Small Volume Resuscitation in a Rat Model of Heatstroke

CLINICAL INVESTIGATION

Small Volume Resuscitation in a Rat Model of Heatstroke Chia-Chyuan Liu, PhD, Bor-Chih Cheng, MD, Mao-Tsun Lin, PhD and Hung-Jung Lin, MD

Abstract: Background: Herein, we compared the effectiveness of different small volume resuscitation in a rat model of heatstroke. Methods: Anesthetized rats, immediately after the onset of heatstroke, were randomizedly divided into 5 groups and given the following: (a) nothing; (b) 0.9% NaCl (1–10 mL/kg of body weight, i.v.); (c) hydroxyethyl starch (HAES) (6%, 1–10 mL/kg of body weight, i.v.); (d) 7.2% NaCl (1–10 mL/kg of body weight, i.v.); and (e) hyper-HAES (6% HAES plus 7.2% NaCl, 1–10 mL/kg of body weight, i.v.). Results: When the untreated or 0.9% NaCl (1–5 mL/kg of body weight)-treated rats underwent heat stress, their survival time values were found to be 20 to 22 minutes. Resuscitation with 10 mL/kg of body weight of 0.9% NaCl, 6% HAES, 7.2% NaCl, or hyper-HAES, their survival time values, respectively, are 93 ⫾ 6, 101 ⫾ 12, 154 ⫾ 18, or 286 ⫾ 21. Apparently, the order of effectiveness in resuscitation of heatstroke is hyper-HAES ⬎ 7.2% NaCl ⬎ 0.9% NaCl or 6% HAES. The heatstroke-induced hypotension, cerebral ischemia and hypoxia, hypercoagulable state, activated inflammation, and hepatic and renal dysfunction can be significantly reduced by hyper-HAES. Conclusions: Our results suggest that hyper-HAES seems superior to 7.2% NaCl or HAES alone in resuscitation of heatstroke. The benefit of hyper-HAES during heatstroke is related to restoration of normal multiorgan function. Key Indexing Terms: Hyper-HAES; Heatstroke; Multiorgan dysfunction; Coagulation; Inflammation; Hypotension; Cerebral ischemia. [Am J Med Sci 2009;337(2):79–87.]

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eatstroke is characterized by hyperpyrexia and multiple organs (in particular, the central nervous system) dysfunction or failure.1,2 Cerebral dysfunctions that occurred during heatstroke, include delirium, convulsion, and coma. These neurological syndromes have been attributed to brain edema, ischemia, and/or injury during heatstroke.2,3 Other organ dysfunctions such as renal and hepatic dysfunction or failure, hypercoagulable state, and systemic inflammation ensue from severe heatstroke.2,4 Small volume resuscitation (SVR) means the rapid administration of a small volume of a hypertonic solution to immediately restore the macro and microcirculation. For example, when patients with refractory hypovolaemic shock were given a small

From the Department of Cosmetic Science (C-CL), Chia-Nan University of Pharmacy and Science, Tainan, Taiwan; Department of Biotechnology (B-CC, M-TL, H-JL), Southern Taiwan University of Technology, Tainan, Taiwan; Departments of Cardiac Surgery (B-CC), Medical Research (M-TL), and Emergency Medicine (H-JL), Chi Mei Medical Center, Tainan, Taiwan; and Department of Emergency Medicine (H-JL), Taipei Medical University, Taipei, Taiwan. Submitted February 19, 2008; accepted in revised form April 23, 2008. This study was supported in part by the grants from the National Science Council of Republic of China (Taipei, Taiwan): NSC95-2314-B384-003, NSC95-2314-B-384-011, and NSC95-2314-B-384-018. Correspondence: Hung-Jung Lin, MD, Department of Emergency Medicine, Chi Mei Medical Center, Tainan, Taiwan 710 (E-mail: [email protected]) or Mao-Tsun Lin, PhD, Department of Medical Research, Chi Mei Medical Center, Tainan, Taiwan 710 (E-mail: [email protected]).

volume of 7.5% NaCl, hemodynamics and renal function were improved.5 In animal studies, infusion of 4 mL/kg of a 7.5% NaCl-solution normalized both; the mean arterial pressure (MAP) and the acid-base balance in hypovolaemic dogs.6 The rapid (2–5 minutes) infusion of a small volume (4 mL/kg b.w.) of a hypertonic solution causes an instant increase of the plasma osmolarity leading to an osmotic gradient between the extra and intravascular space. The mobilization of endogenous fluid leads to an immediate increase of the intravascular volume within seconds of bolus administration of the hypertonic solution.7 In addition, the combination of hypertonic saline and a colloidal component is superior to hypertonic saline alone.8 The additional administration of a colloid prolongs the circulatory stabilization and increases the survival rate.8 –10 Indeed, as shown in the present study, hyper hydroxyethyl starch (HAES) (the combination of 7.2% NaCl and 6% HAES) is superior to 7.2% NACl or 6% HAES alone in amelioration of multiorgan dysfunction that occurred during heatstroke in a rat model.

