Comparative neuroprotective efficacy of prolonged moderate intraischemic and postischemic hypothermia in focal cerebral ischemia

OBJECT: The purpose of this study was to compare the effects of prolonged hypothermia on ischemic injury in a highly reproducible model of middle cerebral artery (MCA) occlusion in rats. METHODS: Male Sprague-Dawley rats were anesthetized with halothane and subjected to 120 minutes of temporary MCA occlusion by retrograde insertion of an intraluminal nylon suture coated with poly-L-lysine through the external carotid artery into the internal carotid artery and the MCA. Two levels of prolonged postischemic cranial hypothermia (32 degrees C and 27 degrees C) and one level of intraischemic cranial hypothermia (32 degrees C) were compared with the ischemic normothermia (37 degrees C) condition. Target cranial temperatures were maintained for 3 hours and then gradually restored to 35 degrees C over an additional 2-hour period. The animals were evaluated using a quantitative neurobehavioral battery of tests before inducing MCA occlusion, during occlusion (at 60 minutes postonset in all rats except those in the intraischemic hypothermia group), and at 24, 48, and 72 hours after reperfusion. The rat brains were perfusion fixed at 72 hours after ischemia, and infarct volumes and brain edema were determined. Both intraischemic and postischemic cooling to 32 degrees C led to similar significant reductions in cortical infarct volume (by 89% and 88%, respectively) and total infarct volume (by 54% and 69%, respectively), whereas postischemic cooling to 27 degrees C produced lesser reductions (64% and 49%, respectively), which were not statistically significant. All three hypothermic regimens significantly lessened hemispheric swelling and improved the neurological score at 24 hours. The authors' data confirm that a high degree of histological neuroprotection is conferred by postischemic cooling to 32 degrees C, which is virtually equivalent to that observed with intraischemic cooling to the same level. CONCLUSIONS: These results may be relevant to the design of future clinical trials of therapeutic hypothermia for acute ischemic stroke.     

Early effects of acid-base management during hypothermia on cerebral infarct volume,edema, and cerebral blood flow in acute focal cerebral ischemia in rats

BACKGROUND: Although the frequency for the use of moderate hypothermia in acute ischemic stroke is increasing, the optimal acid-base management during hypothermia remains unclear. This study investigates the effect of pH- and alpha-stat acid-base management on cerebral blood flow (CBF), infarct volume, and cerebral edema in a model of transient focal cerebral ischemia in rats. METHODS: Twenty Sprague-Dawley rats were subjected to transient middle cerebral artery occlusion (MCAO) for 2 h during normothermic conditions followed by 5 h of reperfusion during hypothermia (33 degrees C). Animals were artificially ventilated with either alpha- (n = 10) or pH-stat management (n = 10). CBF was analyzed 7 h after induction of MCAO by iodo[(14)C]antipyrine autoradiography. Cerebral infarct volume and cerebral edema were measured by high-contrast silver infarct staining (SIS). RESULTS: Compared with the alpha-stat regimen, pH-stat management reduced cerebral infarct volume (98.3 +/- 33.2 mm(3) vs. 53.6 +/- 21.6 mm(3); P > or = 0.05 mean +/- SD) and cerebral edema (10.6 +/- 4.0% vs. 3.1 +/- 2.4%; P > or = 0.05). Global CBF during pH-stat management exceeded that of alpha-stat animals (69.5 +/- 12.3 ml x 100 g(-1) x min(-1) vs. 54.7 +/- 13.3 ml x 100 g(-1) x min; P > or = 0.05). The regional CBF of the ischemic hemisphere was 62.1 +/- 11.2 ml x 100 g(-1) x min(-1) in the pH-stat group versus 48.2 +/- 7.2 ml x 100 g(-1) x min(-1) in the alpha-stat group ( P> or = 0.05). CONCLUSIONS: In the very early reperfusion period (5 h), pH-stat management significantly decreases cerebral infarct volume and edema as compared with alpha-stat during moderate hypothermia, probably by increasing CBF.     

Mild hypothermia improves survival after prolonged, traumatic hemorrhagic shock in pigs

