Cardiac Intra-op Mgmt (pt 2/2) Flashcards
List the basic sequence during CPB
-Go on bypass
-Cool patient
-Cross clamp aorta
-Arrest heart with cardioplegia
-Do operation
-Warm patient
-Unclamp aorta
-Pacing wires
-Prepare for weaning
-Come off bypass
Why do they cross clamp the aorta?
-Don’t want cardioplegia solution going throughout the body
-Clamp proximal to cannula
-MAP will drop briefly
-Surgeon will say “flows down” to perfusion
How do you arrest the heart?
-Cardioplegia infused antegrade through the coronaries or retrograde through the coronary sinus to arrest the heart.
-Myocardial blood supply is interrupted by placement of aortic XC: must arrest myocardium (with cardioplegia)
-Antegrade technique achieved by administering cardioplegia solution directly into the aortic root between the aortic valve and XC
-Interval between placement of XC and administration of cardioplegia kept to a minimum to prevent any warm ischemia
-Solution usually high in potassium, which arrests heart in diastole
-Retrograde administration occurs through the coronary sinus
-Can be placed under TEE guidance
Which bypass grafts are done first?
-Distal SVGs placed on most severely diseased coronaries first, to facilitate administration of additional cardioplegia via vein graft to distal stenosis
-IMA often constructed last because of its fragility and shorter length.
When does rewarming begin?
Rewarming typically begins when final distal anastomosis is begun.
-Brain warms faster than body (may need additional anesthetic)
-High risk for recall with rewarming!
-Vasodilators facilitate rewarming by improving distribution of blood and permitting higher pump flow rates
-Avoid shivering with adequate anesthesia and muscle relaxation
-Additional Heparin may be required as metabolic rate normalizes
-Rewarming should be complete (37 C) by the end of the procedure.
-May need to defib the heart once it’s warm.
How do you determine the rate of rewarming?
-Rate of rewarming depends on max safe temp gradient between water temp in the heat exchanger and the blood.
-Must be <10 C. Some use max of 6-8 C
-Higher gradient = inc risk of microbubbles
Why do you need to de-air the heart?
Air may collect in the pulmonary veins, LA, or LV which will be aspirated through aortic root vent (Antegrade Cardioplegia Line) prior to XC release.
-Temporarily raising the CVP and inflating the lungs will fill LV and permit easier surgical aspiration of intracavity air
-Residual air detected using TEE
How do you unclamp the aorta?
-Aorta may be unclamped, then an aortic side clamp placed to allow for proximal anastomosis while cardioplegia washed out of heart
-Partial occlusion clamp allows blood flow to these proximal grafts.
-Proximals may be completed with aortic clamp in place in order to reduce instrumentation of aorta
What are the “C”s in the checklist for termination of CPB?
1) Core (Bladder) Temperature >36 (Ideally 36.5). Nasopharyngeal shouldn’t exceed 37.5
2) Conduction – 80-100 bpm
-Sinus Rhythm > Atrial Pacing > AV Pacing > Ventricular Pacing
-Patients with AS/Hypertensive heart disease, atrial kick can contribute up to 40% of SV
3) Calcium - >1.0
-Often treated by perfusionist
4) Cardiac Output:
-Normal? Are ventricles actually getting blood out?
5) Cells – Hgb >7.5 (patient will be getting blood back from the pump and the 2 units you pulled off earlier)
6) Coagulation – FFP/Platelets/Cryo
What are the “V”s in the checklist for termination of CPB?
1) Ventilation – Re-expand with big breaths
-May be requested by surgeon prior to removal of cross clamp to assist with de-airing heart (open procedures)
-FiO2 100%
2) Vaporizer on – anesthesia is your responsibility again when the pump is off
3) Volume Expanders – Crystalloid and Albumin
-Crystalloid is preferred; albumin is expensive & has not shown long-term benefit
4) Visualization – Look at the heart to assess function
-Look over the drape!
