HSC Section 6 Nov2016 Green Book

TABLE I. Descriptive Statistics for the Entire Sample Stratified by Gender.

TABLE II. ETT Sizes for the Entire Sample.

Entire Sample, N 5 123

Female, n 5 47

Male, n 5 76

P Value

ETT Size, mm Entire Sample

Female

Male

Variable

6.0

12 (9.8%)

8 (17.0%)

4 (5.3%)

Age, yr

63.1 (15.3)

65.1 (14.2)

61.9 (15.9)

.2636

6.5 7.0

3 (2.4%)

2 (4.3%)

1 (1.3%) 4 (5.3%)

BMI, kg/m 2

32.4 (11.8)

33.5 (12.5)

31.7 (11.3)

.3919

12 (9.8%)

8 (17.0%)

CT AP, mm 20.8 (4.4)

18.8 (4.4)

22.1 (4.0)

< .0001

7.5

42 (34.2%)

21 (44.7%)

21 (27.6%)

CT width, mm 17.2 (3.5)

15.6 (2.8)

18.3 (3.6)

.7164

8.0 8.5

52 (42.3%)

8 (17.0%)

44 (57.9%)

Airway area, mm 2

294.8 (112.8) 240.0 (87.4) 328.8 (113.7) < .0001

1 (0.8%)

0 (0%)

1 (1.3%)

9.0

1 (0.8%)

0 (0%)

1 (1.3%)

Values for age, BMI, CT AP, CT width, and airway area reflect the average (mean) calculation. Standard deviation is noted in parentheses AP 5 anterior-posterior diameter; BMI 5 body mass index; CT 5 com- puted tomography.

categorical variables. Data are described for the full sample and stratified by gender. Comparison across gender was accom- plished using the two-sample t test and Pearson v 2 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. 10 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 5 endotracheal tube. 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 ( P 5 .0389). For every 1 kg/m 2 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.

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

TABLE III. BMI Classification and Mean ETT Sizes.

Mean ETT Sizes, mm

BMI, kg/m 2

Males

Females

Males Females All

Underweight

4

1

7.5 N/A 7.5

Normal

18 15

9

7.69 6.88 7.42 7.70 6.95 7.40

Overweight

10

Obese

39

27

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 5 < 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 5 body mass index; ETT 5 endotracheal tube.

Laryngoscope 125: May 2015

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

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