Securing the airway, ventilation and procedural sedation

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Chapter 2 Securing the airway, ventilation and procedural sedation

Paul L. Gaudry, Andrew Finckh, Judy Alford

SECURING THE AIRWAY

(Paul Gaudry)

Assessment and stabilisation of the airway have priority over other aspects of resuscitation in patients with life-threatening illness or injury.

Differences between the airway anatomies of children and adults

The anatomy of the airways of infants and young children differs significantly from that of older children and adults in ways that are relevant to airway management:

1. larger and more mobile head, which tends to flex the neck in the supine position
2. larger tongue, more prominent oropharyngeal tonsils and larger epiglottis
3. higher and more anterior larynx in an infant (cervical vertebrae 3–4) than in a child or an adult (cervical vertebrae 5–6)
4. narrowest at cricoid cartilage rather than at vocal cords
5. smaller diameter and shorter length of trachea
6. small amounts of mucosal swelling producing large effects on airway resistance.

Causes of airway obstruction and respiratory failure

1. Decreased level of consciousness (cerebrovascular accident, seizure, infection, poisoning, head injury, near-drowning)
2. Trauma (maxillofacial fractures, blunt and penetrating neck injuries, laryngotracheal and bronchial rupture, chest injury, spinal cord injury)
3. Burns (face and neck burns, inhalational burns)
4. Foreign bodies (supraglottic, trachea, bronchus, oesophagus)
5. Infection (peritonsillar abscess, retropharyngeal abscess, epiglottitis, croup, pneumonia)
6. Inflammation (angioneurotic oedema, caustic ingestion, asthma, aspiration pneumonitis, parenchymal lung disease)
7. Shock (haemorrhagic, septic, anaphylactic, spinal)
8. Tumours (pharynx, larynx, trachea, bronchus)
9. Generalised weakness (neuropathies, myopathies)
10. Congenital anomalies in children (vascular ring)

Assessment and anticipation of airway obstruction

Establish whether the airway is patent and protected, threatened, or partially or completely obstructed. A patent airway is an absolute first priority. Protection from aspiration is only a relative priority and does not take priority over initial assessment and treatment of the patient’s breathing and circulation.

1. Observe and listen for air movement and the rate and depth of respirations (at the mouth and nose, movement of the chest wall, presence of tracheal tug).
2. Listen for noisy or abnormal sounds (gurgling, snoring, choking, coughing, stridor, wheeze).
3. Assess the sound and quality of the voice (weak, painful, hoarse).
4. Determine the level of consciousness (Glasgow Coma Scale score).
5. Inspect the mouth for foreign body.
6. Test the tone of the jaw, mouth and oropharyngeal muscles.
7. Test the gag reflex.
8. Feel the maxillofacial and neck regions (swelling, deformity, subcutaneous emphysema).

Factors confounding airway management

Shape of face. A poor seal between the face and mask impedes bag-valve-mask ventilation. Causes are a beard, edentia, emaciation, obesity, facial trauma and burns.

Difficult airway anatomy. Impedes direct laryngoscopy and endotracheal intubation. Evaluate the anatomy before both elective and emergency endotracheal intubation. Focus on protruding maxilla relative to mandible (macrognathia), high arched palate, poor dentition, large tongue (macroglossia), short neck, limited mouth opening (intercisor gap). Test for neck mobility if cervical spine injury is not an issue. A sternomental distance less than 12.5 cm in an adult is the best predictor of ‘difficult’ intubation. Remember the airway anatomy of children relative to adults. Anticipate ‘difficult’ intubation in certain congenital syndromes such as Down syndrome and Pierre Robin syndrome.

Upper airway obstruction. Initially the airway may only be threatened, but the pathological process may be progressive, as with burns and infection or movement of a foreign body. Priority must be given to securing the airway, as delay may itself precipitate complete obstruction. Intravenous sedation may also precipitate complete obstruction and should be avoided. If anaesthesia is required, inhalational induction may be preferred and relaxants avoided until bag-valve-mask ventilation is confirmed.

Cervical spine injury. Head and neck immobilisation must be maintained in the victim of blunt trauma until injury to the cervical spine is definitely excluded. If endotracheal intubation is indicated, it must be achieved without flexion, extension or distraction of the neck. Intubation should be performed while an assistant maintains in-line immobilisation, without traction, of the head and neck.

Full stomach. All seriously ill or injured patients requiring intubation must be presumed to have a full stomach. Apply cricoid pressure during intubation to prevent regurgitation and aspiration.

