Table 3 -.
Associations between preoperative hemoglobin and outcomes according to sex
| Males |
Females |
|||||||
|---|---|---|---|---|---|---|---|---|
| Hb less than 14* | Hb above 14* | Hb less than 13* | Hb above 13* | |||||
| Outcome | Estimate (95% CI) per g/dL decrease | p | Estimate (95% CI) per g/dL increase | p | Estimate (95% CI) per g/dL decrease | p | Estimate (95% CI) per g/dL increase | p |
| Acute kidney injury | 1.10 (0.99 to 1.22) | 0.076 | 1.00 (0.79 to 1.26) | 0.980 | 1.49 (1.23 to 1.81) | <.001 | 0.90 (0.56 to 1.45) | 0.668 |
| Any perioperative RBCs | 2.56 (2.27 to 2.88) | <.001 | 0.74 (0.60 to 0.91) | 0.005** | 2.90 (2.33 to 3.60) | <.001 | 0.57 (0.47 to 0.69) | <.001** |
| Return to OR | 0.94 (0.85 to 1.04) | 0.256 | 0.76 (0.60 to 0.97) | 0.030** | 1.27 (1.11 to 1.45) | <.001 | 1.21 (0.98 to 1.49) | 0.074** |
| Vascular complications | 1.04 (0.87 to 1.23) | 0.681 | 0.93 (0.61 to 1.42) | 0.734 | 1.26 (0.96 to 1.67) | 0.101 | 1.54 (1.02 to 2.32) | 0.038** |
| Hospital length of stay† | 1.02 (1.01 to 1.04) | <.001 | 0.97 (0.95 to 0.99) | 0.009 | 1.05 (1.03 to 1.07) | <.001 | 1.02 (1.00 to 1.05) | 0.097** |
Results are from multivariable piecewise linear or logistic regression models. Estimates are odds ratios unless noted and reflect the sex-specific increase in odds associated with each 1 g/dL change (i.e. increase or decrease as noted) in hemoglobin within the given range. For each outcome, a model was fit with covariates, piecewise linear splines for males with knot at 14 g/dL, and piecewise linear splines for females with knot at 13 g/dL. Estimates for males and females are estimated from the same model. Covariables included type of surgery (valve vs. CABG), age, sex, BSA, smoking history, history of moderate to severe kidney disease, MI, stroke, diabetes, preoperative creatinine, platelets, and cardio-pulmonary bypass duration.
Indicates significant evidence (p<0.05) to suggest a difference in the relationship above vs below the knot point. Tests of whether associations differed above and below the knot point for each sex were performed. For males: p=0.540, <.001, 0.030, 0.887, and 0.607 for outcomes Acute kidney injury, Any perioperative RBCs, Return to OR, Vascular complications, and Hospital length of stay, respectively. For females: p=0.323, 0.004, 0.004, 0.027, and <.001 for outcomes Acute kidney injury, Any perioperative RBCs, Return to OR, Vascular complications, and Hospital length of stay, respectively.
The current ‘full’ model with sex-specific linear splines and different sex-specific knot points was compared to a reduced model assuming no sex-specific associations and a common knot at 13g/dL using Akaike Information Criterion (where lower indicates better fit). The current model suggested better fit for AKI (AIC=2410 vs 2417), Return to OR (3599 vs 3610), Vascular Complications (1262 vs 1263), and length of stay (2062 vs 2071), but not for Any perioperative RBCS (AIC=4344 vs 4343).
Estimates reflect the sex-specific multiplicative increase in geometric mean associated with each 1 g/dL change (i.e. increase or decrease as noted) in hemoglobin within the given range.