Haemodynamic Monitoring Flashcards
What urine output suggests good renal blood flow?
> 0.5mL/kg/hr
What does lactic acidosis suggest?
Inadequate tissue perfusion
Does blood pressure affect organ blood flow?
Within normal ranges, organ blood flow is constant, irrespective of blood pressure.
At the extremes of blood pressure, organ blood flow is affected.
In critical illness, autoregulation can be impaired, so blood flow may be dependent on blood pressure throughout the range.
Non-invasive BP monitoring: tendency for error?
Over-estimate BP at low pressures and under-estimate BP at high pressures.
Non-invasive BP monitoring: most important determinant of accuracy?
Cuff size (width should be 40% of arm circumference; length should be twice circumference)
Excessively wide cuffs underestimate BP
Excessively narrow cuffs overestimate BP.
How to check an arterial line for underdamping:
Place a manual BP cuff on the limb.
Inflate the cuff until the arterial line is flat. Deflate slowly until pulsation is just detected on arterial trace.
This is the true systolic BP.
Which matters more: diastolic or systolic or mean BP?
In patients with high risk of bleeding, the systolic BP is most important.
Diastolic BP is major determinant of L ventricular coronary blood flow, and is therefore most important in patients with poor coronary blood flow.
Mean arterial pressure is a major determinant of perfusion pressure of other organs.
How do you use CVP to tell if a patient is underfilled?
Measure the difference between the CVP measured before and 5 minutes after a fluid bolus
- Difference of 0-3mmHg = probably underfilled
- Difference of 3-5mmHg = probably adequately filled
- Difference of >5mmHg = probably overfilled
Why do underfilled patients have little change in their CVP when given a single fluid bolus?
There is little change in end diastolic pressure (and hence CVP) in a pateint with a low end diastolic volume.
How is pulse pressure variation used to estiamte fluid status?
Pulse pressure variation (variation in pulse pressure during different phases of mechanical ventilation) is greater in pateitns who are likely to respond to fluid.
A pulse pressure variation of >15% indicates the patient is likely to respond to fluid.
What does a passive leg raise simulate when assessing fluid responsiveness?
Passive leg raise can be considered a reversible fluid challenge of 500mL blood.
How do you use a passive leg raise to assess fluid status?
A rise in pulse pressure by 10% on passive leg raising suggests hypovolaemia
