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Cardiovascular monitoring

  • Cardiac output is the 'gold standard' measure of cardiovascular function
  • Measurement normally requires invasive pressure monitoring
  • Cardiovascular function can however be assessed non-invasively with:
    • Electrocardiogram
    • Blood pressure
    • Central venous pressure
    • Urine output
  • BP can be monitored with a cuff (intermittent) or arterial line (continuous)
  • In the absence of vasoconstriction provides a good estimate of cardiac output

The ECG

  • Provides information on heart rate and rhythm
  • Also serves as valuable monitor of electrolyte abnormalities
  • A 12-lead ECG provides information on myocardial ischaemia or infarction
  • ECG  monitoring essential for:
    • All patients in ITU or HDU
    • Patients with poor cardiac reserve
    • Patients receiving vasoactive drugs
    • Patients with drug toxicity
    • Monitoring of electrolyte disturbances

Arterial pressure monitoring

  • Invasive arterial pressure monitoring requires:
    • An arterial cannula
    • A monitoring line
    • A transducer
    • A monitoring system
  • Provides information on
    • Systolic and diastolic pressure
    • Arterial waveform
  • Complications and problems associated with invasive monitoring include
    • Over and under dampening
    • Incorrect zeroing
    • Haematoma
    • Distal ischaemia
    • Inadvertent drug injection
    • Disconnection and haemorrhage
    • Infection

Central venous pressure

  • Clinical assessment of jugular venous pressure is unreliable
  • Central venous system can be cannulated by internal jugular or subclavian route
  • Complications of CVP lines include:
    • Pneumothorax
    • Arterial puncture
    • Air embolism
    • Infection
  • Site at which transducers are zeroed are very variable
  • Also change with patient movement
  • Changes in pressure rather than absolute values are important
  • A fluid bolus = 200 ml of colloid given as quickly as possible
  • A low CVP with transient increase with fluid bolus = hypovolaemia
  • A high CVP with persistent increase with fluid bolus = hypervolaemia
  • CVP measurement allows assessment of the cardiac pre-load

Cardiac output and left sided pressures

  • f both ventricle are functioning normally pre-load will allow assessment of cardiac output
  • Ischaemic heart disease or sepsis LV function can be reduced
  • Pulmonary hypertension reduces RV function
  • In these situation assessment of left heart pressures may be important
  • Also a measure of cardiac output may be need
  • Cardiac output can be measured either
    • Invasively - pulmonary artery catheter
    • Non-invasively - oesophageal doppler

Swan-Ganz catheter

  • Balloon-tipped catheter inserted through central vein
  • Floated through right side of heart into pulmonary artery
  • Balloon allows 'wedging' in branch of pulmonary artery
  • Pressure recorded is pulmonary capillary wedge pressure
  • Good estimate of left atrial pressure
  • Tip of catheter contains a thermistor
  • Cardiac output can also be measured using thermodilution principal
  • If blood pressure and cardiac output are known vascular resistance can be calculated
  • Complications of a Swan-Ganz catheter are:
    • Arrhythmias
    • Knotting and misplacement
    • Cardiac valve trauma
    • Pulmonary infarction
    • Pulmonary artery rupture
    • Balloon rupture
    • Catheter thrombosis or embolism

Primary haemodynamic data

  • Heart rate
  • Mean arterial pressure
  • Central venous pressure
  • Mean pulmonary artery pressure
  • Mean pulmonary artery occlusion pressure
  • Cardiac output
  • Ventricular ejection fraction

Derived haemodynamic data

  • Cardiac index
  • Stroke volume
  • Stroke volume index
  • Systemic vascular resistance
  • Systemic vascular resistance index
  • Pulmonary vascular resistance index
  • Left ventricular stroke work index
  • Right ventricular stroke work index
  • Oxygen delivery
  • Oxygen consumption

Bibliography

Cruz K,  Franklin C.  The pulmonary artery catheter:  uses and controversies.  Crit Care Clin 2001;  17:  271-291.

Williams G, Grounds M,  Rhodes A.  Pulmonary artery catheter.  Curr Opin Crit Care 2002;  8:  251-256

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