Hemodynamic monitoring Flashcards
Describe the set-up for invasive arterial blood pressure monitoring
(summarized)
- arterial catheter
- non-compliant tubing with 3-way stopcock
- transducer (at the level of right atrium) connected to monitor
- bag of 0.9%NaCl with heparin 1 unit/mL kept pressurized at 300 mHg and running at 3 mL/h connected to circuit to prevent backflow and maintain patency
- all lines primed / flushed with the heparinized saline before connection
Need to level and zero the circuit
Name complications of invasive blood pressure monitoring
- Hemorrhage
- Infection
- Distal limb necrosis
- Thrombosis
- Excessive heparinization
How to assess damping with invasive arterial pressure monitoring
Dynamic response / square wave test: open fast flush and count oscillations after square wave before return to baseline.
Optimal damping = 1-2 oscillations after square wave, amplitude of each oscillation no greater than 1/3 of previous one and interval between oscillations < 30 msec
Overdamping = no oscillations after square wave
Underdamping = multiple oscillations
How does overdamping influence the arterial waveform? Underdamping?
Overdamping -> lower SBP, higher DBP, loss of dicrotic notch
Underdamping -> higher SBP, lower DBP, artifacts on waveform
What are causes of overdamping / underdamping in invasive blood pressure monitoring
Overdamping: clot in catheter, catheter agains vessel wall, kinked catheter / tubing, air bubbles in system, compliant tubing
Underdamping: excessively long tubing, multiple 3-way stopcocks
How to calculate pulse pressure variation? What value is associated with fluid responsiveness?
PPV (%) = 100*(PPmax-PPmin)/[(PPmax + PPmin)/2]
Values >10% associated with fluid responsiveness, values >13% correlate with hypotension and fluid responsiveness
Explain why peripheral PPV overestimates central PPV
- Forward (or incident) wave travels from the left ventricle to the periphery – its amplitude is based on ventricular contraction and pulse wave velocity
- Backward (or reflected) wave travels in the opposite direction – generated by reflexion of forward wave
- Both waves superimpose in order to create the pressure waveform
- In the aorta, rise of systolic pressure is determined by aortic compliance and SV
- As the arterial pressure waveform moves into the periphery (more compliant, smaller conduit), the pulse pressure is amplified
- MAP remains unchanged to mildly decreased
Where should the transducer or the bottom of the manometer be placed for CVP monitoring
At the level of the right atrium ->manubrium in lateral recumbency / point of shoulder in sternal recumbency
Draw and explain a CVP waveform
a wave = right atrial contraction
c wave = bulging of tricuspid valve
v wave = blood flowing into right atrium
x descent = ventricular contraction / ejection
y descent = emptying of right atrium after opening of tricuspid valve
What is a normal CVP
0-5 cmH2O
(/!\ measured in cmH2O)
What do changes in CVP indicate
High > 10 cmH2O: volume overload, right sided heart failure, pericardial disease, pulmonic stenosis, marked pleural effusion / pneumothorax
Low < 10 cmH2O: hypovolemia or vasodilation
How will CVP change following a fluid challenge in a hypovolemic patient? Euvolemic? Hypervolemic?
Hypovolemic: no change in CVP or mild transient increase
Euvolemic: increase of 2-4 cmH2O and return to baseline within 15 min
Hypervolemic: increase > 4 cmH2O and return to baseline > 30 min
What is the normal CO for dogs and cats
Dogs: 125-200 ml/kg/min
Cats: 120 ml/kg/min
What values can be measured or calculated with a Swan-Ganz catheter
- Pulmonary artery pressure
- Pulmonary artery occlusion pressure (= pulmonary wedge pressure) -> indicates preload to left heart
- Right atrial pressure (= central venous pressure)
- CO with thermodilution
- SvO2 (central venous and mixed venous)
Calculated:
- Cardiac index (= CO/body surface area)
- Stroke volume (= CO/HR)
- Stroke volume index (= SV/body surface area)
- Systemic vascular resistance (= (MAP-RAP)/cardiac index)
- DO2, O2 consumption, O2 extraction
Label this waveform from a Swan-Ganz catheter being inserted and indicate what are the pressures
See picture
What is the difference between mixed venous oxygen saturation (SvO2) and central venous oxygen saturation (ScvO2)
- Mixed venous = measured from pulmonary artery
Normal = 70-75% - Central venous = measured from jugular vein / cranial vena cava -> only reflects cranial half of the body (can be a little lower because brain consumes a lot of O2)
Normal = 65-70%
Usually correlate quite well but in severe shock can vary up to 18% (ScvO2 will be higher than SvO2 because cerebral perfusion is prioritized over splanchnic)
What does SvO2 indicate and how can it be used
It indicates oxygen extraction by tissues => reflects systemic oxygen balance and cumulative oxygen debt
SvO2 > 70% can be an endpoint of hemodynamic resuscitation.
