Exploring effects of remote ischemic preconditioning in a pig model of hypothermic circulatory arrest.

OBJECTIVES: During aortic and cardiac surgery, risks for mortality and morbidity are inevitable. Surgical setups involving deep hypothermic circulatory arrest (DHCA) are effective to achieve organ protection against ischemic injury. The aim of this study was to identify humoural factors mediating additive protective effects of remote ischemic preconditioning (RIPC) in a porcine model of DHCA. DESIGN: Twenty-two pigs were randomized into the RIPC group (n = 11) and the control group (n = 11). The RIPC group underwent four 5-minute hind limb ischemia-reperfusion cycles prior to cardiopulmonary bypass and DHCA. All animals underwent identical surgical procedures including 60 min DHCA at 18 °C. Blood samples were collected from vena cava and sagittal sinus at several time points. After the 8-hour follow-up period, the brain, heart, and kidney tissue samples were collected for tissue analyses. RESULTS: Serum levels of brain damage marker S100B recovered faster in the RIPC group, after 4 hours of the arrest, (p < .05). Systemic lactate levels were lower and cardiac index was higher in the RIPC group postoperatively. Immunohistochemical cerebellum regional scores of antioxidant response regulator Nrf2 were better in the RIPC group (mean: 1.1, IQR: 0.0-2.5) compared with the control group (mean: 0.0, IQR: 0.0-0.0), reaching borderline statistical significance (p = .064). RIPC induced detectable modulations of plasma proteome and metabolites. CONCLUSIONS: The faster recovery of S100B, lower systemic lactate levels and favourable regional antioxidant response suggest possible neuronal cellular and mitochondrial protection by RIPC, whereas better cardiac index underlines functional effects of RIPC. The exact humoural factor remains unclear.

Pharmacological Preconditioning with Diazoxide in the Experimental Hypothermic Circulatory Arrest Model.

BACKGROUND: Hypothermic circulatory arrest includes a remarkable risk for neurological injury. Diazoxide, a mitochondrial adenosine triphosphate-dependent potassium ion (K+ATP) channel opener, is known to have cardioprotective effects. We assessed its efficacy in preventing ischemic injury in a clinically relevant animal model. Methods: Eighteen piglets were randomized into a diazoxide group (n = 9) and a control group (n = 9). Animals underwent 60 minutes of hypothermic circulatory arrest at 18°C. Diazoxide (5 mg/kg + 10 mL NaOH + 40 mL NaCl) was infused during the cooling phase. Metabolic and hemodynamic data were collected throughout the experiment. After 24-hour follow-up, whole brain, heart, and kidney biopsy specimens were collected for analysis. Results: Cerebellar Cytochrome-C and caspase-3 activation was higher in the control group (P = .02 and P = .016, respectively). Antioxidant activity tended to be higher in the diazoxide group (P = .099). Throughout the experiment, the oxygen consumption ratio was higher in the control animals (Pg = .04), as were the lactate levels (Pg = .02). Cardiac function tended to be better in diazoxide-treated animals. Conclusion: Diazoxide might confer neuroprotective effect as implied by the immunohistochemical analysis of the brain. Additionally, the circulatory effects of diazoxide were beneficial, supporting its neuroprotective effect.

Safety and biodistribution study of bone marrow-derived mesenchymal stromal cells and mononuclear cells and the impact of the administration route in an intact porcine model.

BACKGROUND AIMS: Bone marrow mononuclear cells (BM-MNCs) and bone marrow-derived mesenchymal stem stromal cells (BM-MSCs) could have therapeutic potential for numerous conditions, including ischemia-related injury. Cells transplanted intravascularly may become entrapped in the lungs, which potentially decreases their therapeutic effect and increases the risk for embolism. METHODS: Twelve pigs were divided into groups of 3 and received (99m)Tc- hydroxymethyl-propylene-amine-oxime-labeled autologous BM-MNCs or allogeneic BM-MSCs by either intravenous (IV) or intra-arterial (IA) transplantation. A whole body scan and single photon emission computed tomography/computed tomography (SPECT/CT) were performed 8 h later, and tissue biopsies were collected for gamma counting. A helical CT scan was also performed on 4 pigs to detect possible pulmonary embolism, 2 after IV BM-MSC injection and 2 after saline injection. RESULTS: The transplantation route had a greater impact on the biodistribution of the BM-MSCs than the BM-MNCs. The BM-MNCs accumulated in the spleen and bones, irrespective of the administration route. The BM-MSCs had relatively higher uptake in the kidneys. The IA transplantation decreased the deposition of BM-MSCs in the lungs and increased uptake in other organs, especially in the liver. Lung atelectases were frequent due to mechanical ventilation and attracted transplanted cells. CT did not reveal any pulmonary embolism. CONCLUSIONS: Both administration routes were found to be safe, but iatrogenic atelectasis might be an issue when cells accumulate in the lungs. The IA administration is effective in avoiding pulmonary entrapment of BM-MSCs. The cell type and administration method both have a major impact on the acute homing.

