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Department of Anesthesia University of Iowa College of Medicine Iowa City, IA
To the Editor:
I read with interest the case report by Kanaya et al. (1). I agree with the authors that the three-dimensional computed tomography (3D-CT) imaging may be useful in assessing the airway of selected patients with known or suspected airway distortion. Their reported patient had undergone total thyroidectomy six years earlier. The authors did not mention why (I suspect because of carcinoma of the thyroid) or whether he had received radiotherapy.
Recently, my colleagues and I tried to identify the variables most useful in predicting difficult laryngoscopy and intubation from various clinical, skeletal (lateral radiographs), and soft tissue (3D-CT imaging) measurements (2). We applied multivariate discriminant analysis to the data collected from a group of confirmed difficult laryngoscopies and intubations (n = 24) and a control group (n = 32). Our analysis indicated that the measurements derived from 3D-CT imaging did not improve the predictability of our models.
We developed two models for prediction; one model is based on clinical measurements only, and the second is based on clinical measurements and one radiologic measurement (2). In the clinical model, we have identified four risk factors that correlated with the predication of difficult laryngoscopy and intubation: thyrosternal distance, thyromental distance, neck circumference, and Mallampati classification. This clinical model is 95.4% sensitive and 91.2% specific, with a positive predictive value of 87.5% (2).
References
Department of Anesthesiology Sapporo Medical University School of Medicine Sapporo, 060-8543 Japan
In response
We appreciate the interest and comments of Dr. Naguib regarding our case report (1). The patient probably received postoperative radiotherapy. However, details of the therapy were not clear because the treatment was done in another hospital 6 yr ago.
Dr. Naguib suggested that a combination of clinical and radiologic tests improved prediction of difficult intubation (2). We agree with Dr. Naguib that increasing preoperative tests results in higher prediction rates for difficult intubation. However, despite careful preoperative evaluation, difficulties will not be predicted in some instances. Thus, most importantly, strategies to manage the unanticipated difficult airway should be preformulated and practiced.
Dr. Naguib also pointed out that the measurements derived from the 3D-CT images did not improve the predictability of their models (2). Three factors could have been responsible for this result. First, the 3D-CT image is not appropriate for dynamic and qualitative airway assessment because we are unable to estimate the stretching of soft tissue. Therefore, the 3D-CT is useful when airway distortion is evident (3). Second, Dr. Naguib et al. (2) did not mention how they perform the 3D-CT scanning. In our study, to simulate an intubating position, the patient was asked to open his mouth fully and extend his tongue as much as possible. Third, in our study, the patient’s airway was superimposed over translucent images of bones. This image allowed us to evaluate the airway more precisely, including its relationship to surrounding tissue.
References
This article has been cited by other articles:
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  K. O. Schoenhage and H. M. Koenig Unanticipated difficult endotracheal intubations in patients with cervical spine instrumentation. Anesth. Analg., March 1, 2006; 102(3): 960 - 963. [Abstract] [Full Text] [PDF]
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