Table 1. Basic characteristics about enrolled studies.

Study Characteristics						Intervention maneuver			Control maneuver		PPCs definition	PPCs endpoint
First author, year	Centers (n)	Patients (n)	Age (year)	BMI (kg/m2)	Surgery procedure	Lung recruitment maneuver	Tidal volume (ml/kg)	PEEP (cmH2O)	Tidal volume (ml/kg)	PEEP (cmH2O)
Ferrando,2018[9]	21	967	≥18	<35	abdominal surgery	step-wise until airway pressure reached 40 cmH2O; performed after intubation, repeat according to patient’s requirement	8	Individualised PEEP	8	5	pneumonitis, atelectasis, dyspnoea, hypoxaemia, pneumothorax, pneumonia, ARDS and so on	the first 7 postoperative days
Nestler,2017[15]	1	50	≥18	≥35	laparoscopic surgery	peak pressure 50cm H2O, PEEP 30cm H2O, respiratory rate 6 bpm, for 10 cycles an RM followed by a decremental PEEP titration and an additional RM was performed before extubation	8	Individualised PEEP	8	5	pneumonia or the need for invasive or non-invasive ventilation	During hospital stay
Choi,2017[19]	1	60	60–80	≤31	RARP	Staircase PEEP (4-16cmH2O), performed after intubation	6–8	5	6–8	5	Atelectasis or decreased saturation	During hospital stay
Aretha,2016[8]	1	90	>18	18–44	cesarean section	Staircase PEEP (0-20cmH2O) until a plateau pressure 45 cmH2O LRM lasted about 3 min and was not repeated	6	8	8	0	Pneumonia or pulmonary embolism	Postoperative day 3
Pi X,2015[16]	1	63	≥60	<35	non-laparoscopic abdominal elective major surgery	The tidal volume was increased 4 ml/kg until plateau pressure of 30 cm H2O three times; recruitment maneuvers were performed in every 30 min after tracheal intubation	7	8	7/9	8/0	dyspnea, pneumonia, pneumothorax, respiratory distress and chronic respiratory failure	During hospital stay
Shen, 2015[22]	1	120	Adult	NM	Thoracic or abdominal surgery	Applying a continuous positive airway pressure of 30cmH2O for 30s; recruitment maneuvers were performed in every 30 min after tracheal intubation	6	6	10	0	Pulmonary infection or atelectasis	The first 7 postoperative days
Hemmes,2014[14]	30	900	≥18	<40	open abdominal surgery	incremental increases in tidal volume; recruitment manoeuvres were performed after induction of anaesthesia, after any disconnection from the ventilator, and just before tracheal extubation	8	12	8	2	hypoxemia, bronchospasm, pulmonary infection, aspiration pneumonitis, ARDS, atelectasis, pulmonary edema, pneumothorax	The first 5 postoperative days
Ge Y,2013[13]	1	60	70–85	Not mention	spinal fusion surgery	PIP = 45cmH2O, Pplat≤30-35cmH2O; recruitment maneuvers repeated every 15 min	6	10	10	0	pulmonary infection, atelectasis, respiratory failure, hypoxemia	The first postoperative day
Futier E, 2013[20]	7	200	≥40	<35	Laparoscopic or non-laparoscopic elective major abdominal surgery	Applying a continuous positive airway pressure of 30cmH2O for 30s; recruitment maneuvers repeated every 30 minutes after tracheal intubation	6–8	6–8	10–12	0	Pneumonia or the need for invasive or noninvasive ventilation for acute respiratory failure	The first 7 postoperative days
Weingarten,2010[17]	1	40	>65	≤35	major open abdominal surgery	Staircase PEEP (0-20cmH2O) Lung recruitment was repeated at 30 and 60 min after the first recruitment and hourly thereafter.	6	12	10	0	acute lung injury, non-cardiogenic pulmonary oedema, pneumonia, atelectasis, pneumothorax	In the recovery room
Whalen,2006[18]	1	20	25–65	>40	laparoscopic bariatric surgery	Staircase PEEP (0-20cmH2O), the peak pressure not exceeding 50cmH2O; the requirement for repeated recruitment depended on the Pao2 response to the preceding maneuver		12	8,	4	pulmonary embolism, respiratory failure requiring mechanical ventilation or delayed tracheal extubation, pneumonia, atelectasis	During hospital stay

BMI: Body mass index; RARP: Robotic-assisted laparoscopic radical prostatectomy; PEEP: Positive end-expiratory pressure; PIP: peak inspiratory pressure; ARDS: acute respiratory distress syndrome