Intra-arterial bone marrow mononuclear cell distribution in experimental global brain ischaemia.

OBJECTIVES: Bone marrow mononuclear cells (BM-MNCs) can ameliorate focal ischaemic brain injury. A global ischaemic brain injury, which can occur after cardiac or thoracic surgery, could be an essential target for BM-MNCs. No studies using BM-MNCs for this indication have been conducted. DESIGN: Ten porcine underwent a global normothermic ischaemic insult, followed by an intra-arterial injection of Technetium(99m)-HMPAO-labelled BM-MNCs after 2, 4, 6, 12 or 24 hours. A whole-body scan and a SPECT/CT were performed 2 hours after the injection. Severity of the injury was assessed with EEG and tissue biopsies were analysed by scintigraphy. RESULTS: The majority of the cells appeared in the lungs and the liver. Only a minimal number of cells were located in the brain. Median distribution of cells between organs in all animals was as follows: lungs 32.7% (30.6-38.2), liver 14.2% (12.0-17.2), spleen 7.3% (3.3-11.3) and kidneys 2.5% (2.0-3.3). The transplanted cells could not be detected within the brain tissue by radionuclide imaging. CONCLUSIONS: Intra-arterially transplanted BM-MNCs did not migrate to the damaged brain tissue in significant quantity when transplanted during the first 24 hours after the global ischaemic insult, contrary to results with models of focal brain injury.

Remote ischemic preconditioning protects the brain against injury after hypothermic circulatory arrest.

BACKGROUND: Ischemic preconditioning (IPC) is a mechanism protecting tissues from injury during ischemia and reperfusion. Remote IPC (RIPC) can be elicited by applying brief periods of ischemia to tissues with ischemic tolerance, thus protecting vital organs more susceptible to ischemic damage. Using a porcine model, we determined whether RIPC of the limb is protective against brain injury caused by hypothermic circulatory arrest (HCA). METHODS AND RESULTS: Twelve piglets were randomized to control and RIPC groups. RIPC was induced in advance of cardiopulmonary bypass by 4 cycles of 5 minutes of ischemia of the hind limb. All animals underwent cardiopulmonary bypass followed by 60 minutes of HCA at 18°C. Brain metabolism and electroencephalographic activity were monitored for 8 hours after HCA. Assessment of neurological status was performed for a week postoperatively. Finally, brain tissue was harvested for histopathological analysis. Study groups were balanced for baseline and intraoperative parameters. Brain lactate concentration was significantly lower (P<0.0001, ANOVA) and recovery of electroencephalographic activity faster (P<0.05, ANOVA) in the RIPC group. RIPC had a beneficial effect on neurological function during the 7-day follow-up (behavioral score; P<0.0001 versus control, ANOVA). Histopathological analysis demonstrated a significant reduction in cerebral injury in RIPC animals (injury score; mean [interquartile range]: control 5.8 [3.8 to 7.5] versus RIPC 1.5 [0.5 to 2.5], P<0.001, t test). CONCLUSIONS: These data demonstrate that RIPC protects the brain against HCA-induced injury, resulting in accelerated recovery of neurological function. RIPC might be neuroprotective in patients undergoing surgery with HCA and improve long-term outcomes. Clinical trials to test this hypothesis are warranted.

Remote ischemic precondition preserves cerebral oxygen tension during hypothermic circulatory arrest.

