Indirect laryngoscopy and soft tissue neck radiographs as predictors of direct laryngoscopic view

ABSTRACT

Prediction of difficult intubation markedly reduces the incidence of anesthesia related morbidity and mortality, several protocols and examination techniques were suggested by investigators, none is fault-proof, and many are expensive. Aim of the study was to examine whether there is correlation between the laryngoscopic grade on direct laryngoscopy and that on indirect laryngoscopy, and if there is correlation between the laryngoscopic grade and two proposed radiological parameters on soft tissue neck radiographs, aiming to find a cheap and reliable mode of preoperative determination of direct laryngoscopic view, Fifty consecutive ASA I or II adult patients scheduled for otolaryngologic procedures under general anesthesia were enrolled into this study. Recruited subjects underwent preanesthetic evaluation of the airway that comprised 1] indirect mirror laryngoscopy by the otolaryngologist to score the laryngeal view. [2] clinical examination of the airway by the anesthesiologist to determine the Mallampati class, the thyromental distance [TMD], and the sternomental distance [SMD], [3] A lateral-view soft-tissue radiograph of the neck to determine two radiological parameters, viz, the distance between the posterior-most point of the hard plate and the superior-most point of the epiglottis [Radiological Parameter A], and the angle between the plane of the epiglottis and the plane of the vocal folds [Radiological Parameter B]. After induction of general anesthesia and skeletal muscle relaxation, the direct laryngoscopic view was scored according to the Cormack-Lehane classification. All laryngoscopies were conducted by the same anesthesiologist, who was blinded to the information obtained by indirect laryngoscopy or by neck radiographs. There was moderate correlation between the laryngoscopic grade on direct laryngoscopy and that on indirect laryngoscopy [rho = -0.618, P < 0.001. There was only mild correlation between Radiological Parameter A and both the direct [rho = -0.346, P < 0.05] and the indirect [rho = -0.337, P < 0.05] laryngoscopic grades. On the other hand, there was high correlation between Radiological Parameter B and the direct laryngoscopic grade [rho = -0.777, P M 0.001], and a moderate correlation between that parameter and the indirect laryngoscopic grade rho = - 0.574, P < 0.001]. A moderate correlation was demonstrated between the direct laryngoscopic grade and the Mallampati class [rho = -0.64, P < 0.001], the TMD [rho = - 0.94, P M 0.0021], and the SMD [rho = -0.564, P < 0.001]. On the other hand, a high correlation was demonstrated between the indirect laryngoscopic grade and he Mallampati class [rho = -768, P < .01], the TMD [rho = -0.713, P < 0.01], and the SMD [rho = -0.747, P < 0.001]. It was concluded that anticipation of difficult laryngoscopy may be enhanced by an integrated approach combining a comprehensive clinical examination of the airway with simple diagnostic aids, which can readily be applied in the clinical setting. In this respect, both indirect laryngoscopy and a plain soft-tissue radiograph of the neck may act as valuable assets to the anesthesiologist