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Laryngoscopy technique

Created: 29/8/2004
Updated: 1/10/2010
 

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Assessment of the airway

Mallampati



The Mallampati Classification is based on the structures visualized with maximal mouth opening and tongue protrusion in the sitting position (originally described without phonation, but others have suggested minimum Mallampati Classification with or without phonation best correlates with intubation difficulty). 

S Rao Mallampati (Indian-born Boston Anaesthetist).
 
 Class I: soft palate, fauces, uvula, pillars
 Class II: soft palate, fauces, portion of uvula
 Class III: soft palate, base of uvula
 Class IV: hard palate only (later added by Samsoon and Young)

Samsoon and Young reviewed a series of obstetrical and general surgical patients who were known difficult intubations and assigned Mallampati classifications. They added a further tier (class IV = no pharyngeal structures visualized) to the Mallampati grading scheme. Samsoon observed that among patients in whom laryngoscopy was known to be difficult, class III and class IV assignments predominated. The Mallampati classification system was further evaluated by Tham who studied the effects of posture, phonation and observer on Mallampati classification. Phonation produced a marked improvement of view and a more favorable classification whereas the supine position resulted in a somewhat worse view and a higher grade assignment. Wilson developed a five factor evaluation mechanism after reviewing the features of patients who had proven to be difficult to intubate. Patient weight, head and neck movement, jaw movement, mandibular size and prominence of the upper incisors were each graded (0-2) and a rank sum score was determined. Of the five factors identified by multivariate analysis as contributing to difficult intubation, obesity was the weakest predictor.

Other predictors of difficulty


 Obesity with short neck
 Reduced neck movement (normal movement exceeds 15o).
 Reduced TMJ movement (inability to protrude the lower teeth beyond the upper, reduced mouth opening)
 Receding mandible
 Thyromental distance of less than 3 fingers (<6.5cm)

It must be borne in mind that the specificity of most predictive tests of difficult intubation is poor.

Reference:

[i] Predicting difficult intubation--worthwhile exercise or pointless ritual?
Anaesthesia. 2002 Feb;57(2):105-9. Review

Laryngoscopy view: Cormack and Lehane




This classification describes the best view possible at laryngoscopy.

 Grade I: complete glottis visible
 Grade II: anterior glottis not seen
 Grade III: epiglottis seen, but not glottis
 Grade IV: epiglottis not seen

Ronald S Cormack (London anaesthetist)
John R Lehane (Oxford anaesthetist)

Laryngoscopy technique


The straight blade is usually used for intubating neonates and infants. The blade is advanced over the posterior border of the epiglottis, which is then lifted to allow view of the larynx.



The curved blade is inserted via the right angle of the mouth and advanced gradually, pushing the tongue to the left until the tip of the blade reaches the vallecula. The laryngoscope is lifted upwards to allow the vocal cords to be seen.

References:

[i] Samsoon GLT, Young JRB: Difficult tracheal intubation: a retrospective study, Anaesthesia 42:487, 1987.
 
[ii] Tham EJ, Gildersleve CD, Sanders LD, et al: Effects of posture, phonation and observer on Mallampati classification, BJA 62:32, 1992.

[iii] Wilson ME, Spiegelhalter D, Robertson JA, et al: Predicting difficult intubation, BJA 61:211, 1988.

[iv] Bond A: Obesity and difficult intubation, Anaesth Intens Care 21:828, 1993.

ArticleDate:20040829
SiteSection: Article
 
   
    
                                            
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