Cardio pulmonary bypass surgery kmch .pptx

This is a ppt on cardiopulmonary bypass and its implications on avr surgery anesthesia

1. Cardiopulmonary bypass (CPB ) circuitry - Avinash.R Moderator – Dr.Kaapian , Dr.Sharmila

2. Introduction: Circulation outside the body, pump – heart, oxygenator – lungs Bloodless surgical field Landmark discovery in 1953 by John Gibbon Respiratory support, noncardiac surgical procedures Early days – anaesthetist were in technical developments We must understand CPB for safe conduct

3. The circuit: Pump - Heart Oxygenator - Lungs Heat exchanger Cannulae Reservoir Filters/ bubble traps Others : safety features

4. Pumps: Roller pump Centrifugal(kinetic) pump

5. Roller pumps: Has 2 rollers positioned on a rotating arm which compress the length of tubing to produce forward flow

6. Output = volume per revolution (stroke volume) × RPM (HR) Resistance – sum of resistance of tubing length, oxygenator, heat exchanger, arterial line filter, cannulae and SVR Arterial line pressure – should not exceed 250 mmHg Flow 2-2.5L/min/ m^2 (50-60ml/kg/min)

7. Centrifugal pumps: Has impellers/ stacked cones within housing When rotated rapidly, negative pressure is created at one inlet, and positive pressure at the other, thus propelling the blood forward.

8. Oxygenators: Bubble oxygenator (used previously) Membrane oxygenator (current)

9. Membrane oxygenator: Microporous(<1micrometer) polypropylene membrane Polymethyl pentene - ECMO Oxygenation by gas blender CO2 exchange by sweep gas flow Placed after the pump Less harmful effects

10. Heat exchanger: Hypothermia Rewarm before CPB termination Lies on the proximal side of oxygenator 2 phases with water passing on one side and blood on the other side External heating cooling device regulates temperature

11. Excessive rewarming – gaseous macroembolism and CVA Rewarming while weaning should not exceed 37°C

12. Cardiotomy and cell savers : Removes blood from surgical field and return it to cardiotomy reservoir on CPB machine Removes Micro aggregates of cells, fats, thrombogenic / fibrinolytic factors Cell savers/ cell salvage washers

13. Vent cannulae : Sources of blood to left heart – Bronchial veins, Thebesian veins, ASD, VSD, PDA, AR Ventricular distension – LV dysfunction Increased oxygen consumption – ischemia LA Hypertension Pulmonary edema Limited surgical exposure

14. Safety features: Low level alarm for arterial pump High arterial line pressure alarm Air/bubble detector alarm of arterial pump Arterial line filters One way check alarms for arterial line, purge lines and vents Bubble detector, O2 sensor, reservoir low level alarm Automatic battery backup

15. Conduct of CPB : Prime Anticoagulation Initiation after cannulation Cardioplegia Anaesthesia and monitoring Ultrafiltration Weaning

16. Prime: Volume necessary to completely de-air the circuit Previously blood was used Clear priming solutions – reduced viscosity, hemodilution Crystalloid alone – tissue edema Mannitol, albumin/FFP ( Paeds ), HMW colloid Balanced electrolyte solutions/RL 1.5-2 L initially for adults + additions Heparin 200-300IU/kg(3U/ml) added to the prime

17. Target Hct on bypass – 21-24% in adults, 28-30% in children Pump flow rate – BSA × C.I

18. Anticoagulation: Before cannulation HEPARIN – 3-5 mins before cannulation 300-400IU/kg Target ACT > 480 s Heparin dose response curve & plasma Heparin conc. measurement

19. Heparin resistance – AT III concentrates and FFP HIT – alternative anticoagulants – Lepirudin Bivalirudin Argotraban Danaproid

20. Cannulae : Arterial cannulation: Cannulated first as volume can be transfused to patient Sites – ascending aorta(m/c) Femoral Axillary Less common – innominate, brachial, left common carotid

21. Dissection (femoral) Malposition Disruption of plaque and systemic embolization Hemorrhage Limb ischemia (femoral)

22. SBP of 90-100 mmHg Decreases intraluminal pressure Decreases wall tension and dissection Soft aorta Less bleeding

23. To reduce the risk of atheromatous plaque during cannulation, Surgeon should feel the aorta for appropriate site for cannulation Epiaortic ultrasound TEE

24. Once placed, de aired and connected to arterial line, ensure line is free of air bubbles Line pressure corresponds patients BP Needle of manometer should swing nicely Pulsatile motion of the fluid in arterial limb Blood velocity at rate of 100-200 cm/s

25. Venous cannulation: Single two stage cannula Bicaval cannula

26. Two stage cannula – performed when RA access is not required Air will be sucked in venous cannula when R.A. is opened E.x . CABG, AVR Bicaval cannula – when RA access is required ASD, MVR

27. Femoral or iliac veins – redo, minimal access surgery, Percutaneous support Left SVC – separate cannulation Atrial arrhythmias Bleeding – transfuse in aortic line Additional vent cannulae – to drain left heart (source – bronchial veins, Thebesian veins, AR, PDA, ASD, VSD)

