Pharmacologic agents in the treatment of ischemia, hemorrhagic shock, and sepsis

Free radical scavengers in anaesthesiology and critical care

Free radicals are highly reactive and unstable compounds. These highly reactive molecules cause oxidative damage to cellular components such as DNA, proteins and lipids. They play central role in the mechanism of cell injury and cell death. Free radical scavengers either prevent these reactive species from being formed, or remove them before they can damage vital components of the cell. Oxidative stress defines an imbalance in production of oxidizing chemical species and their effective removal by protective antioxidants and scavenger enzymes. Evidence of massive oxidative stress is well established in critical illnesses characterized by tissue ischaemia-reperfusion injury and by an intense systemic inflammatory response such as during sepsis and acute respiratory distress syndrome, acute lung injury. Several clinical trials have been performed in order to reduce oxidative stress by supplementation of antioxidants alone or in combination with standard therapies. Antioxidant supplementation at an early stage of illness may lead to improved therapies in the treatment of critically ill patients. Several intravenous anaesthetic drugs act as reactive oxygen species scavengers. Anaesthetic preconditioning is of particular interest to anaesthesiologist, in which lasting protection of myocardium is elicited by brief exposure to a inhalational anaesthetic agent. These anasthetics may also mediate protective effects in other organs, such as the brain and kidney It is important for the anaesthesiologist to understand the mechanism of damage caused by free radicals and how free radical scavengers work so that this knowledge can be applied to varied pathological conditions. The topic was hand searched in text books and electronically searched from PubMed and Google scholar using text words.

Effect of naloxone on immune responses after hemorrhagic shock

OBJECTIVE

To determine whether naloxone administration after hemorrhagic shock has any beneficial or deleterious effect on immune responses.

BACKGROUND DATA

Hemorrhagic shock is known to produce immunodepression in both humans and experimental animals. Although studies suggest that endogenous opioids play a role in immune regulation in adverse circulatory conditions, it remains controversial whether these opioids exert beneficial or detrimental effects on immunity after shock. Moreover, little information is available concerning the effects of opioid receptor blockade using naloxone on cell-mediated immunity and endocrine responses after shock.

METHODS

Male C3H/HeN mice (25 g) were bled to and maintained at a mean arterial blood pressure of 35+/-5 mm Hg for 1 hr. The shed blood was then returned along with lactated Ringer's solution (two times the shed blood volume) to provide fluid resuscitation. The animals were randomized to receive either naloxone (1 mg/kg i.v.) or an equal volume of vehicle (saline) after the shed blood was returned, i.e., immediately before crystalloid resuscitation, and were killed at 2 hrs after resuscitation to obtain splenocytes, macrophages (peritoneal and splenic), and blood.

MEASUREMENTS AND MAIN RESULTS

Bioassays revealed significantly decreased release of all studied interleukins (interleukins-1, -2, -3, and -6) by peritoneal and splenic macrophages as well as significantly decreased splenocyte proliferative capacity after shock in vehicle-treated mice. Naloxone administration after hemorrhage resulted in either similar or even more decreased levels of interleukin release compared with vehicle-treated hemorrhaged mice. Significantly increased plasma corticosterone concentrations were observed in vehicle-treated animals compared with control animals. Naloxone administration did not have any significant effects on corticosterone plasma concentrations after hemorrhage.

CONCLUSIONS

These findings indicate the importance of the endogenous opioid system for the maintenance of immunity in adverse circulatory conditions, i.e., hemorrhage. Although additional studies involving different doses and/or times of naloxone administration may provide different results, the present findings raise the concern that naloxone administration in the traumatized host may have deleterious effects because it decreases peritoneal macrophage and splenic immune functions.

Hepatocellular dysfunction after severe hypotension in the absence of blood loss is associated with the increased IL-6 and PGE2

Although hepatocellular dysfunction occurs following trauma and hemorrhagic shock, whether severe hypotension even in the absence of blood loss depresses hepatocellular function remains unknown. The aim of this study, therefore, was to determine whether chemically induced severe hypotension causes hepatocellular dysfunction and, if so, whether IL-6 and PGE2 are associated with this dysfunction. To study this, hypotension was induced in adult male rats by intravenous infusion of a high dosage of ATP-MgCl2 solution (3.2 +/- 0.45 micromol/min/kg body wt) for 60 min. Blood pressure decreased from 108 +/- 6 mm Hg to an average of 43 mm Hg during the infusion period and returned to normal levels immediately after the completion of ATP-MgCl2 infusion. At 0 and 4 h after hypotension, hepatocellular function [i.e., maximum velocity of indocyanine green clearance (Vmax) and its efficiency (Km)] was measured using a fiberoptic catheter and in vivo hemoreflectometer. Cardiac output was determined by dye dilution. Microvascular blood flow was assessed by laser Doppler flowmetry. Plasma levels of PGE2 and IL-6 were measured by radioimmunoassay and bioassay, respectively. The results indicate that severe hypotension in the absence of any blood loss depresses hepatocellular function (i.e., decreased Vmax and Km) despite stable cardiac output and hepatic perfusion at 0 and 4 h after the completion of hypotension. Moreover, severe hypotension resulted in significantly increased plasma levels of PGE2 (only at 0 h) and IL-6. Thus, chemically induced severe hypotension in the absence of any blood loss, which does not significantly reduce cardiac output and hepatic perfusion, depresses hepatocellular function and upregulates IL-6 and PGE2 production.

