Oesophageal aspiration. An oesophageal aspirator is a large syringe or a self-inflating bulb (Fig. 23.5.1), which attaches to the proximal end of the endotracheal tube. The aspirator differentiates between an oesophageal versus a tracheal placement because the oesophagus is a collapsible structure under negative pressure, while the trachea is not. Successful air aspiration is highly associated with trachea placement. It has been determined that the oesophageal aspiration modality has a sensitivity of 99% and specificity of 100% in confirming endotracheal tube placement in patients weighing more than 20 kg.

End-tidal colorimetric capnometry (Fig. 23.5.2). The capnometer attaches to the proximal end of the endotracheal tube and detects the presence of CO₂ within the tube. The capnometer will display a yellow (CO₂ present) or purple (CO₂ absent) colour in the indicator window, which generally correlates with a tracheal or oesophageal intubation, respectively. Multiple studies find that a yellow colour change has a 100% positive predictive value for correct endotracheal tube placement. When used for a poorly perfused patient (e.g. cardiac arrest), however, there will often be no yellow colour change because of expected low CO₂ levels. This is the primary limitation when using this modality. Colorimetric capnometry is not commonly used in hospital. Table 23.5.1 provides a mnemonic to help remember the colour scheme.

Digital capnography (Fig. 23.5.3). This latest technology continuously detects and displays the partial pressure of CO₂ at the proximal end of the endotracheal tube. In adult cardiac arrest patients, a pCO₂ < 5 mmHg correlates with an extremely poor prognosis. Digital capnography is the standard for confirmation of intubations.