When is Capnography Useful in the ED? Part II
- Sep 11th, 2017
- Brit Long
Authors: Brit Long, MD (@long_brit, EM Attending Physician, San Antonio, TX) and Michael Vivirito, RN, CEN (Joint Base Elmendorf Richardson Medical Center, Emergency Medicine) // Edited by: Alex Koyfman, MD (@EMHighAK)
A 33-year-old female with a history of type 1 diabetes presents with polyuria, nausea/vomiting, and generalized weakness. Her blood glucose is 420. She is tachycardic and tachypneic, but the rest of her VS are normal. You place her on waveform capnography, which demonstrates EtCO2 of 16 mm Hg.
You order a liter of LR and ask the nurse to obtain a VBG, ECG, CBC, urinalysis, HCG, electrolyte panel, and ketones to start. You diagnose DKA, and the nurse looks at you in surprise and asks about the capnography.
We know capnography may be utilized for cardiac arrest, verification of endotracheal tube placement, and procedural sedation, but what other uses are possible? For Part I, see http://www.emdocs.net/capnography-useful-ed-part/
EtCO2 has been studied in critically ill patients and in trauma.1-7 EtCO2 correlates with blood pressure, lactate, pH, bicarbonate, and base excess. Studies have demonstrated that mortality increases as EtCO2 levels decrease.8-10 This post will provide some background on capnography use in trauma, metabolic acidosis, sepsis, PE, obstructive lung disease, and fluid responsiveness. You may be surprised at what the literature reveals…
In trauma, EtCO2 levels less than 25 mm Hg are associated with decreased blood pressure and cardiac output, and more importantly, increased mortality.11,12 For patients with head trauma, high serum carbon dioxide results in cerebral vasodilation, while lower values result in vasoconstriction.12 Capnography can be used to prognosticate outcomes and risk of mortality in severe trauma. In a study evaluating mortality in blunt trauma patients undergoing intubation, survivors on average demonstrated EtCO2 4 mm Hg higher than nonsurvivors (30.8 mm Hg in survivors and 26.3 mm Hg in nonsurvivors).13 In penetrating trauma, EtCO2 demonstrates a strong inverse relationship with lactate, with an odds ratio of 20.4 for requiring emergent operation.14 If levels are less than 30 mm Hg, increased risk of severe injury is likely, and decreased levels also predict need for blood transfusion.15,16 Capnography should not be used in isolation as a marker for injury, but only with other markers for severe trauma.
Yes, that’s right…Capnography can be used in the diagnosis of metabolic acidosis, predominantly associated with diabetic ketoacidosis (DKA) and gastroenteritis.17-22 As acidosis worsens, bicarbonate decreases and results in increased minute ventilation for respiratory compensation.17-22 This decreases EtCO2. The lower the EtCO2 the more severe the acidosis, and EtCO2 correlates with venous pH and bicarbonate.17,18,22 There are a variety of cutoff levels for EtCO2. Solmeinpur et al. found a sensitivity of 90% and specificity of 90% for DKA with a capnography value of 24.5 mmHg for adults.18 Dierde et al. found 29 mm Hg in pediatric patients with DKA demonstrates a sensitivity of 83% with specificity of 100% for diagnosis.19 A level of 36 mm Hg demonstrates a sensitivity close to 100%, while less than 20 mm Hg may possess a specificity of 100% .23 For acidosis in general, levels less than 25 mm Hg and greater than 36 mm Hg display a specificity of 84% for metabolic acidosis and sensitivity of 98% for excluding metabolic acidosis.17 As you can see, further study is needed in determining optimal values, but low EtCO2 supports a diagnosis of DKA or metabolic acidosis.
