Cerebral hemodynamics in patients with acute severe head trauma

Deep Sedation in Traumatic Brain Injury Patients

Traumatic brain injury (TBI) is one of the leading causes of mortality and disability in adults. In cases of severe TBI, preventing secondary brain injury by managing intracranial hypertension during the acute phase is a critical treatment challenge. Among surgical and medical interventions to control intracranial pressure (ICP), deep sedation can provide comfort to patients and directly control ICP by regulating cerebral metabolism. However, insufficient sedation does not achieve the intended treatment goals, and excessive sedation can lead to fatal sedative-related complications. Therefore, it is important to continuously monitor and titrate sedatives by measuring the appropriate depth of sedation. In this review, we discuss the effectiveness of deep sedation, techniques to monitor the depth of sedation, and the clinical use of recommended sedatives, barbiturates, and propofol in TBI.

Safety and Tolerability of 23.4% Hypertonic Saline Administered Over 2 to 5 Minutes for the Treatment of Cerebral Herniation and Intracranial Pressure Elevation

BACKGROUND

Hyperosmolar therapy is the cornerstone of medical management of sustained elevated intracranial pressure from cerebral edema. Acute intracranial hypertension and herniation is a medical emergency that requires rapid treatment and stabilization to prevent secondary brain injury or death. Intravenous hypertonic sodium chloride (NaCl) 23.4% is an effective treatment modality commonly used in this setting. Because of its high osmolarity, use has historically been limited primarily to central venous line administration as an intermittent infusion due to concerns about thrombophlebitis, injection site pain, and tissue necrosis or injury with extravasation. The objective of this analysis was to prospectively evaluate the safety of administration of 23.4% NaCl as a rapid intravenous push over 2-5 min.

METHODS

A prospective analysis of patients admitted between April 2021 and December 2021 who received 23.4% NaCl intravenous push over 2-5 min in a central or peripheral line was performed. Safety end points included incidence of new onset hypotension [defined as systolic blood pressure (SBP) < 90 mm Hg or SBP decrease of at least 20 mm Hg], bradycardia (defined as heart rate < 50 beats per minute), and infusion site reactions documented within 1 h of administration. For secondary safety outcomes, highest and lowest SBP and lowest heart rates documented within 1 h before 23.4% NaCl administration were compared with values collected within 1 h post administration and evaluated by mixed-design analysis of variance test with adjustment for peripheral versus central line administration.

RESULTS

We identified 32 patients who received 79 administrations of 23.4% NaCl through a central line or peripheral line during the study period. An SBP decrease of at least 20 mm Hg was observed in 13% of patients, an SBP < 90 mm Hg occurred in 16% of patients, and bradycardia occurred in 3% of patients who received 23.4% NaCl. Injection site pain was reported by one patient without documented thrombophlebitis, cellulitis, or tissue damage. Pain was not reported during two subsequent administrations in the same patient. There was no documented occurrence of soft tissue injury or necrosis in any patient. Compared with baseline vital signs before 23.4% NaCl administration, no difference in vital signs post administration was observed.

CONCLUSIONS

Central and peripheral administration of 23.4% NaCl over 2-5 min was well tolerated, and incidence of hypotension, bradycardia, or infusion site-related adverse events was rare.

Aspects on the Physiological and Biochemical Foundations of Neurocritical Care

Neurocritical care (NCC) is a branch of intensive care medicine characterized by specific physiological and biochemical monitoring techniques necessary for identifying cerebral adverse events and for evaluating specific therapies. Information is primarily obtained from physiological variables related to intracranial pressure (ICP) and cerebral blood flow (CBF) and from physiological and biochemical variables related to cerebral energy metabolism. Non-surgical therapies developed for treating increased ICP are based on knowledge regarding transport of water across the intact and injured blood-brain barrier (BBB) and the regulation of CBF. Brain volume is strictly controlled as the BBB permeability to crystalloids is very low restricting net transport of water across the capillary wall. Cerebral pressure autoregulation prevents changes in intracranial blood volume and intracapillary hydrostatic pressure at variations in arterial blood pressure. Information regarding cerebral oxidative metabolism is obtained from measurements of brain tissue oxygen tension (PbtO2) and biochemical data obtained from intracerebral microdialysis. As interstitial lactate/pyruvate (LP) ratio instantaneously reflects shifts in intracellular cytoplasmatic redox state, it is an important indicator of compromised cerebral oxidative metabolism. The combined information obtained from PbtO2, LP ratio, and the pattern of biochemical variables reveals whether impaired oxidative metabolism is due to insufficient perfusion (ischemia) or mitochondrial dysfunction. Intracerebral microdialysis and PbtO2 give information from a very small volume of tissue. Accordingly, clinical interpretation of the data must be based on information of the probe location in relation to focal brain damage. Attempts to evaluate global cerebral energy state from microdialysis of intraventricular fluid and from the LP ratio of the draining venous blood have recently been presented. To be of clinical relevance, the information from all monitoring techniques should be presented bedside online. Accordingly, in the future, the chemical variables obtained from microdialysis will probably be analyzed by biochemical sensors.

Age-related carbon dioxide reactivity in children after moderate and severe traumatic brain injury

OBJECTIVE The objective of this study is to assess carbon dioxide reactivity (CO2R) in children following traumatic brain injury (TBI). METHODS This prospective observational study enrolled children younger than 18 years old following moderate and severe TBI. Thirty-eight mechanically ventilated children had daily CO2R testing performed by measuring changes in their bilateral middle cerebral artery flow velocities using transcranial Doppler ultrasonography (TCD) after a transient increase in minute ventilation. The cohort was divided into 3 age groups: younger than 2 years (n = 12); 2 to 5 years old (n = 9); and older than 5 years (n = 17). RESULTS Children younger than 2 years old had a lower mean CO2R over time. The 2-5-year-old age group had higher mean CO2R than younger patients (p = 0.01), and the highest CO2R values compared with either of the other age groups (vs > 5 years old, p = 0.046; vs < 2 years old, p = 0.002). Having a lower minimum CO2R had a statistically significant negative effect on outcome at discharge (p = 0.0413). Impaired CO2R beyond Postinjury Day 4 trended toward having an effect on outcome at discharge (p = 0.0855). CONCLUSIONS Abnormal CO2R is prevalent in children following TBI, and the degree of impairment varies by age. No clinical or laboratory parameters were identified as risk factors for impaired CO2R. Lower minimum CO2R values are associated with worse outcome at discharge.

Critical Care Management of Increased Intracranial Pressure

Increased intracranial pressure (ICP) is a pathologic state common to a variety of serious neurologic conditions, all of which are characterized by the addition of volume to the intracranial vault. Hence all ICP therapies are directed toward reducing intracranial volume. Elevated ICP can lead to brain damage or death by two principle mechanisms: (1) global hypoxic-ischemic injury, which results from reduction of cerebral perfusion pressure (CPP) and cerebral blood flow, and (2) mechanical compression, displacement, and herniation of brain tissue, which results from mass effect associated with compartmentalized ICP gradients. In unmonitored patients with acute neurologic deterioration, head elevation (30 degrees), hyperventilation (pCO2 26-30 mmHg), and mannitol (1.0-1.5 g/kg) can lower ICP within minutes. Fluid-coupled ventricular catheters and intraparenchymal pressure transducers are the most accurate and reliable devices for measuring ICP in the intensive care unit (ICU) setting. In a monitored patient, treatment of critical ICP elevation (>20 mmHg) should proceed in the following steps: (1) consideration of repeat computed tomography (CT) scanning or consideration of definitive neurosurgical intervention, (2) intravenous sedation to attain a quiet, motionless state, (3) optimization of CPP to levels between 70 and 110 mmHg, (4) osmotherapy with mannitol or hypertonic saline, (5) hyperventilation (pCO2 26-30 mmHg), (6) high-dose pentobarbital therapy, and (7) systemic cooling to attain moderate hypothermia (32-33°C). Placement of an ICP monitor and use of a stepwise treatment algorithm are both essential for managing ICP effectively in the ICU setting.

Cerebral blood flow and transcranial doppler sonography measurements of CO2-reactivity in acute traumatic brain injured patients

BACKGROUND

Cerebral blood flow (CBF) measurements are helpful in managing patients with traumatic brain injury (TBI), and testing the cerebrovascular reactivity to CO(2) provides information about injury severity and outcome. The complexity and potential hazard of performing CBF measurements limits routine clinical use. An alternative approach is to measure the CBF velocity using bedside, non-invasive, and transcranial Doppler (TCD) sonography. This study was performed to investigate if TCD is a useful alternative to CBF in patients with severe TBI.

