RBC Storage Lesion Studies in Humans and Experimental Models of Shock

Abstract

The finding of toxicity in a meta-analysis of observational clinical studies of transfused longer stored red blood cells (RBC) and ethical issues surrounding aging blood for human studies prompted us to develop an experimental model of RBC transfusion. Transfusing older RBCs during canine pneumonia increased mortality rates. Toxicity was associated with in vivo hemolysis with release of cell-free hemoglobin (CFH) and iron. CFH can scavenge nitric oxide, causing vasoconstriction and endothelial injury. Iron, an essential bacterial nutrient, can worsen infections. This toxicity was seen at commonly transfused blood volumes (2 units) and was altered by the severity of pneumonia. Washing longer-stored RBCs mitigated these detrimental effects, but washing fresh RBCs actually increased them. In contrast to septic shock, transfused longer stored RBCs proved beneficial in hemorrhagic shock by decreasing reperfusion injury. Intravenous iron was equivalent in toxicity to transfusion of longer stored RBCs and both should be avoided during infection. Storage of longer-stored RBCs at 2 °C instead of higher standard temperatures (4-6 °C) minimized the release of CFH and iron. Haptoglobin, a plasma protein that binds CFH and increases its clearance, minimizes the toxic effects of longer-stored RBCs during infection and is a biologically plausible novel approach to treat septic shock.

Keywords: blood transfusion; cell free hemoglobin; haptoglobin; iron; pneumonia; sepsis; shock.

Figure 1.

Meta-analysis of the effects of transfusion of old vs. new blood on mortality. The data marker size is proportional to the inverse variance of each point estimate. Meta-analysis of 21 studies revealed a highly statistically significant difference in mortality favoring transfusion of new blood vs. old blood with respect to mortality [odds ratio 1.16, 95% confidence interval (CI) 1.07–1.24, p = 0.0001]. From: Wang, D.; Sun, J.; Solomon, S.B.; Klein, H.G.; Natanson, C. Transfusion of older stored blood and risk of death: a meta-analysis. Transfusion 2012, 52, 1184–1195, doi:10.1111/j.1537-2995.2011.03466.x.

Figure 2.

Kaplan–Meier survival curves and lung injury plots for canines receiving longer stored vs. fresher red blood cells (RBCs). (A) Proportion of animals surviving over the study period of 96 h comparing canines inoculated with S. aureus intrabronchially and subsequently exchange transfused with RBCs stored for 42 days (solid circle, solid line) or RBCs stored for 7 days (open circle, dashed line) RBCs. (B) Serial makers of lung injury. Arterial-alveolar oxygen gradient increase demonstrates worsening lung injury in the canines with S. aureus pneumonia that received longer stored 42-day-old (solid circle, solid line) vs. fresh 7-day-old (open circle, dashed line) RBCs at 24 h (p = 0.005) and 48 h (p = 0.01) after bacterial inoculation. From: Solomon, S.B.; Wang, D.; Sun, J.; Kanias, T.; Feng, J.; Helms, C.C.; Solomon, M.A.; Alimchandani, M.; Quezado, M.; Gladwin, M.T., et al. Mortality increases after massive exchange transfusion with older stored blood in canines with experimental pneumonia. Blood 2013, 121, 1663–1672, doi:10.1182/blood-2012-10-462945.

Figure 3.

Kaplan–Meier survival curves, hemodynamic assessments, and lung injury plots of septic canines receiving haptoglobin infusion therapy with and without RBC transfusion. (A) Proportion of canines surviving after either receiving haptoglobin (dashed line) or no haptoglobin (solid line) infusion after intrabronchial S. aureus challenge and subsequent RBC exchange transfusion. (B) Kaplan–Meier survival curves of septic animals not undergoing exchange transfusion but receiving haptoglobin (dashed line) or no haptoglobin (solid line) infusions. P values denoted by asterisks indicate a statistically significant differences between each panel group using stratified log rank tests. (C and D) Mean shock scores (+ standard error of the mean (SEM)) at different serial time points. The shock score assesses the amount of vasopressor support (norepinephrine) needed to maintain a given mean arterial pressure (MAP) at the normal level in canines (80 mmHg). The shock score is compared throughout the 96 h study period in canines receiving haptoglobin infusion therapy (closed circle, solid line) and not receiving haptoglobin infusion therapy (open circle, dashed line) in the presence of (C) or absence of (B) RBC exchange transfusion. The mean baseline values for canines were used to plot a common origin from which changes from baseline were plotted for each study group. Asterisks and their associated p values indicate where there are significant changes in each group over time. Crosses and their associated p values indicate statistically significant differences between groups receiving haptoglobin infusion and those that did not receive haptoglobin infusion. (E and F) represent mean (+SEM) lung injury scores (LIS) over serial time points throughout the study. LIS is a global marker of lung damage and represents a composite of mean pulmonary artery pressure, alveolar-arterial oxygen gradient, plateau pressure, oxygen saturation, and respiratory rate. (E) demonstrates the LIS over time in canines undergoing exchange transfusion of RBCs receiving (open circle, dashed line) or not receiving (closed circle, solid line) haptoglobin infusions. (F) shows the LIS over time in animals not undergoing RBC exchange transfusion but receiving (open circle, dashed line) or not receiving (closed circle, solid line) haptoglobin infusions. Changes in the LIS from baseline are shown for each of the groups plotted from a common origin which was established from the mean value for the canines at baseline. Asterisks and their associated p value denote statistically significant changes over time. Crosses and their associated p value denote statistically significant differences between the haptoglobin and no haptoglobin group at a given time point. We were able to account for repeated measurements and the pairing of animals within each cycle based on contrasts in linear mixed models which were used to analyze all variables (except survival). From: Remy, K.E.; Cortes-Puch, I.; Solomon, S.B.; Sun, J.; Pockros, B.M.; Feng, J.; Lertora, J.J.; Hantgan, R.R.; Liu, X.; Perlegas, A., et al. Haptoglobin improves shock, lung injury, and survival in canine pneumonia. JCI Insight 2018, 3, doi:10.1172/jci.insight.123013.