Effect of small-volume resuscitation on intracranial pressure and related cerebral variables

Improving on Laboratory Traumatic Brain Injury Models to Achieve Better Results

Experimental modeling of traumatic brain injury (TBI) in animals has identified several potential means and interventions that might have beneficial applications for treating traumatic brain injury clinically. Several of these interventions have been applied and tried with humans that are at different phases of testing (completed, prematurely terminated and others in progress). The promising results achieved in the laboratory with animal models have not been replicated with human trails as expected. This review will highlight some insights and significance attained via laboratory animal modeling of TBI as well as factors that require incorporation into the experimental studies that could help in translating results from laboratory to the bedside. Major progress has been made due to laboratory studies; in explaining the mechanisms as well as pathophysiological features of brain damage after TBI. Attempts to intervene in the cascade of events occurring after TBI all rely heavily on the knowledge from basic laboratory investigations. In looking to discover treatment, this review will endeavor to sight and state some central discrepancies between laboratory models and clinical scenarios.

The role of hypertonic saline dextran in trauma resuscitation

Modern trauma management has recognized the importance of using conservative fluid resuscitation regimes in order to prevent complications from fluid overload arising. Hypertonic/hyperoncotic fluids appear to provide an ideal means of facilitating this, requiring only small volumes to rapidly elevate blood pressure. Hypertonic saline dextran (HSD) was introduced in 1985 but its take up has been slow, a large part of this has been due to the lack of human trials and concerns about complications.

The current evidence has been reviewed and it is clear that HSD is an efficient means of correcting hypotension, doing so mainly by the mobilizing endogenous water. It is becoming apparent that early administration has the potential to modulate the inflammatory cascade in patients at risk of developing adult respiratory distress syndrome (ARDS) and multiorgan failure. This is reflected in the handful of human trials that show a trend towards increased survival (particularly for head injuries) and a possible reduction in ARDS. The side effect profile appears to be good, even in the presence of dehydration or penetrating trauma.

Published human trials have methodological problems and lack of power of study this has led to a reliance on animal studies. Clearly there is great potential, but before large-scale prehospital usage can be justified further well-conducted randomized human trials are needed.

Effect of a hypertonic balanced ketone solution on plasma, CSF and brain beta-hydroxybutyrate levels and acid-base status

PURPOSE

Although glucose is the main source of energy for the human brain, ketones play an important role during starvation or injury. The purpose of our study was to investigate the metabolic effects of a novel hypertonic sodium ketone solution in normal animals.

METHODS

Adult Sprague-Dawley rats (420-570 g) were divided into three groups of five, one control and two study arms. The control group received an intravenous infusion of 3 % NaCl at 5 ml/kg/h. The animals in the two study arms were assigned to receive one of the two formulations of ketone solutions, containing hypertonic saline with 40 and 120 mmol/l beta-hydroxybutyrate, respectively. This was infused for 6 h and then the animal was euthanized and brains removed and frozen.

RESULTS

Both blood and cerebrospinal fluid (CSF) levels of beta-hydroxybutyrate (BHB) demonstrated strong evidence of a change over time (p < 0.0001). There was also strong evidence of a difference between groups (p < 0.0001). Multiple comparisons showed all these means were statistically different (p < 0.05). Measurement of BHB levels in brain tissue found strong evidence of a difference between groups (p < 0.0001) with control: 0.15 mmol/l (0.01), BHB 40: 0.19 mmol/l (0.01), and BHB 120: 0.28 mmol/l (0.01). Multiple comparisons showed all these means were statistically different (p < 0.05). There were no differences over time (p = 0.31) or between groups (p = 0.33) or an interaction between groups and time (p = 0.47) for base excess.

CONCLUSION

The IV infusions of hypertonic saline/BHB are feasible and lead to increased plasma, CSF and brain levels of BHB without significant acid/base effects.

Hyperosmolar therapy for intracranial hypertension

The use of hyperosmolar agents for intracranial hypertension was introduced in the early 20th century and remains a mainstay of therapy for patients with cerebral edema. Both animal and human studies have demonstrated the efficacy of two hyperosmolar agents, mannitol and hypertonic saline, in reducing intracranial pressure via volume redistribution, plasma expansion, rheologic modifications, and anti-inflammatory effects. However, because of physician and institutional variation in therapeutic practices, lack of standardized protocols for initiation and administration of therapy, patient heterogeneity, and a paucity of randomized controlled trials have yielded little class I evidence on which clinical decisions can be based, most current evidence regarding the use of hyperosmolar therapy is derived from retrospective analyses (class III) and case series (class IV). In this review, we summarize the available evidence regarding the use of hyperosmolar therapy with mannitol or hypertonic saline for the medical management of intracranial hypertension and present a comprehensive discussion of the evidence associated with various theoretical and practical concerns related to initiation, dosage, and monitoring of therapy.

