Capnography alone is imperfect for endotracheal tube placement confirmation during emergency intubation¹

Abstract

This analysis primarily sought to determine the effectiveness of end-tidal capnography for tube placement confirmation during emergency airway management. Secondary objectives were validation of the rate of unanticipated esophageal placement during emergency intubation and quantification of the portion of intubations performed in patients with cardiac arrest where capnography is not recommended. The study was performed in two phases. For the primary objective, a meta-analysis was performed on all experimental capnography trials enrolling emergency populations. For the secondary objectives, inadvertent esophageal intubation and cardiac arrest rates were calculated from a large prospective multicenter observational study of emergency intubation cases. Data analysis included calculation of descriptive statistics, sensitivity, specificity, and confidence intervals (CI). Based on 2,192 intubations, a meta-analysis of previous capnography trials resulted in an aggregate sensitivity of 93% (95% CI 92–94%) and an aggregate specificity of 97% (CI 93–99%) for emergency tube placement confirmation. Thus, for emergency capnography use, the false-negative failure rate (tube in trachea but capnography reports esophagus) was 7% and the false-positive rate (tube in esophagus but capnography reports trachea) was 3%. This translates to potential harm for one patient in every 10 treated with capnographic confirmation alone (number needed to harm: 14 for false-negative, 33 for false-positive, and 10 for both). A further literature review demonstrated no sole method of tube placement confirmation is completely foolproof. Of 4,602 consecutive intubations reported to the National Emergency Airway Registry, 4% of emergency intubation attempts resulted in accidental esophageal intubation, and 10% occurred in nontraumatic cardiac arrest patients. During tracheal intubation of critically ill patients, it is concluded that the rate of accidental esophageal tube placement warrants continued improvement in emergency airway techniques. Misidentification of esophageal placement in the emergency setting may occur with capnography. Multiple methods of tube placement confirmation are superior to any single method because no single method has perfect accuracy.

Introduction

What this comes down to is hubris: sinful pride. I know that I can intubate. I know where that tube is. The problem with being wrong is it won’t hurt my pride, but it might kill somebody. [Comment on the fatal complication of missed esophageal tube placement. Cory Slovis, MD, Chairman, Vanderbilt Emergency Medicine residency. Interview CBS Evening News (John Roberts, anchor), Jan 1, 1999.]

Emergency intubation of the critically ill patient provides liberal opportunity for misfortune. Whereas successful completion may be lifesaving, failure often hastens patient death. The science and practice of emergency intubation has progressed significantly within the past decade (1). Rapid-sequence intubation (RSI) has nearly replaced intubation minus paralysis (IMP) as standard of care for both emergency trauma and medical patients 2, 3, 4. Decreased complication rates during emergency intubation can be attributed to greater acceptance of rapid-sequence techniques, intensive training of emergency physicians (EPs) within specialty training programs, improvement in failure detection, and increased training in rescue techniques. Future advances in emergency intubation now largely focus on early recognition of unanticipated esophageal intubation 5, 6, 7. Two previous prospective series totaling 530 patients showed that such unanticipated tube placement occurs in 8% of intubation attempts 4, 8.

For EPs, portable capnography has become widely available for use in tube confirmation, providing one method of recognizing improper esophageal tube placement. However, capnography has two major disadvantages for emergency use. First, it functions poorly for the portion of patients intubated for disorders that limit or terminate production of exhaled CO₂ and is not recommended for primary tube confirmation in such cases (5). In some centers where intubation occurs frequently for cardiac arrest, such cases may represent a significant portion of intubations. Second, capnography requires a trial of ventilation. In previously fasted elective surgery patients, accidental esophageal intubation is usually of little consequence because these patients are adequately pre-oxygenated, denitrogenated, and have empty stomachs. In contrast, patients undergoing emergency intubation have not fasted and often cannot receive an adequate period of pre-oxygenation because of the illness at hand. A trial of esophageal ventilation in these cases may be catastrophic because of rapid hypoxia and large-volume aspiration of gastric contents 5, 6, 7, 8, 9.

Despite the marketing of capnographic devices for emergency department (ED) intubation confirmation, most previous capnography studies have focused on nonemergent populations whose illnesses are not complicated by low flow or cardiac arrest states. Accordingly, the primary objective of this study was the quantification of overall success and failure rates of capnographic confirmation in populations of emergency patients. Secondary objectives were validation of previously reported rates of unanticipated esophageal intubation in emergency populations and quantification of the portion of emergency intubations performed in patients with cardiac arrest, where capnography is expected to fail.