[Experimental and clinical investigations on the treatment of brain edema by intravenous glycerin administration]

Osmotherapy for elevated intracranial pressure: a critical reappraisal

The administration of osmotic agents is one of the principal strategies to lower elevated intracranial pressure (ICP) and to increase cerebral perfusion pressure. Of the 3 osmotic agents frequently used (mannitol, glycerol and sorbitol), each has characteristic advantages and disadvantages. In addition to renal filtration, sorbitol [elimination half-life (t1/2beta) approximately 1h] and glycerol (t1/2beta 0.2 to 1h) are metabolised, mainly by the liver. The risk of these compounds accumulating in patients with renal insufficiency is low. However, both compounds frequently affect glucose metabolism, leading to an increase in the serum glucose concentration. Mannitol is almost exclusively renally filtered and possesses the slowest elimination from serum (t1/2beta 2 to 4h). The t1/2beta of mannitol is markedly increased in patients with renal insufficiency, but it does not interfere with glucose metabolism. Entry into the cerebrospinal fluid (CSF) is highest with glycerol [CSF: serum ratio of the areas under the concentration-time curves (AUC(CSF): AUCs) approximately 0.25], intermediate with mannitol (AUC(CSF): AUCs approximately 0.15) and lowest with sorbitol (AUC(CSF): AUCs approximately 0.10). The elimination of all osmotic agents from the CSF compartment is substantially slower than from serum. During the elimination phase, the CSF-to-serum osmotic gradient is temporarily reversed. This is one cause of the paradoxical rise of ICP above the pretreatment level sometimes observed with osmotherapeutics. The ability of mannitol, glycerol and sorbitol to lower elevated ICP has been extensively documented. However, whether the use of osmotic agents, particularly with repeated application, improves outcome remains unproven. Therefore, these agents should only be used to treat manifest elevations of ICP, not for prophylaxis of brain oedema.

Temporary reversal of serum to cerebrospinal fluid glycerol concentration gradient after intravenous infusion of glycerol

Glycerol 50 g infused i.v. over 2 to 6 h is widely used to treat cerebral oedema in patients with acute stroke. Its transit through the blood-cerebrospinal fluid barrier in subjects with uninflamed meninges has now been examined. In 7 patients with an external ventriculostomy for occlusive hydrocephalus, each of whom was given 500 ml of a 10% solution IV over 4 h, serum and CSF were repeatedly sampled during and after the infusion and glycerol was measured enzymatically. The highest serum glycerol level of 191-923 mg/l was observed at the end of the infusion. The maximum CSF glycerol of 18.7-110.8 mg/l was attained 0-1 h after the end of the infusion. Elimination both from serum and CSF approximated a single-exponential decay; the elimination half-life from serum was 0.29-0.56 h compared to 1.03-3.68 h from CSF. In six of the seven cases there was a temporary reversal of the serum/CSF concentration gradient during glycerol elimination. The ratios of the AUCs of CSF and serum, which describe the overall penetration of glycerol into CSF, ranged from 0.09-0.31. In conclusion, the serum level of glycerol produced by giving 50 g IV glycerol over 4 h may not be sufficiently high reliably dehydrate to brain tissue in many patients, and the slow elimination of glycerol from the CSF may be related to the so-called rebound phenomenon.

Clinical pharmacokinetic considerations in the treatment of increased intracranial pressure

Life-threatening increased intracranial pressure can be reversed by a variety of drugs. These compounds all have some disadvantages, producing rebound effects, severe coma or cardiovascular depression and electrolyte imbalance. However, reduction of intracranial pressure is a prerequisite for recovery and the benefits of treatment outweigh the risks. