[Treatment of hypovolemia in brain injured patients]

The appropriate administration of intravenous fluids in neurosurgical patients remains an area of disagreement between neurosurgeons and anaesthetists. Fluid restriction has long been advocated by the former and is widely believed to reduce or prevent the formation of cerebral oedema. However, such restriction can lead to hypovolaemia which in turn can result in haemodynamic instability. Thus, brain homeostasis should be aimed for through adequate fluid administration and normal or slightly elevated mean arterial pressure. The properties of the endothelium differ between the brain and the remainder of the body. In most non CNS tissues the size of the junctions between endothelial cells averages 65 A. Proteins do not cross these gaps while sodium does. In the brain, the junction size is only 7 A, which is too small to allow crossing by sodium. Investigations with changes in osmotic and oncotic pressure have demonstrated that: 1) reducing osmolality results in oedema formation in all tissues including normal brain; 2) a decrease in oncotic pressure is only associated with peripheral oedema but not in the brain; 3) in case of brain injury, a decrease in osmolality elicits oedema in the part of brain which remained normal; 4) similarly, a decrease in oncotic pressure does not cause an increase in brain oedema in the injured part of the brain. Thus, a major reduction in oncotic pressure is unimportant for the brain, whereas changes in total osmolality are the dominant driving force at this level. To conclude, in a hypovolaemic patient with severe head injury, the crystalloid of choice is NaCl 0.9% and the colloid of choice is hydroxyethylstarch, both with an osmolality > 300 mosm.kg-1. Ringer-lactate is hypoosmotic (255 mosm.kg-1) and may cause or increase cerebral oedema. Mean arterial pressure should be maintained above 80 mmHg.

[Oncotic pressure and hemodilution]

The appropriate fluid therapy in neurosurgical patients remains an area of disagreement between neurosurgeons and anaesthesiologists. Fluid restriction has long been practiced in patients with brain pathology, in order to reduce or prevent the formation of cerebral oedema. This grows from a fear that rapid administration of fluids, particularly noncolloidal fluids, can enhance cerebral oedema, although there is a lack of experimental evidence to substantiate this belief. On the other hand, fluid restriction can lead to relative hypovolaemia, causing haemodynamic instability during anaesthesia and influence defavourably cerebral perfusion. The appropriate fluid management of patients with brain pathology requires a careful review of the Starling's law and a clear understanding of osmolality, oncotic pressure (OP) and the nature of the blood-brain barrier (BBB). The Starling equation of ultrafiltration states that the net movement of fluid between the intra- and extravascular compartments is the result of the summated influences of the pressure gradients (hydrostatic pressure, OP, and osmotic pressure) between those compartments and the properties of the barriers (capillary endothelium) that separate them. In most peripheral tissues this barrier is freely permeable to small molecules and ions and net fluid movement depends on intravascular hydrostatic pressure and OP. Under normal circumstances, intraluminal hydrostatic pressure is higher than interstitial pressure, favouring water egress. By contrast, intraluminal OP is higher than interstitial OP, favouring water retention. These forces do not balance exactly, and fluid accumulation is prevented by the lymphatics. If this net movement exceeds the capacity of the lymphatic clearance mechanisms, fluid accumulates, which is the definition of oedema.(ABSTRACT TRUNCATED AT 250 WORDS)

[Acute stage of spinal injury (physiopathology). "Ischemic damage to the spinal cord"]

Several pathophysiological events follow spinal cord trauma. Vascular abnormality and changes in spinal cord blood perfusion occur immediately after injury primarily within the gray matter. Progressive biochemical and histological alterations take place both in gray and white matter subsequently. The significant metabolic and ionic alterations, all of which are interdependent (reduction in energy substrate, enzymes and neurotransmitters release alterations, ionic fluxes changes) result either in loss of functional activity or structural integrity in the injured spinal cord and remains a matter of speculation.

