Summary
Difficult intubation has been classified into four grades, according to the view obtainable at laryngoscopy. Frequency analysis suggests that, in obstetrics, the main cause of trouble is grade 3, in which the epiglottis can be seen, but not the cords. This group is fairly rare so that a proportion of anaesthetists will not meet the problem in their first few years and may thus be unprepared for it in obstetrics. However the problem can be simulated in routine anaesthesia, so that a drill for managing it can be practised. Laryngoscopy is carried out as usual, then the blade is lowered so that the epiglottis descends and hides the cords. Intubation has to be done blind, using the Macintosh method. This can be helpful as part of the training before starting in the maternity department, supplementing the Aberdeen drill.
A photographic version of the Mallampati test was developed and applied to 242 pregnant patients at 12 weeks' gestation and again at 38 weeks' gestation. At 38 weeks the number of grade 4 cases had increased by 34% (P < 0.001). This is in agreement with other evidence which suggests that difficult laryngoscopy is slightly more frequent in obstetrics (1.7%) than in general surgery (1.3%). The increase in Mallampati score correlated with gain in body weight (r = 0.3, P < 0.001), which gives some support to the concept that fluid retention is the underlying cause. We conclude that pharyngeal oedema causes some hindrance to tracheal intubation in obstetrics, but not enough to explain the high failure rate reported. A case is made for rationalizing the management of difficult intubation. Our data also show that more research is needed on factors which affect Mallampati's test, particularly neck extension.
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