OBJECTIVES: Remote ischemic preconditioning (RIPC) is a novel and promising method of mitigating neurological injury. In previous animal studies, RIPC has provided substantial neuroprotective effects. We hypothesized that the promising neuroprotective properties were a consequence of a better oxygen consumption profile during hypothermic circulatory arrest (HCA). DESIGN: Six 7-week-old female pigs were randomly assigned to undergo the 60 minutes of HCA with the right hind leg receiving transient RIPC preoperatively and six animals were assigned to a control group that underwent 60 minutes of HCA without any preconditioning. A combined temperature/oxygen-tension probe was inserted into the parietal cortex of each animal to monitor cerebral oxygen tension during experiments. RESULTS: The RIPC group had significantly higher cerebral oxygen tension readings throughout the HCA. Statistically significant differences were measured from the 20 minute time point onwards in every time point up to the 60 minute time point. CONCLUSIONS: This study shows that RIPC performed before HCA conserves the cerebral oxygen tension during a circulatory arrest. RIPC could possibly prolong the safe operating time during HCA as cerebral oxygen content is preserved throughout circulatory arrest.

Spinal cord injury during selective cerebral perfusion and segmental artery occlusion: an experimental study.

OBJECTIVES: Since selective cerebral perfusion (SCP) has been used in aortic arch surgical procedures, the core temperature during lower body circulatory arrest (LBCA) has been steadily rising. Simultaneously, the use of a frozen elephant trunk (FET) graft has been increasing. The safe period of LBCA in relation to spinal cord ischaemic tolerance in combination with segmental artery occlusion by the FET procedure has not been defined. METHODS: Sixteen pigs were assigned to undergo 65 (n = 10) or 90 min (n = 6) of SCP at 28°C with LBCA in combination with occlusion of the 8 uppermost segmental arteries in the thoracic (Th) aorta (15-20 cm FET, Th8-level). The follow-up period consisted of a 6-h intensive period and a 5-day observation period. Near-infrared spectroscopy of the collateral network was used to determine spinal cord oxygenation. The neurological status of the patients was evaluated daily, and the brain and the spinal cord were harvested for a histopathological analysis. RESULTS: Five out of 6 pigs after 90 min and 1 out of 10 pigs after 65 min of LBCA died within 48 h of multiorgan failure. Of the survivors in the 65-min group, 6 out of 9 had paraparesis/paraplegia; the remaining 3 reached normal function. The lone survivor after 90 min of LBCA was paraplegic. Nadir near-infrared spectroscopy of the collateral network values at Th8 and Th10 were 34 (±5) and 39 (±4), and they were reached within 35 min of SCP in both groups. CONCLUSIONS: An extended FET graft with LBCA and SCP durations >65 min at 28°C results in a poor outcome.

Priming protects the spinal cord in an experimental aortic occlusion model.

OBJECTIVES: Paraplegia is a devastating complication in aortic aneurysm surgery. Modifying the spinal cord vasculature is a promising method in spinal cord protection. The aim of this study was to assess whether the spinal cord can be primed by occluding thoracic segmental arteries before simulated aneurysm repair in a porcine model. METHODS: Twelve piglets were randomly assigned to the priming group (6) and the control group (6). Eight uppermost thoracic segmental arteries were occluded at 5-minute intervals in the priming group before a 25-minute aortic crossclamp. In the control group, the aorta was crossclamped for 25 minutes. During the first 5 minutes, 8 segmental arteries were occluded. After the aortic crossclamping, piglets were observed under anesthesia for 5 hours and followed up 5 days postoperatively. Near-infrared spectroscopy, motor-evoked potentials, blood samples, neurology with the modified Tarlov score, and histopathology of the spinal cord were assessed. RESULTS: The median Tarlov score during the first postoperative day was higher in the priming group than in the control group (P = .001). At the end, 50% of the control animals had paraplegia compared with 0% of paraplegia in the priming group. The mean regional histopathologic score differed between the priming group and the control group (P = .02). The priming group had higher motor-evoked potentials during the operation at separate time points. The lactate levels were lower in the priming group compared with the control group (Pg = .001, Pg×t = .18). CONCLUSIONS: Acute priming protects the spinal cord from ischemic injury in an experimental aortic crossclamp model.

Minimized and conventional cardiopulmonary bypass damage intestinal mucosal integrity.

