Effects of red blood cell transfusion in central venous saturation and lactate levels in patients with septic shock

Introduction

Transfusion of red blood cells has been used with the objective of improving oxygen delivery to the tissues in the critically ill patient. However, the appropriate hemoglobin (Hb) level is still controversial in septic shock patients [1, 2]. The objective of this study was to evaluate the effect of red blood cell transfusion on the central venous saturation (SvcO₂) and lactate levels in patients with septic shock with two different levels of Hb.

Methods

Patients with less than 48 hours of septic shock and Hb levels under 9.0 g/dl were randomized to maintain Hb over 9.0 g/dl (Group 1) or over 7.0 g/dl (Group 2). Before and up to 1 hour after each transfusion, Hb, lactate and SvcO₂ were determined. Results were expressed as median (25% to 75% percentile) or percentage and analyzed through chi-square or Mann-Whitney test. P < 0.05 was considered significant.

Results

Forty-six patients were included with a total of 74 transfusions, being 39 in Group 1 and 35 in Group 2, without any difference in demographic or hemodynamic data between the groups. Before and after Hb levels were 8.5 (8.2 to 8.7) g/dl and 9.4 (9.1 to 9.5) g/dl in Group 1 (P = 0.000) and 6.8 (6.6 to 6.9) g/dl and 7.6 (7.4 to 7.8) g/dl in Group 2 (P = 0.000). A reduction in median lactate after transfusion was found in Group 2 patients (22.0 (18.1 to 29.1) mg/dl and 20.0 (16.3 to 25.2) mg/dl, P = 0.005) but not in Group 1 (17.2 (16.3 to 23.9) mg/dl and 18.1 (15.4 to 21.8) mg/dl, P = 0.23). The same occurred regarding SvcO₂ with improved values only in Group 2 (68.0 (64.0 to 72.0)% and 72.0 (69.0 to 75.0)% in Group 2, P < 0.000) and not in Group 1 (72.0 (69.0 to 74.0)% and 72.0 (71.0 to 73.0)%, P = 0.98). In patients with altered lactate levels a reduction was found regardless of the basal levels of hemoglobin (P = 0.002 and P = 0.001 for Groups 1 and 2, respectively). The same was demonstrated in patients with SvcO₂ <70% (P = 0.007 and P = 0.000 for Groups 1 and 2, respectively). On the other hand, patients with normal levels of both perfusion parameters did not present a worsening of those variables, either in Group 1 or Group 2.

Conclusions

Red blood cell transfusion improved tissue perfusion in patients with signs of hypoperfusion regardless of basal levels of Hb. Transfusion did not seem to worsen tissue perfusion in patients without signs of hypoperfusion, even in the group with Hb levels above 9.0 g/dl.