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tracheotomy in 76 males and 47 females to include height,

weight, calculated BMI, age, and gender. Two hundred eighty

patients were noted to have undergone tracheotomy over a 4-

year period, but 157 patients were excluded due to malignancy

involving the tracheal airway or with suboptimal imaging pre-

cluding accurate assessment of the tracheal dimensions. This

excluded any patient who required placement of an ETT at the

time of the CT study, or any other intervention such as a naso-

gastric tube that might impinge on the membranous tracheal

wall dimensions. None of the patients included in this study

had a prior tracheostomy or airway procedure. All of the

included patients were spontaneously breathing and in a supine

position at the time of the CT study. In all cases, the reason for

ETT and tracheostomy placement was ventilator-dependent

respiratory failure.

We noted the size of the ETT in place at the time of the

tracheotomy procedure and documented this for each patient.

Axial CT measurements were analyzed at the level of the first

tracheal ring, as this was the area most commonly associated

with the presence of a balloon cuff and thus the most likely

area for tracheal injury.

7–9

We did not measure the level of the

cricoid due to the circumferential cartilage ring structure at

this level, making the airway less likely to be compressed or

narrowed.

Measurements included the anterior-posterior diameter

(CT AP) as well as the width (CT width) of the trachea at this

point. Cross-sectional airway areas were also calculated and

compared. Data are described using means and standard devia-

tion for continuous variables and frequency and percentages for

categorical variables. Data are described for the full sample and

stratified by gender. Comparison across gender was accom-

plished using the two-sample

test and Pearson

tests, as

appropriate. Pearson correlation was estimated between the

continuous variables. Finally, linear regression was used to

identify predictors of airway size. BMI classification was taken

from current World Health Organization standards.

RESULTS

Descriptive statistics for the entire sample size

including age, BMI, CT AP, and CT width are shown in

Table I, and the ETT sizes placed at the time of trache-

ostomy are shown in Table II. These statistics are strati-

fied by gender. The BMI range for males was 14 to 70

and was 17 to 75 for females. Using these outlier

patients as examples, the male with a BMI of 14 had an

anterior-posterior tracheal airway measurement of

26 mm and a width of 21 mm. The male with a BMI of

70 had an anterior-posterior tracheal airway measure-

ment of 24 mm and a width of 20 mm for comparison.

The female with the BMI of 17 had an anterior-posterior

tracheal airway measurement of 16 mm and a width of

15 mm. The female with the BMI of 75 had an anterior-

posterior tracheal airway measurement of 14 mm and a

width of 10 mm.

We have also included the mean ETT sizes calcu-

lated for the entire sample stratified by BMI classifica-

tion. We found that for both obese men and women, the

higher the BMI, the higher the average ETT size. Specif-

ically, compared with normal sized patients, men and

women who were obese had on average 0.14 and 0.51

mm-larger ETTs placed, respectively. This is demon-

strated in Table III.

Most importantly, findings from the linear regres-

sion models yielded significant associations between

BMI and tracheal airway dimensions. Specifically, BMI

was inversely related to tracheal width after controlling

for gender and age (

.0389). For every 1 kg/m

increase in BMI, the tracheal width decreased by

0.05 mm. In addition, although not statistically signifi-

cant, on linear regression analysis there was a trend for

the airway area to decrease as the BMI increased.

TABLE I.

Descriptive Statistics for the Entire Sample Stratified by Gender.

Variable

Entire Sample,

123

Female,

Male,

Value

Age, yr

63.1 (15.3)

65.1 (14.2)

61.9 (15.9)

.2636

BMI, kg/m

32.4 (11.8)

33.5 (12.5)

31.7 (11.3)

.3919

CT AP, mm 20.8 (4.4)

18.8 (4.4)

22.1 (4.0)

.0001

CT width, mm 17.2 (3.5)

15.6 (2.8)

18.3 (3.6)

.7164

Airway area,

294.8 (112.8) 240.0 (87.4) 328.8 (113.7)

.0001

Values for age, BMI, CT AP, CT width, and airway area reflect the

average (mean) calculation. Standard deviation is noted in parentheses

anterior-posterior diameter; BMI

body mass index; CT

com-

puted tomography.

TABLE II.

ETT Sizes for the Entire Sample.

ETT Size, mm Entire Sample

Female

Male

6.0

12 (9.8%)

8 (17.0%)

4 (5.3%)

6.5

3 (2.4%)

2 (4.3%)

1 (1.3%)

7.0

12 (9.8%)

8 (17.0%)

4 (5.3%)

7.5

42 (34.2%)

21 (44.7%)

21 (27.6%)

8.0

52 (42.3%)

8 (17.0%)

44 (57.9%)

8.5

1 (0.8%)

0 (0%)

1 (1.3%)

9.0

1 (0.8%)

0 (0%)

1 (1.3%)

ETT sizes are all standardized numbers based on internal diameter in

millimeters. Numbers in columns designate number of patients. Percen-

tages designate the percentage of patients who had the specified size of

tube placed.

ETT

endotracheal tube.

TABLE III.

BMI Classification and Mean ETT Sizes.

BMI, kg/m

Males

Females

Mean ETT Sizes, mm

Males Females All

Underweight

7.5 N/A 7.5

Normal

7.69 6.88 7.42

Overweight

7.70 6.95 7.40

Obese

7.83 7.39 7.65

Range 14–70 Range 17–75

The number in each table row for the columns titled Males and

Females reflects the number of patients in each category.

Underweight: BMI

18.50, Normal: BMI 18.50–24.99, Overweight: BMI

25–29.99, Obese: BMI 30. Mean ETT sizes are all based on internal diam-

eter in millimeters.

BMI

body mass index; ETT

endotracheal tube.

Laryngoscope 125: May 2015

D’Anza et al.: BMI and Tracheal Airway Size

157