Limited haemodynamic reserves. A patient with any form of shock is subject to haemodynamic deterioration during intubation, from the drugs used to facilitate intubation or from hypoxaemia before or during intubation. Preintubation oxygenation volume resuscitation and sometimes inotrope support are needed. The drugs used, and especially the drug dosage, must be individualised.

Head injury. Autoregulation of cerebral blood flow is impaired in head injury. The therapeutic aim before, during and after intubation is to maximise the chance to maintain arterial blood pressure and minimise the rise in intracranial pressure.

Manoeuvres to open or maintain the airway

The coma position. Turn the patient on the side. This allows the tongue to fall forwards and to one side to drain fluid from the mouth and reduce the risk of aspiration. When necessary, suction and laryngoscopy can be performed with the patient in the left lateral Trendelenburg position.

Head tilt. Extend the head at the atlanto-occipital joint by placing one hand on the forehead. This is usually combined with either chin lift or jaw thrust.

Chin lift. Lift the jaw forward and support it with the mouth slightly open.

Jaw thrust. Grasp the angles of the jaw and lift forward. Maximum jaw thrust may minimise the amount of head tilt needed to secure the airway when cervical spine injury is anticipated.

Neck lift. Lift the neck into the ‘sniffing position’. This is less effective than the head tilt/chin lift or head tilt/jaw thrust manoeuvres. It is contraindicated when cervical spine injury is a possibility.

Manoeuvres to relieve foreign body obstruction

If the patient is capable of air movement, spontaneous coughing and breathing should be encouraged. The patient with poor or no air movement requires immediate help.

Back blows. Deliver four forcible blows between the scapulae with the heel of the hand. This may relieve partial or complete obstruction.

Chest thrust. Deliver four chest compressions with the hands over the sternum with the patient lying or sitting.

Finger sweep. To relieve obstruction in the oropharynx. Not recommended in infants.

Heimlich manoeuvre. Deliver thrusts with the fist over the upper abdomen or lower chest with the patient standing, sitting or lying prone. Not recommended in infants.

Repeated sequence. Back blows, chest thrust, finger sweep, Heimlich manoeuvre and mouth-to-mouth ventilation is recommended.

Infants under 1 year of age. The recommended sequence is back blows, chest thrust and mouth-to-mouth ventilation.

Oropharyngeal and nasopharyngeal airways

Oropharyngeal airway (Guedel airway). Must be placed over the tongue, so the tongue is lifted off the hypopharynx. Insert using a tongue depressor or insert concave side up and then rotate 180°. Only tolerated if gag reflex is impaired. Can be used as a bite block in the intubated patient.

Nasopharyngeal airway. Lubricate well and insert through medial and inferior aspect of nasal cavity. Can be inserted in patients with tightly clenched teeth. Tolerated even if the patient has an active gag reflex. Tip needs to lie behind the tongue and low in the hypopharynx but above the larynx.

Types of ventilation

Mouth-to-mask ventilation

Mask should incorporate a one-way valve. It is preferable to mouth-to-mouth ventilation.

Patients can be adequately ventilated until definitive assisted ventilation techniques are obtained.

Bag-valve-mask ventilation

Use 2 L bag for adults and children over 5 years of age, 500 mL bag for younger children and infants, 250 mL bag for premature infants.

Jackson Rees circuit is only suitable for use by an experienced resuscitator.

Mask-face seal is maintained with even pressure using thumb and index finger on the mask and the other fingers applying chin lift or jaw thrust, depending on the size of the patient. A second resuscitator may be needed to assist with jaw thrust.

Endotracheal intubation

Endotracheal intubation is the most effective and reliable means of securing an airway. It provides airway patency, prevents aspiration, assures oxygenation and permits high ventilatory pressures and the use of positive end-expiratory pressure. It readily allows suctioning and can be used for administration of drugs if there is no intravenous access.

