Intracranial and systemic effects of osmotic and oncotic therapy in experimental cerebral edema

Repeated Oral Administration of Human Serum Albumin Protects from the Cerebral Ischemia in Rat Brain Following MCAO

Albumin is known to have neuroprotective effects. The protein has a long half-life circulation, and its effects can therefore persist for a long time to aid in the recovery of brain ischemia. In the present study, we investigated the neuroprotective effects of human serum albumin (HSA) on brain hemodynamics. Albumin is administrated using repeated oral gavage to the rodents. Sprague-Dawley rats underwent middle cerebral artery occlusion procedures and served as a stroke model. Afterwards, 25% human serum albumin (1.25 g/kg) or saline (5 ml/kg) was orally administrated for 2 weeks in alternating days. After 2 weeks, the rodents were assessed for levels of brain ischemia. Our testing battery consists of behavioral tests and in vivo optical imaging sessions. Modified neurological severity scores (mNSS) were obtained to assess the levels of ischemia and the effects of HSA oral administration. We found that the experimental group demonstrated larger hemodynamic responses following sensory stimulation than controls that were administered with saline. HSA administration resulted in more significant changes in cerebral blood volume following direct cortical electric stimulation. In addition, the mNSS of the treatment group was lower than the control group. In particular, brain tissue staining revealed that the infarct size was also much smaller with HSA administration. This study provides support for the efficacy of HSA, and that long-term oral administration of HSA may induce neuroprotective effects against brain ischemia.

Analytic Reviews : Fluid Resuscitation in Head Injury

Head injury, either alone or in combination with hy povolemic shock, is the leading cause of traumatic death in this country. Factors contributing to mortality in clude the primary impact injury as well as subsequent ischemia and hypoperfusion. Intravenous fluid therapy is required in all of these patients. However, fluid ther apy may increase brain swelling and cerebral edema formation which could lead to an increase in intracra nial pressure and a reduction in cerebral perfusion pres sure. The use of standard fluid therapy has been ques tioned, and novel therapies involving hyperosmolar and hypertonic solutions are now being investigated. This review covers recent advances in the understanding of the effects of fluid resuscitation on the brain. It also includes a brief summary of the determinants of trans- capillary fluid exchange and a review of relevant cere bral circulatory physiology and the physiological aberra tions produced by brain injury.

Flow Augmentation in Acute Ischemic Stroke

There is an urgent need for additional therapeutic options for acute ischemic stroke considering the major pitfalls of the options available. Herein, we briefly review the role of cerebral blood flow, collaterals, vasoreactivity, and reperfusion injury in acute ischemic stroke. Then, we reviewed pharmacological and interventional measures such as volume expansion and induced hypertension, intra-aortic balloon counterpulsation, partial aortic occlusion, extracranial-intracranial carotid bypass surgery, sphenopalatine ganglion stimulation, and transcranial laser therapy with regard to their effects on flow augmentation and neuroprotection.

Effect of mannitol on cerebrovascular pressure reactivity in patients with intracranial hypertension

BACKGROUND/PURPOSE

Mannitol is commonly used in patients with increased intracranial pressure (ICP), but its effect on cerebrovascular pressure reactivity (CVPR) is uncertain. We analyzed the changes of pressure reactivity index (PRx) during the course of mannitol treatment.

METHODS

Twenty-one patients who received mannitol treatment for increased ICP were recruited prospectively. Continuous waveforms of arterial blood pressure (ABP) and ICP were collected simultaneously for 60 minutes (10 minutes at baseline and 50 minutes since mannitol administration) during 37 events of mannitol treatment. The correlation coefficients between the mean ABP and ICP were averaged every 10 minutes and labeled as the PRx. The linear correlation of six time points of PRx in each event was calculated to represent the trend of CVPR changes. The negative slope of correlation was defined as improvement in CVPR under mannitol treatment and vice versa.

RESULTS

At baseline, the average of ICP was 26.0 ± 9.1 mmHg and the values of PRx were significantly correlated with ICP (p = 0.0044, r = 0.46). After mannitol administration, the average of ICP decreased significantly to 21.2 ± 11.1 mmHg (p = 0.036), and CVPR improved in 59.4 % of all events. Further analysis showed that low baseline cerebral perfusion pressure was the only hemodynamic parameter significant association with the improvement of CVPR after mannitol treatment (p = 0.039).

CONCLUSION

Despite lowering ICP, mannitol may have diverse effects on CVPR in patients with intracranial hypertension. Our study suggests that mannitol infusion may have a beneficial effect on CVPR, particularly in those with a low cerebral perfusion pressure at baseline.

Intraventricular albumin: an optional agent in experimental post-traumatic brain edema

HYPOTHESIS

Human albumin may be effective in the treatment of posttraumatic brain edema due to its hyperoncotic features. Therefore, the aim of the experimental study presented in this paper has two points: the first is to evaluate the efficacy of intraventricular hyperoncotic human albumin on post-traumatic brain edema and the second is to try to show the appropriate posttraumatic time window for albumin administration.

METHOD

Traumatic brain injury and subsequent edema was formed by a model of impact acceleration injury in rats. Human albumin was administered via intraventricular route by using a stereotactic head holder. All animals in each group were decapitated 24 hours after the procedure and the effect of albumin was evaluated by measurement of tissue specific gravity.

RESULTS

Tissue specific gravity decreased in edematous tissue (trauma indicator), increased after albumin administration at the 12th (p < 0.001), and both at the 1st and 12th hour of the trauma (edema treatment; p < 0.001). On the other hand, albumin administered at the 12th, and at both the 1st and 12th hours in the rats without trauma has caused the formation of the brain edema.

CONCLUSION

We conclude that human albumin is effective in cytotoxic, but not in vasogenic edema and exerts its best anti-edematous effect at the 12th hour of severe head trauma and this study may help future studies that will try to show the effects of albumin with different time modalities after severe head injury.

Fluid therapy and the use of albumin in the treatment of severe traumatic brain injury

BACKGROUND

Evidence-based guidelines for severe traumatic brain injury (TBI) do not include strategies for fluid administration. The protocol used in this study includes albumin administration to maintain normal colloid osmotic pressure and advocates a neutral to slightly negative fluid balance. The aim of this study was to analyze the occurrence of organ failure and the mortality in patients with severe TBI treated by a protocol that includes defined strategies for fluid therapy.

METHODS

Ninety-three patients with severe TBI and Glasgow Coma Score <or=8 were included during 1998-2001. Medical records of the first 10 days were retrieved. Organ dysfunction was evaluated with the Sequential Organ Failure Assessment (SOFA) score. Mortality was assessed after 10 and 28 days, 6 and 18 months.

