The last decades less invasive monitoring and analytical tools have been developed for the evaluation of myocardial mechanics in clinical praxis. In critical care, these are longed-for complements to pulmonary artery catheter monitoring, additionally offering previously inaccessible information. This work is aimed, during fluid-replacement and oxygen therapy, to determine the physiological interface of ventricular and vascular mechanical properties, which result in the transfer of blood from the heart to appropriate circulatory beds. In prospective clinical studies we investigated previously cardiovascular healthy adults during hyperoxemia, and during preoperative acute normovolemic hemodilution or early fluid resuscitation of severe burn victims. Echocardiography was used in all studies, transthoracic for healthy volunteers and transesophageal for patients. For vascular parameters and for control purposes pulmonary artery Swan-Ganz catheter, calibrated external pulse recordings, whole body impedance cardiography, and transpulmonel thermodilution method were applied. We detected no significant change in blood pressure or heart rate, the two most often used parameters for patient monitoring. During preoperative acute normovolemic hemodilution a reduction of hemoglobin to 80 g/l did not compromise systolic or diastolic myocardial function. Cardiac volumes and flow increased with a concomitant fall in systemic vascular resistance while oxygen delivery seemed maintained. Supplemental oxygen therapy resulted in a linear dose-response between arterial oxygen and cardiovascular parameters, suggesting a direct vascular effect. Cardiac flow decreased and vascular resistance increased from hyperoxemia, and a decrease of venous return implied extracardial blood-pooling. Severe burns result in hypovolemic shock if not properly treated. The commonly used Parkland fluid replacement strategy, with urinary output and mean arterial pressure as endpoints, has recently been questioned. Applying this strategy, only transient early central hypovolemia was recorded, while dimensional preload, global left ventricular systolic function and oxygen delivery or consumption remained within normal ranges during the first 36 hours after accident. Signs of restrictive left ventricular diastolic function were detected in all patients and regional unstable systolic dysfunction was recognized in every other patient, and was consistent with myocardial marker leakage. Severe burns thereby cause myocardial stiffness and systolic regional dysfunction, which may not be prevented only by central normovolemia and adequate oxygenation. / On the day of the defence date the status of article II was: In Press.

Cerebral perfusion is optimized during hemodilution by both β1- and β2-adrenergic mechanisms. Antagonism of the β2-adrenoreceptor can impair cerebral vasodilation. We hypothesized that treatment with a highly β1-specific antagonist (nebivolol) would minimize the degree of cerebral hypoxia during hemodilution. Anesthetized rats were randomized to receive vehicle or nebivolol (1.25 or 2.5 mg/kg intravenously) prior to hemodilution. In vehicle-treated rats, hemodilution increased cardiac output (CO) and regional cerebral blood flow (rCBF) while microvascular brain PO2 (PBrO2) decreased. Both nebivolol doses reduced heart rate and attenuated the CO response to hemodilution. Only the higher dose of nebivolol attenuated the rCBF response to hemodilution and caused a further reduction in PBrO2. Brain hypoxic protein levels were only increased in the high dose nebivolol group. High dose nebivolol treatment resulted in drug levels near its affinity for the β2-adrenoreceptor supporting the hypothesis that cerebral perfusion is maintained by β2-dependent mechanisms during hemodilution.

Cerebral perfusion is optimized during hemodilution by both β1- and β2-adrenergic mechanisms. Antagonism of the β2-adrenoreceptor can impair cerebral vasodilation. We hypothesized that treatment with a highly β1-specific antagonist (nebivolol) would minimize the degree of cerebral hypoxia during hemodilution. Anesthetized rats were randomized to receive vehicle or nebivolol (1.25 or 2.5 mg/kg intravenously) prior to hemodilution. In vehicle-treated rats, hemodilution increased cardiac output (CO) and regional cerebral blood flow (rCBF) while microvascular brain PO2 (PBrO2) decreased. Both nebivolol doses reduced heart rate and attenuated the CO response to hemodilution. Only the higher dose of nebivolol attenuated the rCBF response to hemodilution and caused a further reduction in PBrO2. Brain hypoxic protein levels were only increased in the high dose nebivolol group. High dose nebivolol treatment resulted in drug levels near its affinity for the β2-adrenoreceptor supporting the hypothesis that cerebral perfusion is maintained by β2-dependent mechanisms during hemodilution.