Clinical review: ketones and brain injury

Although much feared by clinicians, the ability to produce ketones has allowed humans to withstand prolonged periods of starvation. At such times, ketones can supply up to 50% of basal energy requirements. More interesting, however, is the fact that ketones can provide as much as 70% of the brain's energy needs, more efficiently than glucose. Studies suggest that during times of acute brain injury, cerebral uptake of ketones increases significantly. Researchers have thus attempted to attenuate the effects of cerebral injury by administering ketones exogenously. Hypertonic saline is commonly utilized for management of intracranial hypertension following cerebral injury. A solution containing both hypertonic saline and ketones may prove ideal for managing the dual problems of refractory intracranial hypertension and low cerebral energy levels. The purpose of the present review is to explore the physiology of ketone body utilization by the brain in health and in a variety of neurological conditions, and to discuss the potential for ketone supplementation as a therapeutic option in traumatic brain injury.

Hemorrhagic shock after experimental traumatic brain injury in mice: effect on neuronal death

Traumatic brain injury (TBI) from blast injury is often complicated by hemorrhagic shock (HS) in victims of terrorist attacks. Most studies of HS after experimental TBI have focused on intracranial pressure; few have explored the effect of HS on neuronal death after TBI, and none have been done in mice. We hypothesized that neuronal death in CA1 hippocampus would be exacerbated by HS after experimental TBI. C57BL6J male mice were anesthetized with isoflurane, mean arterial blood pressure (MAP) was monitored, and controlled cortical impact (CCI) delivered to the left parietal cortex followed by continued anesthesia (CCI-only), or either 60 or 90 min of volume-controlled HS. Parallel 60- or 90-min HS-only groups were also studied. After HS (+/-CCI), 6% hetastarch was used targeting MAP of > or =50 mm Hg during a 30-min Pre-Hospital resuscitation phase. Then, shed blood was re-infused, and hetastarch was given targeting MAP of > or =60 mm Hg during a 30-min Definitive Care phase. Neurological injury was evaluated at 24 h (fluorojade C) or 7 days (CA1 and CA3 hippocampal neuron counts). HS reduced MAP to 30-40 mm Hg in all groups, p < 0.05 versus CCI-only. Ipsilateral CA1 neuron counts in the 90-min CCI+HS group were reduced at 16.5 +/- 14.1 versus 30.8 +/- 6.8, 32.3 +/- 7.6, 30.6 +/- 2.2, 28.1 +/- 2.2 neurons/100 mum in CCI-only, 60-min HS-only, 90-min HS-only, and 60-min CCI+HS, respectively, all p < 0.05. CA3 neuron counts did not differ between groups. Fluorojade C staining confirmed neurodegeneration in CA1 in the 90-min CCI+HS group. Our data suggest a critical time window for exacerbation of neuronal death by HS after CCI and may have implications for blast injury victims in austere environments where definitive management is delayed.

Hypertonic saline: a clinical review

Literature suggest that hypertonic saline (HTS) solution with sodium chloride concentration greater than the physiologic 0.9% can be useful in controlling elevated intracranial pressure (ICP) and as a resuscitative agent in multiple settings including traumatic brain injury (TBI). In this review, we discuss HTS mechanisms of action, adverse effects, and current clinical studies. Studies show that HTS administered during the resuscitation of patients with a TBI improves neurological outcome. HTS also has positive effects on elevated ICP from multiple etiologies, and for shock resuscitation. However, a prospective randomized Australian study using an aggressive resuscitation protocol in trauma patients showed no difference in amount of fluids administered during prehospital resuscitation, and no differences in ICP control or neurological outcome. The role of HTS in prehospital resuscitation is yet to be determined. The most important factor in improving outcomes may be prevention of hypotension and preservation of cerebral blood flow. In regards to control of elevated ICP during the inpatient course, HTS appears safe and effective. Although clinicians currently use HTS with some success, significant questions remain as to the dose and manner of HTS infusion. Direct protocol comparisons should be performed to improve and standardize patient care.

