Difference Between Waveform Capnography
Waveform capnography to today’s paramedic is what it felt like with the invention of the washing machine becoming available to generations of people who grew up using a wash board. Now that people have a machine to do the work for them, they cannot imagine going back to hand washing. The same holds true for capnography. Now having real-time feedback of patient conditions, providers cannot conceive going back to the delayed readings of pulse oximetry. The hope for medical professionals is that “60 days, 60 weeks, and 60 years from now all providers cannot imagine life without capnography.” (Thibeault. 2015). This irreplaceable tool is used to prove that blood is going round and round the body and air is going in and out of the body efficiently enough to sustain life. Multiple studies and research have proven time and time again the importance and dependability of end-tidal carbon dioxide, ETCO2, in the reading of waveform capnography for medical professionals to verify an advanced airway placement and/or to determine return of spontaneous circulation, ROSC, in cardiac arrest. Waveform capnography provides objective, continuous confirmation of airway location and immediate feedback if advanced tubes are improperly inserted. (Thibeault. 2015).
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This paper is going to outline what capnography is, the difference between waveform capnography and pulse oximetry, and why the ALS provider should consider using this tool as a basic diagnostic in patients with a respiratory concern by means of non-invasive monitoring.
Waveform capnography is the reading displayed via waveform and digital number used to interpret CO2 exhaled from the body. ETCO2 is the “partial pressure or maximal concentration of carbon dioxide (CO2) at the end of an exhaled breath, which is expressed as percentage of CO2 or mmHg.” (Press. 2015). This concentration of CO2 is what is displayed on a screen. The CO2 is a reflected number of cardiac output (CO) and pulmonary blood flow as CO2 is moved by the circulatory system from the heart to the lungs. As blood flow reaches the lungs, CO2 is expelled. At the same time, oxygen is absorbed; traveling back to the heart and then pumped throughout the body; measured by a pulse oximeter. The CO2 is then exhaled. With a ETCO2 being used, the paramedic can determine a course of treatment for the patient based off the digital reading and waveform produced by this exhaled CO2. Specifically, ETCO2 waveforms provide medical personal with a tool for fast and dependable analyses of pulmonary pathophysiology. (Press. 2015). The 2010 The American Heart Association (AHA) found capnography so vital, they placed it in the guidelines for “Advanced Cardiac Life Support and Emergency Cardiac Care,” as well as the pediatric version, stating “providers should observe persistent waveform capnography with ventilation to confirm and monitor correct placement of endotracheal tube placement in the field, the transport vehicle, on arrival at the hospital and after any patient transfer, to reduce the risk of unrecognized ET tube misplacement or displacement” (Thibeault. 2015). The AHA found from a study published in 2005 from Annals of Emergency Medicine, 23% of field intubations misplaced the tube when not using a form of capnography to verify placement. (Capnography. 2016). A tube placed in the esophagus and not in the proper location of the trachea, means air is being pumped into the stomach. This can lead to emesis, which can lead to aspiration, which ultimately can lead to death. If not caught fast enough, a patient can die from hypoxia, due to air not being moved to the lungs, thus no cellular level exchange of gas, thus no oxygen going to the essential organs of the body to maintain life. The body needs oxygen to function. Without sufficient amounts, brain damage can occur and death.
The book Anaesthesia and Intensive Care, “The history of capnography,” notes the encounter of carbon dioxide dating back to the Romans. The deadly gas (known as “evil air”) killed dogs who entered various caves with humans; who were able to tolerate the gases only while they remained upright. Unknown to the Romans the “evil air” was seeping in through the cracks in the floor of the caves. During the 17th century, Jan Baptist van Helmont, discovered gas being expelled during the burning of wood, calling it “spiritus sylvestre.” In 1755, Joseph Black, found mixing acid with limestone would produce the gas. Black called it “fixed air.” Throughout the course of history many documentations and experimentation led to defined properties outlining carbon dioxide. The physical measurement of CO2 would not come for many years after these findings, as gases were not fully understood. As gas laws are claimed, including Boyle, Gay Lussac and Kelvin, discoveries associated with CO2 on a cellular level continued to rise. In the 1850’s light absorption with different densities of air, and gases in liquids in the was discovered. In 1859, Michael Faraday noted the different “invisible gases” (oxygen, hydrogen, nitrogen) are not affected by radiant heat, but water vapor. Faraday continued to find that without CO2 gas in the atmosphere, Earth would be “held fast in the iron grip of frost;” today called the greenhouse effect. (Westhorpe. 2010). In 1865, Tyndall found CO2 to be in expired breath.
