Capnography In The Pediatric Emergency Department: Clinical Applications

Table of Contents

 

1. Abstract
2. Case Presentation
3. Introduction
   1. The History Of Capnography
   2. Review Of The Technology
4. Applications Of Capnography In The Intubated Patient
   1. Endotracheal Tube Placement Confirmation
      1. Subjective And Qualitative Confirmation Measures
      2. Quantitative Confirmation Measures
   2. Maintenance Of Endotracheal Intubation
   3. Maintenance Of Normal Ventilation
5. Critical Appraisal Of The Literature
6. Use Of Capnography In Cardiopulmonary Resuscitation
   1. Endotracheal Tube Placement Confirmation
   2. Assessment Of Efficacy Of Cardiopulmonary Resuscitation
   3. Detection Of Return Of Spontaneous Circulation
7. Applications Of Capnography In The Nonintubated Patient
   1. Bradypneic Hypoventilation
   2. Hypopneic Hypoventilation
      1. Procedural Sedation
      2. Current Guidelines For Monitoring Patients During Sedation
8. Other Applications Of Capnography
   1. Applications In Altered Mental Status And Seizures
   2. Applications In Lower Airway Disease
      1. Asthma
   3. Measurement Of Airway Obstruction
      1. Bronchiolitis
   4. Applications In Patients With Metabolic Derangements
      1. Diabetic Ketoacidosis
      2. Gastroenteritis
   5. Current Utilization Patterns
   6. Cost-Effectiveness Of Capnography
9. Summary
10. Risk Management Pitfalls For Pediatric Capnography
11. Case Conclusions
12. Clinical Pathway For Capnography In The Emergency Department
13. Tables and Figures
    1. Table 1. Summary Of Ventilation Patterns In Nonintubated Patients
    2. Table 2. Risk Factors For Severe Disease And Apnea In Infants With Bronchiolitis
    3. Figure 1. Sidestream Carbon Dioxide Sampling Line For Intubated Patients
    4. Figure 2. Nasal-Oral Cannula Attached To Portable Capnography Monitor
    5. Figure 3. Normal Carbon Dioxide Waveform On Capnography
    6. Figure 4. Colorimetric Carbon Dioxide Detector
    7. Figure 5. Capnogram Trend During Cardiopulmonary Resuscitation
    8. Figure 6. Capnogram Trend Indicating Return Of Spontaneous Circulation
    9. Figure 7. Shape Of Capnograph In Obstructive Lower Airway Disease
    10. Figure 8. Capnography Waveform
14. References

Abstract

Capnography, often referred to by emergency clinicians as end-tidal carbon dioxide monitoring, is a noninvasive method of measuring cardiopulmonary and metabolic parameters that can be utilized in many clinical applications. Growing evidence in the literature in support of the use of capnography has led to increased clinical use of this modality in many pediatric subspecialties. Understanding capnography and the literature supporting its practice will advance its use by emergency clinicians in the pediatric emergency department, promoting improved patient care and safety. This issue reviews the technology and physiology involved in measuring exhaled carbon dioxide and the interpretation of waveforms, and it highlights uses for capnography in pediatric patients in the emergency department. Uses include confirmation of intubation, maintenance of ventilation in intubated and nonintubated children, monitoring of effectiveness of cardiopulmonary resuscitation, and as an adjunct for monitoring of sedated children and children with lower respiratory disease and metabolic derangements.

Key words: capnography, capnometry, colorimetric capnography, end-tidal carbon dioxide

Case Presentation

On a weekday afternoon in your pediatric ED, a worried mother brings in her 4-year-old daughter, who fell from a piece of playground equipment at her daycare center. She has an obvious deformity of her left forearm, and radiographs confirm displaced fractures of the distal radius and ulna. You inform the mother that her daughter’s injury will require a closed reduction by your institution’s orthopedic team and that you would like to sedate her for the procedure. While doing your presedation assessment, you note that the patient’s pulse oximetry reading is 93%, breath sounds are decreased over both lung fields,and there is an occasional wheeze. The nurse places a nasal cannula on the child and administers supplemental oxygen at a rate of 2 L/min. Her oximetry reading rises to 98%. The mother informs you that her daughter has had 2 or 3 episodes of wheezing in the past, all related to concurrent upper respiratory infections. How will you evaluate this patient’s current respiratory status? Will you maintain the child on supplemental oxygen during the sedation? How will you monitor her respiratory parameters during the sedation?