EFFECTS OF HYPERTONIC ARGININE ON CEREBRAL BLOOD FLOW AND INTRACRANIAL PRESSURE AFTER TRAUMATIC BRAIN INJURY COMBINED WITH HEMORRHAGIC HYPOTENSION

Hypertonic saline solutions improve cerebral blood flow (CBF) when used for acute resuscitation from hemorrhagic hypotension accompanying some models of traumatic brain injury (TBI); however, the duration of increased CBF is brief. Because the nitric oxide synthase substrate l-arginine provides prolonged improvement in CBF after TBI, we investigated whether a hypertonic resuscitation fluid containing l-arginine would improve CBF in comparison to hypertonic saline without l-arginine in a model of moderate, paramedian, fluid-percussion TBI followed immediately by hemorrhagic hypotension (mean arterial pressure [MAP] = 60 mm Hg for 45 min). Sprague-Dawley rats were anesthetized with 4.0% isoflurane, intubated and ventilated with 1.5%-2.0% isoflurane in oxygen/air (50:50). After preparation for TBI and measurement of CBF using laser Doppler flowmetry and measurement of intracranial pressure (ICP) using an implanted transducer, rats were subjected to moderate (2.0 atm) TBI, hemorrhaged for 45 min, and randomly assigned to receive an infusion of hypertonic saline (7.5%, 2,400 mOsm total; 6 mL/kg; n = 6) or hypertonic saline with 50, 100, or 300 mg/kg L-arginine (2,400 mOsm; 6 mL/kg; n = 6 in each of the three dose groups) and then monitored for 120 min after the end of infusion. CBF was measured continuously and calculated as a percent of the pre-TBI baseline during the hemorrhage period, after reinfusion of one of the hypertonic arginine solutions, and 30, 60, and 120 min after reinfusion. All four hypertonic solutions initially improved MAP, which, by 120 min after infusion, had decreased nearly to the levels observed during hemorrhage. ICP remained below baseline levels during resuscitation in all groups, although ICP was slightly greater (P = NS) than baseline in the hypertonic saline group. CBF increased similarly in all groups during infusion and then decreased similarly in all groups. At 120 min after infusion, CBF was highest in the group infused with hypertonic saline, but the difference was not significant. We conclude that the improvement of MAP, ICP, and CBF produced by hypertonic saline alone after TBI and hemorrhagic hypotension is not significantly enhanced by the addition of L-arginine at these doses.

The Use of Hypertonic Saline for Treating Intracranial Hypertension After Traumatic Brain Injury

The past decade has witnessed a resurgence of interest in the use of hypertonic saline for low-volume resuscitation after trauma. Preliminary studies suggested that benefits are limited to a subgroup of trauma patients with brain injury, but a recent study of prehospital administration of hypertonic saline to patients with traumatic brain injury failed to confirm a benefit. Animal and human studies have demonstrated that hypertonic saline has clinically desirable physiological effects on cerebral blood flow, intracranial pressure, and inflammatory responses in models of neurotrauma. There are few clinical studies in traumatic brain injury with patient survival as an end point. In this review, we examined the experimental and clinical knowledge of hypertonic saline as an osmotherapeutic agent in neurotrauma.

Ketamine for rapid sequence induction in patients with head injury in the emergency department

OBJECTIVE

To examine the evidence regarding the use of ketamine for induction of anaesthesia in patients with head injury in the ED.

METHOD

A literature review using the key words ketamine, head injury and intracranial pressure.

RESULTS

Advice from early literature guiding against the use of ketamine in head injury has been met with widespread acceptance, as reflected by current practice. That evidence is conflicting and inconclusive in regards to the safety of using ketamine in head injury. A review of the literature to date suggests that ketamine could be a safe and useful addition to our available treatment modalities. The key to this argument rests on specific pharmacological properties of ketamine, and their effects on the cerebral haemodynamics and cellular physiology of brain tissue that has been exposed to traumatic injury.

CONCLUSION

In the modern acute management of head-injured patients, ketamine might be a suitable agent for induction of anaesthesia, particularly in those patients with potential cardiovascular instability.

A Pig Model with Secondary Increase of Intracranial Pressure after Severe Traumatic Brain Injury and Temporary Blood Loss

There is a lack of animal models of traumatic brain injury (TBI) that adequately simulate the longterm changes in intracranial pressure (ICP) increase following clinical TBI. We therefore reproduced the clinical scenario in an animal model of TBI and studied long-term postinjury changes in ICP and indices of brain injury. After induction of anesthesia, juvenile piglets were randomly traumatized using fluid-percussion injury (FPI) to induce either moderate (mTBI = 6 pigs: 3.2 +/- 0.6 atm) or severe (sTBI = 7 pigs: 4.1 +/- 1.0 atm) TBI. Injury was followed by a 30% withdrawal of blood volume. ICP and systemic hemodynamic were monitored continuously. Repeated measurements of global cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMRO2) were performed at baseline, at the end of blood withdrawal, after volume replacement, and at 8 and 24 h postinjury. Histological and immunocytochemical studies have also performed. ICP peaked immediately following FPI (mTBI: 33 +/- 16 mm Hg; sTBI: 47 +/- 14 mm Hg, p < 0.05) in both groups. In the sTBI group, we noted a second peak at 5 +/- 1.5 h postinjury. This second ICP peak was accompanied by a 50% reduction in CBF (44 +/- 31 mL . min . 100 g(-1)) and CMRO(2) (2.5 +/- 2.0 mL . min . 100 g(1)). Moderate TBI typically resulted in focal pathological change whereas sTBI caused more diffuse change, particularly in terms of the ensuing axonal damage. We thus describe an animal model of severe TBI with a reproducible secondary ICP increase accompanied by patterns of diffuse brain damage. This model may be helpful in the study of pathogenetic relevance of concomitant affections and verify new therapeutic approaches in severe TBI.