RESULTS

The total fluid balance was positive on days 1-3, and negative on days 4-10. The crystalloid balance was negative from day 2. The mean serum albumin was 38+/-6 g/l. Colloids constituted 40-60% of the total fluids given per day. Furosemide was administered to 94% of all patients. Severe organ failure defined as SOFA >or=3 was evident only for respiratory failure, which was observed in 29%. None developed renal failure. After 28 days, mortality was 11% and, after 18 months, it was 14%.

CONCLUSIONS

A protocol including albumin administration in combination with a neutral to a slightly negative fluid balance was associated with low mortality in patients with severe TBI in spite of a relatively high frequency (29%) of respiratory failure, assessed with the SOFA score.

Small-volume resuscitation with hyperoncotic albumin: a systematic review of randomized clinical trials

Background

Small-volume resuscitation can rapidly correct hypovolemia. Hyperoncotic albumin solutions, long in clinical use, are suitable for small-volume resuscitation; however, their clinical benefits remain uncertain.

Methods

Randomized clinical trials comparing hyperoncotic albumin with a control regimen for volume expansion were sought by multiple methods, including computer searches of bibliographic databases, perusal of reference lists, and manual searching. Major findings were qualitatively summarized. In addition, a quantitative meta-analysis was performed on available survival data.

Results

In all, 25 randomized clinical trials with a total of 1,485 patients were included. In surgery, hyperoncotic albumin preserved renal function and reduced intestinal edema compared with control fluids. In trauma and sepsis, cardiac index and oxygenation were higher after administration of hydroxyethyl starch than hyperoncotic albumin. Improved treatment response and renal function, shorter hospital stay and lower costs of care were reported in patients with liver disease receiving hyperoncotic albumin. Edema and morbidity were decreased in high-risk neonates after hyperoncotic albumin administration. Disability was reduced by therapy with hyperoncotic albumin in brain injury. There was no evidence of deleterious effects attributable to hyperoncotic albumin. Survival was unaffected by hyperoncotic albumin (pooled relative risk, 0.95; 95% confidence interval 0.78 to 1.17).

Conclusion

In some clinical indications, randomized trial evidence has suggested certain benefits of hyperoncotic albumin such as reductions in morbidity, renal impairment and edema. However, further clinical trials are needed, particularly in surgery, trauma and sepsis.

Osmotic therapy: fact and fiction

This review examines the available data on the use of osmotic agents in patients with head injury and ischemic stroke, summarizes the physiological effects of osmotic agents, and presents the leading hypotheses regarding the mechanism by which they reduce ICP. Finally, it addresses the validity of the following commonly held beliefs: mannitol accumulates in injured brain; mannitol shrinks only normal brain and can increase midline shift; osmolality can be used to monitor mannitol administration; mannitol should be not be administered if osmolality is >320 mOsm; and hypertonic saline is equally effective as mannitol.

Neurointensive care of the nonaccidentally injured child

Childhood victims of NAT with severe brain injury require a multidisciplinary approach to their management if a good outcome is to occur. Despite the grave prognosis of these patients, an initial aggressive treatment strategy is warranted, because enough children go on to a meaningful life. A vigilant evaluation for multisystem injuries and vigorous resuscitation should be followed by prompt surgical intervention as indicated. Most NAT victims do not require surgical treatment of their brain injury, but do require ICP monitoring. A stepwise approach to the treatment of elevated ICP optimizes CPP, minimizes secondary brain injury, and increases the chances of a meaningful recovery. The future holds promise for these patients because a concerted effort is underway to understand pediatric TBI on a molecular level, and targeted therapies based on current basic research will certainly improve the neurointensive care, and eventual neurologic outcomes, of these children.

Neuroprotective effect of treatment with human albumin in permanent focal cerebral ischemia: histopathology and cortical perfusion studies

In recent experimental studies, we demonstrated a highly beneficial neuroprotective effect of moderate- to high-dose human albumin treatment of transient focal cerebral ischemia, but we did not define the effect of albumin therapy in permanent focal cerebral ischemia. In this study, anesthetized Sprague-Dawley rats were subjected to permanent middle cerebral artery occlusion by retrograde insertion of an intraluminal nylon suture coated with poly-L-lysine. Albumin was administered i.v. at 2 h after onset of middle cerebral artery occlusion, in doses of either 1.25 (n=8) or 2.5 g/kg (n=6). In a separate group of animals, albumin (2.5 g/kg) was given 1 h after middle cerebral artery occlusion (n=6). Vehicle-treated rats (n=6) received 0.9% saline in equivalent volumes. Neurological status was evaluated during and 24 h after middle cerebral artery occlusion. One day after middle cerebral artery occlusion, infarct volumes and brain edema were determined. In a separate group of animals, cortical perfusion was assessed by Laser-Doppler perfusion imaging. Albumin (1.25 g/kg; n=3) or vehicle (sodium chloride 0.9%; n=3) was administered at 2 h after onset of middle cerebral artery occlusion. Higher-dose albumin therapy (2.5 g/kg) significantly improved the neurological score compared to vehicle rats at 24 h, when administered at either 1 or 2 h after middle cerebral artery occlusion. Total infarct volume was reduced by albumin (2.5 g/kg given at 2 h) by 32% compared with vehicle-treated rats. Both albumin doses (1.25 and 2.5 g/kg) significantly reduced cortical and striatal infarct areas at several coronal levels when administered at 2 h after middle cerebral artery occlusion. Brain swelling was not affected by albumin treatment. Cortical perfusion declined during middle cerebral artery occlusion in both groups. Treatment with albumin led to 48% increases in cortical perfusion (P<0.002), but saline caused no change. These results support a beneficial effect of albumin therapy in permanent focal cerebral ischemia.

Human albumin therapy of acute ischemic stroke: marked neuroprotective efficacy at moderate doses and with a broad therapeutic window

BACKGROUND AND PURPOSE

We examined the neuroprotective efficacy of moderate-dose human albumin therapy in acute focal ischemic stroke and defined the therapeutic window after stroke onset, within which this therapy would confer neurobehavioral and histopathological neuroprotection.

