Effects of arterial and venous pressure alterations on transcapillary fluid exchange during raised tissue pressure

Critical Evaluation of the Lund Concept for Treatment of Severe Traumatic Head Injury, 25 Years after Its Introduction

When introduced in 1992, the Lund concept (LC) was the first complete guideline for treatment of severe traumatic brain injury (s-TBI). It was a theoretical approach, based mainly on general physiological principles-i.e., of brain volume control and optimization of brain perfusion and oxygenation of the penumbra zone. The concept gave relatively strict outlines for cerebral perfusion pressure, fluid therapy, ventilation, sedation, nutrition, the use of vasopressors, and osmotherapy. The LC strives for treatment of the pathophysiological mechanisms behind symptoms rather than just treating the symptoms. The treatment is standardized, with less need for individualization. Alternative guidelines published a few years later (e.g., the Brain Trauma Foundation guidelines and European guidelines) were mainly based on meta-analytic approaches from clinical outcome studies and to some extent from systematic reviews. When introduced, they differed extensively from the LC. We still lack any large randomized outcome study comparing the whole concept of BTF guidelines with other guidelines including the LC. From that point of view, there is limited clinical evidence favoring any of the s-TBI guidelines used today. In principle, the LC has not been changed since its introduction. Some components of the alternative guidelines have approached those in the LC. In this review, I discuss some important principles of brain hemodynamics that have been lodestars during formulation of the LC. Aspects of ventilation, nutrition, and temperature control are also discussed. I critically evaluate the most important components of the LC 25 years after its introduction, based on hemodynamic principles and on the results of own an others experimental and human studies that have been published since then.

Revised CT angiography venous score with consideration of infratentorial circulation value for diagnosing brain death

BACKGROUND

Computed tomography angiography (CTA) is largely performed in European countries as an ancillary test for diagnosing brain death. However, CTA suffers from a lack of sensitivity, especially in patients who have previously undergone decompressive craniectomy. The aim of this study was to assess the performance of a revised four-point venous CTA score, including non-opacification of the infratentorial venous circulation, for diagnosing brain death.

METHODS

A preliminary study of 43 control patients with normal CTAs confirmed that the infratentorial superior petrosal vein (SPV) was consistently visible. Therefore, 76 patients (including ten with decompressive craniectomy) who were investigated with 83 CTAs to confirm clinical brain death were consecutively enrolled between July 2011 and July 2013 at a university centre. The image analysis consisted of recording non-opacification of the cortical segment of the middle cerebral artery and internal cerebral vein (ICV), which were used as the reference CTA score, as well as non-opacification of the SPV. The diagnostic performance of the revised four-point venous CTA score based on the non-opacification of both the ICV and SPV was assessed and compared with that of the reference CTA score.

RESULTS

The revised four-point venous CTA score showed a sensitivity of 95 % for confirming clinical brain death versus a sensitivity of 88 % with the reference CTA score. Non-opacification of the SPV was observed in 95 % of the patients. In the decompressive craniectomy group, the revised four-point CTA score showed a sensitivity of 100 % compared with a sensitivity of 80 % using the reference CTA score.

CONCLUSION

Compared with the reference CTA score, the revised four-point venous CTA score based on ICV and SPV non-opacification showed superior diagnostic performance for confirming brain death, including for patients with decompressive craniectomy.

The Lund concept for the treatment of patients with severe traumatic brain injury

Two different main concepts for the treatment of a severe traumatic brain injury have been established during the last 15 years, namely the more conventional concept recommended in well-established guidelines (eg, U.S. Guideline, European Guideline, Addelbrook's Guideline from Cambridge), on the one hand, and the Lund concept from the University Hospital of Lund, Sweden, on the other. Owing to the lack of well-controlled randomized outcome studies comparing these 2 main therapeutic approaches, we cannot conclude that one is better than the other. This paper is the PRO part in a PRO-CON debate in this journal on the Lund concept. Although the Lund concept is based on a physiology-oriented approach dealing with the hemodynamic principles of brain volume and brain perfusion regulation, traditional treatments are primarily based on a meta-analytic approach from clinical studies. High cerebral perfusion pressure has been an essential goal in the conventional treatments (the cerebral perfusion pressure-guided approach), even though it has been modified in a recent up date of U.S. guidelines. The Lund concept has instead concentrated on management of brain edema and intracranial pressure, along with improvement of cerebral perfusion and oxygenation (the intracranial pressure and perfusion-guided approach). Although conventional guidelines are restricted to clinical data from meta-analytic surveys, the physiological approach of Lund therapy finds support in both experimental and clinical studies. It offers a wider base and can also provide recommendations regarding fluid therapy, lung protection, optimal hemoglobin concentration, temperature control, the use of decompressive craniotomy, and ventricular drainage. This paper puts forward arguments in support of Lund therapy.