METHOD

CBF and TCD flow velocity measurements and cerebrovascular reactivity to hypocapnia were simultaneously evaluated in 27 patients with acute TBI. Measurements were performed preoperatively during controlled normocapnia and hypocapnia in patients scheduled for hematoma evacuation under general anesthesia.

MAIN FINDING AND CONCLUSION

Although the lack of statistical correlation between the calculated reactivity indices, there was a significant decrease in TCD-mean flow velocity and a decrease in CBF with hypocapnia. CBF and TCD do not seem to be directly interchangeable in determining CO(2)-reactivity in TBI, despite both methods demonstrating deviation in the same direction during hypocapnia. TCD and CBF measurements both provide useful information on cerebrovascular events which, although not interchangeable, may complement each other in clinical scenarios.

Therapeutic hypothermia for adult viral meningoencephalitis

BACKGROUND

Despite the advances in critical care, severe viral meningoencephalitis continues to impose high rates of morbidity and mortality. Consequently, new treatment strategies are needed and we present therapeutic hypothermia (TH) as one of the possible efficacious treatment tools.

METHODS

We present the case series in an adult intensive care unit of a tertiary care hospital. Eleven patients suffering from severe viral meningoencephalitis were treated with hypothermia. The major indication for TH was severely impaired consciousness associated with carbon dioxide reactivity loss assessed by Transcranial Doppler. Besides from the established treatment, all the patients underwent TH. Mild hypothermia (rectal temperature of 32-34°C) was maintained with continuous veno-venous hemofiltration.

RESULTS

Median Glasgow coma scale score in our patients at admission was 8 (3-10) and median Acute Physiology and Chronic Health Evaluation score was 24 (12-32). The overall mortality rate was 9% (1/11). Among survivors, the outcome was favorable in five patients [Glasgow Outcome Scale score (GOS) 4-5]. Remaining five patients had severe residual neurological deficit (GOS 3). Median GCS at discharge was 15 (8-15). With respect to disease severity, the outcome in presented patients was generally satisfactory.

CONCLUSIONS

Our results suggest that use of mild hypothermia in selected adult patients with viral meningoencephalitis could be a promising treatment tool.

Prospective observational cohort study of cerebrovascular CO2 reactivity in patients with inflammatory CNS diseases

The purpose of this study was to evaluate the significance of cerebrovascular CO(2) reactivity (CO(2) R) in the course and outcome of inflammatory central nervous system (CNS) diseases. Sixty-eight patients with inflammatory CNS diseases and 30 healthy volunteers were included in this prospective observational cohort study. The observational period was between January 2005 and May 2009. The CO(2) R was measured by transcranial Doppler (TCD) ultrasound using the breath-holding method. We compared patients with normal CO(2) R (breath-holding index [BHI(m)] ≥ 1.18 = BHI(N) group) with patients who showed impaired CO(2) R (BHI(m) < 1.18 = BHI(R) group). We also analyzed the association of impaired CO(2) R with the etiology, severity, and outcome of disease. When compared to the BHI(N) group, the patients from the BHI(R) group were older, had a heavier consciousness disturbance, experienced more frequent respiratory failure, and, subsequently, had worse outcomes. There were no fatalities among the 28 patients in the BHI(N) group. The comparison of subjects with bacterial and non-bacterial meningitis revealed no significant differences. The unfavorable outcome of disease (Glasgow Outcome Scale [GOS] score 1-3) was significantly more common in subjects with impaired CO(2) R (62.5% vs. 10.7%). Logistic regression analysis was performed in order to establish the prognostic value of BHI(m). The outcome variable was unfavorable outcome (GOS 1-3), while the independent variables were age, Glasgow Coma Scale (GCS) score, and BHI(m). The age and BHI(m) showed the strongest influence on disease outcome. A decrease of BHI(m) for each 0.1 unit increased the risk of unfavorable outcome by 17%. Our study emphasizes the importance of CO(2) R assessment in patients with inflammatory CNS diseases.

Cerebrovascular pathophysiology in pediatric traumatic brain injury

BACKGROUND

Traumatic brain injury (TBI) is the leading cause of traumatic morbidity and mortality in children. Although there is increasing information concerning TBI in adults and experimental animal models, relatively little is known regarding cerebrovascular pathophysiology specific to children.

MATERIALS

A review of the pertinent medical literature.

RESULTS

Systemic and cerebral hemodynamic factors such as hypotension, hypoxia, hyperglycemia, and fever are associated with poor outcome in pediatric TBI. Similarly, cerebral autoregulation is often impaired after TBI and may adversely affect outcome, especially if systemic hemodynamics are altered. Furthermore, CO2 vasoreactivity may be altered after pediatric TBI and lead to either cerebral ischemia or hyperemia.

CONCLUSIONS

Understanding the effect of pediatric TBI on the cerebral circulation is needed to potentially develop protocols to improve outcome in this vulnerable population. Specifically, changes in pediatric cerebrovascular physiology and pathophysiology, including CO2 vasoreactivity and pressure autoregulation, must be understood and their mechanism elucidated.

Hyper flow and intracranial hypertension in diffuse axonal injury: an update to gennarelli doctrine

Twelve consecutive paediatric (six) and adult (six) patients harbouring a neuroradiological pattern consistent with diffuse axonal injury (DAI) along with slit ventricles underwent haemodynamic study in the Intensive Care Unit of our University. All the patients had GCS scores less than 8 after a severe brain injury. serial head computed tomography (CT) and magnetic resonance (MR) scans demonstrated a radiological pattern of DAI. Transcranial Doppler Sonography (TCD) of the middle cerebral arteries was performed through the temporal bone window in all the patients. All patients but one underwent a continuous monitoring of intracranial pressure (ICP) and cerebral extraction of 02 (CEO2). Therapy with barbiturates and hyperventilation was necessary in all the cases. In two patients (one adult and one paediatric) a bilateral decompressive craniectomy was performed in order to decrease a severe intracranial hypertension. Hyperflow along with intracranial hypertension, variably responsive to barbiturate therapy, was observed in all the patients by means of TCD and CEO2. In our patients intracranial hypertension along with hyperflow syndrome were found associated with DAI. Medical as well as surgical treatments were tailored according to the haemodynamic study.

Management of intracranial hypertension

Effective management of intracranial hypertension involves meticulous avoidance of factors that precipitate or aggravate increased intracranial pressure. When intracranial pressure becomes elevated, it is important to rule out new mass lesions that should be surgically evacuated. Medical management of increased intracranial pressure should include sedation, drainage of cerebrospinal fluid, and osmotherapy with either mannitol or hypertonic saline. For intracranial hypertension refractory to initial medical management, barbiturate coma, hypothermia, or decompressive craniectomy should be considered. Steroids are not indicated and may be harmful in the treatment of intracranial hypertension resulting from traumatic brain injury.

Management of intracranial hypertension

Effective treatment of intracranial hypertension involves meticulous avoidance of factors that precipitate or aggravate increased intracranial pressure. When intracranial pressure becomes elevated, it is important to rule out new mass lesions that should be surgically evacuated. medical management of increased intracranial pressure should include sedation and paralysis, drainage of cerebrospinal fluid, and osmotherapy with either mannitol or hypertonic saline. For intracranial hypertension refractory to initial medical management, barbiturate coma, hypothermia, or decompressive craniectomy should be considered. Steroids are not indicated and may be harmful in the treatment of intracranial hypertension resulting from traumatic brain injury.

Haemodynamic patterns in children with posttraumatic diffuse brain swelling. A preliminary study in 6 cases with neuroradiological features consistent with diffuse axonal injury

BACKGROUND

In the present report we describe the cerebral haemodynamics and the neuroradiological findings observed in six consecutive children, three males and three females aged 4-15.6 yrs (mean age 8.95) displaying a neuroradiological pattern consistent with diffuse axonal injury (DAI) along with slit ventricles.

METHODS

All the patients were admitted to the Paediatric Intensive Care Unit with GCS scores less than 8 after a severe brain injury. Serial head computed to mography (CT) and magnetic resonance (MR) scans demonstrated a radiological pattern of DAI. Transcranial Doppler Sonography (TCD) of the middle cerebral arteries was performed through the temporal bone window in all the patients. All patients but one underwent a continuous monitoring of intracranial pressure (ICP) and cerebral extraction of O(2) (CEO(2)). Treatment with barbiturates and hyperventilation was necessary in all the cases. In one patient, a bilateral decompressive cran iectomy was performed in order to decrease severe in tracranial hypertension.