SUBJECTS AND METHODS Animals Experiments were performed in male adult SparagueDawley rats (weighing 265–288 g) obtained from the Animal Resource Center of the National Science Council (Taipei, Taiwan, Republic of China). The animals were housed 4 to a cage at an ambient temperature of 22 ⫾ 1°C, with a 12-hour light/dark cycle. Pelleted rat chow and tap water were available ad libitum. The experimental protocols were approved by the Animal Committee of the Chi Mei Medical Center. Animal care and experiments were conducted according to the National Science Council guidelines. They were allowed to become acclimated for 1 week. Adequate anesthesia was maintained to abolish the corneal reflex and pain reflexes induced by tail pinching throughout all experiments by an i.p. dose of urethane (1.4 g/kg of body weight). At the end of the experiments, control rats and any rats that had survived heatstroke were killed with an overdose of urethane. Rats under anesthesia were randomized into 7 major groups: (a) normothermic controls (NC, n ⫽ 8); (b) untreated heatstroke rats 关(HS), n ⫽ 8兴; (c) HS rats treated with 0.9% NaCl solution (1–20 mL/kg, i.v.); (d) HS rats treated with 7.2% NaCl solution (1–10 mL/kg, i.v.); (e) (HAES; 1–10 mL/kg, i.v., 6%; Fresenius Kabi Deutschland GmbH, Bad Homburg, Germany); and (f) HyperHAES (1–10 mL/kg, i.v.; Fresenius Kabi Deutschland GmbH, Bad Homburg, Germany). Before induction of HS, the core temperature (Tco) of urethane-anesthetized rats was maintained at about 36°C with a folded heating pad except during heat stress at a room temperature of 24°C. HS was induced by increasing the temperature of the folded heating pad to 43°C with circulating hot water. The instant at which MAP dropped to a value of 25 mm Hg from the peak level was about 70 minutes after the initiation of heat stress, this time

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point was arbitrarily taken as the onset of HS.11 Then, the heating pad was removed and the animals were allowed to recover at room temperature (24°C). Surgery and Physiologic Parameter Monitoring The right femoral artery and vein of rats were cannulated with polyethylene tubing under urethane anesthesia for blood pressure monitoring and drug administration, respectively. The animals were positioned in a stereotaxic apparatus (Kopf 1406; Grass Instrument, Quincy, MA) to insert probes for measurement of brain temperature, PO2 and cerebral blood flow (CBF).12 A 100-␮m-diameter thermocouple and two 230-␮m fibers were attached to the organ probe. This combined probe measures oxygen, temperature, and microvascular blood flow. The measurement requires OxyLite and OxyFlo instruments; OxyLite 2000 (Oxford Optronix, Oxford, UK) is a two-channel device (measuring PO2 and temperature at 2 sites simultaneously), whereas OxyFlo 2000 is a two-channel laser Doppler perfusion monitoring instrument. The OxyLite has been designed to operate in conjunction with the OxyFlo. The combination of these 2 instruments provides simultaneous tissue blood flow, oxygenation, and temperature data. Under anesthesia, the animal was placed in a stereotaxic apparatus, and the combined probe was implanted into the hypothalamus using the atlas and coordinates of Paxinos and Watson.13 Tco was monitored continuously by a thermocouple, whereas MAP and heart rate were continuously monitored with a pressure transducer. Biochemical Determination For biochemical determination, each animal was killed at each time point, and whole blood (7 mL) was obtained from the heart puncture and collected into sodium citrate tubes for plasma. The 3 different time points were the following: (1) 0 minutes before the initiation of heat stress, (2) 70 minutes after the start of heat exposure (or immediately after the onset of HS), and (3) 85 minutes after initiation of heat exposure (or 15 minutes after the onset of HS). The plasma levels of activated partial thromboplastin time, prothrombin time, and D-dimer were measured by automated coagulation instruments (SYSMEX CA-1500, Kobe, Japan). The platelet counts were measured by automated blood cell counting instruments (Beckman Coulter LH750, Miami, FL), whereas the plasma levels of aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase were determined by spectrophotometry (HITACHI 7600, Tokyo, Japan). For determination of protein C, to obtain the plasma, 1 part of sodium citrate solution (0.1 mol/L) was mixed carefully with 9 parts of venous blood, avoiding the formation of foam. Protein C, in the sample, was activated by specific venom activator. The resulting protein C activator was assayed in a kinetic test by measuring the increase in absorbance at 405 nm. The reagents for the determination of protein C activity were provided by Berichrom Protein C (Dade Behring Marburg GmbH, Marburg, Germany). Arterial blood hematocrit was measured via a blood gas analyzer (Nova Biochemical, Waltham, MA). Measurements of Cellular Ischemia and Damage Markers For determination of extracellular glutamate, glycerol, and lactate-to-pyruvate ratio, the microdialysis probe was stereotaxically implanted into the hypothalamus, according to the atlas and coordinates of Paxinos and Watson.13 After a midline incision, the skull was exposed and a burr hole was made in the skull for the insertion of a dialysis probe (4 mm in length, CMA/12, Carnegie Medicine, Stockholm, Sweden). The pro-

