Cardiac Output monitoring Flashcards
What is the normal CO in dogs and cats?
120-200 mL/kg/min
What is the cardiac index?
CO divided by the animal’s body surface area in L/min/m2
Explain the Frank-Starling principle and curve
Explains that stroke volume increases as cardiac end-diastolic volume increases, i.e., more blood means increased stretych of cardiac myofibrils –> improves contractility
myofibrils have a maximal stretch –> when starling-curve reaches plateau, i.e., fluid-unresponsive state
Where should the tip of a central venous catheter used to measure CVP be located?
within the vena cava, just proximal to the right atrium
Describe a traditional fluid challenge using CVP and how to interpret its results
CVP measurement whil giving 20 mL/kg isotonic crystalloids or 5 mL/kg colloids
normal blood volume –> CVP should increase by 2-5 cm H2O and return to baseline within 15-20 min
fluid overload/ poor cardiac function –> CVP increased by > 5 cm H2O
fluid responsive –> CVP does not increase or decreases to baseline quickly
List 5 differentials for elevated CVP
- increased blood volume
- poor ventricular function
- increased vascular tone
- increased intrathoracic pressure (PPV)
- increased intraabdominal pressure
Explain the Fick’s principle of cardiac output measurement
Considered the orignial gold standard
goes by the principle that VO2 must equal CO x (CaO2 - CvO2)
can rearrange this equation to:
CO = VO2 / (CaO2 - CvO2)
CaO2 and CvO2 measured (CvO2 with mixed venous sample ideally via pulmonary atery catheter) - in volume/volume (mL/L)
VO2 - determined by measuring inspired by expired volume of O2 per min (mL/min)
–> L/min CO
modified technique with CO2 measurement, teremd “noninvasive CO mon.”
Name 3 examples of indicators used for indicator dolution method for CO monitoring
- lithium
- cold saline (thermo dilution)
- dye
What are the two different methods of indicator dilution methods for CO monitoring? Describe the methods
Transpulmonary thermodilution
- patient receives indicator into bloodstream (e.g., jugular vein)
- indicator is sampled downstream (e.g., femoral artery)
- time-dilution curve of indicator found in the downstream sample is generated - used to derive CO
Pulmonary artery thermodilution
- patient receives indicator into the RA
- indicator is sampled downstream in the pumonary artery
Explain pulse contour analysis
Arterial blood pressure waveform is measured and analyzed in conjunction with traditional CO monitoring, i.e., thermodilution (PiCCO) or lithium dilution (LiDCO).
The traditional CO measurement is used for calibration - then software uses pulse contour analysis of the arterial waveform for continued CO monitoring
Describe Pulse Pressure Analysis for CO monitoring
Similar to pulse contour analysis but does not require a traditional dilution technique for callibration
software uses variation in arterial blood pressure waveform to calculate SV –> is then multiplied by HR to get CO
found to be unsuitable in anesthetized dogs compared to transpulmonary or pulmonary artery thermodilution
Describe how CO can be estimated with transthoracic echocardiography
SV calculated from:
- velocity of blood flow in the left ventricular outflow tract
- x cross-sectional area of the left ventricular outflow tract
… x HR = CO
Explain how CO measured using esophageal Doppler
esophageal doppler measure blood flow velocity in the descending aorta x aortic diameter …. = SV
… x HR = CO
What is USCOM?
Ultrasound CO monitor
- uses transortic and transpulmonary blood flow tracings to then calculate CO and SV
Problem: standard aortic diameter is pre-dermined in the machine (for adult and pediatric human patients) –> would need to first peform an echo in veterinary patients and enter aortic diameter into the machine
What is bioimpedance and bioreactance?
Bioimpedance
- applies high-frequency electric current of a known amplitude and frequency across the thorax
- amount of resistance/impedance varies in relation to amount of fluid in the thorax
Bioreactance
- electric current of known frequency is applied across the thorax
- measures reactance/frequency or phase shift of the electric current
- delay in phase shift = increased SV