METHODS

Sprague-Dawley rats were anesthetized with halothane/nitrous oxide and received 2-hour middle cerebral artery occlusion (MCAo) by a poly-L-lysine-coated intraluminal suture. Neurological status was evaluated during occlusion (60 minutes) and daily for 3 days after MCAo. In the dose-response study, human albumin doses of either of 0.63 or 1.25 g/kg or saline vehicle (5 mL/kg) were given intravenously immediately after suture removal. In the therapeutic window study, a human albumin dose of 1.25 g/kg was administered intravenously at 2 hours, 3 hours, 4 hours, or 5 hours after onset of MCAo. Three days after MCAo, brains were perfusion-fixed, and infarct volumes and brain swelling were determined.

RESULTS

Moderate-dose albumin therapy significantly improved the neurological score at 24 hours, 48 hours, and 72 hours and significantly reduced total infarct volume (by 67% and 58%, respectively, at the 1.25- and 0.63-g/kg doses). Cortical and striatal infarct volumes were also significantly reduced by both doses. Brain swelling was virtually eliminated by albumin treatment. Even when albumin therapy (1.25 g/kg) was initiated as late as 4 hours after onset of MCAo, it improved the neurological score and markedly reduced infarct volumes in cortex (by 68%), subcortical regions (by 52%), and total infarct (by 61%).

CONCLUSIONS

Moderate-dose albumin therapy markedly improves neurological function and reduces infarction volume and brain swelling, even when treatment is delayed up to 4 hours after onset of ischemia.

Effects of fluid management on edema volume and midline shift in a rat model of ischemic stroke

BACKGROUND AND PURPOSE

The purpose of this study was to investigate the effects of fluid management on brain water content (BW) and midline shift (MLS) after a focal cerebral ischemic insult.

METHODS

A suture model was used to induce focal cerebral ischemia for 90 minutes (n=44). The rats were randomly assigned to 3 groups 2. 5 hours after reperfusion: dehydration (n=24), control (n=8), or hydration (n=12). BW was obtained with the wet-dry weight method 24 hours after middle cerebral artery (MCA) occlusion. In addition, MRI were obtained (n=31) 24 hours after the onset of ischemia so that the ratio of hemispheric volumes ipsilateral (IH) and contralateral (CH) to the infarct and the extent of MLS could be obtained.

RESULTS

Across the range from moderate dehydration to intravascular volume expansion with isotonic saline, BW of the IH increased linearly as a function of change in body weight (r(2)=0.89), whereas few changes in relation to body weight were observed in CH, indicating a preferential effect of fluid management on the infarcted hemisphere. Furthermore, the hemispheric volume ratio (IH/CH) and MLS also increased in relation to changes in body weight. However, paradoxical increases in BW, IH/CH, and extent of MLS were observed in comparison with controls when severe dehydration was produced with high-dose mannitol.

CONCLUSIONS

Changes in ischemic BW by fluid management correlated closely with changes in body weight except when high-dose mannitol was used. Mannitol, as a dehydrating agent, may be associated with bimodal effects, with a high dose aggravating ischemic BW.

Treatment of acute hyponatremia: ensuring the excretion of a predictable amount of electrolyte-free water

BACKGROUND

Hypertonic saline is the recommended therapy to shrink swollen brain cells in patients with acute hyponatremia accompanied by seizures.

OBJECTIVES

In the absence of hypertonic saline, hypertonic mannitol will shrink the cell volume. Because mannitol is excreted rapidly, our aim was to ensure that it would be excreted with electrolyte-free water (EFW) and to evaluate the renal mechanisms responsible for EFW excretion.

DESIGN

A randomized, prospective, placebo-controlled study in rats was carried out in a research laboratory.

SUBJECTS

Adult male Wistar rats.

INTERVENTIONS

The control group of rats (n = 6) was administered hypotonic saline, a loop diuretic, vasopressin, and glucose by the intraperitoneal route; in the experimental group (n = 6), glucose was replaced with mannitol. Plasma electrolytes were measured at 0 and 210 mins, and balances for water, sodium, and potassium were obtained from 0 to 90 mins and from 90 to 210 mins.

MEASUREMENTS AND MAIN RESULTS

Virtually 100% of the administered mannitol was excreted within 210 mins, and half was excreted in the first 90 mins. The urine contained EFW only in the mannitol group because of a larger volume in the first 90 mins (EFW, 3.7 mL) and to a lower excretion of NaCl in the next 120 mins (EFW, 3.5 mL).

CONCLUSIONS

The combined use of mannitol and a loop diuretic caused the excretion of a predictable volume of EFW because the urine was iso-osmotic to plasma and contained all the administered mannitol. The calculated decrease in intracellular fluid volume was equivalent when mannitol was retained or excreted.

Interleukin-1 receptor antagonist attenuates regional neuronal cell death and cognitive dysfunction after experimental brain injury

The effect of systemic administration of human recombinant interleukin-1 receptor antagonist (rhIL-1ra) on behavioral outcome and histopathologic damage after lateral fluid-percussion brain injury of moderate severity was evaluated. In study 1, brain-injured Sprague Dawley rats received timed subcutaneous injections beginning 15 minutes after injury of either 100 mg/kg rhIL-1ra (high dose, total dose = 1900 mg/kg), 10 mg/kg rhIL-1ra (low dose, total dose = 190 mg/kg), or vehicle over 7 days. No effect of low-dose rhIL-1ra was observed in study 1. High-dose rhIL-1ra significantly attenuated posttraumatic neuronal loss in the injured hippocampal CA3 region (P < 0.05), dentate hilus (P < 0.05), and cortex (P < 0.05) but impaired recovery of motor function at 7 days after trauma (P < 0.05). In study 2, rats were pretrained to learn a visuospatial task in a Morris water maze, subjected to fluid-percussion brain injury or sham treatment, and randomly assigned to receive multiple subcutaneous injections at timed intervals of 100 mg/kg rhIL-1ra (total dose = 900 mg/kg) or vehicle over 42 hours, followed by continuous infusion of a lower concentration of rhIL-1ra (20 mg/kg/day, total dose = 100 mg/kg), or vehicle for 5 days using subcutaneously implanted osmotic minipumps. Postinjury administration of rhIL-1ra significantly attenuated cognitive deficits compared with vehicle-treated animals at 42 hours (P < 0.05) but did not affect motor function at 48 hours, 1 week, and 2 weeks. These results suggest that inhibitors of cytokine pathways may be therapeutically useful for the treatment of brain trauma.

Diffusion-weighted magnetic resonance imaging confirms marked neuroprotective efficacy of albumin therapy in focal cerebral ischemia

BACKGROUND AND PURPOSE

We have recently shown high-dose human serum albumin therapy to confer marked histological protection in experimental middle cerebral artery occlusion (MCAo). We have now used diffusion-weighted magnetic resonance imaging (DWI) in conjunction with morphological methods to expand our understanding of this therapeutic approach.