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cedures for measurements of cellular ischemic and damage markers were described previously.11 Determination of Serum Tumor Necrosis Factor-alpha Blood samples were allowed to clot for 2 hours at room temperature or overnight at 2 to 8°C before centrifuging for 20 minutes at approximately 2000g. Serum was quickly removed from these plasma samples and assayed for tumor necrosis factor-alpha (TNF-␣) immediately. The DuoSet Enzyme-linked immunosorbent assay (ELISA) Development System rat TNF-␣ kit (R&D Systems, Minneapolis, MN) was used for measuring the levels of active rat TNF-␣ present in serum. This assay employs the quantitative colorimetric sandwich ELISA technique. Histologic Verification At the end of each experiment, the brain would be removed, fixed in 10% neutral buffered formalin and embedded in paraffin blocks. Serial (10 ␮m) sections of the brain through the striatum were stained with hematoxylin and eosin for microscopic evaluation. The extent of striatal neuronal damage was scored on a scale of 0 to 3, modified from the grading system of Pulsinelli et al,14 in which 0 is normal, 1 means that ⬃30% of the neurons are damaged, 2 means that ⬃60% of neurons are damaged, and 3 means that 100% of that neurons are damaged. Each hemisphere was evaluated independently without the examiner knowing the experimental conditions. When examined for neuronal damage in gray matter, only areas other than those invaded by probes were assessed. Statistical Analysis Data are presented as the mean ⫾ standard deviation. For the data presented in Table 1 and Figures 1– 4, KruskalWallis H test was used for factorial experiments, whereas Dunn’s test was used for post hoc multiple comparisons among means. The Wilcoxon tests were used for evaluation of neuronal damage scores. The Wilcoxon test converts the scores or values of a variable to ranks, requires calculation of a sum of the ranks, and provides critical values for the sum necessary to test the null hypothesis at a given significant levels. These data were presented as “median”, followed by first (Q1) and third (Q3) quartile. A P value less than 0.05 was calculated as statistical significance.

RESULTS Small Volume Resuscitation Improves Survival During Heatstroke Table 1 summarizes the effects of heat exposure (43°C for 70 minutes) on survival time in different groups of rats. It can be seen from the table that the survival time was found to be 17 to 23 minutes for untreated HS rats. Treatment with 10 mL per kg of body weight of 0.9% NaCl, the survival time values were increased to new values of 36 ⫾ 5 minute. In addition, immediately after the onset of heatstroke, intravenous injection of 10 mL per kg of body weight of 7.2% NaCl solution, 6% HAES, or Hyper-HAES, respectively increased the survival time to a new value of 154 ⫾ 18, 101 ⫾ 12, or 286 ⫾ 21 minutes. Hyper-HAES Attenuates Cerebrovascular Dysfunction During Heatstroke Figures 1–2 summarize the Tco, MAP, intracranial pressure (ICP), cerebral perfusion pressure (CPP), brain PO2, brain temperature, CBF, and hypothalamic levels of glutamate, glycVolume 337, Number 2, February 2009

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TABLE 1. The survival time values for normothermic rats, untreated heatstroke rats, 0.9% NaCl solution-treated heatstroke rats, 7.2% NaCl solution-treated heatstroke rats, 6% HAES-treated heatstroke rats, or hyper-HAES-treated heatstroke Treatment group

Survival time (min)