The next generation in shock resuscitation

Resuscitation of the severely injured patient who presents in shock has improved greatly, following focused wartime experience and insight from laboratory and clinical studies. Further benefit is probable from technologies that are being brought into clinical use, especially hypertonic saline dextran, haemoglobin-based oxygen carriers, less invasive early monitors, and medical informatics. These technologies could improve the potential of prehospital and early hospital care to pre-empt or more rapidly reverse hypoxaemia, hypovolaemia, and onset of shock. Damage control surgery and definitive interventional radiology will probably combine with more real-time detection and intervention for hypothermia, coagulopathy, and acidosis, to avoid extreme pathophysiology and the "bloody vicious cycle". Although now widely practised as standard of care in the USA and Europe, shock resuscitation strategies involving haemoglobin replacement and fluid volume loading to regain tissue perfusion and oxygenation vary between trauma centres. One of the difficulties is the scarcity of published evidence for or against seemingly basic intervention strategies, such as early or large-volume fluid loading. Standardised protocols for resuscitation, representing the best and most current knowledge of the clinical process, could be devised and widely implemented as interactive computerised applications among trauma centres in the USA and Europe. Prevention of injury is preferable and feasible, but early care of the severely injured patient and modulation of exaggerated systemic inflammatory response due to transfusion and other complications of traditional strategies will probably provide the next generation of improvements in shock resuscitation.

Cerebral Perfusion Pressure Elevation with Oxygen-Carrying Pressor after Traumatic Brain Injury and Hypotension in Swine

BACKGROUND

Previously, we had shown that elevation of cerebral perfusion pressure, using pressors, improved short-term outcomes after traumatic brain injury and hemorrhagic shock in swine. The current study evaluates outcomes after resuscitation with diaspirin cross-linked hemoglobin (DCLHb)--a hemoglobin-based oxygen carrier with pressor activity--in the same swine model of traumatic brain injury and hemorrhagic shock.

METHODS

Anesthetized and ventilated swine received traumatic brain injury via cortical fluid percussion (6-8 atm) followed by 45% blood volume hemorrhage. One hour later, animals were randomized to either a control group (SAL) resuscitated with normal saline equal to three times shed blood volume or to one of two experimental groups resuscitated with DCLHb. The two experimental groups consisted of a low-dose group, resuscitated with 250 mL of DCLHb (Hb1), and a high-dose group, resuscitated with 500 mL of DCLHb (Hb2). Animals were observed for 210 minutes postresuscitation. Outcomes evaluated were cerebral oxygenation by measuring partial pressure and saturation of oxygen in cerebrovenous blood; cerebral function by evaluating the preservation and magnitude of cerebrovascular carbon dioxide reactivity; and brain structural damage by semiquantitatively assessing beta amyloid precursor protein positive axons.

RESULTS

Postresuscitation, cerebral perfusion pressure was higher in the DCLHb groups (p < 0.05, Hb1 and Hb2 vs. SAL), and intracranial pressure was lower in the Hb2 group (p < 0.05 vs. SAL). Cerebrovenous oxygen level was similar in all groups (p > 0.05). At baseline, 5% carbon dioxide evoked a 16 +/- 1% increase in cerebrovenous oxygen saturation, indicating vasodilatation. At 210 minutes, this response was nearly absent in SAL (4 +/- 4%) (p < 0.05 vs. baseline) and Hb1 (1 +/- 5%), but was partially preserved in Hb2 (9 +/- 5%). There was no intergroup difference in beta amyloid precursor protein positive axons. Five of 20 SAL and 0 of 13 DCLHb animals developed brain death (flat electroencephalogram) (p = 0.05, SAL vs. DCLHb). Postresuscitation, DCLHb animals maintained higher mean pulmonary arterial pressure (28 +/- 1 mm Hg, SAL; 42 +/- 1 mm Hg, Hb1; 45 +/- 1 mm Hg, Hb2) (p < 0.05, Hb1 and Hb2 vs. SAL) and lower cardiac output (3.9 +/- 1.6 L/min, SAL; 2.6 +/- 0.1 L/min, Hb1; 2.7 +/- 0.1 L/min, Hb2) (p < 0.05, Hb1 and Hb2 vs. SAL). Three Hb2 animals died as a result of cardiac failure, and one SAL animal died as a result of irreversible shock.

