Table 4.

Limitations associated with each method.

Study	Method	Limitation noticed during study:
Zadel et al. (2015)	Capnography	•Capnography failed to distinguish between endotracheal and endobronchial intubation comparing to POCUS and auscultation (i.e., capnography results were normal before and after the correction of orotracheal tube placement)
Grmec (2002)	Auscultation	The use of auscultation to confirm tube position was dependent on the examiner's experience: •In the false positive result in non-arrest patients, the air passing through the oesophagus was incorrectly identified as breath sounds. •However, in false-negative results, emergency physicians were not able to hear the breath sounds clearly due to obesity or incorrect description of breath sounds as stomach gurgling in some conditions such as aspiration, excessive secretions, or pulmonary oedema.
Pelucio et al. (1997) and Marley et al. (1996)	ODD	•ODD may show false ‘normal’ test results, i.e., correct tracheal intubation while tube in the oesophagus, if the ETT cuff was not inflating properly as “the seal provided by the cuff may be necessary to create adequate oesophageal collapse and thereby resistance when the syringe is pulled back”. •Moreover, ODD may show false ‘abnormal’ results and not recognize tracheal intubation if there are any foreign materials that occluded the tracheal tube, such as pulmonary oedema, blood, or vomitus, or if the tube is deeply intubated in the mainstem bronchus.
Schaller et al. (1997)	Colorimetric ETCO2 detector	•It was noticed that in cardiac arrest patients, the sensitivity of ETCO2 detection device was lower for the assessment of correct tube position, comparing to ODD. •The CO2 detector device failed to change color and remained purple, i.e., oesophageal intubation; while the ETT was correctly in the trachea in four arrest patients, and therefore, it was associated with prolonged time of using the device for the final decision making.
Hayden et al. (1995)	Colorimetric ETCO2 detector	•Colorimetric ETCO2 detector failed to record color changes in some patients when the device became contaminated with medications, vomitus, or secretions. •Moreover, it failed to register any color changes in 25 patients with cardiac arrest although the tube was verified clinically to be in the right position in all patients.