# RBC Storage Lesion Studies in Humans and Experimental Models of Shock
## 6 Role of Severity of Infection on Risks Associated with Transfused Older Stored RBCs  
Next we investigated how increasing the bacterial doses and severity of infection would influence the risks associated with the age of stored blood transfused [13]. Animals underwent intra-bronchial challenge with one of four doses of bacteria; 0 (n = 8), \(1.0\times 10^{9}\) (n = 8), \(1.25\times 10^{9}\) (n = 24), or \(1.5\times 10^{9}\) (n  
Figure 2: Kaplan–Meier survival curves and lung injury plots for amines 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: [PERSON]; [PERSON]; [PERSON]; [PERSON] [PERSON]; [PERSON] [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON], 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.  
= 8) _S. aureus_ colony-forming units/kg and then were exchange-transfused with either fresh (7-day-old) or longer stored (42-day-old) canine universal donor RBCs (80 mL/kg in four divided doses). In both the absence of bacteria and in the presence of increasing doses of bacterial challenges, the levels of CFH and iron were similarly significantly higher when longer-stored RBCs were transfused in comparison to fresh RBCs. However, without bacterial challenge, there was no mortality or measurable end organ injury regardless of the length of time RBCs were stored before transfusion. Infection was required for transfused RBC to increase mortality differentially by length of storage. As the dose of bacterial challenge increased, longer-stored RBCs most profoundly and significantly increased mortality with the middle dose of bacteria. This middle dose of bacteria (\(1.25\times 10^{9}\) CFUs) caused, with fresh RBC transfusion and infection, a mortality rate of \(\sim\)30% which increased to 100% when longer stored RBCs were transfused instead. When animals were challenged with a low dose of bacteria (\(1.0\times 10^{9}\) CFUs) and fresh blood transfusion, there was 0 % observed mortality rate and with the highest dose bacteria challenge (\(1.5\times 10^{9}\) CFUs) and fresh blood transfusion, there was a 100% observed mortality. Longer stored RBCs nominally but not significantly increased mortality with the low and high dose bacteria. This is in part a power issue regarding the number animals studied, but is also consistent with the notion that a nutrient like iron would have less effect on a mild, less severe infection where iron is unlikely to be able to significantly augment the lethality. In contrast, with the high-dose bacteria, the infection becomes so lethal so rapidly that augmenting it further with a bacterial nutritional factor like iron does not result in an observable difference in this model. These data suggest that an established infection is one of the requirements that augment toxicity for transfused older RBCs. It further suggests that transfusion of older RBCs in septic subjects results in an increased risk from infection and that this risk follows a specific infection dose-response relationship consistent with a nutrient like iron worsening the infection.