Basics of cardiopulmonary bypass Dr. S. Parthasarathy MD., DA., DNB, MD (Acu), Dip. Diab.DCA, Dip. Software statistics, Phd (physio) Mahatma Gandhi Medical college and research institute , puducherry , India

Why do we need ?? Unlike nasal polyp ,gut Cardiac surgery needs a motionless, bloodless surgical field

Definition Cardiopulmonary bypass(CPB) is a form of extracorporeal circulation It temporarily takes over the function of the heart and lungs during surgery, maintaining the circulation of blood and the oxygen content of the body Don’t think it stops with two functions ??

four major functions 1) oxygenation and carbon dioxide elimination, (2) circulation of blood, (3) systemic cooling and rewarming, (4) diversion of blood from the heart to provide a bloodless surgical field.

When to use ?? Cardiac Noncardiac Thoracic aortic surgeries , mediastinal masses, we cant intubate in a respiratory obstruction , lung transplantation, liver transplantation DHCA in neurosurgical procedures

The process Typically, blood is gravity drained from the heart and lungs to a reservoir via venous cannulation and tubing, returned oxygenated to the cannulated arterial system by utilizing a pump and artificial lung (oxygenator or gas-exchanger).

Venous arterial + venous

Gravity based venous flow Height Tubings CVP Determine venous flow arterial Aorta is preferred – large , less pressure more flow , dissection chance is less

Oxygen flow meter and blender

Oxygenator and heat exchanger Water

oxygenators provided gas exchange by contact of a blood film to an oxygen rich atmosphere (e.g. disc oxygenators) by bubbling oxygen through blood (e.g. bubble oxygenators). Pump ?? Modern day oxygenators provide gas exchange to blood through a membrane (e.g. sheet and hollow-fibre oxygenators).

Bubble oxygenator

Need to have a defoaming matrix

artificial lung The artificial lung material is more gas permeable to CO2 than O2; silicone membranes have a CO2:O2 transmission ratio of about 5 : 1. 0.05 to 0.3 µm ( PP, area but thickness) law ?? CO2 transfer – difficult to predict Sweep gas !!

Artificial lungs Diffusional distances are greater (approximately 200 mm in comparison with 10 mm in the human alveolus) surface area for gas exchange is 1.7–3.5 m2 compared with 70–100 m2 in the human lung.

Arterial line

Hemotherm CPB is performed under systemic hypothermia (typically a nasopharyngeal temperature of 25–32C) Single tank and double tank are available

Arterial and venous cannula

The tubing and cannulae are manufactured of clear polyvinyl chloride, while the oxygenator casing and connectors consist of polycarbonate.

Why should we so many ??

Cardioplegia Solution of potassium – aortic root – diastolic arrest concentration of approximately 20 mmol litre Anterograde or retrograde Warm or cold blood or crystalloid 1:2 or 1:1 0r 1:4 mixing Glutamate, aspartate, mannitol Nicorandil or esmolol cardioplegia

cardioplegia ?? Non-cardioplegic techniques include the use of moderate systemic hypothermia (i.e. core temperature of 30–32C) with short periods of aortic cross-clamping and ventricular fibrillation (VF). Also beating heart surgeries !!

Cardiotomy and vent The suckers attached to the CPB circuit allow blood to be salvaged from the operative field to be returned to the circuit via the reservoir.

Vent suckers specifically used to drain blood that has not been directly removed from the heart by the venous pipes. The most common sites for placing dedicated vents are: • the aortic root; • the left ventricle; • the right superior pulmonary vein; • the left ventricular apex; • the left atrium or pulmonary artery.

Why we need venting to prevent distension of the heart; • to reduce myocardial re-warming; • to evacuate air from the cardiac chambers during the de-airing phase of the procedure; • to improve surgical exposure; • to create a dry surgical field, especially during the distal coronary anastamosis phase of CABG surgery

Roller pumps -- Produces flow Nearly occlusive Nonpulsatile or pulsatile Low flow and low cost afterload – ok Low priming volume

Problems Tubing rupture Hemolysis Air embolism

Centrifugal pumps Produces pressure Superior for right or left heart bypass Preferred for long-term bypass nonocclusive After load sensitive But large priming vol and cost ??

Centrifugal pumps CPs consist nest of smooth plastic cones within a plastic casing. These impellers or cones are magnetically coupled (at the base) with an electric motor when rotated rapidly, generate a centrifugal force to the blood, which is received by the pump body CF == Mass of blood * radius of pump head* speed of revolutions (RPM)

Filters Haemofilters (haemoconcentrators or ultrafilters) are utilized in CPB circuitry to remove excess fluid and electrolytes, attenuate inflammatory mediators and raise haematocrit. These devices mainly consist of a hollow-fibre semipermeable membrane to allow the passage of water and electrolytes from the blood to a filtrate compartment.

Inline monitoring systems

Aortic cross clamp cross-clamp is placed across the ascending aorta above the coronary ostia and proximal to the aortic cannula, isolating the coronary circulation preventing blood entering the chambers of the heart. ACC time ??

Priming solution The cardiopulmonary bypass (CPB) circuit must be primed with a fluid solution, (1500 ml to 2 litres) so that adequate flow rates can be rapidly achieved on initiation of CPB without risk of air embolism. Crystalloid, colloids and blood Mannitol, sodabicarb, heparin, steroids – additives 17 % hematocrit tolerated

Back to square one !!

Partial bypass ?? T.A Operation No oxygenator

CPB starts an extremely complex and multifactorial response involving activation of complement, platelets, neutrophils, monocytes and macrophages, thus initiating the coagulation, fibrinolytic and kallikrein cascades.

Neurologic dysfunction, pulmonary dysfunction, renal dysfunction, hematologic abnormalities. SIRS

The fundamentals Check and prime Monitoring lines, temperature, blood gases, urine _ GA- narcotics Incision, sternotomy Heparinization Cannulation – pump on ACC and cardioplegia, surgery – oxygen ! Agent? ACC off , ( O2 + agent) warm, investigations, TEE, hemodynamics, pump off , protamine, cannulae off – suturing

Thank you