Sepsis is a common diagnosis, and emergency physicians use a variety of assessments to assist with diagnosis and resuscitation, such as lactate.24-26 Similar to metabolic acidosis, capnography and EtCO2 decrease as lactate increases, and literature suggests capnography levels can be used as a marker for resuscitation in sepsis.27-31 One study finds EtCO2 levels less than 25 mm Hg to occur in 78% of patients, and this level was associated with higher mortality.27 Other literature finds a level less than 35 mm Hg to correlate with lactate > 4 mmol/L and SOFA score > 2.28 Capnography is associated with serum bicarbonate, lactate, and anion gap, and EtCO2 levels are significantly lower in those patients who suffer mortality. A level less than 31 mmol/L demonstrated a 93% sensitivity for mortality in sepsis.30,31 Hunter et al. evaluated EtCO2 as a prehospital and triage marker, finding levels less than 25 mm Hg to be a reliable marker for sepsis, with area under the curve (AUC) 99% for sepsis, 80% for severe sepsis, and 70% for mortality.27 However, other studies suggest capnography may not correlate with lactate and outcomes.29 More research is needed, and a normal capnography reading should not be used to rule out sepsis.29 Low EtCO2 levels can be used to assess resuscitation and prognosticate in conjunction with other measures.
Pulmonary Embolism (PE)
PE can be a challenging diagnosis, often relying on clinical gestalt and risk stratification.32 Capnography can demonstrate a specific type of waveform in patients with PE. While ventilation remains approximately the same, perfusion is decreased in the segment supplied by the affected blood vessel.33-38 Alveolar dead space increases, and expired CO2 decreases. This increases blood PaCO2 and the EtCO2 gradient.33-38 The waveform may display flattened alveolar plateau and decreased EtCO2.
A meta-analysis finds sensitivity 80%, specificity 49%, and area under the summary receiver operating characteristic curve (AUROC) 84% for diagnosis of PE using capnography.37 The authors of this study state capnography may be used to rule out PE if used in patients stratified as low risk for PE.37-39 When combined with Wells score < 4, EtCO2 > 36 mm Hg possesses a negative predictive value of 98%.39,40 Another study sought to combine clinical gestalt, D dimer, and capnography, with a level of 32 mm Hg and low risk by stratification possessing a sensitivity of 100% for ruling out PE.41 Other areas of research include alveolar dead space measurement and alveolar dead space fraction via capnography, but these are not ready for primetime.38,39,42-44 Capnography for diagnosis of PE requires more study, especially the potential to combine this with clinical gestalt and/or D dimer.
Asthma, COPD, and Heart Failure
Pulmonary conditions such as asthma, COPD, and heart failure can also be challenging in the ED. Along with clinical assessment, EtCO2 can provide important information with regards to disease severity and assessing treatment response.45-49 Bronchospasm and airway obstruction demonstrate a shark-fin appearance (with steep phase III).49,50 Early in disease, EtCO2 will slightly decrease as the patient begins to compensate. However, if the exacerbation becomes severe and the patient worsens, EtCO2 will increase.2-6,51-54 In prehospital patients with asthma or COPD, EtCO2 high levels (> 50 mm Hg) and low levels (< than 28 mm Hg) are associated with greater rates of intubation, ICU admission, and mortality.51-55 Similar to the prior conditions, EtCO2 should only be used as an adjunctive measure to follow resuscitation and treatment. It may help diagnose or suggest a specific condition when used with history, exam, and other assessments.
EtCO2 can assess ventilation in patients who have seized and are post-ictal. Similar to procedural sedation, capnography can detect hypoventilation faster than pulse oximetry (which missed 5 patients with pulse oximetry > 97% and EtCO2 greater than 70 torr).56
Investigators have sought a reliable tool to assess fluid responsiveness, and recently passive leg raise while monitoring cardiac output has demonstrated promise.57-59 EtCO2 has been evaluated in mechanically ventilated patients, and patients with fluid responsiveness demonstrate an increase by at least 5% in EtCO2.57-60 Increase by 2 mm Hg demonstrates high specificity (93-96%), but sensitivity is 60%.60 No increase or increase by less than 2 mm Hg demonstrates a NPV of 86%.61,62 A recent study finds AUC 83% for predicting fluid responsiveness using capnography, and capnography outperformed pulse pressure variation, systolic blood pressure, heart rate, and mean blood pressure in patients undergoing mechanical ventilation.63
We have discussed a significant number of conditions, and capnography provides important information on patient status. However, it should only be used as an adjunct to the rest of your clinical assessment. The table below shows what conditions can change EtCO2. Remember, there are several components of the waveform that should be considered (http://www.emdocs.net/capnography-useful-ed-part/).1-7
Capnography possesses several important limits. This assessment works best for patients with a specific ventilation, perfusion, or metabolism issue. Patients with mixed pathophysiology (yes, our patients in the ED) create challenges for interpretation.1-7,64,65 Low tidal volumes, poor perfusion, the specific type and location of the device (mainstream versus sidestream devices), and false readings (stomach content, carbonated beverages) can hamper the use of this test.1-7,64-67 As discussed, capnography should only supplement other markers and clinical assessment. It is not ready for use in isolation.