Introdução: A anemia aguda tem sido associada com distúrbios neurofisiológicos e cognitivos em pacientes saudáveis. Evidências experimentais sugerem que a hemodiluição pode aumentar lesões cerebrais, limitando o suprimento de oxigênio ao tecido cerebral. No entanto, o mecanismo exato pelo qual as lesões cerebrais ocorrem em pacientes anêmicos ainda não está claramente definido. O objetivo desse estudo foi avaliar os precursores da apoptose neuronal Bax, Bcl-x no córtex frontal, atividade das caspases 3 e 9 na fração citosólica do hipocampo e na fração mitocondrial do córtex frontal, assim como a fragmentação do DNA na fração nuclear e mitocondrial do córtex frontal, após hemodiluição normovolêmica aguda. Métodos: Vinte e quatro porcos foram anestesiados e randomizados em 4 grupos de 6 animais: Controle, hemodiluição normovolêmica aguda (HNA) com hematócrito alvo de 15% (Ht 15%), HNA com hematócrito alvo de 10% (Ht 10%) e hipóxia-hipóxica (HH). A HNA foi realizada com 1ml de hidroxetil amido (130/0,4) por ml de sangue retirado, até o hematócrito alvo desejado (10 ou 15%). O HH consistiu de ventilação com baixa fração expirada de O2 (FiO2), sendo de 6% por 60 minutos, servindo como grupo controle positivo. Os animais do grupo controle não sofreram nenhuma dessas intervenções. As proteínas pró-apoptótica Bax e anti-apoptótica Bcl-x foram avaliadas por Western blotting nas frações nucleares e mitocondriais do córtex frontal. A atividade das caspases 3 e 9 foi avaliada nas frações mitocondrial e citosólica do hipocampo por espectrofluorometria. A fragmentação do DNA foi avaliada por eletroforese nas frações nuclear e mitocondrial do córtex frontal. Os dados foram comparados por análise de variância (ANOVA) seguida por teste de Tukey (p<0,05). Resultados: Não foi observada diferença significativa entre os grupos controle, Ht 15% e Ht 10% em relação à proteína pró-apoptótica Bax nas frações nuclear e mitocondrial. Entretanto, o grupo HH foi significativamente diferente dos grupos controle e Ht 15% na fração nuclear e de todos os grupos na fração mitocondrial. Não foi encontrada diferença significativa em relação à Bcl-x. A atividade das caspases 3 e 9 nas frações mitocondrial e nuclear foi diferente no grupo HH quando comparado com os demais grupos. Não foi observada diferença significativa em relação à fragmentação do DNA entre os grupos controle, Ht 15% e Ht 10%. Conclusão: A avaliação dos precursores da apoptose demonstrou que a hemodiluição normovolêmica aguda com hematócrito alvo de 15% e 10% não induziu apoptose, sugerindo que a oxigenação cerebral foi preservada / Background: Acute anemia has been associated with neurophysiologic and cognitive dysfunctions in healthy patients. Experimental evidences suggest that hemodilution may increase cerebral lesions, limiting oxygen supply to the brain tissue. Nevertheless, the exact mechanisms through which cerebral lesions occur in anemic patients havent been clearly defined. Therefore, the objective of the present study was to evaluate neuronal apoptosis precursors Bax, Bcl-x in the frontal cortex, caspase 3 and 9 activity in the mitochondrial and cytosolic fractions of the hippocampus, even as DNA fragmentation in the mitochondrial and nuclear fractions of the frontal cortex after acute normovolemic hemodilution. Methods: Twenty four pigs were anesthetized and randomized into 4 groups of 6 animals: sham, acute normovolemic hemodilution (ANH) to reach a hematocrit of 15% (Ht 15%), ANH to reach a hematocrit of 10% (Ht 10%) and hypoxic-hipoxia (HH). ANH was performed with 1ml hydroxyethyl starch 130/0.4 (HES) per ml of blood withdrawn to the desired target hematocrit (10 or 15%). HH consisted of ventilation with low fraction of inspired oxygen (FiO2) of 6% for 60 minutes, serving as a positive control group. Sham animals were not involved in any of these interventions. Pro-apoptotic Bax and anti-apoptotic Bcl-x proteins were evaluated by Western blotting in nuclear and mitochondrial fractions of the frontal cortex and activities of caspases-3 and-9 were evaluated in the mitochondrial and cytosolic fractions of the hippocampus by spectrofluorometry. DNA fragmentation was evaluated