1. Normothermic controls ⬎480 (8) 2. Untreated heatstroke rats 20 ⫾ 3 (8)a 3. 0.9% NaCl solution (1 mL/kg, i.v.)-treated 21 ⫾ 2 (8)a heatstroke rats 4. 0.9% NaCl solution (5 mL/kg, i.v.)-treated 22 ⫾ 3 (8)a heatstroke rats 5. 0.9% NaCl solution (10 mL/kg, i.v.)-treated 36 ⫾ 5 (8)a heatstroke rats 6. 0.9% NaCl solution (20 mL/kg, i.v.)-treated 93 ⫾ 6 (8)a heatstroke rats 7. 7.2% NaCl solution (1 mL/kg, i.v.)-treated 80 ⫾ 3 (8)a heatstroke rats 8. 7.2% NaCl solution (5 mL/kg, i.v.)-treated 85 ⫾ 7 (8)a,b heatstroke rats 9. 7.2% NaCl solution (10 mL/kg, i.v.)-treated 154 ⫾ 18 (8)a,b heatstroke rats 10. 6% HAES (1 mL/kg, i.v.)-treated 21 ⫾ 2 (8)a heatstroke rats 11. 6% HAES (5 mL/kg, i.v.)-treated 33 ⫾ 4 (8)a,b heatstroke rats 12. 6% HAES (10 mL/kg, i.v.)-treated 101 ⫾ 12 (8)a,b heatstroke rats 13. Hyper-HAES (1 mL/kg, i.v.)-treated 49 ⫾ 4 (8)a,b,c heatstroke rats 14. Hyper-HAES (5 mL/kg, i.v.)-treated 127 ⫾ 15 (8)a,b,c heatstroke rats 15. Hyper-HAES (10 mL/kg, i.v.)-treated 286 ⫾ 21 (8)a,b,c heatstroke rats All heatstroke rats had heat exposure (43°C) withdrawn exactly at 70 min and were then allowed to recover at room temperature (24°C). Data are mean ⫾ SEM, followed by number of animals (n) in parentheses. Group 1 rats were killed approximately 480 min after the initiation of heat exposure (or at the end of the experiments) with an overdose of urethane. a P ⬍ 0.05 in comparison with group 1. b P ⬍ 0.05 in comparison with group 3, group 4, or group 5. c P ⬍ 0.05 in comparison with groups 7–11 (ANOVA followed by Duncan test). ANOVA indicates analysis of variance; SEM, standard error of mean.

erol, and lactate-to-pyruvate ratio for NC, untreated HS rats, and Hyper-HAES-treated HS rats. It can be seen from these figures that core and brain temperatures, ICP, and hypothalamic levels of glutamate, glycerol, and lactate-to-pyruvate ratio for the untreated HS rats were all significantly higher at 70 to 85 minutes after the initiation of heat exposure than they were for the NC (P ⬍ 0.05). In contrast, MAP, CPP, CBF and brain PO2 values were all significantly lower than those of the NC (P ⬍ 0.05). Resuscitation with Hyper-HAES at the time point of heatstroke onset or 70 minutes after start of heat stress significantly attenuated hypotension, cerebral hypoperfusion, brain hypoxia and ischemia and increased hypothalamic levels of glutamate, glycerol, and lactate-to-pyruvate ratio that occurred during heatstroke. In separate experiments, 15 minutes after the onset of heatstroke, animals were killed for determination of neuronal © 2009 Lippincott Williams & Wilkins

damage score in hypothalamus. After the onset of heatstroke, animals treated with normal saline or untreated displayed higher values of hypothalamic neuronal damage score 关2 (2,2)兴 compared with those of NC 关0 (0,0)兴. However, with HyperHAES treatment, neuroprotection ensued 关0 (0.25, 0.75)兴. Under microscopic examination, striatal neurons seemed shrunken with structureless and/or eosinophilic cytoplasma and shrunken nucleus (Figure 3) in a saline-treated HS rat. Heatstroke-induced neuronal damage was greatly reduced by hyper-HAES therapy (Figure 3). Hyper-HAES Attenuates Hypercoagulable State During Heatstroke Figure 4 depicts the plasma levels of activated partial thromboplastin time, prothrombin time, platelet count, protein C, and D-dimer for NC (n ⫽ 8), untreated HS rats (n ⫽ 8), and Hyper-HAES-treated HS rats (n ⫽ 8). It can be seen from the figure that activated partial thromboplastin time, prothrombin time, D-dimer and TNF-␣ values for the untreated HS rats were all significantly higher at 85 minutes after the initiation of heat stress than they were for the NC (P ⬍ 0.05). In contrast, the values for plasma levels of protein C were significantly lower than those of the NC (P ⬍ 0.05). Resuscitation with HyperHAES, at the time point of onset of heatstroke, significantly attenuated the increased plasma levels of activated partial thromboplastin time, prothrombin time, D-dimer and TNF-␣ as well as the decreased plasma levels of protein C during heatstroke (P ⬍ 0.05). Hyper-HAES Attenuates Hepatic and Renal Dysfunction During Heatstroke Figure 5 depicts the plasma levels of creatinine, serum urea nitrogen, aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase for NC (n ⫽ 8), untreated HS rats (n ⫽ 8), and hyperbaric oxygen-treated HS rats (n ⫽ 8). It can be seen from the figure that the plasma levels of these parameters in untreated HS rats were all significantly higher at 85 minute after the start of heat exposure than they were for NC (P ⬍ 0.05). Resuscitation with Hyper-HAES at the time point of onset of heatstroke significantly attenuated the heatstrokeinduced increased plasma levels of all these parameters (P ⬍ 0.05).

