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thought to compromise upper airway patency, especially

when obese patients are supine.

Obese subjects have been shown to have increased

positive end expiratory pressures due to extrinsic com-

pression of surrounding tissues.

Based on the current

study results, these relationships may also extend to the

tracheal airway. The cartilage framework is more resist-

ant to external thoracic pressures than the soft tissues

of the lungs, oropharynx, or hypopharynx; however, the

lack of caudal traction may be playing a role in the

increased collapsibility and resultant decreased caliber

of the airway. This may be especially pronounced as it

relates to the membranous portion of the trachea as evi-

denced in the significantly decreased airway width of

the obese study subjects. Other factors, such as genetic

differences in cartilage composition, strength of sur-

rounding musculature, inherent conditions of the tra-

chea, such as tracheomalacia, could all be contributing.

Further studies are needed to better examine these rela-

tionships in the trachea.

It is worth mentioning that when compared to

females, males were found to have larger tracheal

dimensions at the first tracheal ring. This is consistent

with previous reports.

As demonstrated in Table I, the study population

had average tracheal airway dimensions that were

slightly smaller than published normative values.

16,17

large radiographic study performed by Breatnach et al.

showed that the average tracheal airway width and AP

diameter were 25 and 27 mm in men and 21 and 23 mm

in women, respectively. These are generally accepted to

be average airway dimensions for a presumably normal-

sized population. Conversely, our patient sample had a

much higher proportion of obese patients compared to

the general population, comprising well over half the

cohort. According to the Centers for Disease Control, the

percentage of the US population that was obese was

35.5% and 35.8% for men and women, respectively.

This would seem to further corroborate the evidence

that there may be an inverse correlation between obesity

and airway size.

A patient with a higher body mass index might be

presumed to have a larger tracheal airway. Anecdotally,

we have found it is not uncommon to see an inappropri-

ately sized ETT chosen for use in such a patient. Our

data corroborate this contention, as obese patients were

found on average to have a larger ETT in place, as

shown in Table III. More importantly, the results of our

study suggest that further research is needed in this

area, as it is incorrect to assume a larger patient

deserves a larger tube based on body size.

There are several limitations to our data. First, our

study represents a retrospective case series of a limited

population without randomization. Other limitations of

this study include the inability to account for any

chronic airway disease, such as tracheomalacia, which

could lead to dynamic airway changes. Patients with

acquired tracheomalacia can have more dynamic

changes of the trachea, which has been noted on CT

imaging studies previously.

Even cross-sectional

changes during breathing and coughing as a result of

changes in head and neck position and intrathoracic

pressure can be noted.

One could make the argument

that a larger ETT is required for obese patients to coun-

teract the compressive forces on the airway. This must

be balanced against the concern for further airway

trauma and resultant complications such as stenosis,

webbing, and ulcerations. The study population is also

nearly exclusively from the intensive care unit, as the

overwhelming majority of the tracheostomies performed

at our institution are due to ventilator-dependent respi-

ratory failure. This may bias the results as it relates to

the type and size of tubes chosen. However, it is pre-

cisely this population of severely ill patients who require

long-term intubation and who we are concerned about

developing complications of tracheal trauma.

CONCLUSION

The population in this study demonstrated signifi-

cant decreases in airway size with increasing BMI.

Obese patients demonstrated radiographic evidence of a

significant decrease in width and area of the airway.

There was a trend for larger ETTs being placed in

patients with a higher BMI. These findings have impli-

cations for airway management in obese populations.

This study does not confirm the need to place a smaller

tube in obese patients, but does suggest that due to

smaller tracheal airway sizes, there may be a higher

risk of airway injury in obese populations. Larger tubes

are not anatomically indicated simply because of a

greater BMI. More research in this population is needed

to address airway management of obese patients. Cur-

rently, there is a lack of literature addressing this topic.

This becomes more important, as population rates of

obesity have become epidemic.

Fig. 3. Airway area (mm

) versus height (inches). Airway area on

the y-axis is measured in mm.

Height (ht) in on x-axis is meas-

ured in inches. The white circle represents one individual male

subject. The solid square represents one individual female subject.

The solid line represents the linear regression analysis for all male

subjects. The dotted line represents the linear regression analysis

for all female subjects. [Color figure can be viewed in the online

issue, which is available at

www.laryngoscope.com.

]

Laryngoscope 125: May 2015

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

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