The first way to measure CO2 was in 1905 by John Haldane using complex mixtures and comparisons of various items from the periodic table - mercury, potassium hydroxide, and sodium. Through this method Haldane found the remaining volume of CO2 of the material after all other elements were removed, thus forming a measurement tool for partial pressure gases. Haldane determined what hyperpnoea was and determined alveolar CO2 pressure in the body. Improved measurements of Haldane’s methods came out in the 1950’s. Needing smaller masses to sample and more accurate results. While these measurements proved vital to the medical profession, these methods were slow and did not provide “real-time” feedback. (Westhorpe. 2010).
As the medical profession expanded and human curiosity sored in the late 1900’s further discoveries leading to the invention of capnography through photo-acoustic spectroscopy, infrared technology, and end tidal. As time continued, discoveries of how gases in the body influence the respiratory and circulatory system and what measuring those gases means to a health care provider. In 1970, capnography became the standard in patient care to be used in anesthesia in Europe. That standard then came to the United States in 1980. (Krauss. 2016). Anesthesiologists began using capnography to balance a thin line between a conscious and unconscious patients, and provide an historic trend of dramatically decreased malpractice suits against doctors; and an even bigger trend of fewer deaths by hypoxia in the operating room. (Kodali. 2013). Infrared technology, capnography, has become the most cost efficient method of measuring and monitoring CO2. (Kodali. 2013). The use of ETCO2 monitoring has made leaps and bounds in the hospital settings. It has since been taken “to the streets,” per say, and used pre-hospital as a reliable form of monitoring a patient’s respiratory status. Medical professionals are now seeing more and more use of capnography to guide treatment and form a working diagnosis of a patient’s condition. Waveform capnography is being used to help monitor persons with asthma, congestive heart failure (CHF), diabetes, shock, acidosis, and in a cardiac arrest; via compression effectiveness and return of spontaneous circulation, ROSC. (Capnography. 2016). With the visualization of waveform, a provider can now essentially “predict” the impending deterioration of patient status. A waveform that which gradually gets shorter could indicate decreased cardiac output, bronchospasms, hypothermia, pulmonary embolism, and even cardiac arrest itself. In cardiac arrest, a sudden increase in wave height could indicate ROSC. Fast short or slow tall waves could indicate hyper- or hypoventilation. (Temple. 2012). While you can see various heights, lengths, and patterns with the capnography, a digital number is also displayed to guide treatment. Normal is 35 mmHg to 45mmHg. Low numbers could indicate the patient is in an alkalotic state and high numbers could indicate the patient is in an acidotic state. Either way, in extreme cases, these states throw the body out of homeostasis and can cause detrimental health issues.
There are two main forms of capnography: mainstream and side stream. Mainstream sensors are placed at the airway of an intubated patient and are known for their reliability and prompt feedback. Sidestream sensors are located away from the airway and require a continuous aspiration from the patient to get to the sensor. This is for the non-intubated patient. (Zoll. 2010). Sidestream essentially is a non-advanced method to monitor a patient. An example of this would be a specially designed nasal cannula used to monitor CO2 in patients whom are symptomatic. A high reading with a form of altered mental status or shortness of breath, could indicate the patient is in a true emergency of hypoventilation and the provider needs to act to secure the airway. If the reading is low, the patient is usually displaying signs of hyperventilation and need to be monitored for possible complications for hypocarbia. Due to the quick feedback and objective assessment provided by the waveform capnography, the provider can quickly determine if the patient has a deteriorating respiratory status act based off early warnings to start interventions. (Capnography. 2016).
The use of continuous waveform capnography with supraglottic, or King LT, airways have now been proven to be just as accurate and effective to monitor the patency and placement. While the King-LT is not considered a form of advanced airway, it is an invasive procedure to place and could be detrimental to the patient if not done properly. (Thibeault. 2015). The King-LT can be placed by an EMT or paramedic. The interpretation of the waveform and numbers is essential to monitoring patient ventilatory status and perfusion status. There is argument about possible other bodily gases influencing this reading. Limited research has been conducted due to the king being a fairly new form of airway management in health care. A study in 2007 by Francis Guyeete compared the success rate of using a King-LT as an alternative airway to the endotracheal tube by a large reginal air medical service. He found of the 26 cases using the altered airway means of a king, 24 were placed correctly in one attempt and two in two attempts. (Guyette. 2009). Capnography was used to monitor the patency of the airway. No additional measures, complications, or surgical interventions were noted.
In an article from an issue of Prehospital Emergency Care “Abstracts for the 2008 NAEMPS Scientific Assembly” include 100 prehospital research abstracts. One specifically entitled “The use of End-tidal Carbon Dioxide Values Obtained During Bag-Valve-Mask Ventilation to Predict Post-Intubation Values.” This article stated, “ETCO2 values obtained during BVM appear to accurately predict values following intubation. This is potentially useful to establish a baseline to improve the reliability of capnometry for ET confirmation and may allow for guidance of CPR and determination of futility…We believe ETCO2 sensors should be applied during BVM rather than waiting until after intubation.” (ETCO2. 2008). While it is unlikely waveform capnography on a BVM will show an accurate reading, it is good practice to use it. When a provider is using a BVM, the possibility of a more advanced airway is likely. By having the measuring devise on the BVM, it is ing should see EMTs also using this as a tool to treat what they can with what they have. This is no longer an age of waiting for a pulse oximeter to tell the provider that the patient is sick, but the age of getting ahead of the condition and stopping the progression from worsening.
