3. Diagnostic criteria for pulmonary complications.

Study	Criteria
Aguero‐Martinez 2012	Respiratory depression
Barrington 2005	Respiratory depression: reintubation
Berendes 2003	Respiratory depression: need of ICU 24 hours due to intermittent respiratory insufficiency
Caputo 2011	Pneumonia: presence of purulent sputum associated with fever and requiring antibiotic therapy according to positive sputum culture
Celik 2015	Respiratory depression: PaCO₂ and PO₂ measurements at baseline and at first, sixth, and 12th hours were followed Pneumonia: fever, C‐reactive protein, leukocyte values, and chest radiography were assessed
de Vries 2002	Respirarory depression: respiratory acidosis Pneumonia: criteria of the Centers for Disease Control and Prevention
El‐Baz 1987	Respiratory depression: respiratory insufficiency requiring intubation and ventilatory support
Fillinger 2002	Respiratory depression: need for mechanical ventilation for 24 hours after surgery or clinical decision to initiate mechanical ventilation after initial tracheal extubation Pneumonia: positive sputum culture and chest radiograph changes
Hansdottir 2006	Respiratory depression: postoperative mechanical ventilation for longer than 24 hours or need for non‐invasive positive‐pressure ventilation Pneumonia: defined as pulmonary infiltrate with positive microbial cultures from sputum or fever, high leukocyte count, or high levels of C‐reactive protein
Kunstyr 2001	Respiratory depression: 8 or fewer breaths per minute and PaCO₂ > 55 kPa
Liem 1992	Respiratory depression: no details provided
Lundstrom 2005	Respiratory depression: constant hypoxaemia on third night after surgery
Mehta 2010	Respiratory depression: no details provided
Neskovic 2013	Respiratory depression: need for re‐intubation Pneumonia: febrile state, with new chest radiography findings
Obersztyn 2018	Respiratory depression: need for respiratory support after extubation
Onan 2013	Pneumonia: no details provided
Royse 2003	Respiratory depression: need for non‐invasive respiratory support or re‐intubation
Scott 2001	Respiratory depression: respiratory failure requiring tracheal re‐intubation or prolonged mechanical ventilation (> 24 hours) Pneumonia: combination of increased white cell count, pyrexia, productive sputum, radiological signs, and positive bacterial growth on culture
Tenenbein 2008	Respiratory depression: no details provided Pneumonia: no details provided
Yilmaz 2007	Pneumonia: respiratory infection
Yung 1997	Respiratory depression: re‐intubation
Zawar 2015	Respiratory depression: re‐intubation

ICU: intensive care unit; kPa: kilopascal; PaCO₂: partial pressure of carbon dioxide; PaO₂: partial pressure of oxygen.