RESULTS

Hyperflow along with intracranial hyper tension, variably responsive to barbiturate medication, was observed in all the patients by means of TCD and CEO(2).

CONCLUSIONS

Intracranial hypertension can be elevated in pediatric posttraumatic hyperflow syndromes associated with DAI. The observation of the time course of the parameters studied allowed us to modify the pharmacological treatment and/or perform surgical decompression (external cerebrospinal fluid (CSF) drainage in five cases; decompressive craniectomy in one case). Compartmental hyperflow TCD pattern was evident in only one patient. Although the limited number of pa tients in our series does not allow definite conclusions, we strongly believe that TCD, with ICP and CEO(2) monitoring, are useful tools in planning surgical strategy in children with neuroradiological signs of DAI.

Physiological and biochemical principles underlying volume-targeted therapy--the "Lund concept"

The optimal therapy of sustained increase in intracranial pressure (ICP) remains controversial. The volume-targeted therapy ("Lund concept") discussed in this article focuses on the physiological volume regulation of the intracranial compartments. The balance between effective transcapillary hydrostatic and osmotic pressures constitutes the driving force for transcapillary fluid exchange. The low permeability for sodium and chloride combined with the high crystalloid osmotic pressure (approximately 5700 mmHg) on both sides of the blood-brain barrier (BBB) counteracts fluid exchange across the intact BBB. Additionally, variations in systemic blood pressure generally are not transmitted to these capillaries because cerebral intracapillary hydrostatic pressure (and blood flow) is physio-logically tightly autoregulated. Under pathophysiological conditions, the BBB may be partially disrupted. Transcapillary water exchange is then determined by the differences in hydrostatic and colloid osmotic pressure between the intra- and extracapillary compartments. Pressure autoregulation of cerebral blood flow is likely to be impaired in these conditions. A high cerebral perfusion pressure accordingly increases intracapillary hydrostatic pressure and leads to increased intracerebral water content and an increase in ICP. The volume-targeted "Lund concept" has been evaluated in experimental and clinical studies to examine the physiological and biochemical (utilizing intracerebral microdialysis) effects, and the clinical experiences have been favorable.

The Lund concept: is this logical?

The optimal therapy of sustained increase in intracranial pressure (ICP) is still controversial. The "Lund concept" is based on the physiological volume regulation of the intracranial compartments. In addition to its other functions the blood-brain barrier (BBB) is the most important regulator of brain volume. Water exchange across the intact BBB is counteracted by the low permeability to crystalloids (mainly Na+ and Cl-) combined with the high osmotic pressure (5,700 mmHg) on both sides of the BBB. If the BBB is disrupted transcapillary water transport will be determined by the differences in hydrostatic and colloid osmotic pressure between the intra- and extracapillary compartments. Under pathological conditions pressure autoregulation of cerebral blood flow is often impaired and intracapillary hydrostatic pressure will depend on variations in systemic blood pressure. The "Lund concept" can be summarized in four paragraphs: I. Reduction of stress response and cerebral energy metabolism; II. Reduction of capillary hydrostatic pressure; III. Maintenance of colloid osmotic pressure and control of fluid balance; IV. Reduction of cerebral blood volume. The efficacy of the treatment protocol has been evaluated in experimental and clinical studies regarding the physiological and biochemical (utilizing intracerebral microdialysis) effects. The clinical experiences have been favourable.

Cerebral pathophysiology and critical care neurology: basic hemodynamic principles, cerebral perfusion, and intracranial pressure

Pediatric neurologic intensive care differs from standard pediatric intensive care in two important respects. First, the diagnosis, monitoring, and management of problems related to disorders of cerebral perfusion and intracranial pressure (ICP) are central to nearly all of pediatric neurologic and neurosurgical intensive care. Second, various clinical problems normally encountered in the intensive care unit (ICU) have additional implications when associated with neurologic disease. Regardless of the cause, treatment should be undertaken as expeditiously as possible and should be based on the principles of resuscitation, reducing the volume of the intracranial contents, and reassessment. This chapter aims to outline some basic principles underlying the diagnosis and management of elevated ICP in children.

Hyperemia following aneurysmal subarachnoid hemorrhage: incidence, diagnosis, clinical features, and outcome

OBJECTIVE

Hyperemia is a known phenomenon after aneurysmal subarachnoid hemorrhage, but only a few reports describe and analyze hyperemia in these patients. This could be the result of diagnostic difficulties in order to identify elevated cerebral blood flow; thus, it seems that hyperemia could be an underdiagnosed clinical state. The aim of the study was to evaluate this phenomenon in comparison with clinical outcome and imaging data in order to describe the frequency of hyperemia after subarachnoid hemorrhage and maybe improve clinical diagnosis.

DESIGN

Retrospective analysis of our cerebral blood flow and transcranial Doppler sonography data bank.

SETTING

. Neurosurgical/Anesthesiological intensive care unit University of Regensburg, Regensburg, Germany.

PATIENTS AND PARTICIPANTS

A total of 37 patients were included (24 women and 13 men). All patients suffered from aneurysmal subarachnoid hemorrhage.

MEASUREMENTS AND RESULTS

Standard transcranial Doppler ultrasonography, as well as the Xenon(133) clearance technique for cerebral blood flow measurements, was employed. We observed 37 increases of flow velocities in 37 patients according to Doppler ultrasonography. In order to distinguish between ischemia and hyperemia a Xenon(133) regional cerebral blood flow examination was performed. Global hyperemia was detected in 5 patients (14%). Hyperemia correlated only to favorable outcome ( p=0.01) and fewer ischemic lesions in the computed tomography ( p<0.05).

CONCLUSION

The results indicate that while global hyperemia is a frequent phenomenon that cannot be detected by standard Doppler ultrasonography or clinical examination, hyperemic cerebral blood flow values following aneurysmatic subarachnoid hemorrhage are correlated to favorable outcome.

Volume-targeted therapy of increased intracranial pressure

Fluid exchange across the intact blood-brain barrier (BBB) is counteracted by the low permeability to crystalloids (mainly Na+ and Cl-) combined with the high osmotic pressure (5,700 mm Hg) on both sides of the BBB. If the BBB is disrupted transcapillary water transport will be determined by the differences in hydrostatic and colloid osmotic pressure between the intra- and extracapillary compartments. Under these pathological conditions pressure autoregulation of cerebral blood flow is likely to be impaired and intracapillary hydrostatic pressure will depend on variations in systemic blood pressure. The volume targeted "Lund concept" can be summarized under four headings: A. Reduction of stress response and cerebral energy metabolism: B. Reduction of capillary hydrostatic pressure; C. Maintenance of colloid osmotic pressure and control of fluid balance: D. Reduction of cerebral blood volume. The efficacy of the protocol has been evaluated in experimental and clinical studies regarding the physiological and biochemical (utilizing intracerebral microdialysis) effects and the clinical experiences have been favourable.

Barbiturates for acute neurological and neurosurgical emergencies--do they still have a role?

A number of clinical studies have reported poor clinical outcomes for patients treated with barbiturate therapy in acute neurological and neurosurgical emergencies. Barbiturate therapy, as currently practised with thiopentone and pentobarbitone at least, is also associated with a prolonged post-infusion period of clinical unresponsiveness. Hence, the popularity of barbiturate therapy for sedation of critically ill neurological and neurosurgical patients has declined over the past decade. A retrospective study of traumatic brain injury patients treated at the Royal North Shore Hospital, Sydney, with high-dose thiopentone therapy between 1987 and 1997 has found disappointing results with a 1-month mortality outcome of 50% (14 of 28 patients). Nevertheless, barbiturate therapy remains a consideration for patients with severe cranial trauma in whom preferred treatments have failed to control intracranial or cerebral perfusion pressures. More favourable results ( approximately 10% 1-month mortality rate) were encountered for patients with refractory vasospasm complicating subarachnoid haemorrhage or intracerebral haemorrhage complicating supratentorial arteriovenous malformation resection. A well designed, prospective and randomised controlled trial may be of value in further determining the role of barbiturate therapy in acute neurovascular emergencies refractory to standard therapy.