by electrophoresis in the mitochondrial and nuclear fraction. Data were compared by analysis of variance (ANOVA) followed by Tukeys test (p<0.05). Results: No statistical significance was found among sham, Ht 15% or Ht 10% groups regarding pro-apoptotic protein Bax, in nuclear or mitochondrial fractions. However, group HH presented significant difference from sham and Ht 15% groups in the nuclear fraction and from all groups in the mitochondrial fraction. No statistical significance was found with Bcl-x. The activities of caspases-3 and-9 in cytosolic and mitochondrial fractions were statisticaly different in group HH when compared with all other groups. No statistical significance was found in relation to DNA fragmentation among sham, Ht 15% or Ht 10%. Conclusion: The evaluation of apoptosis precursors demonstrated that ANH with target hematocrit 15% and 10% did not induce neuronal lesion, suggesting that cerebral oxygenation was preserved

O objetivo desse estudo foi avaliar o comportamento da coagulação sanguínea em dois graus de profundidade de hemodiluição superficial com Ht de 30% e profunda com Ht de 20%, nas situações in vivo e in vitro, tendo como grupo controle os próprios pacientes não hemodiluídos. Para isso foram selecionados 13 pacientes ASA I ou II, submetidos à cirurgia de grande porte. A hemodiluição in vivo foi realizada segundo a fórmula de Gross até a obtenção dos hematócritos pretendidos. O sangue retirado foi reposto com solução de ringer com lactato na proporção de 3 ml para cada ml de sangue retirado e foi devolvido ao paciente ao final do procedimento anestésico. Avaliação hemodinâmica foi realizada continuamente e registrada a cada 15 minutos. Foram colhidos exames para os testes de coagulação nos momentos M1 antes da hemodiluição, M2 hemodiluição até hemataócrito de 30% e M3 hemodiluição até hematócrito de 20%. A hemodiluição in vitro foi realizada com a adição de ringer lactato a volume de sangue previamente colhido. O volume de ringer lactato acrescentado obedeceu à fórmula C1V1 = C2V2, onde C1 é o hematócrito inicial, o V1é o volume de sangue no tubo de ensaio, C2 é o hematócrito pretendido e V2 o volume final do tubo de ensaio. Amostras de sangue para os testes de coagulação foram colhidas em M2 e M3. A média de idade foi de 39,85 ± 18,39. O volume de sangue retirado para o obtenção dos hematócritos de 30% e 20% foi de 1158,5 ± 425,79 ml e 2211,31 ± 726.22 ml, respectivamente. Não houve diferença entre a pressão arterial média e a frequência cardíaca nos 3 momentos. Houve diminuição da temperatura em M2. A contagem de plaquetas diminuiu em M2 e M3. Os testes de coagulação in vivo mostraram aumento do TP, INR, TTPA, TT tanto em M2 quanto em M3. Houve diminuição da concentração de fibrinogênio em M2 e M3. Os testes de coagulação in vitro apresentaram comportamento semelhante. Quando se comparou o TP in vivo com o TP in vitro houve diferença estatística em M3. Nos demais testes in vivo comparados com os in vitro não houve diferença estatística em todos os momentos analisados. Conclui-se que a hemodiluição afeta os testes de coagulação e que a hemodiluição in vivo ou in vitro apresenta o mesmo comportamento no tocante aos testes de coagulação. / The objective of the present study was to evaluate the behavior of blood clotting at two hemodilution levels - superficial with 30% hematocrit (Ht), and profound with 20% Ht, in in vivo and in vitro situations, with the same non-hemodiluted patients serving as the control group. Thirteen ASA I or ASA II patients submitted to major surgery were selected for this purpose. In vivo hemodilution was performed by the formula of Gross until the intended hematocrits were obtained. The blood removed was replaced with Ringer lactate solution at the proportion of 3 ml per ml removed blood and was returned to the patient at the end of the anesthetic procedure. Continuous hemodynamic evaluation was performed and recorded at 15 minute intervals. Samples were obtained for the clotting tests at time T1 before hemodilution, T2 hemodilution to 30% hematocrit, and T3 - hemodilution to 20% hematocrit. In vitro hemodilution was performed by the addition of Ringer lactate to a