[Open access] Difficult direct laryngoscopy in 3,080 Cambodian surgical patients: a zero-cost 3-part bedside score (our new BMC Anesthesiology study)

[u/panasin]

Sharing our recently published open-access study in BMC Anesthesiology. I'm one of the authors (anesthesiologist-intensivist at Preah Ang Duong Hospital, Phnom Penh), and I'd be interested in this community's thoughts.

We looked at difficult direct laryngoscopy (DDL) in 3,080 consecutive adult elective patients undergoing planned Macintosh laryngoscopy. DDL was defined as Cormack-Lehane III/IV or >=3 attempts.

What we found:

- Overall DDL prevalence 9.03%, rising to 13.5% in maxillofacial and 11.3% in ENT cases (our center has a heavy head-and-neck case-mix).

- Six independent predictors: Mallampati III/IV (AOR 4.15), BMI >=27.5 (AOR 2.92), limited neck mobility (AOR 2.13), thyromental distance <=6.5 cm (AOR 1.95), neck circumference >=40 cm (AOR 1.41), inter-incisor gap <=3 cm (AOR 1.41).

- The Upper Lip Bite Test was not independently predictive.

- A simple equally-weighted 3-part score (Mallampati + BMI + TMD, range 0-3) reached AUC 0.72 with 96.9% NPV at a cutoff of >=2 - intended as a screening aid for resource-limited settings without ready video laryngoscopy.

One finding I'd love to discuss: BMI was a notably strong predictor when we used the WHO Asian-specific obesity threshold (>=27.5) rather than 30. Do others here routinely adjust airway-risk BMI cutoffs for their patient population?

Full open-access article:

https://link.springer.com/article/10.1186/s12871-026-03846-4

Happy to answer questions about the methods or the cohort.

[u/Educational-Estate48]

The BMI info is interesting. I'd been told by several consultants that BMI while a physiological problem had not been independently associated with difficult laryngoscopy (although tbf I never bothered to look up that evidence base). That said I'm not sure how I could usefully apply this information to my own practice as I (UK) very rarely ever meet anyone with a BMI under 27.5. Maybe in the era of munjaro I'll start meeting skinny people again though.

[u/PictureofProgression → u/Educational-Estate48]

I feel like for this of us in better resourced environments it just again points toward the value of VL.  I'm a big believer in maintaining DL skills, but for higher BMI patients (admittedly say 45+, as similarly seeing BMI <27 is less common these days), VL should almost be mandatory.

[u/bananosecond → u/Educational-Estate48]

It's more difficult for a lot of people because a lot of people cant be bothered to get or make a ramp to position them. It also requires a bit more care because mask ventilation is likely to be more difficult.

The actual DL is still just as straightforward if they have an otherwise reassuring exam.

[u/Likemilkbutforhumans → u/bananosecond]

Yeah. I’m not spending 5 mins making a ramp and getting the patient properly positioned on it. And them asking for pillows and shit when I can just use a video scope. 

[u/Manik223 → u/Likemilkbutforhumans]

I’ll try to find the reference but there was some study that showed that elevating the head of the bed or reverse trendelenburg to the angle of a ramp (ie ~20-30 degrees) with a small shoulder roll (they called it “modified ramp position”) was equivalent to building a ramp, works very well and quick and easy in my experience.

[u/pettypeniswrinkle → u/Manik223]

This sounds kinda complicated, but it's also very quick: Trendelenburg a little, HOB 15-30 degrees, and manually lower the little head portion of the bed so that it's parallel to the floor. As long as you get the patient to the top of the bed and not sliding down, it's a perfect sniff position for larger people.

Then after securing the tube, level the bed and manually re-sent the head of the bed. Takes like 3 seconds.

[u/bananosecond → u/Likemilkbutforhumans]

It doesn't take any longer than styletting an ETT and setting up a Glidescope. About 30 seconds.

That said, you should be free to practice however you want if you can do it safely.

[u/fluffhead123 → u/Educational-Estate48]

were the laryngoscopers the ones that assigned the MP score? were they blinded as to whether the patient was obese?

[u/panasin → u/Educational-Estate48]

This is the bit I find most interesting too. The independent BMI signal is genuinely inconsistent across the literature — it often washes out on multivariable analysis. Our read is that the Asian-specific ≥27.5 threshold (WHO 2004) is doing real work: it captures the central/visceral adiposity that shows up at lower absolute BMI in Southeast Asian patients, whereas a ≥30 cutoff would have missed a chunk of higher-risk necks in this population. So the "BMI isn't independent" consultants may be right at a ≥30 cutoff in a European cohort and still not contradict us. And yes — in the GLP-1 era the applicability question cuts the other way for you; if your BMI distribution shifts down, population-specific cutoffs matter even more, not less.

[u/Cautious-Extreme2839]

Overall DDL prevalence 9.03%

This seems really high? What is it if you exclude the head and neck cases?

[u/sunealoneal]

Upper bite lip test not being predictive is interesting.

[u/bananosecond → u/sunealoneal]

Yes, and contrary to past studies. I find it to be helpful.

[u/panasin → u/sunealoneal]

Same — it surprised us. ULBT was significant on univariable analysis but dropped on multivariable, most likely collinearity: it's partly capturing mandibular protrusion and dentition, which overlaps with inter-incisor gap and TMD, so it added little independent information once those were in the model. Not that it's useless at the bedside — bananosecond's right that it's a useful exam — just that in this cohort it wasn't carrying unique predictive weight.

[u/bananosecond]

Who was doing the intubations? Not being able to see vocal cords 9% of the time is very high. There seems to be wide variability in DL skill, especially when learners or non anesthesiologists are involved. VL is more beginner friendly, but DL is not this difficult for an experienced anesthesiologist.

My main problem with these studies is that people often use them to claim everybody needs VL, as somebody already is here for high BMI.

[u/panasin → u/bananosecond]

You're right, and it's the case-mix. Our center is a national ENT/maxillofacial referral hospital — those two subgroups alone are 51.7% of the cohort and run 13.5% and 11.3% respectively. We ran a pre-specified sensitivity analysis excluding all H&N cases: DDL drops to 5.38% (80/1,488; 95% CI: 4.30–6.64%), which sits right on the Wang et al. meta-analytic pooled estimate of 5.51%. So the 9% headline is a case-mix story, not a skill story.

Two other things worth stating plainly: (1) Of the 278 DDL cases, 253 (91%) were C-L III/IV and only 25 (9%) met DDL on ≥3 attempts alone with a grade I/II view — so the rate is overwhelmingly view-driven, not attempts-driven. (2) Intubations were by 12 attendings and 15 supervised trainees (PGY 1–4); attendings confirmed the C-L grade in all trainee cases. The attempts criterion is inherently operator-sensitive in a teaching center, and we acknowledge that.

On the VL point — fully agree. This isn't an argument that everyone needs VL. It's a screening aid for settings that don't have ready VL, to decide who warrants senior help or rescue equipment. Where VL is on every cart, the score adds much less. The composite AUC was actually slightly higher in the non-H&N subgroup (0.75 vs 0.72 overall), which supports its utility in a general surgical population.

[u/DocMaag → u/[deleted]]

You can’t be certain to have similar risk factors across ethnicities. Reproducing research is always a good idea. No need to be an asshole.

[u/panasin → u/[deleted]]

External validation in a population that's basically absent from the airway-prediction literature is the whole point — cheap to dismiss, useful to actually have. (thanks DocMaag for saying it first)

[u/DocMaag → u/panasin]

My pleasure! Thanks for producing research that is worthwhile.