Characteristics and distribution of variables by day versus night surgery in primary cohort
| Patient characteristics | Day surgery (n=3 22 327) | Night surgery (n=27 908) | Standardised difference |
| Sex, male, n (%) | 141 869 (44.0%) | 14 213 (49.0%) | 0.139 |
| Age (years), mean±SD | 54.08±16.47 | 52.77±18.77 | 0.074 |
| BMI (kg/m2), mean±SD* | 28.35±6.85 | 27.79±6.91 | 0.081 |
| ASA status, median (IQR)* | 2 (2 to 3) | 2 (2 to 3) | −0.241 |
| ASA ≥3, n (%)* | 108 366 (33.8%) | 113 029 (46.9%) | −0.269 |
| Admission type, n (%)* | −0.703 | ||
| Ambulatory | 119 881 (37.6%) | 3536 (12.9%) | |
| Same day admission | 143 328 (45.0%) | 12 407 (45.3%) | |
| Inpatient | 55 680 (17.4%) | 11 469 (41.8%) | |
| Institution | 0.146 | ||
| A | 186 593 (57.9%) | 18 127 (64.9%) | |
| B | 135 734 (42.1%) | 9781 (35.1%) | |
| Intraoperative data | |||
| Duration of surgery (min), median (IQR)* | 132.00 (85.00 to 205.00) | 113.00 (80.00 to 165.00) | 0.234 |
| Handover of anaesthesia care, n (%) | 28 827 (8.9%) | 6093 (21.8%) | −0.363 |
| Emergency surgery, n (%)* | 9464 (2.9%) | 10 868 (39.0%) | −0.987 |
| Work RVUs, median (IQR)* | 12.75 (7.03 to 19.61) | 10.93 (7.07 to 17.80) | 0.159 |
| Packed red blood cell units transfused intraoperatively, n (%) | −0.191 | ||
| 0 units | 311 914 (96.8%) | 25 785 (92.4%) | |
| 1 unit | 4475 (1.4%) | 819 (2.9%) | |
| 2 units | 3745 (1.2%) | 666 (2.4%) | |
| ≥3 units | 2193 (0.7%) | 638 (2.3%) | |
| Intraoperative hypotensive minutes of MAP <55 mm Hg, median (IQR) | 0.00 (0.00 to 2.00) | 0.00 (0.00 to 3.00) | −0.036 |
| Total intraoperative vasopressor dose, norepinephrine equivalent (mg), median (IQR) | 0.01 (0.00 to 0.10) | 0.01 (0.00 to 0.12) | −0.016 |
| Median SpO2/FiO2 ratio, median (IQR) * | 184.21 (161.29 to 222.27) | 178.57 (147.06 to 206.25) | 0.190 |
Frequency distributions of patient comorbidities and surgical services by day versus night surgery are provided in the online supplemental eTables 3 and 4. Characteristics and distribution of variables by day versus night surgery for the complete-case cohort are provided in the online supplemental eTable 5. Normally distributed continuous variables were expressed as mean (±SD), non-normally distributed variables as median (IQR), and categorical variables as frequency (percentages).
*Variables with missing data; Characteristics and distribution of variables by day versus night surgery are presented for cases with observed data.
ASA, American Society of Anesthesiologist’s Physical Status Classification System; BMI, body mass index; CCI, Charlson Comorbidity Index; MAP, mean arterial pressure; RVUs, relative value units.