previously collected blood volume. The added Ringer lactate followed the formula C1V1 = C2V2, where C1 is the initial hematocrit, V1 is the blood volume in the test tube, C2 is the intended hematocrit, and V2 the final volume in the test tube. Blood samples for the clotting tests were obtained at T2 and T3. Mean patient age was 39.85 ± 18.39 years. The blood volume removed for the determination of 30% and 20% hematocrit was 1158.5 ± 425.79 ml and 2211.31 ± 726.22 ml, respectively. There was no difference in mean arterial pressure or heart rate at the 3 times. There was a fall in temperature at T3 and a fall in platelet count at T2 and T3. The in vivo clotting tests showed an increase of PT, INR, APTT, TT at both T2 and T3. There was a reduction of fibrinogen concentration at T2 and T3. The in vitro clotting tests showed a similar behavior. When TP in vivo was compared to TP in vitro a statistically significant difference was observed at T3. No statistically significant differences were observed between the remaining in vivo and in vitro tests. We conclude that hemodilution affects the clotting tests and that in vivo or in vitro hemodilution presents the same behavior regarding clotting tests.

Stroke is a major health problem in all developed countries. These studies, performed in a stroke unit at a medical department, were designed to characterize essential clinical features of the different cerebrovascular disorders on admission to hospital, to evaluate the efficacy of admitting unselected stroke patients to a stroke unit and, to evaluate hemodilution as a therapeutical regime in patients with cerebral infarction. A prospective registry included 409 patients admitted to the stroke unit over a five-year period. Modern diagnostic equipment (CT scan and CSF analyses) and strict diagnostic criteria revealed a diagnostic distribution of 11% hemorrhagic, 76% ischemic cerebrovascular lesions and 13% TIAs. Mean age varied between 65.8 and 77.5 years in the various diagnostic groups with the highest in patients with embolic cerebral infarctions. Concomitant disorders affecting the cardiovascular system were highly prevalent and only 14% was free of such diseases prior to the stroke. In a comparative prospective study, over 16 months, no differences were found between patients treated in the stroke unit (n = 110) and the general medical wards (n = 183) regarding prognostic indicators on admission such as age, concomitant disorders and neurological symptoms. The stroke patients treated in the stroke unit had a statistically significant better prognosis regarding functional outcome and the need for long-term hospitalization was reduced up to one year after the stroke when compared to patients treated in general medical wards. All stroke patients seemed to benefit with the possible exception of patients in coma on admission. These results were achieved within the same or shorter length of initial hospital stay for patients in the stroke unit. Neither overall mortality, nor mortality in subgroups of prognostic importance was significantly affected by the stroke unit regime. Rapid hemodilution in the early phase of cerebral infarction by the combination of venesection and administration of dextran 40 was evaluated in a prospective controlled trial. After randomization 52 hemodi- luted and 50 control patients were comparable in prognostic variables. Signs of blood-brain-barrier breakdown and hemorrhagic admixture to the cerebrospinal fluid in the acute phase were less frequent in hemodiluted subjects. The hemodi luted patients showed a significantly higher degree of early improvement and fewer progressions. Neurological and functional disability in survivors and need for long-term hospitalization was significantly reduced at 3 months and at one year after the stroke compared to controls. Mortality was not affected. / digitalisering@umu

