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You are in Home >> Exams >> Mitchell Anaesthetic Notes


Cardiac anaesthesia

Created: 20/6/2006
Updated: 10/1/2007
 

Management of pericardial tamponade post bypass surgery

  • Issues
    • Emergency complication of bypass surgery requiring immediate surgical consultation
    • Simultaneous diagnosis and management
    • Accumulation of blood in enclosed pericardial space limits atrial and ventricular filling
  • Features
    • Fall in cardiac output
      • Hypotension, narrow pulse pressure
    • High filling pressures
      • Increase in PAOP, CVP
    • Failure of mediastinal drainage
      • Large volume drainage early followed by clots
  • Management
    • ABCDE priorities
      • Secure airway, ventilate with 100% O2
      • Support circulation
        • High filling pressures, tachycardia
    • Surgical intervention
      • Remove clot from pericardium in theatre if there is time for transfer
  • Anaesthesia
    • Reanaesthetizing post-bypass patient
    • Preparation
      • Routine check of anaesthetic machine and equipment
      • Pressor and dilator drugs, heparin for bypass
      • Check Hb, platelets, coagulation status, acid-base status
      • Notify blood bank
      • Haemodynamic support
        • IV fluid, pacing to 90-140/min
        • Continue inotropes from ICU
    • Monitoring
      • Invasive monitoring (arterial and PA catheter) usually in situ
      • TOE may give useful information about tamponade and ventricular function
    • Induction
      • Fentanyl 10-20 µg/kg, pancuronium
        • Consider sux if reintubation required (may be difficult)
      • Small dose of thiopentone or ketamine
    • Maintenance
      • High degree of vigilance for complications, arrhythmias
      • May require going onto bypass
      • Monitoring of Hb, ABG, coagulation
    • Postoperative
      • Return to ICU intubated and ventilated

Preparation for going onto and coming off cardiopulmonary bypass

Check list for bypass

  • Before cannulation
    • Anticoagulation
      • Heparin dose 300-400 U/kg
      • ACT >300 s
    • Haemodynamics
      • Systolic BP <100 mmHg
      • ECG recorded
      • CVP adequate for caval cannulation
    • Ventilation
      • Compliance recorded
      • ABG and acid-base satisfactory
  • Before running on CPB
    • Anaesthesia and paralysis confirmed
    • CPB circuit has no bubbles, correctly connected and clamps off
    • IV fluid ceased and urine recorded
  • First minutes of CPB
    • Adequate flows and pressures
    • Obvious oxygenation of aortic cannula blood
    • Cease ventilation when arrested
    • Continue ABG, ACT measurement

During CPB

  • Anticoagulation
    • Maintain ACT >400 s
    • Inspect circuit and reservoir for fibrin
  • ABG, acid-base
    • ABG normal (a stat)
    • PvO2 >40 mmHg, SvO2 >60%
    • Hct 18-22%
  • Haemodynamics
    • MAP 40-90 mmHg, PAP <15 mmHg, CVP <0
    • Quiescent ECG
  • Temperature
    • Monitor hypothermia and rewarming
  • Neurological
    • Facial oedema, pupils, EEG (if monitored), paralysis
  • Renal
    • UO >1 ml/kg/h, no haemolysis
  • Pump
    • Pressure and flow appropriate
    • Venous return appropriate
    • Fluid balance

Coming off CPB

  • Rewarming
    • Neurological unresponsiveness
    • Adequate ACT, normal ABG, pH, electrolytes
    • Vasodilation for even rewarming
    • Defibrillation ± pacing
  • Prior to coming off
    • ABG, Hct, K+
    • Core and peripheral temperatures
    • Suitable rhythm
    • Controlled MAP
    • Filling, vasodilation, CVP, PAP
    • Reinflate lungs, Valsalva
    • Vent arterial air, verify with TOE
  • Weaning CPB
    • Preload
      • CVP, PAOP
      • Filling and vasodilation
    • Ventricular function
      • dP/dt on arterial trace
      • CO, TOE
      • Inotropes if indicated
    • Return of reservoir blood ± haemodilution blood
  • After discontinuation
    • Protamine to normalize ACT
    • Correction of coagulopathy, thrombocytopenia if indicated
    • Haemodynamic management (pacing, filling, inotropes, vasodilation)
    • Maintenance of anaesthesia
    • Preparation for ICU transfer

