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Prediction of difficult intubation: are we talking about the same thing?

Rennes, France

To the Editor:

Preoperative screening to identify those patients in whom tracheal intubation could be difficult or impossible may save lives.^1–4 The existing bedside measurements of: thyromental distance, forward protrusion of the mandible, interincisor gap, atlanto-occipital extension, and the Mallampati test,² have been shown, when taken separately, to be neither sensitive nor specific for routine use. Combinations of various measurements in a multivariate model are being used in the hope of improving the ability to predict (sensitivity and specificity) difficult intubation.⁵ Despite the abundance of literature in this area (more than 1700 manuscripts referenced in the National Library of Medicine), the tools used to measure the relevant criteria are often not described.⁶ How are these measurements taken? Are any investigator-dependent -variables taken into consideration that could influence the validity of these results?⁷

To obviate these difficulties, we use a ruler (Figure) known in France (French patent no. 9103007) as "RAPIDE", an acronym that stands for Réglette d'Anesthésie Prédictive d'une Intubation DifficilE (which could be translated as Ruler for Anesthesiologists to Predict Intubation Difficulties - RAPID). Notched callipers are used to measure the interincisor gap; while pointed callipers are used to measure the thyromental distance and protrusion of the mandible. A half-protractor assists in the measurement of angulations (e.g., atlanto-occipital extension). The Mallampati views are shown for direct comparison. The mean normal values for each sex are presented on the ruler.

View larger version (108K): [in this window] [in a new window]   FIGURE Ruler for anesthesiologists to predict intubation difficulties - RAPID.

View larger version (91K): [in this window] [in a new window]   FIGURE Saline-filled LMA revealing two holes made during the stellate ganglion block (photographed by Mario Martin, Centre Universitaire de Santé de l'Estrie).

1 Wilson ME. Predicting difficult intubation. Br J Anaesth 1993; 71: 333–4.[Free Full Text]

2 Mallampati SR, Gatt SP, Gugino LD, et al. A clinical sign to predict difficult intubation: a prospective study. Can Anaesth Soc J 1985; 32: 429–34.[Medline]

3 Cormack RS, Lehane J. Difficult tracheal intubation in obstetrics. Anaesthesia 1984; 39: 1105–11.[Medline]

4 Samsoon GL, Young JR. Difficult tracheal intubation: a retrospective study. Anaesthesia 1987; 42: 487–90.[Medline]

5 Rocke DA, Murray WB, Rout CC, Gouws E. Relative risk analysis of factors associated with difficult intubation in obstetric anesthesia. Anesthesiology 1992; 77: 67–73.[Medline]

6 Horton WA, Fahy L, Charters P. Defining a standard intubating position using "angle finder". Br J Anaesth 1989; 62: 6–12.[Abstract/Free Full Text]

7 Rose DK, Cohen MM. The incidence of airway problems depends on the definition used. Can J Anaesth 1996; 43: 30–4.[Abstract/Free Full Text]

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