Straight blades improve visualization of the larynx while curved blades increase ease of intubation: a comparison of the Macintosh, Miller, McCoy, Belscope and Lee-Fiberview blades

Abstract

To compare the Macintosh (M), McCoy (MC), Miller (MIL), Belscope (BP) and Lee-Fiberview (LF) laryngoscopes with respect to the grade of laryngeal visualization and the difficulty of intubation. We included 500 patients scheduled to undergo elective surgery and who required tracheal intubation. Patients were randomly assigned to five groups of 100 patients each. Anesthesia was induced intravenously using 1-3 mg.kg(-1) of propofol, fentanyl 1.5 microg.kg(-1) and atracurium 0.5 mg.kg(-1) or suxamethonium 1 mg.kg(-1). The laryngeal view was classified according to Cormack and Lehane. The degree of difficulty with intubation was rated as: Grade 1, intubation easy; Grade 2, intubation requiring an increased anterior lifting force and assistance to pull the right corner of the mouth upwards to increase space; Grade 3, intubation requiring multiple attempts and a curved stylet; Grade 4, failure to intubate with the assigned laryngoscope. Data were examined using analysis of variance, chi(2) or Fisher test, Student's t test and odds ratio. P < 0.05 was considered statistically significant. Laryngoscopic views obtained with the BP and MIL laryngoscopes were similar, and better than with the other types of laryngoscopes (P < 0.001). The levering tip of the MC blade (P = 0.02) and the fibreoptic device of the LF (P < 0.001) significantly improved the laryngoscopic view. Regarding the degree of difficulty with intubation, the best results were obtained with the MC and M blades (P < 0.001). Laryngoscopy was better with straight blades but curved blades provided better intubating conditions.