Airway assessment Dr James Hayward SHO Anaesthetics Worthing

Introduction Respiratory events are the most common anaesthetic related injuries, following dental damage. Three main causes: Inadequate ventilation Oesophageal intubation Difficult tracheal intubation Difficult tracheal intubation accounts for 17% of the respiratory related injuries and results in significant morbidity and mortality. Estimated that up to 28% of all anaesthetic related deaths are secondary to the inability to mask ventilate or intubate. Prediction of the difficult airway allows time for proper selection of equipment, technique and personnel experienced in difficult airways

Airway Nasal and oral cavities Pharynx Larynx Trachea and large bronchi

Difficult airway ASA definition of difficult airway: “The clinical situation in which a conventionally trained anaesthetist experiences difficulty with mask ventilation, difficulty with tracheal intubation or both.”

Difficult ventilation The inability of a trained anesthetist to maintain the oxygen saturation > 90% using a face mask for ventilation and 100% inspired oxygen, provided that the pre-ventilation oxygen saturation level was within the normal range.

Difficult intubation More than 3 attempts Longer than 10 minutes Failure of optimal best attempt

Predictors of difficulty to face mask ventilate (OBESE) The Obese (body mass index > 26 kg/m2) The Bearded The Elderly (older than 55 y) The Snorers The Edentulous

Prevalence Difficult face mask Difficult LMA Difficult intubation 0.1% - 5% Difficult LMA 0.2% - 1% Difficult intubation 1-2% of normal surgical population 50% of rheumatic cervical disease

Causes of difficult airway Stiffness Arthritis of neck/jaw/larynx. Fixation devices Scleroderma Diabetes Deformity Cervical and craniofacial Burns/trauma/infection Swelling Infection/tumour/trauma/burns Anaphylaxis/haematoma/acromegaly Reflexes Cough/breathholding Laryngospasm/salivation/regurgitation Foreign body Other – Pregnant/full stomach/VIP

Airway assessment History General examination Specific tests Patient/notes/chart/medic-alert/spam letter Difficulty Surgery/burns Concurrent disease Reflux/recent meals General examination Do they just look difficult? Dentition (prominent upper incisors, receding chin) Distortion (edema, blood, vomits, tumor, infection) Disproportion (short chin-to-larynx distance, bull neck, large tongue, small mouth) Dysmobility (TMJ and cervical spine) Massively obese or pregnant Beards +/- tubes Specific tests Investigations. Nasoendoscopy X-ray CT/MRI Flow volume loop

Mallampati Score Sensitivity: 44% - 81% Specificity: 60% - 80% Roughly corresponds to Cormack and Lehane’s laryngoscopy views Class I (easy)—visualization of the soft palate, fauces, uvula, and both anterior and posterior pillars Class II—visualization of the soft palate, fauces, and uvula Class III—visualization of the soft palate and the base of the uvula Class IV (difficult)—the soft palate is not visible at all This scoring system was first introduced in 1985 in the Canadian Anesthesia Society Journal based on the work of Mallampati. Place the patient in a seated position and have them hold head in a neutral position with mouth open wide and the tongue fully extended. MENTION MODIFIED -

Thyromental distance Measure from upper edge of thyroid cartilage to chin with the head fully extended. Normal is approx 7cm Relatively unreliable test unless combined with other tests. Grade 3 or 4 Mallampati who also had a thyromental distance of less than 7cm were likely to present difficulty with intubation. Sensitivity: 90.9% Specificity: 81.5% Thyromental distance A short thyromental distance equates with an anterior larynx that is at a more acute angle and also results in less space for the tongue to be compressed into by the laryngoscope blade. This is a measurement taken from the thyroid notch to the tip of the jaw with the head extended. The normal distance is 6.5cm or greater and is dependant on a number of anatomical factors including the position of the larynx. If the distance is greater than 6.5cm, conventional intubation is usually possible. If it is less than 6cm intubation may be impossible [3]. By combining the modified Mallampati and thyromental distance, Frerk showed that patients who fulfilled the criteria of Grade 3 or 4 Mallampati who also had a thyromental distance of less than 7cm were likely to present difficulty with intubation [4]. Frerk suggests that using this combined approach should predict the majority of difficult intubations. A 7cm marker can be used (eg a cut off pencil or an appropriate number of examiners fingers) to determine whether the thyromental distance is greater that 7cm.

Atlanto-occipital movement The patient is asked to hold head erect, facing directly to the front, then he is asked to extend the head maximally and the examiner estimates the angle traversed by the occlusal surface of upper teeth. Visual assessment or using a goniometer. Grade I >35 degrees Grade II 22-34 degrees Grade III 12–21 degrees Grade IV <12 degrees Assesses feasibility to make the optimal intubation position with alignment of oral, pharyngeal and laryngeal axes into a straight line. Limited A-O joint extension Spondylosis, rheumatoid arthritis, halo-jacket fixation, and in patients with symptoms indicating nerve compression with cervical extension. Atlanto-Occipital Joint Distance Atlantooccipital joint extension may be measured when the head is held erect and facing forward. The angle between the erect and extended planes of the occlusal surface of the upper teeth is measured and equals the degree of atlantooccipital joint extension. The "normal" amount of extension equals 35 degrees. Almost all extension of the head on the neck takes place at the atlantooccipital joint. The atlas or the first cervical vertebra is a ring of bone. It does not have a body or spine which would hamper the backward movement of the head. Therefore the greater the atlantooccipital distance in the neutral position, the greater degree of extension that is possible Conversely, if the occiput and the atlas are already in contact in the neutral position, no extension can take place at the atlantooccipital joint. Because there is a wide variation in atlantooccipital joint distance in the population, it is important to assess head extension at the atlantooccipital joint. Additionally, limited A-O joint extension is present in certain pathological states such as spondylosis, rheumatoid arthritis, halo-jacket fixation, and in patients with symptoms indicating nerve compression with cervical extension. In these patients, it is even more important than usual to raise the occiput above the shoulders prior to laryngoscopy. Check neck extension on to the chest. Limitation of neck extension (< 30 degrees) may interfere with the sniffing position and limit the laryngoscopic view

