
Multivariate analysis
OR (95% CI)
n = 1.624*

β

Risk score^{a}


Age, years

≤ 50

1
  
51–80

1.4 (0.6–3.3)

0.331

3

> 80

5.1 (1.9–13.3)

1.619

16

Preoperative SpO_{2}, %

≥ 96

1
  
91–95

2.2 (1.2–4.2)

0.802

8

≤ 90

10.7 (4.1–28.1)

2.375

24

RTI in preceding month

5.5 (2.6–11.5)

1.698

17

Preoperative anemia (Hb ≤ 10 g/dL)

3.0 (1.4–6.5)

1.105

11

Surgical incision

Peripheral

1
  
Upper abdomen

4.4 (2.3–8.5)

1.480

15

Intrathoracic

11.4 (4.9–26.0)

2.431

24

Duration of surgery, hours

≤ 2

1
  
> 2–3

4.9 (2.4–10.1)

1.593

16

> 3

9.7 (4.7–19.9)

2.268

23

Emergency procedure

2.2 (1.0–4.5)

0.768

8

 Three patients were excluded because of a missing value for some variables. Logistic regression model constructed with the development subsample, cindex = 0.90; HosmerLemeshow chisquare test = 7.862; P = 0.447
 CI confidence interval, Hb hemoglobin, OR odds ratio, PPC postoperative pulmonary complications, RTI respiratory tract infection, SpO2 oxyhemoglobin saturation by pulse oximetry (breathing room air in the supine position)
 ^{a}Simplified risk score was the sum of each logistic regression coefficient (β) multiplied by 10, after rounding off