Download Cardiopulmonary Bypass

Cardiopulmonary Bypass
James Hayward
Introduction
• Provides a stationary, relatively dry operating field.
• Consists of:
– Venous catheter(s)
• IVC or RA
• Suction catheters feeding into venous return
– Reservoir
– Pumps
• Centrifugal
• Roller
– Oxygenator
– Arterial return cannula
• Added extras
– Filter
– Cardioplegia
– Heat exchanger
• Circuit used to be primed with whole blood but now Hartmann’s is used.
– Usually 1.5 – 2l
– 5,000units heparin to coat the circuit.
– Will result in significant haemodilution
Pumps
• Centrifugal
– Series of rotating cones
– Better but more expensive
– Less platelet damage/activation
– Less gaseous and particulate microemboli
• Roller
– Commoner and cheaper
– Degree of occlusion adjustable
– Will activate platelets
Emboli
• Large embolic load
– Particles – atheroma
– Fluids – fat from sternotomy
– Gas e.g. Microbubbles
• Embolic load is a significant factor in postoperative organ dysfunction.
• Filters
– Depth, screen, micropore
Heparin
• Mucopolysaccharide 3000 – 40,000Da
• Potentiates antithrombin III which inhibits thrombin,
IXa, Xa, XIa, XIIa
• 300-400iu are given via central vein prior to
cannulation. Aiming for ACT >480secs (3times baseline)
• The clotting cascade will get activated.
– Cell lysis, vasodilation, histamine release, neutrophil, and
macrophage chemotaxis.
– Increased capillary permeability.
– This inflammatory reaction is responsible for the postoperative organ dysfunction.
Pump flow/pressure
• Flow required essentially depends on oxygen
consumption of patient.
– O2 consumption is usually 4ml/kg/min.
– Flow is usually 2-2.5l/min/m2
• Pressure is usually between 50-70mmHg
• Drop in SVR going on pump due to
haemodilution.
• Watch CVP – if increases may be due to
impaired venous collection.
Temperature and pH
• Little difference in neurological outcomes following
normo/hypothermic CPB
– Mild – 33-35
– Moderate 28-23
– Deep – 22-27
• Acid-base
– CO2 becomes more soluble as temperature is reduced and so pH
rises.
– Alpha stat
• Total CO2 stores are maintained the pH will increase as the temperature
decreases.
• Preferred management strategy.
– pH stat
• Additional CO2 is added to the blood to maintain pH in the range of
7.35 – 7.45
– I still don’t understand this
Electrolytes
• Hypokalaemia and hyperkalaemia both occur
• Frequent decrease in serum magnesium and
calcium
• Administration of 2g magnesium at the end of
bypass may be beneficial
• Hypo/hyperglycaemia
– Both implicated in post-bypass reperfusion injury
– Aim to maintain glucose <8mmol/l
Anaesthetic technique of choice
• Do what you like.
• Usual recipe:
– High dose opiod
– Induction agent
– Long acting relaxant
• Maintenance
– TIVA
– Vapour
Cold Crystalloid Cardioplegia
• During cross-clamp the heart is ischaemic and without
protection this will lead to extensive myocardial damage.
• Cold crystalloid cardioplegia
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Na 147
K 20
Mg 16
Calcium 2
Chloride 204
Procaine 1
Hyperkalaemia causes the heart to arrest in diastole
Multiple dosing can be used
Low viscosity
Has the potential benefits of hypothermia
Blood Cardioplegia
• During cross-clamp the heart is ischaemic and
without protection this will lead to extensive
myocardial damage
• Improves oxygen carriage compared to
crystalloid cardioplegia
• Provides antioxidants to myocardium
• Warm blood cardioplegia may reduce
reperfusion injury
Antero/retrograde Cardioplegia
• If anterograde plegia solution may not reach
the entire myocardium if critical stenoses
exist.
– Via the coronary ostia or into ascending aorta
(which would depend on a competent aortic
valve)
• Retrograde plegia via the coronary ostia my be
required.
Cross-clamp fibrillation
• Can be an alternative to cardioplegia
• Allows the preservation of myocardial ATP
values
• Reduces the release of troponin
• May improve post-operative ventricular
function
Complications of CPB
Getting off bypass
• Rewarming to 35-36
– Core-peripheral gradient should be less than 6 degrees.
– Ensure properly re-warmed as shivering will significantly increase
oxygen consumption
– But don’t overwarm!
• If open heart procedure then any gases must be removed
• Pacing
– Ventricular pacing if in AF, or absent atrial activity.
– Atrial pacing in severe bradycardias with intact AV node
– Sequential pacing if AV block
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Correct electrolytes and pH
Ventilate
Reassess NMJ
Inotropes/vasopressor support
Causes of failure to wean off CPB
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Poor pre-operative function
Inadequate myocardial protection
Prolonged cross-clamp time
Imperfect surgery
Electrolyte imbalance
Acidosis
Arrhythmias
Intra-aortic balloon counter pulsation
• Lecture in itself
• Complications
– Malposition
– Vascular damage
– Haemorrhage
– Thrombosis
– Infection
– Confusion
– Compartment syndrome
Heparin reversal
• Only once fully off filter and stable
• Protamine
– Sulphated polycationic peptide
– 1mg protamine / 100 units heparin
• 40,000units heparin = 400mg protamine
– Strong bond between negative heparin and positive protamine
– Cautious injection – if given over 5mins most of the adverse
effects are avoided
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Systemic vasodilation
Increased PVR and pulmonary hypertension
Impaired LV function
Thrombocytopaenia
Leucopaenia
Fibrinolysis
Anaphylaxis
Post-bypass bleeding
• Haemodilution of all blood products
• Platelet function may be abnormal
• If heparinisation was inadequate the clotting pathway may have been
activated resulting in consumption of the clotting cascade
• Factors predisposing to bleeding post CPB
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Repeat surgery
Know coagulopathy
Ingestion of aspirin, warfarin or other anticoagulants
Local or systemic sepsis
Profound hypothermia
Prolonged bypass time
Inadequate heparinisation
Inadequate reversal of heparin
Severe haemodilution
Cyanotic congenital heart disease
Advances in CPB
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Heparin coated circuits
– Major advantage is that they have been shown to reduce the need for systemic anticoagulation and
therefore might reduce post-operative bleeding.
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Phosphorlycholine coated circuits
– Aims to mimic the cell membrane and thereby reduce the interaction between plasma proteins and
the circuit surface. This might in turn reduce the inflammatory response.
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Membrane oxygenation
– Mainly membrane oxygenation replacing bubble and discs.
– Oxygen flows along the microtubules and bloods.
– Over time deposits accumulate and resistance increases, heparin coating of oxygenation surfaces
might serve to reduce this effect.
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Mini-bypass
– Integrated venous bubble trap, heat exchanger, oxygenation and pump and combined cell salvage.
– Lower volume circuit
– Disadvantages are that it does not accommodate a vent so there may be persistent coronary artery
back bleeding.
– Increased risk of air embolism
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Cell salvage
– Commonly used
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CVVHDF on circuit
– Reduces peripheral tissue oedema
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Retrograde autologous priming
Continuous in-line monitoring
Thanks
www.gaslog.org.uk