Table 2.
Association between hemoglobin and methemoglobin before and after surgery
| Unadjusted change in methemoglobin per 25 g/L difference in hemoglobin concentration (95% CI) | Adjusted change in methemoglobin per 25 g/L difference in hemoglobin concentration (95% CI) | |
|---|---|---|
| Pre-Surgical Hb vs. Pre-Surgical MetHb | ||
| No anemia (150 g/L vs. 125 g/L) | −0.11 (−0.15 to −0.08)a | −0.12 (−0.16 to −0.08)a |
| Mild anemia (125 g/L vs. 100 g/L) | −0.02 (−0.05 to 0.01) | −0.01 (−0.04 to 0.02) |
| Moderate anemia (100 g/L vs. 75 g/L) | 0.02 (−0.03 to 0.06) | 0.03 (−0.02 to 0.07) |
| Severe anemia (75 g/L vs. 50 g/L) | 0.02 (−0.03 to 0.06) | 0.03 (−0.02 to 0.07) |
| Post-Surgical Hb vs. Post-Surgical MetHb | ||
| No anemia (150 g/L vs. 125 g/L) | −0.24 (−0.30 to −0.19)a | −0.24 (−0.30 to −0.18)a |
| Mild anemia (125 g/L vs. 100 g/L) | −0.20 (−0.24 to −0.15)a | −0.19 (−0.23 to −0.15)a |
| Moderate anemia (100 g/L vs. 75 g/L) | 0.02 (−0.03 to 0.07) | 0.07 (0.00–0.13) |
| Severe anemia (75 g/L vs. 50 g/L) | 0.06 (0.00–0.12) | 0.02 (−0.03 to 0.07) |
| Delta Hb vs. Post-Surgical MetHb | ||
| per 25 g/L increase in Hb (linear) | −0.02 (−0.05 to 0.00) | −0.03 (−0.06 to −0.01)a |
There was statistical evidence for non-linear associations between pre-surgical hemoglobin versus pre-surgical methemoglobin, and post-surgical hemoglobin versus post-surgical methemoglobin; therefore, hemoglobin was modeled as a non-linear term in these models. Models adjusted for age, sex, diabetes status, preoperative renal function, preoperative left ventricular function, baseline chronic pulmonary disease, planned surgery, and red blood cell transfusion. CI, Confidence interval; Hb, hemoglobin concentration; MetHb, methemoglobin.
a
p < 0.05.