- 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 |