This paper is going to outline what capnography is, the difference between waveform capnography and pulse oximetry, and why the ALS provider should consider using this tool as a basic diagnostic in patients with a respiratory concern by means of non-invasive monitoring.
Waveform capnography is the reading displayed via waveform and digital number used to interpret CO2 exhaled from the body. ETCO2 is the “partial pressure or maximal concentration of carbon dioxide (CO2) at the end of an exhaled breath, which is expressed as percentage of CO2 or mmHg.” (Press. 2015). This concentration of CO2 is what is displayed on a screen. The CO2 is a reflected number of cardiac output (CO) and pulmonary blood flow as CO2 is moved by the circulatory system from the heart to the lungs. As blood flow reaches the lungs, CO2 is expelled. At the same time, oxygen is absorbed; traveling back to the heart and then pumped throughout the body; measured by a pulse oximeter. The CO2 is then exhaled. With a ETCO2 being used, the paramedic can determine a course of treatment for the patient based off the digital reading and waveform produced by this exhaled CO2. Specifically, ETCO2 waveforms provide medical personal with a tool for fast and dependable analyses of pulmonary pathophysiology. (Press. 2015). The 2010 The American Heart Association (AHA) found capnography so vital, they placed it in the guidelines for “Advanced Cardiac Life Support and Emergency Cardiac Care,” as well as the pediatric version, stating “providers should observe persistent waveform capnography with ventilation to confirm and monitor correct placement of endotracheal tube placement in the field, the transport vehicle, on arrival at the hospital and after any patient transfer, to reduce the risk of unrecognized ET tube misplacement or displacement” (Thibeault. 2015). The AHA found from a study published in 2005 from Annals of Emergency Medicine, 23% of field intubations misplaced the tube when not using a form of capnography to verify placement. (Capnography. 2016). A tube placed in the esophagus and not in the proper location of the trachea, means air is being pumped into the stomach. This can lead to emesis, which can lead to aspiration, which ultimately can lead to death. If not caught fast enough, a patient can die from hypoxia, due to air not being moved to the lungs, thus no cellular level exchange of gas, thus no oxygen going to the essential organs of the body to maintain life. The body needs oxygen to function. Without sufficient amounts, brain damage can occur and death.
The book Anaesthesia and Intensive Care, “The history of capnography,” notes the encounter of carbon dioxide dating back to the Romans. The deadly gas (known as “evil air”) killed dogs who entered various caves with humans; who were able to tolerate the gases only while they remained upright. Unknown to the Romans the “evil air” was seeping in through the cracks in the floor of the caves. During the 17th century, Jan Baptist van Helmont, discovered gas being expelled during the burning of wood, calling it “spiritus sylvestre.” In 1755, Joseph Black, found mixing acid with limestone would produce the gas. Black called it “fixed air.” Throughout the course of history many documentations and experimentation led to defined properties outlining carbon dioxide. The physical measurement of CO2 would not come for many years after these findings, as gases were not fully understood. As gas laws are claimed, including Boyle, Gay Lussac and Kelvin, discoveries associated with CO2 on a cellular level continued to rise. In the 1850’s light absorption with different densities of air, and gases in liquids in the was discovered. In 1859, Michael Faraday noted the different “invisible gases” (oxygen, hydrogen, nitrogen) are not affected by radiant heat, but water vapor. Faraday continued to find that without CO2 gas in the atmosphere, Earth would be “held fast in the iron grip of frost;” today called the greenhouse effect. (Westhorpe. 2010). In 1865, Tyndall found CO2 to be in expired breath.
The first way to measure CO2 was in 1905 by John Haldane using complex mixtures and comparisons of various items from the periodic table - mercury, potassium hydroxide, and sodium. Through this method Haldane found the remaining volume of CO2 of the material after all other elements were removed, thus forming a measurement tool for partial pressure gases. Haldane determined what hyperpnoea was and determined alveolar CO2 pressure in the body. Improved measurements of Haldane’s methods came out in the 1950’s. Needing smaller masses to sample and more accurate results. While these measurements proved vital to the medical profession, these methods were slow and did not provide “real-time” feedback. (Westhorpe. 2010).
