EMS Airway Clinic

The debate over whether to intubate cardiac arrest patients remains strong. Photo Kevin Link

Recently, I came across a destitute colleague who had just responded to a code for a cardiac arrest. During the arrest, the patient was intubated successfully, without interruption of compressions. I was puzzled. Why was my colleague distressed? Surely, she had done her job well, securing the airway in a prompt and efficient manner.

As it turns out, another provider had questioned numerous elements of her care. First, the other provider debated whether to give a paralytic. The other provider vehemently argued that a paralytic was indicated to “best optimize the chance of success.” My colleague did not feel that a paralytic was indicated in cardiac arrest, and intubated without the use of any additional medications.

After the argument about the paralytic, the other provider then had the nerve to question whether the patient should have even been intubated at all! In point of fact, intubation in cardiac arrest is quite controversial, and my downtrodden colleague had every right to feel frustrated.

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Although endotracheal intubation has long been regarded as the “gold standard” for cardiac arrest, recent guidelines de-emphasize the procedure, especially if intubation is to be achieved at the expense of other evidence-based interventions (i.e., CPR and electrical therapy) associated with improved survival and better neurological outcomes.(1,2)

Now I will admit that when I first read this recommendation, it was difficult to digest. As a paramedic, anesthesiologist, and intensivist, I’ve never thought twice about securing an airway with an endotracheal tube during a cardiac arrest. Historically, to do otherwise would be considered malpractice! However, when one examines the recent literature, it is understandable why intubation for cardiac arrest remains a provocative topic. For starters, the reader is referred to a comprehensive and well-written review on this topic by Dr. J.V. Nable et al.(1)

Intubation has not been shown to positively impact outcomes for cardiac arrest patients, and there are several explanations for this somewhat counterintuitive finding.

First, intubation during cardiac arrest is not always straightforward, and in at least one study, 30% of patients required more than one attempt.(3)

Second, the learning curve to attain competence is steep—one study suggests up to 60 intubations are required to become proficient—and in some systems, EMS providers do not have opportunities maintain this skill.(4) As Nable et al write, “maintaining proficiency in endotracheal intubation is a significant barrier for many prehospital providers.”(1) In Wang et al, intubation success by medics was only 78%.(3)

Third, intubation is followed by positive pressure ventilation (PPV), and PPV has been shown to decrease preload, lower cardiac output, and negatively impact the effectiveness of chest compressions.(1)

Fourth, intubation may require interruption of chest compressions, and this has clearly been linked with worse outcomes.(5) For the abovementioned reasons, in some countries, such as the U.K., a case has been made for abandoning intubation altogether in cardiac arrest.(6)

Coming back to my colleague’s dilemma regarding paralysis for intubation in cardiac arrest, this is also a contentious topic. On one hand, paralysis may enhance intubating conditions and facilitate prompt control of the airway, thereby avoiding airway trauma with multiple laryngoscopic attempts, and preventing aspiration. Moreover, the most feared complication of paralysis—the “can’t intubate, can’t ventilate” scenario—is relatively rare. In one study of more than 6,000 trauma patients at our institution (University of Maryland R Adams Cowley Shock Trauma Center in Baltimore), only four patients required a surgical airway.(7)

On the other hand, the hazards of positive pressure ventilation, hyperkalemia associated with succinylcholine, and the rare instance of failed intubation in a paralyzed patient with a difficult airway, all pose an unacceptable risk/benefit in cardiac arrest. The decision to use paralytics is as difficult as deciding to intubate in cardiac arrest, and the use of these agents can only be recommended for the most highly trained providers.

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What about supraglottic airways? This class of airways includes the laryngeal mask airway (LMA), Combitube, laryngeal tube and other various proprietary devices. Although these devices do not represent a “definitive airway,” several studies have shown equivalent outcomes when these devices were compared to endotracheal intubation in cardiac arrest.(1,8) Supraglottic airways have several advantages over intubation. Learning curves are easier, the devices can be placed faster, and there may be fewer complications during device insertion.(9)

To date, no one device has been shown to be conclusively superior to another. Patients eligible for placement of a supraglottic airway require adequate mouth opening, no underlying severe lung disease (i.e., decreased lung compliance), and low risk for aspiration.(1)

At the end of the day, airway management for cardiac arrest may be achieved according to the proficiency and resources available to the provider. EMS providers should not be discouraged by the literature! Airway management is still important. In one study by Wong et al, the best short-term survival was seen in patients who had an advanced airway placed within five minutes of the arrest.(10)

