Clinical Applications
Capnography is a non-invasive method for monitoring the level of carbon dioxide in exhaled breath (EtCO2), to assess a patient?s ventilatory status. A true capnograph produces both an EtCO2 value as well as a waveform, or capnogram. Capnographs are useful for monitoring ventilator status, warning of airway leaks and ventilator circuit disconnections, and ensuring proper endotracheal tube placement. Capnography also helps clinicians diagnose specific medical conditions, make treatment decisions, and assess efficacy of code efforts and predict outcome.
Microstream® makes EtCO2 monitoring feasible with nonintubated
patients and thereby broadens the applications for capnography
beyond these traditional functions. For example, capnography can
alert clinicians to episodes of hypoventilation as well as help them assess ventilation and treatment of asthma and COPD (chronic
obstructive pulmonary disease) patients. It also provides safety
monitoring during procedural sedation, in keeping with current ASA
standards[1] that mandate CO2 monitoring for all anesthetized
patients, whether they are intubated or not.
Drawbacks of Conventional Technology
All capnographs measure CO2 concentration using either mainstream
or sidestream configurations. In mainstream capnographs, the sensor
is located on a special airway adapter so CO2 is measured directly in
the patient?s breathing circuit. In sidestream capnographs, a sample of
exhaled breath is aspirated from the breathing circuit to a sensor
residing inside the monitor.
The problem of moisture and secretions entering and clogging the
breathing circuit has plagued both types of capnographs since their
inception. Not only does this problem inconvenience the caregiver, but
it also interrupts monitoring and can cause inaccurate measurements.
Conventional capnography has other drawbacks as well:
- The CO2 sensors are cross-sensitive to anesthetic gases.
- Mainstream systems require larger airway adapters that increase dead space in the breathing circuit.
- The added weight of the adapter on the endotracheal tube can cause kinking and accidental extubation.
- Sidestream capnographs are not accurate in neonatal and pediatric patients because they compete with the patient?s tidal volume
- Mainstream capnographs cannot accommodate nonintubated patients.
[1] American Society of Anesthesiologists (ASA). Basic Standards for
Intraoperative Monitoring; 1999
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