Airway Assessment Flashcards
What is the purpose of an airway assessment prior to induction of anaesthesia?
To identify potentially problematic:
- Difficult laryngoscopy
- Difficult BMV
- Difficult percutaneous airway
What are the three basic decisions needed before induction of anaesthesia in every patient?
- Awake v asleep
- Standard v Percutaneous
- Spont vent v apnoea
What tests predict difficult laryngoscopy?
- Inter-incisor distance <4cm
- Mandibular prognathism
- Occipito-atlanto-axial extension
- Malampati (limited value)
- Thyromental distance (Limited value)
How common is the difficult airway?
Intubation is difficult in 1/50, impossible in 1/2000 (up to 1/300 in emergencies/pregnancy).
BMV is difficult in 1/20, impossible in 1/1500.
Most common cause of anaesthesia-related mortality (30%).
What diseases are associated with difficult airway management?
Congenital: Trisomy 21 Pierre-Robin Klipp-Feil Treacher-Collins
Acquired: Obesity Pregancy Rheumatoid Arthritis Ank Spond Acromegaly Local infections (eg Ludwig Angina)
Iatrogenic:
Radiotherapy
Cervical Fusion
Laryngeal surgery
How accurate are predictors of difficult intubation?
Poorly sensitive (<5% of predicted difficult airways actually are)
What are the markers of difficult BMV? How sensitive are they?
Oxford Handbook lists five factors, any two of which have >70% sensitivity and specificity:
- Age>55
- BMI >26
- Snoring
- Beard
- Absence of teeth
BOAST (Beard obesity age snoring teeth)
What is the sensory innervation of the upper airway?
Nasal cavity: Greater and lesser palatine nerves (ophthalmic and maxillary brs CN V) and anterior ethmoidal nerve (CN I)
Oropharynx: maxillary br CN V (sensation anterior 2/3 tongue, taste from CN VII); glossopharyngeal (posterior 1/3 tongue)
Laryngopharynx via vagus:
• Superior laryngeal nerve: external (motor to inferior pharyngeal constrictor) and internal (sensation to larynx above vocal cords) laryngeal brs
• Recurrent laryngeal nerve: intrinsic laryngeal mm and visceral sensation below vocal folds
Gag reflex afferent arc is glossopharyngeal nerve and efferent arc is vagus nerve (pharyngeal branches).
What premedication is required prior to fibreoptic intubation?
- Anti-sialagogue (glycopyrrolate 0.4mg IV) – improves visualisation via scope and improved penetration of topicalised LA
- Sedatives – rapid offset and easily reversed agents are ideal for potential loss of airway with sedation (midazolam, dexmedetomidine - no resp depression, fentanyl or alfentanil)
What techniques for anaesthetising the airway exist?
- Topical gels and sprays (upper airway)
- Nebulisers (entire airway)
- Spray as you go (larynx and trachea)
- Nerve blocks (particular distributions)
What type of LA would you use, method, and the pros and cons of topicalised LA to the airway?
• Lignocaine 2-4% (or lignocaine-phenylephrine spray for nasal intubation to prevent epistaxis)
• Methods
o Nebuliser: patient inhales deeply for 15-30min (results in blood levels much lower than 5mg/L)
Pros: simple
Cons: variable density of anaesthesia with intact cough reflex and requires pt to comply with deep breathing (difficult with obstructed airway).
o Atomisation: spray as you go; uses venturi effect
o Transtracheal injection through cricothyroid membrane via 22G IVC
Pros: quickly produces excellent subglottic topical anaesthesia which is spread superiorly by coughing
Con: invasive; need to ensure needle out prior to injection or risk injury during cough
What individual airway nerve blocks can be performed to assist with airway instrumentation?
• Need bilateral blockade for intubation using laryngoscope or fibreoptic scope
• Glossopharyngeal nerve block – posterior oropharynx, tongue and pharyngeal surface of epiglottis blocks afferent arc of gag reflex.
o Intraoral approach:
Topicalise the tongue
22G needle places 5ml LA with adrenaline submucosally at caudal aspect of tonsillar pillar
Aspiration prior to injection as close to carotid a
o Not adequate as a solo technique due to deep pressure and lack of motor blockade
• Superior laryngeal nerve block – internal branch blocks sensation to remaining laryngopharyngeal structures and passes 2-4mm inferior to greater cornu of hyoid bone.
o Supine with head extended
o Prep with alcowipe
o Identify greater cornu of hyoid by palpating laterally along upper borders of thyroid cartilage
o 25G needle inserted anteroinferomedially to contact cornu of hyoid then walked down to pierce thyrohyoid membrane OR contact superior border thyroid lamina (2cm lateral to thyroid notch) and walk upwards
o Inject 2ml 2% lignocaine after aspirating for blood or air
o Contradindicated if pt refuses, anticoagulation or distorted anatomy
o May also be performed non-invasively post topicalisation by grasping tongue and placing LA-soaked pledgets into pyriform fossa on either side of the root of tongue for 5-10 min.
• Recurrent laryngeal nerve block – vocal folds and trachea
o Direct blockade of recurrent laryngeal nerve contraindicated as it provides motor innervation for all laryngeal mm except cricothyroid.
o Transtracheal injection using 20 or 22G needle, aspirating for air then injecting quickly and withdrawing needle. Coughing spreads LA cranially and motor function remains intact.
Risk factors for dental damage:
o Patient Dental pathology or prostheses Abnormal jaw alignment Isolated teeth o Anaesthetic RSI Difficult airway Macintosh blade Oropharyngeal airway
Management of dental trauma during airway management:
o Immediate mx: Locate tooth fragment to prevent aspiration and assess if dentine or pulp exposed, will need urgent dental referral
o Open disclosure to pt re nature of injury, attempts to prevent
o Obtain medicolegal advice from insurer / hospital risk manager
o Refer to dentist (do not offer to pay)
o Documentation
Factors predisposing to aspiration
• Patient o Unfasted/delayed gastric emptying o Obese, pregnancy o GIT: GORD; hiatus hernia; intestinal obstruction o Neuro: Loss of upper airway reflexes – stroke, sedation, etc o Advanced age • Surgical o Abdominal or laparascopic surgery o Trauma o Steep Trendelenburg position • Anaesthetic o Difficult BMV gastric insufflation o Insufficient depth of anaesthesia o No cuffed ETT o Drugs: opioids, anticholinergics and GA agents LOS tone