Introdução: Os hidroxietilamidos (HES) são considerados expansores plasmáticos efetivos em pacientes submetidos a procedimentos cirúrgicos de grande porte. Entretanto, seu uso clínico é limitado principalmente por sua interferência na hemostasia, representada por alterações da função plaquetária e na coagulação. A extensão dessas alterações está relacionada ao seu ipeso molecular ou à sua substituição molar. Este estudo clínico, foi realizado durante cirurgia de artroplastia de quadril em pacientes adultos para comparar os efeitos do HES (130/0,4) e a solução de Ringer lactato em relação ao sangramento intra-operatório, parâmetros hemodinâmicos, alterações na coagulação, necessidade de transfusões e resultados clínicos. Métodos: Quarenta e oito pacientes candidatos à cirurgia de artroplastia total de quadril sob anestesia subaracnoidea foram distribuídos aleatoriamente em dois grupos 24 pacientes foram selecionados para receber HES (30 ml/kg após anestesia) e 24 pacientes para receber solução de Ringer lactato (30ml/kg). O período de observação teve início após a indução da anestesia e terminou 5 horas após o termino do procedimento cirúrgico. Durante esse período o critério para a infusão de doses adicionais de fluido (10ml/kg de Solução de Ringer lactato para ambos os grupos) foi pressão arterial sistólica inferior a 90 mmHg e/ou um decréscimo de 20% da pressão arterial inicial, frequência cardíaca acima de 100 bpm, e/ou débito urinário menor de 0,4ml/kg/h. Vasopressor foi utilizado nos casos em que a hipotensão persistiu, após a reposição de volume. Transfusão de concentrado de hemácias foi administrada nos pacientes que se mantiveram instáveis hemodinamicamente após bolus adicionais de Ringer lactato ou vasopressor, Parâmetros hemodinâmicos foram mensurados em três períodos da cirurgia; dados bioquímicos foram coletados e testes da coagulação realizados e comparados. Os pacientes foram acompanhados durante sua internação hospitalar. Resultados: Os grupos foram uniformes em relação aos dados demográficos, tipo e duração da cirurgia, assim como a doenças pré-existentes. Não foram observadas diferenças significativas em relação aos parâmetros hemodinâmicos ou temperatura corporal durante o estudo. Os testes de coagulação, função plaquetária, análise de gases sanguíneos e dados bioquímicos mostraramse semelhantes entre os grupos. Perdas sanguíneas foram significativamente maiores no grupo HES (1296x890,p=0,04), necessitou de menos unidades de concentrado de hemácias durante o período observacional (17%versus46%, p=0,029) apresentou menores taxas de infecção (0 versus 4 ,p<0,03), comparado ao grupo Ringer lactato. Conclusões: Em cirurgia de artroplastia total de quadrill, a hemodiluição com hidroxietilamido resultou em maiores taxas de sangramento, menos transfusões sanguíneas e menos infecção pós-operatória. / Introduction: Hydroxyethyl starches (HES) are considered effective plasma expanders in patients undergoing major surgeries. However, the clinical use of HES is limited mainly by their affection of hemostasis, detectable by impaired platelet function and altered coagulation. The extent of such alteration has classically been related to the molecular weight or molar substitution of the used HES solution. This prospective, randomized study was performed during hip arthroplasty in adult patients under spinal anesthesia to compare the effects of HES 130/0.4 with lactateds Ringer solution regarding intraoperative bleeding, hemodynamic parameters, coagulation profile, transfusion requirements and clinical outcomes. Methods: Forty eight patients scheduled to hip arthroplasty after spinal anesthesia were randomized in two groups 24 patients were allocated to receive HES 130/0.4 (30 ml/Kg just after anesthesia) and 24 patients were signaled to receive lactateds Ringer solution (30 ml/Kg). The observational period started after the induction of anesthesia and finished 5 hours after the end of the surgery. During this period, the triggers for infusion of additional boluses of fluids (10 ml/Kg of lactateds Ringer for both groups) were a systolic blood pressure lower than 90 mmHg and/or a decrease of 20% from baseline, a heart rate higher than 100 bpm, and/or a urine output lower than 0.4 ml.Kg-1.h-1. Vasopressors were used if there was persistent hypotension despite of fluid reposition. Red blood cell transfusion was administered if patient remained unstable despite of additional boluses of Ringer or vasopressors, according to