Table 2. Intraoperative Characteristics, Ventilation, and Oxygenation.
| Low tidal volume (n = 614) | Conventional tidal volume (n = 592) | Absolute difference (95% CI) | P value | |
|---|---|---|---|---|
| Tidal volume | ||||
| Absolute, mL | ||||
| Mean (SD) | 396.6 (83.5) | 611.1 (111.9) | −214.5 (−225.7 to −203.2)a | <.001 |
| Median (IQR) | 395 (340-446) | 620 (525-700) | ||
| Adjusted, mL/kg PBWb | ||||
| Mean (SD) | 6.3 (1.0) | 9.7 (1.0) | −3.4 (−3.5 to −3.3)a | <.001 |
| Median (IQR) | 6.0 (6.0-6.1) | 10.0 (9.8-10.0) | ||
| PEEP, cm H2O | ||||
| Mean (SD) | 5.0 (1.0) | 5.0 (1.0) | 0.0 (−0.0 to 0.0)a | .33 |
| Median (IQR) | 5 (5-5) | 5 (5-5) | ||
| Highest peak pressure, mean (SD), cm H2O | 22.7 (6.2) | 25.1 (6.3) | −2.4 (−3.1 to −1.7)a | <.001 |
| Respiratory rate, mean (SD), /min | ||||
| Lowest | 12.4 (2.6) | 9.2 (2.0) | 3.2 (2.9 to 3.4)a | <.001 |
| Highest | 16.2 (3.4) | 11.6 (2.5) | 4.6 (4.2 to 4.9)a | <.001 |
| Lowest Spo2, mean (SD), % | 96.5 (2.4) | 96.9 (2.3) | −0.4 (−0.6 to −0.1)a | <.01 |
| Fio2, mean (SD), % | ||||
| Lowest | 47.6 (11.9) | 47.4 (12.2) | 0.2 (−1.2 to 1.6)a | .78 |
| Highest | 71.1 (22.0) | 70.4 (22.6) | 0.7 (−1.9 to 3.2)a | .60 |
| Highest end-tidal carbon dioxide, mean (SD), mm Hg | 41.3 (5.5) | 37.4 (4.9) | 3.9 (3.3 to 4.5)a | <.001 |
| Arterial blood gas measurements after induction | ||||
| pH, mean (SD) | 7.37 (0.05) | 7.41 (0.05) | −0.04 (−0.05 to −0.04)a | <.001 |
| Pao2, mean (SD), mm Hg | 231.0 (94.1) | 237.8 (88.2) | −6.8 (−17.5 to 3.8)a | .21 |
| Paco2, mean (SD), mm Hg | 44.0 (5.8) | 39.1 (5.1) | 4.9 (4.3 to 5.5)a | <.001 |
| Bicarbonate, mean (SD), mmol/L | 25.0 (2.1) | 24.5 (2.5) | 0.5 (0.2 to 0.7)a | <.01 |
| Pao2/Fio2, mean (SD) | 412.3 (143.1) | 426.8 (130.0) | −14.5 (−30.7 to 1.6)a | .08 |
| Base excess, mean (SD) | 0.2 (2.5) | 0.5 (2.4) | −0.2 (−0.5 to 0.0)a | .08 |
| Hemoglobin, mean (SD), g/dL | 12.5 (1.8) | 12.4 (1.7) | 0.3 (−1.7 to 2.4)a | .73 |
| Lactate, mean (SD), mmol/L | 1.2 (0.5) | 1.3 (0.7) | −0.1 (−0.2 to −0.0)a | <.01 |
| Hypoxemia, No. (%)c | 0 | 0 | ||
| Acidosis, No. (%)d | 36 (6.3) | 5 (0.9) | 5.3 (3.3 to 7.6)e | <.001 |
| Hypercapnia, No. (%)f | 6 (1.0) | 1 (0.2) | 0.8 (−0.0 to 1.9)e | .06 |
| Arterial blood gas measurements prior to closure | ||||
| pH, mean (SD) | 7.34 (0.06) | 7.38 (0.06) | −0.04 (−0.05 to −0.04)a | <.001 |
| Pao2, mean (SD), mm Hg | 192.2 (71.2) | 197.1 (68.9) | −4.9 (−13.3 to 3.4)a | .25 |
| Paco2, mean (SD), mm Hg | 46.1 (7.8) | 40.4 (6.3) | 5.6 (4.8 to 6.5)a | <.001 |
| Bicarbonate, mean (SD), mmol/L | 24.0 (2.2) | 23.6 (2.6) | 0.4 (0.1 to 0.7)a | <.01 |
| Pao2/Fio2, mean (SD) | 387.3 (138.7) | 400.0 (127.7) | −12.7 (−28.7 to 3.4)a | .12 |
| Base excess, mean (SD) | −1.2 (2.7) | −0.9 (2.4) | −0.2 (−0.5 to 0.1)a | .12 |
| Hemoglobin, mean (SD), g/dL | 12.1 (1.8) | 12.0 (1.8) | 0.5 (−1.6 to 2.7)a | .63 |
| Lactate, mean (SD), mmol/L | 1.4 (0.7) | 1.6 (1.4) | −0.2 (−0.4 to −0.1)a | <.01 |
| Hypoxemia, No. (%)c | 2 (0.4) | 0 | ||
| Acidosis, No. (%)d | 113 (20.4) | 42 (7.8) | 12.6 (8.6 to 16.7)e | <.001 |
| Hypercapnia, No. (%)f | 24 (4.3) | 6 (1.1) | 3.2 (1.4 to 5.2)e | <.01 |
| Duration of surgery, min | ||||
| Mean (SD) | 223.6 (127.1) | 212.8 (121.0) | 10.7 (−3.4 to 24.9)a | .14 |
| Median (IQR) | 189 (135-267) | 185 (140-249) | ||
| Use of regional anesthesia, No. (%)g | 180 (30.0) | 164 (28.0) | 2.0 (−3.2 to 7.1)e | .46 |
| Epidural | 16 (2.7) | 9 (1.5) | 1.1 (−0.5 to 2.8)e | .17 |
| Spinal opioid | 106 (17.7) | 93 (15.9) | 1.8 (−2.5 to 6.0)e | .41 |
| TAP/abdominal blockh | 33 (5.5) | 25 (4.3) | 1.2 (−1.2 to 3.7)e | .33 |
| Otheri | 84 (14.0) | 78 (13.4) | 0.6 (−3.3 to 4.6)e | .75 |
Abbreviations: Fio2, fraction of inspired oxygen; IQR, interquartile range; Pao2, partial pressure of oxygen; Paco2, partial pressure of carbon dioxide; PEEP, positive end-expiratory pressure; Spo2, arterial oxygen saturation measured by pulse oximetry.
Mean difference from a generalized linear model considering a Gaussian distribution.
Predicted body weight (PBW) was calculated as 50 + 0.91 × (height [cm] – 152.4) for men and 45.5 + 0.91 × (height [cm] – 152.4) for women.
Defined as Pao2 <60 mm Hg.
Defined as pH <7.30.
Risk difference from a generalized linear model considering a binomial distribution with an identity link.
Defined as Paco2 >60 mm Hg.
In addition to general anesthesia.
Transversus abdominis plane block (TAP) is defined as block of a peripheral nerve designed to anesthetize the nerves supplying the anterior abdominal wall (T6 to L1).
Other: brachial plexus block, femoral nerve block, fascia iliaca block, sciatic nerve block, intercostal nerve block, interpleural catheter, wound catheter.