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What is room air?
- 21% oxygen
- 71% nitrogen
- 1% carbon dioxide and other gases
Where does gas exchange take place?
lungs and tissues - in capillary beds
What is capnography?
exhaled CO2 concentration and is an accurate indicator of arterial circulation and CO2 concentration
Why don't we breathe all of the CO2 out?
- the animal needs CO2 to maintain an acid base balance
- if the animal breathed all the CO2 out then it would become alkalotic
What are the four main things that affect ETCO2?
- pulmonary perfusion
- alveolar ventilation
- technical error
What metabolism causes could cause a decreaesd ETCO2?
- muscle relaxants
What metabolism causes could cause an increased ETCO2?
- malignant hyperthermia
- sodium bicarbonate
- tourniquet release
What about pulmonary perfusion could cause a decreased ETCO2?
- decreased cardiac output
- pulmonary embolism
- cardiac arrest
What about pulmonary perfusion could cause an increased ETCO2?
- increased cardiac output
- increased blood pressure
What about alveolar ventilation could cause a decreased ETCO2?
- partial airway obstruction
- pulmonary edema
What about alveolar ventilation could cause an increased ETCO2?
What technical errors could cause a decreased ETCO2?
- sampling leaks
- sampling fresh gas flow
- obstructed endotracheal tube
What technical errors could cause an increased ETCO2?
- exhausted CO2 absorber
- inadequate fresh gas flow
- leaks in the breathing circuit
- faulty valves
What is hyperventilation?
depleats CO2 and causes body to stop breathing so CO2 will build back up to stimulate breathing again
What are the most common causes of an increase ETCO2?
alveolar ventilation (hypoventilation and rebreathing) and technical error (exhausted CO2 absorber, inadequate fresh gas flow, leaks in the breathing circuit, faulty valves)
When in ETCO2 is increased what do we look at first? Then what do we do?
- first look at INCO2
- if INCO2 is normal then the cause is hypoventilation
- if INCO2 is increased then the cause is a technical error
If the ETCO2 is decreased what do we determine next?
- if it is low then there could be a low cardiac output, hypotension, hypovolemia, embolism (rules these out first)
- then look for hyperventilation or technical error (these are the most common)
- if it is ZERO then look for apnea, obstruction in the endotracheal tube, or a disconnection in the machine