RE4: Chapter 24: Anesthesia for Cardiac Surgery Part 1 Flashcards
Coronary perfusion pressure (CPP) equals?
CPP is equal to the aortic diastolic blood pressure minus the left ventricular end-diastolic pressure (LVEDP)
CPP = ADP - LVEDP
What is the single most frequent complications after cardiac surgery?
Myocardial injury and/or infarction
What area of the heart is at the greatest risk for ischemia?
Subendocardium because it is exposed to the highest pressure especially at the peak of systole.
CPP is autoregulated between what MAPs?
MAP of 60 to 140mmHg
Patients with CAD, perfusion becomes dependent on what?
Perfusion is pressure dependent especially when MAP drops below 70mmHg
Blood flow to the LV is largely confined to systole or diastole?
Diastole - 80% of blood flow occurs during diastole when the pressure is low. See figure 24-3.
What is the most significant cause of perioperative ischemia?
Heart rate
Therefore, maintaining an adequate aortic mean pressure and a low heart rate is critical with patients with CAD or an elevated LVEDP.
True or False. Diastolic dysfunction precedes systolic dysfunction.
True.
Diastolic dysfunction make the ventricle stiff (increase LVEDP) and less compliant.
True or False. Regional wall motion abnormalities occur on echo before changes on the ECG.
True
Regional wall motion abnormalities are a sign of systolic dysfunction.
What is the most sensitive intraoperative monitor for detecting myocardial ischemia?
TEE
What is the single best ECG lead for detecting myocardial ischemia?
V5 - placed correctly at the 5th intercostal space anterior axillary line.
Define stunning.
Reversible contractile dysfunction from brief periods of ischemia that last less than 20 minutes and necrosis or cell death is prevented.
Define ischemic preconditioning and given an example.
The phenomenon whereby a short period of ischemia improves the heart’s ability to tolerate subsequently longer periods of ischemic insult.
All inhalation all anesthetics mimic this preconditioning effect.
Define hibernation.
Where LV contractile function is reduced to match the amount of oxygen available.
Hibernation LVs will have improved function after CPB compared to stunned myocardiums.
What is the difference between supply and demand ischemia?
SUPPLY ischemia causes an increase in ventricular compliance (dilation = eccentric hypertrophy) and a decrease in contractility whereas DEMAND ischemia reduces compliance (stiffening) without initially impacting contractility.
Eccentric or concentric hypertrophy is associated with systolic dysfunction?
Eccentric hypertrophy (dilation) due to chronic volume overload of the LV. The dilated heart eventually becomes unable to contract effectively = systolic dysfunction.
What is eccentric hypertrophy?
Series replication of sarcomeres
LV wall dilation
In this shape, the heart is unable to contract effectively leading to systolic dysfunction!!!
The degree of systolic dysfunction is commonly expressed as what?
Ejection fraction
What is the equation for EF?
EF = SV / EDV (end diastolic volume)
Normal EF is 55% or greater
Diastolic dysfunction or diastolic heart failure resulted from chronic pressure loads or volumes loads?
Pressure loads!!
This causes the myocardium to thicken (concentric hypertrophy) and compliance to decrease.
Tends to have an increased LVEDP
What is concentric hypertrophy?
Parallel replication of sarcomeres
LV wall thickening
What are the main differences between diastolic HF and systolic HF?
Diastolic HF - EF is preserved (>40%) and concentric LHV
Systolic HF - EF is depresses (<40%) and eccentric LVH
What are anesthetic considerations for systolic and diastolic dysfunction?
Systolic - preload is already increased, so AVOID FLUID OVERLOAD, contractility is reduced, may need INOTROPIC SUPPORT
Diastolic - VOLUME IS NEEDED to stretch non compliant LV, will need HIGHER MAP to perfuse thick myocardium, SLOW TO NORMAL HR to maximize diastolic time
Right heart failure is most caused by what?
Symptoms?
Left heart failure
RHF causes systemic venous congestion, hepatomegaly, and peripheral edema.
What are the main goals of CPB?
Provide a motionless heart in a bloodless field while vital organs continue to be adequately oxygenated.
Provides respiration (O2 and CO2)
Circulation
Regulation of body temp
What are the 5 basic components of CPB?
- Venous reservoir
- Main pump
- Oxygenator
- Heat exchanger
- Arterial filter
What is cardioplegia?
Chemical solution that stops the heart’s electrical activity and protects it during the procedure.
What is an appropriate MAP and cardiac index during CPB?
MAP 50-60
CI 2.0 - 2.4 L/minute/m2
What is the cannulas of the CBP made of?
Polyvinyl chloride (PVC) with a biocompatible coating to decrease the inflammatory response associated with CPB and to preserve blood components.
