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Principles I Test 4
Cardiac Output Monitoring
| Question | Answer |
|---|---|
| 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
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