Post-bypass bleeding

  • Issues
    • Postoperative patient with multiple possible causes of impaired haemostasis
    • Usually in ICU setting
    • May be an emergency depending on severity: simultaneous diagnosis and management
  • Priorities
    • ABCDE if necessary (tamponade, rapid bleed)
    • Aim for haemodynamic stability, assessment, correction of abnormalities
      • In practice, treatment may be empirical in order to achieve stability
  • Assessment
    • History
      • Medical problems (e.g. renal failure, hepatic dysfunction)
      • Preoperative drug therapy (e.g. aspirin, warfarin)
      • Operative detail: duration of CPB, transfusion requirement
    • Examination
      • Rate, source and nature of bleeding (general vs localized, arterial vs haemoserous)
      • Relation to position if drain tube losses only
    • Tests
      • ACT prior to leaving theatre
      • APTT, INR, platelets
      • DIC screen
      • Thromboelastography
  • Management
    • Surgical haemostasis
    • Reversal of residual heparinization
    • Replacement of platelets and desmopressin
    • Replacement of clotting factors
    • Prevention of secondary fibrinolysis, DIC

Patient assessment for cardiac surgery

  • Epidemiology
    • IHD in 20% of adult surgical patients, 70% of vascular patients
    • Perioperative AMI has 15-70% mortality
  • Cardiovascular
    • History, examination
      • Angina, exercise tolerance, dyspnoea, palpitations
      • Hypertension
      • Medication, previous procedures
      • Other vascular disease: aneurysms, carotid or peripheral disease
      • Signs of cardiac failure or valve dysfunction
    • ECG, exercise ECG
      • HR and BP at which ischaemia was evident
      • Leads which showed ischaemia best
      • Evidence of ventricular dysfunction
    • Echocardiography
      • Condition of aorta and coronaries, LV function, valve function
      • Regional wall motion abnormalities
      • Stress echo has good discriminatory power
    • Coronary angiogram
      • Static test, no indication of exercise ischaemia
      • Location of lesions --> ECG leads to monitor
      • Results of previous revascularization procedures
      • LVgram indicates LV function (not best test)
    • Radionuclide angiocardiography
      • Perfusion defects ± stress, ventricular ejection
    • Cardiac catheter
      • Valve function and gradients, ventricular pressure, output
      • Quantification of shunts
  • Other tests
    • FBE, U&E, LFT, XM, ABG (sometimes at induction)
    • Of questionable value: clotting, urinalysis
  • Noncardiac disease of interest
    • Condition should be optimized before elective surgery
    • Endocrine
      • Obesity, thyroid dysfunction, adrenal dysfunction, phaeochromocytoma
      • Diabetes
        • Autonomic lability, silent ischaemia, slowed gastric emptying
    • Haematological
      • Anaemia, coagulopathy, haemolytic conditions
    • Respiratory
      • Smoking, asthma, COAD, infection, pulmonary embolism
    • Other
      • Renal failure, cirrhosis, peptic ulcer disease, drug dependence, connective tissue diseases
  • Medications
    • Decision to continue or cease in consultation with cardiologist
    • Continue
      • Antianginals, β-blockers, antidysrhythmics, most antihypertensives
    • Usually continue
      • Aspirin, Ca2+ channel blockers, digoxin, most other agents
    • Maybe cease
      • ACE inhibitors (worsen hypotension)
    • Usually cease
      • Diuretics, oral hypoglycaemics (substitute insulin)
  • Other preparation
    • Consent
    • Height, weight, BSA
    • Washing, shaving, fasting

Anaesthesia for cardiac surgery


Premedication

  • Anxiolytic and sedative, avoid hypotension and marked hypercarbia
    • Diazepam 0.1-0.2 mg/kg plus morphine 0.1 mg/kg or lorazepam and fentanyl, or Omnopon and scopolamine
  • Reduced risk of ischaemia
    • Nitrate, β-blocker, clonidine