Neurologic injury and mechanical ventilation

Mechanical ventilation in neurologically injured patients presents a number of unique challenges. Patients who are intubated due to a primary neurologic injury often experience respiratory phenomena secondary to that injury, including elevation of intracranial pressure (ICP) in response to mechanical ventilation and variations in respiratory patterns. These problems often require unique ventilator strategies that are designed to minimize the impact of the ventilator on ICP and brain oxygenation. Balancing the need to maintain brain oxygenation and control of ICP can be complicated by the effects of ventilator management on ICP. We will examine the consequences of ventilator management as they relate to parameters that affect ICP and brain oxygenation in patients who have neurologic injury.

The “Lund Concept” for the treatment of severe head trauma – physiological principles and clinical application

The Lund Concept is an approach to the treatment of severe brain trauma that is mainly based on hypotheses originating from basic physiological principles regarding brain volume and cerebral perfusion regulation. Its main attributes have found support in experimental and clinical studies. This review explains the principles of the Lund Concept and is intended to serve as the current guide for its clinical application. The therapy has two main goals: (1) to reduce or prevent an increase in ICP (ICP-targeted goal) and (2) to improve perfusion and oxygenation around contusions (perfusion-targeted goal). The Lund therapy considers the consequences of a disrupted blood-brain barrier for development of brain oedema and the specific consequences of a rigid dura/cranium for general cerebral haemodynamics. It calls attention to the importance of improving perfusion and oxygenation of the injured areas of the brain. This is achieved by normal blood oxygenation, by maintaining normovolaemia with normal haematocrit and plasma protein concentrations, and by antagonizing vasoconstriction through reduction of catecholamine concentration in plasma and sympathetic discharge (minimizing stress and by refraining from vasoconstrictors and active cooling). The therapeutic measures mean normalization of all essential haemodynamic parameters (blood pressure, plasma oncotic pressure, plasma and erythrocyte volumes, PaO(2), PaCO(2)) the use of enteral nutrition, and avoidance of overnutrition. To date, clinical outcome studies using the Lund Concept have shown favourable results.

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.

Mechanisms behind postspinal headache and brain stem compression following lumbar dural puncture--a physiological approach

BACKGROUND

The cause of postspinal headache and its specific characteristics are unknown, and whether lumbar dural puncture (LP) triggers brain-stem compression in patients with brain oedema is still controversial.

METHODS

Hydrostatic effects of distal opening of the dural sac towards the atmosphere are described and applied to the normal brain and the brain with disrupted BBB. Analogue analyses from previous results using an isolated skeletal muscle enclosed in a rigid shell were applied to the brain in an attempt to simulate and verify the haemodynamic effects of distal opening of the spinal canal.

RESULTS

The theoretical considerations and the experimental results are compatible with the hypothesis that hydrostatic effects of distal opening of the fluid-filled spinal canal may obliterate the normal subdural venous collapse after a change from the horizontal to vertical position, which may be compatible with postural postspinal headache as occurring close to pain-sensitive meningeal regions. The hydrostatic forces may also initiate transcapillary filtration and aggravate oedema when permeability is increased, which may cause a narrower situation in the brain stem region, perhaps aggravated by venous stasis and a Cushing reflex-induced increase in blood pressure. An magnetic resonance imaging (MRI) picture illustrates how this scenario may separate the subdural space into an upper high- and a lower low-pressure cavity, pressing the brain downwards with sagging of the brain. A life-threatening positive feedback situation for brain-stem compression may develop.

CONCLUSION

The present study strongly suggests that postspinal headache and brain-stem compression and other LP-related effects are predictable following LP, without involving CSF leakage, and can be explained by hydrostatic effects triggered by distal opening of the normally closed dural space to the atmosphere.

Effects on intracranial pressure of dural puncture in supine and head-elevated positions. A study on the cat

BACKGROUND

Lumbar dural puncture may reduce intracranial pressure (ICP) due to a hydrostatic pressure gradient created by distal opening of the spinal fluid column towards the atmosphere. The magnitude of the reduction in hydrostatic force on the brain should depend on the vertical distance between the brain and the dural opening, and thus will increase by head elevation. No studies have analyzed ICP after dural puncture in supine and upright positions.

METHODS

This study on the cat records ICP, mean arterial pressure, and central venous pressure before and after dural puncture in supine and head-elevated positions. The dural puncture was performed at a level corresponding to the lumbar region.

RESULTS

Initially ICP was 10.9 +/- 1.9 mmHg (mean +/- SD), which decreased to 5.1 +/- 2.0 mmHg after 24.5 cm (18 mmHg) of head elevation (n = 7). Intracranial pressure decreased to 5.2 +/-3.5 mmHg following dural puncture in the supine position and to -11.3 +/- 4.2 mmHg after the head elevation (n = 7). Active drainage of CSF fluid in the supine position in a volume similar to that spontaneously drained after head elevation reduced ICP by 2.0 +/- 0.5 mmHg (n = 3).

CONCLUSIONS

The results show that a significant ICP reduction may occur following opening of the spinal canal. The reduction can be explained more by hydrostatic forces than by loss of CSF; also explaining why it is more significant when upright than supine. The decrease in ICP increases transvascular pressure, which may induce the disappearance of the normally present subdural venous collapse with an increase in venous blood volume.

Severe traumatic brain injury in pediatric patients: treatment and outcome using an intracranial pressure targeted therapy—the Lund concept

OBJECTIVE

This study evaluated the outcome of treatment according to the Lund concept in children with severe traumatic brain injury and investigated whether the preset goals of the protocol were achieved.

DESIGN AND SETTING

A two-center retrospective study in neurointensive care units at university hospitals.

PATIENTS

Forty-one children with severe traumatic brain injury from blunt trauma and arriving at hospital within 24 h after injury. Median age was 8.8 years (range 3 months-14.2 years), Glasgow Coma Scale 7 (3-8), and Injury Severity Score 25 (16-75). All children had pathological findings on initial computed tomography. All developed intracranial hypertension, and survivors required intensive care longer than 72 h.

INTERVENTIONS

Treatment according to the principles of the Lund concept.

MEASUREMENTS AND RESULTS

Neurosurgery was required in 46% of the children. Survival rate was 93% and favorable outcome (Glasgow Outcome Score 4 or 5) was 80% at long-term follow-up (median 12 months postinjury, range 2.5-26). The preset physiological and biochemical goals were achieved in over 90% of observations.

CONCLUSIONS

Treating pediatric patients with severe traumatic brain injury, according to the Lund concept, results in a favorable outcome when the protocol is followed.

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.

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.

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.

Arterial hypertension increases intracranial pressure in cat after opening of the blood-brain barrier

BACKGROUND

Increased permeability for small solutes in brain capillaries means that a change in hydrostatic capillary pressure may influence transcapillary fluid exchange according to the Starling fluid equilibrium, and a high arterial pressure may cause transcapillary fluid filtration and raised intracranial pressure. This could be of clinical relevance in states of disrupted blood-brain barrier such as meningitis and after a severe head injury, especially since these patients quite often are spontaneously hypertensive, and hypertensive therapy is sometimes used to increase cerebral perfusion pressure. This study on cat investigated the long-term relation between arterial pressure and intracranial pressure in a state of disrupted blood-brain barrier.

METHOD

Endotoxin was given intrathecally to open the blood-brain barrier and depress cerebral autoregulation. Arterial pressure was increased by about 30 mm Hg during 5 hours by dopamine and angiotensin II infusion. The immediate fall in intracranial pressure after normalization of blood pressure reflects the blood volume component of an intracranial pressure increase.