As the medical profession expanded and human curiosity sored in the late 1900’s further discoveries leading to the invention of capnography through photo-acoustic spectroscopy, infrared technology, and end tidal. As time continued, discoveries of how gases in the body influence the respiratory and circulatory system and what measuring those gases means to a health care provider. In 1970, capnography became the standard in patient care to be used in anesthesia in Europe. That standard then came to the United States in 1980. (Krauss. 2016). Anesthesiologists began using capnography to balance a thin line between a conscious and unconscious patients, and provide an historic trend of dramatically decreased malpractice suits against doctors; and an even bigger trend of fewer deaths by hypoxia in the operating room. (Kodali. 2013). Infrared technology, capnography, has become the most cost efficient method of measuring and monitoring CO2. (Kodali. 2013). The use of ETCO2 monitoring has made leaps and bounds in the hospital settings. It has since been taken “to the streets,” per say, and used pre-hospital as a reliable form of monitoring a patient’s respiratory status. Medical professionals are now seeing more and more use of capnography to guide treatment and form a working diagnosis of a patient’s condition. Waveform capnography is being used to help monitor persons with asthma, congestive heart failure (CHF), diabetes, shock, acidosis, and in a cardiac arrest; via compression effectiveness and return of spontaneous circulation, ROSC. (Capnography. 2016). With the visualization of waveform, a provider can now essentially “predict” the impending deterioration of patient status. A waveform that which gradually gets shorter could indicate decreased cardiac output, bronchospasms, hypothermia, pulmonary embolism, and even cardiac arrest itself. In cardiac arrest, a sudden increase in wave height could indicate ROSC. Fast short or slow tall waves could indicate hyper- or hypoventilation. (Temple. 2012). While you can see various heights, lengths, and patterns with the capnography, a digital number is also displayed to guide treatment. Normal is 35 mmHg to 45mmHg. Low numbers could indicate the patient is in an alkalotic state and high numbers could indicate the patient is in an acidotic state. Either way, in extreme cases, these states throw the body out of homeostasis and can cause detrimental health issues.
There are two main forms of capnography: mainstream and side stream. Mainstream sensors are placed at the airway of an intubated patient and are known for their reliability and prompt feedback. Sidestream sensors are located away from the airway and require a continuous aspiration from the patient to get to the sensor. This is for the non-intubated patient. (Zoll. 2010). Sidestream essentially is a non-advanced method to monitor a patient. An example of this would be a specially designed nasal cannula used to monitor CO2 in patients whom are symptomatic. A high reading with a form of altered mental status or shortness of breath, could indicate the patient is in a true emergency of hypoventilation and the provider needs to act to secure the airway. If the reading is low, the patient is usually displaying signs of hyperventilation and need to be monitored for possible complications for hypocarbia. Due to the quick feedback and objective assessment provided by the waveform capnography, the provider can quickly determine if the patient has a deteriorating respiratory status act based off early warnings to start interventions. (Capnography. 2016).
The use of continuous waveform capnography with supraglottic, or King LT, airways have now been proven to be just as accurate and effective to monitor the patency and placement. While the King-LT is not considered a form of advanced airway, it is an invasive procedure to place and could be detrimental to the patient if not done properly. (Thibeault. 2015). The King-LT can be placed by an EMT or paramedic. The interpretation of the waveform and numbers is essential to monitoring patient ventilatory status and perfusion status. There is argument about possible other bodily gases influencing this reading. Limited research has been conducted due to the king being a fairly new form of airway management in health care. A study in 2007 by Francis Guyeete compared the success rate of using a King-LT as an alternative airway to the endotracheal tube by a large reginal air medical service. He found of the 26 cases using the altered airway means of a king, 24 were placed correctly in one attempt and two in two attempts. (Guyette. 2009). Capnography was used to monitor the patency of the airway. No additional measures, complications, or surgical interventions were noted.
In an article from an issue of Prehospital Emergency Care “Abstracts for the 2008 NAEMPS Scientific Assembly” include 100 prehospital research abstracts. One specifically entitled “The use of End-tidal Carbon Dioxide Values Obtained During Bag-Valve-Mask Ventilation to Predict Post-Intubation Values.” This article stated, “ETCO2 values obtained during BVM appear to accurately predict values following intubation. This is potentially useful to establish a baseline to improve the reliability of capnometry for ET confirmation and may allow for guidance of CPR and determination of futility…We believe ETCO2 sensors should be applied during BVM rather than waiting until after intubation.” (ETCO2. 2008). While it is unlikely waveform capnography on a BVM will show an accurate reading, it is good practice to use it. When a provider is using a BVM, the possibility of a more advanced airway is likely. By having the measuring devise on the BVM, it is ing should see EMTs also using this as a tool to treat what they can with what they have. This is no longer an age of waiting for a pulse oximeter to tell the provider that the patient is sick, but the age of getting ahead of the condition and stopping the progression from worsening.