PT - JOURNAL ARTICLE AU - Taha Almufti AU - Franz Eversheim AU - Brett Johnson AU - Gabriel Ayonmigbesimi Akra TI - Platypnoea–orthodeoxia after left total knee replacement AID - 10.1136/bcr-2019-230771 DP - 2019 Oct 01 TA - BMJ Case Reports PG - e230771 VI - 12 IP - 10 4099 - http://casereports.bmj.com/content/12/10/e230771.short 4100 - http://casereports.bmj.com/content/12/10/e230771.full SO - BMJ Case Reports2019 Oct 01; 12 AB - Platypnoea–orthodeoxia syndrome (POS) is a rare disorder characterised by both dyspnoea (platypnoea) and arterial desaturation (orthodeoxia) in the upright position, with improvement in the supine position. We report an unusual case in which an 82-year-old woman developed severe hypoxaemia with POS after left total knee replacement. A significant difference in alveolar–arterial blood gas oxygen tension was demonstrated, and hypoxaemia failed to respond to 100% oxygen supply. A patent foramen ovale with a right-to-left shunt was evident on transoesophageal echocardiogram employing colour Doppler and agitated normal saline studies. Interestingly, the patient’s symptoms resolved within 6 months with ongoing chest physiotherapy, without surgical or medical intervention.