We are delighted that our report has stimulated some interesting discussion on the challenges of end-tidal carbon dioxide monitoring.1Dr. Her describes his experience with a new type of endotracheal tube, which has a built-in end-tidal carbon dioxide monitoring port (Mallinckrodt Inc., St. Louis, MO). We agree that the complication seen in our patient could have been avoided with this form of tube because dislodgement and distal migration are less likely. There are some other advantages that should be noted. Because the monitoring line does not occupy the inner lumen, airway resistance is not increased. This is particularly relevant for very low-birth-weight infants, where 2.0- to 2.5-mm uncuffed endotracheal tubes are commonly used and airway resistance is most likely to be affected. This type of tube can be easily used with an appropriate end-tidal measuring system, provided the sample volume aspirated does not compromise the delivered tidal volume.

There are some limitations that need to be pointed out. The additional tubing may become entangled with other tubes (e.g. , nasogastric tube) or may be pulled on by an active patient, both potentiating an accidental extubation. If the tube is inadvertently cut (e.g. , during tube suturing or taping) or the stopcock is left open to the atmosphere, a leak may occur, leading to ventilator autocycling and suboptimal tidal volume delivery. If used chronically for long-standing ventilated patients, the sampling line may become occluded by mucous or water secondary to circuit humidification. Finally, the current cost of the device may prohibit widespread use.

Although continuous end-tidal carbon dioxide is a close measure of arterial carbon dioxide partial pressure in patients with normal ventilation and perfusion, it does not guarantee appropriate tube position.2It is most useful for trending or screening patients for abnormal carbon dioxide values. This type of endotracheal tube may be useful for patients requiring short-term procedural intubation in the operating room or during high-risk neonatal transport, where the risk of endotracheal tube migration/dislodgement is high. The reliability of this device needs careful prospective evaluation.

*Hospital for Sick Children, Toronto, Ontario, Canada. patrick.mcnamara@sickkids.ca

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Noble JJ: Carbon-dioxide monitors: Exhaled gas (capnographs, capnometry, end-tidal CO2monitors). Pediatr Emerg Care 1993; 9:244–6