DISCUSSION The present results show that the order of the effectiveness of various SVR in a heatstroke model is hyper-HAES ⬎ 7.2% NaCl or 6% HAES ⬎ 0.9% NaCl. In fact, the effect of 7.2% NaCl component of Hyper-HAES is of short duration. After 30 minutes, NaCl is distributed over the whole extracellular space. However, 6% HAES component of HyperHAES prolongs the volume effect. Therefore, the discrepancy between the Hyper-HAES and NaCl or 6% HAES component can be explained by the volume effect. Apparently, the hyper-HAES possessed larger volume effect than those of its components. In human heatstroke patients, increased plasma levels of alanine aminotransferase, aspartate amino transaminase, alkaline phosphatase, blood urea nitrogen, and creatinine would occur as clinical biomarkers of hepatic and renal tissue damage.15,16 The lactate/pyruvate ratio is a well-known marker of cell ischemia, that is, an inadequate supply of oxygen and glucose.17,18 Glycerol is a marker of how severely cells are affected by the ongoing pathology.19,20 Excessive concentrations of glutamate have been shown in primary21 or secondary22 ischemic brain tissue. As shown in the present results, at

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FIGURE 1. Effects of heat stress (Ta 43°C for 70 minute) on core temperature (Tco), mean arterial pressure (MAP), brain PO2, brain temperature (Tb), cerebral blood flow (CBF), intracranial pressure (ICP), and cerebral perfusion pressure (CPP). Open circles indicated values at Ta of 43°C in 8 rats treated with normal saline (10 mL/kg, i.v.) immediately after the initiation of heatstroke. Another 8 rats were used as normothermic controls (NC) (open triangle). Solid circles indicated values at Ta of 43°C in 8 rats treated with Hyper-HAES (10 mL/kg, i.v.) immediately after the initiation of heatstroke. Points represent means ⫾ SEM. *P ⬍ 0.05 compared with those of NC. †P ⬍ 0.05 compared with saline-treated group (at 43°C) 关Analysis of variance (ANOVA) followed by Duncan test兴.

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FIGURE 3. Histopathologic examination of neuronal damage. Top panel, striatum in a normothermic rat (NC). Middle panel, striatum in a HS rat treated with normal saline (HS ⫹ S); striatum in a HS rat treated with normal saline (HS ⫹ S); neurons seemed shrunken. Bottom panel, striatum in HS rat treated with hyper-HAES (HS ⫹ hyper-HAES) (hematoxylin and eosin; original magnification ⫻400). FIGURE 2. Effects of heat stress (Ta 43°C for 70 minute) on extracellular levels of glutamate, glycerol, and lactate–pyruvate ratio in the hypothalamus. Open circles indicated values at Ta of 43°C in 8 rats treated with normal saline (10 mL/kg, i.v.) immediately after the initiation of heatstroke. Solid circles indicated values at Ta of 43°C in 8 rats treated with hyper-HAES (10 mL/kg, i.v.) immediately after the initiation of heatstroke. Another 8 rats were used as normothermic controls (NC) (open triangle). Points represent means ⫾ SEM. *P ⬍ 0.05 compared with those of NC. †P ⬍ 0.05 compared with those of salinetreated heatstroke rats 关Analysis of variance (ANOVA) followed by Duncan test兴.