Shortly after that, a member of your nursing staff asks you to speak with the parent of an 18-month-old boy you evaluated 30 minutes ago. The patient had a 3-day history of fever, vomiting and diarrhea, and poor fluid intake, and he had not had a wet diaper in almost 24 hours. On your exam, you noted him to be tired appearing, tachycardic for age, with dry lips, and a capillary refill of approximately 3 seconds. His abdomen was soft and nontender. You ordered a serum electrolyte panel and requested that the nurse place an IV catheter for hydration. The nurse tells you that she has been unable to obtain blood or place the IV despite multiple attempts. The mother does not want her child to have any more needle punctures or attempts at IV placement, and she asks you if the blood test and IV are absolutely necessary. How will you respond to this mother? Is there a noninvasive objective measure that can help you to determine the severity of this child’s dehydration?

As you consider your options, EMTs rush in with an intubated teenager. CPR is in progress. They tell you that they were flagged down by a group of the boy’s friends at a nearby park. The boy collapsed during a game of basketball, and he was apneic and pulseless on the scene. The EMTs tell you that automated external defibrillator pads were placed immediately, and no shock was indicated. Since the park was very near the hospital, they chose to “scoop and run," and 1 of the EMTs intubated him in the ambulance en route. The intubating EMT tells you he did appreciate breath sounds in both axillae after the endotracheal tube was placed, although it was difficult to hear in the moving ambulance with the sirens blaring. He reports a “positive color change” on the colorimetric CO2 detector, but states that the color was more beige than bright yellow. He did see the endotracheal tube go through the vocal cords and some watervapor in the tube while he was bagging, so he is sure he intubated the trachea. A resident working with you takes over the manual ventilations of the patient and directs an intern to take over chest compressions from the EMT team. A nurse places the boy on a monitor and checks the femoral pulse during compressions. She reports that she can palpate a pulse with each compression and tells the intern he is compressing effectively. The resident suggests that the intern stop chest compressions for a moment to check whether there is a cardiac rhythm on the monitor. Is the resuscitation of this patient optimal? Are there more objective indicators that can be used to confirm endotracheal intubation and maximize the quality of the CPR your team is providing?

Introduction

The History Of Capnography

Capnography is the measurement and monitoring of the partial pressure of carbon dioxide (CO2) in exhaled breaths, and it is often referred to as end-tidal carbon dioxide (ETCO2) monitoring. The modernday ability to measure ETCO2 and the insight it provides into human metabolism and cardiopulmonary physiology has been over a century in the making.¹

Some of the earliest experiments in CO2 measurement were by John Tyndall, a professor of natural philosophy from the United Kingdom. In the mid-1860s, he experimented with carbonic acid and discovered that CO2 was superior to oxygen, nitrogen, and hydrogen in the absorption and transmission of radiant heat. In 1905, John Scott Haldane created an early spectrometer that was able to measure the volume and calculate the percentage of CO2 in a mixture of gases. In his studies of respiratory physiology (often using himself as a subject), he was one of the earliest investigators to suggest that human respiratory drive is exquisitely sensitive to the rising partial pressure of CO2 in alveolar air.² The first modern capnograph is attributed to Karl Friedrich Luft. The “Luft cell” (1937) made use of infrared technology to measure CO2 concentration, and it continues to be the technologic basis of modern-day CO2 measurement.²