Efficacy of hyperventilation, blood pressure elevation, and metabolic suppression therapy in controlling intracranial pressure after head injury

OBJECT

Hyperventilation therapy, blood pressure augmentation, and metabolic suppression therapy are often used to reduce intracranial pressure (ICP) and improve cerebral perfusion pressure (CPP) in intubated head-injured patients. In this study, as part of routine vasoreactivity testing, these three therapies were assessed in their effectiveness in reducing ICP.

METHODS

Thirty-three patients with a mean age of 33 +/- 13 years and a median Glasgow Coma Scale (GCS) score of 7 underwent a total of 70 vasoreactivity testing sessions from postinjury Days 0 to 13. After an initial 133Xe cerebral blood flow (CBF) assessment, transcranial Doppler ultrasonography recordings of the middle cerebral arteries were obtained to assess blood flow velocity changes resulting from transient hyperventilation (57 studies in 27 patients), phenylephrine-induced hypertension (55 studies in 26 patients), and propofol-induced metabolic suppression (43 studies in 21 patients). Changes in ICP, mean arterial blood pressure (MABP), CPP, PaCO2, and jugular venous oxygen saturation (SjvO2) were recorded. With hyperventilation therapy, patients experienced a mean decrease in PaCO2 from 35 +/- 5 to 27 +/- 5 mm Hg and in ICP from 20 +/- 11 to 13 +/- 8 mm Hg (p < 0.001). In no patient who underwent hyperventilation therapy did SjvO2 fall below 55%. With induced hypertension, MABP in patients increased by 14 +/- 5 mm Hg and ICP increased from 16 +/- 9 to 19 +/- 9 mm Hg (p = 0.001). With the aid of metabolic suppression, MABP remained stable and ICP decreased from 20 +/- 10 to 16 +/- 11 mm Hg (p < 0.001). A decrease in ICP of more than 20% below the baseline value was observed in 77.2, 5.5, and 48.8% of hyperventilation, induced-hypertension, and metabolic suppression tests, respectively (p < 0.001 for all comparisons). Predictors of an effective reduction in ICP included a high PaCO2 for hyperventilation, a high study GCS score for induced hypertension, and a high PaCO2 and a high CBF for metabolic suppression.

CONCLUSIONS

Of the three modalities tested to reduce ICP, hyperventilation therapy was the most consistently effective, metabolic suppression therapy was variably effective, and induced hypertension was generally ineffective and in some instances significantly raised ICP. The results of this study suggest that hyperventilation may be used more aggressively to control ICP in head-injured patients, provided it is performed in conjunction with monitoring of SjvO2.

Continuous cerebral autoregulation monitoring by cross-correlation analysis: evaluation in healthy volunteers

OBJECTIVE

In a former study, we applied cross-correlation (CC) analysis to recordings of arterial blood pressure (BP), intracranial pressure (ICP), and intracranial blood flow velocity (FV). A lack of significant time delay and a positive correlation coefficient of slow oscillations between these parameters was interpreted as indicative of impaired cerebral autoregulation, whereas a significant time delay and a negative correlation was regarded as preserved autoregulation. To test this hypothesis, cross-correlation was applied on recordings of BP and FV (CC [BP --> FV]) in healthy volunteers with a presumably preserved cerebral autoregulation.

DESIGN

Study of a diagnostic test.

SUBJECTS

A total of 17 healthy volunteers.

MEASUREMENTS AND MAIN RESULTS

BP was recorded by using a tonometric device, and bilateral FV in the middle cerebral arteries (MCA) was measured by transcranial Doppler sonography. Signals were sampled at a resting horizontal position for 29 mins. Cluster analysis showed a mean +/- sd time delay for CC [BP --> FV(MCA right)] of 6.45 +/- 2.1 secs, and for CC [BP --> FV(MCA left) ] of 6.09 +/- 1.8 secs. The mean correlation coefficient was -.33 +/-.17 for the left and -.36 +/-.09 for the right side. In about 30%, differing results with a correlation coefficient between -.2 and.2 and a time delay near zero were found. Cross-correlation between left and right FV showed a mean time delay of 0.09 +/- 0.18 secs, with a mean correlation coefficient of.82 +/-.16. CONCLUSION Spontaneous slow oscillations of BP and FV were detected, and cross-correlation analysis showed a negative correlation and a positive time delay in about 70% of the examinations. These findings corroborate the hypothesis that CC [BP --> FV] might be able to assess the status of cerebral autoregulation continuously. The observed time delay between BP and FV oscillations is in good agreement with former studies on the dynamic properties of cerebral autoregulation.

Volume-targeted therapy of increased intracranial pressure: the Lund concept unifies surgical and non-surgical treatments

Opinions differ widely on the various treatment protocols for sustained increase in intracranial pressure (ICP). This review focuses on the physiological volume regulation of the intracranial compartments. Based on these mechanisms we describe a protocol called 'volume-targeted' ('Lund concept') for treatment of increased ICP. The driving force for transcapillary fluid exchange is determined by the balance between effective transcapillary hydrostatic and osmotic pressures. Fluid exchange across the intact blood-brain barrier (BBB) is counteracted by the low permeability to crystalloids (mainly Na+ and Cl-) combined with the high osmotic pressure (5500 mmHg) on both sides of the BBB. This contrasts to most other capillary regions where the osmotic pressure is mainly derived from the plasma proteins (approximately 25 mmHg). Accordingly, the level of the cerebral perfusion pressure (CPP) is of less importance under physiological conditions. In addition cerebral intracapillary hydrostatic pressure (and cerebral blood flow) is physiologically tightly autoregulated, and variations in systemic blood pressure are generally not transmitted to these capillaries. If the BBB is disrupted, transcapillary water transport will be determined by the differences in hydrostatic and colloid osmotic pressure between the intra- and extracapillary compartments. Under these pathological conditions, pressure autoregulation of cerebral blood flow is likely to be impaired and intracapillary hydrostatic pressure will depend on variations in systemic blood pressure. The volume-targeted 'Lund concept' can be summarized under four headings: (1) Reduction of stress response and cerebral energy metabolism; (2) reduction of capillary hydrostatic pressure; (3) maintenance of colloid osmotic pressure and control of fluid balance; and (4) reduction of cerebral blood volume. The efficacy of the protocol has been evaluated in experimental and clinical studies regarding the physiological and biochemical (utilizing intracerebral microdialysis) effects, and the clinical experiences have been favorable.

Cerebral hemodynamic effects of pentobarbital coma in head-injured patients

The purpose of this study was to examine the changes in cerebral hemodynamics of head-injured patients undergoing barbiturate treatment of refractory intracranial hypertension. Cerebral blood flow (CBF) and metabolism variables were measured in 67 severely head-injured patients at the following times: before the loading dose of pentobarbital; after the loading dose of pentobarbital (average pentobarbital level 28.1+/-8.3 microg/mL); and 3 days later, when the peak pentobarbital level averaged 42.5+/-17.2 microg/mL. Intracranial pressure (ICP) and mean arterial blood pressure (MAP) were decreased by the loading dose of pentobarbital by an average of 12 and 9 mm Hg, respectively. Cerebral perfusion pressure (CPP) was unchanged when the entire group was analyzed together. CBF, cerebral oxygen consumption (CMR(O)2), and arteriovenous oxygen difference (AVD(O)2) were significantly decreased after the loading dose of pentobarbital, by 20%, 31%, and 11%, respectively. The average cerebrovascular resistance (CVR) was increased by 20%. The change in CMR(O)2 with the loading dose of pentobarbital was closely related to the pretreatment value (n = 67, r2 = 0.65, p < .001). Thirty (45%) of the patients had a "good ICP response," with a reduction in ICP from 34+/-9 to 15+/-5 mm Hg after the initial loading dose of pentobarbital. Twenty-seven (40%) of the patients had a "partial ICP response," with ICP decreasing but still remaining above 20 mm Hg after the loading dose of pentobarbital. In the remaining 10 patients, ICP did not change or even increased after pentobarbital. In the 30 patients with a good ICP response, pretreatment CMR(O)2 and AVD(O)2 were greater before administration of pentobarbital, and CMR(O)2 and AVD(O)2 decreased more with the loading dose of pentobarbital, than in the patients with partial or no ICP response. The outcome was significantly better in the patients with a good or partial ICP response to pentobarbital, with 21% of these patients having a good recovery or moderate disability at 3 months after injury, compared with 100% persistent vegetative state or death in the nonresponders. In summary, barbiturate coma can be a useful treatment modality for acutely reducing ICP in selected patients. Patients with overwhelmingly severe injuries are not likely to benefit, partly because their CMR(O)2 is already markedly reduced by the injury and partly because their outcome is already predetermined by the injury. Patients with systemic hypotension are not likely to have a good response because hypotension limits the amount of barbiturates that can be given.