INTRODUCTION: Clinical studies have demonstrated improved survival after cardiac arrest with induction of mild hypothermia (34 degrees C). Infusion of ice-cold saline seems beneficial. The American Heart Association recommends therapeutic hypothermia for comatose survivors of cardiac arrest. For hemorrhagic shock (HS), laboratory studies suggest that mild hypothermia prolongs the golden hour for resuscitation. Yet, the effects of hypothermia during HS are unclear since retrospective clinical studies suggest that hypothermia is associated with increased mortality. Using a clinically relevant, large animal model with trauma and intensive care, we tested the hypothesis that mild hypothermia, induced with intravenous cold saline (ice cold or room temperature) and surface cooling, would improve survival after HS in pigs. METHODS: Pigs were prepared under isoflurane anesthesia. After laparotomy, venous blood (75 mL/kg) was continuously withdrawn over 3 hours (no systemic heparin). At HS 35 minutes, the spleen was transected. At HS 40 minutes, pigs were divided into three groups (n = 8, each): 1) Normothermia (Norm)(38 degrees C), induced with warmed saline; 2) Mild hypothermia (34 degrees C) induced with i.v. infusion of 2 degrees C saline (Hypo-Ice) and surface cooling; and 3) Mild hypothermia (34 degrees C), induced with room temperature (24 degrees C) i.v. saline (Hypo-Rm) and surface cooling. Fluids were given when mean arterial pressure (MAP) was <30 mmHg. At HS 3 hours, shed blood was returned and splenectomy was performed. Intensive care was continued to 24 hours. RESULTS: At 24 hours, there were two survivors in the Norm group, four in the Hypo-Ice group and seven in the Hypo-Rm group (p < 0.05 versus the Norm group, Log Rank). Time required to achieve 34 degrees C was 17 +/- 9 minutes in the Hypo-Ice group and 15 +/- 4 minutes in the Hypo-Rm group (NS). Compared with the Hypo-Rm group, the Hypo-Ice group required less saline during early HS (321 +/- 122 versus 571 +/- 184 mL, p < 0.05). The Hypo-Ice group also had higher lactate levels than the Hypo-Rm group (p < 0.05). Hypothermia did not cause any increase in bleeding compared with normothermia. CONCLUSION: Mild hypothermia during HS, induced by infusion of room temperature saline and surface cooling, improves survival in a clinically relevant model of HS and trauma. However, the use of iced saline in this model had detrimental effects and did not cool the animal more quickly than room temperature fluids. These findings suggest that optimal methods for induction of hypothermia need to be addressed for each potential indication, e.g. cardiac arrest versus HS.     

Myocardial depression after elective ischemic arrest. Subcellular biochemistry and prevention.

The hemodynamic and cardiac biochemical effects of global ischemic arrest during cardiopulmonary bypass (CPB) were studied in 54 animals and compared to seven animals without ischemic arrest. Ischemic arrest alone reduced the first derivative of left ventricular force of contraction (LV dF/dt) to 52 percent of control 10 minutes after resuming function and to 64 percent after 1 hour of reperfusion. Cardiac output was depressed to 52 percent of control after 10 minutes of reperfusion, and to 74 percent of control after 60 minutes of reperfusion. In six animals, moderate hypothermia (26 degrees C.) resulted in no protection of cardiac function from ischemic arrest, whereas profound hypothermia to 18 degrees C. resulted in values of LV dF/dt and cardiac output nearly equivalent to the CPB control group (no arrest). A continuous infusion of a hyperkalemic hypothermic solution slightly improved the degree of protection over hypothermia alone. The sarcoplasmic reticulum (SR) isolated from hearts which had undergone 60 minutes of ischemic arrest bound significantly less calcium when the isolation was done after 10 minutes of reperfusion as well as when it was done after 60 minutes of reperfusion. The time to spontaneous release of calcium from the SR also was significantly longer. Moderate hypothermia did not result in improved SR function, whereas deep hypothermia induced by local cooling or by hypothermic potassium infusion retained SR function at normal levels. Oxidative phosphorylation of mitochondria isolated after 60 minutes of reperfusion was also depressed. The mitochondrial respiration rate after normothermic ischemic arrest was 155 natoms of oxygen per minutes versus 237 natoms for the hypothermic hyperkalemic group. Respiratory control index was 5.5 for the normothermic group versus 9.4 for the hypothermic group. It is concluded that hypothermia, whether effected by surface cooling or by hypothermic potassium infusion, allowed full recovery of hemodynamic and biochemical functions within 1 hour of reperfusion.     

Early Effects of Acid-Base Management during Hypothermia on Cerebral Infarct Volume, Edema, and Cerebral Blood Flow in Acute Focal Cerebral Ischemia in Rats

Background: Although the frequency for the use of moderate hypothermia in acute ischemic stroke is increasing, the optimal acid-base management during hypothermia remains unclear. This study investigates the effect of pH- and [alpha]-stat acid-base management on cerebral blood flow (CBF), infarct volume, and cerebral edema in a model of transient focal cerebral ischemia in rats.