Does neutrophil-mediated oxidative stress play any significant role in producing hepatocellular dysfunction during early sepsis?

BACKGROUND

Although previous studies have indicated that hepatocellular dysfunction during early sepsis can be prevented by prior neutrophil depletion, it remains unknown whether the changes in hepatic oxidative stress induced by activated neutrophils are responsible for the salutary effect of neutropenia on hepatocellular function.

MATERIALS AND METHODS

Neutropenia was induced in the rat by intravenous injection of immunoglobulins directly against rat neutrophils (anti-neutrophil Ig) at 16 and 2 h prior to the initiation of cecal ligation and puncture (CLP, i.e., an animal model of polymicrobial sepsis) or sham operation. Neutropenia was confirmed by peripheral blood smears. Neutrophil-competent control animals were given nonimmunized Ig prior to the onset of sepsis. Sham animals received anti-neutrophil Ig or control Ig. The levels of reduced glutathione (GSH) and oxidized glutathione (GSSG) in the liver were determined at 5 h after CLP (i.e., the early, hyperdynamic stage of sepsis) or sham operation by high performance liquid chromatography.

RESULTS

Although the levels of hepatic GSH and GSSG decreased significantly at 5 h after CLP, irrespective of neutropenia, the ratio of GSSG/GSH was not significantly altered under such conditions. The decrease in hepatic glutathione concentrations in septic animals may represent the decreased synthesis or increased efflux into the bile or circulation.

CONCLUSION

Since neutrophil depletion did not significantly affect hepatic levels of GSH and GSSG as well as the GSSG/GSH ratio but prevented the occurrence of hepatocellular dysfunction, factors other than oxidative stress are likely to be the mechanism responsible for depressing hepatocellular function during the early, hyperdynamic stage of sepsis.

Effects of small-volume bolus treatment with intravenous normal saline and 7.5 per cent saline in combination with 6 per cent dextran-40 on metabolic acidosis and survival in burned mice

Standard murine burn models include the administration of intraperitoneal (i.p.) saline solutions which are intended to resuscitate the animals during subsequent burn shock. Prehospital administration of small volumes of concentrated salt solutions has been recommended for the early treatment of haemorrhagic shock, and have also been utilized for burn shock. We studied the effects of bolus intravenous (i.v.) hypertonic saline (HS) or hypertonic saline/dextran-40 (HS + DEX) on animal survival and acid-base balance following 25 per cent total body surface area, full-thickness burn injury in mice. I.v. injections were administered via a tail vein immediately prior to burn injury. Some mice received 1 ml i.p. normal saline (NS) immediately after burn injury. Acid-base balance of vena caval blood was measured during the period of maximal metabolic acidosis following burn injury (12 h postburn). Preburn i.v. administration of 5 ml/kg of HS or HS+DEX, followed by 1 ml i.p. NS, only slightly decreased the degree of metabolic acidosis compared to animals receiving i.p. fluid alone, the standard resuscitation regimen for burned mice. Preburn i.v. administration of 0.2 ml volumes of HS or HS + DEX, without i.p. fluid administration, resulted in extremely high mortality. Immediate preburn i.v. administration of HS or HS + DEX did not eliminate metabolic acidosis in this murine burn model, and markedly increased the mortality when subsequent i.p. fluids were not administered. The degree of metabolic acidosis in the murine experimental burn model has not previously been clearly described. Furthermore, adequate fluid resuscitation of these animals may be difficult to achieve without indwelling vascular catheters which could deliver continuous i.v. fluids following burn injury.

Effect of corticotropin releasing factor on acid-base alterations and bacterial translocation in a murine model of thermal injury

Corticotropin-releasing factor (CRF) is a 41 amino acid polypeptide produced by the hypothalamus which has been shown to decrease inflammation and tissue oedema when administered following burns, cold and acid injuries in some animal models, and to increase mesenteric blood flow. We determined whether systemic administration of CRF to burned mice would decrease metabolic acidosis and protect the gastrointestinal (GI) tract from ischaemic injury leading to bacterial translocation (BT). Synthetic CRF was administered by intraperitoneal injection in doses of 20 and 200 micrograms/kg to mice immediately following 25 and 32 per cent TBSA burn injuries; the doses were repeated at 8 and 16 h postburn. Severe metabolic acidosis, measured 12 h after burn injury, was not improved in mice which received CRF treatment. Bacterial translocation, measured by quantifying bacteria in mesenteric lymph nodes harvested from animals 48 h postburn, was also not decreased with CRF treatment. CRF does not improve general tissue perfusion nor decrease GI derangements leading to bacterial translocation in this animal model of burn injury.