What are examples of prime to fill the CPB circuit?
What can occur when prime is added to the patient’s circulating vol?
Isotonic balanced electrolyte solutions such as LR, plasmalyte-A, or normosol-R
Prime can cause dilutional anemia to occur and it is NOT unusual for the Hct to fall to 22 - 25%
What two compartments make up the venous reservoir?
One for the venous drainage from the heart and the other fro the blood suctioned or vented directly from the surgical field known as the cardiotomy.
Why does the fluid level in the venous reservoir need to be sufficiently high?
To prevent air from entering the main pump and causing an air embolism.
What are two different types of pumps used in CPB?
Roller pump and centrifugal pump
What are the main differences between the two pumps?
The flow from the centrifugal pump (more common) will vary with changes in preload and afterload; however the roller pump has the disadvantage of increasing the destruction of blood elements
Where is the arterial filter usually placed in the CPB circuit?
What is the pore size?
Blood passes through the arterial filter before returning to the arterial cannula and the rest of the body.
Pore size is 21 to 40um and acts as an air bubble trap and filters thrombi, fat globules, Ca and tissue debris from entering the circulation.
What is the purpose of the LV vent and where is it placed?
The LV vent is a catheter placed in the LV through the right superior pulmonary vein for the purpose of draining blood that accumulated in the cavity. (Due to the bronchial arteries and thebesian vessels)
What is the standard heparin dose for CPB?
300 to 400 units/kg and preferably administered in a central IV
What is a preferred ACT following heparin administration?
> 400 seconds is necessary before CPB is initiated.
Drawn 3 to 5 minutes after heparin administrations
Normal value is 80 -120 seconds
What is heparin resistance?
ACT < 380 seconds despite administration of 400units/kg of IV heparin
What two things are done during CPB to protect the myocardium?
- Mild to moderate systemic hypothermia
2. Cold cardioplegia
The cerebral metabolic rate decreases _____% for every degree Celsius decrease in brain temperature.
6-7%
What is a “hotshot”
Just before releasing the aortic cross clamp, a single dose of warm blood (37C) cardioplegia is administered. This is called a “hotshot” which contains metabolic substrates which have been found to accelerate myocardial recovery from global ischemia.
What is the difference between antegrade and retrograde cardioplegia?
Antegrade cardioplegia is delivered into the aortic root proximal to the the aortic clamp and down into the coronary arteries
Retrograde cardioplegia is delivered via the coronary sinus and cardiac veins.
How often is cardioplegia administered to the heart remains asystolic?
Every 15 minutes.
What would you see when myocardial preservation is inadequate?
Electrical activity may reappear on the ECG between doses of cardioplegia.
What are two types of antifibrinolytics used during CBP and why are they used?
Amicar or tranexamic acid
Reduces surgical bleeding by inhibiting plasmin, which is the key enzyme in the fibrinolytic cascade.
(TXA is 5-10x more potent and more expensive, thus not commonly used)
What is the purpose of ultrafiltration?
Ultrafiltration raises the hematocrit, thus is most often performed in an effort to prevent transfusing a patient who has a low Hgb level.
What are the most commonly pathophysiologic mechanisms for organ dysfunction after CPB?
SIRS and ischemia
What is the recommended glucose management for patients undergoing CPB?
Maintain BS 180mg/dL or less.
Check BS ever 1/2 to 1 hour.
DM and hyperglycemia are associated with increased sternal wound infections, extended stays, recurrence of angina, postop mortality and decreased long-term survival.
When is the safest time to place an arterial line for a patient planning to have CPB?
Safest to place prior to induction, using sedation as tolerated
Why must special precaution be taken when a PAC is placed in a patient with LBBB? When should a PAC be avoided?
About 3% of the time, the patient will develop CHB. Thus a defibrillator or pacing pads should be prophylactically placed before insertion of the catheter.
PACs should be avoided in patients that had a pacemaker leads placed in the past 6 weeks because of the possibility of lead displacement.
What is the most sensitive clinical monitor for detecting wall motion abnormalities caused by myocardial ischemia?
TEE
What are absolute contraindications for TEE?
Pathological conditions of the esophagus including strictures, diverticula, tumors, traumatic interruption, or recent suture lines.
What are the advantages and disadvantages of volatile anesthetics?
Advantages: preconditioning effect EXCEPTION: patients with severe LV dysfunction who cannot tolerate any further cardiac depression.
Disadvantages: myocardial depression, vasodilation, hypotension and lowers the arrhythmogenic threshold to catecholamines
What are induction agents of choice for this patient pop.?
Etomidate or propofol
However, if adrenal insufficiency is suspected, a dose of steroids such as hydrocortisone 100mg may be administered.
