identification of hypoperfusion Flashcards
(22 cards)
What is meant by downstream and upstream parameters
- Downstream = measures perfusion at the level of the organ/cell
- Upstream = measures perfusion at the level of the heart (measuring the variables from the tree of life).
List Upstream parameters and the methods of assessing them
- Preload (pulmonary capillary wedge pressure, CVP, pulse pressure variation)
- contractility (c - pocus)
- Afterload (arterial BP)
- HR (ECG, physical exam)
- CO quantification (thermal/indicator dilution, pulse contour analysis)
- O2 content (PaO2, Hb, SPO2)
list downstream parameters and the methods of assessing them
- Physical exam perfusion parameters x6
- Oragan function (UOP, biochem changes)
- Cellular waste (lactate pH, gastric tonometry)
- oxygen extraction ratio (VO2)
- Microcirculatory derangements (direct video microscopy, near infared spectroscopy)
What is lactate a measure of?
How sensitive is it?
- A proportional measure of decreased perfusion.
- insensitive in the early stages due to compensatory mechanisms trying to maintain tissue oxygen extraction.
- increased exponentially in cats - mild to moderate hypoperfusion results in a small lactate increase than dogs.
list the types of hyperlactaemia and what they represent
- Type A, hypoperfusion of increased metabolic demand (eg seizures)
- Type B1, resulting from disease eg hepatic disease, DM, neoplasia, endocrine.
- Type B2, associated with drugs/toxins eg steroids
- Type B3, congenital disease eg steroids
Type A most common
How can lactate be used prognostically
- Delta lactate/lactate clearance most useful. take serial measurements.
- Normal lactate at presentation predicts survival better than high predicts death.
What is gastric tonometry/use?
- Meaures the amount of Co2 in GI tissue.
- gas permeable baloon filled with saline inserted into stomach and allowed to equilibrate.
-PICO2 of saline then measured
-advantage; GI suspecptable to hypoperfusion, possibly a an early marker
-disadvantage, needs NG tube and time to equibrilate
A downstream measure of cellular waste
how is central/mixed venous oxygen saturation measured? Use?
-Uses O2 that remains in venous blood as a marker of tissue O2 consumption.
- mixed venous blood from PA
- norm 65-70%, low SVO2 is decresed delivery or increased consumption (shock)
downstream measure
What is the oxygen extraction ration
- using mixed venous blood
- assess relationship between DO2 and VO2
- Possible good for early shock as DO2 reduced while VO2 remains.
? clicical utility
downstream assessment
How are microcirulatory derangements assessed
- Video microscopy of the mucocutaneous areas
- near infrared spectroscopy to assess local oxyhaemoglobin
- research use only
downstream assessment
What is CVP
- Intrathoracic venacava pressure measured but a catheter sitting at the level of the right artrium
- Used as a close approximate of right artrial pressue
What is the proposed use of CVP
- If tricuspid valve is open then right artrial pressure = right ventricular end diastolic pressure, therefore a marker of right sided preload
- Idea is that CVP can be used to assess volume status, fluid responsiveness and the effect of any haemodynamic treatment.
What other factors could effect the CVP
- Resp cycle variations
- venous return (blood volume, vasomotor tone and venous wall compliance)
- right atrial wall funtion (HR, contracitility and tricuspid insufficiency)
- Extravascular pressures either abdominal or intrathoracic (eg tension pneumothorax)
WHat might high or low CVP values tell you?
normal is 0-5cmH2O
- high suggests volume overload, right cardiac dysfunction or pleural effusion
- low inadequate vacular filling due to hypovolaemia or vasodilation
why might CVP be useful in fluid therapy
- Guide the need for extra volume, esp where risk of overload is high.
- EG if recieves bolus, CVP increases then rapidly drops again, may indicate more fluids needed.
- if CVP raises and remains high further IVFT no likely useful.
What concerns make the use of CVP controversial
- Poor coorelation between ventricular filling pressure and ventricular filling volume, may not predict preload as well as once thought.
- euvolaemic patients sometimes respond to a fluid bolus with an increase in CVP
- likely to predict if the right heart can tolerate more fluid but not if the left heart needs it.
What is pulmonary artery catheteristation
A multilumen catheter placed in the jugular and fluroscopically guided into the the pulmonary artery. (can also be assisted by monitoring waveforms)
What is the proposed use of pulmoary artery catheters
- Measure diastolic, sustolic and mean PA pressures.
- Could be used for CVP
- measure centra venous oxygen saturation, pulmonary capillary wedge pressure and CO (dilution techniques)
- Can derive SVR, oxygen extraction ratio and cardiac index
What are the risks of PA catheter placement
- Thrombolic events (thrombi, air, quidewire, tip)
- dysrrhytmias, vtach
- pneumothorax, haemorrhage, infection.
- PA rupture (exteme)
- never in unstable cardiac patients or patients with coagulopathies.
now rare: Risk>benefits
What does thermodilution measure/how
- PA catheter with a thermistor placed.
- Set volume cold saline injected
- thermistor measures tempertaure changes in the surrounding blood as saline injected.
- Machine calculates cardiac output based on this data
What is lithium dilution measuring/how
note an important advantage over thermal dilution.
- Advantage over thermal dilution as can be performed using peripherial venous or arterial catheter.
- lithium injected IV - concentration measured at an arterial catheter electrode over time.
- software uses pulse power analysis to calculate CO.
what is pulmonary capillary wedge pressure
reflects left arterial filling pressure as it equilibrates across the capillary bed
- therefore a measure of left preload
- reduced = volume depletion