Monitoring 

  • Routine
    • SpO2, ECG with ST analysis, arterial line, PA catheter (CVC in some units), temperature (core and peripheral), IDC with burette, large peripheral IV
    • All in place before induction
    • Priorities: volume status and contractility assessment to guide therapy
  • If indicated
    • Oesophageal stethoscope can monitor HR, breathing without interference
    • PA catheter (unless routine) for CO, PAOP
    • TOE
    • Cerebral function monitor for deep hypothermia
  • Bedside tests
    • ABG, Na+, K+, Hb, glucose, ACT (? thromboelastography)
  • Induction
    • Traditional
      • Fentanyl 10-30 µg/kg, pancuronium 0.1 mg/kg, propofol minimum required dose
    • Additional drugs
      • Antibiotics, e-aminocaproic acid or aprotinin, Mg2+
      • Heparin pre-bypass
      • Pressors and vasodilators as required
    • “Fast track”
      • Propofol, isoflurane, fentanyl or remifentanil
      • Requires normothermia, haemodynamic stability and coagulation at end of case
    • Thoracic epidural
      • Improved analgesia, decreased stress response
      • Risks unknown, may be no better than β-blockade
    • Off-bypass CAGS
      • Conventional anaesthetic, grafts performed on beating heart
      • Requires low CO, low O2 demand during grafting as coronary vessel is occluded
        • Fill, posture head down, reduce heart rate
  • Maintenance
    • Usually air, O2, isoflurane ± propofol infusion for bypass
  • Bypass
    • Going onto and coming off bypass
      • Venous return usually from SVC and IVC
        • Total or partial bypass
      • Additional input from sucker and LV vent if present
      • Reservoir in bypass machine
      • Oxygenator (membrane or bubble)
      • Heat exchanger
      • Pump (usually non-occlusive roller)
      • Bubble catcher and filter
      • Arterial infusion usually ascending aorta
        • Output commonly set at typical CO for patient (approx. 5 L/min)
        • MAP set by dilator/pressor infusion (approx. 70 mmHg)
      • Management of pH, PCO2
        • No temperature correction (a-stat) is conventional

Postoperative 

  • Transfer to ICU
    • Oxygen and means of ventilation
    • Continuous monitoring (ECG, SpO2, BP), pacemaker if necessary
    • Infusion devices for drugs
    • Assistance for emergencies
    • Sedative, analgesic and resuscitation drugs
    • Advance notice to ICU
  • Analgesia
    • Narcotic infusion, PCA, oral adjuvant agents

Doses

Bolus Infusion Prepare
Pressors
Methoxamine 2-100 mg
Phenylephrine 50-100 µg
Metaraminol 0.1-2 mg 40-500 µg/min 10 mg in 20 ml
Ephedrine 5-30 mg 30 mg in 6 ml
Noradrenaline 1-10 µg 1-60 µg/min 1.5 mg in 25 ml
Inotropes
Dobutamine 2-20 µg/kg/min 3•BW mg in 50 ml
Dopamine 2-15 µg/kg/min 3•BW mg in 50 ml
Isoprenaline 1-5 µg 0.5-5 µg/min 200 µg in 20 ml
Adrenaline 2-50 µg 1-60 µg/min 1.5 mg in 25 ml
Milrinone 50-75 µg/kg 0.4-0.8 µg/kg/min
CaCl2 0.25-1 g
Glucagon 3-10 mg
Vasodilators
GTN 50-500 µg/min 15 mg in 25 ml
SNP 0.2-8 µg/kg/min 50 mg in 500 ml
Phentolamine 1 mg 0.5-7 µg/kg/min
PGE1 0.05-0.5 µg/kg/min
Hydralazine 5 mg <40 mg/h


 

