Salem, et al - Difficult Mask Ventilation - What needs improvement?

Question 1

When faced with a DMV (difficult mask ventilation not the department of motor vehicles), what does the ASA emphasize as the initial courses of action?

Answer 1

1. Two person bag masking with one person on the bag and one person performing a two handed jaw thrust.
2. If only one person is available, perform two handed jaw thrust, change ventilator settings to mechanical and see if you can push air.
3. To free up your hands, you can use a jaw strap (which is what those yellow/blue rings on the bag masks are used to secure) if you really need to do something else - this can also be used to improve the mask seal.

Question 2

There are two distinct mechanisms under which laryngospams occur. Describe them.

Answer 2

Glottic shutter: response controlled by intrinsic laryngeal muscles. Basically, inspiration draws vocal cords close (due to the Bernoulli effect) and this closure is usually opposed by the tone of abductor muscles. If the tone of these muscles are severely ablated, there will be inspiratory stridor and possible glottic closure (although usually this is incomplete, hence the descriptor ‘shutter’.

Ball-valve closure: controlled by both intrinsic and extrinsic laryngeal muscles. Basically, both the glottis and false cords snap shut and is due to a reactive response (defensive) rather than a muscle tone relaxation effect seen in glottic shutter.

Question 3

How do we deal with glottic shutter laryngospasm?

Answer 3

Positive airway pressure abolishes the inspiratory stridor.

Question 4

How do we deal with ball-valve closure laryngospasm.

Answer 4

Positive airway pressure actually worsens this!

Two-handed jaw thrust usually opens the vocal cords up in this situation. However, administration of propofol or sux for muscle relaxation may be necessary (followed by BMV or intubation).

Question 5

There is a school of thought that with-holding NMB from suspected difficult airway patients may be useful in that the patients can be awakened in case airway security is found to be impossible. What is the authors’ response to this?

Answer 5

Clinical studies have shown this course of action to be inconclusively beneficial at best.

Instead, the plan to wake the patient may lead to low-dose administration of induction agents.

Low does induction agents and lack of MRs may itself lead to difficult airway security. NMB may actually make airway security easier due to the relaxation of laryngeal muscles.