Myocardial protection part 2 Flashcards
heart takes up oxygen over time so blood cardioplegia must
be delivered over time not a volume
Four Main Objectives of Cardioplegia
- Immediate/sustained electromechanical arrest
- Rapid/sustained homogenous myocardial cooling
- Maintenance of therapeutic additives in effective concentrations
- Periodic washout of metabolic inhibitors
Two Main Goals of Cardioplegia
Prevent myocardial ischemic damage
(induction/maintenance)
Prevent/minimize injury
(reperfusion)
limit these detrimental changes to heart
rapid cellular conversion from aerobic (O2) to anaerobic metabolism (no O2)
• high-energy phosphate (e.g. ATP) depletion • intracellular acidosis • calcium influx • cell membrane disruption
• Intracellular Ca+2 accumulation • Cellular edema (inability to consume oxygen)
Cardioplegia Setups (types)
Crystalloid • Single pass system Blood • Fixed ratio • Bridged • Non-bridged • Variable/controlled ratio MPS • Microplegia
3 Phases of Cardioplegia
I. Induction of arrest II. Maintenance of arrest III. Reperfusion
Cold Induction Solutions: Crystalloid and Blood
ECF cardioplegia solution Potassium depolarization arrest
• Depolarizes the cardiac myocyte with hyperkalemia
• Ca2+ATPase and Na+/K+ATPase still operative and need energy
Pure Crystalloid Cardioplegia Induction Advantages
• History of use • Ease • Cheap, low viscosity
Pure Crystalloid Cardioplegia Induction pitfalls
- Cellular edema •Low O2 capacity • Left shift oxy-Hgb curve •Activates platelets, leukocytes, and complement
- Impaired membrane stabilization• Hemodilution
Lactated Ringer’s 1000 mL electrolyte concentration
KCL 20 mEq MgCl 32 mEq Mannitol 12.5 g NaHCO2 6.5 mEq. Add prior to use Procaine 10% 2.7 mL
Normosol 1000 mL concentrations
NaHCO2 35 mEq KCL 35 mEq Mannitol 25% 12.5 g
Add prior to use Lidocaine 75 mg Ntg 500 mcg Albumin 25% 12.5 g
Cold Blood Cardioplegia Induction Advantages
O2 carrying capacity Reduced hemodilution Buffering/oncotic effects O2 radical scavengers present
Cold Blood Cardioplegia Induction pitfalls
Sludging Oxy-Hgb curve disruption •Possible red cell damage
Warm Blood Cardioplegia Induction Advantages
- Improved aerobic metabolism
- Improved LV function
- Improves compromised hearts
Warm Blood Cardioplegia Induction pitfalls
•Expensive due to additives
Example: Warm Induction Solution (8:1)
• D50 11ml • D5 27ml• CPD 67ml• THAM •83ml Aspartate/Glutamate •62ml KCL 2meq/L 60mEq •Lidocaine 100mg
Low Potassium Maintenance
Usually every 15 to 20 minutes Cold blood cardioplegia or crystalloid Restores arrest post wash-out
Preparation for Reperfusion
• Substrate-enhanced warm cardioplegia • Limit calcium • Limit PO2 •Controlled reperfusion
The endothelium is damaged during ischemia,
damage can increase through unregulated reperfusion
Upon XC MAP → 40 mmHg for 1-2 minutes. Removal: MAP → 70 mmHg after 2 minutes.
• De-air adequately • Avoid ventricular distension
The “Hot Shot” (when?)
Just prior to removal of the aortic cross clamp
In addition to cross clamp drugs
Whats in the hot shot
• Aspartate Glutamate • Tham • Dextrose • CPD
Due to cost – warm blood may be substituted
Typical Warm Reperfusion Solution
- THAM (0.3 M) solution – 225 mL • CPD–225mL • Dextrose 50% - 40 mL • MSA/MSG 0.46 M – 250 mL
- Dextrose 5% - 200 mL • KCl (2 mEq/L) – 15 mL
Custodial Cardioplegia (HTK) Histidine-Tryptophan-Ketoglutarate
- Intracellular cardioplegia solution • Low sodium concentration
- Histidine • Tryptophan • Mannitol
Benefits of HTK Cardioplegia
- Initial use: organ preservation • Now used in cardiac surgery
- Longer safe time of ischemia • During valve surgery • Minimally invasive procedures
Del Nido Solution (4:1)
Plasmalyte base which is similar to ECF: • 140 mEq/L sodium • 5m Eq/L potasium • 3 mEq/L magnesium
• 98 mEq/L chloride • 27 mEq/L acetate • 23 mEq/L gluconate
del nido solution additives
Mannitol 20% MgSO4 50% NaHCO2 8.4% KCL 2 mEq/L Lidocaine 1 %
16.3 mL 4 mL 13 mL 13 mL 13 mL
additional solutions
• Plegisol ,Baxter Cardioplegia, St. Thomas Solution, University of Wisconsin Solution
Warm Continuous Retrograde Blood Cardioplegia
• Lichtenstein (1991) suggested that the heart could be maintained at
37oC throughout the cross clamp period to enhance perioperative myocardial function.
