Confirmation of Endotracheal Tube Placement Following Intubation (see Airway Management)
General Comments
End-Tidal Carbon Dioxide Detection is Most Accurate Means of Confirming Endotracheal Tube Placement in the Non-Cardiac Arrest Patient: end-tidal carbon dioxide detection is a standard of care practice to confirm appropriate endotracheal intubation
In the Setting of Cardiac Arrest (without a Detectable Pulse), Gas Exchange in the Lungs is Markedly Decreased and Carbon Dioxide May Not Be Detectable Despite Appropriate ETT Positioning in the Trachea (Crit Care Med, 1985) [MEDLINE]
However, the Detection of Carbon Dioxide Which Persists for 6 Breaths in the Cardiac Arrest Patient Indicates Appropriate Endotracheal Tube Positioning in the Trachea
Colorimetric Carbon Dioxide Indicator
Principle/Technique: qualitative (not quantitative) colorimetric carbon dioxide indicators (Easy Cap II, etc) use litmus paper that tidally changes (breath by breath) from purple to yellow in the presence of exhaled carbon dioxide
ETCO2 <0.5%: purple
ETCO2 0.5-2%: tan
ETCO2 >2%: yellow
False-Positive Results: carbon dioxide detection (yellow color change) with esophageal intubation
Difficult Intubation with Prolonged Bag Ventilation: air previously pushed into the stomach during bag ventilation may cause yellow color change during the first few breaths
However, if Color Remains Yellow After >4-5 breaths, this Indicates Endotracheal Intubation
Epinephrine (see Epinephrine): acidic medication which can cause (non-tidal) yellow color change
Ingestion of Carbonated Liquids
Lidocaine (see Lidocaine): acidic medication which can cause (non-tidal) yellow color change
Regurgitation of Gastric Contents During Intubation: gastric acid can cause (non-tidal) yellow color change
False-Negative Results: lack of carbon dioxide detection (lack of yellow color change) even with successful endotracheal intubation
Acute Pulmonary Embolism (PE) (see Acute Pulmonary Embolism): due to decreased pulmonary blood flow and decreased delivery of carbon dioxide to the lungs
Airway Obstruction: indicator may not turn yellow, due to poor carbon dioxide exchange across the obstructed airway (Emerg Med J, 2003) [MEDLINE]
Significant Hypotension/Cardiac Arrest (Especially with Poor Quality CPR) (see Hypotension and Cardiac Arrest): due to decreased pulmonary blood flow and decreased delivery of carbon dioxide to the lungs
If Chest Compressions are Adequate (with Adequate Blood Flow to the Lungs), Indicator Will Likely Turn Yellow
Indicator Has Only 69% Sensitivity for Endotracheal Intubation When Used During Cardiopulmonary Resuscitation (Ann Emerg Med, 1992) [MEDLINE]
Clinical Efficacy
Sensitivity of End-Tidal Carbon Dioxide Detection Approaches 100% in Non-Cardiac Arrest Patients
Sensitivity of End-Tidal Carbon Dioxide Detection is Variable in Cardiac Arrest Patients: ranges from 62-100% in various studies (depending on the modality used and the duration of cardiac arrest)
In Non-Cardiac Arrest, Infrared Capnometry and Infrared Capnography Have a 100% Sensitivity/100% Specificity in Detecting Endotracheal Intubation (Intensive Care Med. 2002) [MEDLINE]
In Cardiac Arrest, Infrared Capnometry Has a 88% Sensitivity/100% Specificity in Detecting Endotracheal Intubation (Intensive Care Med. 2002) [MEDLINE]
Principle/Technique: end-tidal carbon dioxide monitor attached to the end of the endotracheal tube uses infrared absorption to detect carbon dioxide quantitatively
Displays Either Waveform Capnography or Digital Readout
Etiology of False-Positive Capnography (Carbon Dioxide Detection with Esophageal Intubation)
Ingestion of Carbonated Liquids