– Capnography possesses many uses in the ED, but many of these are under study.
– EtCO2 is reliable in monitoring ETT placement, ETT confirmation, monitoring compression adequacy in CPR, evaluating for ROSC, and detecting hypoventilation in procedural sedation (see Part I).
– EtCO2 is associated with lactate levels: as lactate elevates, EtCO2 typically decreases.
– In states with acidosis and poor perfusion, such as DKA, hemorrhage, trauma, and sepsis, capnography can be used as an adjunct to clinical assessment.
– EtCO2 is promising for use in PE, specifically as a tool for further risk stratification, but it is not ready for primetime.
– Capnography can be used to assess treatment response in conditions with airway obstruction, as well as for hypoventilation in the post-ictal state.
– Elevation > 2 mm Hg with IV fluid load may suggest fluid responsiveness.
– Further study is needed for this promising clinical marker.
- Kodali BS. Capnography outside the operating rooms. 2013 Jan;118(1):192-201.
- Nassar BS, Schmidt GA. Capnography During Critical Illness. 2016 Feb;149(2):576-85.
- Thompson JE, Jaffe MB. Capnographic waveforms in the mechanically ventilated patient. Respir Care. 2005 Jan;50(1):100-8; discussion 108-9.
- Blanch L, Romero PV, Lucangelo U. Volumetric capnography in the mechanically ventilated patient. Minerva Anestesiol. 2006 Jun;72(6):577-85.
- Zwerneman K. End-tidal carbon dioxide monitoring: a VITAL sign worth watching. Crit Care Nurs Clin North Am.2006 Jun;18(2):217-25, xi.
- Manifold CA, Davids N, Villers LC, et al. Capnography for the nonintubated patient in the emergency setting. Journ Emerg Med 2013;45(4):626-32.
- Ward KR,Yealy DM. End-tidal carbon dioxide monitoring in emergency medicine, Part 1: Basic principles. Acad Emerg Med. 1998 Jun;5(6):628-36.
- Kheng CP, Rahman NH. The use of end-tidal carbon dioxide monitoring in patients with hypotension in the emergency department. Intern Emerg Med. 2012;5:31.
- Pishbin E, Ahmadi GD, Sharifi MD, et al. The correlation between end-tidal carbon dioxide and arterial blood gas parameters in patients evaluated for metabolic acid-base disorders. Electronic Physician. 2015;7(3):1095-1101.
- McGillicuddy DC,Tang A, Cataldo L, et al. Evaluation of end-tidal carbon dioxide role in predicting elevated SOFA scores and lactic acidosis. Intern Emerg Med. 2009 Feb;4(1):41-4.
- Dubin A,Murias G, Estenssoro E, et al. End-tidal CO2 pressure determinants during hemorrhagic shock. Intensive Care Med. 2000 Nov;26(11):1619-23.
- Dunham CM, Chirichella TJ, Gruber BS, et al. In emergently ventilated trauma patients, low end-tidal CO2 and low cardiac output are associated and correlate with hemodynamic instability, hemorrhage, abnormal pupils, and death. BMC Anesthesiol.2013 Sep 11;13(1):20.
