Changes in blood hemoglobin and blood gases PaO2 and PaCO2 in severe COPD over a three-year telemonitored program of long-term oxygen treatment

Background: Information on the effects of long-term oxygen treatment (LTOT) on blood hemoglobin (Hb) in severe COPD are limited. The aim was to assess blood Hb values in severe COPD, and investigate the time-course of both Hb and blood gas changes during a 3-year telemetric LTOT. Methods: A cohort of 132 severe COPD patients (94 males; 71.4 years +/- 8.8 sd), newly admitted to the tele-LTOT program, was investigated. Subjects were divided according to their original blood Hb: group A: < 13 g/dL; group B: >= 13 < 15 g/dL; group C: >= 5 < 16 g/dL; group D: >= 16 g/dL. Blood Hb (g/dL), PaO2 and PaCO2 (mmHg), SaO(2) (%), and BMI were measured at LTOT admission (t(0)), and at least quarterly over three years (t(1)-t(3)). Wilcoxon test was used to compare t(0) vs. t(1) values; linear regression to assess a possible Hb-BMI relationship; ANOVA to compare changes in Hb time-courses over the 3 years. Results: LTOT induced a systematic increase of PaO2, and changes were significant since the first year (from 52.1 mmHg +/- 6.6sd to 65.1 mmHg +/- 8.7 sd, p < 0.001). Changes in SaO(2) were quite similar. Comparable and equally significant trends were seen in all subgroups (p < 0.001). PaCO2 dropped within the first year of LTOT (from 49.4 mmHg +/- 9.1sd to 45.9 mmHg +/- 7.5 sd, p < 0.001): the t(0)-t(1) comparison proved significant (p < 0.01) only in subgroups with the highest basal Hb, who showed a further PaCO2 decline over the remaining two years (p < 0.001). Hb tended to normalization during LTOT only in subgroups with basal Hb > 15 g/dl (ANOVA p < 0.001); anemic subjects (Hb < 13 g/dl) ameliorated not significantly in the same period (ANOVA = 0.5). Survival was independent of the original blood Hb. Anemia and polyglobulia are differently prevalent in COPD, the latter being the most represented in our cohort. LTOT affected both conditions, but to a different extent and according to different time-courses. The most striking Hb improvement was in polyglobulic patients in whom also PaO2, PaCO2 and SaO(2) dramatically improved. In anemic subjects effects were smaller and slower, oxygenation being equally ameliorated by LTOT. Conclusions: LTOT effects on Hb and PaCO2 are regulated by an Hb-dependent gradient which seems independent of the original impairment of blood gases and of effects on oxygenation.