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.                                                                                                                                    
                                                                             

Dissecting The ASA Difficult Airway Algorithm-Part 1

     The 2013 version of the ASA Difficult Airway Algorithm was the second major upgrade that was carried out to recognize changes in accepted practice and available technology.

     Dr Archie Brain went through a series of prototypes of LMA to achieve transition of the mask from the mouth and nose area in the Pharynx close to the Laryngeal opening.
The recognition of the utility of the LMA device in rescue of patients who were either difficult laryngoscopy, difficult intubation, or cannot intubate -cannot ventilate , was an important event that allowed practitioners to transition to a totally different technique from multiple direct laryngoscopy attempts . Thus the 2003 Algorithm identified the use of the LMA at several stages including first use and rescue .

     The 2013 Algorithm changes Identified Video Laryngoscopy as a new and accepted asset in first use as well as rescue. The advent of the highly Angled 60 degree GlideScope, invented by Dr John Pacey , resulted in  widespread use of a video camera enabled laryngoscope that transferred the view point from the oral opening to a position in the pharynx looking at the larynx. The geometry of this device was uniquely effective. Now the Algorithm speaks of considering Video Laryngoscopy as a first choice , as a rescue device, and in conjunction with extubation strategies. 

            
                                                    ASA DIFFICULT AIRWAY ALGORITHM- 2013 MODIFICATION 
                                                                            Introductory Considerations

    1. Assess the likelihood and clinical impact of basic management problems: 
• Difficulty with patient cooperation or consent

• Difficult mask ventilation
• Difficult supraglottic airway placement
• Difficult laryngoscopy
• Difficult intubation
• Difficult surgical airway access

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

3. Consider the relative merits and feasibility of basic management choices:
• Awake intubation vs. intubation after induction of general anesthesia
• Non-invasive technique vs. invasive techniques for the initial approach to intubation • Video-assisted laryngoscopy as an initial approach to intubation
• Preservation vs. ablation of spontaneous ventilation 

4. Develop primary and alternative strategies:

                                                                         Dr Pacey's Comment

                                         Firstly  begin by considering the Items in Checklist 1.

• Difficulty with Patient cooperation or consent clearly complicates any evaluation , premedication, pre oxygenation, intubation (may reduce options for example for Flexible awake strategies).             Evaluate?
• Mask Ventilation difficulty is a combination of caregiver skill set , patient features like beards , facial architecture , and other equipment issues .                                                                                    Evaluate?
• This is a new concept "Difficult SGA placement" can be due to mouth size ,neck fixation, radiation , prior surgery and can result in failure to protect the airway or ventilate.                                                 Evaluate?
• Difficult Laryngoscopy with ?DL, ?VL, Radiation could for example cause this. The term is importantly separated out from difficult intubation because they are separate problems to be considered .    Evaluate?
• Difficult Intubation can occur for example with DL or VL if the operator is an infrequent or poorly trained and experienced incubator or if , for example, there is a physical mass in or around the larynx    Evaluate?
• Difficult Surgical Airway access may be caused by many factors , obesity, burns, lack of training , to mention a few . Will you want to call surgical help in advance or place a guide wire in the neck? Evaluate?

Should a checklist be printed  and used as a guide? perhaps but the main point is to separate out these issues and be sure to consider them in the plan. A written checklist may have the effect of bringing up the performance of the less experienced and in this way affecting the quality of care given.

In the next post we will work our way down the ASA Algorithm into items 2,3,4.