- Deakin CD, Sado DM, Coats TJ, Davies G. Prehospital end-tidal carbon dioxide concentration and outcome in major trauma. J Trauma 2004; 57:65.
- Caputo ND,Fraser RM, Paliga A, et al. Nasal cannula end-tidal CO2 correlates with serum lactate levels and odds of operative intervention in penetrating trauma patients: a prospective cohort study. J Trauma Acute Care Surg. 2012 Nov;73(5):1202-7.
- Williams DJ,Guirgis FW, Morrissey TK, et al. End-tidal carbon dioxide and occult injury in trauma patients: ETCO2 does not rule out severe injury. Am J Emerg Med. 2016 Nov;34(11):2146-2149.
- Stone ME Jr,Kalata S, Liveris A, et al. End-tidal CO2 on admission is associated with hemorrhagic shock and predicts the need for massive transfusion as defined by the critical administration threshold: A pilot study. 2017 Jan;48(1):51-57.
- Kartal M, Eray O, Rinnert S, et al. ETCO₂: a predictive tool for excluding metabolic disturbances in nonintubated patients. Am J Emerg Med 2011; 29:65.
- Solmeinpur H, et al. Predictive Value of Capnography for Diagnosis in Patients with Suspected Diabetic Ketoacidosis in the Emergency Department. West J Emerg Med 2013; (www.escholarship.org/uc/item/5qz744fv).
- Deirdre M, Fearon, Dale W, et al. End-tidal Carbon Dioxide Predicts the Presence and Severity of Acidosis in Children with Diabetes. Acad Emerg Med. 2002;9(12):1373-1378.
- Gilhotra Y, Porter P. Predicting diabetic ketoacidosis in children by measuring end-tidal CO2 via non-invasive nasal capnography. J Paediatr Child Health. 2007;43(10):677-680.
- Taghizadieh A, Pouraghaei M, Moharamzadeh P, et al. Comparison of end-tidal carbon dioxide and arterial blood bicarbonate levels in patients with metabolic acidosis referred to emergency medicine. Journal of Cardiovascular and Thoracic Research. 2016;8(3):98-101.
- Agus MS,Alexander JL, Mantell PA. Continuous non-invasive end-tidal CO2 monitoring in pediatric inpatients with diabetic ketoacidosis. Pediatr Diabetes. 2006 Aug;7(4):196-200.
- Bou Chebl R, Madden B, Belsky J, Harmouche E, Yessayan L. Diagnostic value of end tidal capnography in patients with hyperglycemia in the emergency department. BMC Emergency Medicine. 2016;16:7.
- Rhodes A, Evans LE, Alhazzani W, et al. Surviving Sepsis Campaign: International Guidelines for the Management of Sepsis and Septic Shock: 2016. Crit Care Med 2017;45:486–552.
- Singer AJ1, Taylor M, Domingo A, et al. Diagnostic characteristics of a clinical screening tool in combination with measuring bedside lactate level in emergency department patients with suspected sepsis. Acad Emerg Med 2014 Aug;21(8):853-7.
- Marik PE, Bellomo R. Lactate clearance as a target of therapy in sepsis: A flawed paradigm. OA Critical Care 2013 Mar 01;1(1):3.
- Hunter CL, Silvestri S, Ralls G, et al. A prehospital screening tool utilizing end-tidal carbon dioxide predicts sepsis and severe sepsis. Am J Emerg Med 2016; 34:813.
- McGillicuddy DC,Tang A, Cataldo L, et al. Evaluation of end-tidal carbon dioxide role in predicting elevated SOFA scores and lactic acidosis. Intern Emerg Med. 2009 Feb;4(1):41-4.
- Guirgis FW,Williams DJ, Kalynych CJ, et al. End-tidal carbon dioxide as a goal of early sepsis therapy. Am J Emerg Med. 2014 Nov;32(11):1351-6.
- Hunter C, et al. The sixth vital sign: prehospital carbon dioxide predicts in hospital mortality and metabolic disturbances. Am J Emerg Med. 2014;32:160-65.