OBJECTIVES: Previous studies have suggested that gastrointestinal integrity is compromised after cardiopulmonary bypass (CPB). We compared the effects of prolonged minimized (MCPB) and conventional CPB (CCPB) on intestinal mucosal integrity by determining mucosal damage, epithelial cell proliferation rate and distribution of tight junction proteins in a porcine model. DESIGN: Fourteen animals were randomly assigned to undergo 240 minutes of mild hypothermic MCPB or CCPB. Ileal and colonic biopsies were obtained prior and at the end of CPB. Mucosal damage was determined under light microscopic evaluation. Immunohistochemistry was used to investigate epithelial expression of Ki-67 as a measure of cell proliferation rate and claudin-1, 2, 3, 4, 5, and 7 as elements of tight junctions. RESULTS: In colonic biopsies, independent of the circuit type used, moderate mucosal damage was observed as indicated by focal epithelial damage, increased epithelial cell proliferation and decreased expression of tight junction protein claudin-4. CONCLUSIONS: Colonic mucosal damage was observed similarly in MCPB and CCPB. Based on these results, the effects of MCPB on intestinal mucosal stability are similar to those of CCPB.

Moderate hypothermia with remote ischaemic preconditioning improves cerebral protection compared to deep hypothermia: a study using a surviving porcine model.

OBJECTIVES: The optimal temperature management of hypothermic circulatory arrest is still controversial. Moderate hypothermia preserves cerebral autoregulation and shortens cardiopulmonary bypass (CPB) duration. However, moderate hypothermia alone has inferior organ protection to deep hypothermia, so adjuncts that increase the ischaemic tolerance are needed. Thus, we hypothesized that a combination of remote ischaemic preconditioning (RIPC) and moderate hypothermia would be superior to deep hypothermia alone. METHODS: Sixteen pigs were randomized to either RIPC or control groups (8 + 8). The RIPC group underwent 4 cycles of transient hind limb ischaemia. The RIPC group underwent cooling with CPB to 24°C, and the control group underwent cooling with CPB to 18°C, followed by a 30-min arrest period and subsequent rewarming to 36°C. Measurements of cerebral metabolism were made from sagittal sinus blood samples and common carotid artery blood flow. The permissible periods of hypothermic circulatory arrest were calculated based on these measurements. Neurological recovery was evaluated daily during a 7-day follow-up, and the brain was harvested for histopathological analysis. RESULTS: Six pigs in the RIPC group reached normal neurological function, but none in the control group reached normal neurological function (P = 0.007). The composite neurological score of all postoperative days was higher in the RIPC group than in the control group [55 (52-58) vs 45 (39-51), P = 0.026]. At 24°C, the estimated permissible periods of hypothermic circulatory arrest were 21 (17-25) min in the RIPC group and 11 (9-13) min in the control group (P = 0.007). CONCLUSIONS: RIPC combined with moderate hypothermia provides superior cerebral protection.

Remote Ischemic Preconditioning in Spinal Cord Protection: A Surviving Porcine Study.

Surgical repair of thoracic aorta can compromise blood flow of the spinal cord. To mitigate spinal cord ischemia (SCI) additional protection methods are needed. In experimental studies remote ischemic preconditioning (RIPC) has proven to be an effective method of protecting organs from ischemia. The aim of the study was to assess efficacy of RIPC in spinal cord protection in a chronic porcine model. Sixteen piglets were assigned into the RIPC group (8) and the control group (8). RIPC was performed using blood pressure cuff in a 5-minute ischemia followed by a 5-minute reperfusion repeating cycles 4 times. The left subclavian artery and all segmental arteries above diaphragm were ligated at 5-minute intervals to accomplish SCI. The follow-up comprised a 4-hour intensive monitoring and a 7-day recovery phase. Blood samples were obtained, motor-evoked potentials and near-infrared spectroscopy (NIRS) of longitudinal back muscles were measured. Paraplegia was assessed every day postoperatively. Histopathological analysis of the spinal cord was performed after 7 days. NIRS values 4 hours after SCI were higher in the RIPC group, 45.5 (44.5-47.0), than in the control group, 41.5 (40.5-44.0) (P = 0.042). Nadir value of NIRS was 43.4 (39.3-46.0) in the RIPC group and 38.9 (38.-40.0) in the control group (P = 0.014). On the first postoperative day the RIPC group reached modified Tarlov score of 3 (2-3) vs 2 (1-2) in the control group (P = 0.024). RIPC hastens the recovery from SCI during the first postoperative day.

