Pulse Oximetry Algorithm for Preflight Evaluation May Identify Patients with COPD Who Can Fly without Further Assessment
DynaMed Weekly Update - Volume 7, Issue 29
Due to reduced cabin pressure, air travel can increase the risk of hypoxemia in patients with COPD. The gold standard for preflight risk assessment in these patients is the hypoxia-altitude simulation test (HAST), which requires arterial blood gas measurement after breathing a gas mixture with 15.1% oxygen (simulating cabin pressure at 8,000 feet altitude). Supplemental in-flight oxygen is recommended for patients with arterial oxygen pressure (PaO2) < 6.6 kPa (49.5 mm Hg) on HAST. Guidelines from the British Thoracic Society (BTS) recommend this test for any patient with resting oxygen saturation (SpO2) at sea level < 95% (Thorax 2011 Sep;66 Suppl 1:i1). The HAST is mildly invasive, relatively difficult to perform, and not widely available. A recent study derived and validated a new algorithm to simplify assessment of the need for supplemental oxygen based on resting and exercise pulse oximetry.
The algorithm was derived in a cohort of 100 patients (mean age 65 years) with moderate to very severe COPD who had been referred for preflight testing. All patients had both HAST evaluation and SpO2 measurement by pulse oximetry at rest and during exercise (6-minute walk test). According to the new algorithm, supplemental oxygen is required if resting SpO2 < 92% or resting SpO2 = 92%-95% AND exercise SpO2 < 84%. Supplemental oxygen would not be required if resting SpO2 > 95% AND exercise SpO2 ≥ 84%. For patients with other pulse oximetry results, the algorithm recommends performing HAST assessment.
The algorithm was validated in an independent cohort of 50 similar patients. All 16 patients who were classified by the algorithm as not needing supplemental oxygen were correctly identified (confirmed by HAST). There were 4 patients who were incorrectly classified as needing oxygen. By the BTS guideline, 27 patients would have required HAST evaluation, but the algorithm indicated HAST for only 20 patients, a reduction of 26%. For predicting the need for in-flight supplemental oxygen, the algorithm had 100% sensitivity and 80% specificity (Thorax 2012 Jul 6 early online). One caveat regarding this algorithm is that pulse oximetry may not accurately reflect arterial oxygenation in certain patients, such as those with hemoglobinopathies.
For more information, see the COPD topic in DynaMed.