CONCLUSION

In this swine model of traumatic brain injury and hemorrhagic shock, resuscitation with DCLHb maintained a higher cerebral perfusion pressure. Low-dose DCLHb (minimal increase in oxygen carriage) failed to significantly improve short-term outcome. With high-dose DCLHb (significant improvement in oxygen carriage), intracranial pressure was lower and cerebrovascular carbon dioxide reactivity was partially preserved; however, this was at the cost of poorer cardiac performance secondary to high afterload.

Secondary injuries in brain trauma: effects of hypothermia

Hypothermia has been shown to be cerebroprotective in traumatized brains. Although a large number of traumatic brain injury (TBI) studies in animals have shown that hypothermia is effective in suppressing a variety of damaging mechanisms, clinical investigations have shown less consistent results. The complexity of damaging mechanisms in human TBI may contribute to these discrepancies. In particular, secondary injuries such as hypotension and hypoxemia may promote poor outcome. However, few experimental TBI studies have employed complex models that included such secondary injuries to clarify the efficacy of hypothermia. This review discusses the effects of hypothermia in various TBI models addressing primary and acute secondary injuries. Included are recently published clinical data using hypothermia as a therapeutic tool for preventing or reducing the detrimental posttraumatic secondary injuries and neurobehavioral deficits. Also discussed are recent successful applications of hypothermia from outside the TBI realm. Based on all available data, some general considerations for the application of hypothermia in TBI patients are given.

Risk factors for intraoperative hypotension in traumatic intracranial hematoma

Patients suffering from traumatic intracranial hemorrhage (TICH) may experience an episode of catastrophic intraoperative hypotension (IHT), after decompression of the brain. The aim of this study was to investigate the risk factors for IHT during emergency craniotomy A total of 67 patients, who underwent emergency craniotomy due to TICH, were divided into two groups: IHT ( n=31 ) or without IHT ( n=36 ). Data concerning (1) age; (2) gender; (3) mechanism of injury; (4) Glasgow Coma Scale (GCS) on admission; (5) abnormality of the pupils (anisocoria or mydriasis); (6) mean arterial blood pressure; (7) heart rate; (8) time elapsed before craniotomy from injury; (9) initial brain CT scans; (10) duration of craniotomy; and (11) total infusion or urine volume until craniotomy were collected prospectively as IHT risk factors. Low GCS score (<5), tachycardia (heart rate >112min(-1)) and hypertension (mean blood pressure >131mmHg) before emergency craniotomy were strongly ( P<0.05 ) associated with IHT. Delayed surgery (>173min until craniotomy) also had a significant ( P<0.005 ) effect on IHT. The risk factors for IHT were considered as a low GCS score on admission, tachycardia, hypertension before emergency craniotomy and delayed surgery. These results suggested the patients with IHT had a high sympathetic tone before emergency craniotomy A sudden reduction in sympathetic tone after surgical decompression of the brain might cause IHT. We concluded that an important factor in the occurrence of IHT was not only the injury severity, but also the balance between sympathetic and parasympathetic activity before decompression surgery.

Traumatic brain injury

PURPOSE OF REVIEW

Management of the patient with traumatic brain injury is a rapidly advancing field, characterized in recent years by an improved understanding of intracranial pathophysiology and ways in which outcomes can be improved. Many traditional therapies, such as fluid restriction and hyperventilation, have been called into question and are no longer recommended. Other proposed therapies, such as deliberate hypothermia, remain controversial. This detailed review of the recent literature helps the reader come to an understanding of current scientific and evidence-based practices in this area, with emphasis on those therapies most likely to be of use to the practicing intensivist.

RECENT FINDINGS

High-quality care of the traumatic brain injury patient demands the integrated activities of a number of different medical and nursing specialties. The best outcomes today are achieved by those systems that are able to focus as a team on the collective goal of minimizing secondary brain injury, and the respiratory therapist adjusting the patient's mechanical ventilation may be just as important to this effort as the attending neurosurgeon. Although the search for new diagnostic, prognostic, and therapeutic modalities continues (many of the more promising of which are reviewed in this article), it is clear that there exists no "silver bullet" therapy that will help all patients. Instead, it is the systematic integration and application of many small advances that will ultimately lead to better outcomes.

