Impact of Hypobarism During Simulated Transport on Critical Care Air Transport Team Performance

Abstract : Rapid, unacclimatized ascent to altitude results in a predictable fall in the partial pressure of oxygen and a reduction in arterial oxygenation. At 8000 feet, alveolar oxygen falls to 71 mmHg (barometric pressure of 564 mmHg). Under normal circumstances, this relative hypobaric hypoxia can be overcome by cardiac and pulmonary compensatory mechanisms. The added stress of caring for a critically ill patient and the physical demands may also impact the level of oxygen desaturation. During Critical Care Air Transport Team Advanced Course validation, three-member teams consisting of a physician, nurse, and respiratory therapist were approached regarding participation. Subjects were instrumented with a standard pulse oximeter with airworthiness approval. A forehead sensor was used to avoid motion artifact and interference with required tasks. The Environmental Symptoms Questionnaire IV (ESQ-IV) was completed by each participant (prior to flight at sea level and at the end of the 2-hour flight). Preflight data captured age, gender, height, weight, body mass index, smoking history, past medical history, and physical exercise history. The average and minimum pulse oximetry saturation (SpO2) and heart rate values were determined over 15-minute intervals from baseline and throughout the first 75 minutes at altitude. Mixed model analysis was used to compare outcomes across the five intervals. F-tests were used to determine whether or not those outcomes changed on average during flight and t-tests determined whether there were statistically significant differences in demographic characteristics or ESQ variables between subjects who were ever hypoxic and those who did not suffer hypoxia (SpO2 90%). One hundred subjects were studied (65 men, 35 women), with a mean age of 34 years and body mass index of 26 m2. At 8000 feet (564 mmHg), the mean SpO2 fell from 98.7 0.66 to 94.4 0.34 (mean standard error).