Table 5 Serum sodium concentrations for total group, arthroplasty type and with and without post-operative hyponatraemia
|  | Hip (n = 493) | Knee (n = 425) | Uni-knee (n = 82) | p-value1 | Hyponatraemia (Na < 135 mmol/L) post-operation (n = 217) | No hyponatraemia (Na ≥ 135 mmol/L) post-operation (n = 783) | p-value2 | Total (n = 1000) |
|---|---|---|---|---|---|---|---|---|
Post-operative Na < 135 mmol/L (n = 1000) | 100 (20.2%) | 101 (23.8%) | 16 (19.5%) | 0.391 | - | - | - | 217 (21.7%) |
Post-operative Na decrease ≥ 5 mmol/L (n = 1000) | *54 (11.0%) | *90 (21.2%) | 13 (15.9%) | < 0.001 | 111 (51.1%) | 106 (13.5%) | < 0.001 | 157 (15.7%) |
Pre-assessment Na (mmol/L) (n = 999) | 139.0 (138.0–141.0) | 140.0 (138.0–141.0) | 140.0 (138.0–141.0) | 0.129 | 138.0 (136.0–140.0) | 140.0 (138.0–141.0) | < 0.001 | 139.0 (138.0–141.0) |
Pre-operative Na (mmol/L) (n = 723) | 139.0 (138.0–141.0) | 139.0 (138.0–141.0) | 140.0 (138.0–141.0) | 0.807 | 138.0 (136.0–140.0) | 140.0 (138.0–141.0) | < 0.001 | 139.0 (138.0–141.0) |
Day 1 Na (mmol/L) (n = 994) | 138.0 (136.0–139.0) | 138.0 (136.0–139.0) | 138.0 (136.0–139.0) | 0.794 | 134.0 (133.0–136.0) | 138.0 (137.0–139.0) | < 0.001 | 138.0 (136.0–139.0) |
Day 2 Na (mmol/L) (n = 501) | *137.0 (135.0–139.0) | *137.0 (134.0–139.0) | 137.0 (135.0–140.0) | 0.039 | 134.0 (132.0–135.0) | 138.0 (137.0–140.0) | < 0.001 | 137.0 (135.0–139.0) |
Minimum post-operative Na (mmol/L) (n = 1000) | 137.0 (135.0–138.0) | 137.0 (135.0–138.0) | 137.0 (135.0–138.0) | 0.475 | 133.0 (131.0–134.0) | 138.0 (136.0–139.0) | < 0.001 | 137.0 (135–138.0) |
Na prior to discharge (mmol/L) (n = 988) | 138.0 (136.0–139.0) | 137.0 (135.0–139.0) | 138.0 (136.0–139.0) | 0.332 | 134.0 (133.0–137.0) | 138.0 (137.0–139.0) | < 0.001 | 138.0 (136.0–139.0) |
Change in Na (mmol/L) (n = 999) | *– 2.0 (– 4.0 to – 1.0) | *– 3.0 (– 5.0 to – 1.0) | – 3.0 (– 4.0 to – 1.0) | 0.012 | – 6.0 (– 8.0 to – 4.0) | – 2.0 (– 3.0 to – 1.0) | < 0.001 | – 3.0 (– 4.0 to – 1.0) |
Blood transfusion | 63 (12.4%) | 31 (7.3%) | 0 (0.0%) | < 0.001 | 44 (20.3%) | 50 (6.4%) | < 0.001 | 94 (9.4%) |
24-h blood loss (n = 989) | *1252.4 (972.6–1585.0) | *1064.5 (809.7–1320.8) | *535.2 (308.1–763.6) | < 0.001 | 1133.7 (869.1–1515.2) | 1109.0 (798.5–1402.4) | 0.128 | 1113.7 (810.8–1428.1) |
48-h blood loss (n = 989) | *1405.2 (1017.8–1794.8) | *1264.7 (929.9–1567.1) | *646.2 (357.5–808.9) | < 0.001 | 1390.3 (989.0–1817.9) | 1264.8 (885.0–1633.9) | 0.003 | 1287.7 (899.9–1675.8) |