is the purpose of administering heparin prior to going on CPB?
prevent activation of the coagulation cascade when the blood leaves the body and contacts the plastic tubing and components
how much heparin should the pt. going on CPB be anticoagulated with?
300 units/kg of heparin
what is the MOA of heparin?
binds with antithrombin III and potentiates its anticoagulant effect
what route should the heparin be delivered?
- CVL
* after withdrawing blood to verify placement
what is checked to verify the effect of heparin prior to CPB?
- activated clotting time (ACT)
- measured 3 min. after (exactly 3 min. so record down to the second the heparin was pushed!)
at what value should ACT be maintained during CPB?
300-500 (approx. 450) seconds
if the patient is resistant to the effect of heparin (suspected by no prolongation in ACT) what should be done?
administer FFP, which contains antithrombin III for the heparin to activate
what hemodynamic change is seen when heparin is administered?
- decrease in arterial BP as much as 10-20%
- if drop is too much for pt. to handle (weak heart, BP already decreased d/t induction agents) may need phenylephrine (alpha)
- no ephedrine since it acts on alpha AND beta which will increase HR and contractility
describe inhalational anesthetic technique for CPB
- IV induction w/ thiopental, propofol, opioids, etomidate, ketamine, or midazolam
- muscle relaxant and volatile agent added
- advantage: can change anesthetic concentration rapidly
- disadvantage: dose-dependent direct cardiac depression, vasodilation
- *avoid N20 d/t expansion of air bubbles
- still uses significant doses of opioids
describe disadvantage of high-dose opioid anesthesia technique for CPB
- awareness
- prolonged respiratory depression
- HTN to stimulus uncontrolled
- can cause bradycardia and muscle rigidity
- Pavulon can be used to offset bradycardia
- add benzo and/or volatile agent to address awareness concerns and HTN
- be careful of synergistic effect of fentanyl and versed on hemodynamics
what doses are seen w/ high dose opioid anesthesia?
Fentanyl
- 15-40 mcg/kg for induction and intubation
- 3-5 mcg/kg boluses to maintain or continuous infusion of 0.3-1 mcg/kg/hr
- total fentanyl given 50-100 mcg/kg
which anesthetic technique is commonly seen with CPB?
a combination of both
- moderate fentanyl, midazolam w/ volatile
- advantage: amnesia, normotensive w/ capability to adjust anesthetic level, moderately quick extubation
describe use of ketamine and midazolam
- ketamine 1-2 mg/kg w/ versed 0.05-0.1 mg/kg at induction
- infusion of ketamine 1.4 mg/kg/hr
- advantages
- pts. w/ poor ventricular function
- allows stable hemodynamics
- maintains SVR, HR
- amnesia
- minimal respiratory depression post-op
what agent is best for fast tracking?
propofol infusion
what is happening during the pre-bypass period?
- induction/intubation
- pre/drape (hypotension, no stimuli)
- sternotomy (tachycardia and HTN)
- retraction
- opening of myocardium (vagal)
- anticoagulation (hypotension)
- cannulation
what is a major concern during sternotomy?
- deflate lungs since expands in front of heart when inflated
- turn off vent and disconnect circuit form machine
- be prepared to give heparin if “redo” pt. has damage to heart d/t scarring
- heart may be stuck to back of chest and if surgeon gashes heart will have to crash on pump STAT!
what are concerns during retraction?
- radial arterial line BP reading may be inaccurate d/t pressure on brachial artery
- head displacement from support by lifting w/ retraction; be sure to put extra padding under to allow head to rest
- ventilation of lungs: want to either decrease Vt/ increase RR or hand bag so lungs don’t inflate into surgeon’s view
- bradycardia and hypotension d/t decreased venous return
what may occur d/t opening of the pericardium?
vagal stimulation: bradycardia and hypotension
what are concerns w/ cannulation?
- aortic: need to reduce arterial SBP 90-100 mmHg
- can be used to infuse crystalloid rapidly
- right atrium: hypotension, arrhythmias (change in P waves) common
what are the most common times of intra-op ischemia?
- *induction: pressure is lower and myocardium not perfused as well
- intubation (SNS stimulation)
- incision (SNS stimulation)
- sternotomy (SNS stimulation)
- *cannulation: pressure is lower
what is observed while going on CPB?
- ACT confirmed
- good flow via venous and arterial cannulas
- no air in circuit
- mean arterial pressure: 30-40 mmHg initially (out of our control; d/t hemodilution, decreased SVR, decreased viscosity)
- will no longer have a SBP or DBP d/t non-pulsatile flow
what is a concern d/t hemodilution?
need for more drugs
- administer additional narcotics, amnestic, and muscle relaxant
- doesn’t matter what twitches are; its the beginning just re dose
on CPB what determines the MAP?
pump flow x SVR
- if constant SVR, MAP proportional to pump flow
- if constant pump flow, MAP proportional to SVR
what are the goals the perfusionist tries to maintain w/ pump flow and MAP?
- flows 2-2.5 L/min/m2 (like cardiac index)
- MAP 50-80 mmHg
what helps achieve myocardial protection to minimize ischemia?