[Group of study SIAARTI of anesthesia and recovery for neurosurgery and neurology. Present and future]

The authors present the results of a survey of anesthesiologists members of the "SIAARTI (Società Italiana di Anestesia, Analgesia, Rianimazione e Terapia Intensiva) Committee for anesthesia and critical care in neurosurgery and neurology". Among the aims of the survey, was to evaluate when the interest in neuroscience of the members of this group started, and the clinical work dedicated to neuroanesthesia and critical care. At present, the group has grown to 143 members. In the questionnaire 105 members indicated the topic discussed for the medical degree thesis, and 87 indicated the thesis discussed for the board in anesthesia. As emerged from the topic of the thesis discussed for the medical degree, in 47% of the responders the interest in anesthesia began during the college. Of this, 6% chose a topic in neuroanesthesia and critical care. During the residency, the interest in neuroscience increased to 33%, that is 32 out of 97 responders discussed a thesis in neuroanesthesia and critical care. Forty-eight per cent of the members performs clinical work "exclusively" in neuroanesthesia, while 39% does it "mainly", and only 13% works in neurosurgery "fiftfully".

[Transcranial Doppler for the monitoring of gas embolism in neurosurgical operations in the sitting position]

The risk of venous air embolism is significant in neurosurgical procedures performed in the sitting position. Monitoring for venous air embolism, therefore, is crucial and can be approached from several aspects. The most sensitive generally applicable clinical method for the detection of intracardiac gas is based on an application of the Doppler principle. The Authors describe the technique used to adapt a transcranial Doppler (TC 2-64 B, EME, Germany), and a probe designed to record the Doppler signal from intracranial arteries (Transcran FP 2, EME, Germany), as precordial Doppler in order to monitor venous air embolism in neurosurgical procedures performed in the sitting position.

[Complications during preoperative embolization in intracranial meningioma]

We report a rare case of meningioma of the parieto-occipital convexity accompanied by hemorrhage in the tumor and in the subdural space that occurred while pre-operative embolization was being applied. The patient, a 48 year old woman, presented sudden headache and, in a few minutes, comatose status and decerebrate rigidity. A quick diagnosis with CT-scan of acute intratumoral and subdural hemorrhage and a rapid intervention on the patient led to complete recovery. The possible reason for the hemorrhage is the sudden change in blood pressure of pathologic small vessels triggered by embolization.

[Postoperative cerebral edema. Physiopathology of the edema and medical therapy]

Cerebral edema complicates many neurosurgical conditions, such as head injuries, neoplasms and infections, and is the direct result of operative trauma. The recognition and the treatment of brain edema are of great practical importance, particularly in those conditions leading to brain herniations and/or intracranial hypertension. Brain edema can be distinguished into two major categories, based on the integrity of the blood brain-barrier (BBB). With intact BBB edema, the crucial pathogenic event is related to disturbances of cellular metabolism and ionic transport. All the cellular elements of brain may undergo swelling, with a concomitant reduction of the extracellular-fluid space of the brain. Open BBB edema, the most common form of brain edema, is characterized by increased permeability of the brain endothelial cells. Brain edema results from the oncotic forces generated from a serum protein influx into the nervous tissue, and edema fluid accumulates primarily in the extracellular space. The non-operative management of brain edema requires attention to the causes that have induced brain edema. Specific pharmacologic therapy with corticosteroids, hyperosmolar agents and furosemide or acetazolamide depend upon accurate assessment of BBB integrity.

[Monitoring of pediatric patients undergoing magnetic resonance diagnosis with a superconducting magnet]

Magnetic resonance imaging (MRI) has presented to anesthesiologists as unique challenge in patient monitoring because of its construction and principles of operation. Ferromagnetic materials within or near the scanner can distort the magnetic field, and monitoring wires act as antennae and this may result in image degradation. Nevertheless, monitoring is mandatory during MRI, especially in a child sedated or in general anesthesia. A monitoring system, made up of commercially available components, was assessed, and its effects on MR (1.5 tesla unit) image quality system determined. Variables monitored included: electrocardiogram and heart rate, (Sirecust 404, ECG cable set MR; Siemens, Enlanger, West Germany); blood pressure via automated sphygmomanometry (Press Mate BP-8800; Colin, Komaki, Japan); and continuous arterial saturation via pulse oximetry (Nellcor 100 E; Nellcor, Inc., Haywood, California). Fluid infusion rate was controlled by means of a plastic deliver (Dial-a-flo; Abbott Labs., Chicago, Illinois). Body temperature was maintained with a heat insulator blanket (Thermadrape, OR Concepts, Inc., Dallas, Texas). The monitoring technique described did not interfere with MRI function or produce image degradation.