SUMMARY

Some issues in traumatic brain injury have now been resolved, and specific recommendations can be made. Fluid therapy directed toward a euvolemic state is now universally recommended, for example, as is the role of intracranial pressure monitoring. Other areas, such as the use of hypertonic saline, remain controversial. In both cases the authors have made an effort to cite the most recent literature, so that readers can draw their own conclusions from the original source material.

Effect of hypertonic saline on cerebral blood flow in poor-grade patients with subarachnoid hemorrhage

BACKGROUND AND PURPOSE

The goal of this study was to examine the effects of hypertonic saline on cerebral blood flow (CBF) in poor-grade patients with subarachnoid hemorrhage.

METHODS

We administered 23.5% hypertonic saline (2 mL/kg IV) 1 time to 10 patients, 2 times to 7 patients, and 3 times to 1 patient. All patients had transcranial Doppler (TCD), intracranial pressure (ICP) monitoring, and analysis of serum sodium and osmolality; 6 had xenon CT (XeCT). Data were used to characterize the changes in CBF, cerebral vascular resistance (CVR), ICP, cerebral perfusion pressure (CPP), and potential rheological mechanisms of action.

RESULTS

In the first treatment episode, CPP increased 26.8% (P=0.0003, at 28.3 minutes) from a rise in mean arterial blood pressure (ABP) of 10.5% (P=0.02, at 22.2 minutes) and a fall in ICP (-74.7%, P=0.002, at 60.0 minutes). Flow velocity (FV) of the middle cerebral artery increased 70.8% (P=0.00005, at 20.0 minutes), resulting in a corresponding fall in estimated CVR (-26.6%, P=0.01, at 16.3 minutes). The half-lives of effects on ABP, CPP, ICP, FV, and estimated CVR were 20.0, 53.6, 139.1, 42.7, and 27.1 minutes, respectively. In the second treatment episode, all these parameters had the same response except estimated CVR, which did not reach statistical significance. XeCT confirmed the increase in CBF (22.9%, P=0.02) without regional differences. A fall in CBF after hypertonic saline was identified in only a single region of interest in a patient in whom baseline flow was low but not infarcted. Serum sodium rose by 11.4 and 8.8 mmol/L, and osmolality rose by 26.7 and 16.3 mosm/L in the first and second treatment episodes, respectively. Hemoglobin decreased by 0.7 and 0.6 g/L and hematocrit decreased by 1.9% and 2.4% in the first and second treatment episodes, respectively.

CONCLUSIONS

We found that 23.5% hypertonic saline increases CBF in poor-grade patients with subarachnoid hemorrhage. These effects are associated with improved indexes of blood rheology. Potential therapeutic benefits are discussed.

Dextran modulates microvascular permeability: effect in isotonic and hypertonic solutions

Hypertonic saline solutions with Dextran (HSD) have been advocated for rapid restoration of intravascular volume. Dextran is thought to increase the duration of action of hypertonic saline (HS) by selectively partitioning the water in the vascular space that has been drawn out of cells by HS. The goal of this study was to define the microvascular permeability modulating activity of Dextran in both isotonic and hypertonic solutions. We hypothesized that Dextran would decrease hydraulic permeability (Lp). Using the modified Landis micro-occlusion technique, single rat mesenteric venules were perfused with either normal Ringers (NR) with 135 mM NaCl or HS with 185 mM NaCl. In sequential cannulations of the venules, 1%, 2%, and 3% of Dextran was added to the NR perfusion (n = 6) and the HS perfusion (n = 6). The Lp was measured at baseline and after perfusion with each Dextran concentration. Baseline Lp measurements for NR and HS solutions were 1.01 +/- 0.034 and 5.14 +/- 1.02, respectively. In the NR group, the 2% and 3% Dextran decreased permeability below baseline levels to 0.79 +/- 0.028 (P < 0.0001) and 0.66 +/- 0.028 (P < 0.0001), respectively. In the HS group, the 2% and 3% Dextran decreased permeability to 1.65 +/- 0.53 (P < 0.0001) and 0.99 +/- 0.2 (P < 0.0001), respectively. All values for Lp are x10(-7) cm s(-1) x cm H2O(-1). The addition of Dextran to isotonic and hypertonic solutions results in a decrease in microvessel permeability. This effect is more pronounced with the perfusion of hypertonic solutions. The results demonstrate the oncotic potential of Dextran and its ability to hold water in the vascular space. Dextran may have a beneficial effect when used for resuscitation with HS by decreasing microvascular permeability and augmenting intravascular volume.

The effect of tonicity and hypertonic solutions on microvascular permeability

BACKGROUND

The effect of hypertonic saline (HS) on microvascular permeability is unclear. We hypothesized that varying degrees of tonicity and HS solutions alter microvascular fluid flux across the endothelium.