the preestablished triggers. Hemodynamic measurements were done in three periods of the surgery, biochemical parameters were analyzed and coagulation tests were performed and compared between groups. After surgery, patients were followed during the hospital stay. Results: The groups were well matched regarding demographic data, type of surgery, and duration of surgery, as well as preexisting diseases. No significant differences in hemodynamic or body temperature were seen during the study. Coagulation variables, platelet function, gases analysis and biochemical parameters were not different between groups. Blood losses were significantly higher in HES 130/0.4 group comparing to Ringers group (1296 x 890 ml, p= 0.046). Despite of that, HES group required less units of blood in the observational period comparing to Ringer group (17% versus 46%, p=0.029). HES group presented lower infection rate compared to Ringer group (0 versus 4 cases, p=0.03). Conclusions: During hip arthroplasty, hemodilution with hydroxyethyl starch 130/0.4 resulted in higher rates of bleeding. However, patients treated with hydroxyethyl starch required less transfusion and presented lower rate of infection.

A hemostasia é um evento biológico passível de ser avaliado e estudado, assim como seus distúrbios. Há situações durante a anestesia que podem cursar com alterações hemostáticas culminando com aumento do sangramento ou até mesmo hemorragias graves. Os tempos de coagulação têm recebido especial atenção tendo-se em vista os diferentes contratempos hemostáticos que pode ocorrer durante o procedimento anestésico-cirúrgico. Sendo assim, nesse estudo buscou-se estabelecer os valores padrões para tempo de protrombina (TP) e de tromboplastina parcial ativada (TTPA) para cães submetidos a diferentes procedimentos cirúrgicos. Foram estudados 50 cães hígidos para padronização dos valores de TTPA e TP utilizando aparelho automático. Os valores de TTPA estavam dentro dos valores de normalidade da literatura (6,9 a 17,6 segundos) e valores de TP discretamente maiores (de 6,65 a 12,8 segundos). Foram estudadas 20 cadelas classificadas como ASA I e 18 cães ASA II e III. Nestes animais observaram-se aumentos significativos de valores de TTPA (de 12,04 para 14,29 segundos em ASA I, com P<0,0378; e de 13,4 para 15,11 segundos nos cães ASA II e III, P<0,0067) e de TP (de 8,36 para 9,7 segundos em ASA I, P<0,0323; e de 8,32 para 9,34 segundos nos caes ASA II e III, P< 0,0084) entre os momentos pré e pós-anestésicos Estes aumentos acompanham quedas da pressão coloidosmótica, indicando que o processo de anestesia, cirurgia e fluidoterapia causam hemodiluição, e conseqüente aumento nos tempo de coagulação. / Hemostasis is a biological event that could be evaluated and studied, just like yours disturbs. There are situations in to anesthetic procedures that could curse with hemostatics disturbs causing bleeding increase or even critical blood loss. The blood clotting times have been received special attention because different hemostatic setbacks that could occur during the anesthetic and surgical procedures. This way, this study look for establish the values for reference to protrombine time (PT) and to activated partial tromboplastin time (APTT) for dogs. Were studied 50 healthy dogs to standardize the values of PT and APTT utilizing an automatic instrument. The APTT values was in agreement with the literature values (6,9 to 17, 6 seconds), and the PT values was discret increased when compared with literature (from 6,65 to 12,8 seconds). Was studied 20 bitches classifieds as ASA I and 18 dogs classifieds as ASA II and III. In this animals observed significant increase values of APTT (from 12,04 to 14,29 seconds in the ASA I, P<0,0378; and from 13,4 to 15,11 seconds in the dogs ASA II and III, P<0,0067) and of PT (from 8,36 to 9,7 seconds in ASA I, P<0,0323; and from 8,32 to 9,34 seconds in the ASA II and III dogs) between the pre and post anesthetic moments. These increases attendance decease in the colloid osmotic pressure, indicating that the anesthetic, surgical and fluid therapy procedures can cause hemodilution, and consequent increase in the blood clotting times.