Cerebral effects of isovolemic hemodilution with crystalloid or colloid solutions

The cerebral effects of iv fluids have not been well defined, particularly the differences between crystalloids and colloids. We thus evaluated the effects of lactated Ringer's (LR) and 6% hetastarch (HES) solutions on brain edema, intracranial pressure (ICP), and cerebral blood flow (CBF) in anesthetized rabbits, using a model of isovolemic hemodilution (IVHD). In this model, arterial blood was removed at a rate of approximately 2 ml/min for one hour and replaced simultaneously with LR or HES in amounts needed to maintain arterial BP and CVP; Hct decreased from approximately 40% to approximately 19%. Thirty-six animals were divided into three groups (n = 12 each): a) IVHD with LR, b) IVHD with HES, and c) maintenance LR without hemodilution. To permit the examination of both acute and delayed fluid effects, each group was further divided into two subgroups (n = 6 each): one in which animals were sacrificed immediately on completion of the one-hour IVHD period (early), and one in which animals were sacrificed 4 h later (late). After sacrifice, brain and skeletal muscle water contents (% H2O) were determined, and the specific gravity (SpGr) of multiple brain samples was measured. Much larger volumes of LR were required to maintain normovolemia as compared with HES, (e.g., totals 203 +/- 68 vs. 76 +/- 18 ml/kg, respectively in late animals) and those given LR had larger increases in body weight and muscle % H2O.(ABSTRACT TRUNCATED AT 250 WORDS)

Local cerebral blood flow and glucose utilization during isoflurane anesthesia in the rat

Volatile anesthetic agents have profound and heterogeneous effects on global and local cerebral blood flow (l-CBF) and metabolism. The relationship between l-CBF and local cerebral glucose uptake (l-CMRg) during isoflurane anesthesia is unknown. Because these relationships might influence neuronal homeostasis during periods of cerebral ischemia of different causes, it becomes important to understand them. Accordingly, the authors evaluated the l-CBF and l-CMRg effects of isoflurane with quantitative autoradiography in normal rats. As the dose of isoflurane increased in a stepwise fashion to 0.5, 1.0 (1.38%), 1.5, and 2.0 MAC levels, the number of structures with a significant (P less than 0.05) l-CBF increase or l-CMRg decrease became greater. At each respective MAC level l-CBF was increased in 0%, 11%, 34%, and 30%, while l-CMRg decreased in 11%, 70%, 74%, and 81% of the structures in which autoradiographic measurements were performed. Between 1.5 MAC and 2.0 MAC the l-CMRg decrease stabilized at about -50% to -70% of cerebral metabolic values obtained in awake control rats in association with attainment of a burst-suppression of isoelectric electroencephalogram. In contrast to these general changes, l-CMRg in two subcortical limbic system structures (dentate gyrus and interpeduncular nucleus) did not decrease, even at the highest doses of isoflurane. L-CBF was significantly (P less than 0.05) increased only at the highest dose ranges (1.5-2.0 MAC) and increased from 34% to 238% in about one-third of the structures evaluated. Isoflurane anesthesia causes heterogeneous changes in l-CBF and metabolism, which are most apparent at doses at or above 1.0 MAC.(ABSTRACT TRUNCATED AT 250 WORDS)

