Methods of Cardiac Output Monitoring

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Introduction & Definition

What is …?

Epidemiology, Clinical Course & Prognosis

How common is …?

  • ..

Aetiology & Risk Factors

What are the causes of …?

Pathophysiology

What are the underlying pathophysiological mechanisms in …?

Presentation

What are the symptoms & signs of …?

Complications

What are the complications of …?

Work-Up Summary

How do you work-up the patient with aortic stenosis?

To Determine Diagnosis
  • Focused history and clinical examination
  • Transthoracic echocardiography
  • To Determine Severity / Prognosis
    • Transthoracic echocardiography
    • Additional tests depending upon clinical features
      • Exercise testing (in asymptomatic patients)
      • CT calcium scoring
      • Exercise stress echo
      • Dobutamine stress echo
      • Cardiac catheterization and determination of transvalvular gradient (also give information about any concurrent coronary artery disease)
      • To Assess for Complications
        • ECG: LVH, LV strain
        • CXR: cardiomegaly, signs of LV failure
        • FBC: haemolytic anaemia
        • Clinical Investigations

          Imaging Investigations

          Management Summary

          How do you work-up the patient with aortic stenosis?

          To Determine Diagnosis
          • Focused history and clinical examination
          • Transthoracic echocardiography
          • To Determine Severity / Prognosis
            • Transthoracic echocardiography
            • Additional tests depending upon clinical features
              • Exercise testing (in asymptomatic patients)
              • CT calcium scoring
              • Exercise stress echo
              • Dobutamine stress echo
              • Cardiac catheterization and determination of transvalvular gradient (also give information about any concurrent coronary artery disease)
              • To Assess for Complications
                • ECG: LVH, LV strain
                • CXR: cardiomegaly, signs of LV failure
                • FBC: haemolytic anaemia
                • Supportive Management

                  Specific Management

                  How can … be treated?

                  Anaesthetic Management Summary

                  Risks
                  • Significant risk of MI and death
                    • Compensatory mechanisms for fixed output state disrupted by anaesthesia
                    • Anaesthesia induces a reduction in SVR
                    • Fixed obstruction in AS impedes compensatory increase in cardiac output
                    • Resulting hypotension can lead to reduced myocardial perfusion and ischaemia
                    • Induces a downward spiral of reduced contractility, further hypotension and ischaemia
                  • Risk of arrhythmias
                    • General anaesthesia can reduce sinus node automaticity
                    • Can lead to nodal rhythms or other arrhythmias (AF or atrial tachycardias)
                  • Risk of infective endocarditis
                  Preload:
                  • LV hypertrophied and compliance is poor
                  • Optimize preload to enable adequate filling of the LV (guided by cardiac output monitoring)
                  • Vasodilators (particularly venodilators such as GTN) should be avoided
                   
                  Rate:
                  • Avoid tachycardia (Aim 50-70)
                    • Reduces diastolic filling time
                    • Reduces the time for coronary perfusion, therefore worsening ischaemia
                    • Increases oxygen demand
                  • Avoid excessive bradycardia
                    • This results in a reduced cardiac output as the stiff ventricle cannot increase the stroke volume to compensate.
                    • The increase in ventricular filling due to longer diastole also increases ventricular wall tension further reducing coronary perfusion.
                   
                  Rhythm: Sinus
                  • Maintain sinus rhythm – vital
                    • Atrial contraction is important for LV filling
                    • Up to 40 % of filling in diastole is due to atrial contraction (normally only 15–20 %)
                    • AF and nodal rhythms are therefore poorly tolerated in these patients
                  • Arrhythmias need aggressive treatment
                   
                  Contractility: Maintain
                  • Maintain myocardial contractility:
                    • Avoid B-blockers or myocardial ischaemia
                  • Increasing myocardial drive does not improve cardiac output and can precipitate ischaemia through increased oxygen consumption
                   