- cardioplegia: cross-clamp aorta
- hypothermia: mild 33-35 C, moderate 26-32 C, deep 20-25 C (most use approx. 32)
- topical cooling w/ icy saline flush (helps cool external of myocardium)
- left ventricular venting
how is cerebral protection achieved during CPB?
- hypothermia (34-36 C) reduces cerebral metabolism to allow low perfusion state and even ischemia
- thiopental to completely suppress EEG activity decreases incidence of neurologic deficits
- alpha stat or pH stat ABG management
- *strokes, brain damage are issues
describe implications during the rewarming phase of CPB
- near completion of procedure
- *limited to 1 degree C per 3-5 min to avoid gas bubble formation (usu. 30-40 min.)
- removes protective effect of hypothermia (consider administration of additional opioid, benzo, and relaxant based on twitch)
- *likely see drop in SVR d/t peripheral vasodilation and wash out of metabolic waste products (phenylephrine)
- potential for arrhythmias as electrical activity begins to return (surgeon may want you to give lidocaine)
- metabolic needs increase, so perfusionist must increase pump flow to 2.6-3.0 L/min/m2
- *sweating normal response to elevated skin temp (NOT sign of light anesthesia)
how should you prepare for separation from the CPB?
- evacuate air from the heart, bypass grafts, and pulmonary vessels
- TEE useful in identifying
- surgeon may ask to give big breaths to ensure no air in pulmonary vessels
what are concerns w/ cross clamp removal?
- cross-clamp is removed to allow myocardium to be perfused and re establish cardiac rhythm
- lidocaine 100-200 mg given just prior to removal of clamp
- if heart fibrillates during rewarming, defibrillation w/ internal paddles will be necessary (5-10 joules since directly on myocardium)
- rhythm needs to be atrial and ventricular sequential w/ rate 80-100
what usually causes persistent asystole?
- hyperkalemia r/t the cardioplegia
- requires AV pacing until potassium metabolized or dialysis
- potassium usu. returns to normal w/o treatment
what is the checklist for weaning from CPB pump?
- adequate systemic rewarming
- check acid-base balance, hct, platelet count, electrolytes
- recalibrate all transducers
- adequate cardiac rhythm and rate
- check EKG for ischemia
- remove all air from chambers, grafts, aorta
- initiate ventilation of lungs
what happens during partial occlusion or partial bypass?
- venous return to the pump is partially restricted allowing blood to enter the RA
- the ventricular ejection begins as assessment of cardiac function occurs
- optimally, PA pressures will be normal w/ good systemic pressure
- if PA pressures rise w/ poor arterial pressure, inotropes and/or vasodilators maybe needed (start at this time)
what are causes of hypotension and what clinical signs might be seen w/ each cause?
- hypovolemia: low art, PCWP, PAP, CVP, CO
- need volume
- vasodilation: low art, low SVR, normal PCWP/PAP/CVP, high CO
- phenylephrine or levophed
- LV failure: low art, high PCWP/PAP/SVR, normal CVP, low CO
- inotrope to increase contractility (epi), IABP, LVAD
- pulm. vasoconstriction: low art/PCWP, high PAP/CVP, low CO
- RV failure: low art, PCWP/PAP, high CVP, low CO
- pulm. dilator, RVAD
describe coming off pump
- if cardiac function during partial pump phase is adequate, the VR is completely occluded
- looking at CO and filling pressures, the perfusionist will transfuse the pt. via the aortic cannula
- reverse trendelenburg allows transfusion w/o overfilling the heart
- cannulas are removed and anticoagulation is reversed w/ protamine
what is the MOA of protamine?
protein that binds w/ heparin to deactivate it by forming an inert salt
what is the dose of protamine?
1-1.3 mg per 100 U of heparin
what are CV effects of protamine?
- hypotension: histamine release, tachycardia
- give over 5 minutes
- give peripherally to dilute complex that causes histamine release in the lungs
- dilute out
- pulmonary HTN: thromboxane release causing pulm. vasoconstriction, pulm. HTN, and bronchoconstriction
- allergic reaction: protamine-containing insulin (NPH); allergic to fish
- pretreat w/ histamine blockers and steroid
what are risk factors for systemic vasodilation and/or pulmonary HTN reactions to protamine?
- valvular heart disease
- preexisting pulmonary HTN
- infusion rate greater than 5 mg/min
- site of administration (give PIV)
- diabetic w/ exposure to protamine-containing insulin (NPH)
- myth: previous vasectomy
what are possible complications during the post pump and post-op period?
- bleeding can be multifactorial: suture lines, thrombocytopenia, decreased clotting factors, re-heparinization, platelet dysfunction
- HTN: systolic arterial pressures are maintained 90-110
- Transportation: O2, monitoring capability, ambu bag, airway equipment, emergency drugs, infusion of vasopressors
what is the goal of fast tracking?
extubate early: 1-4 hrs. post-op
what is the risk of fast tracking?
may have greater myocardial ischemia in early post-op period
what is the strict criteria for fast tracking?
- normal ventricular and valvular function
- under 70 y/o
- uncomplicated surgery (not valvular)
- no disorders early post-op
what is the ideal agent that allows fast tracking?
propofol
- can be infused throughout surgery, yet allow rapid recovery
- advantage: allows early mobilization and ultimately discharge home, saving money