Warm Continuous Retrograde Blood Cardioplegia Normothermic patients experienced a lower incidence
of post-operative low output syndrome with no differences in mortality or myocardial infarction.
Warm retrograde cardioplegia flow must be
> 100 mL/min to minimize myocardial lactate production
Single Clamp Technique
One clamp episode One unclamp episode Distals and proximals done during one ischemic time
• Used with calcified stiff aortas
Side Biting Clamp Technique
Two clamp episodes Two unclamping episodes Distals done during first ischemic time Proximals done during second ischemic time
• Ischemic time is only with fully clamped aorta
• Shorter clamp times
Intermittent Crossclamp
- Increased risk of stroke • Not commonly used
* Clamp time is the sum of all fully ischemic times
Fibrillatory Arrest Creates a nearly motionless heart by placing an
alternating current generator in contact with the left ventricle.
fib arrest Left side of heart can be opened without the fear
of ejecting air into the aorta.
fib arrest should be used in conjunction with
hypothermia
Fibrillatory Arrest Advantages:
• Avoid cross clamp • Quiescent heart with coronary perfusion
fib arrest Disadvantages:
•Higher energy requirement than arrested heart • Spontaneous ejection will result in air emboli
Keep MAP elevated
Additional Strategies to Enhance Protection
• Anesthetic agents (↑ preconditioning) • Acute normovolemic hemodilution (↓ A fib) • Neutrophil depletion (↓ V fib) • Erythropoietin (↓ myocardial injury) • N-acetylcysteine (↓ oxidative stress) • Deferoxamine (↓lipid peroxidation) • Statins (↑NO release)
Monitoring Effectiveness for the Perfusionist GOAL:
optimize uniformity and effectiveness of delivery
(especially retrograde)
• Temperature • pH •Electrical Activity
Monitoring - Temperature Thermo coupled needle usually inserted
septal muscle (myocardial temp probe)
monitoring temp. Ensure delivery of
adequate dose (is it going where it belongs?)
monitoring temp. See efficacy of delivery
• Antegrade - cases of aortic insufficiency • Retrograde - cannula position ( in RA?)
Determine when next dose needed use
timers
reasons for failure to arrest
• Aortic insufficiency • Cross-clamp or cardioplegia needle malpositioned. • Inadequate solution (low potassium) • Low flow? • Low pressure? • Temperature?
Myocardial Protection for Off-Pump Procedures
Regional ischemia unavoidable
• May become global problem when multiple vessels grafted
Use of suction-based stabilizers has reduced the problem of working on a moving target
• Provide good exposure without excess compression of ventricle
Ischemic preconditioning
• Brief period of vessel occlusion before occluding for construction of the anastomosis
Myocardial Protection: Off-Pump Procedures cont.
Myocardial Protection: Off-Pump Procedures
• Keep normal to high systemic blood pressure • May increase flow through collaterals vessels
• Attach proximal end of graft before attaching distal • Immediate re-establishment of flow to ischemic area
• Use of intracoronary shunt
• Perfusion-assisted direct coronary artery bypass (PADCAB)
• Perfuse completed grafts
K ACTION
electromechanical arrest
Na action
↓ edema/intracelluar Ca++ buildup
Ca++ action
Membrane stabilization
NaHCO3 action
↑ pH
THAM action
↑ pH
glucose action
Substrate, ↑ Osmolarity, ↓ edema
Mannitol
↑ Osmolarity
high potassium solution concentrations
KCl 100mmol/L. THAM 12mmol/L. MgSO4 9 mmol/L Dextrose 250 mmol/L CPD 20ML
low potassium solution concentrations
KCL 40 mmol/L THAM 12 mmol/L MgSO4 9 mmol/L
Dextrose 250 mmol/l CPD 20 mL