RESULTS

Increased arterial pressure had no effect on intracranial pressure before endotoxin. Endotoxin infusion increased intracranial pressure from the normal value of 10 to 12 mm Hg. and at steady state by almost 10 mm Hg. Intracranial pressure increased further after the arterial pressure increase. At steady state (achieved within 5 hours), this increase was almost as great as the arterial pressure increase, and about 80% persisted when measured directly after normalization of the arterial pressure.

CONCLUSION

Increased arterial pressure in a state of disrupted blood-brain barrier increases intracranial pressure, mainly because of brain edema. This stresses that arterial hypertension may be deleterious in conditions such as meningitis or after a brain trauma.

Improved outcome after severe head injury with a new therapy based on principles for brain volume regulation and preserved microcirculation

OBJECTIVE

To assess the new "Lund therapy" of posttraumatic brain edema, based on principles for brain-volume regulation and improved microcirculation.

DESIGN

A prospective, nonrandomized outcome study over a 5-yr period on severely head-injured patients with increased intracranial pressure, comparing the results with a historical control group with the same selection criteria for patients who were treated according to conventional principles.

SETTING

General intensive care unit of a university hospital.

PATIENTS

Fifty-three consecutive head-injured patients with a Glasgow Coma Score of <8, and with increased intracranial pressure (>25 mm Hg), despite conventional treatment.

INTERVENTIONS

Interstitial fluid resorption was obtained by lowering intracapillary hydrostatic pressure, by preserving normal colloid osmotic pressure, and by maintaining a normovolemic (normal albumin/serum and hemoglobin/serum), not overtransfused patient. Intracapillary pressure was reduced by the combination of precapillary vasoconstriction (low-dose thiopental, dihydroergotamine) and reduction of mean arterial pressure, the latter attained with a beta1-antagonist (metoprolol 0.2 to 0.3 mg/kg/24 hrs iv) and an alpha2-agonist (clonidine 0.4 to 0.8 microg/kg x 4 to 6 iv). Clonidine, in combination with normovolemia, also improves microcirculation by reducing catecholamines in plasma. Intracranial blood volume was reduced by arterial (low-dose thiopental sodium and dihydroergotamine) and large-vein (dihydroergotamine) vasoconstriction. The start dose of dihydroergotamine (maximum 0.9 microg/kg/hr) was successively reduced toward discontinuation within 4 to 5 days.

MEASUREMENTS AND MAIN RESULTS

There were 8% of patients who died and the neurologic conditions of 13% remained severely damaged, compared with 47% and 11%, respectively, for the control group.

CONCLUSIONS

The low mortality compared with previous outcome studies strongly indicates that this therapy improves outcome for severe head injuries. However, a randomized, controlled study is needed to reach general acceptance of this new therapy.

The capillary filtration coefficient for evaluation of capillary fluid permeability in cat calf muscles

Measuring the capillary filtration coefficient (CFC) from the transvascular fluid filtration following a fixed increase in transcapillary hydrostatic pressure is a common method to estimate capillary hydraulic permeability (conductivity) in an organ. Constant flow pump perfusion with an artificial perfusate and a maximally dilated vascular bed are often used in CFC studies to avoid influence on CFC of variations in vascular tone, blood flow and perfusion pressure. The present study evaluates if capillary hydraulic conductivity can be estimated by the CFC method, when analyzed on a denervated cat skeletal muscle with quite well-preserved local vascular control and perfused with autologous blood. CFC was estimated by increasing venous pressure and by decreasing tissue pressure, and both during autoperfusion and pressure controlled pump perfusion. A constant filtration rate was achieved 3-4 min after the transcapillary pressure elevation, giving a CFC around 0.0090 mL min-1 mmHg-1 100 g. The CFC did not change with arterial pressure or with reduced vascular tone using the tissue pressure method, but decreased slightly with increased arterial pressure and reduced vascular tone using the venous pressure method. CFC variations with arterial pressure were larger during pump perfusion in which myogenic reactivity is depressed, indicating that influence of myogenic tone on CFC is small. We conclude that CFC can be used to evaluate capillary hydraulic conductivity, and also when arterial pressure, vascular tone and blood flow are altered within reasonable physiological limits during the experiment, and the tissue pressure method and autoperfusion is to be preferred.

