Elsevier

Resuscitation

Volume 72, Issue 2, February 2007, Pages 306-318
Resuscitation

Experimental paper
Hemorrhagic shock resuscitation with carbon monoxide saturated blood

https://doi.org/10.1016/j.resuscitation.2006.06.021Get rights and content

Summary

The response to exchange transfusion with red blood cells (RBCs) saturated with carbon monoxide (CO) in amelioration of microvascular function and providing tissue protection in hemorrhagic shock resuscitation was investigated in the hamster chamber window model. Shock was induced by the withdrawal of 50% of blood volume (BV). Blood volume was restored 1 h after hemorrhage with a single volume infusion (resuscitation) of 25% BV with fresh RBCs (saturated or unsaturated with CO) suspended in human serum albumin (HSA). Hemorrhage, shock and resuscitation were monitored continuously in terms of mean arterial pressure (MAP), microvascular blood flow, capillary perfusion and systemic gas parameters. Eight hours after resuscitation, Annexin V and propidium iodide (PI) were injected into the window chamber to study tissue viability, and labeled cells were observed by using intravital epifluorescence microscopy. TUNEL staining was performed on the tissue to confirm in vivo results. Systemic and microvascular restoration were not different with or without CO up to 90 min after resuscitation. CO concentration decreased over 90 min, increasing oxygen carrying capacity and gradually reoxygenating the tissue. CO saturated blood partially mitigated cell injury at 8 h after resuscitation. The precise cellular mechanisms involved require further elucidation. CO is a novel experimental strategy to improve tissue viability and requires the appropriated preclinical studies to confirm its efficacy.

Introduction

Treatment of blood loss and hemorrhagic shock begins with the infusion of plasma expanders to restitute vascular volume and, upon continued exsanguination, is followed by the restitution of oxygen carrying capacity with blood transfusions. The decision to transfuse blood depends on a variety of factors including the estimated magnitude of the blood loss, measurements of tissue pO2 and the concern that the progressing anemia will lead to a condition where oxygen carrying capacity may be insufficient to supply the metabolic demand. Trauma and hemorrhage can lead to the development of end-organ damage, a deregulated systemic inflammatory response, and ultimately result in multiple organ dysfunction syndromes.1 At the cellular level, these inflammatory responses involve the initiation of signaling cascades and the activation of many prototypical molecular pathways, resulting in the generation of multiple stressor products, including cytoprotective responses.

Several studies have demonstrated that the expression of cytoprotective reaction in the setting of hemorrhagic shock can determine the outcome.2 Final tissue injury after hemorrhage can be exacerbated by pharmacological inhibition of heme-oxygenase-1 (HO-1) enzymatic activity and nitric oxide (NO).2 Conversely, induction of HO-1 before hemorrhage can ameliorate the resultant organ injury. HO-1 is the rate-limiting enzyme in catalyzing the breakdown of heme into its by-products of free iron, biliverdin and carbon monoxide (CO), and is induced by multiple stressors, including cytokines, lipopolysaccharide, oxidative stress, and NO.3 CO, in particular, has been demonstrated to possess anti-inflammatory and antiapoptotic properties.4, 5, 6 Different studies have previously shown that CO can decrease inflammatory response to cytokines in a model of endotoxic shock while simultaneously increasing anti-inflammatory cytokines levels.3, 4, 5, 6

Volume restitution with plasma expanders and autotransfusion as a response to hemorrhage, dilute the blood components. In particular, the dilution of red blood cells (RBCs) lowers blood viscosity, and therefore the viscosity dependant component of peripheral vascular resistance. Experimental studies in hemorrhagic shock showed the threshold for blood/plasma viscosity required to maintain microvascular perfusion and particularly functional capillary density (FCD).7, 8, 9, 10 According to these findings, maintenance of FCD differentiates between survival and non-survival in conditions of prolonged hemorrhagic shock even though oxygen carrying capacity and tissue oxygen are the same.7

Blood transfusions have immediate subjective as well as physiological beneficial effects which are not fully explained by the restoration of oxygen carrying capacity since this occurs as much as several hours later, depending on the storage period. Recent studies have shown that an increase in hematocrit (Hct) after blood transfusion in a normal organism led to a rapid increase in NO production via restored shear stress.11 Similar effects were obtained when Hct was decreased via hemodilution and plasma viscosity was increased, raising shear stress and consequently augmenting the levels of perivascular NO at the microcirculation, producing a stable and homogeneously perfused microcirculation.12 Therefore, the beneficial effect of blood transfusions may be, in part, linked to the increase or restoration of shear stress and mechanotransduction by blood viscosity.

This study analyzes systemic, microcirculatory and tissue cellular effects in the hamster window chamber model after subjected to acute hemorrhagic shock and resuscitation. Resuscitation was performed infusing CO saturated or unsaturated RBCs suspended in 10% human serum albumin (HSA) to obtain the necessary colloidal osmotic pressure (COP) for resuscitation. The concentration of RBCs in the resuscitation blood matched the hamster Hct before resuscitation. However, the objective was not to increase or restore to baseline blood viscosity, but only to maintain blood rheological properties, change oxygen carrying capacity and establish CO effects.

Section snippets

Animal preparation

Investigations were performed in male Golden Syrian Hamsters fitted with a dorsal chamber window.13 This model has been extensively used for investigation of the intact microvasculature of adipose, subcutaneous tissue and skeletal muscle in conscious animals for extended periods.10, 14 A complete description of the preparation is given in references.10, 14 Pentobarbital sodium (50 mg/kg, i.p.) is used for window implantation and for carotid artery and jugular vein catheterization. Four to five

Results

A total of 18 animals (60.9 ± 4.2 g) were studied. Animals were assigned randomly to the experimental groups: CORBC (n = 6; 59.2 ± 5.0 g); O2RBC (n = 6; 61.6 ± 4.1 g); and, NR (n = 6; 60.2 ± 3.9 g).

Discussion

The principal finding of this study is that resuscitation with CORBC and O2RBC provides an identical recovery of systemic and microvascular conditions. Both resuscitated groups achieved and sustained similar level of recovery. This is remarkable because, O2RBC group had increased oxygen carrying capacity by 25% after resuscitation compared to CORB group, which did not receive the RBC's functional oxygen capacity. Identical amounts of RBCs were infused in CORBC and O2RBC groups, but oxygen

Acknowledgments

This work has been supported by grants R01-HL76182 to AGT, R24-64395, R01-62354 and R01-62318 to MI.

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    A Spanish translated version of the summary of this article appears as Appendix in the final online version at doi:10.1016/j.resuscitation.2006.06.021.

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