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Anesthesiology:
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Predicting Difficult Intubation

Rincón, David A. M.D.

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To the Editor:—

In their meta-analysis, Shiga et al.1 review the diagnostic accuracy of bedside tests for predicting difficult intubation in patients with no airway pathological features. This analysis did not take into account tests proposed by other authors, such as the upper lip bite test2 or indirect laryngoscopy,3 probably because of the exclusion criteria that were applied. The authors carried out an analysis with a Bayesian focus based on sensitivity, specificity, and likelihood ratios in which they suggest that “combinations of individual test or risk factors add some incremental diagnostic value in comparison to the value of each test alone.” This would lead us to think that the addition of likelihood ratios from various tests is useful in predicting difficult laryngoscopy. However, this focus makes two big assumptions. The first is that sensitivity, specificity, and likelihood ratios are not modified with the incidence, and the second is that the tests used to modify the probability are completely independent. Although the first assumption is not true, that is not a limitation for clinical application of this tool. However, the second assumption does not permit application of this approach to the prediction of difficult laryngoscopy, in that the tests are based on physical examination of the head and neck, which makes it impossible to suppose that they are independent. Also, the authors do not directly take into account the agreement between observers, which is another factor that interferes with the operational performance of a diagnostic test.
In addition, the evaluated outcome is only useful for predicting difficult laryngoscopy. Other studies have shown the poor correlation between the Cormack classification and difficulty in intubation.4 Given the above, it is clear that clinical research on the prediction of a difficult airway should focus on multivariable analysis to predict difficult intubation5 and difficult mask ventilation,6 which both permits the combination of interdependent tests and also evaluates outcomes with greater clinical interest.
David A. Rincón M.D.
Universidad Nacional de Colombia, Bogotá, Colombia. darinconv@unal.edu.co
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References

1. Shiga T, Wajima Z, Inoue T, Sakamoto A: Predicting difficult intubation in apparently normal patients: A meta-analysis of bedside screening test performance. Anesthesiology 2005; 103:429–37

2. Eberhart LHJ, Arndt C, Cierpka T, Schwanekamp J, Wolf H, Putzke C: The reliability and validity of the upper lip bite test compared with the Mallampati classification to predict difficult laryngoscopy: An external prospective evaluation. Anesth Analg 2005; 101:284–9

3. Yamamoto K, Tsubokawa T, Shibata K, Ohmura S, Nitta S, Kobayashi T: Predicting difficult intubation with indirect laryngoscopy. Anesthesiology 1997; 86:316–21

4. Garcia-Guiral M, Garcia-Amigueti F, Ortells-Polo MA, Muinos-Haro P, Gallego-Gonzalez J, Carral-Olondris JN: Relación entre el grado de laringoscopia y de dificultad de intubación. Rev Esp Anestesiol Reanim 1997 Mar;44:93–7.

5. Adnet F, Borron SW, Racine SX, Clemessy JL, Fournier JL, Plaisance P, Lapandry C: The Intubation Difficulty Scale (IDS): Proposal and evaluation of a new score characterizing the complexity of endotracheal intubation. Anesthesiology 1997; 87:1290–7

6. Langeron O, Masso E, Huraux C, Guggiari M, Bianchi A, Coriat P, Riou B. Prediction of difficult mask ventilation. Anesthesiology 2000; 92:1229–36

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