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By Bob Sullivan
Capnography during CPR care is a critical tool during cardiac arrest response, providing real-time feedback on CPR effectiveness and patient status. Continuous waveform capnography and end-tidal CO2 (ETCO2) monitoring during CPR help EMS providers assess ventilation, confirm airway placement and guide resuscitation efforts. Here are five essential facts about using capnography during CPR.
1. Capnography may offer the first sign that CPR is needed
End-tidal CO2 (ETCO2) detection requires air movement in and out of the lungs (ventilation), CO2 production from cellular metabolism, and blood flow to the lungs to excrete the CO2. A change in any of those will be immediately detected with continous waveform capnography, which is valuable information while caring for critically ill and injured patients.
Besides constant palpation of a carotid pulse, waveform capnography is the most reliable prehospital monitoring device to detect the immediate loss of circulation. As soon as the heart stops, the capnography waveform will disappear and the ETCO2 reading will change to zero. This is even true for patients with good air movement while receiving positive pressure ventilation.
Waveform capnography is also useful for hypotensive patients with decreased mentation, where detection of a carotid pulse can be difficult. If a waveform is produced with exhalation, some circulation is present.
Other monitoring devices are less reliable for detecting cardiac arrest. Pulse-oximetry depends on circulation at the location where the probe is placed, which is inconsistent in patients in shock or with cold extremities.
The tracing on an ECG monitor may not even change after the patient loses pulses; the patient’s heart may still have electrical activity but no pumping action. This is especially true in bradycardic patients receiving transcutaneous pacing. If a capnography waveform is lost, check for a pulse immediately, and initiate CPR if one cannot be felt. If a pulse is felt, then check for breathing, because respiratory arrest will also cause a loss of ETCO2. If the patient has a pulse and is not breathing, initiate positive pressure ventilation. If the patient has a pulse and is breathing, look for a problem with the capnography circuit, such as secretions in the filter or kinks in the tubing.
2. Capnography during CPR measures response
Consistent, high-quality chest compressions are essential for successful cardiac arrest resuscitation. The depth of each compression should be at least 2 inches, but not greater than 2.4 inches, the hands must come completely off the chest on the upstroke, compressions should be delivered at a rate of 100-120 time a minute, with pauses only for compressor changes.
Several devices are available that provide real-time feedback on compression quality. These prompt the compressor to adjust their technique, and detect the need to change compressors due to fatigue. ETCO2 during CPR provides feedback on how effective compressions are at perfusing vital organs. Both are important to guide treatment, and both should be applied as early as possible.
A higher ETCO2 reading during resuscitation correlates with improved cardiac output and patient outcomes. An ETCO2 reading above 15 mmHG indicates compressions are generating perfusion [1]. The higher the ETCO2, the better the perfusion generated by CPR, and the better the chances of survival are. Compressions may also generate small capnography waveforms from passive air exchange between ventilations, which also provides feedback on compression rate.
Low ETCO2 (below 10 mmHG) may be caused by either poor compression technique, or from low perfusion and metabolism after a long downtime or shock despite good compressions. Compression feedback helps determine whether compression adjustments can make perfusion better, and ETCO2 shows when good compressions do not generate effective perfusion.
3. Continuous waveform capnography guides ventilation rates and confirms airway placement
Excessive positive pressure ventilation can occur during resuscitation and is extremely harmful [1]. Delivering ventilation too frequently or too forcefully increases intrathoracic pressure, which decreases the amount of blood circulated with compressions. Hyperventilation also causes vasoconstriction and decreased perfusion to the brain.
The AHA recommends that ventilations should be delivered every 5-6 seconds, and that each breath should be given over 1 second, causing visible chest rise [1]. Timing ventilation can be difficult under stress during resuscitation, and when applied, waveform capnography has been shown to reduce the incidence of patient hyperventilation [2].
Through a circuit connected to a BVM or advanced airway device, each ventilation will produce a waveform and the respiratory rate will be displayed with the ETCO2 reading. When an advanced airway is placed, waveform capnography is the most reliable method to confirm placement, and documented proof that the airway remained in place throughout the course of care.
4. Capnography during CPR can guide termination decisions
Determining when to stop resuscitation efforts is one of the most difficult decisions EMS providers face. ETCO2 can help differentiate when efforts should continue and when they are futile. In patients receiving high-quality chest compressions, who have an advanced airway placed, a persistent ETCO2 reading below 10 mmHG after 20 minutes of resuscitation is an indication to terminate efforts [1]. However, a high ETCO2 shows that CPR is providing effective circulation to vital organs — essentially doing the heart’s job while defibrillation and medications are administered to get it beating on its own.
The PART trial identified temporal increases in ETCO2 were associated with increased odds of ROSC, suggesting value in using continuous waveform capnography during OHCA resuscitation to guide decisions.
5. A spike in ETCO2 during CPR is the first sign of ROSC
A sudden increase in ETCO2 during CPR is often the first sign of return of spontaneous circulation (ROSC), even before a carotid pulse can be detected. Because impaired circulation during arrest causes CO2 to build up in the bloodstream, the initial ETCO2 reading may initially be higher than the normal 35-45 mmHg range as it gets washed out of the lungs. Remember that a waveform with ventilation and no compressions means that there must be circulation taking place, so pause compressions and check a pulse if a spike in ETCO2. A few minutes after the initial increase, use ETCO2 to titrate the ventilation rate and tidal volume to maintain an ETCO2 reading between 35 and 40 mmHG [3].
Patients with ROSC are at high risk for rearrest, especially in the first 10 minutes. With ventilation at the appropriate rate, a steady decline in ETCO2 indicates that CPR may soon be needed, or that a vasopressor is needed to support blood pressure. If the ETCO2 is abruptly lost, it may be caused by rearrest or displacement of the advanced airway. First check a pulse, and then confirm airway placement.
Waveform capnography provides information about both circulation and ventilation before, during, and after cardiac arrest. Apply the device early in resuscitation, and apply the information it provides to clinical decisions.
References
- Neumar RW, Otto CW, Link MS, et al. Part 8: adult advanced cardiac life support: 2010 American Heart Association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care. Circulation 2010; 122 (suppl 3): S729-S767.
- Davis DP, Dunford JV, Ochs M, et al. The use of quantitative end-tidal capnometry to avoid inadvertent severe hyperventilation in patients with head injury after paramedic rapid sequence intubation. J Trauma 2004; 56(4):808-814, Apr 2004.
- White RD, Goodman BW, Svoboda MA. Neurologic recovery following prolonged out-of-hospital cardiac arrest with resuscitation guided by continuous capnography. Mayo Clinic Proceedings 2011; 86 (6): 544-548.
- Peberdy MA, Callaway CW, Neumar RW, et al. Part 9: post-cardiac care: 2010 American Heart Association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care. Circulation 2010; 122 (suppl 3): S768-S786.
This article, originally published in October 2015, has been updated with new resources and a video.
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