Introduction to Cardiopulmonary bypass.

1. Cardiopulmonary Bypass A Presentation on

2. History The first operation performed using cardiopulmonary bypass and open cardiotomy was on April 5, 1951 by Dr. Clarence Dennis at the University of Minnesota. This was following four years of experiments with dogs.

3. History The first successful open heart procedure on a human using bypass machine was performed by John Gibbon on May 6, 1953 in Philadelphia. The operation was correction of an ASD on an 18 year-old girl.

4. Cardiopulmonary Bypass Basic Bypass System : Blood drained from the venous system utilizing gravity through : Cannulas in SVC and IVC Single cannula in right atrium into the venous reservoir It is pumped into the membrane oxygenator Returned to the system via a cannula usually placed in distal ascending aorta

5. Cardiopulmonary Bypass Complete Bypass System (many additional components): Consolidation of: Membrane oxygenator Venous reservoir Heat exchanger In one unit Added microfilter bubble trap to arterial line Blood suctions depending on the operation from : Surgical field Cardiac chambers +/- Aortic root Optionally, but increasingly recommended field blood is washed in a cell saver system and returned to the perfusate as packed cells Partial and occluding clamps on venous and arterial lines in addition to adjusting pump flow to direct and regulate flow. Sites for obtaining blood samples Sensors for monitoring: Pressures Temperatures O2 Sats Blood Gases pH Various safety devices Cardioplegic system to administer cardioplegic solutions at controlled: Coposition Rate Temperature A haemoconcentrator system

6. Cardiopulmonary Bypass Complete Bypass System (Stages): Blood drained from a single “two-stage” catheter into the reservoir Blood is pumped through : First the heat exchanger Then the membrane oxygenator Arterilized blood passes through a filter/bubble trap to the aortic cannula Blood aspirated from vents and suction systems enters a separate cardiotomy reservoir (contains a microfilter) before joining the venous reservoir Cardioplegic System: Fed by a spur from the arterial line Cardioplegic solution added Pumped through a separate heat exchanger into the : Antegrade Retrograde catheters

7. Venous Blood Flow

8. Venous Drainage Venous blood enters the circuit by gravity or siphonage into a reservoir placed 40-70 cm below the level of the heart. The amount of blood drained is determined by: CVP Intravascular volume Venous compliance Medications Sympathetic tone Anaesthesia ∆ H Resistance in cannulas, tubing, and connectors Absence of air within the system Chattering / Fluttering : Inadequate blood volume Excessive siphon pressure Compliant venous or atrial walls collapse against cannular intake openings. Corrected by adding vlume to the patient.

9. Venous Cannulation Venous Cannulas : Made out of flexible plastic +/- wire reinforcement. Tips: Straight or angled From rigid plastic or metal Determining Size: Patient size Anticipated flow rate Index of catheter flow indices For and average adult : 30 F SVC + 34 F IVC / Single 42 F Single Cavoatrial Insertion : Through a purse string Right atrial appendage / lateral atrial wall / directly in IVC and SVC

10. Venous Cannulation Venous Cannulation Techniques: Bicaval + caval tourniquets to prevent bleeding and air entry when entering right heart. Caval tourniquet should not be tightened before decompressing the atrium because of coronary sinus return. - caval tapes if working on left atrium and mitral valve Single Atrial Cavo-atrial

11. Venous Cannulation Bicaval + caval tourniquets to prevent bleeding and air entry when entering right heart. - caval tapes if working on left atrium and mitral valve

12. Venous Cannulation Atrial (“Single Cannula”) Suffices for most of the: Aortic Valve Coronary Artery Surgery Elevation of the heart might partially kink the junction of the SVC and the right atrium Cavo-atrial (“two-stage”) is the method of choice for most of the operations Entered through right atrial appendage More stable and better drainage than a single cannula Proper positioning is critical

13. Venous Cannulation Other approaches: Femoral / Iliac Open / Percutaneous Indications: Emergency closed cardiopulmonary assist Support of particularly ill patients before anaesthesia induction Prevention of management of bleeding complications during sternotomy Reoperations Certain aortic and thoracic surgery Application of CPB without sternotomy Special cannulas : Long Ultra thin Wire-reinforced For adequate flow rates : Large cannulas TOE-guided advancing into the right atrium

14. Venous Drainage Augmented or Assisted Venous Drainage : Negative pressure using a roller pump or centrifugal pump / regulated vacuum to a closed hard-shell venous reservoir. Allows use of smaller diameter catheters Helpful when long, peripheral catheters are used Negative pressure risks : Aspiration of gross or microscopic air and causing cerebral injury Hemolysis Air aspiration into the blood compartment of membrane oxygenators Positive pressure in the venous reservoir: Air entry into the venous lines and right heart These risks require : Safety monitoring devices Adherence to detailed protocols

15. Venous Return Low Venous Return: Low venous pressure Hypovolemia Drug-induced venous dilatation Inadequate ∆ H Small Cannula Cannula obstruction Air Locks Excessive Flow Resistance Partial obstruction of the venous return causes right ventricular distension and impairment of later contractility.