1. Approximate tube size (internal diameter) in adults is 7.5–8.0 mm in females and 8.0–8.5 mm in males. In pre-term infants use 2.5 mm, 3.0 mm in term infants, 3.5 mm in 3- to 9-month-olds, 4.0 mm in 9- to 24-month-olds. Tube size for patients over the age of 2 years is calculated from the formula:

image

2. Uncuffed tubes are used in patients under the age of 8–10 years, allowing for an audible leak to prevent excessive pressure on the subglottis. Large-volume, low-pressure cuffs are used in older children and adults.
3. Orotracheal intubation is faster and easier than nasotracheal intubation.
4. In children, once orotracheal intubation is accomplished and the patient is stable, repeat direct laryngoscopy and nasotracheal intubation is often undertaken. The reasons are easier fixation and suctioning of a nasal tube.
image

Figure 2.1 Cormack-Lehane laryngoscopic grading system

Technique of orotracheal intubation

1. Precheck equipment (airways, tubes, introducers, forceps, bag-valve-mask, laryngoscopes).
2. Oxygen, suction and monitoring equipment must be available.
3. Skilled assistance is invaluable (with knowledge of the equipment used, to provide in-line manual immobilisation of the head and neck and to apply cricoid pressure).
4. The ‘sniffing’ position allows optimal visualisation of the vocal cords.
5. Be calm and orderly.
6. Monitor oxygen saturation, electrocardiogram and blood pressure during the procedure.
7. ‘Stiffen’ the tube to aid manipulation of the tube tip, by placing a lubricated ‘introducer’ inside the tube.
8. Aid visualisation of the larynx by the application of backward, upward, rightward pressure (BURP) to the thyroid cartilage.
9. Maintain visualisation of the tube passing through the vocal cords until the proximal end of the cuff is 2 cm beyond the cords.
10. Observation and auscultation should be performed to verify bilateral lung expansion.
11. Secure the tube in position, then insert an intragastric tube.
12. Capnography is ideal to confirm tube placement in the trachea.
13. Chest X-ray will ascertain the position of the tube tip in relation to the carina.

Rapid sequence induction (RSI)

This is employed to induce unconsciousness and muscular paralysis to provide optimal intubating conditions, to avoid aspiration from a probable full stomach and to protect against reflex bradycardia and raised intracranial pressure due to manipulation of the airway. It is contraindicated if ‘difficult’ intubation is predicted and successful bag-valve-mask ventilation is considered unlikely. This will depend on the patient, the equipment and assistance available and the skill of the operator.

1. Preoxygenation. Administration of 100% oxygen, using a well-fitting bag-mask for 2 minutes, will result in 95–98% nitrogen washout. This will protect against hypoxia during apnoea for up to 8 minutes. Manual ventilation is preferably avoided until intubation is accomplished.
2. Simultaneous in-line manual immobilisation of the head and neck. Used in the blunt trauma victim when cervical spine injury is a possibility.
3. Cricoid pressure. As soon as consciousness is lost, cricoid pressure is applied with the thumb and index finger to compress the oesophagus between the cricoid cartilage and the cervical spine. Compression is maintained until the tube cuff is inflated. This technique helps to prevent regurgitation and aspiration, but is contraindicated if the patient vomits. It should not be confused with BURP to bring the vocal cords into view.

Note: At this time, the routine application of cricoid pressure is considered a standard of care. There is, however, no evidence absolutely supporting its routine use in RSI.

When properly applied by a trained individual, cricoid pressure tends to improve laryngoscopy. It can also be used to assist in the BURP manoeuvre (backward, upward, rightward pressure). The BURP manoeuvre can improve laryngoscopic view by one grade.

It should be remembered that improperly applied cricoid pressure can render laryngoscopy more difficult.

4. Secure intravenous infusion site, for fluid and drug administration.
5. Atropine (10–20 μg/kg) is given as pretreatment to prevent bradycardia, which is more likely in children under 8 years of age and after repeated doses of suxamethonium.
6. Induction. Thiopentone 2.5% (3–5 mg/kg) induces unconsciousness within seconds of a single intravenous dose; its duration is a few minutes. Use a smaller dose (1–2 mg/kg) if depressed level of consciousness is already present. Its main side effects are cardiovascular and respiratory depression. Hypotension is managed with intravenous fluids. The dose must be reduced if there is already hypovolaemia or hypoxaemia. Propofol (2.0–2.5 mg/kg) also induces unconsciousness; a single induction dose lasts 5–10 minutes; avoid in children under 3 years. Alternatives are midazolam (0.1–0.2 mg/kg) combined with morphine (0.1–0.2 mg/kg) or fentanyl (2–4 μg/kg). Preinduction treatment of depressed cardiac output (from hypovolaemia, hypoxaemia, septic or cardiogenic shock) and titrating the drug dose against response are important, regardless of the agent. Lignocaine 1.5 mg/kg may be used as pretreatment in patients at risk of elevation of intracranial pressure.
7. Suxamethonium

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