- Hunter C, et al. End-tidal carbon dioxide is associated with mortality and lactate in patients with suspected sepsis. Am J Emerg Med. 2013;31:64-71.
- Kearon C, Akl EA, Ornelas J, Blaivas A, et al. Antithrombotic therapy for VTE disease: CHEST guideline and expert panel report. Chest 2016;149:315–52.
- Chopin C, Fesard P, Mangalaboyi J, et al. Use of capnography in diagnosis of pulmonary embolism during acute respiratory failure of chronic obstructive pulmonary disease. Crit Care Med. 1990;18(4): 353-357.
- Robin ED, Julian DG, Travis DM, Crump CH. A physiologic approach to the diagnosis of acute pulmonary embolism. N Engl J Med. 1959;260(12):586-591.
- Kline JA, Israel EG, Michelson EA, et al. Diagnostic accuracy of a bedside D-dimer assay and alveolar dead-space measurement for rapid exclusion of pulmonary embolism: a multicenter study. JAMA. 2001;285(6):761-768.
- Johanning JM,Veverka TJ, Bays RA, et al. Evaluation of suspected pulmonary embolism utilizing end-tidal CO2 and D-dimer. Am J Surg. 1999 Aug;178(2):98-102.
- Manara A, D’hoore W, Thys F. Capnography as a diagnostic tool for pulmonary embolism: a meta-analysis. Ann Emerg Med. 2013;62(6): 584-591.
- Verschuren F, Sanchez O, Righini M, et al. Volumetric or time- based capnography for excluding pulmonary embolism in outpatients? J Thromb Haemost. 2010;8:60-67.
- Sanchez O, Wermert D, Faisy C, et al. Clinical probability and alveolar dead space measurement for suspected pulmonary embolism in patients with abnormal D-dimer test result. J Thromb Haemost. 2006;4:1517-1522.
- Hemnes AR, Newman AL, Rosenbaum B, et al. Bedside end-tidal CO2 tension as a screening tool to exclude pulmonary embolism. Eur Resp J. 2010;35:735-41.
- Riaz I,Jacob B. Pulmonary embolism in Bradford, UK: role of end-tidal CO2 as a screening tool. Clin Med (Lond). 2014 Apr;14(2):128-33.
- Kurt OK, Alpar S, Sipit T, et al. The diagnostic role of capnography in pulmonary embolism. Am J Emerg Med. 2010; 28:460-5.
- Basiri R, Kamali Yazdi E, Bizhani A, Sepehri Shamloo A. The Diagnostic Value of End-tidal Carbon Dioxide (EtCO2) and Alveolar Dead Space (AVDS) in Patients with Suspected Pulmonary Thrombo-embolism (PTE). J Cardiothorac Med. 2015; 3(2):303-308.
- Yüksel M,Pekdemir M, Yilmaz S, et al. Diagnostic accuracy of noninvasive end-tidal carbon dioxide measurement in emergency department patients with suspected pulmonary embolism. Turk J Med Sci. 2016 Jan 5;46(1):84-90.
- Cinar O,Acar YA, Arziman I, et al. Can mainstream end-tidal carbon dioxide measurement accurately predict the arterial carbon dioxide level of patients with acute dyspnea in ED. Am J Emerg Med. 2012 Feb;30(2):358-61.
- You B,Peslin R, Duvivier C, et al. Expiratory capnography in asthma: evaluation of various shape indices. Eur Respir J. 1994 Feb;7(2):318-23.
- Egleston CV, Ben Aslam H, Lambert MA. Capnography for monitoring non-intubated spontaneously breathing patients in an emergency room setting. Journal of Accident & Emergency Medicine. 1997;14(4):222-224.
- Liu JM,Hu HC, Shi MH, et al. [The significance of volumetric capnography in assessment of asthmatic acute exacerbation staging]. Zhonghua Jie He He Hu Xi Za Zhi. 2008 Mar;31(3):186-90.
- Brown RH, Brooker A, Wise RA, et al. Forced Expiratory Capnography and Chronic Obstructive Pulmonary Disease (COPD). Journal of breath research. 2013;7(1):017108.
