CORRESPONDENCE
End-tidal Carbon Dioxide Monitoring in the Emergency Department To the Editor We have read with interest the article by Burton et al. discussing the end-tidal carbon monoxide (ETCO2) abnormalities that occur before oxygen desaturation or observed hypoventilation.1 For several years, we have been using ETCO2 monitoring in our emergency department to confirm the position of endotracheal tubes and the effectiveness of cardiopulmonary resuscitation during cardiac arrests. More recently, we have systematically used capnography in noninvasive monitoring of nonintubated patients who are likely to have respiratory decompensation (congestive heart failure, chronic obstructive pulmonary disease, drug poisoning, acute asthma, trauma, and so on). In 100 nonintubated adult patients without any known preexisting pulmonary or bronchial pathology, we have found a high concordance between ETCO2 and partial pressure of carbon dioxide (PaCO2). Using a Bland–Altman matrix2 (in a given patient, the difference between PaCO2 and ETCO2 is plotted against the mean of the same values), only one patient was found to be outside the 5–mm Hg limits of agreement. All patients had a plateau phase in the capnogram curve. These findings are in keeping with those found by other investigators.3,4 However, in 50 patients with preexisting pulmonary or bronchial pathology (median age, 46 years; interquartile range, 20–52 years), 21 patients were outside the 5-mm Hg limits of agreement (positive difference = 8.2 2.5 mm Hg, n = 15; negative difference = 27.5 1.7 mm Hg, n = 6). In our clinical practice, this poor concordance can be explained because of the impossibility of getting a plateau phase in the expiratory capnogram (dCO2/dt) in 11 patients and/or tachypnea in 14 patients (respiratory rate >25 breaths/min). In those patients, defects in the ventilation/perfusion ratio should not be excluded, notably in patients with chronic obstructive pulmonary disease (n = 14). The capnogram shape is modified by bronchial obstruction, and it has been shown that there is a correlation between dCO2/dt and the peak expiratory flow rate.5 In theory, the approximation of PaCO2 by ETCO2 pressure is so strong that a plateau phase can be found in the
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ISSN 1069-6563 PII ISSN 1069-6563583
capnogram, hence the point in visualizing this curve, allowing both validation of the measurement of ETCO2 pressure and assessment of the effectiveness of bronchodilatating treatments. Our findings are not inconsistent with those of Burton et al.,1 because our measurement methods involving anxious patients (or sedated patients), difficulty in getting calm breathing, and history of chronic obstructive pulmonary disease may have caused problems in getting a stable curve (in frequency and amplitude). doi: 10.1197/j.aem.2006.06.037
Gerald Kierzek, MD Thomas Jactat, MD Florence Dumas, MD Jean-Louis Pourriat, MD (
[email protected]) Department of Emergency Medicine Hotel-Dieu Hospital Assistance Publique-Hoˆpitaux de Paris Universite´ Rene´ Descartes Paris, France References 1. Burton JH, Harrah JD, Germann CA, Dillon DC. Does end-tidal dioxide monitoring detect respiratory events prior to current sedation monitoring practices. Acad Emerg Med. 2006; 13:500–4. 2. Bland JM, Altman DG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet. 1986; 1:307–10. 3. Plewa MC, Sikora S, Engoren M, Tome D, Thomas J, Deuster A. Evaluation of capnography in nonintubated emergency department patients with respiratory distress. Acad Emerg Med. 1995; 2:901–8. 4. Barton CW, Wang ESJ. Correlation of end-tidal CO2 measurements to arterial PaCO2 in nonintubated patients. Ann Emerg Med. 1994; 23:560–3. 5. Yaron M, Padyk P, Hutsinpiller M, Cairns CB. Utility of the expiratory capnogram in the assessment of bronchospasm. Ann Emerg Med. 1996; 28:403–7.
ª 2006 by the Society for Academic Emergency Medicine