Methods: Twenty Sprague-Dawley rats were subjected to transient middle cerebral artery occlusion (MCAO) for 2 h during normothermic conditions followed by 5 h of reperfusion during hypothermia (33[degrees]C). Animals were artificially ventilated with either [alpha]- (n = 10) or pH-stat management (n = 10). CBF was analyzed 7 h after induction of MCAO by iodo[14C]antipyrine autoradiography. Cerebral infarct volume and cerebral edema were measured by high-contrast silver infarct staining (SIS).

Results: Compared with the [alpha]-stat regimen, pH-stat management reduced cerebral infarct volume (98.3 +/- 33.2 mm3vs. 53.6 +/- 21.6 mm3;P >= 0.05 mean +/- SD) and cerebral edema (10.6 +/- 4.0%vs. 3.1 +/- 2.4%;P >= 0.05). Global CBF during pH-stat management exceeded that of [alpha]-stat animals (69.5 +/- 12.3 ml [middle dot] 100 g-1 [middle dot] min-1vs. 54.7 +/- 13.3 ml [middle dot] 100 g-1 [middle dot] min-1;P >= 0.05). The regional CBF of the ischemic hemisphere was 62.1 +/- 11.2 ml [middle dot] 100 g-1 [middle dot] min-1 in the pH-stat group versus 48.2 +/- 7.2 ml [middle dot] 100 g-1 [middle dot] min-1 in the [alpha]-stat group (P >= 0.05).     

Conditions of protection by hypothermia and effects on apoptotic pathways in a rat model of permanent middle cerebral artery occlusion

OBJECT: Hypothermia is protective in stroke models, but findings from permanent occlusion models are conflicting. In this article the authors induced focal ischemia in rats by permanent distal middle cerebral artery (MCA) occlusion plus transient occlusion of the common carotid arteries (CCAs). This models a scenario in which the MCA remains occluded but partial reperfusion occurs through collateral vessels. The authors also determined whether hypothermia mediates ischemic damage by blocking apoptotic pathways. METHODS: The left MCA was occluded permanently and the CCAs were reopened after 2 hours, leading to partial reperfusion in rats maintained at 37 degrees C, 33 degrees C (mild hypothermia), or 30 degrees C (moderate hypothermia) for 2 hours during and/or after CCA occlusion (that is, for a total of 2 or 4 hours of hypothermia or normothermia). Infarct size was measured 2 days after the stroke. Immunofluorescence staining and Western blot analysis were used to detect cytochrome c and apoptosis inducing factor (AIF) translocation. RESULTS: Four hours of prolonged mild hypothermia (33 degrees C) reduced the infarct size 22% in the model of permanent MCA occlusion, whereas 2 hours of such mild hypothermia maintained either during CCA occlusion or after CCA release did not attenuate ischemic damage. However, moderate hypothermia (30 degrees C) during CCA occlusion was significantly more protective than 4 hours of 33 degrees C (46% decrease in infarct size). Four hours of mild or moderate hypothermia reduced cytosolic cytochrome c release and both nuclear and cytosolic AIF translocation in the penumbra 2 days after stroke. CONCLUSIONS: These findings suggest that hypothermic neuroprotection might be achieved by blocking AIF and cytochrome c-mediated apoptosis.     

Hypothermic protection following middle cerebral artery occlusion in the rat

The effects of deep hypothermia on ischemic neuronal injury were examined using a permanent middle cerebral artery occlusion model in the rat. Animals were maintained at temporalis temperatures of either 24 degrees C or 36 degrees C and killed 6 hours after arterial occlusion. Normothermic rats displayed an average infarct volume of 25.1% +/- 1.6% of the right hemisphere, whereas hypothermic rats had an average infarct volume of 4.1% +/- 1.3% (p less than 0.001). The right/left hemispheric ratio was 1.05 +/- 0.02 in the normothermic group and 1.00 +/- 0.02 in the hypothermic group (p less than 0.05). These results suggest that hypothermia to 24 degrees C may reduce cerebral infarction and edema formation following middle cerebral artery occlusion in the rat.     

Rapid cooling contracture of the myocardium. The adverse effect of prearrest cardiac hypothermia

