Once the score from the questionnaire has been obtained, along with concerns and suspicions for OSAHS, an appropriate investigation needs to be performed. An overnight pulse oximetry is the first-line diagnostic tool to confirm a diagnosis. A modified sleep study is also used as a diagnostic tool; this can give important data on the severity of the OSA, detecting apnoeas and hypopnoeas according to their frequency, duration, oxygenation or oxygen desaturation.