Combined Effects of Air Transport, Intubation Lead

Newswise — Intubation and decreased barometric pressures encountered during high altitude transport may lead to an increased rate of vocal cord paralysis of military burn victims. This is a finding of a retrospective study conducted by otolaryngologist—head and neck surgeons at the Brook Army Medical Center in Texas.

Partial or complete vocal cord paresis or paralysis can result in impaired communication, swallowing, as well as an inability to produce an effective cough. This condition occurs most often due to an interruption in nerve conduction from the brainstem to the laryngeal muscles along the course of the vagus and recurrent laryngeal nerves. This interruption is attributed to a wide range of reasons, including adverse response to medical or surgical treatment, neoplasms of the base of skull, or a penetrating injury to the neck.

Despite a complete evaluation, 10-27 percent of patients with partial or full vocal cord paralysis will fail to demonstrate a clear cause for their laryngeal dysfunction, and are classified as having idiopathic vocal cord paresis. Frequently, burn injured patients fall into this group. They endure a prolonged hospital stay, often in the burn intensive care unit, where ventilator support, numerous attempts at central venous access, and nasogastric tube placement for nutrition are commonplace. Their bodies often undergo massive fluid shifts, prolonged periods of immobilization, and require the constant attention of highly trained medical staff.

Burn injured patients undergo extreme psychological and physical demands during a prolonged recovery from a painful and often disfiguring injury. Frustrations with interpersonal communication, aspiration pneumonia, and difficulties with normal diet may delay an otherwise difficult recovery.

Burn injured patients within the Department of Defense (DOD) are preferentially transported to the Burn Center, located at Brook Army Medical Center (BAMC) in San Antonio, Texas. With increased exposure to improvised explosive devices during the military's present engagements, there have been a significant number of burn and blast injuries.

The Otolaryngology service at the BAMC noted an increased number of vocal cord paralysis consults from the facility's Burn Center. Accordingly, a study was undertaken to identify the cause or causes of vocal cord paralysis in these burn-injured patients, in an attempt to reduce morbidity among already injured servicemen. The authors of "Vocal Fold Dysfunction in the Burn Injured Patient," are Travis J. Pfannenstiel MD, David K. Hayes MD, and Karen V. Myers, all from the Brooke Army Medical Center, Fort Sam Houston; and Thomas J. Gal MD MPH, at the Wilford Hall Medical Center, Lackland AFB, all in Texas. Their findings are being presented at the Annual Meeting of the American Laryngological Association, being held May 19-20, 2006, at the Hyatt-Regency Hotel in Chicago, IL.

Methodology: All patients admitted to the Burn Service between June 2002 and November 2004 who underwent evaluation by a speech pathologist were included in this analysis. Patients were excluded if there were any surgical intervention or penetrating injury known to place the recurrent laryngeal nerve at risk or any pre-existing condition known to cause vocal cord paralysis. Vocal cord paresis was defined as partial or total immobility of either or both vocal cords, ascertained by videostroboscopy.

Data on identified subjects included age, gender, height, weight, body mass index (BMI), total body surface area burn (TBSA), pre-existing medical conditions, length of hospital and intensive care unit (ICU) stay, presence of inhalational injury, number of intubations, duration of intubation, longest duration of intubation, site of intubation (BAMC, Combat Support Hospital, non-DOD facility, or field), tracheotomy, duration of intubation prior to tracheotomy), days with nasogastric tube placed, use of vasopressors, history of transfusion, and internal jugular catheter placement (attempts left/right, # lines left/right). Subjects deemed having vocal cord paralaysis were further classified by side (left, right, or bilateral). In this case-control study, the primary outcome was to determine differences in dependent variables across groups defined by vocal cord paresis.

Results: Speech pathologists identified 52 patients at the BAMC Burn Center with hoarseness or dysphagia. Of these, 25 were diagnosed with vocal cord paralysis. The distribution was that 17 had left vocal cord paresis, six patients had right cord paresis, and two patients had bilateral cord paresis.

Univariate analysis using logistic regression was performed to determine factors associated with the presence of vocal cord paresis in this cohort. Of the 19 variables examined, only a history of intubation during overseas transportation of these patients was significantly associated with the development of vocal cord paralysis in this cohort. Patients who arrived to the Burn Center with a history of intubation during overseas transport demonstrated a 4.5-fold increased risk of vocal cord paresis. Multivariate analysis did not demonstrate any additional variables of significance. However, when adjusted for the severity of burn (TBSA), the odds ratio for risk of vocal cord paresis associated with overseas transport increased to 9.83. The risk of vocal cord paresis increased three percent for each percentage increase in burn surface area.

Conclusions: Vocal cord paresis in the intensive care population is frequently attributed to intubation injury. It is well known that prolonged intubation increases the risk of vocal cord paresis. Patients intubated longer than six days have been reported to have a 20-26 percent incidence of post extubation vocal cord paresis. In this review, patients with and without vocal cord paresis were intubated for similar lengths of time. Unique to this cohort is the disproportionate number of patients who were not only intubated for extended lengths of time, but were also transported overseas by air from combat arenas to appropriate centers of care in the U.S. The increased relative risk of vocal cord paresis may stem from the effects of differences in endotracheal cuff pressures encountered during overseas transport. It is possible that decreased barometric pressures encountered during high altitude transport cause increases in the volume of the endotracheal cuff and thereby traumatize both the trachea and possibly the recurrent laryngeal nerve.

The results of this study have compelled military aeromedical evacuation teams to investigate their current management of intubated patients in flight, and the results of these interventions are forthcoming.