What is the antibiotic of choice for cardiac surgeries?
Beta-lactam antibiotic who are NOT at increased risk for MRSA.
Patients with increased risk of MRSA, should have vanco added.
What is the goal during precardiopulmonary bypass period?
Hemodynamic stability
What are the common periods of stimulation during this period?
Intubation, incision, sternal split and spread, sympathetic nerve dissection, pericardial incision and aortic cannulation.
Should you treat hypokalemia during the pre-CPB period?
No because cardioplegia solution contains significant amts of potassium.
During what period is the highest rate of recall in cardiac surgeries?
Incision to bypass
Is the arterial or venous cannula placed first?
Arterial cannula
Before the aortic cannula is placed, the SBP should be reduced to what?
SBP of 90 to 100mmHg or a MAP less than 70mmHg to decrease the risk of aortic dissection
After the venous cannula is placed, the perfusionist may initiate retrograde autologous priming (wrap). What can you do to help facilitate this process?
This process requires an increased BP.
If the surgeon places a catheter for retrograde cardioplegia, what should you anticipate?
The surgeon will need to lift the heart to Palpate the coronary sinus. The lifting of the heart leads to hypotension and dysrhythmias. For this reason, the surgeon may place this cannula after bypass has been initiated.
What initiates CPB bypass?
- Perfusionist releases the venous clamp, allowing the blood to fill the venous reservoir; then the arterial clamp is removed, initiating CPB
Acceptable venous drainage usually correlates with a CVP less than ____mmHg
5
What is the most ominous reason for significant persistent hypotension (MAP <30mmHg)?
Aortic dissection - diagnosis confirmed by TEE
CPB must be discontinued until the aorta can be recannulated distal to the dissection.
What does aortic cross-clamp represent?
The beginning of cardiac arrest.
The surgeon usually asks the perfusionist to decrease CPB flow while the aortic cross-clamp is applied. Following X-clamp, full CPB flow is resumed and cardioplegia is infused.
After cardioplegia is given, does the heart arrest during systole or diastole?
Diastole
What is the flow rate on CPB?
50-60mL/kg/min to reach a CI of 2.0-2.5L/min/m2
What is an adequate urine output during CPB?
1mL/kg/HR
What are the criteria for separation of CPB?
Normal Temp of 36 - 37C Normalized blood gases Air clearance Stable cardiac rate and rhythm (sinus and HR between 80-90) Ability to ventilate
If fibrillation occurs, the heart is defibrillated with internal cardiac paddles placed directly on the myocardium at _____ joules.
10-20 Joules
What are common pacemaker setting used following discontinuation of CPB? Advantage vs. disadvantage
Asynchronous pacing mode - VOO or DOO
This prevents electrocautery-induced pacemaker inhibition.
However, asynchronous pacing modes place the pt at risk for developing Vfib as a result of R-on-T phenomenon. Thus, the pacer should be converted to a synchronous mode as soon as electrocautery use becomes limited.
Upon d/c of CPB, the lungs should be reinflated to a positive pressure what ____cm H2O?
The lungs should be gently reinflated manually limiting the positive pressure to 30cm H2O. The anesthetist should also be visually inspecting the lungs as they reinflate.
What situation should overinflation of the lungs be avoided?
Following a CABG because an in-situ ITA bypass graft may be stretched or even disrupted following hyperinflation of the lungs
If ventricular function if marginal, what inotropes should be considered?
epinephrine, dopamine, or dobutamine
If hypotension persists, what vasoconstrictor should be considered?
Norepinephrine
What initiates separation from CPB?
The perfusionist clamps the venous return FIRST to facilitate filling of the RV. Once adequate volume is given through the in-situ arterial cannula, the arterial cannula is clamped SECOND and this signals the separation from CPB.
What is the goal BP during decannulation?
BP of 90mmHg or MAP or 70mmHg or less
What cannula is removed first?
The atrial (venous) cannula is removed first, then the aortic (arterial) cannula is removed second.
What is the recommended protamine dose and where should it be administered?
The normal dose is one milligram of protamine to reverse every 100units of heparin.
Ex. Heparin dose of 30,000 units would require 300mg of protamine for reversal
A test dose of 10mg is first administered peripherally, followed by a slow push of the remaining dose to avoid hypotension
Following CPB, postop bleeding and cardiac tamponade can occur. What are the classic clinical indications of cardiac tamponade?
- Pulses paradoxus - drop in SBP > 10mmHg on inspiration
- Electrical alternates - cyclic alteration in the magnitude of P waves, QRS complexes and T waves
- Beck triad - low BP, jugular venous distention and distant heart sounds