METHODS

Hydraulic permeability (L(p)) is a measure of water flow across the endothelial barrier. L(p) was measured in cannulated rat mesenteric venules using the modified Landis micro-occlusion technique. The effect of tonicity was tested by measuring L(p) after successive perfusions with Ringers' solutions of varying sodium chloride (NaCl) concentrations (85, 135, 185, and 235 mM) (n = 6). Additional venules were perfused with control Ringers' ([NaCl] = 135 mM) and measures of L(p) were obtained after subsequent perfusions with 7% NaCl followed by 7% NaCl with 6% dextran (n = 6).

RESULTS

Tonicity had a significant dose-dependent effect on L(p) (P < 0.0001). Perfusion with 7% NaCl significantly increased L(p) (P < 0.0001). The addition of 6% dextran to 7% NaCl significantly decreased L(p) compared with perfusion with 7% NaCl alone (P = 0.002).

CONCLUSIONS

We conclude that (1) tonicity influences microvascular permeability, (2) HS increases microvascular permeability, and (3) the addition of dextran to HS greatly attenuates this response. These findings suggest an important role for tonicity and a possible deleterious effect of HS in modulating microvascular permeability as well as the benefit of dextran with HS for maintaining intravascular volume.

Current controversies in shock and resuscitation

Many controversies and uncertainties surround resuscitation of hemorrhagic shock caused by vascular trauma. Whereas the basic pathophysiology is better understood, much remains to be learned about the many immunologic cascades that lead to problems beyond those of initial fluid resuscitation or operative hemostasis. Fluid therapy is on the verge of significant advances with substitute oxygen carriers, yet surgeons are still beset with questions of how much and what type of initial fluid to provide. Finally, the parameters chosen to guide therapy and the methods used to monitor patients present other interesting issues.

The simple model versus the super model: translating experimental traumatic brain injury research to the bedside

Despite considerable investigation in rodent models of traumatic brain injury (TBI), no novel therapy has been successfully translated from bench to bedside. Although well-described limitations of clinical trails may account for these failures, several modeling factors may also contribute to the lack of therapeutic translation from the laboratory to the clinic. Specifically, models of TBI may omit one or more critical, clinically relevant pathophysiologic features. In this invited review article, the impact of the limited incorporation of several important clinical pathophysiologic factors in TBI, namely secondary insults (i.e., hypotension and/or hypoxemia), coma, and aspects of standard neurointensive care monitoring and management strategies (i.e., intracranial pressure [ICP] monitoring and ICP-directed therapies, sedation, mechanical ventilation, and cardiovascular support) are discussed. Comparative studies in rodent and large animal models of TBI (which may, in some cases, represent super models) are also presented. We conclude that therapeutic breakthroughs will likely require a multidisciplinary approach, involving investigation in a range of models, including clinically relevant modifications of established animal models, along with development and application of new innovations in clinical trial design.

Advances in the management of pediatric trauma

BACKGROUND

Numerous important advances have been made in the management of trauma in childhood in prevention, prehospitalization and intrahospital care, postoperative management, and rehabilitation. As with adult trauma care, the development of trauma systems has impacted greatly on morbidity and mortality in injured children.

DATA SOURCES

Recent literature was searched for information regarding selected aspects of pediatric trauma care where significant improvements in outcome have occurred. The specific areas selected because of their contribution to improved outcomes include changes in the organization of care including the establishment of trauma centers and trauma systems, understanding trauma physiology as a basis for care, selective management of blunt trauma, management of burn injury, and prevention.

CONCLUSION

Because of the various advances in the understanding of the effects of injury that have been translated to improved approaches to treatment, overall treatment mortality in childhood has dropped 45% over the last 20 years and mortality with burn injury has been reduced by half in patients with over 60% of body surface burn and almost eliminated below that level unless there are additional circumstances. Nonetheless, trauma is still the leading cause of death in childhood, so continuing commitment by pediatric surgeons to advancing trauma care for children is in order as well as providing education for adult surgeons willing to commit themselves to care of the injured child.

Management of raised intracranial pressure in children

Children suffer a significant number of head injuries as a result of their high activity levels, immature developmental skills and increased head-to-body mass ratio. Primary brain injury is irreversible, but secondary insults can be limited. Central to this is the management of raised intracranial pressure (ICP). The pathophysiology of head injury can explain some of the causes of raised ICP. Monitoring of ICP is important and this is closely linked to the maintenance of an adequate cerebral perfusion pressure and the importance of normovolaemia. Other interventions that have been shown to limit rises in ICP are appropriate use of positioning, mechanical ventilation and drug therapy. Less common therapies include jugular venous bulb oxygen saturation monitoring and the use of trometamol (THAM). Most nursing interventions do not actively reduce ICP, but they are central to its management. Reducing stimuli, avoiding cluster care, manual hyperinflation and limiting routine endotracheal suction may prevent an accumulative rise in ICP. Based on this literature review, it is possible to divide these interventions into first and second tier treatments, as shown in the protocol. Much of the suggested management will occur simultaneously, but it is important to assess the child's own response to each intervention and thus tailor treatment to minimize secondary brain injury.

