Travis Anderson

Induced hypothermia by central venous infusion: Saline ice slurry versus chilled saline

Objective:Surface cooling improves outcome in selected comatose survivors of cardiac arrest. Internal cooling with considerable volumes of intravenous cold saline may accelerate hypothermia induction. This study compares core temperatures in swine after central catheter infusions of saline ice slurry (saline with smoothed 100-&mgr;m-size ice particles) vs. an equal volume of chilled saline. We hypothesized that slurry would achieve core hypothermia (32–34°C) more consistently and at a faster rate. Design:A total of 11 swine were randomized to receive microparticulate ice slurry, chilled saline infusion, or anesthesia alone in a monitored laboratory setting. Interventions:Intravenous bolus (50 mL/kg) of slurry or chilled 1.5% NaCl saline. Slurry was composed of a 1:1 mixture of ice and distilled H2O plus NaCl. Measurements:Cerebral cortex, tympanic membrane, inferior vena cava, rectal temperatures, electrocardiogram, arterial blood pressure, and arterial oxygen saturation were recorded for 1 hr after bolus. Main Results:Compared with anesthetized controls, core brain temperatures of the saline and slurry groups dropped by 3.4 ± 0.4°C and 5.3 ± 0.7°C (p = .009), respectively. With an infusion rate of 120 mL/min, cooling rates for the saline and slurry groups were −11.6 ± 1.8°C/hr and −18.2 ± 2.9°C/hr, respectively, during the first 20 mins. Four of four animals in the slurry group vs. zero of four animals in the saline group achieved target cortical temperatures of <34°C. Conclusions:Cold intravenous fluids rapidly induce hypothermia in swine with intact circulation. A two-phase (liquid plus ice) saline slurry cools more rapidly than an equal volume of cold saline at 0°C. Ice-slurry could be a significant improvement over other cooling methods when rate of cooling and limited infusion volumes are important to the clinician.

Cytotoxicity induced by grape seed proanthocyanidins: role of nitric oxide.

Grape seed proanthocyanidin extract (GPSE) at high doses has been shown to exhibit cytotoxicity that is associated with increased apoptotic cell death. Nitric oxide (NO), being a regulator of apoptosis, can be increased in production by the administration of GSPE. In a chick cardiomyocyte study, we demonstrated that high-dose (500 μg/ml) GSPE produces a significantly high level of NO that contributes to increased apoptotic cell death detected by propidium iodide and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) staining. It is also associated with the depletion of intracellular glutathione (GSH), probably due to increased consumption by NO with the formation of S-nitrosoglutathione. Co-treatment with L-NAME, a NO synthase inhibitor, results in reduction of NO and apoptotic cell death. The decline in reduced GSH/oxidized GSH (GSSG) ratio is also reversed. N-Acetylcysteine, a thiol compound that reacts directly with NO, can reduce the increased NO generation and reverse the decreased GSH/GSSG ratio, thereby attenuating the cytotoxicity induced by high-dose GSPE. Taken together, these results suggest that endogenous NO synthase (NOS) activation and excessive NO production play a key role in the pathogenesis of high-dose GSPE-induced cytotoxicity.

Altering CO2 during reperfusion of ischemic cardiomyocytes modifies mitochondrial oxidant injury.

Objective:Acute changes in tissue CO2 and pH during reperfusion of the ischemic heart may affect ischemia/reperfusion injury. We tested whether gradual vs. acute decreases in CO2 after cardiomyocyte ischemia affect reperfusion oxidants and injury. Design:Comparative laboratory investigation. Setting:Institutional laboratory. Subjects:Embryonic chick cardiomyocytes. Interventions:Microscope fields of approximately 500 chick cardiomyocytes were monitored throughout 1 hr of simulated ischemia (Po2 of 3–5 torr, Pco2 of 144 torr, pH 6.8), followed by 3 hrs of reperfusion (Po2 of 149 torr, Pco2 of 36 torr, pH 7.4), and compared with cells reperfused with relative hypercarbia (Pco2 of 71 torr, pH 6.8) or hypocarbia (Pco2 of 7 torr, pH 7.9). Measurements and Main Results:The measured outcomes included cell viability (via propidium iodide) and oxidant generation (reactive oxygen species via 2′,7′-dichlorofluorescin oxidation and nitric oxide [NO] via 4,5-diaminofluorescein diacetate oxidation). Compared with normocarbic reperfusion, hypercarbia significantly reduced cell death from 54.8% ± 4.0% to 26.3% ± 2.8% (p < .001), significantly decreased reperfusion reactive oxygen species (p < .05), and increased NO at a later phase of reperfusion (p < .01). The NO synthase inhibitor N-nitro-l-arginine methyl ester (200 &mgr;M) reversed this oxidant attenuation (p < .05), NO increase (p < .05), and the cardioprotection conferred by hypercarbic reperfusion (increasing death to 54.3% ± 6.0% [p < .05]). Conversely, hypocarbic reperfusion increased cell death to 80.4% ± 4.5% (p < .01). It also increased reactive oxygen species by almost two-fold (p = .052), without affecting the NO level thereafter. Increased reactive oxygen species was attenuated by the mitochondrial complex III inhibitor stigmatellin (20 nM) when given at reperfusion (p < .05). Cell death also decreased from 85.9% ± 4.5% to 52.2% ± 6.5% (p < .01). The nicotinamide adenine dinucleotide phosphate oxidase inhibitor apocynin (300 &mgr;M) had no effect on reperfusion reactive oxygen species. Conclusions:Altering CO2 content during reperfusion can significantly affect myocardial postresuscitation injury, in part by modifying mitochondrial oxidants and NO synthase-induced NO production.