Low ScvO2 is associated with increased mortality
What can lead to erroneous interpretation of SvO2
- Abnormal hemoglobin concentration
- Hypoxemia (low SaO2)
- Large difference between SvO2 and ScvO2 in severe shock
- Impaired O2 extraction by tissues (sepsis) -> falsely elevated
For each type of shock (hypovolemic, obstructive, cardiogenic, maldistributive) indicate if CO, contractility, and SVR are increased or decreased
Hypovolemic: decreased CO / increased contractility / increased SVR
Obstructive: decreased / normal to increased / increased
Cardiogenic: decreased / decreased / increased
Maldistributive: increased or decreased / increased or decreased / decreased
What are limitations of the Fick’s methods of CO monitoring
- Requires intubation (+ ventilation for NICO)
- Requires pulmonary artery catheter for O2 consumption method
- Requires rebreathing for CO2 production method (size limitation + issue with pulmonary disease)
- Not real time
- Affected by shunting (intracardiac / intrapulmonary)
CO = [Oxygen consumption (VO2) / arteriovenous oxygen difference (Ca-Cv)] x 100
List possible complications of Swan-Ganz catheter
- Gas pulmonary embolism
- Cardiac perforation
- Pulmonary hemorrhage
- Arrhythmias
- Pneumothorax
- Thrombosis / PTE
Name methods of CO monitoring
- Fick’s method (O2 consumption or NICO for CO2 production)
- Indicator dilution method (thermodilution and lithium dilution)
- Arterial waveform analysis (pulse contour analysis, pulse pressure analysis = PiCCO, PulseCO)
- Echocardiography (doppler and non-doppler)
- Transthoracic ultrasound
List methods to assess intravascular volume
Static markers:
- Physical exam findings (mentation, HR, pulse quality, MM colour, CRT, temperature, jugular vein distension, urine output)
- MAP
- Shock index
- Lactate
- CVP
- Pulmonary artery occlusion pressure
- Cardiac POCUS (left atrial size, left ventricular size, wall thickness)
- Caudal vena cava diameter
Dynamic markers:
- Any change in static markers following fluid challenge
- Caudal vena cava collapsibility
- Pulse pressure variation, systolic pressure variation, stroke volume variation
- Plethysmographic variability index
CVC collapsibility index meaning
> 50% suggestive of hypovolemia
<50% suggestive of fluid overload
What parameters (other than fluid responsiveness) affect PPV
- Tidal volume
- PIP and PEEP
- Patient’s spontaneous respiratory efforts
- Chest wall compliance (low compliance will increase PPV)
- Pulmonary compliance (low compliance will decrease PPV)
- Cardiac disorders (arrhythmias)
- Right heart failure
- Intra-abdominal pressure
What is the vena cava collapsibility index
CVCci = (CVCd max - CVCd min) / CVCdmax
CVC diameter measured throughout inspiration and expiration to measure the index of the difference in diameter
What influences the CVC collapsibility index (other than volume status)
- Right-sided cardiac dysfunction
- Respiratory effort
- Intra-abdominal effort
- Pressure artifact
What CVC collapsibility index has been associated with fluid responsiveness
> 30% in dogs (50% in humans)
True or false: patients need to be mechanically ventilated for measurement of CVC collapsibility index
False (spontaneous breathing is fine)
What happens to CVP, RA pressure, SV, SBP during spontaneous inspiration and expiration?
Inspiration:
- CVP falls
- RA pressure falls
- SV decreases
- SBP decreases
Expiration:
- CVP increases
- RA pressure increases
- SV increases
- SBP increases
- Reversed in PPV
In thermodilution, how does the area under the curve relate t CO.
See picture
A 2021 JVECC paper compared coccygeal and radial artery Doppler blood pressure measurements in sick cats with and without abnormalities in tissue perfusion. What was the conclusion of this study?
- Median coccygeal SBP is significantly greater than radial SBP in sick cats with both normal perfusion and hypoperfusion.
- Agreement between coccygeal and radial SBP is poor in cats and cannot be used interchangeably.
- Recommend obtaining SBP from both sites initially and choosing to monitor and trend changes with the one site that correlates most with physical examination findings.