Acute homing of bone marrow-derived mononuclear cells in intramyocardial vs. intracoronary transplantation.

OBJECTIVES: Cell homing optimisation after transplantation is critical in myocardial infarction (MI) cell therapy. DESIGN: Eight pigs were randomized to receiving autologous purified (111)indium-labeled bone marrow mononuclear cells (BMMCs) (10(8) cells/2 ml) by intramyocardial (IM) (n=4) or by intracoronary (IC) (n=4) transplantation after 90 minutes occlusion of the CX-coronary artery. Dual isotope SPECT imaging was performed 2 and 24 hours postoperatively. Two animals were additionally analyzed on the sixth postoperative day. Tissue samples from the major organs were analyzed. RESULTS: In SPECT imaging revealed that BMMCs administered using IM injection remained in the injured area. In contrast, minor proportion of IC transplanted cells remained in the myocardium, as most of the cells showed homing in the lungs. Analysis of the biopsies showed a seven-fold greater number of cells in the myocardium for the IM method and a 10-fold greater number of cells in the lungs in the IC group (p < 0.001). CONCLUSIONS: In producing persistently high cell homing at the infarction site, the IM transplantation is superior to the IC transplantation. However, the IC administration might be more specific in targeting injured capillaries and epithelial cells within the infarcted myocardium.

Potential preanalytical errors in whole-blood analysis: effect of syringe sample volume on blood gas, electrolyte and lactate values.

BACKGROUND: Arterial blood samples are sensitive to bias because of the physiological properties of blood. Several errors can occur in the preanalytical phase leading to incorrect diagnosis and improper treatment of patients. Collection of a blood specimen, as well as its handling and transport, belong to the key factors to affect the accuracy and good quality of clinical laboratory analysis. METHODS: The aim of this study was to validate the effect of different sample volumes on the blood gas, electrolyte and lactate values using 3 mL Rapidlyte plastic syringes with filter cap and Rapidlab 865 blood gas analyser. Also, the stability of blood gas analyser parameters with different sample volume was studied. RESULTS: No substantial change in blood gas, electrolyte and lactate parameters was found when the results of 3 mL, 1.8 mL sample volumes in the 3 mL syringes were compared. The sample volume of 1.0 mL or 1.5 mL in the 3 mL syringe is not suitable for the measurement of oxygen tension, especially when accurate results of pO(2) and arterial blood is needed for patient's diagnosis. CONCLUSIONS: The minimum sample volume when blood gases, electrolytes and lactate are all measured with the Rapidlab system should be 1.8 mL using 3 mL Rapidlyte plastic syringe with filtercap. According to this study <1.8 mL sample volumes can provide inaccurate results and can impose biases on measurements.

Imagery-induced relaxation in children's postoperative pain relief: a randomized pilot study.

This study aimed to test the efficacy of imagery and relaxation in hospitalized children's postoperative pain relief. Sixty children aged 8-12 years who had undergone appendectomy or upper/lower limb surgery and had been randomly assigned to the experimental group (n(1) = 30) listened to an imagery trip CD, whereas those in the control group (n(2) = 30) received standard care. An investigator-developed questionnaire was used, and the intensity of pain was assessed using a visual analogue scale: before (Phase 1), immediately after (Phase 2), and 1 hour after (Phase 3) intervention or standard care. The children in the experimental group reported having significantly less pain (p < .001) than the control children based on a comparison of VAS pain scores in Phases 1 and 2. There were no significant differences in nurse-assessed pain scores. The type and time of operation were related to pain intensity in children. The nurses underestimated the pain of pediatric patients. The imagery trip CD can be used to reduce children's postoperative pain in a hospital setting, although its effect is short-lasting.

Exploring Spinal Cord Protection by Remote Ischemic Preconditioning: An Experimental Study.