16. Venous Cannulation and Drainage Complications Atrial arrhythmias Atrial / Caval tears and bleeding Air embolization Injury or obstruction due to catheter malposition Reversing arterial and venous lines Unexpected decannulation Placing tapes around the cavae may lacerate: Branches Nearby vessels (right pulmonary artery) Cava itself Catheters may compromise venous return to the right atrium before or after the CPB Venous catheters and/or caval tapes may displace or compromise : CV monitoring PA monitoring Catheters (as do these catheters to the function of venous catheters and / or caval tapes) Entrapment of the intra-cardiac catheter by a suture Improper purse suture placement obstructing the cava when tied

17. Arterial Cannulation Arterial Cannulas: The tip is the narrowest part. Hence, the high pressure differentials, jets, turbulence, and cavitation. High velocity jets : Damage aortic wall Dislodge atheroemboli Produce dissections Disturb flow to nearby vessels Cause cavitation and haemolysis (pressure differences > 100 mmHg cause excessive haemolysis and protein denaturation)

18. Arterial Cannulation Stroke: Increased left-sided stroke following cardiac surgery, due to sand-blasting effect of end-hole aortic cannulas directing debris into the left CCA. Prevention : Aortic cannulas with only side ports are designed to minimize jet effects and better distribute arch vessel perfusion and pressure and may be associated with fewer strokes. Dual-stream aortic perfusion catheter featuring an inflatable horizontal streaming baffle? Protecting arch vessels from any kind of emboli and allowing selective cerebral hypothermia A new type with side-port that deploys a 120-µm mesh filter to remove particulate emboli beyond the ascending aorta. Despite the increased pressure gradient by 50%, this catheter has removed an average of 8 emboli in almost all the patients in the study utilizing this catheter.

19. Dual-Stream Aortic Cannula

20. Dual-Stream Aortic Cannula

21. Dual-Stream Aortic Cannula

22. Arterial Cannulation Sites : Proximal Aorta Innominate Artery Distal Aortic Arch Femoral External Iliac Axillary Subclavian The choice is influenced by : The planned operation The Distribution of atherosclerotic disease

23. Ascending Aortic Cannulation Cannulation: 2 purse strings (1.0 – 1.3 cm diameter) partially through the aortic wall. MAP of 60-80 mm Hg. 4-5 mm full0thickness stab wound Insert the cannula under a finger Position the cannula to direct the flow to the mid transverse aorta Proper placement is confirmed by noting pulsatile pressure in the aortic line monitor and equivalent pressure in the radial artery.

24. Complications Difficult Insertion Bleeding Tear in the Aortic Wall Intramural or Malposition of the Cannula Tip Atheromatous Emboli Failure to Remove All Air From the Arterial Line After Connection Injury to the Aortic Back Wall Inadequate or Excessive Cerebral Blood Flow Inadvertent Decannulation Aortic Dissection

25. Complications Detection: Monitoring the aortic line and radial artery pressures Asymmetric cooling of the face or neck may suggest a problem with cerebral blood flow Late Complication: Late Bleeding Infected or Non-infected false aneurysms

26. Other Parts Venous Reservoir Oxygenator Heat Exchangers

27. Other Parts Pumps Filters and Bubble Traps Tubing and Connectors Cardiotomy Reservoir and Field Suction Venting the Heart Cardioplegia Delivery Systems Haemoconcentrators Perfusion Monitors and Safety Devices

28. Venting the Heart Concept: Avoiding distension of either ventricles during the arrest. Distension is detrimental to subsequent contractility. The distension and fibrillation in right ventricle is not as important as it is in the left side. Blood enters the left ventricle via: Pulmonary venous return from the blood: Escaping the atrial and venous drainage system Coming from the coronary sinus and thebesian veins Bronchial venous blood Blood regurgitating through the aortic valve Blood from undiagnosed interventricular or interatrial defects Volume of blood which might be entering left ventricle from: Bronchial venous blood : 140 ± 182 mL/min Noncoronary collateral flow : 48 ± 74 mL/min

29. Venting the Heart Method : Direct left ventricular venting through apex : now is nearly an obsolete method and rarely used Most often utilizing a multihole, soft-tip catheter placed in: Junction of the right superior pulmonary vein and left atrium Left atrial appendage ± Passage into the left ventricle Other : Placing a suction in pulmonary artery Passing a catheter retrograde through the aortic valve while working on the mitral valve Using cardioplegia line as a venting system while not being used as the delivery system Drainage: Drained to cardiotomy reservoir Roller pump, vacuum source, gravity drainage Monitoring is essential for malfunction: Inspection and palpation to detect distension TOE Direct measurement of left atrial and pulmonary arterial pressures CABG : No need for venting If the heart can not remain docompressed during distal anastomosesa vent should be inserted.