[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.

Effects of sevoflurane on intracranial pressure, cerebral blood flow and cerebral metabolism. A dose-response study in patients subjected to craniotomy for cerebral tumours

BACKGROUND

Studies concerning the cerebrovascular effects of sevoflurane in patients with space-occupying lesions are few. This study was carried out as a dose-response study comparing the effects of increasing sevoflurane concentration (1.5% (0.7 MAC) to 2.5% (1.3 MAC)) on cerebral blood flow (CBF), intracranial pressure (ICP), cerebrovascular resistance (CVR), metabolic rate of oxygen (CMRO2) and CO2-reactivity in patients subjected to craniotomy for supratentorial brain tumours.

METHODS

Anaesthesia was induced with propofol/fentanyl/atracurium and maintained with 1.5% sevoflurane in air/oxygen at normocapnia. Blood pressure was maintained constant by ephedrine. In group 1 (n = 10), the patients received continuously 1.5% sevoflurane. Subdural ICP, CBF and CMRO2 were measured twice at 30-min intervals. In group 2 (n = 10), sevoflurane concentration was increased from 1.5% to 2.5% after CBF1. CBF2 was measured after 20 min during 2.5% sevoflurane. Finally, CO2-reactivity was studied in both groups.

RESULTS

In group 1, no time-dependent alterations in CBF, CVR, ICP and CMRO2 were found. In group 2, an increase in sevoflurane from 1.5% to 2.5% resulted in an increase in CBF from 29 +/- 10 to 34 +/- 12 ml 100 g-1 min-1 and a decrease in CVR from 2.7 +/- 0.9 to 2.3 +/- 1.2 mmHg ml-1 min 100 g (P < 0.05), while ICP and CMRO2 were unchanged. CO2-reactivity was maintained at 1.5% and 2.5% sevoflurane.

CONCLUSION

Sevoflurane is a cerebral vasodilator in patients with cerebral tumours. Sevoflurane increases CBF and decreases CVR in a dose-dependent manner. CO2-reactivity is preserved during 1.5% and 2.5% sevoflurane.

Cerebral hemodynamic response to CO2 after severe head injury: clinical and prognostic implications

OBJECTIVE

To study the cerebrovascular reactivity to CO2 after severe head injury to establish the clinical and prognostic relevance of CO2 reactivity.

METHODS

Cerebrovascular reactivity to CO2 was studied in 20 patients with severe head injuries at 3.0+/-1.8 days after trauma onset. Two cerebral blood flow studies were performed to measure CO2 reactivity: the first study in a condition of normocapnia and the second study in a condition of relative hypocapnia.

RESULTS

Global reactivity was superimposable to that found in awake, normocapnic subjects and did not correlate with age and Glasgow Coma Scale score but was dependent on the type of brain lesion. Moreover, reactivity correlated with outcome in patients studied after the first 3 days after trauma.

CONCLUSIONS

Our data suggest that cerebrovascular reactivity is (a) almost preserved after a severe head injury; (b) significantly influenced by type of brain lesion; (c) prognostically relevant only in patients studied after the first 3 days after trauma.

Evaluation of hemodynamic responses in head injury patients with transcranial Doppler monitoring

Transcranial Doppler (TCD) can monitor middle cerebral artery (MCA) velocity which can be recorded simultaneously with other physiologic parameters such as end tidal (Et) CO2, arterial blood pressure and intracranial pressure (ICP), in head injured patients. Relative changes in MCA velocity can be used to reflect relative MCA blood flow changes during ICP waves, and also to evaluate cerebral autoregulation, CO2 reactivity and hemodynamic responses to mannitol and barbiturates. The utility and practicality of short intervals of TCD monitoring to evaluate hemodynamic responses, was evaluated in a group of 22 head injured patients (average Glasgow coma score 6). During ICP A waves, MCA velocity always decreased during the peak of the wave, and during ICP B waves, fluctuated synchronously with the ICP. Dynamic cerebral autoregulation, and reactivity to CO2, were reduced within 48 hours of admission. Impaired cerebral autoregulation within 48 hours of admission did not correlate with outcome at 1 month. Mannitol infusion caused an increase in MCA velocity (15.4 +/- 7.9%) which was significantly correlated to the impairment of dynamic autoregulation (r = 0.54, p < 0.0001). The MCA velocity response to a test dose of barbiturates was significantly correlated to the ICP (r = 0.61, p < 0.01) response as well as to the CO2 reactivity (r = 0.37, p < 0.05). Continuous MCA velocity monitoring using TCD may be useful in evaluating a variety of hemodynamic responses in head injury patients and may replace more cumbersome cerebral blood flow techniques which have been used in the past for these purposes.

Effects of dihydroergotamine and sumatriptan on isolated human cerebral and peripheral arteries and veins

BACKGROUND

Pharmacological cerebral vasoconstriction has recently been suggested as treatment for patients with increased intracranial pressure (ICP) after severe traumatic brain lesions. Hypothetically, a moderate constriction of precapillary resistance vessels might be advantageous since it decreases intracapillary blood pressure, and a contraction of cerebral veins might effectively reduce intracranial blood volume and ICP. This report examines the in vitro effects of two vasoconstrictors, dihydroergotamine (DHE) and sumatriptan, which may be considered for treatment of increased ICP.

METHODS

The reactivity of isolated small human cerebral subcutaneous and omental arteries and veins were studied during exposure to different concentrations of DHE and sumatriptan.

RESULTS

Both sumatriptan and DHE induced concentration-dependent contractions in human cerebral arteries and veins and 50% of maximum contractions were obtained at significantly lower concentrations of DHE than of sumatriptan. The maximum contraction of cerebral arteries was significantly higher with sumatriptan than with DHE. Both drugs caused contractions of subcutaneous arteries at concentrations of 10(-7)-10(-6)M, which is within the therapeutic concentration range of sumatriptan, while no effect was obtained in omental vessels.

CONCLUSIONS

Both DHE and sumatriptan cause contraction of isolated human cortical arteries and veins at very low concentrations. The differences observed between the two drugs may be explained by the fact that DHE is an alpha-adrenergic as well as a 5-HT agonist while sumatriptan acts specifically on 5-HT receptors. The study supports the hypothesis underlying the use of DHE for the treatment of increased ICP in patients with severe traumatic brain lesions.

Cerebral blood flow as a predictor of outcome following traumatic brain injury

As part of a prospective study of the cerebrovascular effects of head injury, 54 moderate and severely injured patients underwent 184 133Xe-cerebral blood flow (CBF) studies to determine the relationship between the period of maximum blood flow and outcome. The lowest blood flows were observed on the day of injury (Day 0) and the highest CBFs were documented on postinjury Days 1 to 5. Patients were divided into three groups based on CBF values obtained during this period of maximum flow: Group 1 (seven patients), CBF less than 33 ml/100 g/minute on all determinations; Group 2 (13 patients), CBF both less than and greater than or equal to 33 ml/100 g/minute; and Group 3 (34 patients), CBF greater than or equal to 33 ml/100 g/minute on all measurements. For Groups 1, 2, and 3, mean CBF during Days 1 to 5 postinjury was 25.7 +/- 4, 36.5 +/- 4.2, and 49.4 +/- 9.3 ml/100 g/minute, respectively, and PaCO2 at the time of the CBF study was 31.4 +/- 6, 32.7 +/- 2.9, and 33.4 +/- 4.7 mm Hg, respectively. There were significant differences across Groups 1, 2, and 3 regarding mean age, percentage of individuals younger than 35 years of age (42.9%, 23.1%, and 76.5%, respectively), incidence of patients requiring evacuation of intradural hematomas (57.1%, 38.5%, and 17.6%, respectively) and incidence of abnormal pupils (57.1%, 61.5%, and 32.4%, respectively). Favorable neurological outcome at 6 months postinjury in Groups 1, 2, and 3 was 0%, 46.2%, and 58.8%, respectively (p < 0.05). Further analysis of patients in Group 3 revealed that of 14 with poor outcomes, six had one or more episodes of hyperemia-associated intracranial hypertension (simultaneous CBF > 55 ml/100 g/minute and ICP > 20 mm Hg). These six patients were unique in having the highest CBFs for postinjury Days 1 to 5 (mean 59.8 ml/100 g/minute) and the most severe degree of intracranial hypertension and reduced cerebral perfusion pressure (p < 0.0001). These results indicate that a phasic elevation in CBF acutely after head injury is a necessary condition for achieving functional recovery. It is postulated that for the majority of patients, this rise in blood flow results from an increase in metabolic demands in the setting of intact vasoreactivity. In a minority of individuals, however, the constellation of supranormal CBF, severe intracranial hypertension, and poor outcome indicates a state of grossly impaired vasoreactivity with uncoupling between blood flow and metabolism.