Priorities in valve disease

  • Mitral stenosis
    • Severity by valve area: normal 4-6 cm2, mild 1.5-2.5 cm2, moderate 1-1.5 cm2, severe =1 cm2
    • Sinus rhythm and normal heart rate are vital for output
    • Maximize LA pressure without pulmonary oedema
      • Increased risks with PA catheter in pulmonary hypertension
    • Pulmonary HT may cause RV failure
  • Mitral regurgitation
    • Severity by regurgitant fraction: >0.6 severe
    • Heart rate normal to high
    • Low SVR increases forward flow (limited by hypotension)
    • Maintain contractility without high preload (dilates LV)
    • Risk of ventricular rupture coming off bypass
      • Loss of chorda tendinae bracing ventricle and increased pressure work
    • IABP may be helpful
  • Aortic regurgitation
    • LV volume overload, gradual hypertrophy, sudden decompensation
    • Severity by regurgitant volume: mild 1-3 L/min, moderate 3-5 L/min, severe >6 L/min
    • Tachycardia reduces LV distension
    • Low SVR increases forward flow (limited by hypotension)
    • Contractility usually impaired
    • Aortic cross-clamp or LV vent may be required
    • Antegrade cardioplegia may be impossible
    • IABP contraindicated
  • Aortic stenosis
    • Severity by valve area (<1 cm2 severe) or pressure gradient
    • High LVEDP (PAOP) to fill non-compliant ventricle
    • Sinus rhythm a high priority, normal heart rate
    • Myocardial O2 balance is impaired by LV hypertrophy and low aortic root pressure
    • Vasodilation may severely impair coronary and cerebral perfusion
  • HOCM
    • Dynamic functional aortic outflow obstruction due to septal hypertrophy
    • Obstruction improves with reduced pressure gradient
      • Vasoconstriction, β-blockade, myocardial depressants
    • Maintain high preload
    • High incidence of arrhythmia

Anaesthesia in the post-transplant patient (BJA 1991; 67: 772-778)

Transplant types 

  • Heart, heart-lung, single lung

Complications

  • Arrhythmia: including fatal VT, sign of rejection
  • Infection related to immunosuppression
    • CMV, HSV, pneumonia with Pneumocystis carinii
  • Neoplasia related to immunosuppression
  • Depression, anxiety, thought disorder
    • May lead to rejection due to medication non-compliance
  • Coronary vessel disease
    • Common (46% at 2 years) without pain (denervated)
    • Presents with lethargy and dyspnoea
    • Routine screening angiography and biopsies for rejection
  • Lung rejection
    • Symptoms similar to infection: desaturation, fever, leukocytosis, opacification

Anaesthesia issues

Denervated heart

    • Rate 90-100 /min, no vagal or sympathetic response
    • Normal response to circulating catecholamines
    • No rate response to baroreceptors, Valsalva, carotid sinus, hypovolaemia, light anaesthesia
    • Dependent on intrinsic regulation of cardiac output
      • Preload dependent  --> stroke volume
      • Must maintain filling pressure
  • Cardiac pharmacology
    • Little effect from cholinergic agents: atropine, neostigmine, suxamethonium
    • β-adrenergic agents and glucagon remain effective
    • Antidysrhythmics and DC reversion remain effective
  • Denervated lung
    • Relatively normal respiratory pattern and maintenance of gases
    • PCO2 response may be blunted
    • No cough in response to irritation of bronchi
      • Extubate awake, encourage active physio
    • Uneven
    • V/Q distribution
    • Bronchoconstriction can occur
  • Usual drug regimen
    • Immunosuppression
      • Must be continued perioperatively
      • Steroid requires supplementation
      • Azathioprine
      • Cyclosporin: nephrotoxicity, hepatotoxicity, hypertension, increased NDB effect
  • Evaluation
    • Consult with treating unit
    • Routine preoperative assessment
  • Technique
    • GA or regional provided filling maintained
    • Meticulous aseptic technique
    • Routine prophylactic antibiotics (? also for line insertion)
    • Isoprenaline for bradycardia (not atropine)
    • Minimize lines, avoid right IJV (used for biopsies)
    • Vigorous physio post-op

Kindly provided by Dr James Mitchell from his pharmacodynamics series


ArticleDate:20060620
SiteSection: Article
 
   
    
                                            
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