Emergency Medicine/Endotracheal Intubation

Placement of endotracheal tube with a laryngoscope

Endotracheal intubation describes the technique of passing a tube through the vocal cords. A cuff is then usually inflated to provide a seal allowing positive pressure ventilation, and to protect the airway from the aspiration of gastric contents or upper airway material.

Indications for endotracheal tube (ETT) placement include: severe hypoxaemia requiring PEEP; hypercapnia with acidosis; inability to protect the airway; to control ventilation in the presence of raised intracranial (or intraocular) pressure; to facilitate certain diagnostic or therapeutic procedures; to allow administration of neuromuscular blockade

Endotracheal placement is a painful and stimulating procedure and requires induction of anaesthesia and muscular relaxation for facilitation. In cooperative patients topical anaesthesia alone can be used.

The classical technique in a starved patient undergoing elective anaesthesia describes the administraion of a hypnotic (sleep inducing) drug, gentle ventilation to check for airway patency, followed by administration of a muscle relaxant. A rapid onset opiate may also be administered to blunt sympathetic response to intubation. The vocal cords are then visualised with the aid of a laryngoscope and the endotracheal tube visualised passing through them. Confirmation of endotracheal placement is sought by 3-point ausculation (both lung fields and the stomach), and capnography. The optimum position for endotracheal intubation is described as 'sniffing the morning air'. This aligns the axes of the oral cavity, pharynx and trachea. The neck is flexed (on a pillow) and the head extended. When intubating it is important not to push the laryngoscope against the persons teeth which could cause discomfort or dental deformations, and can lead to malpractice.

In the practice of emergency medicine, ideal intubating conditions as described above are rare. Patients are almost always unstarved or have other factors which may contribute to delayed gastric emptying. Additionally many patients are unstable or hypoxaemic. A technique known as 'rapid-sequence induction' is often used.

Rapid Sequence Induction

Here the step of checking airway patency prior to administration of muscle relaxation is omitted with the aim of securing the airway as quickly as possible. A pre-calculated dose of hypnotic, followed immediately by a rapidly aciting muscle relaxant, are administered. Cricoid pressure by a trained assistant is applied. As soon as adequate intubation conditions are deemed to have been obtained, direct laryngoscopy followed by endotracheal intubation is performed. In patients with suspected cervical spine injury, patients are generally removed from their hard-collars just prior to induction, and the spine is immobilised by manual in-line stabilisation. This can impair the view of the larynx with conventional laryngoscopy.

Because the ability to ventilate prior to administration of muscle is not determined, the 'can't intubate, can't ventilate' scenario is always possible. This represents an immediate threat to life, and it is important that one is familiar with a 'failed intubation drill'.