-Assess ventricular & valvular function, intracardiac air with TEE
What are the “P”s in the checklist for termination of CPB?
1) Predictors – First attempt at weaning is always the best
-Low EF, Renal Disease, Female, Elderly, Prolonged (>2 hr) CPB Time
-Check all the boxes – if you’re not ready to come off, tell the surgeon to wait!
-Are they making urine? VS normal?
2) Pressure – Arterial and PAP must be adequate
-Arterial diastolic pressure must be adequate to provide perfusion
-Pulmonary artery pressure must Not be high, due to risk of RV failure
3) Pacer – Pacemaker must be functional and capturing
4) Pressors – Inotrope, Vasopressor & Vasodilator
-In line and infusing – most cases will require inotropic support (Epi 2-4mcg/min)
5) Potassium: <6.0
-Insulin administration to rapidly reduce potassium may be required
6) Protamine
-Dose provided by perfusionist based on heparin activity
-Premature protamine administration is Catastrophic
Describe the steps of termination of CPB.
1) Perfusionist decreases venous drainage to “fill the heart”
2) Heart “fills” and begins to eject
-Look for pulsatile waveforms on ABP & PAP
3) Assessment of ventricular & valvular function with eyes & TEE
4) Reduction of arterial inflow by perfusionist
-“What are you flowing?” “4 Liters” “Come down to 2 liters”
5) Progressive reduction of arterial flow by perfusionist to 0 - “Off Bypass”
6) Volume administration from CPB Pump
7) Protamine Administration
What is the most complicated, tenuous time of cardiac surgery?
Progressive reduction of arterial flow by perfusionist to 0 - “Off Bypass”
-Continuous assessment of preload, contractility, rhythm and ABP/PAP
-THIS IS THE MOST COMPLICATED, TENUOUS TIME OF CARDIAC SURGERY
-LV & RV Contractility must remain adequate – Epinephrine boluses may be needed to get heart going.
-Diastolic perfusion pressure must remain adequate - Vasopressor infusion
-Hypertension must be avoided to prevent stress on suture lines (AVOID HTN due to risk of blowing graft). SBP 100-120 is good.
-Volume status must be carefully monitored to prevent RV distension and subsequent failure
How does volume administration from the CPB pump happen?
-Surgeon will remove the venous cannula & close the hole in the right atrium
-Arrhythmias and hypotension are common
-Blood in Venous Cannula will be returned to CPB Reservoir
-Residual volume in the CPB Reservoir will be administered through the aortic cannula
-“How much you got left?” “I’ve got 500” ”Give me 100”
-Good Ventricular function + Volume = Increase in blood pressure due to increase in CO
-If BP does not increase with volume administration, you are probably at the flat portion of the Frank-Starling Curve – More volume will not improve your situation!
-Maintain vigilance – Assess BiVentricular Function, maintain normotension, avoid RV overload
Describe how you should administer Protamine?
Protamine = basic; Heparin = acidic; Acid/Base reaction = Neutralization
-Test Dose – Administer 1-2ml then wait 30-60 seconds
-Rapid administration can cause hypotension, anaphylaxis, or anaphylactoid rxn.
-Announce to room when protamine administration is Halfway
-Once protamine is about halfway infused, can start pulling Aortic Cannula
-Draw ACT (& ABG) 3 minutes after full dose given
-You can never go too slowly with Protamine – But you can definitely go too fast
-Everyone gets hypotension
Describe anaphylaxis reaction to Protamine.
Hypotension, bronchospasm etc.
Happens very quickly. Don’t give more Protamine.
Describe anaphylactoid reaction to Protamine.
Hypotension, 3x elevation in PA Pressures, RV Failure
Can tx with Benadryl or steroids
What is the dosing of Heparin for CPB?
