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Principles I Test 4

Cardiac Output Monitoring

What is normal O2 consumption? 1 - 3 or 1 - 4 mlO2/kg/min
What is primarily the limiting factor in O2 delivery to the tissues? cardiac output
Which has more of an effect on O2 delivery: cardiac output or FiO2? cardiac output
Does hemoglobin have an impact on the amount of oxygen delivered to this tissues? Yes! a dramatic effect; hub of 4 - 5 is when our body shifts from aerobic to anaerobic metabolism
_____________ is the primary compensatory mechanism that responds to an oxygenation challenge. cardiac output
Cardiac output monitoring helps to provide a global picture of the patient's overall __________ status circulatory
Cardiac output monitoring yields information regarding O2 _______ and O2 ________ delivery & consumption
CO = _______ x ________ HR x SV
What is the definition of stroke volume? the amount of blood pumped per heart beat
What 3 things determine stroke volume? preload, after load, & contractility
What is the largest determinate of preload? venous return
Preload basically indicates what? fluid volume status
What is after load? systemic vascular resistance
What effect do most of our anesthetic drugs have on contractility? decrease contractility
What is the normal value for cardiac output? 4 - 8 L/min
What is the normal value for stroke volume? 60 - 100 (approx 70) ml/beat
How do you measure cardiac output via the thermodilution method? inject 2.5 - 10 ml of fluid colder than body temp into right atrium and PA catheter senses temperature of blood in contact with it
What is the relationship between the degree of temperature change and cardiac output in the thermodilution method of cardiac output measurement? change in temperature is inversely proportional to cardiac output; (temp change minimal with high blood flow; temp change greater with minimal blood flow)
How do you derive the thermodilution curve? by plotting the temperature as a function of time
What can cause an inaccurate cardiac output estimation via the thermodilution method? rapid fluid bolus, respiratory variation, post-bypass pump temp drift, tricuspid valve regurgitation, high PEEP, intracardiac shunt, low flow states
Explain the continuous thermodilution method of cardiac output measurement. Uses small heat signal instead of cold via a specialized PA catheter; updates CO averages every 30 seconds, average readings over 3 - 6 minutes
What are the advantages of continuous thermodilution method over traditional thermodilution method? respiratory variations are not a factor, eliminates time consuming admin of thermal injectate, reduced chance of inaccuracy since "human error" element taken out of play
What are the weaknesses of continuous thermodilution method of cardiac output measurement? rapid central IV bolus infusions & post bypass pump fluid still decrease accuracy; approximate 10 minute delay can cause acute changes to be inaccurate
How does an esophageal doppler work to determine cardiac output? small probe inserted into esophagus that estimates SV of blood in descending aorta (which is 70% of CO); formulate applied that estimates remaining 30% of CO and adds it to measured total to produce total CO estimation
What are the weaknesses of the esophageal doppler method of cardiac output measurement? dependent upon many assumptions & nomograms which hinder accuracy in a variety of clinical situations; contraindicated in esophageal pathology and coagulopathy
Explain the partial CO2 rebreathing method of estimating cardiac output. ETCO2 reflects pulmonary capillary blood flow; this requires tracheal intubation and mechanical ventilation
How is cardiac output calculated via an arterial pressure waveform? calculates stroke volume from area under waveform; requires a well defined waveform since the dicrotic notch indicates end-systole
What are the strengths of arterial pressure waveform cardiac output measurement? provides a beat to beat cardiac output measurement and its accuracy compares to PAC/Swann thermodilution method
What are the weaknesses of arterial pressure waveform cardiac output measurement? frequent dysrhythmias and tachycardia can result in low SV and can affect accuracy
What are 3 methods of calculating cardiac output via the arterial pressure waveform? LiDCO, PiCCO, and Flo Trac
Explain the thoracic bioimpedance method of measuring cardiac output changes in thoracic volume cause changes in thoracic resistance (bioimpedance) to low amplitude, high frequency currents; 4 sets of electrodes on chest used to measure this
What are the weaknesses of the thoracic bioimpedance method of measuring cardiac output? accuracy affected by electrical interference, incorrect placement of electrodes, previous heart surgery, aortic valve disease, acute changes in sympathetic nervous function (spinal block); can't use in open heart cases
Created by: Mary Beth