Etiology of False-Negative Capnography (No Carbon Dioxide Detection with Endotracheal Intubation)
Acute Pulmonary Embolism (PE) (see Acute Pulmonary Embolism): due to decreased pulmonary blood flow and decreased delivery of carbon dioxide to the lungs
Contamination of the Detector with Gastric Contents
Severe Airflow Obstruction: due to poor carbon dioxide exchange across the obstructed airway (Emerg Med J, 2003) [MEDLINE]
Significant Hypotension/Cardiac Arrest (Especially with Poor Quality CPR) (see Hypotension and Cardiac Arrest): due to decreased pulmonary blood flow and decreased delivery of carbon dioxide to the lungs
Clinical Efficacy
Sensitivity of End-Tidal Carbon Dioxide Detection Approaches 100% in Non-Cardiac Arrest Patients
Sensitivity of End-Tidal Carbon Dioxide Detection is Variable in Cardiac Arrest Patients: ranges from 62-100% in various studies (depending on the modality used and the duration of cardiac arrest)
In Non-Cardiac Arrest, Infrared Capnometry and Infrared Capnography Have a 100% Sensitivity/100% Specificity in Detecting Endotracheal Intubation (Intensive Care Med. 2002) [MEDLINE]
In Cardiac Arrest, Infrared Capnometry Has a 88% Sensitivity/100% Specificity in Detecting Endotracheal Intubation (Intensive Care Med. 2002) [MEDLINE]
Recommendations (American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care, 2015) (Circulation, 2015) [MEDLINE]
Although No Clinical Study Has Examined Whether Titrating Resuscitative Efforts to Physiologic Parameters During CPR Improves Outcome, it is Reasonable to Utilize Physiologic Parameters (Quantitative Waveform Capnography, Arterial Relaxation Diastolic Pressure, Arterial Pressure Monitoring, and Central Venous Oxygen Saturation) When Feasible to Optimize Quality of CPR, Guide Vasopressor Therapy and Detect ROSC (Class IIb, LOE C-EO)
Confirmation of Endotracheal Tube Placement
Continuous Waveform Capnography is Recommended in Addition to Clinical Assessment as the Most Reliable Method of Confirming and Monitoring Correct Endotracheal Tube Placement (Class I, LOE C-LD)
If Continuous Waveform Capnometry is Not Available, a Nonwaveform CO2 Detector, Esophageal Detector Device, or Ultrasound Used by an Experienced Operator is a Reasonable Alternative (Class IIa, LOE C-LD)
In Intubated Patients with Cardiac Arrest, Failure to Achieve an ETCO2 >10 mm Hg by Waveform Capnography After 20 minutes of CPR May Be Considered as One Component of a Multimodal Approach to Decide When to End Resuscitative Efforts, But it Should Not Be Used in Isolation (Class IIb, LOE C-LD)
Studies from Which this Recommendation is Derived Only Included Intubated Patients
Systematic Review of Diagnostic Accuracy of Methods to Verify Nasogastric Tube Placement in Mechanically Ventilated Patients (JBI Database System Rev Implement Rep, 2015) [MEDLINE]
Colorimetric Capnography Detected Nasogastric Tube Position with Very High Accuracy (Level 2b Evidence)
Sensitivity: 88-100%
Specificity: 99-100%
However, Further Research is Required to Determine the Best Implementation of this Technology: since colorimetric capnographs do not have manufactured NG tube adaptors, etc
Technique
Principles
Capnography: non-invasive measurement of carbon dioxide in exhaled breath
Physiologic Information Determined by Capnography
Effectiveness of Ventilation: how effectively carbon dioxide is being exhaled
Three Parameters from Capnography Yield Clinical Information
ETCO2 Value
Shape of the Capnography Waveform
Difference Between pCO2 and ETCO2
The pCO2- ETCO2 Difference is Usually Around 5 mm Hg: due to mixing of alveolar gases (which contain carbon dioxide) with dead space gases (which do not contain carbon dioxide)