-Initial dose prior to CPB is 300 units/kg
-Dosed based on baseline ACT - will be determined by Perfusion
-Heparin distributes primarily into the plasma compartment; seldom reason for initial dose >35-40k regardless of weight
-CPB priming solution should contain heparin at ~the same concentration as that of the patient’s blood at onset of CPB
-Dosing for off-pump is controversial
-Draw ACT 3 minutes after administration
-Need ACT > 450 to cannulate.
What is the MOA of Heparin?
Binds to ATIII, which potentiates the action of ATIII more than 1000-fold, thereby inhibiting thrombin and factor Xa, as well as IXa, XIa, and XIIa.
-Inhibition of thrombin requires simultaneous binding of heparin to both ATIII and thrombin, whereas inhibition of factor Xa requires only that heparin binds to ATIII
-Thrombin inhibition therefore requires a longer saccharide chain, and shorter chains can selectively inhibit Xa
How does Protamine neutralize Heparin?
-Strongly cationic protamine combines with strongly anionic heparin to produce stable complex devoid of anticoagulant activity
-Combine in proportion to weight: 1 mg protamine neutralizes 1 mg (~100 units) heparin
-Dose of protamine required should match amount of heparin remaining in patient’s blood circulation at time of neutralization
What is the dose of Protamine?
-Dose provided by perfusion based on heparin activity.
-Most often, 25-50 mg protamine will complete neutralization
-Draw ACT & ABG 3 minutes after full dose is given
Describe administration of Protamine.
-Go slow - hypotension
-Continuous infusion rather than hand-operated technique highly recommended by the text
-Injected dose of protamine cannot neutralize heparin bound to plasma proteins or within endothelial cells
-Release of heparin from these stored areas after initial protamine administration may result in reappearance of heparin anticoagulant effect (heparin rebound)
-Post-protamine ACT should return to <10% above patient’s baseline
When is Amicar used?
Better to use it prophylactically: give at beginning of case before going on pump.
-Reduce bleeding
-Decrease need for blood transfusion during CPB
Benefits of Amicar and TXA have been demonstrated in multiple meta-analyses to reduce bleeding in cardiac surgery when used prophylactically rather than as rescue agents
What is the MOA of Amicar?
-Amicar & TXA act as lysine analogs and bind to lysine-binding sites of plasmin and plasminogen
-Form reversible complex with plasmin which then inhibits fibrinolysis (natural breakdown of clots)
-Fibrin degradation products inhibit platelet function thus plasmin inhibition may protect platelets
What is the goal of off-pump CABG?
To avoid the risks and complications associated with CPB (SIRS, Hemodilution) and Aortic Cross clamping (debris embolization)
Why is ATIII important?
-AT3 is needed to bind Heparin.
-If deficiency is present, can replace ATIII, or administer FFP.
-AT III can be provided in the form of FFP, liquid plasma, and AT III concentrates
What is the monitoring for OP CABG?
Monitoring, preop mgmt very similar to standard CABG
-CPP is maintained by keeping a HIGH map during distals (MAP 90-100)
What is unique about volume administration and OP CABG?
-Require increased volume administration
-No hemodilution from bypass prime
-Use fluid as treatment for hemodynamic changes
What is unique about temperature during OPCABG?
Not corrected on pump… so ACTIVE WARMING throughout case is necessary
What about heparinization with OPCABG?
-Partial (>300) or Full (>400/450) depends on the surgeon. Still monitor Q30
-In case of urgent bypass needed
T/F: You always give Amicar with OPCABG.
False; Antifibrinolytics not routinely used bc blood is not exposed to bypass pump
What is different about management of the patient during OP CABG?
-Heart is lifted to provide exposure and stabilizers are used- lead to increased hemodynamic and ischemic issues
-CPP is maintained by keeping a HIGH map during distals (MAP 90-100)
-Blood loss is hidden due to CO2 “Blower” facilitating visualization
Apex is verticalized:
-Chambers compressed, vessel torsion
-Watch for ischemic changes on ECG and TEE
-Treat with VOLUME, PRESSORS, and STEEP T-berg
