Capnography is a monitoring technique that measures the concentration of carbon dioxide (CO2) in exhaled breath. This measurement offers important insights into a patient’s metabolic state, circulation, and ventilation. During Cardiopulmonary Resuscitation (CPR), capnography has become a valuable tool, providing real-time feedback that can help improve the quality of chest compressions and guide resuscitation efforts.
Understanding Capnography
Capnography involves the continuous measurement of carbon dioxide levels at the end of exhalation, known as end-tidal carbon dioxide (ETCO2). This exhaled CO2 originates from cellular metabolism and is transported by the blood to the lungs for exhalation. The amount of CO2 present in exhaled breath therefore reflects the body’s metabolic activity and the efficiency of blood flow to the lungs.
The capnograph device works by connecting a sensor to the patient’s breathing circuit, often at the airway opening. This sensor uses infrared light to detect CO2 molecules in the exhaled gas. The device then displays the ETCO2 value as a number and simultaneously generates a waveform that graphically represents the CO2 concentration over time during the breathing cycle.
A typical capnography waveform shows a rise in CO2 during exhalation, a plateau when alveolar gas is sampled, and then a sharp drop to zero during inhalation. The numerical ETCO2 value typically represents the peak CO2 concentration at the end of the exhalation phase. Understanding both the numerical value and the shape of this waveform provides information about a patient’s respiratory and circulatory status.
The Role of Capnography in CPR
Capnography offers objective, continuous feedback during CPR that traditional assessment methods cannot provide. It assesses the effectiveness of chest compressions. Adequate chest compressions are necessary to circulate blood and deliver oxygen to vital organs, and capnography indicates whether these compressions are generating sufficient blood flow.
Another application is confirming the proper placement of an endotracheal tube, which is inserted into the trachea to secure the airway during resuscitation. The presence of consistent carbon dioxide in exhaled breath confirms that the tube is correctly positioned in the airway rather than in the esophagus. This immediate verification is crucial for effective ventilation.
Capnography also serves as an early indicator of the return of spontaneous circulation (ROSC). A sudden and sustained increase in the ETCO2 value can signal that the heart has begun pumping effectively again, restoring blood flow. This feedback allows healthcare providers to quickly identify when resuscitation efforts are succeeding and adapt their approach.
Interpreting Capnography Readings During CPR
A consistently low ETCO2 reading, below 10 to 20 mmHg, suggests that the chest compressions are not generating adequate blood flow to the lungs. This low value can indicate poor quality compressions.
A sudden, sustained increase in the ETCO2 value, rising to 35-45 mmHg or more, is a primary indicator of the return of spontaneous circulation (ROSC). This rise reflects improved cardiac output and a restoration of blood flow that delivers CO2 from the tissues to the lungs. Observing this change allows providers to transition from chest compressions to post-resuscitation care.
Analyzing the capnography waveform provides critical information. A normal, square-like waveform confirms that the endotracheal tube is correctly placed in the trachea and that ventilation is effective. The absence of a waveform or an inconsistent, erratic pattern indicates that the tube is misplaced, such as in the esophagus, requiring immediate repositioning.
Changes in the waveform shape during CPR can also signal other issues. An irregular or sloped waveform might suggest partial airway obstruction, bronchospasm, or problems with the ventilation device. Monitoring these waveform changes allows healthcare providers to identify and address problems related to ventilation and airway management in real-time.
Guiding Resuscitation Efforts with Capnography
Capnography data informs real-time decisions and adjustments during resuscitation efforts. If the ETCO2 value remains consistently low, it prompts providers to evaluate and improve the quality of chest compressions. This might involve adjusting the depth or rate of compressions.
Upon observing a sudden and sustained increase in ETCO2, which signals ROSC, healthcare teams can immediately cease chest compressions. This allows for a swift transition to post-resuscitation care, focusing on stabilizing the patient’s breathing and circulation. Such timely recognition helps minimize unnecessary compressions and facilitates the next phase of treatment.
Capnography provides continuous, objective feedback that allows for a data-driven approach to CPR. This immediate insight into the effectiveness of interventions helps guide a team’s actions without requiring pauses in compressions for manual pulse checks. By providing a direct measure of circulatory function, capnography enables healthcare providers to optimize their efforts and improve resuscitation outcomes.