Effects of hypertonic saline-dextran solution on regional blood flow and thrombogenicity in PTFE grafts in the vena cava of the rabbit

OBJECTIVES

to study the effects of hypervolaemic haemodilution with hypertonic saline-dextran solution (HSD) on regional blood flow and thrombogenicity of small diameter polytetrafluoroethylene (PTFE) grafts.

DESIGN

blood flow in rabbit aorta, vena cava and femoral, renal and ear arteries was determined in five groups: controls, isovolaemic haemodilution with dextran-70 (10 ml/kg body weight (b.w. )), hypervolaemic haemodilution (10 ml/kg b.w.) with either dextran-70, 7.5% NaCl or a combination of dextran and NaCl (HSD). In a second series PTFE grafts were inserted into the vena cava of rabbits treated with hypervolaemic haemodilution with dextran, hypertonic saline or HSD and examined after two days.

RESULTS

blood flow increased in aorta, vena cava and femoral artery after haemodilution. The increase was transient in animals treated with hypertonic NaCl alone but sustained in the dextran-70 groups. The grafts from animals treated with hypertonic saline alone had a lower thrombus mass and higher blood flow compared to those from rabbits haemodiluted with dextran-70 only, indicating that both dextran and NaCl have antithrombotic effects. Superior results were obtained with HSD solution.

CONCLUSIONS

HSD solution has a strong flow-promoting action in several vascular beds and beneficial effects on the patency of small diameter vessel grafts.

Hemoglobin-based oxygen carriers: development and clinical potential

This article addresses issues involved in the development of hemoglobin-based oxygen carriers and provides a focused overview of the 4 hemoglobin-based oxygen carriers with emergency medicine application currently in clinical trials.

Effects of hypertonic saline hydroxyethyl starch solution and mannitol in patients with increased intracranial pressure after stroke

BACKGROUND AND PURPOSE

The purpose of this study was to prospectively evaluate a protocol with hypertonic saline hydroxyethyl starch (HS-HES) and mannitol in stroke patients with increased intracranial pressure (ICP).

METHODS

We studied 30 episodes of ICP crisis in 9 patients. ICP crisis was defined as (1) a rise of ICP of more than 25 mm Hg (n = 22), or (2) pupillary abnormality (n=3), or (3) a combination of both (n=5). Baseline treatment was performed according to a standardized protocol. For initial treatment, the patients were randomly assigned to either infusion of 100 mL HS-HES or 40 g mannitol over 15 minutes. For repeated treatments the 2 substances were alternated. ICP, blood pressure, and cerebral perfusion pressure (CPP) were monitored over 4 hours. Blood gases, hematocrit, blood osmolarity, and sodium were measured before and 15 and 60 minutes after the start of infusion. Treatment was regarded as effective if ICP decreased >10% below baseline value or if the pupillary reaction had normalized.

RESULTS

Treatment was effective in all 16 HS-HES-treated and in 10 of 14 mannitol-treated episodes. ICP decreased from baseline values in both groups, P < 0.01. The maximum ICP decrease was 11.4 mm Hg (after 25 minutes) in the HS-HES-treated group and 6.4 mm Hg (after 45 minutes) in the mannitol-treated group. There was no constant effect on CPP in the HS-HES-treated group, whereas CPP rose significantly in the mannitol-treated group. Blood osmolarity rose by 6.2 mmol/L in the mannitol-treated group and by 10.5 mmol/L in the HS-HES-treated group; sodium fell by 3.2 mmol/L in the mannitol and rose by 4.1 mmol/L in the HS-HES-treated group.

CONCLUSIONS

Infusion of 40 g mannitol and 100 mL HS-HES decreases increased ICP after stroke. The maximum effect occurs after the end of infusion and is visible over 4 hours. HS-HES seems to lower ICP more effectively but does not increase CPP as much as does mannitol.

Current concepts in treatment of closed head injury

Standards for management of severe closed head injury should help to establish a foundation for routine care and ongoing research. Studies of cerebral blood flow, oxygenation and metabolism suggest a pattern seen in patients with low c\scores on the Glasgow Coma Scale (GCS), who are known to have poor outcomes. Moderate hypothermia, although improving outcome for patients with GCS of 5-7, has not been beneficial for patients with lower GCS scores.