To the Editor:
Amour and colleagues compared single-use with reusable metal laryngoscope blades and found better laryngeal exposure and more successful intubation with the former.1Laryngeal visualization and subsequent tracheal intubation are dependent, however, on many other factors besides the blade type. Upper airway anatomy, experience of the laryngoscopist, adequate relaxation, patient's head and neck position, external laryngeal manipulation, blade size, and the laryngoscope lifting force are all factors that can dramatically affect the ability to visualize the larynx.2Therefore, to separate out the effect of one factor on laryngeal visualization, all of the other factors will have to be standardized. The authors should be applauded for trying to control most of the factors. Two important factors, however, were not addressed: the use of external laryngeal manipulation and the laryngoscope lifting force. There was no mention in the study of whether external laryngeal manipulation was used in some patients, all patients, or none; whether it was used during the first attempt, second attempt, both, or neither; and most importantly, whether the documented laryngoscopic grade was the one before or after its application, if it was applied. The use of external laryngeal manipulation can improve visualization by a whole grade and, in some patients, can be the factor that makes the difference between intubation failure and success.3Similarly, there was no mention of whether any attempt was made to standardize the laryngoscope lifting force. Increasing the force can be accompanied by a change in the resultant view, and this increase can occur in response to a poor view without the laryngoscopist even being aware of it.4The forces applied during laryngoscopy can be measured, and thus controlled, by a device that can be used for both clinical research and patient care purposes.5There is no doubt that the metal single-use blade provided better illumination, but was the difference in the results solely caused by the light factor or also influenced by the effect of the other factors that were not addressed? The results could have been more informative if these two factors were also standardized, especially because, as the authors themselves mentioned, it is extremely difficult to keep such a study blinded.
*Department of Anesthesiology, Medical College of Wisconsin, Milwaukee, Wisconsin. email@example.com