INTRODUÇÃO: Em pacientes vítimas de trauma crânio-encefálico é fundamental que se restabeleça a volemia intravascular, quando associado à hipotensão arterial, com o intento de manter a pressão de perfusão e não agravar a lesão do sistema nervoso central. A hipovolemia pode ser corrigida com infusão rápida de soluções cristalóides e/ou colóides, quando hemoderivados não estão disponíveis. Nesta condição, o hematócrito (Ht) pode reduzir-se para valores muito baixos. A anemia aguda altera a viscosidade do sangue e pode interferir na reatividade vascular encefálica. O objetivo deste estudo foi avaliar a pressão intracraniana(PIC) na presença de lesão criogênica encefálica, quando se realiza hemodiluição aguda com Ringer lactato ou hidroxietilamido 450/0,7 a 6%, estabelecendo-se como meta reduzir o hematócrito de 40% para 35% ou para 27%. MÉTODOS: Foram utilizados 35 cães machos sem raça definida, cujo hematócrito inicial era superior a 40%, anestesiados e submetidos à lesão encefálica criogênica durante 20 minutos. Após foram aleatoriamente distribuídos em 5 grupos experimentais: HES35, hemodiluídos com hidroxietilamido até Ht de 35%; RL35, hemodiluídos com Ringer lactato até Ht de 35%; HES27, hemodiluídos com hidroxietilamido até Ht de 27%; RL 27, hemodiluídos com Ringer lactato até Ht de 27%; e controle, sem hemodiluição. As variáveis hemodinâmicas sistêmicas foram obtidas por meio de cateter de artéria pulmonar; a PIC foi medida por sensor introduzido no espaço subaracnóideo no hemisfério contralateral à lesão criogênica; as variáveis laboratoriais foram obtidas de amostras de sangue arterial. RESULTADOS: A lesão criogênica encefálica levou a aumento da PIC em todos os animais, sem diferença entre os grupos(p>0,5). Este aumento foi exacerbado somente nos animais hemodiluídos até hematócrito de 27%(p<0,03). A solução utilizada não influenciou o comportamento da PIC(p>0,5). / Objective: Brain injury is responsible for significant morbidity and mortality in trauma patients, but controversy still exists over optimal fluid management for these patients. This study aimed to investigate the effects of acute hemodilution with hydroxyethyl starch (HES) or lactated Ringer\'s solution (LR) in intracranial pressure(ICP) and cerebral perfusion pressure in dogs submitted to a cryogenic brain injury model. Design: Prospective laboratory animal study. Setting: Research laboratory in a teaching hospital. Subjects: Thirty-five male mongrel dogs. Interventions: Animals were enrolled to 5 groups: control, hemodilution with lactated Ringer\'s solution (RL) or hydroxyethyl starch (HES) 6% to an hematocrit target of 27% or 35%. Measurements and Main Results: ICP and CPP levels were measured after cryogenic brain injury. Hemodilution promotes an increment of ICP levels, which decreases CPP when hematocrit target was estimated in 27% after hemodilution. However, no differences were observed regarding crystalloid or colloid solution used for hemodilution in ICP and CPP levels. Conclusions: Hemodilution to a low hematocrit level increases ICP and decreases CPP scores in dogs submitted to a cryogenic brain injury. These results suggest that excessive hemodilution to a hematocrit below 30% should be avoided in traumatic brain injury patients.

