CPB weaning

 CROSS CLAMP- good visualisation of surgical fields but may result in myocardial ischaemia without adequate protection


 MYOCARDIAL PRESERVATION
crystalloid cardioplegia
Na 147 K 20 Mg 16 Ca 2 Cl 204 procaine 1 mmol/L
cold

does not prevent ion fluxes and continued influx of Ca, Cl , contributing to depletion of ATP and intracellular calcium overload, thought to be critical in development of myocardial stunning

blood cardioplegia
- most common protective strategy
-however- cold blood cardioplegia- increased viscosity- limits myocardial perfusion
-if warm- may reduce reperfusion injury
-improves o2 carriage (compared to crystalloids)
-improves buffering capacity
-multiple doses may be used
-provides antioxidants

for anterograde (via ascending aorta or aortic sinus, with competent AV, Aortic root pressure of at least 60mmHg for coronary perfusion)

alternative cardioplegia methods (without protection)
- intermittent aortic cross clamp/ induced VF

weaning from CPB
- rewarmed to naso/oeso temp 35-36
-core-periph difference <6 degrees)
-shivering-BAD
-overheting-BAD (>36)

intracardiac procedure- de-airing
epicardial pacing wires to protect against arrhythmias
acid base imbalances, electrolytes
ventilation recommenced
anaesthesia/analgesia/nmba suppplemented
monitors
myocardial support instituted

separation
-stable heart rhythm, warm, all above factors addressed
-venous line partially clamped-heart fills
-pump speed reduced-if BP maintains-->
-venous line fully clamped
-pump stopped when heart is appropriately filled and functioning well. (may need tropes, optimal hr)
-can continue to fill with arterial line  


 causes of failure to wean
poor preop ventricular function
inadequate myocardial protection
prolonged cross clamp time
imperfect surgical repair
electrolyte imbalance
acidosis
arrhythmias