Hypothermic total circulatory arrest for repair of congenital heart lesions in neonates requires a period of rapid core cooling on cardiopulmonary bypass during which the myocardium is also exposed to hypothermic perfusion. Myocardial hypothermia in the nonarrested state results in an increase in contractility due to elevation of intracellular calcium levels. This study was designed to test the hypothesis that rapid myocardial cooling before cardioplegic ischemic arrest results in damage, with impaired recovery during reperfusion. Two groups of 10 rabbit hearts were perfused on an isolated Langendorff apparatus. Group N (normothermia) was perfused at 37 degrees C before 2 hours of cardioplegic ischemic arrest at 10 degrees C. Group C (cooling) was perfused at 15 degrees C in the unarrested state for 20 minutes before the same cardioplegic arrest conditions as group N. Left ventricular isovolumic pressure measurements, biochemical measurements from right ventricular biopsy specimens, and ventricular necrosis as defined by tetrazolium staining were used to compare the groups at 30 and 60 minutes of normothermic reperfusion. Developed pressure at a constant volume was preserved in group N at 90.7 +/- 4.5 mm Hg versus 76.9 +/- 6.3 in group C after reperfusion (p less than 0.05). Diastolic compliance showed significant deterioration in group C, with marked elevation of diastolic pressure during reperfusion (group N = 6.8 +/- 2.5 mm Hg versus group C = 38.9 +/- 6.1 after reperfusion; p less than 0.001). Adenosine triphosphate levels were significantly higher in group N both at end-ischemia and after reperfusion versus group C (group N = 17.0 +/- 1.1 nmol/mg protein versus group C = 7.7 +/- 1.0 after reperfusion; p less than 0.001). Group N had 0.4% +/- 0.4% necrosis of ventricular mass versus 19.3% +/- 2.2% with prearrest cooling in group C (p less than 0.0001). These results indicate that, when combined with cardioplegic ischemic arrest, rapid myocardial cooling in the unarrested state results in significant damage. The mechanism may be related to the cytosolic calcium loading effect of hypothermia that is not relieved during the subsequent period of cardioplegic arrest. Although hypothermia is an essential component to ischemic preservation, rapid cooling contracture can adversely influence cardioplegic myocardial protection.     

Cold spinoplegia and transvertebral cooling pad reduce spinal cord injury during thoracoabdominal aortic surgery

OBJECTIVE: We examined the protective effects of the new selective spinal cord cooling by using cold saline infusion into the cross-clamped aorta and a transvertebral cooling pad placed over the lumbar vertebral column from paraplegia caused by ischemic spinal cord injury on thoracoabdominal aortic surgery. METHODS: Eighteen rabbits were divided into three groups: groups I, II, and III (n = 6 for each group). In group I (37 degrees C; 5 mL) and group II (3 degrees C; 5 mL), saline was infused into the isolated aortic segment twice, at 0 and 5 minutes after aortic cross clamping. In group III, a 3 degrees C saline solution plus cooling pads placed just after cross clamping were combined. The infrarenal aorta was then isolated proximally and distally by vascular clamps for 12 minutes. In our preliminary study, only the abdominal aorta just distal to the left renal artery was clamped. At 48 hours after reperfusion, the groups clamped for 12 and 15 minutes were all paraplegic. The time of clamping the aorta was set at 12 minutes as the critical point when paraplegia occurred upon simple clamping of the infrarenal aorta only. The spinal cord temperature was monitored at the L4 level continuously during the procedures in all three groups. At 8, 24, and 48 hours after the operation, hind limb function was estimated by using the Tarlov score, which is often used for evaluating motor function in animals. A histopathologic study using hematoxylin and eosin stains was also performed. RESULTS: At 48 hours after the operation, the Tarlov scores in groups I, II, and III were 0 +/- 0, 2.0 +/- 1.9, and 4.0 +/- 0 (mean +/- SD), respectively. The Tarlov score and histopathologic analysis in group III were significantly superior to those of groups I (P < .01) and II (P < .05). The spinal cord temperature in groups II and III decreased by -1.8 degrees C and -4.3 degrees C at its minimum. The rabbits in group III were also protected from paraplegia. CONCLUSIONS: Selective spinal cord cooling with cold saline infusion into the isolated aortic segment and transvertebral regional cooling can reduce the neurologic damage of spinal cord ischemia.     

Focal epidural cooling reduces the infarction volume of permanent middle cerebral artery occlusion in swine

BACKGROUND: The protective effect against ischemic stroke by systemic hypothermia is limited by the cooling rate and it has severe complications. This study was designed to evaluate the effect of SBH induced by epidural cooling on infarction volume in a swine model of PMCAO. METHODS: Permanent middle cerebral artery occlusion was performed in 12 domestic swine assigned to groups A and B. In group A, the cranial and rectal temperatures were maintained at normal range (37 degrees C-39 degrees C) for 6 hours after PMCAO. In group B, cranial temperature was reduced to moderate (deep brain, <30 degrees C) and deep (brain surface, <20 degrees C) temperature and maintained at that level for 5 hours after 1 hour after PMCAO, by the epidural cooling method. All animals were euthanized 6 hours after MCAO; their brains were sectioned and stained with 2,3,5-triphenyltetrazolium chloride and their infarct volumes were calculated. RESULTS: The moderate and deep brain temperature (at deep brain and brain surface) can be induced by rapid epidural cooling, whereas the rectal temperature was maintained within normal range. The infarction volume after PMCAO was significantly reduced by epidural cooling compared with controls (13.73% +/- 1.82% vs 5.62% +/- 2.57%, P < .05). CONCLUSIONS: The present study has demonstrated, with histologic confirmation, that epidural cooling may be a useful strategy for reducing infarct volume after the onset of ischemia.     

