Notes fr Lecture by J Heinle 080812
-prebypass, just made pts hypothermic
-1953 Gibbon did first CPB case, went well, but the subsequent ones did not go well so he stopped.
-1954 Lilihei did cross circulation bypass with the parent
Goal:
-provide a bloodless field
blood into heat exchanger/reservoir, heat exchanger, oxygenator, and then to the pt.
Levels of Support...:
-Bypass
-Cross Clamp (= Ischemic time - no Q to heart)
-Circ Arrest = no perfusion anywhere in body (or alternatively Antegrade Q only- selective Q to brain)
Start cooling after you go on bypass.
-If we work inside the heart, must stop the heart = Cross Clamp time (body perfused, but not the heart), this is the Ischemic Time
-Some pts need Circ Arrest (or selective cerebral perfusion), where you drain all blood from body and stop all perfusion or near all (with just brain perfused, e.g. to work on the arch)
Cannula in atrium - drain venous blood to a reservoir. Then pump from that to an oxygenator and heat exchanger, then pass that through filters and send back to the aorta.
Must heperinize so you don't clot from blood-plastic interaction. Goal ACTs >400, but often >600!
Blood outside heart also gets put into reservoir via suction...
Cardioplegia is introduced to stop the heart
-first cool heart, then give this high K+ solution to stop the heart
Extracorporial circuit
-3.5-4m2 of plastic and metal one is exposed to on avg adult...
Arterial Blood Pump
-Roller vs Centrifugal blood flow
Stockert S3 Pump
-Roller head, nonpulsatile, very precise, can do flow from infant to adult
Q goal d/o BSA and pt's weight
Oxygenator
-Hollow Fiber membrane - microporous, with blood pumped through/around the membrane, for O2 diffusion into the blood. Oxygenation d/o FiO2 to the oxygenator as well as Q thru it...
Pump Prime Components
-dilute the pt's blood
-must prime bc you can't drain the blood into an empty circuit
-Use pRBC +FFP in smaller babies, if >17kg, can try to just use colloid with 25% albumin +/- FFP
-Additives: heparin, NaHCo3, KCl, CaCl, D5W - all made to match pt's intrinsic blood...
Heat Exchanger
-induce hypothermia and then return to normothermia
Filter
-remove WBCs
-remove emboli
Ultrafiltration
-remove inflammatory mediators & free water --> pts not very edematous postop...
-can hemoconcentrate to increase Hct
-remove K
-increase osmotic P
Steps to CPB:
1- Sternotomy
-saw through sternum...
2- Cannulae and Cath Position
-Arterial cannula in Ao for inflow
-R side cannula- usually SVC and IVC, sometimes just one in RAA
-may need to also cannulate a LSVC etc
3) Initiation
4) Cooling - to 18 degr C, brain needs 10% Nl oxygen at this pt
5) Cross Clamp = Cardiac Ischemia
-the cardioplegia is cooled to 4degr C so that is what the heart temp is, to minimize O2 need
-now now heart movement after getting high K, very relaxed
-Ao is cross clamped--> no Q to coronaries, then give the cardioplegia solution...
-Give cardioplegia via a cath into the Ao root, q20 minutes
6) Circ Arrest
7) Warming
8) Cardiac Reperfusion
-de-air the heart, then remove cross clamp so blood rinses out the heart's cardioplegia solution--> it rewarms and then starts beating
9) Termination of CPB
-drain the reservoir by tightening down the venous return so Q to pt stays in the pt --> pulsatile wave form etc returns
Postbypass pt has high ACTs, very coagulopathic, very pro inflammatory, etc, w fresh sutures in heart... so must take care against bleeding...