The decision to use neuromuscular blockade for emergency intubation hinges on the provider’s bedside assessment of difficulty with either laryngoscopy or rescue mask ventilation. If significant difficulty is predicted and laryngoscopy, intubation, or mask ventilation is not expected to be successful, then neuromuscular blockers are often withheld to avoid a failed airway situation.
The LEMON Assessment
Although videolaryngoscopy (VL) has largely eliminated the specter of difficult laryngoscopy, many providers still do not have reliable access to VL and rely on conventional laryngoscopes for airway management. The LEMON assessment (L = Look externally, E – Evaluate the 3:3:2 rule, M = Mallampati score, O = Obstruction, N = Neck mobility) was first described by Walls and Murphy in 2000 as a bedside screening tool to identify patients who might be challenging with direct laryngoscopy (DL).1 Until recently, only one emergency department–based validation study existed.2
Recent operating room registry data suggest that bedside assessments done by anesthesiologists have limited predictive capability.3 Performance of the modified LEMON assessment (LEMON without Mallampati or thyromental distance) in predicting difficult intubation was recently reported from a multicenter Japanese registry of emergency department patients who underwent DL.4 In this study of 3,313 patients with a first attempt performed with DL, the modified LEMON assessment had a sensitivity of 86% and a negative predictive value of 98%. The definition of “difficult intubation” was any patient requiring two or more intubation attempts. The bottom line is that the LEMON assessment is quick, easy, and free! If a patient has a completely normal LEMON assessment, then intubation is unlikely to be challenging and neuromuscular blockade can be used as part of rapid-sequence intubation.
1. Walls RM, Murphy ME, Manual of emergency airway management. 4th ed, Philadelphia: Lippincott Williams & Wilkins; 2012. 8–21.
2. Reed MJ, Dunn MJ, McKeown DW. Can an airway assessment score predict difficulty at intubation in the emergency department? Emerg Med J 2005;22:99–102.
3. Norskov AK, Rosenstock CV, Wetterslev J, et al. Diagnostic accuracy of anaesthesiologists’ prediction of difficult airway management in daily clinical practice: a cohort study of 188 064 patients registered in the Danish Anaesthesia Database. Anesthesia 2015;70:272–81.
4. Hagiwara Y, Watase H, Okamoto H, et al. Prospective validation of the modified LEMON criteria to predict difficult intubation in the ED. Am J Emerg Med 2015;33:1492–6.
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Written by Calvin A Brown III, MD
Assistant Professor, Harvard Medical School, Director of Faculty Affairs, Department of Emergency Medicine, Brigham and Women’s Hospital, Boston, MA