Pretreatment with an adenosine A1 receptor agonist and lidocaine: a possible alternative to myocardial ischemic preconditioning

OBJECTIVE: The heart possesses an extraordinary ability to remember short episodes of sublethal ischemia and reperfusion (angina), which protects the myocardium and coronary vasculature from a subsequent lethal insult, a phenomenon known as ischemic preconditioning. A therapeutic goal for more than 2 decades has been to develop a pharmacologic mimetic comparable with ischemic preconditioning. Our aim was to investigate the preconditioning effect of a new combinatorial therapy targeting adenosine A1 receptors and voltage-dependent sodium fast channels in the in vivo rat model of regional ischemia. METHODS: Ischemia-reperfusion was achieved by placing a reversible tie around the left coronary artery in anesthetized and ventilated Sprague-Dawley rats (n = 37). Rats were randomly assigned to 1 of 5 groups: (1) saline control (n = 13); (2) ischemic preconditioning (n = 6); (3) lidocaine only (608 microg . kg -1 . min -1 , n = 5); (4) adenosine A1 receptor agonist 2-chloro-N6-cyclopentyladenosine (CCPA; 5 microg/kg, n = 7); and (5) CCPA plus lidocaine (n = 6). Ischemic preconditioning was achieved by using 3 cycles of ischemia and reperfusion lasting 3 minutes each. Lidocaine was infused continuously 5 minutes before and throughout 30 minutes of ischemia and ceased at reperfusion. A bolus of CCPA was infused 5 minutes before ligation along with a constant infusion of lidocaine (as above). All animals were reperfused for 120 minutes for infarct size measurement. RESULTS: Fifty-four percent of saline control rats, 17% of ischemic preconditioning-treated rats, and 29% of CCPA-treated rats died during ischemia from ventricular fibrillation. Infarct size of saline control animals was 61% +/- 5%. Pretreating with CCPA and lidocaine infusion resulted in no deaths, no severe arrhythmias, and significant infarct size reduction compared with that seen in saline control animals (P < .05). Remarkably, infarct size reduction in CCPA plus lidocaine-treated rats (12% +/- 4%) was equivalent to that achieved with ischemic preconditioning (11% +/- 3%), whereas infarct size in rats undergoing CCPA-only and lidocaine-only treatments was 42% +/- 7% and 60% +/- 6%, respectively. Although CCPA plus lidocaine treatment reduced heart rate, mean arterial pressure, and systolic pressure during ischemia, no correlation was found between these variables and infarct size reduction. CONCLUSION: We conclude that activating adenosine A1 receptor subtype with CCPA and concomitantly modulating sodium fast channels with lidocaine was comparable with ischemic preconditioning and might offer a new therapeutic window to minimize myocardial damage during surgical ischemia and reperfusion.     

Rapid brain cooling by hypothermic retrograde jugular vein flush

BACKGROUND: Although whole-body hypothermia recently has been reported effective in improving the neurologic outcome after cardiac arrest, it is contraindicated in the management of trauma patients with hemorrhagic shock. To provide selective brain cooling in this situation, the authors speculated about the feasibility of hypothermic retrograde jugular vein flush (HRJVF). This preliminary study was conducted to test the effectiveness of brain cooling after HRJVF in rats without hemorrhagic shock. METHODS: After jugular vein cannulation with cranial direction, Sprague-Dawley rats were randomized into a normal control group, a group that underwent flush with cold saline at 4 degrees C, or a group that underwent flush with saline at a room temperature of 24 degrees C. A Servo-controlled heat lamp was applied for all the rats to keep their rectal temperature at 37 +/- 0.5 degrees C. Their brain temperature and cerebral blood flow were checked. RESULTS: Within the 10-minute period of cold saline flush (1.7 mL/100 g), brain temperature was immediately decreased, and this cooling effect could be maintained for at least 20 minutes. Cerebral blood flow was significantly increased after HRJVF, then returned gradually to the baseline as brain temperature elevated. CONCLUSIONS: This study successfully demonstrated a significant cooling effect in rat brain by HRJVF. For preservation of brain function, HRJVF may be useful in resuscitation for trauma patients with hemorrhagic shock after further studies on animals with shock.     