INTRODUÇÃO: Em pacientes vítimas de trauma crânio-encefálico é fundamental que se restabeleça a volemia intravascular, quando associado à hipotensão arterial, com o intento de manter a pressão de perfusão e não agravar a lesão do sistema nervoso central. A hipovolemia pode ser corrigida com infusão rápida de soluções cristalóides e/ou colóides, quando hemoderivados não estão disponíveis. Nesta condição, o hematócrito (Ht) pode reduzir-se para valores muito baixos. A anemia aguda altera a viscosidade do sangue e pode interferir na reatividade vascular encefálica. O objetivo deste estudo foi avaliar a pressão intracraniana(PIC) na presença de lesão criogênica encefálica, quando se realiza hemodiluição aguda com Ringer lactato ou hidroxietilamido 450/0,7 a 6%, estabelecendo-se como meta reduzir o hematócrito de 40% para 35% ou para 27%. MÉTODOS: Foram utilizados 35 cães machos sem raça definida, cujo hematócrito inicial era superior a 40%, anestesiados e submetidos à lesão encefálica criogênica durante 20 minutos. Após foram aleatoriamente distribuídos em 5 grupos experimentais: HES35, hemodiluídos com hidroxietilamido até Ht de 35%; RL35, hemodiluídos com Ringer lactato até Ht de 35%; HES27, hemodiluídos com hidroxietilamido até Ht de 27%; RL 27, hemodiluídos com Ringer lactato até Ht de 27%; e controle, sem hemodiluição. As variáveis hemodinâmicas sistêmicas foram obtidas por meio de cateter de artéria pulmonar; a PIC foi medida por sensor introduzido no espaço subaracnóideo no hemisfério contralateral à lesão criogênica; as variáveis laboratoriais foram obtidas de amostras de sangue arterial. RESULTADOS: A lesão criogênica encefálica levou a aumento da PIC em todos os animais, sem diferença entre os grupos(p>0,5). Este aumento foi exacerbado somente nos animais hemodiluídos até hematócrito de 27%(p<0,03). A solução utilizada não influenciou o comportamento da PIC(p>0,5). / Objective: Brain injury is responsible for significant morbidity and mortality in trauma patients, but controversy still exists over optimal fluid management for these patients. This study aimed to investigate the effects of acute hemodilution with hydroxyethyl starch (HES) or lactated Ringer\'s solution (LR) in intracranial pressure(ICP) and cerebral perfusion pressure in dogs submitted to a cryogenic brain injury model. Design: Prospective laboratory animal study. Setting: Research laboratory in a teaching hospital. Subjects: Thirty-five male mongrel dogs. Interventions: Animals were enrolled to 5 groups: control, hemodilution with lactated Ringer\'s solution (RL) or hydroxyethyl starch (HES) 6% to an hematocrit target of 27% or 35%. Measurements and Main Results: ICP and CPP levels were measured after cryogenic brain injury. Hemodilution promotes an increment of ICP levels, which decreases CPP when hematocrit target was estimated in 27% after hemodilution. However, no differences were observed regarding crystalloid or colloid solution used for hemodilution in ICP and CPP levels. Conclusions: Hemodilution to a low hematocrit level increases ICP and decreases CPP scores in dogs submitted to a cryogenic brain injury. These results suggest that excessive hemodilution to a hematocrit below 30% should be avoided in traumatic brain injury patients.