This Difference is a Surrogate for the Amount of Physiologic Dead Space
Shape of the Capnography Waveform
Waveform Phases
Inspiratory Phases
Phase 0
Expiratory Phases
Phase I (Dead Space Ventilation Phase): dead space ventilation (no expired carbon dioxide)
Phase II (Initial Exhalation Phase): rapid increase in breath carbon dioxide concentration as it emerges from the alveoli and reaches the upper airway
Phase III (Plateau Phase): alveolar plateau (exhalation of carbon dioxide from the alveoli)
If All of the Alveoli Had the Same pCO2, Phase III Would Be Flat
However, Due to Normal Variability in the V/Q Ratios Throughout the Lung, Phase III Usually Has a Slight Upward Slope (Due to Alveoli with Longer Time Constants with Relatively Larger Amounts of Carbon Dioxide Emptying Later in the Phase)
Waveform Configuration
Normal Waveform: rectangular (almost square wave) capnogram with gradient between the alveolar (end-tidal) and arterial carbon dioxide concentration of 0-5 mm Hg
Waveform in Obstructive Lung Disease: impairment of expiratory flow with phase II becoming rounded due to slowed exhalation of carbon dioxide
Decreased Slope of Phase II and Increased Slope of Phase III (Giving Waveform a “Shark Fin” Appearance) Indicates the Presence of Airway Obstruction
Difference Between pCO2 and ETCO2
The pCO2 – ETCO2 Difference is Usually Around 5 mm Hg: due to mixing of alveolar gases (which contain carbon dioxide) with dead space gases (which do not contain carbon dioxide)
Physiologic States Which Result in the pCO2 – ETCO2 Difference Increasing
Presence of Alveolar Dead Space
Example: acute pulmonary embolism would increase dead space and decrease the ETCO2 (and increase the pCO2 – ETCO2 difference)
Capnography During Critical Illness. Chest. 2016 Feb;149(2):576-85. doi: 10.1378/chest.15-1369. Epub 2016 Jan 12 [MEDLINE]
Monitoring of Cardiac Arrest Resuscitation
Part 7: Adult Advanced Cardiovascular Life Support: 2015 American Heart Association Guidelines Update for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation. 2015 Nov 3;132(18 Suppl 2):S444-64. doi: 10.1161/CIR.0000000000000261 [MEDLINE]
Evaluation of Obstructive Lung Disease
Capnogram shape in obstructive lung disease. Anesth Analg. 2005;100:884–888 [MEDLINE]
Correlations between capnographic waveforms and peak flow meter measurement in emergency department management of asthma. Int J Emerg Med. 2009 Feb 24;2(2):83-9. doi: 10.1007/s12245-009-0088-9 [MEDLINE]
Accidental intubation of the oesophagus. Anaesth Intensive Care. 1980;8(2):183 [MEDLINE]
End-tidal CO2 as a guide to successful cardiopulmonary resuscitation: a preliminary report. Crit Care Med. 1985;13(11):910 [MEDLINE]
Esophageal intubation: a review of detection techniques. Anesth Analg. 1986;65(8):886 [MEDLINE]
Unrecognized endobronchial intubation of emergency patients. Ann Emerg Med. 1989;18(8):853 [MEDLINE]
A comparative study of methods of detection of esophageal intubation. Anesth Analg. 1989;69(5):627 [MEDLINE]
Multicenter study of a portable, hand-size, colorimetric end-tidal carbon dioxide detection device. Ann Emerg Med. 1992 May;21(5):518-23 [MEDLINE]
Comparison of three different methods to confirm tracheal tube placement in emergency intubation. Intensive Care Med. 2002;28(6):701 [MEDLINE]
Towards evidence based emergency medicine: best BETs from the Manchester Royal Infirmary. Colourimetric CO(2) detector compared with capnography for confirming ET tube placement. Emerg Med J. 2003 May;20(3):265-6 [MEDLINE]
Diagnostic accuracy of methods used to verify nasogastric tube position in mechanically ventilated adult patients: a systematic review. JBI Database System Rev Implement Rep. 2015;13(1):188 [MEDLINE]
