EMTs, nurses, and other types of clinicians learn valuable information by studying their patients’ waveform capnography. It helps predict the outcome of resuscitation, and it can help watch cardiac output during CPR and help monitor seated patients.
But what is waveform capnography exactly? Whether you work in the medical field or simply want to understand more about the technology used by clinicians, this article will explain 7 things you should know about interpreting waveform capnography.
Waveform Capnography Explained
Waveform capnography is a vital sign that provides clinicians with information on a patient’s ventilation. Capnography waveform helps clinicians objectively evaluate a patient’s ventilatory status. It does this by tracking the carbon dioxide in a patient’s breath.
This vital gives clinicians clues about the circulatory and metabolic systems as well, which can help in a patient’s treatment plan.
1. Waveform Capnography Helps Check Ventilation
The most basic use of capnography is to monitor a patient’s ventilation. It provides a number and a graph that allows clinicians to assess breathing trends. Capnography can give early warning signs of an impending crisis.
When a person hyperventilates, their CO2 levels decrease. Hyperventilation is a symptom of many different conditions, from anxiety to bronchospasm. Co2 levels also decrease during cardiac arrest, hypotension, decreased cardiac output, and severe pulmonary edema.
When a person hypoventilates, their CO2 goes up. Hypoventilation can be caused by various conditions from head trauma, stroke, an overdose, sedation, or even intoxication. A patient’s CO2 may be high due to increased breathing, fever, pain, depressed respirations, sepsis, or even chronic hypercapnia.
Some diseases may also cause a patient’s C02 to go up and then down, such as asthma. When interpreting the waveform capnography, it is more important to pay attention to the graph’s trend than the specific number.
If you begin to see the graph steadily rise, the patient may soon need intubation or help to breathe. In the case of a heroin overdose, some states permit clinicians to administer Narcan to unresponsive patients who are suspected of opiate overdoses and with a respiratory rate of less than 10.
Monitoring the CO2 levels of patients can help clinicians better gauge the patient’s ventilation.
2. Use Waveform Capnography to Assist, Maintain, and Confirm Intubation
One way to confirm tracheal intubation is by monitoring the patient’s C02. A nice waveform indicates the presence of C02 and shows that the ET tube is placed correctly in the trachea.
The American Heart Association states in its CPR and ECG guidelines that when exhaled C02 is detected during a cardiac arrest, it is usually a reliable indicator that the ET tube is positioned correctly in the patient’s trachea.
This may not necessarily hold true for cases of greatly prolonged downtime before the initiation of CPR. Massive pulmonary embolisms block blood flow to the lungs, which can also lead the patients to be difficult to assess the C02 values of a patient. CPR is also necessary to generate the waveform.
Continuous waveform capnography can also assist with difficult intubations where patients are spontaneously breathing. Clinicians are able to attach the capnography filter to the ET tube before intubation and use the monitor to assist with the placement.
This system can also be implemented in nasal intubation. If you decide to use this method, you may see CPR oscillations on the monitor screen immediately after intubation being replaced with larger waveforms once the ambu bag has been attached, and ventilation has begun.
Make sure you access equal lung sounds because waveform capnography cannot detect right main-stem intubations.
3. Use Waveform Capnography to Measure Cardiac Output During CPR
Monitoring a patient’s C02 also measures their cardiac output. Measuring the C02 can come in handy when you are trying to measure the effectiveness of CPR efforts.
When you see a decrease in C02, have a new person start performing chest compressions. If you see an increase in C02 output, it could be a sign that the last rescuer grew tired, and the new rescuer was able to provide better compressions.
Rescuers should ideally replace themselves every two minutes because chest compressions during CPR should be hard, fast, and deep.
Set up the monitor where the rescuers can view the readings as well as the ECG waveform generated by their compressions. It’s a best practice to encourage rescuers to keep the C02 levels as high as they can during the process.
