Article Notes
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It would also be feasible for recording, analysis and reporting to occur entirely at the bedside on a smartphone. ↩
What’s so interesting?
De Carvalho and co. show that pre-operative voice analysis can be predictive of difficult laryngoscopy.
I’d never thought about that...
The authors describe how different frequency components and acoustic qualities of the voice are, at least partly, determined by the shape and size of different anatomical areas of the vocal tract. By analysing the most intense frequencies (voice formants) within the voice spectrum they were able to correlate components with difficult laryngoscopy, namely Cormack & Lehane grade 3 or 4.
The practicalities
During pre-anaesthetic assessment, 467 elective general surgical patients were asked to pronounce each of the five vowels, corresponding to base phonemes. This was recorded on a smartphone and then later processed and analysed on a laptop computer.1
They found...
A model using voice ‘formants’ could reliably predict difficult laryngoscopy with a ROC-AUC of 0.761 (ie. 76% probability that it correctly classifies a patient as difficult or not). When combined with the modified Mallampati this improved to 92%.
The big picture
While interesting, it’s worth remembering that using voice formants (76%) did not perform as well as modified Mallampati alone (87%), and that this performance is also surprisingly much better than those from the most recent Cochrane meta-analysis (2018) of bedside airway assessment. Over 133 studies the Cochrane review reported a summary sensitivity of only 53% and specificity of 80% for the modified Mallampati (vs 100% and 75% respectively for this study).
Although this is an interesting and novel new test, it’s just not that simple... Screening for an uncommon outcome using tests with imperfect sensitivity and specificity is already problematic, but doubly so when we are not always certain which outcome we should be screening for (laryngoscopy, intubation, ventilation, oxygenation...).
As an airway screening test, voice analysis is both different and also more of the same.
Daniel Jolley
See also the reply letter from Audra Webber and Melissa Kreso: Informed Consent for Sugammadex and Oral Contraceptives: Through the Looking Glass.
Daniel Jolley
The authors suggest a possible revision of anaesthesia consent, such as:
"You may receive medications during your anesthetic that could interfere with the effectiveness of oral contraceptives. If you are using oral contraceptives, consider alternative methods of birth control for 7 days following your anesthetic." This disclosure would cover potential interactions with sugammadex, antibiotics, and other medications.
Daniel Jolley
Note the authors: “So long as neostigmine and glycopyrrolate are available and not prohibitively expensive, we should make a point in our practice to not use sugammadex for rocuronium reversal in women of childbearing age in situations where neostigmine and glycopyrrolate will have equal effectiveness.”
Daniel Jolley
Why?
Although often used to manage chronic pain acutely, the longer-term benefits of ketamine infusions remain uncertain. Despite this there has been significant growth in using ketamine infusions to treat chronic pain, rationalised by ketamine’s expected effect to reduce central sensitisation.
What?
This meta-analysis identified a small benefit for up to two weeks after a ketamine infusion, although little evidence of longer-term benefit. There appears to be a dose-response effect, suggesting greater efficacy with high-dose ketamine infusions.
The underlying problem...
Most research on ketamine infusions focuses on perioperative analgesia. Trials invetsigating ketamine infusions for chronic pain are universally small, lack standardisation and are often low quality.
This meta-analysis unfortunately does not add clarity to the question of whether ketamine infusions have long-term benefit in chronic pain syndromes. Clinicians will continue to need to judge indication on a case-by-case basis...
Daniel Jolley