Effect of acute phase response on phenytoin metabolism in neurotrauma patients

The purpose of this prospective study was to correlate measures of the acute phase response, associated therapeutic interventions, and other clinical variables with the process of altered drug metabolism previously observed in patients with severe neurotrauma. Nine patients with severe head injury (Glasgow Coma Scale < or = 8) requiring intravenous phenytoin were included in the study. A loading dose of phenytoin was followed by daily maintenance doses. Serial blood samples were taken after the loading dose and every even-numbered study day for 10 to 14 days for measurement of total and unbound concentrations of phenytoin, interleukin-1 beta, interleukin-6 (IL-6), tumor necrosis factor alpha, alpha 1-acid-glycoprotein, C-reactive protein, and albumin. Time-invariant and time-variant Michaelis-Menten models were fit to the phenytoin concentration-time data. Protein intake was closely monitored. The mean (+/- SEM) unbound fraction of phenytoin increased from 0.17 +/- 0.02 on day 1 to 0.24 +/- 0.04 on day 10 (P < 0.05). The time-variant model was superior in describing the concentration-time data of unbound phenytoin in eight of nine patients. Mean (+/- SEM) pharmacokinetic parameter estimates for unbound phenytoin were: Vmax delta = 605 +/- 92 mg/day, VmaxB = 149 +/- 26.3 mg/day, K(ind) = 0.013 +/- 0.004 hr-1. Interleukin-6 was the only cytokine with significant concentration changes over time; it was inversely correlated with Vmax,t. Peak concentrations of interleukin-6 also proved to be inversely correlated with VmaxB. The daily amount of protein administered was significantly correlated with Vmax,t. Significant alterations in the metabolism of phenytoin occur after severe neurotrauma. The etiology of these changes is probably multifaceted. These results suggest that low initial phenytoin Vmax may be explained by the presence of interleukin-6. An increase in oxidative metabolism that correlated with nutritional protein administration was observed later in these patients.

Quantitative cerebral blood flow and metabolism determination in the first 48 hours after severe head injury with a new dynamic SPECT device

OBJECTIVE

To determine cerebral blood flow (CBF) and metabolism in the acute phase after severe head injury by a new dynamic SPECT device using 133Xenon and to evaluate a possible role of CBF and metabolism in the determination of prognosis.

DESIGN

Prospective study.

SETTING

General intensive care unit in a universitary teaching hospital.

SUBJECTS

23 severely head injured patients having CT scan and CBF determination, intracranial pressure (ICP) and jugular bulb oxygen saturation monitoring in the first 48 hours.

MEASUREMENTS AND MAIN RESULTS

CBF varied from 18.0 to 60.0 ml/100 g/min. No correlation was found between early CBF and severity of trauma evaluated with the Glasgow Coma Score (GCS) (F = 2.151, p = 0.142) and between CBF and prognosis at 6 months evaluated with Glasgow outcome score (GOS) (F = 0.491, p = 0.622: rs = 0.251, p = 0.246). CMRO2 was depressed in relation to the severity of injury, specifically ranging from 0.9 +/- 0.5 ml/100 g/min in patients with GCS 3 to 1.7 +/- 0.8 ml/100 g/min in patients with GCS 6-7. In no patient with CMRO2 less than 0.8 ml/100 g/min was a good outcome observed. A significant correlation was found between GCS and GOS (rs = 0.699, p = 0.0002), between CMRO2 and GOS (F = 4.303, p = 0.031; rs = 0.525, p = 0.013) and between AJDO2 and GOS (F = 3.602, p = 0.046; rs = 0.491, p = 0.017). Fronto-occipital ratio (F/O) of CBF distribution was significantly lower than normal values (chi 2 = 18.658, p = 0.001) but did not correlate either with prognosis (chi 2 = 1.626, p = 0.443) or with severity (chi 2 = 1.913, p = 0.384).

CONCLUSIONS

CBF in the first 48 hours after trauma varies within a large range of values and is not correlated with severity and prognosis. Clinical evaluation with GCS and CMRO2 are much more reliable indicators of severity of head trauma and have a significant role in the determination of prognosis. F/O ration is significantly altered from normal values confirming "post-traumatic hypofrontalism" but does not correlate with severity and prognosis.

Estimation of cerebral blood flow at bedside by continuous jugular thermodilution

The Kety-Schmidt technique can be regarded as the reference method for the measurement of cerebral blood flow (CBF). However, the method is somewhat cumbersome for routine use in the intensive care unit (ICU) at the beside. The continuous thermodilution technique developed many years ago for the measurement of coronary sinus blood flow can be applied for the measurement of jugular blood flow (JBF). However, the measurement of JBF by thermodilution has never been validated using the Kety-Schmidt reference method. We first validate the continuous thermodilution in vitro by comparison with a volumetric flow. The thermodilution method is accurate for flows between 50 and 900 ml min-1 with a mean difference volumetric-thermodilution flow of -1 +/- 18 ml min-1 (mean +/- SD), and precise with a coefficient of variability ranging between 1.21% and 2.50%. In vivo accuracy was assessed by comparing in 15 comatose patients CBF measured using the Kety-Schmidt (CBFKS) method and estimated from JBF measured by thermodilution (CBFTH) at four levels of arterial PaCO2 (25, 30, 35, and 40 mm Hg). The mean difference CBFKS-CBFTH is -0.9 +/- 3.6 ml min-1 100 g-1. In vivo precision of the method was good, with a coefficient of variability of 4.1% in mean. We conclude that jugular continuous thermodilution technique is a reliable method for estimating CBF at the bedside. This technique allows repeated measurements jugular bulb blood sampling for brain metabolic studies.

Hyperemia following traumatic brain injury: relationship to intracranial hypertension and outcome

The role of posttraumatic hyperemia in the development of raised intracranial pressure (ICP) has important pathophysiological and therapeutic implications. To determine the relationship between hyperemia (cerebral blood flow (CBF) > 55 ml/100 g/minute), intracranial hypertension (ICP > 20 mm Hg), and neurological outcome, 193 simultaneous measurements of ICP and CBF (xenon-133 method) were obtained in 59 patients with moderate and severe head injury. Hyperemia was associated with an increased incidence of simultaneous intracranial hypertension compared to nonhyperemic CBF measurements (32.2% vs. 21.6%, respectively; p < 0.059). However, in 78% of blood flow studies in which ICP was greater than 20 mm Hg, CBF was less than or equal to 55 ml/100 g/minute. At least one episode of hyperemia was documented in 34% of patients, all of whom had a Glasgow Coma Scale (GCS) score of 9 or below. In 12 individuals with hyperemia without simultaneous intracranial hypertension, ICP was greater than 20 mm Hg for an average of 11 +/- 16 hours and favorable outcomes were seen in 75% of patients. In contrast, in eight individuals with hyperemia and at least one episode of hyperemia-associated intracranial hypertension, ICP was greater than 20 mm Hg for an average of 148 +/- 84 hours (p < 0.001), and a favorable outcome was seen in only one patient (p < 0.001). Compared to the remainder of the cohort, patients with hyperemia-associated intracranial hypertension were distinctive in being the youngest, exhibiting the lowest GCS scores (all < or = 6), and having the highest incidence of effaced basilar cisterns and intractable intracranial hypertension. In the majority of individuals with hyperemia-associated intracranial hypertension, their clinical profile suggests the occurrence of a severe initial insult with resultant gross impairment of metabolic vasoreactivity and pressure autoregulation. In a minority of these patients, however, high CBF may be coupled to a hypermetabolic state, given their responsiveness to metabolic suppressive therapy. In patients with hyperemia but without intracranial hypertension, elevated CBF is also likely to be a manifestation of appropriate coupling to increased metabolic demand consistent with a generally favorable outcome. This study supports the concept that there are multiple etiologies of both elevated blood flow and intracranial hypertension after head injury.

