Effect of anemia on tissue oxygenation saturation and the tissue deoxygenation rate during ischemia

Introduction

The hypothesis was that anemia, independently of hemodynamic stability, affects tissue oxygenation saturation (StO₂) and the deoxygenation rate during stagnant ischemia. The blood hemoglobin concentration is determinant of oxygen delivery. In anemic patients, oxygen delivery decreases and oxygen extraction is increased. This leads to decreased venous hemoglobin saturation and a lower tissue oxygen saturation. The rate of tissue deoxygenation during ischemia is dependent on oxygen consumption and on the amount of oxygen available in the tissue [1].

Methods

In a prospective observational study we included 340 patients in the medical emergency room. On admission, StO₂ and the tissue deoxygenation rate during ischemia were measured by near-infrared spectroscopy. Patients were divided into four groups according to hemoglobin concentration and hemodynamic (HD) stability: Group 1 (nonanemic, HD-stable patients), Group 2 (anemic, HD-stable patients), Group 3 (nonanemic, HD-unstable patients), Group 4 (anemic, HD-unstable patients). Differences in StO₂ and the rate of tissue deoxygenation were analyzed.

Results

Anemic groups had a significantly lower hemoglobin concentration compared with nonanemic groups (138 ± 16 vs. 76.5 ± 15 g/l, P < 0.001). HD-unstable groups had significantly higher lactate levels compared with HD-stable groups (1.6 ± 0.6 vs. 3.9 ± 1.6 mmol/l, P < 0.001). The results are presented in Table 1. StO₂ in Groups 2 and 3 was comparable, while the difference in the deoxygenation rate in these groups was significant (P = 0.007).

Table 1 abstract P238

Conclusion

Anemia significantly affects StO₂ and the deoxy-genation rate. It probably contributes to lower StO₂ equally as HD instability. In contrast to HD instability, anemia causes more rapid deoxygenation during ischemia.