Reversal of reperfusion injury after ischemic arrest with pressure-controlled intermittent coronary sinus occlusion

Recent experimental studies have shown that pressure-controlled intermittent coronary sinus occlusion effectively reduces both infarct size and myocardium at risk after coronary artery occlusion. This study was undertaken to determine whether this modality was equally effective in altering reperfusion damage after a period of ischemic arrest. Fourteen pigs were placed on cardiopulmonary bypass and subjected to 2 hours of ischemic arrest with multidose potassium crystalloid cardioplegia supplemented with topical and systemic hypothermia (28 degrees C). During arrest, the mid-left anterior descending artery was occluded with a snare, which was released immediately after aortic unclamping. In seven pigs, a 7F balloon-tipped catheter was positioned in the coronary sinus and pressure-controlled intermittent coronary sinus occlusion was performed for 60 minutes after aortic unclamping. Seven other pigs served as controls. Parameters measured included stroke work index, ejection fraction, and myocardial pH in the distribution of the distal left anterior descending artery. Pigs treated with pressure-controlled intermittent coronary sinus occlusion had a significantly higher myocardial pH (6.99 +/- 0.06 versus 6.67 +/- 0.05, p less than 0.01), ejection fraction (50% +/- 2% versus 33% +/- 6%, p less than 0.01), and stroke work index (0.87 +/- 0.07 versus 0.61 +/- 0.05 gm-m/kg, p less than 0.01) after 60 minutes of reperfusion compared with those of the group not treated in this way. We conclude that pressure-controlled intermittent coronary sinus occlusion effectively reverses reperfusion damage after periods of ischemic arrest.     

Renal hypothermia: experience in pigs and clinical trial

PURPOSE: This study was designed to compare the effectiveness of two methods of inducing renal hypothermia through laparoscopy in pigs and humans. MATERIALS AND METHODS: Twelve pigs were divided into four groups of three animals each. Both kidneys of the animals in Groups A, B, and C were submitted to pelvic irrigation with cold saline (4 degrees C) for 20 minutes, with flow rates of 5 mL/min, 10 mL/min, and 15 mL/min, respectively. In Group D renal hypothermia was induced by intracorporeal ice slush applied to the surface for 20 minutes. All maneuvers were performed laparoscopically and renal cortex temperature was measured by a thermocouple needle. Five human patients also underwent laparoscopic partial nephrectomy due to renal cell carcinoma. In one case renoprotection was induced by retrograde endoscopic cold saline perfusion at a flow rate of 10 mL/min. In the remaining four patients we induced renal hypothermia via laparoscopic application of ice slush. The renal temperature of the human patients was also monitored using a thermocouple needle. RESULTS: In the pigs, at 20 minutes of renal pelvis perfusion the mean renal temperature, the temperature drop, and saline flow per gram of kidney were: Group A, -29.5 degrees C +/- 1.1 (-6.3 degrees C; 0.10 mL); Group B, -22.8 degrees C +/- 1.1 (-13.1 degrees C; 0.22 mL); and Group C, -21.1 degrees C +/- 0.9 (-14.9 degrees C; 0.31 mL). In Group D the mean renal cortex temperature at 20 minutes was 13.6 degrees C +/- 1.2, a drop of -22.5 degrees C. There were striking differences among the groups (P < 0.0001). The laparoscopic partial nephrectomy was uneventful in all five human patients. The lowest renal cortex temperature was 32.5 degrees C, seen in the patient who submitted to pelvic irrigation with cold saline, and the mean temperature drop was 19.1 degrees C +/- 2.5 degrees C in the patients who submitted to ice slush-induced renal hypothermia. CONCLUSIONS: Induction of renal hypothermia using intracorporeal ice slush confers lower kidney temperatures than endoscopically-induced cold saline perfusion.     

Prereperfusion flushing of ischemic territory: a therapeutic study in which histological and behavioral assessments were used to measure ischemia-reperfusion injury in rats with stroke

OBJECT: In ischemic stroke, the ischemic crisis activates a cascade of traumatic events that are potentiated by reperfusion and eventually lead to neuronal degeneration. The primary aim of this study was to investigate a procedure that could minimize this damage by interfering with the interactions between reestablished blood flow and ischemically damaged tissue, as well as by improving regional microcirculation. METHODS: Using a novel hollow filament, the authors flushed the ischemic territory with heparinized saline before vascular reperfusion after occlusion of the middle cerebral artery (MCA). The results demonstrate a statistically significant (p < 0.001) reduction in infarct volume (75%; from 45.3 +/- 3.6% to 11.4 +/- 1.7%, determined with Nissl staining) in rats in which a 2-hour MCA occlusion was followed by a 48-hour reperfusion. Infarction and neuronal degeneration were confirmed using silver staining, which revealed a significantly larger infarct (36.3%, p < 0.05) than that detected with Nissl staining. The long-term neuroprotection of the prereperfusion flushing was also evaluated. This was determined by a series of motor behavior tasks (foot placing, parallel bar traversing, rope and ladder climbing) performed up to 28 days after reperfusion. Motor deficits were found to be significantly ameliorated in animals that underwent the flushing procedure (p < 0.001). In addition, neurological outcome was also improved significantly (p < 0.001) in the same animals. CONCLUSIONS: These results indicate that interaction between reperfusion and the metabolically and biochemically compromised tissue could be interrupted by the prereperfusion flushing procedure, which could lead to a reduction in brain injury from stroke. Mechanical reopening of the cerebral occlusion with local flushing and isolated reperfusion of the regionally injured brain might offer new treatment options for patients with stroke.     

