Capnography Flashcards
What is capnometry?
Measurement of CO2 concentrations in respired gases and a numerical display of the expired concentration
What is capnography?
Measurement of CO2 concentrations in respired gases and graphical display of the CO2 wavefrom
What is a capnogram?
Display of the CO2 waveform
Why is the measurement of respired gases useful during anaesthsia?
Hype/hyperventilation Information about CO Presence of re-breathing V/Q mismatch Alveolar dead space (when combined with monitoring PaCO2) Detection of equipment errors Detect pulmonary embolism
How is CO2 measured?
infra red light
IR is absorbed at different frequencies by different molecules
The amount of light absorbed is proportinal to the IR absorbing substance
What are the two methods of capnography?
Side stream ( sampling line from endotracheal tube to machine) Mainstream (the devise that measures CO2 sits in the aiway)
What are the advantages and disadvantages of side stream capnography?
Advantages Can be used in non intubated patients resilient easy to connect easy to disinfect (new sampling line) Disadvantages Slow response time water vapour can condense in sampling line and cause obstruction can become kinked
What are the advantageous and disadvantages of the mainstream capnography?
No sampling line rapid No effect of water pressure ( Water evapourates) No scavenging needed No obstruction of line Disadvantages new sensors add to drag on breathing system vulnerable to damage difficult to clean only used in intubated patient
What is low V/Q mismatch and why may it occur?
Poor ventilation, good perfusion
Mucus pluggin of the bronchioles
ET tube in mainstem bronchus
atelectasis
What is high V/Q mismatch and what may cause it?
Good ventilation poor perfusion
pulmonary embolism
low cardiac output
cardiac arrect
What is end tidal CO2?
Concentration of CO2 measured at the end of expiration
What is the normal difference between PaCO2 and ET CO2?
less than 5 mmHg
an increase indicates an increase in alveolar deadspace (Increase in number of alveoli that are ventilated but not perfused (CO)
What may increase cardiac output during anaesthesia?
Increased blood pressure
Increased sympathetic nerve activity (lightening of anaesthesia, drugs)
Increased body temperature
What will a increased cardiac output result in?
Increased delivery of CO2 from the peripheral tissues to the lungs, increased PaCO2 and Increased ETCO2
What might a decreased cardiac output be caused by during anaesthesia?
Hypovolamia
hypothermia
obstruction to venous return (pneumothroax)
Decreased production of CO2 and decreased delivery to the lungs
Decreased Paco2 and decreased ETco2
Increased alveolar dead space (ventilated not perfused)
increase the difference between Paco2 and CO2
