Table 4. Linear mixed-effects model to describe the effect of variables on COHb levels in the absence of sepsis.
| Variables included in model† | Estimate (standard error) | t value | P |
|---|---|---|---|
| ln Age | -4.97 x10-2 (2.91 x10-2) | -1.71 | 0.087 |
| (ln Age)2 | -0.11 (1.47 x10-2) | -7.13 | 2.68 x10-12 |
| (ln Age)3 | 1.48 x10-2 (2.75 x10-3) | 5.39 | 9.77 x10-8 |
| Oxyhemoglobin (%) | 6.54 x10-3 (1.67 x10-3) | 3.92 | 9.83 x10-5 |
| Gestational age (weeks) | -8.45 x10-2 (1.66 x10-2) | -5.09 | 3.55 x10-5 |
| pH | -0.53 (0.23) | 2.32 | 0.020 |
| Hemoglobin g/L | 1.92 x10-3 (7.39 x10-4) | 2.60 | 9.49 x10-3 |
| Variables eliminated from model | |||
| Unit (St Mary’s / QCCH) | NS | ||
| Atmospheric CO (ppm) | NS | ||
| Gender | NS | ||
| Methemoglobin (%) | NS | ||
| Birthweight (g) | NS | ||
| Recent blood transfusion | NS | ||
| Outcome (survived/died) | NS |
†Based on 674 observations; all models include subject identity as a random factor. NS, not significant (P>0.05) and therefore removed sequentially from model.