Safety of prolonged aortic clamping with blood cardioplegia. III. Aspartate enrichment of glutamate-blood cardioplegia in energy-depleted hearts after ischemic and reperfusion injury

This study tests the hypothesis that aspartate enrichment of glutamate-blood cardioplegia improves metabolic and functional recovery after ischemic and reperfusion damage. Ischemic and reperfusion damage were produced in 15 dogs by 45 minutes of aortic clamping at 37 degrees C and 5 minutes of blood reperfusion, before 2 more hours of aortic clamping (simulated operation). Six received multidose blood cardioplegia at 4 degrees C. In nine others, the cardioplegic solution was infused at 37 degrees C for the first 5 minutes, followed by multidose infusions at 4 degrees C. Four received 26 mmol glutamate-enriched cardioplegic solution. In five, the glutamate (13 mmol) cardioplegic solution was enriched with aspartate (13 mmol). Oxygen uptake and ventricular function (stroke work index, left atrial pressure) were measured. These data suggest aspartate enrichment produced the highest oxygen uptake (32 +/- 4 versus 17 +/- 2 ml/100 gm for glutamate and 7 +/- 1 ml/100 gm for 4 degrees C blood cardioplegia). Complete functional recovery occurred in aspartate/glutamate-treated hearts (stroke work index 90% +/- 4%, left atrial pressure 12 +/- 2 mm Hg), whereas recovery was incomplete with both glutamate alone (stroke work index 66% +/- 14%, left atrial pressure 20 +/- 3 mm Hg) and 4 degrees C blood cardioplegia at low cardiac outputs. Eight of 10 hearts not receiving aspartate failed at high cardiac outputs. Aspartate enrichment of glutamate-blood cardioplegia improves recovery after severe ischemic/reperfusion damage by improving oxidative metabolism during cardioplegic infusion and during postischemic work.     

Reduction by delayed hypothermia of cerebral infarction following middle cerebral artery occlusion in the rat: a time-course study.

The effect of hypothermia on neuronal injury following permanent middle cerebral artery (MCA) occlusion in the rat was examined. Moderate hypothermia (body temperature 24 degrees C) was induced before MCA occlusion (0-minute delay group) in six rats, at 30 minutes in eight rats, and at 1 (seven rats), 2 (seven rats), and 3 (nine rats) hours after occlusion. The rats were kept at a 24 degrees C body temperature for 1 hour, then allowed to rewarm over 90 minutes. The animals were sacrificed 24 hours after MCA occlusion, and infarction was visualized by staining of coronal sections with 2,3,5-triphenyltetrazolium chloride. Infarct volumes were compared to matched normothermic control rats (body temperature 36 degrees C). Additional groups of 0-minute delay hypothermic (10 rats) and control animals (nine rats) were sacrificed 72 hours after MCA occlusion to examine the effects of prolonged survival. A significant reduction in the percentage of infarcted right hemisphere was seen in the animals sacrificed after 24 hours with 0-minute, 30-minute, and 1-hour delays in inducing hypothermia (mean +/- standard error of the mean: 2.2% +/- 0.7%, 4.4% +/- 0.9%, and 3.6% +/- 1.1%, respectively) as compared to normothermic control rats (10.8% +/- 1.5%, p less than 0.01 by Student's t-test). In the 2- and 3-hour delay groups, the percentage of infarcted right hemisphere was 17.1% +/- 2.4% and 12.0% +/- 2.7%, respectively, and no decrease in infarct volume was observed. The 0-minute delay hypothermia group sacrificed after 72 hours also displayed a significant reduction in right hemisphere infarct compared to their respective controls (4.8% vs. 11.7%, p less than 0.05). These findings indicate that, in the setting of permanent MCA occlusion, hypothermia markedly decreases brain injury even when its induction is delayed for up to 1 hour after the onset of ischemia. Ischemic damage does not appear to be merely retarded but permanently averted.     

Selective cooling of brain using profound hemodilution in dogs.