- Scano G, Spinelli A, Duranti R, et al. Carbon dioxide responsiveness in COPD patients with and without chronic hypercapnia. European Respiratory Journal 1995;8:78-85.
- Langhan ML,Zonfrillo MR, Spiro DM. Quantitative end-tidal carbon dioxide in acute exacerbations of asthma. J Pediatr. 2008 Jun;152(6):829-32.
- Nagurka R,Bechmann S, Gluckman W, et al. Utility of initial prehospital end-tidal carbon dioxide measurements to predict poor outcomes in adult asthmatic patients. Prehosp Emerg Care. 2014 Apr-Jun;18(2):180-4.
- Romero PV, Rodriguez B, de Oliveira D, Blanch L, Manresa F. Volumetric capnography and chronic obstructive pulmonary disease staging. International Journal of Chronic Obstructive Pulmonary Disease. 2007;2(3):381-391.
- Mieloszyk RJ, Verghese GC, Deitch K, et al. Automated quantitative analysis of capnogram shape for COPD-normal and COPD-CHF classification. IEEE Trans Biomed Eng 2014; 61:2882.
- Arena R, Myers J, Abella J, et al. The Partial Pressure of Resting End-Tidal Carbon Dioxide Predicts Major Cardiac Events In Patients with Systolic Heart Failure. American heart journal. 2008;156(5):982-988.
- Abramo TJ, Wiebe RA, Scott S, Goto CS, McIntire DD. Noninvasive capnometry monitoring for respiratory status during pediatric seizures. Crit Care Med 1997;25:1242–6.
- Monnet X, Bataille A, Magalhaes E, et al. End-tidal carbon dioxide is better than arterial pressure for predicting volume responsiveness by the passive leg raising test. Intensive Care Med. 2013;39(1):93-100.
- Young A, Marik PE, Sibole S, et al. Changes in end tidal carbon dioxide and volumetric carbon dioxide as predictors of volume responsiveness in hemodynamically unstable patients. J Cardiothorac Vasc Anesth. 2013;27(4):681-684.
- Monge García MI, Gil Cano A, Gracia Romero M, et al. Non-invasive assessment of fluid responsiveness by changes in partial end-tidal CO2 pressure during a passive leg-raising maneuver. Annals of Intensive Care. 2012;2:9.
- Xiao-ting W,Hua Z, Da-wei L, et al. Changes in end-tidal CO2 could predict fluid responsiveness in the passive leg raising test but not in the mini-fluid challenge test: A prospective and observational study. J Crit Care. 2015 Oct;30(5):1061-6.
- Jacquet-Lagrèze M,Baudin F, David JS, et al. End-tidal carbon dioxide variation after a 100- and a 500-ml fluid challenge to assess fluid responsiveness. Ann Intensive Care. 2016 Dec;6(1):37.
- Toupin F,Clairoux A, Deschamps A, et al. Assessment of fluid responsiveness with end-tidal carbon dioxide using a simplified passive leg raising maneuver: a prospective observational study. Can J Anaesth. 2016 Sep;63(9):1033-41.
- Lakhal K,Nay MA, Kamel T, et al. Change in end-tidal carbon dioxide outperforms other surrogates for change in cardiac output during fluid challenge. Br J Anaesth. 2017 Mar 1;118(3):355-362.
- Lee SW,Hong YS, Han C, et al. Concordance of end-tidal carbon dioxide and arterial carbon dioxide in severe traumatic brain injury. J Trauma. 2009 Sep;67(3):526-30.
- Bhende MS, Thompson AE. Gastric juice, drugs, and end-tidal carbon dioxide detectors. Pediatrics. 1992;90(6):1005.
- O’Flaherty D, Adams AP. False-positives with the end-tidal carbon dioxide detector. Anesth Analg. 1992 Mar;74(3):467-8.
- Qureshi S,Park K, Sturmann K, et al. The effect of carbonated beverages on colorimetric end-tidal CO(2) determination. Acad Emerg Med. 2000 Oct;7(10):1169.