28. Methods of confirmation: Visualising complete decompression of right heart Low CVP and PA pressure zero Improper size or placement – hampered venous return and elevates CVP Venous clamp gradually released, full CPB Ventilation discontinued

29. Myocardial protection – Cardioplegia : CPB – decreases contractile work and MVO2 Chemical Cardioplegia – minimal O2 consumption and effective myocardial protection MVO2 further decreased by Hypothermia Cardioplegia – eliminates electro mechanical activity Hypothermia – reduces basal metabolism

30. Routes – Aortic root ( antegrade ) Coronary ostia (after opening the root – AR) Coronary sinus (retrograde) 20ml/kg (1-1.5lit) with 150mmHg applied to bag Supplemented every 20-30mins(half the initial dose) Cardioplegia solution should properly reach coronary circulation and should not enter LV

31. Retrograde Cardioplegia advantages: Uniform distribution distal to coronary obstruction Preserves hypertrophied myocardium Reduces incidence of postoperative SVT Aortic valve surgery eliminates the need for ostial cannulation Redo surgery

32. Disadvantages: Coronary sinus injury Delay in cardiac arrest Inadequate preservation of RV Need for bicaval cannulation (but advanced stylet guided catheters are available now)

33. Hot shots – 2° Cardioplegia Brief continuous infusion of cardioplegia solution just before the release of aortic cross clamp Warm 37°C Oxygen – cellular repair rather than electromechanical work

34. Ischemic preconditioning: Endogenous form of myocardial protection Before the long ischemic insult, 5 minutes of ischemia and 5 minutes of reperfusion Adenosine OPCABG Volatile anaesthetic – minimises ischemia reperfusion injury, improves myocardial oxygen balance, free radical scavenging

35. Maintenance: Pharmacokinetics of our drugs are affected due to Hemodilution Hypothermia Alterations of organ perfusion Acid base status Sequestration of drugs in lungs and CPB circuit Effect of SIRS

36. Hemodilution – Lowers plasma concentration Lightening of anaesthesia? Hemodilution also lowers protein conc. and the plasma ratio of free drug is increased Hepatic perfusion and metabolism reduced – redistribution of newly administered drug is decreased

37. Muscle relaxants – hemodilution acutely reduce neuromuscular blocking effects since water soluble Boluses of opioids/ BZD/ muscle relaxant at the onset of CPB

38. Amnesia :
Recall is unlikely in hypothermia < 30°C
Risk of awareness during rewarming and after CPB
Thiopental/ Propofol / BZD/ volatile agents once pulmonary circulation is established

39. Monitoring: Hct ABG & Electrolytes, Sugars MAP 50-70mmHg ACT Temperature Urine output (1ml/kg/hr) every 30 mins Low CVP Adequate reservoir volume

40. Blood gas management: Alpha stat (Temperature uncorrected) pH stat(Temperature Corrected) Hypothermia increases solubility of pCO2 in blood – alkalosis Temp decreases PaCO2 decreases

41. Alpa stat: Maintains pH at 7.4 and pCO2 at 40 without addition of exogenous CO2 Maintains cerebral autoregulation Non homogeneous brain cooling Limits micro emboli

42. pH stat: Maintains pH 7.4, pCO2 at 40 by adding CO2 to oxygenator gas supply Autoregulation lost (excessive cerebral blood flow) Homogeneous cooling More risk of embolism to brain

43. Temperature management: Hypothermia – reduces systemic oxygen consumption 9% per 1°C Slow the rate of warming of heart when cold cardioplegia is used Neuroprotection ? Hyperthermia is harmful – during rewarming, postoperative period

44. Ultrafiltration: Removes inflammatory mediators and excess fluid during and after CPB Reducing blood loss and transfusion requirements Conventional – during CPB by hemofilter attached to CPB circuit Modified – after CPB prior to protamine

45. Weaning from CPB: Gradual Temperature should not exceed 37°C Temperature gradient b/w core and periphery should not exceed 10°C ABG normal Chambers adequately de-aired Ventilation restarted Normal rate and sinus rhythm

46. Start inotropes if required Defib if VT/VF Inability to wean – Hypovolemia/ myocardial dysfunction/ vasoplegia IABP/ ECMO if unsuccessful Protamine 1:1 – 1:1.3 Decannulate venous first, then artery Maintain components of anaesthesia

47. Disasters during CPB: Malposition of arterial cannula Aortic dissection Massive air embolism Coagulopathy after CPB(Persistent inability to raise ACT > 400s) Clots Allergy – protamine/ transfusion Failure to initiate ventilation before termination of CPB

48. References: Deepak Tempe’s clinical practice of cardiac anaesthesia – 3 rd edition Video lectures from RAA online Review article by Dr.Sarkar M prabhu on basics of CPB published in IJA Morgan’s 7 th edition/ Miller’s 9 th edition. - Thank you_/\_