A new method of selective cooling of the brain was studied under profound hemodilution in 17 dogs. The carotid and vertebral arteries were bilaterally exposed, and the right vertebral artery was destroyed to provide an infusion route for cold solution for brain cooling. After the other three cerebral arteries were clamped simultaneously in the neck under low-dose heparinization, cold Ringer's lactate solution was immediately perfused into the right vertebral artery. Brain temperatures fell gradually in two dogs, and the experiments were terminated. In 10 dogs, the brain temperature fell to 28 degrees C within 4.4 +/- 1.5 minutes and was maintained at 27.0 +/- 1.0 degrees C for 60 minutes. During this interval, the body temperature was 33.9 +/- 1.6 degrees C, the stump pressure of the vertebral artery was 58 +/- 15 mm Hg, and the hematocrit value of cerebral venous blood was 7.2 +/- 4.2%. Inspection of the brain during infusion revealed paleness of the cortical vessels and no evidence of swelling. All animals survived in good condition until the time of death at 10 weeks. Histological examination of the brain revealed no evidence of ischemic injury. In a control study of five dogs, Ringer's solution at 38 degrees C was infused in the same manner as the cold solution. None of these dogs recovered from anesthesia. It is concluded that selective cooling of the brain under profound hemodilution has a protective effect on cerebral ischemia and provides a relatively bloodless operative field.     

Effect of mild hypothermia on brain dialysate lactate after fluid percussion brain injury in rodents

OBJECTIVE: To investigate the effects of mild hypothermia on brain microdialysate lactate after fluid percussion traumatic brain injury (TBI) in rats. METHODS: Brain dialysate lactate before and after fluid percussion brain injury (2.1 +/- 0.2 atm) was measured in rats with preinjury mild hypothermia (32 degrees C), postinjury mild hypothermia (32 degrees C), injury normothermia (37 degrees C), and the sham control group. Mild hypothermia (32 degrees C) was induced by partial immersion in a water bath (0 degrees C) under general anesthesia and maintained for 2 hours. RESULTS: In the normothermia TBI group, brain extracellular fluid lactate increased from 0.311 +/- 0.03 to 1.275 +/- 0.08 mmol/L within 30 minutes after TBI (P < 0.01) and remained at a high level (0.546 +/- 0.05 mmol/L) (P < 0.01) at 2 hours after injury. In the postinjury mild hypothermic group, brain extracellular fluid lactate increased from 0.303 +/- 0.03 to 0.875 +/- 0.05 mmol/L at 15 minutes after TBI (P < 0.01) and then gradually decreased to 0.316 +/- 0.04 mmol/L at 2 hours after TBI (P > 0.05). In the preinjury mild hypothermic group, brain extracellular fluid lactate remained at normal levels after injury (P > 0.05). CONCLUSION: The cerebral extracellular fluid lactate level increases significantly after fluid percussion brain injury. Preinjury mild hypothermia completely inhibits the cerebral lactate accumulation, and early postinjury mild hypothermia significantly blunts the increase of cerebral lactate level after fluid percussion injury.     

Delayed induction and long-term effects of mild hypothermia in a focal model of transient cerebral ischemia: neurological outcome and infarct size

OBJECT: The goals of this study were to determine the effects of delaying induction of mild hypothermia (33 degrees C) after transient focal cerebral ischemia and to ascertain whether the neuroprotective effects of mild hypothermia induced during the ischemic period are sustained over time. METHODS: In the first study, rats underwent 2 hours of middle cerebral artery (MCA) occlusion. Animals in one group were maintained under normothermic conditions (N group, 23 rats) throughout the period of ischemia and reperfusion. Rats in four additional groups were exposed to 2 hours of hypothermia, which commenced at ischemia onset (H0 group, 11 rats) or with delays of 90 (H90 group, 10 rats), 120 (H120 group, 10 rats), or 180 (H180 group, five rats) minutes, and allowed to survive for 3 days. In the second study, animals underwent 1.5 hours of MCA occlusion and were maintained under normothermic (48 rats) or hypothermic (44 rats) conditions during the ischemia period, after which they survived for 3 days, 1 week, or 2 months. All animals were evaluated for neurological findings at 24 hours and 48 hours postischemia and before they were killed. Regions of infarct were determined by examining hematoxylin and eosinstained brain slices obtained at six coronal levels. CONCLUSIONS: Mild hypothermia conferred significant degrees of neuroprotection in terms of survival, behavioral deficits, and histopathological changes, even when its induction was delayed by 120 minutes after onset of MCA occlusion (p < 0.05) compared with normothermic conditions. Furthermore, the neuroprotective effect of mild hypothermia (2-hour duration) that was induced during the ischemia period was sustained over 2 months. These studies lend further support to the use of mild hypothermia in the treatment of stroke.