Study On The Effect And Influencing Factors Of Step - Like Increasing Oxygen Concentration Strategy On Resuscitation Of Hemorrhagic Shock

Background:Hemorrhagic shock is one of the common critical disease in clinics. HS impairs oxygen delivery, causes cellular and tissue hypoxia, and may ultimately result in multiple organ dysfunction syndrome. Common treatment algorithms involve immediate bleeding control, appropriate fluid resuscitation, and adequate oxygen administration. To restore tissue and systemic oxygenation as soon as possible, hyperoxic resuscitation has been the routine method during clinical HS management. However, researchers and clinicians are more aware of the damage that oxygen may cause, the potential side effects of hyperoxic resuscitation could offset the benefits, too much oxygen may be associated with vasoconstriction and the oxidative burst. To alleviate oxidative injury during resuscitation from HS, hypoxemic resuscitation, which can be achieved by breathing a high fraction of inspiration O2, was proposed. This is understood as a consequence of reducing the ‘‘fuel’’ that drives the fire of oxidative stress by limiting the amount of oxygen available during the reperfusion phase. However, it may be accompanied with inadequate oxygen delivery.The optimal medical oxygen administration strategy is still controversial, and improving oxygenation and mitigating oxidative stress simultaneously during resuscitation from severe HS seems to be contradictory goals.Post-conditioning(Po C), a series of ischemia/reperfusion or hypoxia/reoxygenation cycles applied at the onset of reperfusion or reoxygenation, is a recently described novel approach to reduce the deleterious effects of I-R injury. It is reported to reduce oxidative stress, reduce mitochondrial calcium overload, improve endothelial function, and reduce inflammation. Po C is considered likely to be an easy and effective manifestation of gradual treatment.The present study proposed and tested a candidate resuscitation strategy-gradually increased oxygen administration(GIOA), which involves making the arterial blood hypoxemic during the early moments of resuscitation, followed by a gradual increase to a hyperoxic state. We hypothesized that GIOA would improve oxygenation without enhancing oxidative stress. In the first part of the study, the effects of GIOA on resuscitaiton from hemorrhagic shock was compared with normoxic resuscitation, hyperoxic resuscitation, and hypoxemic resuscitation. In the second part of the study, we studied the details of GIOA, such as whether hypoxemia at onset of resuscitation is imperative and the optimal timing of hypoxemic status are to be identified. In the third part of the study, we studied the cytoprotective and mitochondrion-protective effect of GIOA. The study may provide theoretic foundation and experimental evidence for the rational utilization of oxygen during hemorrhagic shock.Part I Proposal and Verification of Gradually Increased Oxygen AdministrationMethods: Rats were subjected to HS, and on resuscitation, the rats were randomly assigned to four groups(n = 8): the normoxic, the hyperoxic, the hypoxemic, and the GIOA groups. Rats were observed for an additional 1 h. Hemodynamics, acid–base status, oxygenation, and oxidative injury were observed and evaluated.Results: Central venous oxygen saturation promptly recovered only in the hyperoxic and the GIOA groups, and the liver tissue partial pressure of oxygen was highest in the GIOA group after resuscitation. Oxidative stress in GIOA group was significantly reduced compared with the hyperoxic group as indicated by the reduced malondialdehyde content, increased catalase activity, and the lower histologic injury scores in the liver. In addition, the tumor necrosis factor-α and interleukin-6 expressions in the liver were markedly decreased in the GIOA group than in the hyperoxic and normoxic groups as shown by the immunohistochemical staining.Conclusions: GIOA improved systemic/tissue oxygenation and mitigated oxidative stress simultaneously after resuscitation from severe HS. GIOA may be a promising strategy to improve resuscitation from HS and deserves further investigation.Part II Study of Factors Influencing Gradually Increased Oxygen AdministrationMethods: After the induction of hemorrhagic shock, the rats were randomized into five groups(n = 9): normoxic group(Normo), hyperoxic group(Hypero), normoxic to hyperoxic group(GIOA1), long-time hypoxemic to hyperoxic group(GIOA2), and short-time hypoxemic to hyperoxic group(GIOA3). Survival was recorded for 96 h, plasma alanine transaminase, oxidative stress, hemodynamics, and blood gas were measured.Results: The mean survival time of the GIOA3 was significantly longer than that of the Normo, Hypero and GIOA2. Plasma alanine transaminase were significantly lower in the Normo, GIOA1 and GIOA3 compared to the Hypero and GIOA2 at 2 h post-resuscitation. Plasma 3-Nitrotyrosine at 2 h post-resuscitation were significantly lower in the GIOA2 and GIOA3 compared to the Normo and Hypero. Central venous oxygen saturation at 2 h post-resuscitation in the GIOA3 was significantly higher than the Normo; however, no significant difference was observed between GIOA1 and Normo. Besides, at 2 h post-resuscitation, mean arterial pressure in the GIOA3 was significantly higher than the GIOA2; however, no significant difference was observed between GIOA1 and GIOA2.Conclusions:(1) GIOA could significantly prolonged survival time compared to normoxemic resuscitation and hyperoxic resuscitation;(2) early moments of GIOA are critical to the benefits; and(3) hypoxemia at onset of resuscitation may be imperative, more work are needed to determine the optimal initial oxygen cocentation of GIOA.Part III The Establishment and Verification of Cell Model for Gradually Increased Oxygen AdministrationMethods: Hypoxia was produced using a plastic chamber containing 5% CO2 and 95%N2 placed in an incubator at 37 °C. Before subjecting to hypoxia, culture medium was changed to Opti-MEM I medium. After 12 h incubation in the hypoxic chamber, cells were then cultured at different oxygen concentrations for 4h. The normoxic group(Normo) in which the fraction of inspiration O2 was 0.210; the hyperoxic group(Hypero) in which the Fi O2 was 0.500; and the GIOA group, in which the Fi O2 increased from 0.165 to 0.210 by 0.015 per 20 min, and from 0.210 to 0.500 by 0.058 per 30 min. Cells at 4h post-resuscitation were collected for analyses of cell viability, intracellular reactive oxygen species, cytochrome c, and intracellular Ca2+ concentration.Results: At 4h post-resuscitation, the cell viability of GIOA was significantly higher compared to the Normo and Hypero. Intracellular reactive oxygen species in the Hypero was significantly higher compared to the Normo and the GIOA, and the Normo was significantly higher than the GIOA. Cytochrome c in the GIOA was significantly lower than the Hypero. And intracellular Ca2+ was significanlt higher in the Hypero than the GIOA.Conclusions: These results indicated that gradually increased oxygen administration may have cytoprotective and mitochondrion-protective effect after hypoxia and reoxygenation.Summary:1. For the first time, the current study proposed the notion of gradually increased oxygen administration. Our study provides novel insight into the oxygen administration strategy, and GIOA seems to be a simple and promising strategy to improve resuscitation from HS.2. Our study showed for the first time that gradually increased oxygen administration improved systemic/tissue oxygenation and mitigated oxidative stress simultaneously after resuscitation from severe HS.3. Our study further showed that early moments of GIOA are critical to the benefits; and hypoxemia at onset of resuscitation may be imperative.4. We showed that GIOA may have cytoprotective and mitochondrion-protective effect after H9C2 cell hypoxia and reoxygenation.5. We built the continuously adjustable O2 system, which layed the foundation for further mechanism research of GIOA.