METHODS

Physiologically controlled Sprague-Dawley rats received 2-hour MCAo by the modified intraluminal suture method. Treated rats received 25% human serum albumin solution (1% by body weight) immediately after the MCA was reopened. Vehicle-treated rats received saline. Computer-based image averaging was used to analyze DWI data obtained 24 hours after MCAo and light-microscopic histopathology obtained at 3 days. In a matched series, plasma osmolality and colloid oncotic pressure, as well as brain water content, were determined.

RESULTS

Albumin therapy, which lowered the hematocrit on average by 37% and raised plasma colloid oncotic pressure by 56%, improved the neurological score throughout the 3-day survival period. Within the ischemic focus, the apparent diffusion coefficient (ADC) computed from DWI data declined by 40% in vehicle-treated rats but was preserved at near-normal levels (8% decline) in albumin-treated rats (P<0.001). Albumin also led to higher ADC values within unlesioned brain regions. Histology revealed large consistent cortical and subcortical infarcts in vehicle-treated rats, while albumin therapy reduced infarct volume at these sites, on average, by 84% and 33%, respectively. Total infarct volume was reduced by 66% and brain swelling was virtually eliminated by albumin treatment. Microscopically, while infarcted regions of vehicle-treated rats had the typical changes of pannecrosis, infarcted zones of albumin-treated brains showed persistence of vascular endothelium and prominent microglial activation, suggesting that albumin therapy may help to preserve the neuropil within zones of residual infarction.

CONCLUSIONS

These findings confirm the striking neuroprotective efficacy of albumin therapy in focal cerebral ischemia and reveal that this effect is associated with DWI normalization and a mitigation of pannecrotic changes within zones of residual injury.

[The internal environment and intracranial hypertension]

Intracranial pressure depends on cerebral tissue volume, cerebrospinal fluid volume (CSFV) and cerebral blood volume (CBV). Physiologically, their sum is constant (Monro-Kelly equation) and ICP remains stable. When the blood brain barrier (BBB) is intact, the volume of cerebral tissue depends on the osmotic pressure gradient. When it is injured, water movements across the BBB depend on the hydrostatic pressure gradient. CBV depends essentially on cerebral blood flow (CBF), which is strongly regulated by cerebral vascular resistances. In experimental studies, a decrease in oncotic pressure does not increase cerebral oedema and intracranial hypertension (ICHT). On the other hand, plasma hypoosmolarity increases cerebral water content and therefore ICP, if the BBB is intact. If it is injured, neither hypoosmolarity nor hypooncotic pressure modify cerebral oedema. Therefore, all hypotonic solutes may aggravate cerebral oedema and are contra-indicated in case of ICHT. On the other hand, hypooncotic solutes do not modify ICP. The osmotic therapy is one of the most important therapeutic tools for acute ICHT. Mannitol remains the treatment of choice. It acts very quickly. An i.v. perfusion of 0.25 g.kg-1 is administered over 20 minutes when ICP increases. Hypertonic saline solutes act in the same way, however they are not more efficient than mannitol. CO2 is the strongest modulating factor of CBF. Hypocapnia, by inducing cerebral vasoconstriction, decreases CBF and CBV. Hyperventilation is an efficient and rapid means for decreasing ICP. However, it cannot be used systematically without an adapted monitoring, as hypocapnia may aggravate cerebral ischaemia. Hyperthermia is an aggravating factor for ICHT, whereas moderate hypothermia seems to be beneficial both for ICP and cerebral metabolism. Hyperglycaemia has no direct effect on cerebral volume, but it may aggravate ICHT by inducing cerebral lactic acidosis and cytotoxic oedemia. Therefore, infusion of glucose solutes is contra-indicated in the first 24 hours following head trauma and blood glucose concentration must be closely monitored and controlled during ICHT episodes.

Multiple-dose mannitol reduces brain water content in a rat model of cortical infarction

BACKGROUND AND PURPOSE

Repeated use of mannitol in the setting of ischemic infarction is a controversial and poorly defined therapeutic intervention. The purpose of this study was to examine the effects of repeated mannitol infusions on brain water content and tissue pressure in a well-defined rat model of focal ischemic stroke.

METHODS

Mannitol infusions (0.5, 1.5, or 2.5 g/kg) were given by intravenous bolus 4 or 24 hours after 90-minute transient cortical ischemia in the territory of the right middle cerebral artery in rats and every 4 hours thereafter for a total of 24 hours. Fluid replacement was limited to 0.5 mL i.v. isotonic saline administered immediately after each mannitol dose. Control rats received 0.5 mL i.v. saline at the same intervals and were otherwise under ad libitum conditions. Water contents (percent H2O) of whole hemispheres and of cortical biopsies were measured with the wet-dry method, and blood samples were analyzed for plasma osmolality and chemistries. In a subgroup of rats, tissue pressure was also measured within the hemisphere ipsilateral to the infarct.

RESULTS

Repeated mannitol infusions resulted in a dose-dependent increase in plasma osmolality and a dose-dependent decrease in the percent H2O of the ischemic middle cerebral artery cortex and ipsilateral hemisphere. In contrast, percent H2O of the contralateral cortex and hemisphere was significantly decreased only in the groups given the highest dose of mannitol (2.5 g/kg). Mannitol infusions at a dose of 1.5 g/kg begun 24 hours after reperfusion were also associated with a significant reduction of tissue pressure.

CONCLUSIONS

In a rat model of ischemic cortical infarction, repeated mannitol infusions resulted primarily in a decrease in the percent H2O of the infarct and ipsilateral hemisphere, as well as decreased tissue pressure.

The effect of mannitol on intracranial pressure in relation to serum osmolality in a cat model of cerebral edema

OBJECTIVE

To determine whether intravenous mannitol administration reduces intracranial pressure (ICP) in a cat model of brain edema by changing serum osmolality.

DESIGN

Prospective, controlled study.

SETTING

Pediatric intensive care unit laboratory in a university hospital.

INTERVENTIONS

Intraparenchymal ICP monitors were placed in 12 adult cats which subsequently underwent 60 min of continuous arteriovenous hemofiltration with countercurrent dialysis (CAVH-D), using sterile water with potassium chloride as a dialysate. The ultrafiltrate was replaced with a hypotonic solution causing a rapid reduction in serum osmolality while maintaining a euvolemic state. In six cats (control group) no further interventions were instituted, while in the six other cats (mannitol group) 1g/kg mannitol was administered intravenously immediately after CAVH-D had been discontinued. ICP was monitored continuously, and serum osmolality was determined at 15-min intervals during CAVH-D and for 30 min thereafter.

