Recent SAM discussion -GlideScope Patient Positioning- how to Analyse.
What are the principles one needs to apply when assessing patient positioning with the highly angled video laryngoscope-GlideScope?
The GlideScope was designed to accept the patient anatomy and provide an airway view by positioning the camera in the pharynx viewing the glottis by lifting the tongue along its length without excessive lifting of the glottis itself. The inspection of Adnet's lateral view of MRI Airway images is instructive. The interception of the MA (mouth angle) and the PA (pharyngeal angle) produces an angle which I have termed the Alpha Angle which is 60 degrees. The GlideScope exploits this underlying information to produce 99.9% usable airway views without excessive lifting of the glottic complex.
Obesity
The obese patient has several features that may make GlideScope laryngoscopy difficult. The first of these is excessive fat deposits in the region of the pharynx. Usually this fat does not prevent viewing as one stays in the midline and can do some extra lifting of the tongue.
There is often a prominent Buffalo Hump fat deposit in the inter scapular region which has the effect of elevating the thorax in a way that allows the neck to extend with consequent head position more posterior. This posterior position of the neck may increase the angle created by the LA (laryngeal angle) and the PA (pharyngeal angle) and make passage of the endotracheal tube more challenging. Placement of a doughnut to pillow under the head to produce a neutral neck angle is probably helpful in most patients to restore normality.
The other consideration that may be useful is to place the patient in a moderate reverse Trendelenberg position, on some form of ramping or table flexion that reduces the work of breathing while intubation is being anticipated. This must be combined with consideration of venous return and cardiovascular status.
Excessive sniffing position may change the angles of the airway adversely so if one does this one must be ready to adjust the neck to a neutral position if tube advancement is an issue
Normal Patient
The normal anatomy accommodates the GlideScope in the neutral neck position which keeps the MA, LA, and PA angles in usual relationship and as far as we know now is the recommended position. Studies on this topic may shed more light in the future.
The factors leading to difficulty advancing the endotracheal tube when using the GlideScope were identified in 2001 when initial studies were done. These are:
1. deep insertion of the GlideScope
2. excessive lifting of the glottis- one must lift the tongue with addition of a slight 2 finger lifting of the blade tip _just enough to give a grade 2 view.
3. Slight withdrawal of the blade will allow the glottic complex to resume its normal position which is adjacent to the posterior pharyngeal wall. This position favors intubation.
