Acute brain swelling in neurosurgical patients

Management of Elevated Intracranial Pressure

Elevated intracranial pressure (ICP) is a primary cause of morbidity and mortality for many neurologic disorders. The relationship between ICP and brain volume is influenced by autoregulatory processes that can become dysfunctional. As a result, neurologic damage can occur by systemic and intracranial insults such as ischemia and excitatory amino acids. Therefore, survival is dependent on optimizing ICP and cerebral perfusion pressure. Treatment of intracranial hypertension requires intensive monitoring and aggressive therapy. Intracranial pressure monitoring techniques such as intraventricular catheters are useful for determining ICP elevations before changes in vital signs and neurologic status. Therapeutic modalities, generally aimed at reducing cerebral blood volume, brain tissue, and cerebrospinal fluid (CSF) volume, include nonpharmacologic (CSF removal, controlled hyperventilation, and elevating the patient’s head) and pharmacologic management. Mannitol and sedation are first-line agents used to lower ICP. Barbiturate coma may be beneficial in patients with elevated ICP refractory to conventional treatment. The use of prophylactic antiseizure therapy and optimal nutrition prevents significant complication. Currently, investigations are directed at discovering useful neuroprotective agents that prevent secondary neurologic injury.

Effect of hyperventilation on extracellular concentrations of glutamate, lactate, pyruvate, and local cerebral blood flow in patients with severe traumatic brain injury

OBJECTIVE

To determine the potential adverse effects of brief periods of hyperventilation commonly used for acute neurologic deterioration.

DESIGN

Prospective clinical trial.

SETTING

University medical school.

PATIENTS

Twenty patients with severe traumatic brain injury.

INTERVENTIONS

The effect of 30 mins of hyperventilation (mean PaCO2, 24.6 mm Hg) on the extracellular metabolites associated with ischemia, and on local cerebral blood flow was studied by using microdialysis and local cerebral blood flow techniques. Normal appearing brain adjacent to evacuated hemorrhagic contusions or underlying evacuated subdural hematomas was studied. Hyperventilation trials were done 24-36 hrs after injury and again at 3-4 days after injury. Dialysate concentrations of glutamate, lactate, and pyruvate were measured before and for 4 hrs after the hyperventilation trials.

MEASUREMENTS AND MAIN RESULTS

At 24-36 hrs, hyperventilation led to a >or=10% increase in the extracellular concentrations of glutamate in 14 of 20 patients, with concentrations in those 14 patients 13.7-395% above baseline; a >or=10% increase in lactate in 7 of 20 patients (11.6-211% above baseline); and a >or=10% increase in the lactate/pyruvate ratio in eight of 20 patients (10.8-227% above baseline). At 3-4 days after injury, ten of 13 patients had an increase in glutamate of >or=10%, while only three of 13 patients had an increase in extracellular lactate and two of 13 patients had an increase in the lactate/pyruvate ratio of this magnitude. The hyperventilation associated increases in extracellular glutamate and lactate concentrations were significant ( P<.05; one-sample Student's -test) at both time points after injury, as was the lactate/pyruvate ratio at 24-36 hrs. A >or=10% decline in local cerebral blood flow was observed with hyperventilation in five of 20 patients at 24-36 hrs (range, 10.2-18.7% below baseline), and in ten of 13 patients studied at 3-4 days (11.3-54% below baseline). There was no correlation with the presence or absence of local CO2 vasoresponsivity and increases in the extracellular metabolites at either the early or late time points.

CONCLUSIONS

In brain tissue adjacent to cerebral contusions or underlying subdural hematomas, even brief periods of hyperventilation can significantly increase extracellular concentrations of mediators of secondary brain injury. These hyperventilation-induced changes are much more common during the first 24-36 hrs after injury than at 3-4 days.

Local cerebral blood flow measured by xenon-enhanced CT during cryogenic brain edema and intracranial hypertension in monkeys

We developed a closed-skull model of freeze injury-induced brain edema, a model classically thought to produce vasogenic edema, and observed the natural course of changes in edema and blood flow using xenon-enhanced computed tomography (CT) in five rhesus monkeys before and for up to 6 h post insult. Intracranial pressure (ICP) gradually rose throughout the duration of the experiment. CT scans and CBF images permitted direct observation of the evolution of the lesion and revealed early ischemia in the periphery of the injury zone that progressed over time in association with edema. Frequency histogram analysis of local CBF (ICBF) demonstrated subtle but potentially important changes in distribution of ICBF between and within hemispheres at various times post insult. Changes in ICBF distribution were phasic and dissociated from increases in ICP in the latter stages of injury. The Xe/CT CBF method can be used to evaluate the effects of injury and therapy on CBF in this and other models of acute brain injury.

Changes in regional cerebral blood flow after hyperventilation in the pig with an induced focal cerebral contusion

Changes in regional cerebral blood flow in anaesthetized pigs with an induced focal cerebral contusion were studied before and after two grades of hyperventilation. A reduction in arterial tension of CO2 with 0.70 mmHg and a further reduction of 0.55 mmHg did not change the CO2 reactivity. Reactivity in both injured and macroscopically normal regions was the same, revealing an average of 39.3% flow change per kPa change in CO2 tension. Regions with low flow after the contusion had an equally big reduction apparently leading to hypoxia because global metabolic rate was unchanged.

Brain tissue pressure: physiological observations in anesthetized cats

This study of direct tissue pressure measurement from brain parenchyma in 25 anesthetized cats focuses on steady-state observations and responses to some common physiological manipulations. Tissue pressure recording by a needle system can be done accurately without significant alterations of the blood-brain barrier, brain water content, regional cerebral blood flow, and cerebrovascular reactivity to changes in PaCO2 and cerebral perfusion pressure. Methodological details, including in vitro and in vivo validation, are described.