Other studies have failed to show any difference between intubation and use of bag-valve mask ventilation (BVM).(11) However the airway is managed, current recommendations still emphasize the importance of providing ventilatory support during cardiac arrest.(2) In jurisdictions where intubation is used for cardiac arrest, providers should perform the procedure with “sufficient frequency to maintain competence within a highly managed system that actively monitors success rates, complications and patient outcomes.”(9)

If intubation is to be considered in cardiac arrest, it should only be attempted if:

• The provider is proficient;
• There are no interruptions in chest compressions; and
• The attempt takes no more than 10 seconds.(2)

Survivors of cardiac arrest who require intensive care management will usually require definitive airway management with endotracheal intubation at some point, but early in the arrest, providers should focus on providing high-quality CPR.(12)

References
1. Nable JV, Lawner BJ, Stephens CT. Airway management in cardiac arrest. Emerg Med Clin N Am. 2012;30:77–90.

2. Neumar RW, Otto CW, Link MS. Part 8: Adult advanced cardiac life support: 2010 American Heart Association guidelines for cardiopulmonary resuscitation. Circulation. 2010;1222(183):S727–S767.

3. Wang HE, Yealy DM. How many attempts are required to accomplish out-of-hospital endotracheal intubation? Acad Emerg Med. 2006;13:373–377.

4. West MR, Jonas MM, Adams AP, et al. A new tracheal tube for difficult intubation. Br J Anaesth. 1996;76:673–679.

5. Kellum MJ, Kennedy KW, Ewy GA. Cardiocerebral resuscitation improves survival of patients with out-of-hospital cardiac arrest. Am J Med. 2006;119:335–340.

6. Deakin CD, Clarke T, Nolan J. A critical reassessment of ambulance service airway management in prehospital care: Joint Royal Colleges Ambulance Liaison Committee Airway Working Group. Emerg Med J. 2008;27:226–233.

7. Stephens CT, Kahntroff S, Dutton RP. The success of emergency endotracheal intubation in trauma patients: A 10-year experience at a major trauma center. Anesth Analg. 2009;109:866–872.

8. Kajino K, Iwami T, Ktamura T, et al. Comparison of supraglottic airway verus endotracheal intubation for the pre-hospital treatment of out-of-hospital cardiac arrest. Critical Care. 2011;15:R236.

9. Thomas MJC. Prehospital intubation in cardiac arrest: The debate continues. Resuscitation. 2011;82:367-368.

10. Wong ML, Carey S, Mader TJ, et al. Time to invasive airway placement and resuscitation outcomes after inhospital cardiopulmonary arrest. Resuscitation. 2010;81:182–186.

11. Shin SS, Ahn KO, Song KJ, et al. Out-of-hospital airway managemetn and cardiac arrest outcomes: A propensity score matched analysis. Resuscitation. 2011. Accessed 18 Feb 2012.

12. Morley PT. The key to advanced airways during cardiac arrest: Well trained and early. Critical Care. 2012;16:104.

Samuel M. Galvagno Jr., DO, PhD

Dr. Galvagno has been involved with prehospital care for more than 19 years. He started his EMS career as a National Ski Patroller in upstate New York, and became an EMT in 1992 in Maryland. Before and while attending medical school at the New York College of Osteopathic Medicine, he was a paramedic in Maryland and New York. He completed his internship at Saint Vincent’s Midtown Hospital in Hell’s Kitchen, New York before working as an emergency physician and flight surgeon in the U.S. Air Force. On leaving active duty, Dr. Galvagno received residency training at Harvard Medical School, Brigham and Woman’s Hospital, followed by a fellowship in Critical Care Medicine at the Johns Hopkins School of Medicine. He also completed a research fellowship and extensive training in epidemiology and biostatistics at the Johns Hopkins Bloomberg School of Public Health; he is due to receive his PhD in 2012 with a thesis focused on helicopter emergency medical services for adults with major trauma. Dr. Galvagno is the author of numerous publications and book chapters, including his own textbook, Emergency Pathophysiology. He is currently an assistant professor in the Divisions of Trauma Anesthesiology and Adult Critical Care Medicine at the R Adams Cowley Shock Trauma Center, Baltimore. He remains active in the U.S. Air Force, and is the director of critical care Air Transport Team (CCATT) operations and assistant chief of professional services at Joint Base Andrews, Maryland. He is board-certified in anesthesiology, adult critical care medicine and public health.

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Combine capnography with pulse oximetry when monitoring ventilation and oxygenation in the prehospital environment. Photos Courtesy Jim Brown, Maryland Institute of Emergency Medical Services Systems

I recently observed a paramedic who made one of the most difficult prehospital clinical decisions I have seen during my 16 years of involvement in prehospital care. We were notified that a motor vehicle crash patient was inbound by helicopter, Category A (the highest in Maryland). Details about the crash were scant, and while the patient was swiftly rolled into our trauma resuscitation unit, I nearly stepped on a slippery, blood-laden tubular object that had fallen off the backboard—the endotracheal tube.

