Australasian Anaesthesia 2011 - Australian and New Zealand ...

60 Australasian Anaesthesia 2011Reappraisal of Adult Airway Management 61ASSESSMENT OF THE ANTERIOR COLUMN:This may be divided into the following:• Volume of the submandibular space• Compliance of the submandibular tissues• Tethering of the inverted triangular pyramid (Anterior Column) at one or more of its apices:– One or both Temporomandibular joints (TMJs) – mechanical “locking” of the TMJ (e.g. zygomatic fractureinvolving TMJ)– Hyoid – bilateral calcification of the stylohyoid ligamentVOLUME OF THE SUBMANDIBULAR SPACEAbsolute reduction in volume –The volume of the Anterior Column is assessed by measuring the three sides of the inverted triangular pyramid(TMJ-incisor, incisor-hyoid and TMJ-TMJ).• TMJ-incisor distance correlates with short mandibular length or retrognathia• Reduction in the incisor-hyoid distance is related to short thyromental distance• Reduced TMJ-TMJ distance is associated with a narrow palateRelative reduction in volume –• Large tongue (e.g. macroglossia that occurs in acromegaly)• Prominent upper front incisors requiring more mandibular protrusion during direct laryngoscopyCOMPLIANCE OF THE SUBMANDIBULAR TISSUESAssessment of submandibular compliance remains largely qualitative based on a history of conditions that maypredispose to low compliance. These include previous radiotherapy to the submandibular area, neck masses,haemorrhage or infection involving the submandibular space and severe burns to the neck and jaw. No convenientobjective measurement of submandibular compliance has so far been reported.Figure 3. History, physical examination and investigations for airway assessment based on the ThreeColumn Model for Direct Laryngoscopy (elements of Model in clear boxes, airway assessment tests inshaded boxes)– full explanation of this figure is found in the original publication in Anaesthesia and Intensive Care30TMJ – temporomandibular jointStaticAirwayPosteriorMiddleLimitedoccipito-atlantoaxialcomplexAirway problemsHistory of currentAirway imagingX-ray, CT Scan,Naso-Short Incisor-hyoid(short thyromental)ASSESSMENT OF THE MIDDLE COLUMN:Assessment of the Middle Column or airway passage for conditions, such as laryngeal tumours and lingual tonsillarhypertrophy, 31 follows a well-established pathway including 1) an adequate history and physical examination, 2)imaging of the airway passage and 3) nasopharyngoscopy. Reliable clinical assessment of the Middle Columnremains elusive when the airway proves unexpectedly difficult to manage, and continues to demand a high degreeof expertise. The effect of changes in tone of the airway musculature and the dynamic effects of positive pressureventilation are difficult to accurately predict during anaesthesia.Model forDirectAbsoluteShort TMJ-incisordistanceShort TMJ-TMJdistanceASSESSMENT OF THE POSTERIOR COLUMN:Measurement of the range of movement of the cervical spine and the ability of the patient to achieve a sniffingposition assesses the Posterior Column. Evaluation of neck and head movement was described by Wilson andco-workers. 32,33 The subject fully extends the head and neck. A pencil is placed flat on the forehead and the patientis asked to fully flex while the observer measures the change of angle in reference to a fixed point. This is thendivided into greater or less than 80°.SUMMARY OF AIRWAY ASSESSMENT BASED ON THE THREE COLUMN MODEL FOR DIRECTLARYNGOSCOPYAirway assessment studies have shown that the more individual tests performed, the better the chance of difficultairway prediction. 34-36 Importantly, when tests assessing Anterior, Middle and Posterior Columns (figure 3) are allincluded, the correlation with difficult intubation is closest. 34,35,37 The relationship of the three columns is shown infigure 3. Notably, the Middle Column is shown between the Anterior and Posterior because changes in the lattertwo have a direct effect on the airway passage. This relationship is discussed further in the next sections wherethe combination of the Theory and the Model is considered in the clinical setting.Volume ofsubmandibularCompliance ofsubmandibularRange ofmovementRelativeProminent upperLarge tongue(MallampatiLow complianceof submandibularLimited mouthDynamicAnteriorRange ofmovement ofstylo-hyoidRestrictedmovement ofPoor mandibularprotrusion in front