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By Vibhu Sharma, MD, MS
Attending Physician, Division of Pulmonary and Critical Care Medicine, John H. Stroger Hospital of Cook County, Assistant Professor of Medicine, Rush University Medical Center, Chicago
Dr. Sharma reports no financial relationships relevant to this field of study.
SYNOPSIS: In this prospective study, use of a flexible bronchoscope as a flexible stylet and a Glidescope to provide visual guidance while intubating patients in the operating room was associated with shorter time to intubation than the use of Glidescope alone.
SOURCE: Mazzinari G, Rovira L, Henao L, et al. Effect of dynamic versus stylet-guided intubation on first-attempt success in difficult airways undergoing Glidescope laryngoscopy: A randomized controlled trial. Anesth Analg 2019;128:1264-1271.
In this prospective study, researchers randomized patients with a predicted difficult airway to either a Glidescope only (G-only) intubation or Glidescope and fiberoptic bronchoscope (G-FOB) group. Overall, 219 patients were evaluated for eligibility, with 160 patients randomized in 1:1 fashion. All patients were scheduled to undergo surgery and were intubated in the operating room. All patients provided written informed consent, after which randomization allocation was revealed. The investigators excluded patients who had mouth opening ≤ 2 cm, planned awake intubation, planned nasal intubation, or those who were ≤ 18 years of age. Difficult airways were assessed quantitatively and assigned an Arné score by a single investigator based on the following parameters:
The Arné score1 was developed as a guide to difficult airways in both the ear, nose, throat and general surgery populations. The criteria that determine the Arné score are instructive with respect to assessment of the airway for intubation difficulty. The score assigns most points to limited mouth opening/mandibular luxation (13 points for inter-incisor gap < 3.5 cm and mandibular luxation < 0), previous knowledge of difficult intubation (10 points), presence of pathologies associated with difficult intubation (5 points), and Mallampati Class IV airway (8 points).
An Arné score > 11 (out of maximum possible 48) or neck circumference to thyromental distance ratio > 4 cm or both were required to enter randomization procedures. The G-only group was intubated using a malleable stylet after the Glidescope had been used to obtain an acceptable view. For the G-FOB group, a two-step procedure was used. The first step was performed by an anesthesiologist and involved insertion of the Glidescope to obtain a view of the glottis. The second step involved handing off the Glidescope to an assistant, followed by using a flexible single-use bronchoscope loaded with an endotracheal tube to guide tube into the trachea. Visualization of the bronchoscope tip was performed using the Glidescope video display only. The bronchoscope was used solely to access the trachea across the vocal cords. Once the tip was safely across, the endotracheal tube loaded onto the bronchoscope was passed in over the scope.
All patients were preoxygenated using standard 100% nonrebreather masks; obese patients were preoxygenated using 100% oxygen and 10 cm H2O continuous positive airway pressure. Neuromuscular blockade was used in all patients. End points for the study were as follows: 1) first-pass intubation success (primary endpoint); 2) time to successful intubation (time from Glidescope blade insertion to inflation of endotracheal cuff); 3) airway injury rate; 4) need for alternative rescue techniques.
The study is remarkable for the recruitment of patients with predicted difficult airways. In total, 97% of patients had a large neck circumference (cervical circumference/thyromental distance of > 4), and 65% had a Mallampati score of III or IV. Almost half of the patients had limited mouth opening (42%) or neck movement (43%). All patients recruited had at least two criteria associated with a difficult airway, and approximately one in 10 had a prior history of a difficult airway. At the onset of the procedure, both groups were matched for total Arné score and Arné score subgroups (as delineated earlier). Oxygen saturation at the onset of laryngoscopy was no different between the groups. The authors performed a logistic regression analysis to generate relative risk ratios for successful intubation at first attempt, with the Arné score subgroups and other variables (including age) as independent factors.
With respect to the primary end point, the G-FOB group was intubated successfully on the first attempt 91% of the time, compared to approximately 61% of the time in the G-only group. Most failures were due to a requirement for repeat laryngoscopy to obtain a better view of the glottis (94%), and the rest (6%) were due to desaturation to below 90%.
The median time to successful intubation was 50 seconds (interquartile range [IQR], 80 seconds) in the G-FOB group compared to 64 seconds (IQR, 24 seconds) in the G-only group. Logistic regression yielded a first-attempt tracheal intubation success relative risk of 3.7 (95% confidence interval [CI], 1.7-8.0) with the G-FOB technique. The airway injury rate was lower in the G-FOB group (1% vs. 10%), as was the need for alternative rescue techniques (4% vs. 24%), both statistically significant with P < 0.035.
Mazzinari et al studied patients who were being intubated in the controlled setting of an operating room and, for this reason, the results of this study cannot be extrapolated to the patient population in the medical intensive care units. Nevertheless, it is instructive to be aware of the techniques described here for use in the difficult airway setting in the medical intensive care unit. Severe complications are frequent in ICUs, regardless of operator type (anesthesiologist vs. non-anesthesiologist).2,3 The “physiologically difficult airway”4 is a more relevant descriptor of scenarios that an intensivist might encounter, and this study opens up a technique that has been described only in the operating room setting for consideration in difficult airway scenarios in the ICU.
The MACOCHA score5 has been used to predict difficult airways in the intensive care unit, and it shares similarities to the Arné score described here, with elements receiving maximal scores being identical (Mallampati III or IV airway, reduced cervical spine mobility, limited mouth opening). The major differences between these two scores are the use of prior difficult airway (frequently difficult if not impossible to gauge in the intensive care unit) and the presence of clinical symptoms of airway pathology or pathologies associated with difficult intubation in the Arné score. Unfortunately, it may be difficult to determine the Mallampati score or other components of the MACOCHA score in the medical intensive care unit. In addition, the physiology of patients in the ICU is necessarily different from that of those in the operating room, and a high level of vigilance is necessary to ensure that every intubation is performed with a backup plan for a failed airway.
Options for difficult airway management in the intensive care unit include ketamine-assisted intubations6 and awake fiberoptic bronchoscopy (FOB)-assisted intubations. Awake FOB intubations in the medical intensive care unit have been described and may be the preferred mode of intubation for critically ill patients at risk for hemodynamic collapse.7 While expert anesthesiology assistance for intubation of difficult airways in the medical intensive care unit may be the standard of care in some institutions, intensivists experienced in the use of video laryngoscopes working in hospitals with limited support staff especially during off hours may find this technique useful. The major limitation with respect to the wide applicability of this study is that the use of disposable single-use bronchoscopes is not commonplace.
In conclusion, intensivists who regularly intubate patients using video laryngoscopes would benefit from reviewing the technique described here to consider it for use in a predicted difficult airway setting. While the technique described in this paper cannot be recommended yet for routine use in difficult airway management in the intensive care unit, it remains an important “backup” for a difficult airway scenario in the right clinical setting.
Financial Disclosure: Critical Care Alert’s Physician Editor Betty Tran, MD, MSc, Nurse Planner Jane Guttendorf, DNP, RN, CRNP, ACNP-BC, CCRN, Peer Reviewer William Thompson, MD, Executive Editor Shelly Morrow Mark, Editor Jason Schneider, Accreditations Manager Amy M. Johnson, MSN, RN, CPN, and Editorial Group Manager Leslie Coplin report no financial relationships relevant to this field of study.