Risk Management Pitfalls For Pediatric Capnography

1. “I confirmed placement of an ETT with a colorimetric CO2 detector, and my patient was on continuous pulse oximetry, so ongoing capnography monitoring was unnecessary.” While colorimetric capnography is useful to quickly confirm that an ETT is in the trachea, an ETT can become dislodged if the tube is not immediately and sufficiently secured, or if the patient moves, is repositioned, or is transported to another location. In infants and children, even slight movements of the head can cause displacement of an ETT. A displaced ETT that goes unrecognized can be catastrophic for the patient. Continuous infrared capnography can detect ETT dislodgement or obstruction in seconds, whereas pulse oximetry may take several minutes to register a decline in oxygenation. The American Heart Association guidelines for both adult and pediatric life support recommend the use of continuous capnography to monitor the position of an ETT.
2. “When providing CPR, I rely on my coworker, who is providing chest compressions, to let me know when he is getting tired and needs to switch. As long as the compressor is pushing hard and fast and is generating a palpable femoral pulse with each compression, the compressions are effective.” Numerous studies confirm that ETCO2 correlates with cardiac output during CPR, and capnography can provide an objective and quantitative measure of the volume of blood flow that is generated by compressions. A drop in the value of ETCO2 on the capnogram can be indicative of compressor fatigue and the need to switch to another provider. (See Figure 5, page 7.) The 2010 American Heart Association Guidelines for CPR now recommend the use of capnography to monitor and optimize the effectiveness of chest compressions.
3. ”The patient was in cardiac arrest, so the ETCO2 was so low that capnography wouldn't have been useful in confirming that the ETT was in the trachea.“ Current-day infrared ETCO2 detectors are extremely sensitive and can detect residual CO2 in the trachea and reveal a recognizable waveform to indicate the ETT is properly placed. (See Figure 6, page 7.) The 2010 American Heart Association guidelines for CPR recommend quantitative waveform capnography to confirm ETT placement in cardiac arrest.9
4. “The only way to know if a cardiac arrest patient is responding to resuscitation is to stop CPR every 2 minutes to check for a pulse.” The 2010 American Heart Association guidelines encourage the use of capnography to monitor and optimize CPR as well as to indicate ROSC. Pauses in CPR should be minimized in order to maintain perfusion pressure to essential organs. An increase in ETCO2 noted during resuscitation indicates an increase in pulmonary blood flow. ROSC is recognized by an abrupt increase in ETCO2 to normal or above-normal levels.
5. “The pulse oximeter said my sedated patient had an oxygen saturation of 100%, so I knew he was breathing effectively.“ While a pulse oximetry reading of 100% is reassuring to the emergency clinician because it indicates oxygen has been effectively delivered to body tissues, it does not reveal any information about how effectively the patient is ventilating. It is possible to have a pulse oximetry reading of 100% in a patient who is hypoventilating. Pediatric patients have smaller functional residual capacity and higher metabolic demands than adults. If uncorrected, hypoventilation in a child can decompensate quickly to apnea and possibly to cardiac arrest. Continuous capnography monitoring can provide prompt (within 1 breath) objective information about changes in a patient’s ventilatory status. While not yet standard of care, many professional organizations encourage the use of waveform capnography in the monitoring of patients receiving procedural sedation.
6. ”My sedated patient had an ETCO2 of 20 mm Hg. That meant he was hyperventilating and I didn't need to worry about respiratory depression.“ Although a high ETCO2 (> 50 mm Hg) is always indicative of hypoventilation, it seems intuitive to assume that a patient who is hyperventilating will breathe down his CO2 and have a low ETCO2 reading; however, this is not always true. As the tidal volume declines, a greater proportion of exhaled ventilation is made up from the dead space. These patients will have a low ETCO2 reading ( < 30 mm Hg), and the amplitude of the waveform on capnography will be markedly reduced. Since the patient with hypopneic hypoventilation will have a normal respiratory rate, this form of hypoventilation is often undetected by emergency clinicians who do not use capnography monitoring.
7. "I knew that after a seizure, a postictal patient may hypoventilate and become hypoxic, so I kept her on continuous pulse oximetry and a nonrebreather mask to provide supplemental oxygen until she was fully awake.“ Postictal patients often have decreased respiratory drive and may have disordered breathing. While it is important to monitor these patients for hypoxia and provide supplemental oxygen as necessary, pulse oximetry will not provide any clinical data about the adequacy of ventilation. Postictal patients receiving supplemental oxygen can have an oximetry reading of 100% and still have significant hypoventilation and acidosis, leading to further neurologic and respiratory compromise. Supplemental oxygen may also increase the time it takes for a pulse oximeter to register a change in respiratory status if the patient becomes apneic. Capnography is very useful as a continuous monitor of ventilation in these patients, and it can give an immediate indication of apnea or severe hypoventilation.
8. “Prehospital providers often inadvertently hyperventilate intubated pediatric patients, but in the case of this head-injured patient, it was probably okay because hyperventilation will help reduce intracranial pressure.” Current evidence suggests that hyperventilation of head-injured patients may actually lead to decreased cerebral perfusion and ischemia and cause worse neurologic outcomes. Current professional guidelines caution against hyperventilation except in cases of impending herniation. Capnography monitoring can help the clinician in maintaining normal ventilation during resuscitative efforts of head-injured patients. Studies have shown that prehospital providers who had access to ETCO2 monitoring were much more likely to maintain normoventilation in head-injured patients than those providers who did not have access to capnography.

Tables and Figures

References

Evidence-based medicine requires a critical appraisal of the literature based upon study methodology and number of subjects. Not all references are equally robust. The findings of a large, prospective, randomized, and blinded trial should carry more weight than a case report.

To help the reader judge the strength of each reference, pertinent information about the study, such as the type of study and the number of patients in the study will be included in bold type following the references, where available. The most informative references cited in this paper, as determined by the author, will be noted by an asterisk (*) next to the number of the reference.

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