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the onset of heatstroke, animals display hypotension, intracranial hypertension, brain hypoperfusion and hypoxia, cerebral ischemia (evidenced by increased glutamate and lactate-topyruvate ratio) and injury (evidenced by glycerol), renal and hepatic dysfunction (evidenced by increased levels of plasma alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, blood urea nitrogen, and creatinine), hypercoagulable state (evidenced by increased levels of plasma prothrombin time, partial thromboplastin time, and D-dimer, and de-

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FIGURE 4. Effects of heat exposure (43°C) on plasma levels of prothrombin time, activated partial thromboplastin time, protein C and tumor necrosis factor-alpha (TNF-␣) in normothermic control rats (NC), 0.9% NaCl solution-treated HS rats (HS ⫹ S) hyperHAES-treated HS rats (HS ⫹ hyper-HAES). *P ⬍ 0.05, compared with normothermic control rats 关Analysis of variance (ANOVA) followed by Duncan’s test兴. †P ⬍ 0.05, compared with saline-treated rats (ANOVA followed by Duncan’s test). The samples were obtained 85 minutes after the initiation of heat exposure in heat stroke rats or the equivalent time in NC.

creased levels of plasma protein C) and activated inflammation (evidenced by increased level of TNF-alpha in plasma). The current findings further demonstrate that hyper-HAES improves survival during heatstroke by attenuating the abovementioned heatstroke reactions.

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The present results are consistent with many previously published investigation. For example, intracranial hypertension after traumatic brain injury can be reduced by hyper-HAES therapy.23–25 Hyper-HAES treatment significantly reduces noreflow areas in a model of global ischemia during cardiopulmoVolume 337, Number 2, February 2009

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FIGURE 5. Effects of heat exposure (43°C) on plasma levels of blood urea nitrogen, creatinine, aspartate and alanine aminotransferase and alkaline phosphatase in normothermic control rats (NC), 0.9% NaCl solution-treated HS rats (HS ⫹ S) or hyper-HAEStreated HS rats (HS ⫹ HyperHAES). *P ⬍ 0.05, compared with normothermic control rats 关Analysis of variance (ANOVA) followed by Duncan’s test兴. †P ⬍ 0.05, compared with saline-treated rats (ANOVA followed by Duncan’s test). The samples were obtained 85 minutes after the initiation of heat exposure in HS rats or the equivalent time in NC.

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nary resuscitation.26 Infarct size as a consequence of an improved regional blood flow and reduced no-flow/low-flow areas in the tissue at risk in the two-vein occlusion model can also be attenuated by Hyper-HAES therapy.27 In prolonged uncontrolled hemorrhagic shock, a titrated intravenous infusion of hyper-HAES can maintain controlled hypotension with one tenth of the volume of titrated lactated Ringer’s solution required, without increasing blood loss.28 In addition, SVR lowers intracranial hypertension and improves CPP in various animal experiments of hemorrhagic shock and head trauma.29 –31 In fact, the rapid infusion of a hypertonic/hyperoncotic solution at 2 to 6 mL/kg of body weight induces an osmotic gradient, with water being drawn into the intravascular compartment and a rapid mobilization of parenchyma fluid,6,32,33 hemodilution, endothelial shrinkage, and improves microvascular flow.7,33 SVR after shock contributes to the microcirculatory and metabolic improvement by increasing cardiac output and decreasing the perivascular resistance.5,23,24,34,35 The microcirculatory and metabolic improvement has been reported in kidney, heart, liver, and small intestine after hyper-HAES therapy.6,34,36 Indeed, as shown in the present results, rapid infusion of a small volume of hyper-HAES fluid (4 mL/kg of body weight) significantly causes amelioration of arterial hypotension, intracranial hypertension, cerebral hypoperfusion, ischemia and hypoxia, activated inflammation, hypercoagulable state, and renal and hepatic dysfunction or failure that occurred during heatstroke. It is believed that hyper-HAES increases instantly the intravascular volume by mobilization of endogenous fluid and stabilizes the volume effect by the additional colloid component.37,38 As the microcirculation is rapidly restored, the potentially life-threatening cascade (eg, activated inflammation response, multiorgan dysfunction or failure, and hypercoagulable state) that occurred during heatstroke can be prevented by hyper-HAES therapy. The current choice for treatment of human heatstroke is whole body cooling.1 However, heatstroke is often fatal after adequate body cooling.39,40 Tissue damage continues to develop after cooling to normal body temperature in 25% of heatstroke-patients.41 It has also been reported that normal volunteers can passively endure a Tco of about 42°C with no or minimal tissue injury.42,43 The present results further demonstrated that, although hyper-HAES therapy did not affect hyperthermia, the heatstroke-induced hypotension, intracranial hypertension, cerebral ischemia and injury, hepatic and renal dysfunction, hypercoagulable state, and activated inflammation were all significantly reduced by hyper-HAES therapy. Our findings promote that in addition to body cooling, hyper-HAES can be considered for treatment of heatstroke victims in clinical trials. As mentioned before, Hyper-HAES is a combination of 6% HAES (200/0.5) and 7.2% NaCl. It is a hypertonic (2464 mOsmol/L) and isooncotic solution. The HAES component of Hyper-HAES is made from waxy maize starch that contains more than 95% amylopectin. Amylopectin consists of a branched chain of glucose molecules. HAES component has a plasma half-life of approximately 4 hours.44 The HAES molecules are degraded by ␣-amylase, leading to the formation of oligosaccharides and polysaccharides of various molecular weights. Small amounts of HAES are transiently stored in the tissues of the liver, spleen, and other organs. Both sodium and chloride are excreted renally. Hyper-HAES is indicated for initial, single dose treatment of acute hypovolemia and shock. The solution is intended for blood volume replacement and is

