Myocardial Protection-Exam 2 Flashcards
What is already in Lactated Ringer’s 1000mL?
KCL 20mEq
MgCl 32 mEq
Mannitol 12.5 g
NaHCO2 6.5 mEq
What do you need to add prior to use in Lactated Ringer’s 1000mL?
Procaine 10% 2.7 mL
What is already in Normosol 1000mL?
NaHCO2 35 mEq
KCL 35 mEq
Mannitol 25% 12.5 g
What do you need to add to Normosol 1000mL prior to use?
Lidocaine 75 mg
Ntg 500 mcg
Albumin 25% 12.5g
Pure Crystalloid Cardioplegia Advantages
Hx of Use
Ease
Cheap
Low viscosity
Pure Crystalloid Cardioplegia Pitfalls
Cellular edema Low O2 capacity left shift oxy-hgb curve Activates plts, leukocytes, and complement Impaired membrane stabilization Hemodilution
What are the two generic crystalloid solutions?
Lactated Ringer’s
Normosol
Cold Blood Cardioplegia Advantages
O2 carrying capacity
Reduced hemodilution
Buffering/oncotic effects
O2 radical scavengers present
Cold Blood Cardioplegia Disadvantages
Sludging
Oxy-Hgb curve disruption
Possible red cell damage
Primary energy source for adults vs kids
Adults: Free fatty acids
Kids: glucose
What is the purpose of dextrose?
Big macromolecules; brings in water
How do you prepare for reperfusion?
Substrate-enhanced warm cardioplegia • Limit calcium • Limit PO2 De-air adequately • Avoid ventricular distension
What pressures do you use in controlled reperfusion?
Upon XC MAP → 40 mmHg for 1-2 minutes.
Removal: MAP → 70 mmHg after 2 minutes.
When do you do a “Hot shot”
Just prior to removal of the aortic cross clamp
What is in a hot shot?
It is in addition to XC drugs.
Aspartate Glutamate
• Tham
• Dextrose
• CPD
Typical Warm Reperfusion SOlution
THAM (0.3 M) solution – 225 mL • CPD – 225 mL • Dextrose 50% - 40 mL • MSA/MSG 0.46 M – 250 mL • Dextrose 5% - 200 mL • KCl (2 mEq/L) – 15 mL
What’s another name for custodial cardioplegia?
HTK
HTK
Histidine- Tryptophan- Ketoglutarate
What is in Custodial cardioplegia?
Intracellular cardioplegia solution • Low sodium concentration • Histidine • Tryptophan • Mannitol
What was HTK initially used for?
Organ preservation
What are the advantages of HTK?
Longer safe time of ischemia
• During valve surgery
• Minimally invasive procedures
Del Nido Solution (4:1) uses what kind of base?
Plasmalyte
What’s in a plasmalyte base?
140 mEq/L sodium • 5m Eq/L potasium • 3 mEq/L magnesium • 98 mEq/L chloride • 27 mEq/L acetate • 23 mEq/L gluconate
What additives do you add to Del Nido solution? (4:1)
Mannitol 20% 16.3 mL MgSO4 50% 4 mL NaHCO2 8.4% 13 mL KCL 2 mEq/L 13 mL Lidocaine 1 % 13 mL
What should be the flow for warm retrograde cardioplegia in order to minimize myocardial lactate production?
> 100 ml/min
What clamp technique is used with calcified and stiff aortas?
Single Clamp Technique
Single Clamp Technique
One clamp episode
• One unclamp episode
• Distals and proximals done during one ischemic time
When is the ischemic time of the Side Biting Clamp technique?
Ischemic time is only with fully
clamped aorta
Side Biting Clamp Technique
Two clamp episodes
• Two unclamping episodes
• Distals done during first ischemic time
• Proximals done during second ischemic time
Shorter clamp times
What is the clamp time within the intermittent clamp technique?
Clamp time is the sum of all
fully ischemic times
Intermittent Crossclamp Risk
Stroke; not commonly used
How is fibrillatory arrest performed?
Creates a nearly motionless heart by placing an
alternating current generator in contact with the left
ventricle.
Fibrillatory Arrest Advantages
Left side of heart can be opened without the fear of ejecting air into the aorta.
Avoid cross clamp
• Quiescent heart with coronary perfusion
What should be used in conjuction with the fibrillatory arrest technique?
hypothermia
Keep MAP elevated
Fibrillatory arrest disadvantages
Higher energy requirement than arrested heart
• Spontaneous ejection will result in air emboli
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)
Anesthetic Agents: Pros and Cons
Pro: Preconditioning; ameliorate deleterious effects of reactive oxygen species
Cons: unclear which agents are best
Acute normovolemic hemodilution: Pros and cons
Pro: less myocardial injury; decreased inotrope requirement; reduced A fib and conduction block
Cons: Efficacy not demonstrated in all patient groups; some patients are too anemic for this tehchnique
Neutrophil Depletion: Pros and Cons
Pros: Decreases post bypass v-fib; lower inotrope use; lower postoperative cardiac enzyme release
Cons: cost; complexity
Erythropoietin: Pros and Cons
Pro: limits myocardial injury
Con: cost
N-acetylcysteine: Pros and Cons
Pro: may reduce oxidative stress
Con: may interfere with preconditioning, cost, complexity
Deferoxamine: Pros and Cons
Pro: decreased lipid peroxidation; increased myocardial protection, LVEF; decreased postoperative wall motion abnormalities
Cons: cost; complexity; not proven in large studies
Statins: Pros and Cons
Pros: increased nitric oxide release; anti-inflammatory properties; antioxidative properties; decreased monocyte adhesion
What 3 parameters do you monitor to determine myocardial protection?T
Temperature
pH
electrical activity
Possible causes of failure to arrest
Aortic insufficiency • Cross-clamp or cardioplegia needle malpositioned. • Inadequate solution (low potassium) • Low flow? • Low pressure? • Temperature?
PADCAB
Perfusion-assisted direct coronary artery bypass; perfuse completed grafts
K+
electromechanical arrest
Na+
↓ edema/intracelluar Ca++ buildup
Ca++
Membrane stabilization
NaHCO3
increase pH
THAM
increase pH
Glucose
Substrate, ↑ Osmolarity, ↓ edema
Mannitol
↑ Osmolarity
High Potassium Common Solution Concentrations
KCl 100 mmol/L THAM 12 mmol/L MgSO4 9 mmol/L Dextrose 250 mmol/l CPD 20 mL
Low Potassium Common Solution Concentrations
KCl 40mml/L THAM 12 mmol/L MgSO4 9 mmol/L Dextrose 250 mmol/l CPD 20 mL
Vein Grafts: Pressure and Flow Rate
50mmHg
50-100 ml/min
Direct Ostial: Pressure and Flow Rate
250 mmHg
50-150 ml/min
What percent of CO is direct ostial?
5-8% of CO
Retrograde: Pressure and Flow rate
40 mmHg
150-200 ml/min
Antegrade: Pressure and Flow Rate
50-100 mmHg aortic root P
250-400 ml/min
150 ml/min/m2
Antegrade Dose
Initial: 10-15 ml/kg
Up to 30 ml/kg
Combined doses
1-1.5L Antegrade
500 ml Retrograde
We should assume the P drop across system is
175 mmHg
P drop is proportional to
Velocity; Shear F, viscosity