Physiologic principles for volume regulation of a tissue enclosed in a rigid shell with application to the injured brain

BACKGROUND

Preservation of a high cerebral perfusion (mean arterial) pressure to prevent ischemia has become the primary focus during treatment of severe head trauma because ischemia is favored as a triggering mechanism behind intracellular brain edema development and poor outcome. A high cerebral perfusion pressure, however, simultaneously may increase the hydrostatic vasogenic edema. The present paper evaluates the mechanisms behind the vasogenic edema by analyzing the physiologic hemodynamic mechanisms controlling the volume of a tissue that is enclosed in a rigid shell, possesses capillaries permeable for solutes, and has depressed autoregulation.

RESULTS AND CONCLUSIONS

We contend that in the long run, the interstitial volume in such a tissue can be reduced only through reduction in arterial inflow pressure providing an otherwise optimal therapy to improve microcirculation. Therefore we argue, in contrast to the conventional view, that antihypertensive and antistress therapy may be of value by reducing the interstitial tissue volume during treatment of brain edema, and that the problem with ischemia during such therapy can be handled when considering an otherwise optimal intensive care. These physiologic principles of interstitial tissue volume regulation form the basic concept for the "Lund therapy" of severe head injuries, which is a new and controversial therapy of posttraumatic brain edema.

Arterial pressure-flow relationship in patients undergoing cardiopulmonary bypass

We determined the arterial pressure-flow relationship experimentally by means of step changes of blood flow in 30 adult patients undergoing cardiopulmonary bypass (CPB). Anesthesia technique was uniform. CPB was nonpulsatile; hypothermia to 25-28 degrees C, and hemodilution to 18%-25% hematocrit were used. During stable bypass, mean arterial pressure was recorded first with blood flow 2.2 L.min-1.m-2. Flow was then increased to 2.9 L.min-1.m-2 for 10 s and reverted to baseline for 1 min. Then it was decreased to 1.45 L.min-1.m-2 for 10 s, and reverted to baseline for 1 min. Subsequently, it was decreased to 0.73 L.min-1.m-2 for 10 s and then reverted to baseline. Similar sets of measurements were repeated after 0.25 mg of phenylephrine and once the patient was rewarmed. The pressure-flow function was individually determined by regression, and the critical pressure estimated by extrapolation to zero flow. All patients had zero-flow critical pressure during hypothermia, with a mean value of 21.8 +/- 6.4 mm Hg (range 8.8-38.9). It increased after 0.25 mg phenylephrine to 25.4 +/- 7.2 mm Hg (range 12.2-43.9, P < 0.001). During normothermia, critical pressure was 21.2 +/- 5 mm Hg (range 13.4-30.9), not significantly different from hypothermia. During hypothermia, the slope of the pressure-flow function (i.e., resistance) was 14.9 +/- 3.5 mm Hg.L-1.min-1.m-2 (range 7.6-22.1). It increased significantly (P < 0.001) after phenylephrine, to 19.7 +/- 6.2 mm Hg.L-1.min-1.m-2 (range 11.4-40.5), and returned to 15.4 +/- 3.4 mm Hg.L-1.min-1.m-2 (range 10.1-24.2) during normothermic bypass. Systemic vascular resistance appeared to vary reciprocally with blood flow, although this finding may represent a mathematical artifact, which can be avoided by using zero-flow critical pressure in the vascular resistance equation.

Aspects on the cerebral perfusion pressure during therapy of a traumatic head injury

An actively raised cerebral perfusion pressure by vasopressors is nowadays often advocated during therapy of a post traumatic brain oedema to improve oxygenation of the brain. In this paper we argue that the arterial pressure not uncritically can be raised as the subsequent increase in hydrostatic capillary pressure may favour transcapillary filtration if the blood-brain barrier is opened for solutes. Further, the use of vasoconstrictor drugs to increase the perfusion pressure may in fact impair oxygenation to the penumbra zones around brain contusions but also to other tissues of the body, like the intestinal mucosa and the kidney. An alternative therapeutical concept which both ensures an adequate oxygenation of the brain and controls the intracranial pressure (ICP) is given. In short, it implies active antistress and sedative treatment, adequate fluid therapy with blood and colloids to normal haemoglobine and albumin values, artificial ventilation to normal PaCO2 and PaO2, and this in combination with antihypertensive and catecholamine reducing treatment with alpha 2-agonist and beta 1-antagonist.

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.