Table 1. Baseline Participant Characteristics.
| Characteristics | Low tidal volume (n = 614) | Conventional tidal volume (n = 592) |
|---|---|---|
| Age, mean (SD), y | 63.5 (11.8) | 63.8 (12.1) |
| Sex, No. (%) | ||
| Male | 366 (59.6) | 346 (58.4) |
| Female | 248 (40.4) | 246 (41.6) |
| Body weight, mean (SD), kg | ||
| Actual | 82.6 (20.1) | 82.9 (18.5) |
| Predicted | 63.0 (10.4) | 63.2 (10.4) |
| Body mass index, mean (SD)a | 29.0 (6.5) | 29.1 (6.2) |
| ARISCAT score, mean (SD)b | 27.7 (11.9) | 27.4 (12.1) |
| No. (%) | n = 554 | n = 518 |
| Low | 193 (34.8) | 196 (37.8) |
| Moderate | 324 (58.5) | 282 (54.4) |
| High | 37 (6.7) | 40 (7.7) |
| American Society of Anesthesiology physical status, No. (%)c | n = 606 | n = 584 |
| 1 (Healthy) | 65 (8.7) | 51 (10.7) |
| 2 (Mild systemic disease) | 225 (38.0) | 222 (37.1) |
| 3 (Severe systemic disease) | 282 (48.6) | 284 (46.5) |
| 4 (Severe systemic disease that is a constant threat to life) | 34 (4.6) | 27 (5.6) |
| Preoperative Spo2, mean (SD), % | 96.8 (1.4) | 96.8 (1.4) |
| <96%, No./total (%) | 107/608 (17.6) | 101/585 (17.3) |
| Preoperative laboratory measurements, mean (SD) | ||
| Bicarbonate, mmol/L | 25.8 (2.6) | 25.8 (2.5) |
| Hemoglobin, g/dL | 13.7 (1.8) | 13.6 (1.8) |
| Creatinine, mg/dL | 1.04 (0.85) | 1.09 (1.01) |
| >1.70, No./total (%) | 20/442 (4.5) | 23/408 (5.6) |
| Comorbidities, No./total (%) | ||
| Hypertension | 301/613 (49.1) | 327/591 (55.3) |
| Obesityd | 225/595 (37.8) | 207/562 (36.8) |
| Diabetes | 119/613 (19.4) | 126/591 (21.3) |
| Current smoker | 100 (16.3) | 109 (18.4) |
| Coronary artery disease | 93/613 (15.2) | 100/591 (16.9) |
| Asthma | 66 (10.7) | 68 (11.5) |
| Chronic obstructive pulmonary disease | 62 (10.1) | 65 (11.0) |
| Obstructive sleep apnea | 59 (9.6) | 63 (10.6) |
| Chronic renal disease | 56/613 (9.1) | 67/591 (11.3) |
| Chronic liver disease | 48/613 (7.8) | 52/591 (8.8) |
| Recent lower respiratory tract infection | 8 (1.3) | 8 (1.4) |
| Interstitial lung disease | 8 (1.3) | 2 (0.3) |
| Bronchiectasis | 1 (0.2) | 1 (0.2) |
| Type of surgery, No./total (%) | ||
| Abdominal | 348 (56.7) | 333/591 (56.3) |
| Laparoscopic | 158/348 (45.4) | 170/333 (51.1) |
| Spine | 125 (20.4) | 120/591 (20.3) |
| Orthopedic | 43 (7.0) | 46/591 (7.8) |
| Plastic | 31 (5.0) | 36/591 (6.1) |
| Vascular | 29 (4.7) | 28/591 (4.7) |
| Ear, nose, and throat | 17 (2.8) | 13/591 (2.2) |
| General | 6 (1.0) | 2/591 (0.3) |
| Other | 15 (2.4) | 13/591 (2.2) |
| Emergency surgery, No./total (%) | 29/613 (4.7) | 17/591 (2.9) |
Abbreviation: Spo2, arterial oxygen saturation measured by pulse oximetry.
SI conversion: To convert creatinine to micromoles per liter, multiply by 88.4.
a
Calculated as weight in kilograms divided by height in meters squared.
b
The Assess Respiratory Risk in Surgical Patients in Catalonia (ARISCAT) score ranges from 0 to 123; higher scores indicate a higher risk of postoperative pulmonary complications. Patients with scores of 26 or greater are considered at intermediate risk; those with a score greater than 44 are considered at high risk.
c
Scores in the American Society of Anesthesiologists physical status classification system range from 1 to 6, with higher scores indicating a more severe condition.
d
Defined as body mass index greater than 30.