30. Cardioplegia Delivery System Solution : 8 to 20 mEq/L potassium Magnesium Carrier : Crystalloid Blood (Preferred) Types: Normothermic : must be transfused continuously Hypothermic : intermittent infusion Delivery: Antegrade: Small cannula in the aortic root Hand-held cannulas directly into the coronary ostia when the aortic valve is exposed Retrograde: Blindly inserted cuffed catheter into the coronary sinus Proper placement is critical Complications: Rupture or perforation of the sinus Haematoma Rupture of the catheter cuff

31. Assembly of Heart-Lung Machine Who assembles the machine? The perfusionist is responsible for setting up and preparing the CPB machine and all the components necessary. Stages : Dry assembly: Use of readily available commercial packs. Takes 10-15 minutes. Can be kept in stand-by for 7 days Priming with fluids: Takes up to 15 minutes Should be used in 8 hours Pre-bypass check list: Conducted by the perfusionist A safety inspection Completing a written pre-bypass checklist Priming: Adult extracorporeal perfusion circuits: 1.5-2.0 litres (30-35% of patient’s blood volume) Balanced electrolyte solution: Hartmann’s Normosol-A Plasma-Lyte Because of the adverse neurological effects: addition of glucose and/or lactate to the prime is avoided Before connection : recirculated through the filter to remove the particulate and air emboli Issues: Haemodilution: Priming volume is about 30-35% of patient’s blood volume Reducing Hct to about 2/3 of the pre-op value Addition of crystalloid cardioplegia further reduces the Hct So what to do? Add a unit of banked blood (with added heparin 2000 units/unit) What is the best hct? No consensus The most common hct value for a perfusate is a 20-25% with moderate hypothermia (25°C-32°C) What is the problem with haemodilution? Reduced viscosity is not a problem Reduced oxygen-carrying capacity Mixed venous O2 Sat < 60% Transfuse Increase the pump flow Other : Sometimes 12.5-50 g of mannitol is added to stimulate the diuresis to reduce the post-operative renal dysfunction Use of autologous blood prime Use of minimal perfusate Smaller and shorter tubes Colloids for priming: controversial Albumin (no proven benefit and definite risks), gelatins, dextrans, and hetastarches (increases the risk of bleeding)

32. Anticoagulation and Reversal Heparin: How much? 300-400 u/kg IV When? Before arterial or venous cannulation. Confirmation? ACT Hepcon Test When? 3 minutes after the administration of heparin. How high is high enough? Minimum ACT : 400 s Recommended ACT : 480 sbecause heparin only partially inhibits thrombin formation Inadequate ACT: Insufficient heparin Up to 500 units / kg Anti-thrombin deficiency If 500 units / kg of heparin fails Then: FFP, Recombinant anti-thrombin During CPB: 1/3 of bolus heparin Q1h ACT Check Q30min If ACT < Target Level : give more heparin Reversal: What? Protamine How much? 1 mg / 100 unit of initial heparin dose Not to exceed 3mg / kg What to expect? Hypotension : due to activation of complement system by protamine-heparin complex. To counteract this, calcium 2 mg / 1 mg protamine is added. Anaphylactic reaction : in patients allergic to protamine insulin After 1/3 of protamine dose avoid returning blood to cardiotomy reservoir Heparin Rebound: Supplemental Protamine

33. Starting Bypass Surgeon requests. Perfusionist and anaesthesiologist start increasing the arterial blood flow while monitoring the patient’s blood pressure and volume levels in all reservoirs. 6 observations: Adequate venous drainagefor the desired flow Acceptable pressure in the arterial line Adequate oxygenation of arterial blood Acceptable systemic arterial pressure Acceptable systemic venous pressure Adequate decompression of the heart. When all of these stable for at least 2 minutes: Lung ventilation may be stopped Perfusion cooling may begin X-Clamp the aorta for arresting the heart.

34. Cardioplegia Antegrade: Blood or crystalloid cardioplegia is delivered: At the aortic root proximal to the aortic x-clamp With the pressure of 60-100 mm Hg By a dedicated roller pump Coronary sinus blood: Captured by the right atrial or unsnaredcaval catheter Arrest time : usually after 30-60 seconds Delay in arrest: Problems with the delivery system Unrecognized AR Retrograde: Cardioplegia solution is delivered: At coronay sinus Flow rate of 200-400 mL/min With the pressure of 30-50 mm Hg Higher pressures injure the coronary sinus Lower pressures indicate: Malposition of the catheter Leakage around the catheter cuff A tear in the coronary sinus Arrest time: slower than the antegrade. 2-4 minutes May provide incomplete protection of right ventricle

35. Cardioplegia Solution Solution 1 (Hypertonic): Na+: 110 mmol / L K+: 72 mmol / L Ca+ +: 1.2 mmol / L Mg+ + : 72 mmol / L Cl- : 332 mmol / L Procaine : 3.5 mg pH : 3.8 Osmolarity : 589 Solution 2 (Isotonic): Na+ : 110 mmol / L K+ : 36 mmol / L Ca+ + : 1.2 mmol / L Mg+ + : 16 mmol/ L Cl- : 180 mmol / L Lidocaine: 0.7 mg pH : 3.8 Osmolarity : 344 Preparation: Add Sodium-Bicarbonate to alkalinize the solution: 18 mLs of 8.4% Sodium-Bicarbonate to 500 mLs bag