The flight paramedic proceeded to tell me that the patient had been intubated in the field and although there had been an appropriate colorimetric change on the CO2 detection device, lung sounds were difficult to appreciate en route and capnographic waveforms were absent. Yet, the patient’s pulse oximeter continued to read 99% the entire time. Nevertheless, the paramedic pulled the tube shortly before arrival, and proceeded to mask ventilate the patient with an oral airway. One might ask, “What on Earth was this paramedic thinking?”

As it turned out, the paramedic made a difficult but supremely commendable and 100% appropriate decision to extubate the patient. The medic later admitted that he struggled with the decision to remove what was thought to be a “perfectly good endotracheal tube.” But in the end, he knew the difference between ventilation and oxygenation, and based on his assessment, he knew that the former was not being accomplished, and that failure of the later would quickly ensue. These two separate—although highly related—processes are often confused and frequently misunderstood, and comprehending the difference is critical in the prehospital arena. Advanced technologies have an important role in monitoring ventilation and oxygenation, and an understanding of the limitations of these devices is a prerequisite for effective use.

Ventilation vs. Oxygenation
Ventilation and oxygenation are separate physiological processes. Ventilation is the act or process of inhaling and exhaling. To evaluate the adequacy of ventilation, a provider must exercise eternal vigilance. Chest rise, compliance (as assessed by the feel of the bag-valve mask), and respiratory rate are qualitative clinical signs that should be used to evaluate the adequacy of ventilation. Capnography, long the standard of care in the operating room and intensive care unit, can also be used to assess ventilation. Also, continuous quantitative waveform capnography has become the standard of care for monitoring endotracheal tube placement.(1) Capnography can be used to assess end-tidal carbon dioxide ( EtCO2) concentration or tension. Normal values of EtCO2 are 35-37 mmHg, and in normal lungs, the EtCO2 approximates the arterial CO2 concentration in the blood with a value that is usually lower by 2 to 5 mmHg.(2) Use of capnography is not limited to intubated patients; nasal cannulas and face masks can be modified to detect EtCO2.

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EtCO2 can be measured by colorimetry and capnography. Colorimetric devices provide continuous, semi-quantitative EtCO2 monitoring. A typical device has the following three color ranges:

Purple—EtCO2 is less than 0.5%
Tan—EtCO2 is 0.5–2%
Yellow—EtCO2 is greater than 2%

Normal EtCO2 is greater than 4%; hence, the device should turn yellow when the endotracheal tube is inserted in patients with intact circulation.(2) False positives may occur when the device is contaminated with acidic substances, such as gastric acid, lidocaine or epinephrine. The device will not provide an accurate reading it is expired or if the tube is clogged with secretions. Causes of increased or decreased EtCO2 are listed in Table 1.(2) One of the most common causes of increased EtCO2 is hypoventilation, since CO2 cannot be removed from the body when air exchange is impaired.

Capnography provides both a waveform and digital reading (mmHg of CO2 in exhaled gas). Capnography is no longer merely a standard for the operating rooms; it is a standard for ensuring ventilation after intubation anywhere, and it is now a fundamental objective means for assessing the adequacy of CPR.(1) For example, if the EtCO2 is less than 10 mmHg, the American Heart Association recommends optimizing chest compressions to improve the quality of CPR.(1,3–4) Capnography has prognostic value for trauma and cardiac arrest patients, and it correlates well with such other physiologic parameters as coronary perfusion pressure and cardiac output.(5) For a more in-depth discussion of the physics and use of capnography in the prehospital setting, visit www.capnography.com.

The pulse oximeter is a good way to ensure adequate oxygenation of your patients.

Oxygenation refers to the process of adding oxygen to the body system. There is no way to reliably measure arterial oxygenation via clinical signs alone. Cyanosis, pallor and other physical findings are not reliable. The pulse oximeter, which relies on a spectral analysis of oxygenated and reduced hemoglobin as governed by the Beer-Lambert law, represents the principle means of assuring adequate oxygenation in a patient.(2) Saturation of peripheral oxygen (SpO2) levels measured with a pulse oximeter correlate highly with arterial oxygenation concentrations.(6) An easy way to remember the correlation between SpO2 and approximate partial pressure of oxygen in arterial blood (PaO2) is presented in Table 2.

