Accuracy of sternomental displacement test and thyromental height test as a predictive measure for difficult airway in elderly surgical patients: a prospective cohort study

Figures & data

Figure 1. Photo I is the sternomental displacement measurement: A at extension and B at neutral position. Photo II is the thyromental height test measurement using a digital depth gauge. Our team captured the photo after the patient’s consent.

Table 1. The demographic data and the studied tests; TMHT, SMDD, and MMT among the difficult and easy laryngoscopy and intubation groups.

		difficult laryngoscopy (n = 21)	easy laryngoscopy (n = 129)	p value	difficult intubation (n = 7)	easy intubation (n = 143)	p value
age (years)		67.1 ± 3.04	68.09 ± 4.26	0.329	67.57 ± 2.51	67.98 ± 4.19	0.799
male sex		17 (80.95%)	66 (51.2%)	0.016*	6 (28.6%)	77 (53.84%)	0.100
BMI (kg/m^2)		27.3 ± 3.44	29.7 ± 4.13	0.389	30.52 ± 2.28	29.79 ± 4.23	0.650
TMHT (mm)		46.02 ± 5.61	52.5 ± 6.73	< 0.001*	46.50 ± 7.89	51.86 ± 6.83	0.046*
SMDD (mm)		34.02 ± 10.73	41.19 ± 16.02	0.040*	28 ± 7.61	40.78 ± 16.64	0.045*
MMT		3 (3–4)	2 (1–2)	< 0.001*	3 (2–4)	2 (1–3)	< 0.001*
added device		10 (47.6%)	3(2.3%)	< 0.001*	3 (42.86%)	10 (6.99%)	0.015*
time needed for intubation (min)		1.52 ± 1.97	1 ± 0.00	0.236
number of intubation trials	1	1 (4.8%)	112(86.8%)	< 0.001*
	2	14 (66.7%)	16(12.4%)
	3	5 (23.8%)	1 (0.8%)
	4	1 (4.8%)	0 (0%)
difficult intubation		6 (28.57%)	1 (0.77%)	< 0.001*
difficult laryngoscopy					6 (85.7%)	15 (10.48%)	<0.001*

Data of age, sex, BMI (body mass index) TMHT (thyromental height test), SMD (sternomental distance), and SMDD (sternomental displacement) were presented as mean ± sd. data of MMT (modified mallampati test) was presented as median (range). * indicates statistically significant p-value.

Figure 2. Roc curves of SMDD, TMHT, SMDD TMHT and SMDD or TMHT for predicting difficult laryngoscopy. (SMDD and TMHT) refers to that both measurements indicated difficult laryngoscopy. (SMDD or TMHT) refers to that either of the two measurements indicated difficult laryngoscopy. TMHT: thyromental height test, SMDD: sternomental displacement distance, roc: receiver operating characteristic curve.

Figure 3. Roc curves of SMDD, TMHT, SMDD TMHT and SMDD or TMHT for predicting difficult intubation. (SMDD and TMHT) refer to that both measurements indicated difficult intubation. (SMDD or TMHT) refers that either of the two measurements indicated difficult intubation. TMHT: thyromental height test, SMDD: sternomental displacement distance, roc: receiver operating characteristic curve.

Table 2. validity of SMDD, TMTH, TMHT or SMDD, and combined TMHT and SMDD for predicting difficult laryngoscopy (DL).

cutoff value	sensitivity (95% ci)	specificity (95% ci)	PPV (95% ci)	NPV (95% ci)	AUC (95% ci)	p value
SMDD (mm) ≤ 35	71.43% (47.8–88.7)	59.69% (50.7–68.2)	22.4% (17.0–28.9)	92.8% (86.5–96.2)	0.692 (0.611 − 0.765)	0.001*
TMHT (mm) ≤ 49.5	85.71% (63.7–97.0)	71.32% (62.7–78.9)	32.7% (26.0–40.2)	96.8% (91.4–98.9)	0.794 (0.721–0.856)	< 0.001*
SMDD ≤ 35 and TMHT ≤ 49.5	57.14% (34.0–78.2)	83.72% (76.2–89.6)	36.4% (25.0–49.5)	92.3% (87.9–95.2)	0.704 (0.624–0.776)	<0.001*
SMDD ≤ 35 or TMHT ≤ 49.5	100% (83.9–100)	46.51% (37.7–55.5)	23.3% (20.6–26.3)	100%	0.733 (0.654–0.801)	<0.001*

(SMDD and TMHT) refer that both measurements indicated DL. (SMDD or TMHT) refers that either of the two measurements indicated DL. *indicates statistically significant p-value. TMHT: thyromental height test, SMDD: sternomental displacement distance, PPV: positive predictive value, NPV: negative predictive value, AUC: area under the receiver operating characteristic curve.

Table 3. Validity of SMDD, TMTH, TMHT or SMDD, and combined TMHT and SMDD for predicting difficult intubation (DI).

cutoff value	sensitivity (95% ci)	specificity (95% ci)	PPV (95% ci)	NPV (95% ci)	AUC (95% ci)	p value
SMDD (mm) ≤ 35	100% (59–100)	58.04% (49.5–66.2)	10.4% (8.8–12.4)	100%	0.814 (0.743–0.873)	<0.001*
TMHT (mm) ≤ 49.5	71.43% (29.0–96.3)	65.03% (56.6–72.8)	9.1% (5.6–14.4)	97.9% (93.5–99.3)	0.719 (0.640–0.790)	0.070
SMDD ≤ 35 and TMHT ≤ 49.5	71.43% (29.0–96.3)	80.42% (73.0–86.6)	15.2% (9.1–24.1)	98.3% (94.7–99.5)	0.759 (0.683–0.825)	0.005*
SMDD ≤ 35 or TMHT ≤ 49.5	100% (49–100)	41.96% (33.8–50.5	7.8% (6.8–8.8)	100%	0.710 (0.630–0.781)	<0.001*

(SMDD and TMHT) refer that both measurements indicated DI. (SMDD or TMHT) refers that either of the two measurements indicated DI. *indicates statistically significant p-value. TMHT: thyromental height test, SMDD: sternomental displacement distance, PPV: positive predictive value, NPV: negative predictive value, AUC: area under the receiver operating characteristic curve.