Transient and partial mitochondrial inhibition for the treatment of postresuscitation injury: Getting it just right

Objective:Within minutes of reperfusing ischemic cardiomyocytes, oxidant stress dramatically increases and is associated with postresuscitation injury. Because mitochondria produce deleterious oxidants and useful metabolic substrates, utilization of electron transport chain inhibitors against reperfusion injury, though promising, must not overly compromise recovery of mitochondrial function. This study sought to further characterize the oxidant source at reperfusion and develop a strategy for therapeutic intervention by manipulation of dose, duration, and the degree of reversibility of mitochondrial inhibition. Design:Comparative laboratory investigation. Setting:Laboratory of a research university. Subjects:Embryonic chick cardiomyocytes. Interventions:Synchronously contracting chick cardiomyocytes were exposed to 1 hr of simulated ischemia and 3 hrs of reperfusion and were monitored for cell viability (propidium iodide) and oxidant generation (dichlorofluorescein). Inhibitors were administered either all course or for the first 15 mins of reperfusion. Measurements and Main Results:Application of diethyldithiocarbamic acid, 2-anthracene-carboxylic acid (rhein tech), and &agr;-nicotinamide adenine dinucleotide dehydrogenase (NADH) demonstrated attenuation of the oxidant burst. In addition, diethyldithiocarbamic acid (1 mM), rhein tech (0.1 &mgr;M), and &agr;-NADH (20 &mgr;M) significantly attenuated cell death from a control of 49.7% ± 6.7% to 15.7% ± 4.7% (n = 5, p < .01), 26.1% ± 4.1% (n = 5, p < .01), and 13.8% ± 1.3% (n = 5, p < .001), respectively. All doses of stigmatellin attenuated reactive oxygen species, but only a 2–20 nM dose during the first 15 mins of reperfusion abrogated cell death from 53.8% ± 3.5% to 10.8% ± 2.9% (n = 5, p < .001). Increased doses and durations of stigmatellin abolished reactive oxygen species but augmented injury. Although rotenone (5 &mgr;M) attenuated reactive oxygen species, no dose or duration of exposure that ameliorated cell death was found. Conclusions:Early events of reperfusion are marked by rapid mitochondrial oxidant generation and postresuscitation injury. Electron transport chain blockade provides an effective method of attenuating reactive oxygen species. However, inhibitor administration should be both transient and reversible to necessitate cardioprotection and successful metabolic recovery.

Preconditioning and the oxidants of sudden death

Sudden cardiac death remains a daunting medical challenge. Rescuers have minutes to defibrillate the heart and prevent ischemic injury to critical organs. Cardiopulmonary resuscitation can extend the window for successful therapy but not for long. Complicating this further is the fact that few new therapies have been proven to protect against the postresuscitation phase of cardiac arrest, when as many as 90% of patients die despite successful defibrillation. Oxidants (both reactive oxygen and nitrogen) likely play critical roles during cardiac arrest, affecting defibrillation success by affecting cardiac gap junctions and after successful defibrillation causing multiorgan damage via direct and programmed cell death. Preconditioning is an intrinsic adaptive response to stress that targets this sequence of events and is highly protective against ischemia/reperfusion injury in the heart, brain, and other critical organs. Thus, how oxidants are affected by preconditioning could provide new insights and therapies for improving both defibrillation success and oxidant-mediated postresuscitation injury of sudden cardiac death.