RESULTS

ICP increased significantly in both the control and mannitol groups during 60 min of CAVH-D. After CAVH-D, ICP was reduced in the mannitol group while ICP remained significantly higher in the control group. An inverse linear correlation was demonstrated between serum osmolality and ICP values in the control group throughout the experiment, as well as during the first 60 min in the mannitol group. However, no such correlation existed in the mannitol group after mannitol administration, as no significant changes in serum osmolality were observed while a marked reduction in ICP values occurred.

CONCLUSION

Mannitol is effective in reducing increased ICP in this model of euvolemic brain edema. However, 15 min after mannitol administration, no relationship between a continued decrease in ICP and a change in serum osmolality could be established. We postulate that the beneficial effect on ICP by mannitol outlasts its possible instantaneous and short-lived effect on serum osmolality.

Long-term high-colloid oncotic therapy for ischemic brain edema in gerbils

BACKGROUND AND PURPOSE

We evaluated the effects of long-term administration of high-colloid oncotic pressure on ischemic brain edema in Mongolian gerbils.

METHODS

Animals that exhibited stroke after 35 minutes of unilateral forebrain ischemia were used. The gerbils were divided into albumin- (1 g/kg body wt, 25% albumin; n = 30) and saline-injected (4 mL/kg; n = 30) groups. Both agents were administered intravenously every 12 hours starting immediately after the recirculation. Plasma colloid oncotic pressure, serum sodium and potassium concentrations, and brain water, sodium, and potassium content were measured 24, 48, and 72 hours after recirculation.

RESULTS

Plasma colloid oncotic pressure at 24, 48, and 72 hours after recirculation was significantly higher in the albumin- (26.1 +/- 2.3 mm Hg) than in the saline-treated group (18.5 +/- 1.9 mm Hg; P < .01), and brain water content of the ischemic hemisphere was significantly lower in the albumin group (79.5%, 80.2%, and 80.5%, respectively) than in the saline group (80.9%, 81.6%, and 82.1%, respectively; P < .05) at all three time points. Brain sodium content at 24 hours was significantly lower in the albumin than in the saline group (P < .05), while brain potassium content at 24 and 48 hours was significantly higher in the albumin than in the saline group (P < .05). The changes in brain water and sodium plus potassium content, which were calculated from differences between the ischemic and nonischemic hemispheres, showed a significant correlation in both groups (P < .01), but there was no significant difference between the linear regression lines for both groups.

CONCLUSIONS

Long-term high-colloid oncotic pressure was effective in treating ischemic brain edema, probably acting by diminishing the bulk flow through the disrupted blood-brain barrier and ameliorating the vasogenic edema.

Treatment of vasogenic brain edema with the novel Cl- transport inhibitor torasemide

The efficacy of the diuretic agent torasemide, which antagonizes the Na+/K+/Cl- cotransport and Cl- channels, was investigated to determine its inhibition of brain edema from a focal cerebral lesion. For this purpose, cold injury of the brain was induced in 50 Sprague-Dawley rats while monitoring arterial blood pressure. The brain was removed for gravimetric assessment of swelling of the traumatized hemisphere 24 h after trauma. The water content was also determined after drying the cerebral hemispheres for 24 h. Animals were divided into five groups. A control group with trauma received vehicle only; two other groups received 1.0 or 10.0 mg torasemide/kg body weight 30 minutes before and 6 h after trauma (n = 10-12). Administration of the drug after the insult was also investigated in animals with application of vehicle or 10.0 mg/kg of torasemide at 30 minutes and 6 h following the brain lesion (n = 8). Torasemide did not affect important physiologic variables, such as the arterial pO2, pCO2, pH, hemoglobin, hematocrit, or plasma osmolality, while increasing blood pressure (p < 0.01). The blood pressure response notwithstanding, treatment significantly attenuated hemispheric brain swelling from trauma. In control animals without treatment, cold injury led to hemispheric swelling of 8.89%. In animals with 1 mg torasemide/kg BW, brain swelling amounted to 8.51% and to 7.04% in animals receiving 10 mg/kg before and after the insult (p < 0.005). Treatment was also found to attenuate the increase in tissue water content from trauma, but without reaching statistical significance. Postinsult treatment with torasemide (10 mg/kg BW) at 30 minutes and 6 h after trauma was again associated with a significant reduction in hemispheric brain swelling, which in this group amounted to 7.46% compared with 9.76% in the untreated controls (p < 0.005). The increase in the cerebral water content from trauma was also significantly blunted in the latter experiments (p < 0.01). The present data indicate a remarkable therapeutic potential of the novel diuretic agent torasemide to reduce vasogenic brain edema from an acute cerebral lesion. It is surmised that the compound specifically interferes with Cl- transport mechanisms, which apparently are activated in edematous brain involving neuronal and glial cells, for example. This conclusion is supported by in vitro observations that torasemide inhibits the swelling of glial cells from acidosis. On the other hand, it is unlikely that gross dehydration of the brain secondary to the induction of diuresis by the agent played a role, because hematocrit and plasma osmolality were not found to be affected.

High colloid oncotic therapy for brain edema with cerebral hemorrhage

We examined the effectiveness of high colloid oncotic pressure (COP) therapy to suppress and/or reduce brain edema associated with putaminal hemorrhage of patients whose clinical grades were grade 3 or 4a classified according to the Japanese neurological grading for putaminal hemorrhage. In the treated group of 11 patients, 25% albumin solution was intravenously administered (50-100 ml/day) with additional use of furosemide (20-40 mg/day) following hematoma removal. The serum COP was maintained at 25-30 mmHg for 2 weeks. In the untreated group of 11 patients, the COP therapy was not applied following hematoma removal. The serum COP was 20-25 mmHg for 2 weeks thereafter. During the 2-week observation period, serum osmolality, electrolyte, and hematocrit levels did not significantly differ between the two groups. The midline structure shift on CT of the treated group was 4.5 mm, which was significantly smaller than that of the untreated group (p < 0.05). The numbers of patients either in the vegetative state or death were 0 and 3, respectively, in the treated and the untreated groups. We concluded that high COP therapy for 2 weeks following hematoma removal was effective to suppress and/or reduce brain edema associated with putaminal hemorrhage, and that this therapy could be continued for 2 weeks without systemic complications.

