Case 1.4 – Introduction to Airway Management

• Optimization of asthma
• Elevated BMI
• Procedure requires PPV and will be of approx 3hours duration
• Post-operative analgesia in presence of laparotomy wound and bowel rehabilitation

In addition to the usual information (detailed in case 1.1):

• (i) Exclude any clinical manifestation of the presenting complaint such as bowel obstruction or severe anaemia (usually an asymptomatic presentation)
• (ii) Asthma: assess severity of disease and treatment history
• (iii) Obesity: relevant to risk of difficult airway management, ease of venous access, monitoring, patient positioning and pressure area care

Airway assessment is critical prior to rendering a patient unconscious and apnoeic.

See case 1.1 for detailed airway assessment components.

(i) Assessment of severity of disease, recent stability and current status:

ie. when diagnosed, symptoms and triggers, frequency of episodes, last episode, "Are you as good as you can be?"

(ii) Treatment history:

ie. regular treatment and compliance, use of steroids, last steroid therapy, hospitalization/ICU admission/ventilation, peak flow monitoring

Regular or recent oral steroid therapy may necessitate steroid supplementation in the perioperative period.

(iii) Management goals:

• Optimize pre-op: may include increasing usual therapy or adding pulse oral steroid therapy
• Continue regular therapy
• Prevent triggers for exacerbation such as unnecessary airway manipulation and exposure to airway irritants (some volatile agents)
• Aggressive post-operative chest physiotherapy and mobilization

Liaise with Respiratory Physician as indicated.

Applies to COAD with reversible component.

The airway begins with the entry points to the oral and nasal cavities and extends to the trachea. Beyond these cavities, it is divided into the oropharynx, the nasopharynx and the hypopharynx, before becoming the larynx and trachea.

Anatomy of the Larynx

The larynx is a cylindrical structure composed of 3 unpaired (thyroid, cricoid and epiglottis) and 3 paired cartilages (arytenoid, corniculate and cuneiform). These are held together by ligaments and muscle. The functions of the larynx are to protect the entry to the trachea and enable phonation.

Innervation

Upper airway:

• CN V1 - anterior ethmoidal nerve to anterior nasal mucous membranes
• CN V2 - sphenopalatine and palatine nerves to posterior nasal mucous membranes, hard and soft palate
• CN V3 - lingual nerve to anterior 2/3 of tongue

Lower Airway:

• CN IX - glossopharyngeal nerve to the soft palate, pharynx, tonsils, vallecula
• CN X - superior laryngeal nerve to epiglottis and the vocal cords
• CN X - recurrent laryngeal nerve to larynx below the vocal cords and trachea

Airway Management is necessarily the anaesthetist's field of expertise. Following administration of drugs that render a patient apnoeic and unable to protect his/her own airway, it is critical to provide him/her with oxygenation and airway protection.

It is critical to remember that providing oxygenation to the patient is the aim, and the means by which this is achieved should always be of secondary concern. (It is very easy to become distracted by the goal of intubation when bag and mask ventilation will allow oxygenation.)

Elective airway management for general anaesthesia must take place under ideal conditions including:

• Appropriately trained assistant present
• Adjustable trolley
• Standard monitoring equipment: SpO₂, NIBP, ECG, oxygen and CO₂ analyser, breathing system disconnect/ventilation failure alarm, anti-hypoxia device
• Suction
• Access to equipment as listed below
• Established venous access (with few exceptions)
• Optimal head position "sniffing the morning air"
• Preoxygenation of patient

Essential to preparation is a clear plan that is communicated to all involved. All team members should take universal precautions for the prevention of disease transmission.

Equipment available:

• Oxygen/Gas delivery system
• Cuff syringe
• Face masks
• Devices to maintain a patent airway without endotracheal intubation: oral and nasopharyngeal airways, laryngeal mask airways (LMA)
• Endotracheal tubes (ETT)
• Laryngoscopes and blades
• Accessory devices: bougie, stylet and Magill forceps
• Advanced airway devices: video laryngoscopes, fibreoptic bronchoscopes and other supraglottic airways
• Cricothyroidotomy kit

Students should familiarize themselves with the appearance and use of this equipment in the operating theatres.

Key points:

• Standard Adult ETT sizes: male 8.0, female 7.0
• Standard adult LMA sizes: male 4-5, female 3-4
• Standard adult laryngoscope blade: Macintosh 3
• Nasal airway/intubation is contraindicated in patients with a bleeding diathesis

Indications for endotracheal intubation:

• Protection of the respiratory tract from aspiration
• Requirement for PPV
• Long duration of surgery
• Secure the airway in various surgical positions, or when surgery is in close proximity to the airway
• Control PaCO₂
• Require tracheobronchial toilet
• Lung isolation
• Respiratory failure

Following intravenous induction, unconsciousness and apnoea is confirmed in the patient before beginning face mask ventilation. This will continue until enough time has elapsed for the muscle relaxant to take effect and provide optimal intubating conditions. During this time, the patient is ventilated with 100% O₂ and volatile agent to maintain anaesthesia.

The laryngoscope is taken with the left hand, passed down the right hand side of the patient's oral cavity to sweep the tongue to the left. Simultaneously, pressure is applied toward the patient's toes to expose the larynx.

Once the optimum view is obtained, the ETT is taken with the right hand and passed between the vocal cords up to the indicator line on the ETT. The cuff is then inflated and the circuit connected to the ETT. Cuff volume should be the minimum volume that prevents audible leak at ventilation pressures between 25 to 30cm H₂O for adults.

Confirmation of correct ETT placement

• Visualise ETT pass through the vocal cords
• Observe chest rise and fall with bag ventilation
• Confirm appropriate end-tidal CO₂ wave-form
• Confirm bilateral and equal breaths sounds on chest auscultation
• Check peak inspiratory pressures

Note length of ETT at teeth and secure ETT.

Potential Complications of Endotracheal Intubation

• Malpositioning: oesophageal or endobronchial intubation, unintentional extubation
• Airway Trauma: dental damage, lacerations, sore throat, vocal cord injury/granuloma, nerve palsies
• Physiologic Responses: hypertension, tachycardia, laryngospasm, raised intracranial and intraocular pressure
• ETT malfunction: cuff tear or herniation
• Cuff injury: tracheal mucosal ulceration/ischaemia