Spurious Fingertip Oxygen Desaturation During the 6-Minute Walk Test in a Patient With NSIP and Raynaud Phenomenon: The Value of Forehead Pulse Oximetry and Transcutaneous Oxygen Tension.

Reduced digital perfusion associated with Raynaud phenomenon may cause spuriously low fingertip pulse oximetry readings during the 6-minute walk test (6MWT), potentially leading to overestimation of exercise-induced hypoxaemia in patients with interstitial lung disease. We report a 39-year-old woman with non-specific interstitial pneumonia and Raynaud phenomenon who underwent repeated 6MWTs. Fingertip SpO2 progressively decreased from 96% to 82%, whereas forehead SpO2 remained stable (93%-98%). Simultaneously, transcutaneous oxygen tension (TcPO2) measured on the volar forearm remained unchanged. Progressive finger cooling and digital pallor were also observed. Fingertip SpO2 rapidly returned to baseline during recovery. These findings suggested that the apparent desaturation reflected reduced digital perfusion rather than true systemic hypoxaemia. This case highlights the potential limitations of fingertip pulse oximetry during exercise in patients with Raynaud phenomenon. Alternative methods of assessing oxygenation, such as forehead pulse oximetry or TcPO2, may be useful during the 6MWT when fingertip SpO2 readings are discordant with the clinical presentation.