Editor—Despite several national consensus guidelines that single-use anaesthesia breathing circuits can be changed weekly, 1 Kramer A. Kranabetter R. Rathgeber J. et al. Infection prevention during anaesthesia ventilation by the use of breathing system filters (BSF): joint recommendation by German society of hospital Hygiene (DGKH) and German society for Anaesthesiology and intensive care (DGAI). GMS Krankenhhyg Interdiszip. 2010; 5: Doc13 Google Scholar , 2 Association of AnaesthetistsGuidelines: infection prevention and control. https://anaesthetists.org/Home/Resources-publications/Guidelines/Infection-prevention-and-control-2020Date: 2020 Google Scholar , 3 Australian and New Zealand College of anaesthetists, faculty of pain medicine. PG28(A) guideline on infection control in anaesthesia. 2015 Google Scholar , 4 Australian and New Zealand College of anaesthetists, faculty of pain medicine. Environmental sustainability audit tool. https://www.anzca.edu.au/resources/environmental-sustainability/eswg-audit-tool-(1).aspxDate: June 2020 Date accessed: October 15, 2023 Google Scholar many institutions around the world still change it more frequently than recommended. As anaesthesia departments around the world move in the direction of environmental sustainability, single-use consumables are frequently scrutinised. Breathing circuits, although recommended for single patient use by manufacturers, are validated for up to 7 days of usage. 1 Kramer A. Kranabetter R. Rathgeber J. et al. Infection prevention during anaesthesia ventilation by the use of breathing system filters (BSF): joint recommendation by German society of hospital Hygiene (DGKH) and German society for Anaesthesiology and intensive care (DGAI). GMS Krankenhhyg Interdiszip. 2010; 5: Doc13 Google Scholar ,2 Association of AnaesthetistsGuidelines: infection prevention and control. https://anaesthetists.org/Home/Resources-publications/Guidelines/Infection-prevention-and-control-2020Date: 2020 Google Scholar Many departments around the world use these circuits for multiple patients, simply by changing the heat and moisture exchange filter (HMEF) between cases. At least three studies have supported the safety of reusing circuits and changing them weekly rather than daily. 5 Hübner N.O. Daeschlein G. Lehmann C. et al. Microbiological safety and cost-effectiveness of weekly breathing circuit changes in combination with heat moisture exchange filters: a prospective longitudinal clinical survey. GMS Krankenhhyg Interdiszip. 2011; 6: Doc15 Google Scholar , 6 McGain F. Algie C.M. O'Toole J. et al. The microbiological and sustainability effects of washing anaesthesia breathing circuits less frequently. Anaesthesia. 2014; 69: 337-342 Google Scholar , 7 Dubler S. Zimmerman S. Fischer M. et al. Bacterial and viral contamination of breathing circuits after extended use—an aspect of patient safety?. Acta Anaesthesiol Scand. 2016; 60: 1251-1260 Google Scholar