Dissecting the ASA Difficult Airway Algorithm -Part 2

     The Algorithm contemplates that the Questions in section 1 will have been addressed in such a way that the knowledge of the physiology , anatomy, and other conditions for executing the mission of "gaining control of the airway" will be supplemented as required to prepare for the crucial decisions of the 3rd step of decision.

     While the team prepares the patient , personnel  and equipment  section 2 prompts for oxygen delivery.
NB : The importance and potential of this step is often under appreciated , particularly now , when advanced airway devices like GlideScope make it much more likely that airway control will be expeditious.

ASA Algorithm second section:

2. Actively pursue opportunities to deliver supplemental oxygen throughout the process of difficult airway management. 

     This oxygenation step provides the team with a most interesting and complex array of choices for the provision of "Pre-oxygenation". Great creativity can be used at this juncture to provide an "Oxygen soak" for the patient that adds oxygen to the tissues and fluids of the body that will extend the time available for challenging airway management should problems develop. There now exists a vast array of permutations and combinations of equipment and strategies to choose from . The possible approaches :  ( in all cases time is essential to provide the tissue soak)

• A Standard 4 minutes of face mask oxygen administration prior to intubation has been studied by Mort in critically ill patients and produced modest improvement. 1
• Apneic oxygenation via Nasal cannula  or nasal tube oxygenation can be useful and can be administered at moderate flow rates. The nasal cannula deep in the pharynx can prolong the effects of enhanced oxygen while the manipulations of tubes and SGAs are carried out. This is not without risk as the development of surgical emphysema can occur when mucosal injury is present and then , rarely , when mucosal injury cannot be found.
• CPAP or BIPAP may provide added pressure to improve the alveolar recruitment and add continuous pressure as well. 
• Rebreathing hoods combined with oxygen delivery to create a very high para oral/ para nasal oxygen concentration.
• Sedation and local anesthesia can allow SGAs such as the I-gel to be placed as an early oxygenation step and thus provide added safety while anesthesia is deepened. The SGA is an excellent bridge to intubation and can allow an FOB , GlideScope or optical stylet to visualize the anterior aspect of the lower pharynx ....  and while this is known and practiced there is considerable finesse required to get the local anesthesia of the Upper airway and the very light sedation optimized. SGA use with the awake patient would be considered to be a highly skilled manoeuvre at this time .    
• oxygen delivery via the airway exchange catheter  may provide an opportunity in certain situations .         
• The proliferation of airway tools makes possible many combined strategies which require full and complete specific equipment training to allow expert performance . Supplemental and apneic oxygenation can reach the level of a " high art"  with such skill.                                                                                                                                                                   1   
  Crit Care Med. 2005 Nov;33(11):2672-5.