Detection of impaired cerebral autoregulation using spectral analysis of intracranial pressure waves

Successful resuscitation following severe traumatic brain injury (TBI) requires rapid evaluation of intracranial pressure (ICP), cerebrovascular reactivity (autoregulation), and cerebral metabolism. During impaired autoregulation, inadequate cerebral blood flow (CBF) can lead to ischemia while excessive CBF can result in elevated ICP. Without information regarding the state of autoregulation, treatment of either situation may ameliorate one problem but exacerbate the other. It has been hypothesized that fast Fourier transform (FFT) analysis of arterial blood pressure (BP) and ICP waves can differentiate states of intact and impaired autoregulation. BP and ICP waves were recorded in canines before and after ischemic injury during arterial normotension, hypertension, and hypotension induced with dopamine or nitroprusside infusion. Transfer functions (TFn) were calculated from FFT spectra as ratios of ICP and BP harmonic peak amplitudes to distinguish states of vasoreactivity. During normotension and hypertension, autoregulation was intact and TF1 averaged 0.05. During hypotension, TF1 averaged 0.22 (8 x baseline, p < 0.010). During impaired autoregulation following ischemic injury, TF1 averaged 0.50 (18 x baseline, p < 0.010; 2 x nitroprusside levels, p < 0.01). This large difference in TF relative to baseline extended over a large range of BP (60 < BP < 180 mm Hg). Based on these data and previous results, it was estimated that TF can differentiate impaired autoregulation from effects solely related to elevated ICP or active vasodilation for ICP < 30-40 mm Hg. This suggests that for specific, but widely applicable physiologic conditions, spectral analysis can identify states of impaired autoregulation and, as an adjunct to traditional monitoring techniques, aid in acute resuscitation and prevention of secondary injury in TBI.

Sumatriptan-induced cerebral vasoconstriction as treatment of experimental intracranial hypertension

BACKGROUND

Increased intracranial pressure (ICP) is a major cause of mortality in severe head injuries and pharmacologically induced cerebral vasoconstriction has been suggested as a possible treatment. In the present study a porcine model of increased ICP was utilized to study the changes in cerebral haemodynamics and energy metabolism induced by a selective 5-hydroxytryptamine1 agonist (sumatriptan).

METHODS

ICP was raised by inflation of two balloons covering both parieto-occipital regions extradurally. The animals were randomized into four groups receiving sumatriptan. 0.01 mg.kg-1 (A), 0.03 mg.kg-1 (B), 0.1 mg.kg-1 (C), and 0.5 mg.kg-1 (D) intravenously over 10 min. Measurements of cerebral blood flow (CBF), arterio-venous oxygen content difference (CavO2), and jugular venous pH (vpH) were performed 5, 20, 40, 60, and 75 min after start of the infusion. ICP, mean arterial pressure, and EEG were recorded continuously. Direct effects of sumatriptan were also compared in cortical arteries and veins in vitro.

RESULTS

Significant decreases in ICP were obtained in groups A, B, and C while group D exhibited a progressive increase in ICP. Significant reductions in CBF, increase in CavO2, and slowing of EEG were observed in groups B, C, and D. Sumatriptan caused moderate constriction of the arteries and a more pronounced dilatation of veins in vitro.

CONCLUSION

The results indicate that a low dose of sumatriptan has the potential to reduce a raised ICP. High doses of sumatriptan cause a further increase of ICP possibly by dilatation of intracerebral veins.

Brain tissue pO2 in relation to cerebral perfusion pressure, TCD findings and TCD-CO2-reactivity after severe head injury

As a reliable continuous monitoring of cerebral blood flow and/or cerebral oxygen metabolism is necessary to prevent secondary ischaemic events after severe head injury (SHI) the authors introduced brain tissue pO2 (ptiO2) monitoring and compared this new parameter with TCD-findings, cerebral perfusion pressure (CPP) and CO2-reactivity over time on 17 patients with a SHI. PtiO2 reflects the balance between the oxygen offered by the cerebral blood flow and the oxygen consumption by the brain tissue. According to TCD-CO2-reactivity PtiO2-CO2-reactivity was introduced. After initially (day 0) low mean values (ptiO2 7.7 +/- 2.6 mmHg, TCD 60.5 +/- 32.0 cm/sec and CPP 64.5 +/- 16.0 mmHg/, ptiO2 increased together with an increase in blood flow velocity of the middle cerebral artery and CPP. The relative hyperaemic phase on days 3 and 4 was followed by a decrease of all three parameters. Although TCD-CO2-reactivity was except for day 0 (1.4 +/- 1.5%), sufficient, ptiO2-CO2-reactivity sometimes showed so-called paradox reactions from day 0 till day 3, meaning an increase of ptiO2 on hyperventilation. Thereafter ptiO2-CO2-reactivity increased, increasing the risk of inducing ischaemia by hyperventilation. The authors concluded that ptiO2-monitoring might become an important tool in our treatment regime for patients requiring haemodynamic monitoring.

CO(2) and indomethacin vasoreactivity in patients with head injury

The purpose of this study was to compare the effect of hyperventilation and indomethacin on cerebral circulation, metabolism and pressures in patients with acute severe head injury in order to see if indomethacin may act supplementary to hyperventilation. Fourteen severely head injured patients entered the study. Intracranial pressure (ICP), mean arterial blood pressure (MABP) and cerebral perfusion pressure (CPP) were monitored continuously. Within the first four days after the trauma the CO(2) and indomethacin vasoreactivities were studied by measurements of cerebral blood flow (CBF) (Cerebrograph 10a, intravenous (133)Xe technique) and arterio-venous difference of oxygen (AVdO(2)). Ischaemia was evaluated from changes in CBF, saturation of oxygen in the jugular bulb (SvjO(2)), lactate and lactate/oxygen index (LOI). Data are presented as medians and ranges, results are significant unless otherwise indicated. Before intervention ICP was well controlled ,(14.8 (9-24) mmHg) and basic CBF level was 39.1 (21.6-75.0) ml/100 g/min). The arterio-venous oxygen differences were generally decreased (AVdO(2) = 4.3 (1.8-8.1) ml/100 ml) indicating moderate luxury perfusion. Levels of CMRO(2) were decreased (1.54 (0.7-3.2) ml/100 g/min) as well. During hyperventilation (delta PaCO(2)=0.88 (0.62-1.55) kPa) CBF decreased with 11.8 (-33.4-29.7) %/kPa and ICP decreased with 3.8 (0-10) mmHg. AVdO(2) increased 34.0 (4.0-139.2) %/kPa, MABP was unchanged, CMRO(2) and CPP increased (delta CPP = 3.9 (-10-20) mmHg). AVD (lactate) and LOI were unchanged. No correlations between CBF responses to hypocapnia and outcomes were observed. An i.v. bolus dose of indomethacin (30 mg) decreased CBF 14.7 (-16.7-57.4)% and ICP decreased 4.3 (-1-17) mmHg. AVdO(2) increased 27.8 (-40.0-66.7)%, MABP (delta MABP = 4.9 (-2-21) mmHg) and CPP (delta CPP = 8.7 (3-29) mmHg) increased while CMRO2 was unchanged. No changes in AVd (lactate) and LOI indicating cerebral ischaemia were found. Compared to hyperventilation (changes per 1 kPa, at PaCO(2) level = 4.05 kPa) the changes in MABP, CPP and CBF were significantly greater after indomethacin, while the changes in AVdO(2), ICP, SvjO(2) and LOI were of the same order of magnitude. No correlation between relative reactivities to indomethacin and CO(2), evaluated from changes in CBF and AVdO(2), or between the decrease in ICP after the two procedures were found. Thus, some patients reacted to indomethacin but not to hyperventilation, and vice versa. These results suggest that indomethacin and hyperventilation might act independently, or in a complementary fashion in the treatment of patients with severe head injury.

