Patients may have anatomically difficult airways or physiologically difficult airways. Both anatomical and physiological factors can lead to peri-intubation complications. My goal for this blog is to describe the factors that may contribute to an anatomically difficult airway and clinical conditions that create a physiological airway. In addition, I will attempt to describe proactive measures to mitigate the risk of peri-intubation complications of difficult airway management.
An anatomically difficult airway can be predicted by historical and examination features. Historical risk factors include any history of the following: stridor, OSA, rheumatoid arthritis or ankylosing spondylitis with cervical spine involvement, Down syndrome, dysmorphic facial features, a mass/prior surgery or radiation therapy involving the oropharynx or neck, history of tracheal stenosis or prior tracheostomy. Clinical conditions that may predict a difficult airway include any of the following: morbid obesity, thick, short neck, macroglossia, angioedema, small mandible, limited ability to open mouth, limited jaw protrusion, suspected cervical spine or neck injury, submandibular or retropharyngeal mass, severe traumatic brain injury, severe maxillofacial or mandibular or laryngeal fractures, and uncontrolled oropharyngeal hemorrhage. Patients with rheumatoid arthritis or ankylosing spondylitis with cervical spine involvement or Down syndrome are at increased risk of C1-C2 subluxation when the neck is placed into sniffing position during endotracheal intubation. If these conditions are present, the safest way to intubate a patient is with cervical spine immobilization as if they has a suspected C-spine fracture.
Management of an anatomically difficult airway depends on how emergent an intubation must be performed. An emergent intubation does not allow for the option of an awake intubation or even preoxygenation. Nevertheless, the operator should always be prepared for alternative methods of intubation if the initial attempt fails. Above all, do not persist with multiple attempts at a failing method.
We at Hospital Procedures Consultants (HPC) use the analogy of two classes of sky divers. The Type A sky diver jumps out of a plane and pulls the rip cord of his/her primary chute when ready to deploy the chute. If the primary chute does not open, this Type A sky diver keeps pulling on the same rip cord that continues to not work and then dies when he hits the ground. The Type B sky diver pulls the rip cord of his/her primary chute when ready to deploy the chute. If the primary chute does not open, this Type B sky diver switches to his/her secondary chute and pulls the rip cord deploying the safety chute allowing for a clean landing. We want you to be prepared with a Plan A, Plan B, Plan C and Plan D before any potentially difficult airway and act like the Type B sky diver.
Plan B may involve the use of video laryngoscopy or a Bougie for stylet-guided intubations. Plan C may involve the use of a supraglottic airway (e.g., a laryngeal mask airway or LMA or a King tube, etc.). Plan D should be a front of the neck airway (FONA) or surgical cricothyroidotomy. Anticipating these possibilities, one should always have these kits readily available before any potentially difficult airway and consider marking the spot with a pen in case a surgical airway is necessary.
The other potential cause of a difficult airway is a physiologically difficult airway. We use the mnemonic HORP KILLS to remember the four conditions predisposing to a physiologically difficult airway: severe hypoxia or metabolic acidosis, hypotension, or RV failure all increase the risk of intubation-related cardiovascular collapse.
- Hypotension (preintubation BP<110/60 or shock index >0.8)
- Management: fluid boluses, low-dose norepinephrine, induction with etomidate 0.15 mg/kg (max 10 mg) or ketamine
- Have push dose pressors immediately available
- Oxygen (Severe hypoxia)
- Preoxygenation with Non-rebreather mask AND high-flow nasal cannula (HFNC) or Noninvasive positive pressure ventilation (BiPAP)
- Apneic oxygenation with HFNC
- Have push dose pressors immediately available
- Right ventricular failure
- Low-dose norepinephrine drip, induction with etomidate 0.15 mg/kg (max 10 mg) or ketamine, and maintain low mean airway pressures post-intubation
- Have push dose pressors immediately available
- pH (Severe metabolic acidosis)
- Attempt to resuscitate patient before intubation if possible
- Have push dose pressors immediately available
- Have norepinephrine drip available
- Use pressure support or pressure control mode
There is an increased risk of cardiovascular collapse and cardiac arrest with a physiologically difficult airway. Therefore, if time allows, patients fair better with maximum resuscitation prior to intubation. Unfortunately, we are often faced with emergent intubations in patients with one of these conditions. In that circumstance, have push dose pressors and norepinephrine infusion immediately available if the patient develops circulatory collapse.
The biggest pearl of wisdom to provide to readers is preparedness. Always have a Plan A, Plan B, Plan C and Plan D prior to any potentially difficult airway. The entire airway team should understand the alternative plans if the initial airway plan fails. Equipment should be readily available for any failed difficult airway. Always mark the site of a potential cricothyroidotomy in advance should this become necessary. Always have push dose pressors and even a norepinephrine infusion readily available for all physiologically difficult airways. Never persist at a failing method of intubation. That is the definition of insanity. Strive to be the Type B sky diver, not the Type A sky diver.
References:
The Physiologically Difficult Airway. Western J Emerg Med. 2015; 16(7): 1109
Difficult Tracheal Intubation in Critically Ill. J Intensive Care. 2018; 6: 49.