BACKGROUND: Paraplegia is one of the most severe complications occurring after the repair of thoracic and thoracoabdominal aortic aneurysms. Remote ischemic preconditioning (RIPC) has been shown to mitigate neurologic damage, and this study assessed its efficacy in preventing spinal cord ischemia. METHODS: The study randomized 16 female pigs into an RIPC group (n = 8) and a control group (n = 8). The RIPC group underwent four cycles of 5-minute ischemia-reperfusion episodes by intermittent occlusion of the left iliac artery. All animals underwent systematic closure of the left subclavian artery and segmental arteries of the descending thoracic aorta to the level of diaphragm. Motor-evoked potential monitoring was performed in both hind limbs. Continuous electrocardiogram and hemodynamics were monitored, and pulmonary artery blood samples were collected. A neurologic assessment was performed 6 hours after the procedure. The thoracic and lumbar portions of the spinal cord were collected for histologic and immunohistochemical analysis. RESULTS: The bilateral motor-evoked potential amplitude responses were higher in the RIPC group (p < 0.05) than in the control group; the difference was detected already before spinal cord ischemia. Paraplegia occurred in 1 control animal. Immunohistochemical total scores of antioxidant response regulator nuclear factor erythroid 2-related factor 2 were better in the RIPC group (11.0; range, 8.5 to 14.0) than in the control group (5.2; range, 1.0 to 9.0; p = 0.023). CONCLUSIONS: RIPC induces electrophysiologic changes in the central nervous system that may confer spinal cord protection extending the resistance to ischemia. The significantly higher nuclear factor erythroid 2-related factor 2 scores suggest better neuronal cell protection against oxidative stress in the RIPC group.

Propofol is associated with impaired brain metabolism during hypothermic circulatory arrest: an experimental microdialysis study.

BACKGROUND: Propofol is a widely used anesthetic in cardiac surgery. It has been shown to increase cerebrovascular resistance resulting in decreased cerebral blood flow. Efficient brain perfusion and tissue oxygenation during cardiopulmonary bypass (CPB) is essential in surgery requiring hypothermic circulatory arrest (HCA). The effects of propofol on brain metabolism are reported in a surviving porcine model of HCA. METHODS: Twenty female juvenile pigs undergoing 75 minutes of HCA at a brain temperature of 18 degrees C were assigned to either propofol- or isoflurane anesthesia combined with alpha-stat perfusion strategy during CPB cooling and rewarming. Brain microdialysis analysis was used for determination of brain metabolism, and tissue oxygen partial pressure and intracranial pressures were also followed-up until 8 hours postoperatively. RESULTS: Brain concentrations of glutamate and glycerol were significantly higher in the propofol group throughout the experiment (P < .01 and P < .01, respectively). The lactate/pyruvate ratio was significantly higher in the propofol group at 6-, 7-, and 8-hour intervals (P < .05, P < .01, and P < .05, respectively). The intracranial pressure was significantly higher at the 8-hour postoperative interval (P < .05) in the propofol group. A trend toward higher brain oxygen concentrations was observed in the isoflurane group. CONCLUSIONS: Anesthesia with propofol as compared with isoflurane is associated with impaired brain metabolism during experimental HCA.

Aprotinin to improve cerebral outcome after hypothermic circulatory arrest: a study in a surviving porcine model.

BACKGROUND: Aprotinin is a serine protease inhibitor, which is usually used during cardiac surgery to reduce blood loss. There is evidence that aprotinin has neuroprotective effects during ischemia. We planned this study to evaluate its potential neuroprotective efficacy during hypothermic circulatory arrest (HCA). METHODS: Twenty piglets with a median weight of 25.7 kg (interquartile range, 23.9-26.6) were randomly assigned to receive aprotinin or placebo prior to a 75-minute period of HCA at 18 degrees C. Brain microdialysis parameters and neurological and histological scores were the primary outcome measures. RESULTS: Changes in brain metabolic parameters and histopathological findings were favorable in the aprotinin group. Brain lactate concentrations were significantly lower in the aprotinin group during the experiment (P = .02) along with blood lactate concentrations in the aprotinin group (P = .023). Brain glucose was significantly higher during the experiment (P = 0.02). Intracranial pressure tended to be higher in the control group. Two of 10 animals in the aprotinin group and 4 of 10 in the control group failed to reach full recovery on the seventh postoperative day. Four animals of 10 in the aprotinin group and 6 animals of 10 in the control group had brain infarction (P = .40). CONCLUSIONS: The present data suggest that aprotinin mitigates cerebral damage and improves neurological outcome following a period of HCA.

Fructose-1,6-bisphosphate supports cerebral energy metabolism in pigs after ischemic brain injury caused by experimental particle embolization.