Cerebral haemodynamic effects of dihydroergotamine in patients with severe traumatic brain lesions

Dihydroergotamine (DHE) is used in our recently introduced therapy of post-traumatic brain oedema and is suggested to reduce ICP through reduction in both cerebral blood volume and brain water content. This study aims at increasing our knowledge of the mechanisms behind the ICP reducing effect of DHE by analysing cerebrovascular effects of a bolus dose of DHE in severely head injured patients (GCS < 8). Mean hemispheric cerebral blood flow (CBF) calculated from the clearance of i.v. 133Xenon, ICP, and cerebral arterio-venous difference in oxygen content (AVDO2), were measured before and after hyperventilation and after a bolus dose of DHE (4 micrograms/kg). The patients were divided into two groups, one with preserved and one with impaired cerebrovascular CO2-reactivity to hyperventilation, the latter being predictive of poor outcome. The haemodynamic effects of DHE were compared to those of hyperventilation. Regional CBF and brain volume SPECT measurements were performed in two patients. DHE increased cerebrovascular resistance (CVR) by about 20% and significantly reduced ICP in both groups of patients, resulting in unchanged AVDO2. Hyperventilation with preserved CO2-reactivity caused a similar decrease in ICP as by DHE but with a much larger increase in CVR (by 70%) and a substantial increase in AVDO2. Hyperventilation with impaired CO2-reactivity reduced ICP but otherwise had no significant cerebrovascular effects. The study supports the concept that the ICP reducing effect of DHE results more from constriction of the large veins than from arterial vasoconstriction, also implying a relatively smaller risk of ischaemia with DHE than with hyperventilation.

Cerebrovascular carbon dioxide reactivity assessed by intracranial pressure dynamics in severely head injured patients

Appropriate management of intracranial pressure (ICP) in severely head injured patients depends in part on the cerebral vessel reactivity to PCO2; loss of CO2 reactivity has been associated with poor outcome. This study describes a new method for evaluating vascular reactivity in head-injured patients by determining the sensitivity of ICP change to alterations in PCO2. This method was combined with measurements of the pressure volume index (PVI), which allowed calculation of blood volume change necessary to alter ICP. The objective of this study was to investigate the ICP response and the blood volume change corresponding to alterations in PCO2 and to examine the correlation of responsivity and outcome as measured on the Glasgow Outcome Scale. The PVI and ICP at different end-tidal PCO2 levels produced by mild hypo- and hyperventilation were obtained in 49 patients with Glasgow Coma Scale scores of less than 8 and over a wide range of PCO2 (25 to 40 mm Hg) in eight patients. Given the assumption that the PVI remained constant during alteration of PaCO2, the estimated blood volume change per torr change of PCO2 was calculated by the following equation: BVR = PVI x delta log(ICP)/delta PCO2, where BVR = blood volume reactivity. The data in this study showed that PVI remained stable with changes in PCO2, thus validating the assumption used in the blood volume estimates. Moreover, the response of ICP to PCO2 alterations followed an exponential curve that could be described in terms of the responsivity indices to capnic stimuli. It was found that responsivity to hypocapnia was reduced by 50% compared to responsivity to hypercapnia measured within 24 hours of injury (p < 0.01). The sensitivity of ICP to estimated blood volume changes in patients with a PVI of less than 15 ml was extremely high with only 4 ml of blood required to raise ICP by 10 mm Hg. The authors conclude from these data that, following traumatic injury, the resistance vessels are in a state of persistent vasoconstriction, possibly due to vasospasm or compression. Furthermore, BVR correlates with outcome on the Glasgow Coma Scale, indicating that assessment of cerebrovascular response within the first 24 hours of injury may be of prognostic value.

Cerebral blood flow and metabolism in children with severe head injury. Part 1: Relation to age, Glasgow coma score, outcome, intracranial pressure, and time after injury

Understanding the pathophysiology of paediatric head trauma is essential for rational acute management. It has been proposed that the response to severe head injury in children differs from that in adults, with increased cerebral blood flow (cerebral hyperaemia) representing the most common cause of raised intracranial pressure, but this has recently been disputed. The relation between the pathophysiological response and time after injury has not been defined in children. This paper describes 151 serial measurements of cerebral blood flow, arteriojugular venous oxygen difference (AJVDO2), and cerebral metabolic rate for oxygen (CMRO2) that were performed in 21 children with severe head injury, mean age 8 (range 2-16) years, Glasgow coma score < or = 8. Absolute cerebral hyperaemia was uncommon, only 10 (7%) of the 151 cerebral blood flow values being at or above the upper limit of the range published in normal children. There was an inverse correlation between cerebral blood flow and intracranial pressure. (r = -0.24, p = 0.009). Contrary to the widespread assumption that cerebral metabolic rate in patients with head injury is always low, CMRO2 was initially within the normal range in 17/21 (81%) children. Both CMRO2 and AJVDO2 fell significantly between the first and third days after injury. There was a non-significant rise in cerebral blood flow over time. These data represent the first evidence that the temporal change in cerebral metabolic rate reported in experimental models of traumatic brain injury also occurs in patients with head injury. The changes in the pathophysiological response over time suggest that the management may need to be modified accordingly. If cerebral metabolic rate and cerebral oxygen extraction are maximal shortly after injury in children with severe head injury then the children are most likely to sustain secondary damage during this period.

A new therapy of post-trauma brain oedema based on haemodynamic principles for brain volume regulation

OBJECTIVE

To evaluate a new therapy of posttraumatic brain oedema, with the main concept that opening of the blood-brain barrier upsets the normal brain volume regulation, inducing oedema formation. This means that transcapillary fluid fluxes will be controlled by hydrostatic capillary and colloid osmotic pressures, rather than by crystalloid osmotic pressure. If so, brain oedema therapy should include reduction of hydrostatic capillary pressure and preservation of normal colloid osmotic pressure.

PATIENTS

11 severely head injured comatose patients with brain swelling, raised intracranial pressure (ICP), and impaired cerebrovascular response to hyperventilation.

INTERVENTIONS

To reduce capillary hydrostatic pressure the patients were given hypotensive therapy (beta 1-antagonist, metoprolol and alpha 2-agonist, clonidine) and a potential precapillary vasoconstrictor (dihydroergotamine). The latter may also decrease cerebral blood volume through venous capacitance constriction. Colloid osmotic pressure was maintained by albumin infusions. The concept implies the need of a negative fluid balance with preserved normovolaemia.

RESULTS

ICP decreased significantly within a few hours of treatment with unaltered perfusion pressure in spite of lowered blood pressure. Of 11 patients 9 survived with good recovery/moderate disability, 2 died. This was compared to outcome in a historical control group with identical entry criteria, given conventional brain oedema therapy, where mortality/vegetativity/severe disability was 100%.

CONCLUSION

The results indicate that the therapy should focus on extracellular rather than intracellular oedema and that ischemia is not the main triggering mechanism behind oedema formation. We suggest that our therapy is superior to conventional therapy by preventing herniation during the healing period of the blood-brain barrier.

[Acid-base equilibrium and the brain]

In physiological conditions, the regulation of acid-base balance in brain maintains a noteworthy stability of cerebral pH. During systemic metabolic acid-base imbalances cerebral pH is well controlled as the blood/brain barrier is slowly and poorly permeable to electrolytes (HCO3- and H+). Cerebral pH is regulated by a modulation of the respiratory drive, triggered by the early alterations of interstitial fluid pH, close to medullary chemoreceptors. As blood/brain barrier is highly permeable to Co2, CSF pH is corrected in a few hours, even in case of severe metabolic acidosis and alkalosis. Conversely, during ventilatory acidosis and alkalosis the cerebral pH varies in the same direction and in the same range than blood pH. Therefore, the brain is better protected against metabolic than ventilatory acid-base imbalances. Ventilatory acidosis and alkalosis are able to impair cerebral blood flow and brain activity through interstitial pH alterations. During respiratory acidosis, [HCO3-] increases in extracellular fluids to control cerebral pH by two main ways: a carbonic anhydrase activation at the blood/brain and blood/CSF barriers level and an increase in chloride shift in glial cells (HCO3- exchanged for Cl-). During respiratory alkalosis, [HCO3-] decreases in extracellular fluids by the opposite changes in HCO3- transport and by an increase in lactic acid synthesis by cerebral cells. The treatment of metabolic acidosis with bicarbonates may induce a cerebral acidosis and worsen a cerebral oedema during ketoacidosis. Moderate hypocapnia carried out to treat intracranial hypertension is mainly effective when cerebral blood flow is high and vascular CO2 reactivity maintained. Hypocapnia may restore an altered cerebral blood flow autoregulation. Instrumental hypocapnia requires a control of cerebral perfusion pressure and cerebral arteriovenous difference for oxygen, to select patients for whom this kind of treatment may be of benefit, to choose the optimal level of hypocapnia and to avoid any deleterious effect. If hypocapnia is maintained over several days, an adaptation of CSF pH may limit the therapeutic effect on the cerebral blood flow and the intracranial pressure.