HSC Section 6 Nov2016 Green Book

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. 18 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. 19 Even cross-sectional changes during breathing and coughing as a result of changes in head and neck position and intrathoracic pressure can be noted. 4 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.

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. 15 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. 3 As demonstrated in Table I, the study population had average tracheal airway dimensions that were slightly smaller than published normative values. 16,17 A 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 Fig. 3. Airway area (mm 2 ) versus height (inches). Airway area on the y-axis is measured in mm. 2 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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