Further assessments Sterno-mental distance Mandibular protrusion Measured from the sternum to the tip of the mandible with the head extended. A sternomental distance of 12.5cm predicts a difficult intubation. Mandibular protrusion If the patient is able to protrude the lower teeth beyond the upper incisors intubation is usually straightforward If the patient cannot get the upper and lower incisors into alignment intubation is likely to be difficult.

Wilson’s risk score Score Weight 0=<90kg 1=>90kg 2=>110kg Head and neck movement 0=Above 90degrees 1=About 90degrees 2=Below 90degrees Jaw movement 0=IG>5cm or SLux >0 1=IG<5cm and SLux = 0 2=IG<5cm and SLux<0 Receding mandible 0=Normal 1=Moderate 2=Severe Buck teeth Head movement assessed with pencil taped to a patient’s forehead. IG = Interincisor gap measured with mouth fully open. SLux = Maximal forward protrusion of the lower incisors beyond the upper incisors.

Results 633 Patients

LEMON trial 156 A+E patients Look Evaluate 3-3-2 Mallampati 114 Grade I 42 Grade II and above Look Facial trauma Large incisors Beard Large tongue Evaluate 3-3-2 Interincisor distance (3 fingers) Hyoidmental distance (3 fingers) Thyroid to floor of mouth (2fingers) Mallampati Obstruction Neck movement – chin to chest US national emergency airway management course devised score

Results No significant difference Sex Age Facial trauma (11.3% vs 12.2%) Large tongue (1.0% vs 4%) Hyoid to chin (35% vs 45%) Mallampati score (p=0.41) Airway obstruction (6.5% vs 14.3%) Neck mobility (16.2% vs 28.6%)

Results (2) Significant difference Comments Large incisors (6.5% vs 28.6%, p<0.001) Reduced inter-incisor difference (38.2% vs 69%, p<0.05) Reduced thyroid to floor of mouth difference (13.4% vs 41.2%, p<0.05) Total correlated with difficulty (r=0.38, p<0.001) Comments Easy to remember and simple. Look criteria Definition of “difficult intubation”

Intubation Equipment TRAINED ASSISTANT Laryngoscopes with a selection of blades Variety of endotracheal tubes Introducers for endotracheal tubes (stylets or flexible bougies) Oral and nasal airways A cricothyroid puncture kit Reliable suction equipment Laryngeal mask airways, sizes 3 AND 4 The safety of laryngoscopy can be increased by preoxygenating the patient prior to induction and attempts at intubation. Intubation is attempted by optimal direct laryngoscopy; optimal head and neck positioning optimal muscle relaxation optimal laryngoscope blade optimal external laryngeal manipulation optimal use of the bougie After intubation correct placement of the tube should be confirmed by: Observing the tube pass through the cords Successful inflation of the chest on manual ventilation Auscultation over both lung fields in the axillae Capnograph If in doubt – take it out Notes: Intubation is attempted by optimal direct laryngoscopy and this has 5 components; - optimal head and neck positioning - optimal muscle relaxation - optimal laryngoscope blade - optimal external laryngeal manipulation - optimal use of the bougie A number of intubation attempts may be undertaken - to change the blade (long, straight McCoy etc), to use the bougie or to apply optimal external laryngeal manipulation. After 3-4 attempts at intubation, it is likely that the practitioner is repeating fruitless attempts and no further attempts should be made. Correct positioning of the tube in the trachea (rather than oesophagus) should always be verified after intubation preferably by two out of the 3 best techniques of visual confirmation of the tube passing through the glottic aperture, six consecutive normal capnograph traces and inflation of the oesophageal detector device. No anaesthetist in the UK is ever expected to anaesthetise without using a working capnograph. It is a deliberate act to stop attempts at direct laryngoscopy, announcing to your assistant 'Failed direct laryngoscopy'. This stops you having yet another attempt and alerts your assistant that you will be going on to Plan B. Start facemask ventilation and ask for a laryngeal mask. Ask for assistance. Go to plan B.

References Practice guidelines for management of the difficult airway: an updated report by the American Society of Anesthesiologists Task Force on Management of the Difficult Airway. Anesthesiology 2003; 98 (5):1269-77 Frerk CM. Predicting difficult intubation. Anaesthesia 1991; 46 (12):1005-8 Verghese C, Brimacombe JR. Survey of laryngeal mask airway usage in 11,910 patients: safety and efficacy for conventional and nonconventional usage. Anesth Analg 1996; 82: 129–33 Gupta S, Sharma R, Jain D. Airway assessment – Predictors of a Difficult Airway. Indian Journal Of Anaesthetics 2005; 49(4) : 257 -262 Wilson M, Spiegelhalter D, Robertson A, Predicting difficult intubation. Br. J. Anaesth. (1988), 61, 211-216 The Difficult Airway Society Website: WWW.DAS.UK.COM Reed M, Dunn M, McKeown D. Can an an airway assessment score predict difficulty at intubation in the emergency department. Emerg Med J 2005;22:99–102.