Prediction of difficult airway management in traumatic cervical spine injury: influence of retropharyngeal space extension

Figures & data

Figure 1 Measurements of RPS in 2nd, 5th and 7th cervical spine level in median sagittal MRI images.

Notes: The thickness of RPS (solid double arrow) is measured by the antero-posterior distance between the posterior margin of pharynx, larynx or trachea and the anterior bony margin of cervical vertebra. The proportion of RPS to vertebral body was calculated as a ratio of the thickness of RPS to A–P diameter of each vertebral body (dotted double arrow) multiplied by 100.
Abbreviations: A–P, antero-posterior; MRI, magnetic resonance imaging; RPS, retropharyngeal space.

Table 1 Characteristics of patients

	Easy laryngoscopy (n=49)	Difficult laryngoscopy (n=13)	P-value
Gender (M/F)	40/9	11/2	1.000
Age (years)	54.9±16.2	55.5±15.4	0.914
Height (cm)	167.4±8.1	168.3±5.6	0.693
Weight (kg)	64.5±10.6	65.4±11.7	0.789
BMI (kg/m^2)	22.9±2.7	23.0±3.2	0.970
ASA PS (I/II/III/IV)	15/25/8/1/0	0/7/5/0/1	0.241
Cause of cervical injury			0.287
Fall down	8	7
Slip down	8	1
Car accident	29	4
Pedestrian accident	4	1
Time elapsed from MRI to surgery (hours)	22.0 (12.5–42.0)	14.0 (6.0–39.0)	0.358

Note: Values are expressed as numbers, mean±SD or median (25th–75th percentile).

Abbreviations: ASA PS, American Society of Anesthesiologist physical status; BMI, body mass index; F, female; M, male; MRI, magnetic resonance imaging.

Table 2 Quantitative measurement of retropharyngeal space between easy and difficult laryngoscopy during anesthesia induction in patients with traumatic cervical spine injury

	Easy laryngoscopy	Difficult laryngoscopy	P-value
MRI findings of cervical spine
Thickness of RPS (mm)† at
C2	5.10 (4.33–5.94)	14.29 (9.75–18.04)	<0.001*
C5	13.65±2.45	15.43±3.52	0.067
C7	13.07±3.17	14.93±4.77	0.142
Proportion of RPS to vertebral body (%)†† at
C2	29.4 (25.0–35.8)	79.0 (54.5–110.4)	<0.001*
C5	80.2±14.2	86.4±24.9	0.305
C7	72.7±15.9	78.1±23.0	0.384
Anteroposterior diameter of airway (mm)
Oropharynx	13.5±4.1	7.9±3.0	0.005**
Hypopharynx	19.3±3.6	13.6±4.1	0.002**
Larynx	19.4±3.2	13.7±4.6	<0.001**
Trachea	14.1±2.3	14.5±2.3	0.706

Notes:

† Anteroposterior distance between the posterior margin of pharynx or trachea and the anterior bony margin of cervical vertebra at the 2nd, 5th and 7th cervical levels, which were measured on median sagittal MRI images.

†† Calculated as a ratio of RPS to A–P diameter of each vertebral body multiplied by 100.

* P<0.05 by the Mann–Whitney rank-sum test between easy and difficult laryngoscopy groups.

** P<0.05 by Student’s t-test between easy and difficult laryngoscopy groups.

Abbreviations: A–P, antero-posterior; MRI, magnetic resonance imaging; RPS, retropharyngeal space.

Table 3 Univariate logistic regression analysis for the prediction of difficult laryngoscopy in patients with traumatic cervical spine injury

	OR	95% CI	P-value
Thickness of RPS at C2 (mm)	2.13	1.38–3.30	<0.001*
Proportion of RPS to vertebral body at C2 (%)	1.13	1.05–1.21	<0.001*
Anteroposterior diameter of airway (mm)
Oropharynx	0.59	0.38–0.91	0.016*
Hypopharynx	0.61	0.40–0.92	0.020*
Larynx	0.61	0.41–0.93	0.021*

Note:

* P<0.05 was considered statistically significant.

Abbreviation: RPS, retropharyngeal space.

Figure 2 ROC curve and AUC of the RPS at the 2nd cervical spine level.

Notes: The areas under the receiver operator characteristic curve are 0.97 (95% CI: 0.94–1.01; p<0.001) and 0.96 (95% CI: 0.92–1.01; p<0.001), respectively. Cutoff values of RPS thickness and the proportion of RPS to the 2nd cervical vertebral body are 7.94 mm and 48.4% (p<0.001 and p<0.001, respectively).
Abbreviations: AUC, area under the curve; ROC, receiver operating characteristic; RPS, retropharyngeal space.

Figure 3 The relationships between laryngoscopic grade using Cormack–Lehane classification and (A) RPS thickness at the 2nd cervical spine level, and (B) proportion of RPS to A–P diameter of the 2nd cervical vertebral body.

Abbreviations: A–P, antero-posterior; RPS, retropharyngeal space.