                  Afterload:
                  • Avoiding hypotension is critical – maintain a high-normal diastolic
                    • Diastolic pressure must be maintained ensure filling of coronary arteries – require larger than usual due to hypertrophied LV
                    • Any hypotension needs to be treated early to avoid spiral of further reductions in coronary perfusion, causing myocardial depression and potentially leading to cardiac arrest
                    • CPR is generally ineffective in these patients unless internal massage can be performed
                  • Afterload essentially fixed below a certain limit due to valvular obstruction:
                    • Reducing SVR has no impact on ejection of blood from the LV, as the obstruction to flow is due to the stenosed valve leading to a fixed cardiac output
                  History & Examination
                  • Full anaesthetic history
                  • Specific areas of focus:
                    • Associated symptoms
                    • Last echo and it’s findings
                    • Cardiology interventions and follow-up
                  • Examination of cardiovascular and respiratory system

                   

                  Investigations
                  • Echo – strongly desirable, consider delaying non-essential surgery until performed:
                    • Severity of stenosis
                    • LV function
                  • Bloods:
                    • FBC to exclude anaemia
                    • Coagulation studies – particularly if on warfarin
                    • U&E and renal function – may be disturbed if on diuretics
                    • BNP
                  • ECG:
                    • LVH / LV strain
                    • Arrhythmias
                  • Chest Xray

                   

                  Risk Assessment & Optimisation
                  • Referral to cardiologist – assistance with decisions regarding:
                    • Appropriateness of surgery
                    • Need for pre-operative intervention:
                      • Aortic valve replacement
                      • TAVI
                      • Balloon valvuloplasty
                  • Lee index or ‘revised cardiac risk’ index tool
                    • Use information to consent appropriately with risks involved

                   

                  Premedication
                  • Consider using anxiolytics to prevent tachycardia
                  Choice
                  • Spinal anaesthesia is traditionally avoided:
                    • Potential for hypotension and vasodilation caused by the rapid onset of sympathetic blockade
                    • Decreased preload and decrease in cardiac output
                    • Decrease in afterload and coronary filling
                  • Cases of carefully titrated anaesthesia using spinal or epidural catheter reported
                  • Limb blocks may be beneficial, either alone or as an adjunct to general anaesthesia.
                   
                  Induction & Maintenance
                  • Extreme care needs to be taken with induction of anaesthesia to avoid hypotension:
                    • Titrate all anaesthetic drugs very carefully
                    • Options include high dose opioids and etomidate or inhalational induction
                  • Use vasopressors to maintain pre-induction blood pressure-levels:
                    • Ensure vasopressor drugs (phenylephrine or metaraminol) at hand
                    • Infusions running peripheral vasopressor during induction facilitate maintenance of pressure
                  Monitoring & Acess
                  • Arterial cannula for invasive blood pressure monitoring:
                    • Should be routine except for short procedures
                    • Consider prior to induction
                  • Central venous line may be useful for vasopressor therapy
                  • PA catheters relatively contraindicated due to risk of arrhythmias 
                   
                  Conduct
                  • See ‘Haemodynamic goals’
                  • Consider use of endocarditis prophylaxis:
                    • Antibiotic prophylaxis not routinely advised (NICE Guidance)
                    • Should be considered in high risk individuals
                  • Monitor plasma potassium regularly given risk of arrhythmias

                     

                    Analgesia

                    • Avoid NASIDs – high risk renal dysfunction
                    • Ensure optimum analgesia to avoid tachycardia
                      Location & Review
                      • HDU / ICU for ongoing BP monitoring:
                        • NCEPOD recommends admission for valve area <1cm2
                        • Should be strongly considered if reduced systolic function
                       
                      Monitoring & Investigations
                      • Monitor for renal dysfunction
                       
                      Analgesia
                      • Avoid NSAIDS – high risk of renal dysfunction
                      • Ensure optimum analgesia to avoid tachycardia
                      • Regional anaesthesia may be beneficial
                       
                      Supportive Care
                      • Continue haemodynamic aims
                      • May require vasopressor infusions and ongoing invasive arterial BP monitoring to maintain haemodynamic stability
                      • Ensure meticulous attention to appropriate intravascular filling

                      Preoperative Management

                      Intraoperative Management

                      Postoperative Management

                      Author

                      The Guidewire
                      Trainee in ICM & Anaesthesia

                      Reviewer

                      The Guidewire
                      Trainee in ICM & Anaesthesia