Table 4.

Outcome analysis

	Non-OLS (n = 130)	OLS (n = 130)	Unadjusted relative risk (95% CI)	P value	Adjusted relative risk (95% CI)a	P valuea
Primary outcomeb
Major postoperative pulmonary and extrapulmonary complications	43 (33.1)	24 (18.5)	0.46 (0.26 to 0.81)	0.010	0.46 (0.26 to 0.82)	0.009
Secondary and post hoc outcomes
Complications within 7 days
Major pulmonary complications	41 (31.5)	24 (18.5)	0.49 (0.28 to 0.88)	0.022	0.49 (0.28 to 0.88)	0.016
Major extrapulmonary complications	6 (4.6)	2 (1.5)	0.32 (0.06 to 1.63)	0.281	0.32 (0.06 to 1.63)	0.171
Acute respiratory failure	39 (30.0)	24 (18.5)	0.53 (0.30 to 0.94)	0.042	0.53 (0.30 to 0.94)	0.031
Modified acute respiratory failurec,f	30 (23.1)	17 (13.1)	0.50 (0.26 to 0.96)	0.052	0.50 (0.26 to 0.96)	0.038
Suspected pneumoniag	16 (12.3)	3 (2.3)	0.17 (0.05 to 0.59)	0.003	0.18 (0.05 to 0.62)	0.007
Sustained hypoxaemia	24 (18.5)	15 (11.5)	0.58 (0.29 to 1.16)	0.164	0.58 (0.29 to 1.16)	0.121
Severe respiratory failured,f	0 (0.0)	0 (0.0)		1.000
All defined major PPCs in one patientf	11 (8.5)	3 (2.3)	0.26 (0.07 to 0.94)	0.051	0.26 (0.07 to 0.98)	0.047
Sepsis	6 (4.6)	2 (1.5)	0.32 (0.06 to 1.63)	0.281	0.32 (0.06 to 1.63)	0.171
Severe sepsis	0 (0.0)	0 (0.0)		1.000
Septic shock	0 (0.0)	0 (0.0)		1.000
SIRS	36 (27.7)	30 (23.1)	0.78 (0.48 to 1.37)	0.476	0.79 (0.44 to 1.41)	0.420
Acute myocardial infarction	0 (0.0)	0 (0.0)		1.000
Intra-abdominal abscess or anastomotic leakage	5 (3.8)	2 (1.5)	0.39 (0.07 to 2.05)	0.447	0.39 (0.07 to 2.05)	0.267
Death within 30 days	0 (0.0)	0 (0.0)		1.000
Admission to the ICU within 30 days	0 (0.0)	1 (0.8)	1.01 (0.99 to 1.02)	1.000
Postoperative hospital stay (days)	9 [8 to 13]	10 [8 to 12]		0.943
Modified postoperative hospital staye,f	9 [8 to 10]	8 [7 to 9]		0.130
Intra-operative complications (n = 140)
Pneumothorax	0 (0.0)	0 (0.0)		1.000
Rescue therapy for desaturation	0 (0.0)	0 (0.0)		1.000
Potentially harmful hypotension	6 (4.3)	21 (15.0)	3.94 (1.54 to 10.09)	0.004	3.32 (1.27 to 8.66)	0.014
Need for vasopressors	12 (8.6)	35 (25.0)	3.56 (1.76 to 7.19)	<0.001	2.98 (1.45 to 6.13)	0.003

Data are number (%) or median [IQR] as appropriate. Ten patients in each group were excluded from the study. All postoperative complications were defined according to consensus criteria (see the main text or the Supplementary Appendix). ICU, intensive care unit; OLS, open-lung strategy; PPCs, postoperative pulmonary complications; SIRS, systemic inflammatory response syndrome.

^aAdjustment was performed for preoperative risk index for PPCs, duration of mechanical ventilation, ASA physical status, abnormalities on chest radiography (and/or having COPD) and intra-operative red blood cells transfusion (and/or intra-operative blood loss ≥300 ml, and/or preoperative haemoglobin <8 g dl⁻¹).

^bThe primary outcome was a composite of major pulmonary complications (acute respiratory failure, suspected pneumonia and sustained hypoxaemia) and extrapulmonary complications (sepsis, severe sepsis, septic shock and death from any cause), defined as positive if any component occurred within the first 7 days after surgery.

^cMet the criterion of acute respiratory failure in twice follow-up or acute respiratory failure with sustained hypoxaemia.

^dExperienced an invasive or noninvasive ventilator therapy, or P_aO₂ less than 60 mmHg or SpO₂ less than 90% when administering oxygen via a nasal catheter at 3 l min⁻¹ or more.

^eOn the basis of the final analysis population (130 patients per group), this analysis excluded the patients who had none of the primary outcome events but had a postoperative hospital stay more than 10 days.

^fPost hoc outcomes.

^gAll of these patients had a postoperative chest X-ray except for three in the non-OLS group.