Therapeutical efficacy of a novel chloride transport blocker and an IP3-analogue in vasogenic brain edema

The efficacy of torasemide, a novel chloride-channel blocker, and of PP56, an IP3 analogue, was currently examined in experimental brain edema. Following trephination in anesthesia rats were subjected to a focal cold injury of the left cerebral hemisphere. Animals of 4 experimental groups receiving either torasemide (i.v. at 30 min before and 6 h after lesion) or PP56 (continuous infusion beginning at 30 min before until 24 h after lesion) at two dose levels were compared with controls administered with i.v. saline. 24 h after trauma the brain was removed from the skull, and the hemispheres were separated in the median plane for gravimetric assessment of hemispheric swelling. Hct, blood gases and body temperature remained constant in all groups. Blood pressure was found to increase in a dose-dependent manner in animals with torasemide. No significant reduction of brain swelling was found in animals with low-dose torasemide (8.51 +/- 0.63%) or low- (7.91 +/- 0.60) and high-dose PP56 (6.85 +/- 1.05%) as compared to the untreated controls. Brain swelling, however, was significantly attenuated by high-dose torasemide to 7.04 +/- 0.36%, as compared to 8.89 +/- 0.29% of the untreated group (p < 0.005). It is currently studied whether torasemide reduces brain swelling when given after the insult.

High colloid oncotic therapy for contusional brain edema

We investigated whether prolonged high colloid oncotic therapy for two weeks can suppress contusional brain edema. Eighteen patients with cerebral contusion were randomly divided into two groups of patients receiving high oncotic pressure (HOP; 26-30 mmHg) treatment and those receiving normal oncotic pressure (NOP; 22-26 mmHg) treatment. Oncotic pressure was maintained for two weeks with administration of a 25% albumin solution with additional use of furosemide. Edema volume was calculated by summation of all measured low-density areas in each CT slice multiplied by 1.0 cm of slice of thickness. We expressed contusional brain edema volume as a percent increase based on each patient's initial CT. The mean percent increase of contusional brain edema in the NOP group was significantly higher than that in the HOP group at 9-15 days (208.9% and 14.0%, respectively) and 16-25 days (188.8% and 10.0%, respectively). There were no complications such as heart failure or renal failure during treatment. All the patients in the HOP group recovered with minimal or no neurological deficit. On the other hand, 30% of patients in the NOP group remained in poor condition. With frequent measurement of oncotic pressure and adjustment of fluids and electrolytes, continuous oncotic therapy for two weeks effectively and safely reduced contusional brain edema.

Effects of retrograde perfusion of the brain with combined drug therapy after focal ischemia in rat brain

BACKGROUND AND PURPOSE

The ischemic edema associated with blood-brain barrier permeability changes and the excess production of free radicals are serious complications in prolonged cerebral ischemia. We examined the efficacy of transvenous perfusion of the brain, starting treatment 5 hours after occlusion of the middle cerebral artery for a period of 2 hours in rats with the combined agents mannitol (10 ml/2 hr) and dexamethasone (1 mg/2 hr) to counter edema and verapamil (0.05 mg/kg/2 hr) for vasodilation.

METHODS

In experiment 1, blood-brain barrier permeability changes were examined in five groups with six rats each: group C rats underwent 7 hours of middle cerebral artery occlusion with no treatment; group V, treatment with verapamil alone; group VD, treatment with verapamil and dexamethasone; group VM, treatment with verapamil and mannitol; and group VDM, treatment with verapamil, dexamethasone, and mannitol. In experiment 2, we examined local cerebral blood flow, ischemic tissue damage volume, and water content of cerebral hemispheres in two groups of 16 rats each subjected to the same treatment as groups C and VDM rats in experiment 1.

RESULTS

There was a significant reduction of blood-brain barrier permeability changes in the ischemic cortex of rats in group VDM compared with rats in the other groups. In the group undergoing transvenous perfusion of the brain with the three combined agents, there was a significant improvement of cerebral blood flow (39-58%, p < 0.05) in the ischemic cortex and reduction of ischemic cerebral damage volume (22%, p < 0.01) and water content of the ischemic hemisphere (p < 0.05) compared with the control group.

CONCLUSIONS

The therapeutic approach using combined agents is effective treatment when initiated within 5 hours of focal cerebral ischemia in rats.

Aggravation of vasogenic cerebral edema by multiple-dose mannitol

The authors investigated the pharmacokinetics of mannitol administered for treatment of vasogenic cerebral edema. A cortical cold injury was produced in 23 cats maintained under general anesthesia for 5 or 21 hours. Control animals received no mannitol, while treatment groups received either a single dose or five doses administered at 4-hour intervals of 0.33 gm/kg radiolabeled mannitol. Liquid scintillation counting was carried out to determine the concentrations of mannitol in the cerebral tissue, cerebrospinal fluid, plasma, and urine. Cerebral water content and linear progression of edema were also measured. Rapid plasma clearance prevented accumulation of mannitol after multiple intravenous injections, as 84% +/- 2% (mean +/- standard error of the mean) of the infused mannitol was excreted through the urine. However, there was progressive accumulation of mannitol within the cerebral tissue, especially in the edematous white matter where it reached a level of 0.33 +/- 0.03 mg/gm after five doses, exceeding the trough plasma concentrations by a ratio of 2.69:1. Water content measurement showed that a single dose of mannitol failed to reduce cerebral water content or edema progression at 4 hours postinjection, while multiple doses produced a 3% increase in water content in edematous regions (p greater than 0.0003). The results of this study demonstrated a reversal of the osmotic concentration gradient between edematous brain and plasma following multiple mannitol injections, associated with exacerbation of vasogenic cerebral edema.

Intensive management of severe head injury

Intensive management of patients with severe head injury offers the best hope of minimizing death and functional disability in a young, working population. Secondary neurologic insult can be decreased by cardiorespiratory support and ICP control from the outset. Rapid neurologic assessment, airway management, and support of circulation are the basis of emergency management for head injury. Patients with severe head injury require intensive care management for two major reasons: management of ICP and management of organ system dysfunction. Care should not be withheld because of initially grim (and inaccurate) prognostic assessment. Newer techniques for assessing the adequacy of cerebral circulation may allow refinement of management strategies in the future.

