An article in Journal Of Clinical Anesthesia describes direct laryngoscopy on awake subjects with remifentanil instead of topical anesthesia. Not for awake intubation, but as a way to predict difficult airways.
The difficult airway is one of the big challenges in anesthesia. We come a long way by optimizing intubating conditions and by having a sensible plan in case of a difficult or impossible airway. But ideally we should be able to predict the difficult airways before they get us into trouble.
The problem is, that the methods we have for predicting difficult airways are not that great. The best we have got is the combination of the Mallampati score and the thyromental distance, which is only about 35% sensitive and 85% specific. Almost useless, considering what could be at stake. Clearly, we could use a better way of finding the difficult airways. The method presented in this study is not it, but is still pretty neat.
In the study authors, Gupta & co, use remifentanil as a sole analgesic in order to allow for direct laryngoscopy and evaluation of the larynx in awake subjects. They then compared laryngoscopy views before and after induction in order to determine if direct laryngoscopy in the awake patient is a viable predictor of difficult laryngoscopy in the sleeping patient.
- Patients were put in a sniffing position.
- O2 3L/min on nasal prongs.
- The remifentanil infusion was, based on weight, started at 0,1-0,6 microg/kg/min.
- The remifentanil infusion was titrated to the point where the subjects struggled to stay awake but still responded to commands.
- If the patient tolerated an oral airway and a forceful jaw-thrust the patient was deemed sedated enough.
- Now the infusion was terminated and the laryngoscopy could proceed.
- Two anesthetists assigned Cormack-Lehane (CL) grades to the airway.
- After laryngoscopy induction was given followed by a relaxant.
- Cormack-Lehane grades were again assigned to the unconscious and relaxed patient.
81 patients were enrolled. Direct laryngoscopy failed in only one of the patients who was graded CL 4. Of the remaining roughly half were graded easy intubations (CL 1 and 2a) while the other half was considered difficult CL grades 2b,3 and 4) while still conscious. CL score for the conscious and unconscious patients are in the table below.
Sensitivity was 100% meaning all the difficult airways were found. Specificity was 57% meaning false positives remain a problem with this method. Partly this is explained by how most airways tend to improve with induction and muscle relaxant. Many of the airways graded difficult improved and were graded easy in the unconscious patients.
Direct laryngoscopy on the still awake paetients was achieved on average after 6,5 minutes. The unconscious patients were intubated on average after 13 minutes.
How does this fit in?
Not sure. Using remifentanil as an adjunct in awake laryngoscopy and awake intubation is hardly news. This could however be an sneaky way of identifying the difficult airways in the suspicious cases.
Those cases where we are unsure if to proceed with a standard induction and muscle relaxant, or if we should take a step back and do an awake intubation. With this method we could, delay that decision until after direct laryngoscopy of a still awake patient.
By then, if we go for induction all we need to add is the anesthetic agent and relaxant. If we instead go for an awake intubation maybe spraying the vocal cords is all we need to intubate? For an awake intubation we could also swap for an awake video laryngoscopy and see if that gives us a view, and awake intubate from there.
An awake look and standard intubation could save us most of the 30-60 minutes that every old-school awake intubation seems to add to theatre time. It could also spare the patient from an awake intubation which, when not done properly, can be very distressing.