Cardiac anaesthesia. Simon May

Transcription

1 Cardiac anaesthesia Simon May

2 Contents Cardiac: Principles of peri-operative management for cardiac surgery Cardiopulmonary bypass, cardioplegia and off pump cardiac surgery Cardiac disease and its implications Risk assessment and scoring systems Antibiotic indications Bleeding and cardiac tamponade Blood coagulability, acid-base and temperature management Cardiac pacing Balloon pump DHCA Congenital heart disease and valvular heart disease

3 Cardiopulmonary bypass

4 Cardiopulmonary bypass Allows cardiac procedures to be performed in a bloodless and motionless surgical field Gas exchanger: Disc oxygenator (traditional), bubble oxygenator or membrane hollow fibre oxygenator. Gas exchange not as good as artificial lung. Think Fick and Graham. Blood pumps: Constant or pulsatile flow. Roller or centrifugal pump. Think Hagen-Poiseuille. Filtration: Prevent debris, fat, fibrin, surgical contamination, gas and bacterial contamination.

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6 Myocardial protection Techniques used to preserve myocardial function and prevent cell death You want diastolic electromechanical arrest Achieved by cardioplegia which can be given antegrade or retrograde. Intermittent or continuous. Cardioplegia contains: Potassium (20mmol/l), reduces myocardial membrane potential Cold crystalloid, cold blood or warm blood Other agents that have been used: Nicorandil, Esmolol, Glutamate, Lignocaine and Aspartate Non cardioplegia techniques: Intermittent cross clamp VF, prolonged VF or ischaemic pre-conditioning

7 Going on bypass Bypass circuit is primed with crystalloid +/- HCO3, Mannitol and blood. Recalculate blood flow rate and estimated haematocrit post on circuit. Heparin iu/Kg given and aim for ACT >480s Surgeon cannulates venous circulation and aorta (other vessels can be used). Lines are primed, cardioplegia given and ventilation is stopped.

8 Coming off bypass Must meet certain criteria Temperature Cardiac stable (rhythm and cardiac output) Normal electrolytes and acceptable acid-base No/minimal clotting concern Surgeon happy about procedure Give Protamine and you are committed!!!!

9 Off pump technique Idea is to avoid complications of bypass, i.e. SIRS, coagulopathy, neurological/renal injury and platelet dysfunction. Requires a stabilisation device attached to the heart and a shunt device. Aim is to maintain stable haemodynamics and rhythm. But challenged by ischaemia and changing position of heart (particularly post/lat surface). Anticoagulation is required (ACT s). Hypothermia should be avoided. ECG is impaired as heart is moved. Pump vs Off pump outcome is controversial

10 Assessing risk

11 Risk scoring Parsonnet scoring system Euroscore and Euroscore II. Uses logistic regression analysis to calculate mortality But also, Cleveland clinic, French, Pons and Ontario systems See Euro J Cardiothoracic surgery

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13 Antibiotics

14 Antibiotics According to NICE guidance the following should have antibiotic cover due to endocarditis risk: Acquired valvular heart disease with stenosis or regurgitation Hypertrophic cardiomyopathy Previous endocarditis Valve replacement Structural congenital heart disease, including corrected or palliative procedures. Excludes atrial septal defect or fully repaired ventricular septal defect or fully repaired patent ductus arteriosus or closure devices which are endothelialised

15 Bleeding and tamponade

16 Cardiac tamponade Need high index of suspicion Constriction of the heart, reduces ventricular filling, hence low output cardiac state Beck (1935): raised JVP, hypotension and quiet heart sounds

17 Blood coagulability, acid-base and temp. management Solubility of gasses in blood increase as temperature decreases alpha stat is uncorrected (i.e. same values as at 37 degrees) ph stat corrects to the temperature concerned which requires addition of Co2 to maintain ph. ph stat during cooling (increased flow so faster) and alpha stat during warming (decreased flow therefore less microemboli).

18 Balloon pump

19 Balloon pump Balloon inflation in diastole and deflation in systole Aim is to improve ventricular performance of the failing heart. Inflation causes displacement of blood proximal and distally. Should improve coronary flow and systemic perfusion by the intrinsic Windkessel effect. Ultimately, improved myocardial oxygen delivery and decrease myocardial workload. Effect is dependant on heart rate, aortic compliance and balloon volume

20 Balloon pump Requires anticoagulation Indications. Contra-indications Complications (change in arterial wave form)

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22 DHCA

23 DHCA Indications Consequences of hypothermia Safe period? Cerebral protection Surgical technique

24 CHD and VHD Massive topic. Think shunt. Think maintain cardiac output.

25 Questions