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not to be used as a substitute for either blood or plasma. Indeed, as demonstrated in the present results, one single i.v. injection of Hyper-HAES is able to restore normal multiorgan function in a rat model of heatstroke. REFERENCES 1. Bouchama A, Knochel JP. Heat stroke. N Engl J Med 2002;346: 1978 – 88. 2. Chang CK, Chang CP, Chiu WT, et al. Prevention and repair of circulatory shock and cerebral ischemia/injury by various agents in experimental heatstroke. Curr Med Chem 2006;13:3145–54. 3. Sharma HS. Heat-related deaths are largely due to brain damage. Indian J Med Res 2005;121:621–3. 4. Glazer JL. Management of heatstroke and heat exhaustion. Am Fam Physician 2005;71:2133– 40. 5. de Felippe J Jr, Timoner J, Velasco IT, et al. Treatment of refractory hypovolaemic shock by 7.5% sodium chloride injections. Lancet 1980; 2:1002– 4. 6. Velasco IT, Pontieri V, Rocha E, et al. Hyperosmotic NaCl and severe hemorrhagic shock. Am J Physiol 1980;239:664 –73. 7. Mazzoni MC, Borgstrom P, Arfors KE, et al. Dynamic fluid redistribution in hyperosmotic resuscitation of hypovolemic hemorrhage. Am J Physiol 1988;255:H629 –H637. 8. Prough DS, Whitley JM, Taylor CL, et al. Small-volume resuscitation from hemorrhagic shock in dogs: effects on systemic hemodynamics and systemic blood flow. Crit Care Med 1991;19:364 –72. 9. Boldt J, Zickmann B, Ballesteros M, et al. Cardiorespiratory responses to hypertonic saline solution in cardiac operations. Ann Thorac Surg 1991;51:610 –5. 10. Smith GJ, Kramer GC, Perron P, et al. A comparison of several hypertonic solutions for resuscitation of bled sheep. J Surg Res 1985; 39:517–28. 11. Chen SH, Chang FM, Chang HK, et al. Human umbilical cord blood-derived CD34⫹ cells cause attenuation of multiorgan dysfunction during experimental heatstroke. Shock 2007;27:663–71. 12. Liu CC, Ke D, Chen ZC, et al. Hydroxyethyl starch produces attenuation of circulatory shock and cerebral ischemia during heatstroke. Shock 2004;22:288 –94. 13. Paxinos G, Watson C. The rat brain in stereotaxic coordinates. New York: Academic press; 1982. 14. Pulsinelli WA, Brierley JB, Plum F. Temporal profile of neuronal damage in a model of transient forebrain ischemia. Ann Neurol 1982; 11:491– 8. 15. Alzeer AH, el Hazmi MA, Warsy AS, et al. Serum enzymes in heat stroke: prognostic implication. Clin Chem 1997;43:1182–7. 16. Bouchama A, De Vol EB. Acid-base alterations in heatstroke. Intensive Care Med 2001;27:680 –5. 17. Hillered L, Persson L. Neurochemical monitoring of the acutely injured human brain. Scand J Clin Lab Invest Suppl 1999;229:9 –18. 18. Hillered L, Persson L, Ponten U, et al. Neurometabolic monitoring of the ischaemic human brain using microdialysis. Acta Neurochir (Wien.). 1990;102:91–7. 19. Ungerstedt U. Microdialysis—a new technique for monitoring local tissue events in the clinic. Acta Anaesthesiol Scand Suppl 1997;110: 123. 20. Hillered L, Valtysson J, Enblad P, et al. Interstitial glycerol as a marker for membrane phospholipid degradation in the acutely injured human brain. J Neurol Neurosurg Psychiatry 1998;64:468 –91. 21. Bullock R, Zauner A, Woodward J, et al. Massive persistent release of excitatory amino acids following human occlusive stroke. Stroke 1995;26:2187–9. 22. Persson L, Hillered L. Chemical monitoring of neurosurgical intensive

