New Risk Index for Miller Blade Aids Adult Intubation
by Michael Vlessides
ChicagoCompared with the Macintosh blade, the Miller might seem like something of an understudy. After all, whereas several multivariate indices of airway risk factors exist to assist in the prediction of difficult laryngoscopy and orotracheal intubation with the Macintosh blade, the Miller has received far less attention.
But that might be changing. Researchers at Ochsner Medical Center, in New Orleans, have developed a multivariate risk index for Miller laryngoscopy in adult elective surgery patients.
Mallampati class, thyromental distance and ability to prognath were predictors for inferior Cormack-Lehane views; modified Mallampati class and head/neck extension predicted increased attempts at orotracheal intubation, the researchers said.
The Miller-2 blade is used most often at our institution, said William B. Landry, MD, staff anesthesiologist at Ochsner. Our practitioners are highly skilled with it, so we thought our institution would be an appropriate place to conduct this study.
Dr. Landry and his colleagues enrolled 978 patients over age 17 years, who were scheduled for elective surgery requiring orotracheal intubation for general anesthesia.
The researchers recorded every patients airway risk factors preoperatively, including modified Mallampati class, mouth opening, thyromental distance, neck extension, ability to prognath, previous history of difficult intubation, sex, weight and height.
The anesthesia provider then recorded, during direct laryngoscopy, the Cormack-Lehane view, the number of attempts required to successfully intubate the patient, and if any subsequent or additional airway devices were needed to intubate the patient, Dr. Landry said.
Intubation succeeded in 96.2% of the 978 patients with the Miller blade, with the remaining patients requiring alternate airway toolsincluding intubating catheters and video laryngoscopesor three attempts at intubation.
Identifying risk factors for difficult intubation is a key task for the anesthesiologist, Dr. Landry said. Inability to intubate and ventilate is probably the single most significant factor related to adverse respiratory events in general anesthesia, he said. A lot of times, as an anesthesiologist you can walk into an exam room, look at a patient from a distance and recognize physical characteristics right away. Some patients, though, are not that easy to identify and you do need some sort of algorithm or physical exam to determine whos going to give you trouble.
Robert S. Greenberg, MD, associate professor of anesthesiology and critical care medicine at The Johns Hopkins Hospital, in Baltimore, said the new study helps illustrate that even in medicine, the magician is sometimes more important than the wand.
But Dr. Greenberg noted that the Ochsner team likely has more experience using Miller blades than most anesthesiology groups, at least for adult patients. I wonder how many other groups have such expertise and how generalizable these results are, he added. In fact, with the apparent pervasive use of adjunctive devices like video laryngoscopy, I wonder if such expertise may be going the way of expert mask management, or even open-drop anesthesia.