BACKGROUND: Fructose-1,6-bisphosphate (FDP) is a high-energy intermediate that enhances glycolysis, preserves cellular adenosine triphosphate stores, and prevents the increase of intracellular calcium in ischemic tissue. Since it has been shown to provide metabolic support to the brain during ischemia, we planned this study to evaluate whether FDP is neuroprotective in the setting of combining hypothermic circulatory arrest (HCA) and irreversible embolic brain ischemic injury. METHODS: Twenty pigs were randomly assigned to receive 2 intravenous infusions of either FDP (500 mg/kg) or saline. The first infusion was given just before a 25-minute period of HCA and the second infusion immediately after HCA. Immediately before HCA, the descending aorta was clamped and 200 mg of albumin-coated polystyrene microspheres (250-750 mm in diameter) were injected into the isolated aortic arch in both study groups. RESULTS: There were no significant differences between the study groups in terms of neurological outcome. Brain lactate/pyruvate ratio was significantly lower (P = .015) and brain pyruvate levels (P = .013) were significantly higher in the FDP group compared with controls. Brain lactate levels were significantly higher 8 hours after HCA (P = .049). CONCLUSION: The administration of FDP before and immediately after HCA combined with embolic brain ischemic injury was associated with significantly lower brain lactate/pyruvate ratio and significantly higher levels of brain pyruvate, as well as lower lactate levels 8 hours after HCA. FDP seems to protect the brain by supporting energy metabolism. The neurological outcome was not improved, most likely resulting from the irreversible nature of the microsphere occlusion.

Remote ischemic preconditioning protects the spinal cord against ischemic insult: An experimental study in a porcine model.

OBJECTIVE: Surgical repair of thoracoabdominal aneurysm jeopardizes the vascularization of the spinal cord, and therefore, despite improvement in surgical techniques, still carries the risk of paraplegia. This study aimed to demonstrate the possible protective effects of remote ischemic preconditioning (RIPC) on the preservation of spinal cord function after segmental artery (SA) occlusion. METHODS: Twenty piglets were randomized into the RIPC group (n = 10) and the control group (n = 10). The RIPC group underwent transient left hind limb ischemia before systematic left subclavian artery and SA occlusion at the level of the diaphragm. Motor-evoked potential (MEP) monitoring was performed from the hind limbs. Afterward, the thoracic and lumbar spinal cords were harvested and analyzed. RESULTS: The elevation of the MEP amplitude after RIPC was statistically significant, whereas amplitude was consistently decreased in the control group. Additionally, the onset latency was significantly shorter after RIPC during SA occlusion. The control group reached a 50% decrease of MEP amplitude in the right hind limb sooner than did the experimental group. CONCLUSIONS: Remote ischemic preconditioning preserves spinal cord function after left subclavian artery and SA occlusion, as indicated by the MEP amplitudes.

Prolonged mild hypothermia after experimental hypothermic circulatory arrest in a chronic porcine model.

OBJECTIVES: We sought to evaluate the potential efficacy of prolonged mild hypothermia after hypothermic circulatory arrest. METHODS: Twenty pigs, after a 75-minute period of hypothermic circulatory arrest, were randomly assigned to be rewarmed to 37 degrees C (normothermia group) or to 32 degrees C and kept at that temperature for 14 hours from the start of rewarming (hypothermia group). RESULTS: The 7-day survival was 30% in the hypothermia group and 70% in the normothermia group (P =.08). The hypothermia group had poorer postoperative behavioral scores than the normothermia group. Prolonged hypothermia was associated with lower oxygen extraction and consumption rates and higher mixed venous oxygen saturation levels during the first hours after hypothermic circulatory arrest. Decreased cardiac index, lower pH, and higher partial pressure of carbon dioxide were observed in the hypothermia group. There was a trend for beneficial effect of prolonged hypothermia in terms of lower brain lactate levels until the 4-hour interval and of intracranial pressure until the 10-hour interval. Postoperatively, total leukocyte and neutrophil counts were lower, and creatine kinase BB was significantly increased in the hypothermia group. At extubation, the hypothermia group had higher oxygen extraction rates and lower brain tissue oxygen tension. CONCLUSIONS: A 14-hour period of mild hypothermia after 75-minute hypothermic circulatory arrest seems to be associated with poor outcome. However, the results of this study suggest that mild hypothermia may preserve its efficacy when it is used for no longer than 4 hours, but the potentials of a shorter period of postoperative mild hypothermia still require further investigation.