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Small Volume Resuscitation in Heat Stroke

care patients using intracerebral microdialysis. J Neurosurg 1992;76: 72– 80. 23. Kreimeier U, Messmer K. Small-volume resuscitation. Baillieres Clin Anaesthesiol 1988;2:545–77. 24. Qureshi AI, Suarez JI. Use of hypertonic saline solutions in treatment of cerebral edema and intracranial hypertension. Crit Care Med 2000; 28:3301–13. 25. Doyle JA, Davis DP, Hoyt DB. The use of hypertonic saline in the treatment of traumatic brain injury. J Trauma 2001;50:367– 83. 26. Fischer M, Hossmann KA. Volume expansion during cardiopulmonary resuscitation reduces cerebral no-reflow. Resuscitation 1996;32: 227– 40. 27. Heimann A, Takeshima T, Alessandri B, et al. Effects of hypertonic/ hyperoncotic treatment after rat cortical vein occlusion. Crit Care Med 2003;31:2495–501.

34. Maningas PA. Resuscitation with 7.5% NaCl in 6% dextran-70 during hemorrhagic shock in swine: effects on organ blood flow. Crit Care Med 1987;15:1121– 6. 35. Bitterman H, Triolo J, Lefer AM. Use of hypertonic saline in the treatment of hemorrhagic shock. Circ Shock 1987;21:271– 83. 36. Jonas J, Heimann A, Strecker U, et al. Hypertonic/hyperoncotic resuscitation after intestinal superior mesenteric artery occlusion: early effects on circulation and intestinal reperfusion. Shock 2000;14:24 –39. 37. Kreimeier U, Thiel M, Messmer K. Hypertonic-hyperoncotic solutions. In: Risberg B, editor.Trauma care-an update. Stockholm: Pharmacia and Upjohn Sverige; 1996.p. 142–53. 38. Vassar MJ, Holcroft JW. Use of hypertonic-hyperoncotic fluids for resuscitation of trauma patients. J Intensive Care Med 1992;7:189 –98. 39. Dematte JE, O’Mara K, Buescher J, et al. Near-fatal heat stroke during the 1995 heat wave in Chicago. Ann Intern Med 1998;129:173–81.

28. Kentner R, Safar P, Prueckner S, et al. Titrated hypertonic/hyperoncotic solution for hypotensive fluid resuscitation during uncontrolled hemorrhagic shock in rats. Resuscitation 2005;65:87–95.

40. Knochel JP, Reed G. Disorder of heat regulation. In: Maxwell MH, Kleeman CR, Marine RG, editors. Clinical disorder of fluid and electrolyte metabolism, 5th ed. New York: McGraw-Hill; 1994. p. 1549–90.

29. Shackford SR. Effect of small-volume resuscitation on intracranial pressure and related cerebral variables. J Trauma 1997;42:S48 –S53.

41. Bouchama A, Cafege A, Devol EB, et al. Ineffectiveness of dantrolene sodium in the treatment of heatstroke. Crit Care Med 1991;19:176 – 80.

30. Berger S, Schurer L, Hartl R, et al. Reduction of post-traumatic intracranial hypertension by hypertonic/hyperoncotic saline/dextran and hypertonic mannitol. Neurosurgery 1995;37:98 –108.

42. Bynum GD, Pandolf KB, Schuette WH, et al. Induced hyperthermia in sedated humans and the concept of critical thermal maximum. Am J Physiol 1978;235:R228 –R236.

31. Sheikh AA, Matsuoka T, Wisner DH. Cerebral effects of resuscitation with hypertonic saline and a new low-sodium hypertonic fluid in hemorrhagic shock and head injury. Crit Care Med 1996;24:1226 –32.

43. Pettigrew RT, Galt JM, Ludgate CM, et al. Circulatory and biochemical effects of whole body hyperthermia. Br J Surg 1974; 61:727–30.

32. Nakayama S, Sibley L, Gunther RA, et al. Small-volume resuscitation with hypertonic saline (2,400 mOsm/liter) during hemorrhagic shock. Circ Shock 1984;13:149 –9.

44. Weidler S. Hydroxyethylsta¨rke-kinetik im Probandenversuch; Einflu␤ von Molekulargewich, Substitution und Substitution sposition. In: Lawin P, Zander J, Weidler B. Hydroxyethylsta¨rke: eine aktuelle u¨bersicht. Schriftenreihe intersivmedizin, Notfallmedizin, Ana¨sthesiologie; Bd 74:45–55; Thieme Verlag Studtgart; 1989.

33. Messmer K, Kreimeier U. Microcirculatory therapy in shock. Resuscitation 1989;(18 Suppl):S51–S61.

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