Influence of changes in arterial pCO2 on cerebral blood flow and metabolism during high-dose barbiturate therapy in dogs

In 13 dogs the response of the cerebral circulation to changes in PaCO2 ranging from 20 to 60 torr was studied before and after administration of high doses of sodium thiopental. Infusion of sufficient barbiturate to produce 30- to 60-second burst suppression in the electroencephalogram was associated with a profound degree of cerebral vasoconstriction, equivalent to that produced by hypocapnia with PaCO2 = 20 torr. Furthermore, once sodium thiopental was administered, no significant difference in cerebral blood flow (CBF) or vascular resistance (CVR) was noted between PaCO2 of 30 and 20 torr. However, changes of approximately 15% in CBF and 30% in CVR were noted between PaCO2 at 40 and 20 torr. These data suggest that hyperventilation of PaCO2 of less than 30 torr may not effectively increase the degree of cerebral vasoconstriction in these circumstances.

Cerebral arterial blood flow and aneurysm surgery. Part 1: local arterial flow dynamics

Cerebral arterial blood flow was monitored in 22 patients undergoing surgery for intracranial saccular aneurysms. An electromagnetic flow probe was used to record the internal carotid artery (ICA) flow in the neck or intracranially in seven patients. The ICA flow ranged between 100 and 175 ml/min (average 144 ml/min). Intracranial flow measurements with specially designed probes were made in 17 patients. The middle cerebral artery (MCA) showed flow values between 75 and 120 ml/min (average 97 ml/min). Flow figures recorded from the proximal anterior cerebral artery (ACA) were lower (average 65 ml/min), and had a wider range from 30 to 110 ml/min. Test occlusion of the terminal ICA showed a retrograde flow in the proximal ACA to the MCA ranging from 15 to 125 ml/min (average 78 ml/min). This test was used to investigate the collateral potential of the anterior portion of the circle of Willis, which is essential to the decision of whether to undertake trap ligation procedures in this location. Flow monitoring in the parent vessel was also of use in some patients to assess flow conditions after the clipping of the aneurysm neck.

Treatment of intracranial hypertension. Analysis of 105 consecutive, continuous recordings of intracranial pressure

One hundred and five consecutive recordings of intracranial pressure (ICP) in 95 patients over a three-year period, using a Scott cannula inserted through a burr hole or a twist drill hole into the anterior horn of the lateral ventricle, represent the patient material for this report. The clinical diagnoses were head injury 32, intracranial tumour 31, aneurysm and arteriovenous malformation 18, brain swelling secondary to systemic disease 8, and brain swelling of unknown etiology 6. ICP exceeded 20 mm/Hg in 86 of the recordings (maximum 110 mm/Hg). Hypertonic mannitol was administered 73 times in 48 patients. ICP was reduced 10% or more (mean 52%) in all but three administrations. The effect of hyperventilation was tested in 50 trials in 34 patients. ICP was reduced 10% or more (mean 47%) in 34 trials. The mean time to maximum reduction of ICP was eight minutes, and ICP returned to control almost immediately after cessation of hyperventilation. Hypothermia was studied in 40 trials in 40 patients. ICP was reduced 10% or more (mean 51%) in half the patients. The infection rate was 6.3% in this four-hospital setting, but four of the six infections were in one hospital. If this hospital is excluded, the infection rate is 3.1%.

Detection of experimental and clinical brain edema using an electrical impedance method

✓ To clarify the development of brain edema, the electrical impedance of white matter was measured with intracerebral implanted electrodes in cold-induced edema in the cat and in cases of edema after major intracranial surgery. Impedance measurements were made at 50 kc using a tetrapolar electrode method with a pair of concentric platinum electrodes. The impedance of the brain gradually decreased 25% after several hours of cold application. The amount of increase of sulfate space of brain showed a good correlation with decrease of impedance. In four postoperative cases of brain tumor, a 7.5% to 25% decrease of impedance was observed within several hours of surgery. A severe case of brain edema, in which the prognosis was poor, showed marked intracranial pressure and 25% decrease of impedance.

Intracranial pressure responses to alterations in arterial carbon dioxide pressure in patients with head injuries

✓ Cerebral vasomotor responses to alterations in arterial carbon dioxide (PaCO2), as manifested by intraventricular pressure changes, were studied in a group of patients with head injuries. These patients could be classified into three types based on various degrees of responsiveness thought to reflect the integrity of their cerebral vasomotor reactivity.

Response of cereborspinal fluid pressure to hyperbaric oxygenation

The response of cerebrospinal fluid pressure (CSFP) to hyperbaric oxygenation (OHP) was investigated in 13 patients with acute cerebral damage and in dogs with or without experimentally produced cerebral damage. To elucidate the mechanism of the CSFP response, continuous measurements of carotid blood flow, arterial blood pressure, central venous pressure, and superior sagittal sinus pressure and CSFP were made before, during and after OHP. There was considerable variation in the response of CSFP to OHP in the patients, but three main patterns emerged; type I (nine cases), CSFP decreased at the beginning and rose again at the end of OHP, type II (two cases), CSFP fell with OHP and remained significantly lower than pretreatment level after it, and type III (two cases), CSFP showed little change with OHP. An animal without cerebral damage commonly showed a type I response of CSFP to OHP; the changes of CSFP at the beginning and end of OHP are mainly due to the changes of the cerebral blood flow. There may be two different actions of OHP on cerebral oedema, one decreasing cerebral oedema and another (mainly affecting the normal brain) producing cerebral oedema. Information obtained from the response of CSFP to OHP may be useful in judging the severity and pathophysiological state of cerebral damage.