Local cerebral blood flow during lidocaine-induced seizures in rats

Neurophysiologic and local cerebral metabolic mapping techniques indicate that seizures associated with lidocaine toxicity originate in subcortical brain structures. Normally local cerebral blood flow (l-CBF) is quantitatively coupled to local cerebral metabolic rate for glucose (l-CMRg). In the present study the response of l-CBF to a lidocaine-induced preconvulsive state (localized seizure activity in the absence of a grand mal seizure) was evaluated in rats anesthetized with 60% nitrous oxide. Lidocaine administered as a bolus (20 mg/kg) followed by an infusion (4 mg/kg) over 5.5 min resulted in progressive alteration in the electroencephalogram (EEG). L-CBF was studied with the 14C-iodoantipyrine autographic method when the preconvulsive EEG pattern consisted of a repetitive spike and wave complex at a frequency of 14 +/- 1 X min-1 complexes, superimposed on practically isoelectric background activity. Under these conditions high doses of lidocaine significantly (P less than 0.05) decreased (range -30% to -68%) l-CBF in 71% of the 34 brain regions studied. The greatest exception to this trend for l-CBF to decrease was observed in the limbic system wherein l-CBF remained within control ranges in eight of the 11 structures evaluated. Qualitative comparison of lidocaine l-CBF changes with l-CMRg changes obtained under similar conditions indicated a general trend for local flow and metabolism to decrease in parallel. Exceptions to this were confined to certain limbic areas (amygdala and hippocampus) in which increases in l-CMRg were more than 100% greater than slight (P greater than 0.05) increases in l-CBF.(ABSTRACT TRUNCATED AT 250 WORDS)

Cerebral effects of isovolemic hemodilution with a hypertonic saline solution

In view of a growing interest in the resuscitative use of hypertonic saline solutions, the authors have examined the cerebral effects of isovolemic hemodilution carried out over 1 hour (hematocrit decreased from 40% to 20%, stable arterial and right arterial pressures), using a hypertonic lactated Ringer's solution (HT-LR: Na+ 252 mEq/liter, osmolality 480 mOsm/liter). Experiments were carried out in anesthetized ventilated rabbits. Measured variables included cerebral blood flow (using the H2 clearance method), intracranial pressure (ICP), the electroencephalogram, spinal cord and skeletal muscle water content (%H2O), and the specific gravity of small (10- to 30-mg) tissue samples taken from different areas of the left hemisphere (including the cortex, thalamus, internal capsule, and hippocampus). The changes produced by HT-LR were compared with those seen in both undiluted control animals and in rabbits hemodiluted with normal saline (Na+ 155 mEq/liter, osmolality 310 mOsm/liter). The results demonstrate that hemodilution with HT-LR leads to the expected increases in serum Na+ and osmolality (158 +/- 6 mEq/liter and 320 +/- 5 mOsm/kg, respectively, mean +/- standard deviation) and that these were accompanied by reductions in the %H2O of all cerebral and extracerebral tissues, increases in the specific gravity of all tissue regions studied, and a decrease in ICP (1.9 +/- 0.7 mm Hg). By contrast, rabbits with hemodilution by normal saline showed no changes in either %H2O or specific gravity, but had significant increases in ICP (3.3 +/- 1.3 mm Hg). Cerebral blood flow increased in all animals hemodiluted with either HT-LR or normal saline by a combined average of +29 ml/100 gm/min. Although these studies were performed in neurologically normal animals, the combination of cerebral changes seen with HT-LR (cerebral dehydration, less peripheral edema, decreased ICP but with increased cerebral blood flow) suggests that this approach may have some advantages over the use of isotonic fluids, and may have some utility in the resuscitation of head-injured patients.

Cerebrovascular effects of prolonged hypocarbia and hypercarbia after experimental global ischemia in cats

Hyperventilation therapy is often recommended after an episode of global cerebral ischemia (cardiac arrest), even though several workers have shown that under such circumstances the cerebral vasculature is unresponsive to changing PaCO2. However, no study has examined the effects of prolonged PaCO2 changes. We therefore studied the cerebrovascular effects of a 3-h period of continuous hypercarbia (40 to 45 torr) or hypocarbia (15 to 20 torr) in cats resuscitated from 12 min of electrically induced ventricular fibrillation. There were no differences in postresuscitation cerebral blood flow (CBF) or EEG, but intracranial pressure was lower in the hypocapnic animals. Furthermore, hypocapnic cats retained some CBF responsiveness to varying PaCO2 levels, while no such response was noted in previously hypercapnic animals. These findings suggest that some measurable changes in postarrest cerebrovascular behavior can result from prolonged hypocapnia (possibly related to tissue pH alterations). Whether such changes will have clinical utility is unclear.