Getting the most out of arterial blood pressure monitoring (M Pinsky)
Arterial pressure waveform – Systolic, mean, diastolic and pulse pressure
Systolic AP (which changes depending on where you measure it)
- LV SV
- Ejection velocity (contractility)
- Arterial elastance
Sepsis reverses the normal pulse pressure amplification down the arterial tree – therefore you would be underestimating the pressure in the aorta.
Diastolic pressure – determines coronary blood flow
- vascular tone
- arterial resistance
- heart rate
Large arteries are capacitor
Faster heart rate means that the diastolic pressure hasn’t had time to stabilise – it may actually be much lower (vasodilatation). Increased HR is the main physiological response to vasodilation to maintain diastolic pressure.
Perfusion pressure = input – output pressure
Pulse pressure influenced by
- Central arterial elastance
- vascular stiffness, blood viscosity
The relationship between stroke volume and arterial pressure is determined by the elastance
Cardiac output monitoring: invasive or non-invasive? (T Scheeren)
- Thermodilution (pulmonary thermodilution is considered the gold standard)
- Pseudo randomised thermo signal (Vigilance)
- pulse contour analysis e.g. Flotrac, Vigileo
- percentage error from 13 to 75%
- Noninvasive Cardiac Output Monitors: A State-of the-Art Review
- Minimally invasive cardiac output technologies in the ICU: putting it all together.
- Doppler techniques
- Pulse contour analysis (without arterial line) e.g. Nexfin
- The accuracy of noninvasive cardiac output and pressure measurements with finger cuff: a concise review.
- CO2 rebreathing method
- Bioimpedence and bioreactance
- Pulse wave transit time
Is CVP useful? PRO (S Magder)
CVP does not
- indicate magnitude of blood volume
- does not predict response to fluid
CVP normally low, elevated CVP needs explanation. CVP single value is not helpful.
Where is your reference/zero point???
What point of the wave are you recording your value?
CVP is best used with some measure of flow. Fall in CO with fall in CVC = return function (volume) problem. Fall in CO but rise in CVC = primarily pump problem
Most useful in response to therapy.
Is CVP useful? CON (P Marik)
CVP is useless (mostly) and harmful (almost always)