Measurement of Forces Applied Using a Macintosh Direct Laryngoscope Compared to GlideScope Video Laryngoscope

Patients undergoing surgery or intensive care management often require a tube to be inserted into the trachea allowing lung ventilation. Usually a laryngoscope is used to allow visualisation of the larynx and facilitate intubation.

During direct laryngoscopy, the blade of the laryngoscope is inserted into the patient's mouth and the structures pulled upwards out of the line of vision. If visualisation is difficult, users often exert excess force on the tissues to obtain an adequate view. Generally the applied force is evaluated by the patient's stress response such as increased heart rate, blood pressure or plasma cortisol levels. These changes, while important, may be confounded by a variety of patient factors, as well as anaesthesia. An increased force may also be associated with tissue trauma, dental damage, and prolonged attempts.

The investigators' objective is to compare the force exerted on patient's tissues by the Macintosh laryngoscope and GlideScope video-laryngoscope. Video-laryngoscopes may be associated with the application of reduced force to the soft tissues of patients during intubation. While this is a common contention, it has not been proven. The GlideScope has a micro camera in the distal portion of the blade meaning a direct line of vision is not required. An adequate view can therefore be obtained with less displacement of tongue tissue. If the force exerted by the video laryngoscope is less, this would have beneficial implications by reducing stress response, neck movement, and trauma.

• Endotracheal Intubation
• Laryngoscopy

• Device: Macintosh (direct vision) laryngoscope
  Macintosh (direct vision) laryngoscope
• Device: GlideScope videolaryngoscope (indirect vision)
  GlideScope videolaryngoscope (indirect vision)

• Active Comparator: Macintosh (direct vision) laryngoscope
  Macintosh (direct vision) laryngoscope
  Intervention: Device: Macintosh (direct vision) laryngoscope
• Active Comparator: GlideScope videolaryngoscope (indirect vision)
  GlideScope videolaryngoscope (indirect vision)
  Intervention: Device: GlideScope videolaryngoscope (indirect vision)

Inclusion Criteria:

• age > 18years
• ASA 1-2
• elective surgery
• endotracheal intubation required (with non-depolarising muscle relaxant)
• signed informed consent

Exclusion Criteria:

• lack of informed consent
• endotracheal intubation not required
• ASA 3-5
• symptomatic gastro-oesophageal reflux
• rapid sequence intubation
• other method of intubation indicated eg fibreoptic, awake tracheostomy
• cervical spine instability
• unstable hypertension
• coronary artery disease
• cerebral disease
• COPD/asthma
• oral/pharyngeal/laryngeal carcinoma
• loose teeth/poor dentition
• Macintosh laryngoscope >size 3 required