Background: Hemorrhagic shock (HS) is associated with the generation of reactive oxygen species, which may contribute to delayed multiple organ system failure and death. Previous studies have shown that the antioxidant Tempol improved physiologic variables, although not necessarily outcome, in septic shock and HS. We hypothesized that the combination of free Tempol with polynitroxylated albumin (PNA)-bound Tempol (which prolongs half-life and decreases toxicity) improves outcome after HS in rats.
Methods: In study 1, HS was induced by blood withdrawal of 3 mL/100 g over 15 minutes. Mean arterial pressure was maintained at 40 mm Hg with either infusion of normal saline or withdrawal of blood from 20 to 90 minutes. Resuscitation (90-270 minutes) was with infusion of shed blood. Observation was to 72 hours. At HS 45 min, albumin (ALB) (n = 10) or PNA + Tempol (n = 10) was infused slowly (1 mL/100 g/h) until 120 minutes. Study 2 was the same as study 1 (n = 6 per group), but terminated at 150 minutes. Study 3 was the same as study 1, but started with ALB or PNA + Tempol (n = 7 per group) at 20 minutes. The primary outcome variable in studies 1 and 3 was survival, whereas the primary outcome variables in study 2 were antioxidant reserve (ability of the serum or tissue homogenate to scavenge peroxyl radicals produced by 2,2'-azobis [2-aminodipropane]-dihydrochloride) in serum and small intestine, and low-molecular-weight thiols in tissues (liver, small intestine, and kidney).
Results: In study 1, 72-hour survival was 1 of 10 (ALB group) versus 2 of 10 (PNA + Tempol group). At 90 minutes, pH was lower in the ALB group versus the PNA + Tempol group (p = 0.02) and remained low. Arterial lactate increased to 8.9 +/- 3.2 (mean +/- SD) versus 6.5 +/- 1.8 mmol/L (p = 0.04) and base excess was -9.6 +/- 4.3 versus -5.2 +/- 3.2 mmol/L (p = 0.01) (ALB vs. PNA + Tempol groups, respectively). In study 2, antioxidant reserve in serum was lower in the ALB group versus the PNA + Tempol group (p = 0.002). There were no differences between groups in antioxidant reserve in the small intestine or low-molecular-weight thiols in liver, kidney, and small intestine. In study 3, 72-hour survival was zero of seven (ALB group) versus five of seven (PNA + Tempol group) (p = 0.02). Heart rate and systolic blood pressure during late HS were higher in the ALB group in studies 1 and 3 (p < 0.05).
Conclusion: When infused early in HS, PNA + Tempol can increase survival. When given late, it significantly improves acid-base and serum antioxidant status, without an effect on survival. Additional studies will be required to determine whether early resuscitation with PNA + Tempol attenuates reactive oxygen species-mediated injury as the mechanism for preventing the progression toward multiple organ failure and death after HS. The results suggest that antioxidant therapy with Tempol deserves further study as a potential adjunct in the initial resuscitation from HS.