But, keep in mind that patients with extended downtimes may have low C02 levels, and a new rescuer may not do much to improve the reading.
During a cardiac arrest, if you begin to see the C02 number shoot up quickly, stop CPR, and check for pulses. This can be a sign of spontaneous circulation.
End-tidal C02 often overshoots the baseline when circulation is restored due to carbon dioxide washing out from the tissue. End-tidal C02 monitoring is an effective and safe way of measuring cardiac output during CPR and is often an early indicator of ROSC in intubated patients.
After a patient is resuscitated, if you see the C02 levels significantly drop, you should immediately check the pulses because you may have to begin CPR again.
4. Forecast the Likelihood of Resuscitation
A carbon dioxide level of 10 mmHg or less measured 20 minutes after the initiation of advanced cardiac life support accurately predicts death in patients with cardiac arrest that have electrical activity but no pulse.
Case studies have shown that patients with high levels of C02 were more likely to be resuscitated than those who did not. The higher the level of C02, the higher the likelihood that the person will be resuscitated.
The difference between survivors and nonsurvivors can be detected in 20 minutes of end-tidal carbon dioxide levels.
Use caution with these numbers. While it is true, a low initial C02 level makes resuscitation less likely than a higher C02 level, there have been patients who have been resuscitated with initial readings lower than 10 mmHg.
Waveform capnography explained the differences in types of cardiac arrests as well. Patients that suffer from asphyxic cardiac arrest have significantly increased initial C02 readings. These readings come down within a minute.
High readings are from a buildup of C02 in the lungs. These readings can help determine it is a traditional cardiac arrest or an asphyxic cardiac arrest that a clinician is dealing with.
5. Use Waveform Capnography to Watch Sedated Patients
Another important use of capnography is to monitor patients receiving pain management or sedation. Capnography can provide evidence of hypoventilation and apnea.
By monitoring a patient’s C02 level, clinicians can report a problem before there are changes in respiration levels. With sedated or intubated patients, it is incredibly important to pay attention to capnography vital signs.
The small notch above the wave indicated when a person is breathing independently and becoming aroused from sedation. Clinicians may want to provide additional information at this point to prevent the patient from waking up.
6. Monitoring Patients with Asthma
Monitoring C02 levels of non-intubated patients is an excellent way to assess the severity of COPD and asthma. It can also help determine the effectiveness of the treatment.
Patients experiencing Bronchospasm will experience a shark fin-like waveform as the patient struggles to exhale a breath. The shape is formed due to uneven alveolar emptying.
Many studies have now confirmed this shape correlates to Bronchospasm. You can tell the severity by the shape on the graph.
Patients with asthma may also benefit from monitoring their C02 levels. Asthma changes greatly with a change in severity. A patient with mild asthma will have their C02 levels drop to below 35 as the patient struggles to breathe and hyperventilate to compensate.
As asthma becomes worse, the patient returns to normal C02 levels. When asthma becomes severe C02 levels will rise to dangerous levels above 60. This is because the patient is tiring and has little air movement.
Successful treatments can help lessen or eliminate the “shark fin” wave shape and return the C02 levels back to a normal range.
7. Monitoring Patients with COPD
Capnography can also show hypoxic drive in COPD retainers. CO2 levels will steadily rise, alerting the clinician to turn on the oxygen before the patient becomes obtunded.
Only around 5% of COPD patients experience hypoxic drive. In these patients monitoring C02 levels will help you to determine if the patient has the right levels of oxygen and prevents hypoventilation.
Interpreting Waveform Capnography is Useful in Many Circumstances
Waveform capnography interpretation is an important and necessary skill for clinicians, doctors, nurses, and EMTs. If you work in the medical field, review these seven ways to interpret and use capnography in your practice.
Infinium Medical is one of the most respected manufacturers of patient monitors and operating room equipment. We make the top of the line waveform capnography equipment that is easy to use and cost-effective. Learn more about our manufacturing process by clicking here.