Toxicology of selected pesticides, drugs, and chemicals. Anticoagulant, cholecalciferol, and bromethalin-based rodenticides

The control of rodent pests is a continuing goal of mankind. To this end, a multitude of rodenticides have been produced, each designed to kill rodents by exerting their toxic effects on various body systems. As examples, veterinarians have had to manage companion animal poisonings due to anticoagulant, sodium fluoroacetate (compound 1080), thallium, barium carbonate, and zinc phosphide-based rodenticides. Many of these rodenticides were introduced because of their anticipated safety in relation to nontarget species; unfortunately, this has not been the case. Veterinarians must attempt to identify the specific rodenticide involved in poisoning cases. Therapeutic success in these poisonings is often more dependent upon symptomatic and supportive care rather than the use of antidotal therapy.

Magnetic resonance studies in human brain oedema following administration of hyperosmotic agents. Special references to relaxation times and proton MRS

Changes of proton relaxation times (T1 and T2) and proton Magnetic Resonance Spectroscopy (MRS) were studied in patients with brain oedema following administration of hyperosmotic agents. Relaxation times of oedema tended to decrease following infusion of hyperosmotic agents. In most patients examined, changes of relaxation times tended to achieve their lowest value at 30-60 minutes after infusion. However, the changes of relaxation times were not uniform. In some patients, relaxation times continued to decrease for more than 2 hours, while in other patients relaxation times which had earlier decreased subsequently had increased at 2 hours. The peak of water components, obtained by SIDAC (Spectroscopic Imaging by Dephasing Amplitude Changing) method was observed to change as did relaxation times. Changes of relaxation times and the peak of water components, obtained by SIDAC (Spectroscopic Imaging by Dephasing Amplitude Changing) method was observed to change as did relaxation times. Changes of relaxation times and the peak of water component may vary depending upon factors including the kinds of lesions causing oedema, phase of oedema (acute or chronic), etc. Proton relaxation times and the peak of water component obtained by proton MRS were useful in evaluating the changes of oedematous area.

The ambivalent effects of early and late administration of mannitol in cold-induced brain oedema

This study was undertaken in order to determine whether early administration of mannitol is different from late administration in its effect on brain oedema. Cold-induced brain oedema, which was confirmed by high resolution CT scan, was produced in 2 groups of cats. In group one mannitol was given early (90 minutes after injury); in group two 3-4 hours after the injury (late). Repeated CT scans following mannitol administration showed that the early group exhibited significantly greater dehydration (p less than 0.0001) while the late group showed significant hydration, in the lesioned hemisphere. The contralateral control hemisphere responded to mannitol with similar dehydration effect in both groups.

The risk of ischaemic brain damage during the use of self-retaining brain retractors

Self-retaining brain retractors (SRBR) are commonly used during intracranial surgery and they are indispensable during microneurosurgery. To evaluate limitations in the employment of SRBR, as well animal as human studies have been performed. In the animal studies, male Wistar rats were used for measurements of regional cerebral blood flow (rCBF) changes during brain retractor pressure (BRP) provided by lead weights. These weights, corresponding to different levels of mm Hg, were applicated for different periods of time on the parietal cortex after craniotomy. In one part of the animal studies different profiles of the application surface of the weights were evaluated. For measurement of the rCBF (n = 41) autoradiography with carbon-14(14C)iodoantipyrine was used as described by Gjedde et al (1980). A neuropathological method (n = 30) was used to reveal possible brain damage after graded BRP. In the rats the thresholds of rCBF, regional cerebral perfusion pressure (rCPP) and time were 20-25 ml/100 g/min, 20 mm Hg and 7-10 minutes respectively. In the human studies only alert patients without neurological deficits (except defects of the visual fields) and in whom preoperative CT-scans did not disclose any sign of infarction were included. BRP beneath as well the tip as the centre of the SRBR and the MABP were recorded continuously. Patients with peroperative complications were excluded. During the operations induced hypotension (n = 20) and mannitol (n = 6) were administrated. The patients (n = 23) had a 3-month follow-up examination. In man the thresholds of rCPP and time were found to be 10 mm Hg and 6-8 minutes, respectively. Other authors have found a rCBF threshold of 10-13 ml/100 g/min (Astrup 1982, Iannotti & Hoff 1983). It is concluded that the results obtained in the rat studies are comparable to the human situation if reservations are made concerning the differences in the thresholds of rCBF and rCPP. The time threshold of cerebral ischaemia seems to be rather equal in rat and in man. If these thresholds are reached, intermittent BRP is absolutely recommendable. It was also found that the most easily-handled retractors, those with a flat profile, did not decrease the rCBF further than other types of retractors.

Traumatic shock and head injury: effects of fluid resuscitation on the brain

The effects of resuscitation of traumatic-hemorrhagic shock on the brain are unknown. Traumatic shock in sheep (fracture/crush injury, 2-hr hemorrhage to 40 mm Hg) was followed by resuscitation to baseline mean arterial pressure. Two groups without brain injury were resuscitated with lactated Ringer's (LR1, n = 7) or albumin (ALB1, n = 6). Focal brain injury was added in two further groups (LR2, n = 6; ALB2, n = 6). Hemodynamics, intracranial pressure (ICP), EEG, and colloid osmotic pressure (COP) were followed. Brain water (BW) and cerebral blood volume (CBV) were compared to those of controls (C, n = 7).

RESULTS

ICP rose in all groups. Animals without brain injury did not have increased brain water. Below are results for brain-injured animals after resuscitation (mean +/- SEM). (table; see text) Maintaining COP during initial resuscitation does not minimize cerebral edema: the effects of LR and ALB were similar in this setting. Focal brain injury causes edema but does not cause large increases in ICP with initial resuscitation.

Effect of mannitol, nimodipine, and indomethacin singly or in combination on cerebral ischemia in rats

The effects of mannitol, nimodipine, and indomethacin on ischemic neuronal injury were examined in 45 rats divided equally into nine groups subjected to 10 minutes of forebrain ischemia. Of two control groups, one received maintenance fluids while the other received a normal saline bolus. In the remaining seven groups, mannitol, nimodipine, and indomethacin were administered singly or in combination 5 minutes before forebrain ischemia. Seven days after ischemia, the brains were perfusion-fixed, sectioned coronally into 2.8-mm slices, and stained with hematoxylin and eosin. Ischemic neurons were directly counted on predetermined regions of standardized serial sections. Considerable amelioration of ischemic injury (ischemic neurons/total neurons) was observed with mannitol (ischemic injury, 7 +/- 5% in the hippocampal CA1/CA2 sectors and 28 +/- 17% in the CA3 sector). This is in contrast to control values of 64 +/- 11% and 80 +/- 6%, respectively, and those obtained in the normal saline group of 70 +/- 10% and 59 +/- 13%, respectively. The beneficial effect with nimodipine reached significance in only the hippocampal CA3 sector (ischemic injury, 35 +/- 21%). Indomethacin showed no significant benefit. Combining the agents resulted in significantly reduced neuronal injury compared with control groups, although the effect was not greater than that achieved with mannitol alone. The degree of ischemic injury was least when all three agents were used in combination (ischemic injury, 12 +/- 12% in the hippocampal CA1/CA2 sectors and 4 +/- 4% in the CA3 sector). Our data support the concept that successfully blocking the ischemic cascade with a single, diversely acting agent or multiple agents will evoke the best beneficial response.

