changes in blood hemoglobin and blood gases pao₂ and paco₂ in severe copd overa three-year telemonitored program of long-term oxygen treatment

Abstract

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), SaO₂ (%), and BMI were measured at LTOT admission (t₀), and at least quarterly over three years (t₁-t₃). Wilcoxon test was used to compare t₀ vs. t₁ 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 SaO₂ 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 t₀-t₁ 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 SaO₂ 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.