Capnography how and why ?
Capnography is the ongoing monitoring of CO2 concentrations, or partial pressures, in breathing gases. Capnography is a noninvasive measure during inhalation and exhalation of partial pressures of CO2 in the airways. Capnography may also be used to measure CO2 production, which is a measure of metabolism. Waveform capnography represents the carbon dioxide (CO2) amount in the breath, assessing ventilation.
Waveform capnography is used in all levels of emergency medical services for a more accurate assessment of patients who are experiencing respiratory distress, cardiac arrest, and shock. In an NICU, waveform capnography may be used for continued monitoring of airway placement and patency, using a variety of airway augments. Waveform capnography is a useful tool for identifying when patients with altered mental status require assisted breathing using bag-valve masks.
When using waveform capnography to help patients who are pulse-gassed for ventilatory assistance, the waveform is seen after every compression as the air enters the lungs.
The benefits of capnography ?
In addition to assessment of tracheal tube patency and location, and of the position of a tracheostomy, capnography may provide further insight into respiratory and cardiovascular functions, both for ventilated and non-ventilated patients. In addition, capnography has other uses in intensive care related to airway management and monitoring of respiratory and cardiovascular function.
Capnography is increasingly used by emergency medical technicians to aid their evaluation and management of patients before transporting them to the hospital. Capnography provides physiological information about ventilation, perfusion, and metabolism, all important in the management of the airway.
Capnography, as it provides a breath-by-breath measure of the patients ventilation, quickly can identify an increasing trend in the patients status, providing the physician an early warning system about the patients breathing state. Capnography provides a graphic depiction of expired CO2 and serves as a noninvasive means to show live CO2 kinetics information for mechanically ventilated patients.
If both circulation and ventilation are stable–a condition that can be achieved only with passive mechanically ventilated patients–CO2 monitoring can be used as a marker for CO2 production. The measured CO2 signal may be recorded either by time (time-based capnography) or by expiratory volume (volumetric capnography).
The value of CO2 end-tidal displayed on a monitor is considered to be that taken when the expiration is complete. Volumetric capnography (VCA) measurements may be performed using a pneumotachograph, measuring both the CO2 expiration volume and tidal volume simultaneously. Oxygenation and capnography measures the last part of the cardiovascular-ventilatory system.
In cases in which capnography is not used, pulse oximetry and visual examination of the rise in chest height are standard methods of monitoring patients receiving sedation. The recommendation for continuous monitoring of ventilation with capnography in the middle and depths of sedation was based on the difficulty of predicting how a single patient would
react to the given sedative.
The ASA and the AAGBI issued revised standards in 2011 for the monitoring of ventilation by capnography in order to improve the safety of patients under sedation, regardless of where they are being sedated for procedure. The AHA has also noted in its new guidelines that capnography, which indirectly measures cardiac output, may also be used to monitor CPR efficacy and to provide early evidence for returning spontaneous circulation (ROSC).