To the Editor:
We thank Drs Adams, Hurtado, and Geracci for bringing to our attention the description of improvised airways by Fisher 1 and the report by Adams and Whitlock of an improvised cricothyroidotomy and the accompanying measurements of air resistance using standard and improvised tracheostomy tubes. 2 We apologize for our failure to identify these publications in our initial study.
Although we accept the finding by Adams and Whitlock that the air resistance created by a ballpoint pen is higher than that of the other devices they tested, 2 we question the conclusion from that study and restated in their letter that a ballpoint pen would be unacceptable to use as a temporary tracheostomy tube. Poiseuille's law states that the volume of air flowing through a tube for a given pressure gradient increases directly with tube radius raised to the fourth power and inversely with tube length. Following Poiseuille's law, the device we tested, 3 with an internal diameter of 3.5 mm and a length of 4 cm, would allow for less than half the volume of air flow than would their ballpoint pen with an internal diameter of 5 mm and a length of 7 cm for a given pressure gradient. However, it is our experience that one can maintain oxygenation adequate to remain conscious for at least 10 minutes on room air while breathing through the device we tested. This experience has been replicated by one of our authors on 2 episodes with no adverse effects except for some tiring of the diaphragm and a mild sensation of suffocation. We are fairly confident that positive pressure ventilation through either our device or through the ballpoint pen described by Adams and Whitlock would allow for sufficient oxygenation to an average-sized adult to prevent hypoxic cardiac arrest or cerebral injury if the patient's pulmonary and cardiac function is otherwise preserved. Using supplemental oxygenation and allowing the patient to exhale through their mouth or nose would further facilitate the use of these small diameter tubes for oxygenation and ventilation.
As Adams and Whitlock describe in the case report portion of their study, the most important considerations in improvisational cricothyroidotomy is having a tube, getting the tube into the trachea, and creating or allowing the patient to achieve some air exchange. Important secondary considerations include one's ability to attach a bag valve device to the tube, secure the tube to the patient's neck, and avoid injury to the posterior wall of the trachea. Although air exchange is certainly easier with larger internal diameter tubes, we believe that devices with internal diameters as small as 3.5 mm would allow for acceptable levels of oxygenation given the pressure gradient achieved using bag valve or mouth-to-tube ventilations. When faced with a patient with a failed airway without a 6.0 cuffed endotracheal tube or a sports bottle straw, we encourage practitioners to put an IV spike and drip chamber or a trimmed ball point pen into a patient's neck.