Without evidence of benefit, an intervention should not be presumed to be beneficial or safe.

- Rogue Medic

If We Are Not Competent With Direct Laryngoscopy, We Should Just Say So – Part II

ResearchBlogging.org
 

Continuing from Part I of a paper that could, at best, be described as a convenience sample, since a quarter of patients were excluded from randomization because of attending physician bias.

What were the authors assuming when comparing GVL (GlideScope Video Laryngoscope) with DL (Direct Laryngoscopy) for intubation?
 

Intuitively, devices such as the indirect video laryngoscope should improve intubation performance. As such, this study tested the hypothesis that achieving better visualization during the intubation with the GlideScope Video Laryngoscope would result in a better airway management performance as measured by shorter intubation times.[1]

 

The authors also intuitively assume that shorter intubation times mean better airway management. This suggests that speed is the most important factor in airway management.
 


Image credit.
 

They are probably still preaching the myth of the Golden Hour at Shock Trauma.

Is speed more important than quality?
 

There is an excellent assessment of intubation attempt in this paper.
 

Confirmation of intubation attempt duration and success was identified using closed-circuit video.[1]

 

We should not be relying on self-reported intubation success, unless we aren’t interested in a study of fiction. We do not accurately report intubation success, so an objective measurement of success is essential. This should be applied to EMS, as well.
 

The failed intubation rate was less than 0.5%, but the participants had already excluded over a quarter of the patients, so how impressive is a half a percent failure on 3/4 of patients?

What is the success rate for all patients?
 

For all of the statistics regarding study measures, a p < 0.05 was chosen as the threshold for determining significance.[1]

 

Secondary outcome measures are free shots at finding something “significant,” so they should be required to achieve a higher standard than the 1 in 20 p value of < 0.05.[2]

 

To account for any potential bias from patients not enrolled owing to attending discretion, comparison analysis was performed between the eligible, enrolled patients and the eligible, nonenrolled patients. The data demonstrates that all groups were proportionally similar in their demographics, injury mechanism, ISS, and arrival vital signs (data not shown).[1]

 

And, according to Dr. Newman in the SMART EM podcast, the Mallampati scores of the excluded patients were similar to those of the included patients.
 

Used alone, the Mallampati tests have limited accuracy for predicting the difficult airway and thus are not useful screening tests.[3]

 

We conclude that the prognostic value of the modified Mallampati score was worse than that estimated by previous meta-analyses. Our assessment shows that the modified Mallampati score is inadequate as a stand-alone test of a difficult laryngoscopy or tracheal intubation, but it may well be a part of a multivariate model for the prediction of a difficult tracheal intubation.[4]

 

Do the demographics, injury mechanism, ISS, and arrival vital signs increase the ability of the Mallapati to predicting difficult intubation?
 


Image credit.
 

How do we know that the difficulty was similar between included patients and excluded patients?

Similar Mallampati scores.

How useful are Mallampati scores at predicting difficulty of intubation?
 

The pooled estimates demonstrated that only 35% of the patients, who underwent tracheal intubation with difficulties, were correctly identified with a modified Mallampati test.[4]

 

Does the Mallampati score work well for predicting difficulty of intubation with a video laryngoscope?
 

The clinical use of videolaryngoscopes may change the accuracy of predictors of difficult tracheal intubation and require a different definition of difficult tracheal intubation.[4]

 

The Mallampati score does not appear to be of much use in comparing the excluded patients from the included patients, but that is what the authors use to assure us that the patients are similar.

Mallampati scores compare one aspect of visibility, but how important is visibility for intubation?

To be continued in Part III.

Footnotes:

[1] Effect of video laryngoscopy on trauma patient survival: a randomized controlled trial.
Yeatts DJ, Dutton RP, Hu PF, Chang YW, Brown CH, Chen H, Grissom TE, Kufera JA, Scalea TM.
J Trauma Acute Care Surg. 2013 Aug;75(2):212-9. doi: 10.1097/TA.0b013e318293103d.
PMID: 23823612 [PubMed – in process]

[2] Do multiple outcome measures require p-value adjustment?
Feise RJ.
BMC Med Res Methodol. 2002 Jun 17;2:8. Review.
PMID: 12069695 [PubMed – indexed for MEDLINE]

Free Full Text from BioMed Central.
 

Standard scientific practice, which is entirely arbitrary, commonly establishes a cutoff point to distinguish statistical significance from non-significance at 0.05. By definition, this means that one test in 20 will appear to be significant when it is really coincidental. When more than one test is used, the chance of finding at least one test statistically significant due to chance and incorrectly declaring a difference increases. When 10 statistically independent tests are performed, the chance of at least one test being significant is no longer 0.05, but 0.40.

 

[3] A systematic review (meta-analysis) of the accuracy of the Mallampati tests to predict the difficult airway.
Lee A, Fan LT, Gin T, Karmakar MK, Ngan Kee WD.
Anesth Analg. 2006 Jun;102(6):1867-78.
PMID: 16717341 [PubMed – indexed for MEDLINE]

[4] Poor prognostic value of the modified Mallampati score: a meta-analysis involving 177 088 patients.
Lundstrøm LH, Vester-Andersen M, Møller AM, Charuluxananan S, L’hermite J, Wetterslev J; Danish Anaesthesia Database.
Br J Anaesth. 2011 Nov;107(5):659-67. doi: 10.1093/bja/aer292. Epub 2011 Sep 26.
PMID: 21948956 [PubMed – indexed for MEDLINE]

Free Full Text from Oxford Journals.

Yeatts DJ, Dutton RP, Hu PF, Chang YW, Brown CH, Chen H, Grissom TE, Kufera JA, & Scalea TM (2013). Effect of video laryngoscopy on trauma patient survival: a randomized controlled trial. The journal of trauma and acute care surgery, 75 (2), 212-9 PMID: 23823612

Lee A, Fan LT, Gin T, Karmakar MK, & Ngan Kee WD (2006). A systematic review (meta-analysis) of the accuracy of the Mallampati tests to predict the difficult airway. Anesthesia and analgesia, 102 (6), 1867-78 PMID: 16717341

Lundstrøm LH, Vester-Andersen M, Møller AM, Charuluxananan S, L’hermite J, Wetterslev J, & Danish Anaesthesia Database (2011). Poor prognostic value of the modified Mallampati score: a meta-analysis involving 177 088 patients. British journal of anaesthesia, 107 (5), 659-67 PMID: 21948956

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Comments

  1. But, but, that’s a paramedic skill. You can’t take it away! The patients will suffer! Or so chant the unwashed masses. I’m just one clown though. Best interest of the patient is a good idea. If only the policies/procedures/guidelines/protocols/managers/doctors/wizards wouldn’t get between us and that….

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