End-tidal capnometry can be a useful surrogate for perfusion monitoring and is a crucial tool in your resuscitation tool kit. In this video, from our Resuscitation Essentials course, you'll discover how end-tidal capnometry can be used to help monitor your patients' wellbeing and what you need to consider in order to avoid misinterpretation of the results.
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[00:00:00] Oxygen is metabolized throughout the body into carbon dioxide by oxidative phosphorylation. This carbon dioxide is circulated via the bloodstream into the lungs, where it's expired and can be measured. This can be done quantitatively with an end-tidal capnometer or capnograph. These are devices which measure the presence of CO2 passing by a sensor, attached near the patient's airway or within the breathing circuit. A report of value is usually in millimeters of
[00:00:30] mercury. This can be useful in several ways. For one, the presence of cyclical waveform confirms communication with the ventilatory system and can be used to confirm endotracheal tube placement. We also know that the rate of generation of carbon dioxide is relatively constant. Therefore, with the constant ventilatory rate, the only changing variable is the rate of circulation, so we can use changes in quantitative end-tidal capnometry as a surrogate for perfusion. More perfusion to the lungs will create a higher level of
[00:01:00] expired carbon dioxide and less perfusion will create less expired carbon dioxide. Very low levels of expired carbon dioxide suggest poor perfusion and obviate the need to interrupt compressions for a pulse check. Prolonged periods of cardiac arrest with very low end-tidal CO2 suggest that a return of spontaneous circulation is unlikely. Of course, other factors may create a low reading as well, including obstructive lung disease, hyperventilation or a large portion of dead space from another cause of poor
[00:02:00] perfusion like a pulmonary embolism. Administration of sodium bicarbonate will increase the amount of carbon dioxide expired, without reflecting an increase in perfusion. In addition to its utility as a surrogate for perfusion monitoring, end-tidal CO2 may also serve as a reliable method to monitor ventilation for a variety of patients, including those at risk for airway obstruction or apnea.