Schnurr 2018.

Study characteristics
Methods	Design: RCT, parallel two‐arm, multicentre study Setting: 3 hospitals in Germany (1 university teaching hospital, 2 general hospitals) Recruitment: April 2015 to June 2016 Maximum follow‐up: 42 days postoperatively
Participants	200 participants undergoing total knee arthroplasty were randomised to one of two groups: Autologous blood transfusion drain (Cell salvage/intervention group): N = 100. M:F 24:76. Mean age 70. Mean BMI 31. Redon drain group (Control/no cell salvage group): N = 100. M:F 31:69. Mean age 70. Mean BMI 30. Demographic and preoperative variables were comparable between the two groups at baseline assessment.
Interventions	Autologous blood transfusion drain (Cell salvage/intervention group): the ABT group received an OrthoPAT (Haemonetics, Braintree, USA) re‐transfusion drain, connected to the intra‐articular drain for 6 hours postoperatively. At 6 hours, the transfusion system was replaced with a Redon drain without vacuum assistance. Redon drain group (Control/no cell salvage group): the Redon group received a Redon drain without vacuum assistance connected to the intra‐articular drain. Drains in both groups were removed after 24 hours.
Outcomes	Outcomes reported: blood loss, number of participants exposed to allogeneic blood transfusion, volume of allogeneic blood transfused, complications
Notes	Transfusion protocol: autologous transfusion was initiated for the following reasons: Collected blood volume > 100 mL and haemoglobin < 100 g/dL Collected blood volume > 100 mL and clinical symptoms of anaemia The following transfusion triggers were used for allogeneic blood transfusions in both groups: In patients with no history of coronary heart disease – haemoglobin < 10 g/dL and symptoms of anaemia or haemoglobin < 7 g/dL without symptoms. In patients with a history of coronary heart disease – haemoglobin < 10 g/dL with symptoms of anaemia or haemoglobin < 9 g/dL without symptoms. When a transfusion was required, a single unit of blood (300 mL) was given and re‐evaluation was performed 6 hours afterwards. Prospective registration status: the study was not prospectively registered with a trials registry Ethical approval: the study was approved by the Institutional Review Board for Ärztekammer Nordrhein, Düsseldorf, Germany (reference number 2014378) Language of publication: English Trial funding: none reported Conflicts of interest: none reported
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Participants were randomised to one of two groups using 200 pre‐prepared sealed (shuffled) envelopes containing the group name. One of the sealed envelopes was selected by the anaesthetist
Allocation concealment (selection bias)	Unclear risk	Sealed envelopes were pre‐prepared prior to randomisation process, no mention of opaqueness
Blinding of participants and personnel (performance bias) Objective outcome: mortality	Low risk	No objective outcomes reported (mortality unlikely to be affected by blinding if reported in future publications)
Blinding of participants and personnel (performance bias) Subjective: transfusion protocol	Low risk	Transfusion protocol in place: (A) Participants with no history of a coronary heart disease: 1. haemoglobin < 10 g/dL and symptoms of anaemia (nausea, vomiting, hypotension, tachycardia, cardiac symptoms); 2. haemoglobin < 7 g/dL with or without symptoms of anaemia. (B) Participants with a history of a coronary heart disease: 1. haemoglobin < 10 g/dL and symptoms of anaemia (nausea, vomiting, hypotension, tachycardia, cardiac symptoms); 2. haemoglobin < 9 g/dL with or without symptoms of anaemia. Where a transfusion was required, a single blood unit (300 mL) was given.
Blinding of participants and personnel (performance bias) Subjective: all other outcomes	Unclear risk	No information is available regarding the blinding of outcome assessors
Blinding of outcome assessment (detection bias) Objective outcomes: mortality and transfusions	Low risk	No objective outcomes reported (mortality unlikely to be affected by blinding if reported in future publications)
Blinding of outcome assessment (detection bias) Subjective outcomes	Unclear risk	No information is available regarding the blinding of outcome assessors, but transfusion protocol and blood loss calculation thorough. Not sure how PJI and wound complications were determined
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	No mention of individuals identified who did not meet criteria or loss to follow‐up
Selective reporting (reporting bias)	High risk	No trial registration or published protocol is available to compare, but there is discrepancy between the described outcome measures in the methodology and those presented in the results.
Other bias	Low risk	No baseline imbalance, conflicts declared (none), funding declared (none)