Despite years of use in a wide variety of settings, even experienced physicians and nurses have significant knowledge deficits regarding the limitations and interpretation of pulse oximetry.(7–9) Pulse oximetry has several limitations. Hypoxia follows hypoventilation, and it may take 30 seconds or more for the pulse oximeter to reflect conditions of life-threatening hypoxia. Relying on the pulse oximeter alone can decrease the margin of safety because corrective actions taken after the pulse oximeter falls may be too late. Hypovolemia, vasoconstriction, peripheral vascular disease or nail polish may cause false readings. It should be noted that pulse oximetry, while a significant technological advance over the past 20 years, has not been reliably shown in all studies to improve outcomes.(10) However, in studies based on closed claims data (i.e., lawsuits), the use of pulse oximetry, at least in the operating room, has been suggested to reduce the serious mishap rate by at least 35%.(11)

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Conclusion
Ideally, when monitoring ventilation and oxygenation in the prehospital environment, capnography should be combined with pulse oximetry. With capnography, providers are able detect respiratory insufficiency early and are able to institute early interventions, thereby preventing arterial oxygen desaturation. However, as with any monitoring technology, the best “monitor” is the provider. Pulse oximeters and capnometers do not treat patients. Integrating the information from your monitors and clinical assessment to make sound clinical decisions is the key to successful airway management. As evidenced by the astute assessment and action of a paramedic, knowing the difference between ventilation and oxygenation is a critical concept that must be understood.

References
1. Neumar RW, Otto CW, Link MS, et al. Part 8: Adult advanced cardiovascular life support, 2010 American Heart Association Guidelines for cardiopulmonary resuscitation and emergency cardiovascular care. Circulation. 2010;122[Suppl 3]:S729–S767.
2. Galvagno SM, Kodali BS. Critical monitoring issues outside the operating room. Anesthesiology Clin. 2009;27(1):141–156.
3. Lewis LM, Stothert J, Standeven J, et al. Correlation of end-tidal carbon dioxide to cerebral perfusion during CPR. Ann Emerg Med. 1992;21(9):1131–1134.
4. Callaham M, Barton C. Prediction of outcome of CPR from end-tidal carbon dioxide concentration. Crit Care Med. 1990;18(4):358–362.
5. Sanders AB, Atlas M, Wy GA, et al. Expired PCO2 as an index of coronary perfusion pressure. Am J Emerg Med. 1985;3(2):147–149.
6. Galvagno SM. Emergency Pathophysiology. Jackson, Wyo.: Teton NewMedia, 2004.
7. Sinex JE. Pulse oximetry: Principles and limitations. Am J Emerg Med. 1999;17(1):59–67.
8. Elliot M, Tate R, Page K. Do clinicians know how to use pulse oximetry? A literature review and clinical implications. Aust Crit Care. 2006;19(4):139–44.
9. Stoneham M, Saville G, Wilson I. Knowledge about pulse oximetry among medical and nursing staff. Lancet. 1994;344(8933):1339–1342.
10. Pedersen T, Dyrlund Pedersen B, Møller AM. Pulse oximetry for perioperative monitoring. Cochrane Database Syst Rev. 2003;3: CD002013.
11. Tinker J, Dull D, Caplan R, et al. Role of monitoring devices in prevention of anesthetic mishaps: a closed claims analysis. Anesthesiology. 1989;71(4): 541–546.

Samuel M. Galvagno Jr., DO, PhD

Dr. Galvagno has been involved with prehospital care for more than 19 years. He started his EMS career as a National Ski Patroller in upstate New York, and became an EMT in 1992 in Maryland. Before and while attending medical school at the New York College of Osteopathic Medicine, he was a paramedic in Maryland and New York. He completed his internship at Saint Vincent’s Midtown Hospital in Hell’s Kitchen, New York before working as an emergency physician and flight surgeon in the U.S. Air Force. On leaving active duty, Dr. Galvagno received residency training at Harvard Medical School, Brigham and Woman’s Hospital, followed by a fellowship in Critical Care Medicine at the Johns Hopkins School of Medicine. He also completed a research fellowship and extensive training in epidemiology and biostatistics at the Johns Hopkins Bloomberg School of Public Health; he is due to receive his PhD in 2012 with a thesis focused on helicopter emergency medical services for adults with major trauma. Dr. Galvagno is the author of numerous publications and book chapters, including his own textbook, Emergency Pathophysiology. He is currently an assistant professor in the Divisions of Trauma Anesthesiology and Adult Critical Care Medicine at the R Adams Cowley Shock Trauma Center, Baltimore. He remains active in the U.S. Air Force, and is the director of critical care Air Transport Team (CCATT) operations and assistant chief of professional services at Joint Base Andrews, Maryland. He is board-certified in anesthesiology, adult critical care medicine and public health.

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