Treatment of resistant intracranial hypertension with hypertonic saline. Report of two cases

The authors describe two patients with traumatic cerebral edema and intracranial hypertension in whom the continued use of mannitol and furosemide resulted in a progressive lessening of the effect of these agents on the intracranial pressure (ICP) and caused prerenal failure. Intravenous administration of hypertonic saline (50 ml and 20 ml of a 5-mmol/ml saline solution over 10 minutes in Cases 1 and 2, respectively) produced a prolonged reduction in the ICP and improved renal function in both cases. It is suggested that if a reduction in ICP without diuresis is required in patients with traumatic cerebral edema, treatment with intravenous hypertonic saline should be considered.

Effect on intracranial pressure of furosemide combined with varying doses and administration rates of mannitol

The first part of this study investigated the combined use of furosemide and mannitol in the treatment of elevated intracranial pressure (ICP). Two groups of dogs were studied to determine if renal excretion of mannitol was altered in the presence of furosemide. No significant difference in excretion was noted between the two groups. Fifteen animals were used in other studies to identify the most advantageous sequence of administration of furosemide and mannitol. Infusion of mannitol followed by furosemide 15 minutes later resulted in the most profound and sustained ICP reduction. The effect on ICP reduction of varying the mannitol dose was observed in studies using single doses of 0.5 gm/kg, 0.75 gm/kg, and 1 gm/kg. The larger mannitol dose, resulting in a greater blood-brain osmotic gradient, proved to be the most efficacious in ICP reduction. A further 15 animals were used in investigations to determine whether changing the rate of delivery of the most effective mannitol dose (1 gm/kg) influenced resultant ICP reduction. The results indicated that rapid administration (2 ml/kg/min) produced higher peak serum concentrations of mannitol and more profound lowering of ICP than the same dose delivered at slower rates.

Protection from ischemia-induced cerebral edema in the rat by U-50488H, a kappa opioid receptor agonist

U-50488 is a specific kappa opioid agonist which produces in rats water diuresis resulting in an elevation of plasma osmolarity. Pretreatment with U-50488H (the methanesulfonate salt) in Fisher rats prior to 4 h of bilateral carotid occlusion prevented the development of edema in the forebrain, and the effect was greater than that from pentobarbital anesthesia. An additional injection of an antidiuretic hormone which prevented the plasma hyperosmolarity also significantly reduced the anticerebral edemic effects of U-50488H. The plasma osmotic effect, however, may not completely account for the ischemic protection produced by U-50488H.

Effects of rapid mannitol infusion on cerebral blood volume. A positron emission tomographic study in dogs and man

Positron emission tomography was used to study the effect of a rapid infusion of mannitol on cerebral blood volume (CBV) in five dogs and in three human subjects. The ability of mannitol to reduce intracranial pressure (ICP) has always been attributed to its osmotic dehydrating effect. The effects of mannitol infusion include increased osmolality, total blood volume, central venous pressure (CVP), and cerebral blood flow, and decreased hematocrit, hemoglobin concentration, serum sodium level, and viscosity. Mannitol's ability to dilate the cerebral vasculature, either directly or indirectly, and thus to transiently increase ICP, is a subject of controversy. By in vivo labeling of red cells with carbon-11, the authors were able to demonstrate an early increase in CBV in dogs of 20%, 27%, and 23% (mean increase, p less than 0.05) at 1, 2, and 3 minutes, respectively, after an infusion of 20% mannitol (2 gm/kg over a 3-minute period). The animals' muscle blood volume increased by 27% (mean increase, p less than 0.05) 2 minutes after infusion. In the human subjects, lower doses and a longer duration of infusion (1 gm/kg over 4 minutes) resulted in an increase in CBV of 8%, 14% (p less than 0.05), and 10% at 1, 2, and 3 minutes, respectively, after infusion. In dogs, ICP increased by 4 mm Hg (mean increase, p less than 0.05) 1 minute after the infusion, before decreasing sharply. The ICP was not measured in the human subjects. Hematocrit, hemoglobin, sodium, potassium, osmolality, heart rate, mean arterial pressure (MAP), and CVP were measured serially. Results of these measurements, as well as the significant decrease in MAP that occurred after mannitol infusion, are discussed. This study demonstrated that rapid mannitol infusion increases CBV and ICP. The increase in muscle blood volume, in the presence of a decreased MAP and an adequate CVP, suggests that mannitol may have caused vasodilation in these experiments.

The effects of rapid infusions of saline and mannitol on cerebral blood volume and intracranial pressure in dogs

The role of osmotic brain dehydration in the early reduction of intracranial pressure (ICP) following mannitol administration has recently been questioned and a decrease in cerebral blood volume (CBV) proposed as the mechanism of action. To evaluate this hypothesis, relative CBV changes before and after mannitol infusion were determined by collimated gamma counting across the biparietal diameter of the exposed skull in six dogs. Red blood cells were labelled with chromium-51. Cerebral blood volume (CBV), total blood volume (TBV), ICP, mean arterial pressure (MAP), central venous pressure (CVP), haematocrit and osmolality were serially measured after infusions of 10 ml X kg-1 of normal saline (control study) and of 20 per cent mannitol (mannitol study). The solutions were administered over a two-minute period; a 30-minute equilibration period intervened between the saline and mannitol infusions. We demonstrated that the mannitol infusion was associated with significant increases in relative CBV (25 per cent), ICP (7 mmHg), CVP (11 cm H2O), and TBV (50 per cent). MAP declined significantly (14 per cent) after mannitol infusion. The administration of saline, although associated with an increase in TBV (18 per cent), was not associated with any significant change in CBV, ICP, MAP or CVP. The increase in relative CBV persisted for 15 minutes after mannitol infusion, while the ICP returned to control within five minutes and continued to decrease. This study supports the fact that after rapid mannitol infusion, ICP begins to decrease only once the dehydrating effect has counteracted the increase in brain bulk caused by the increase in cerebral blood volume.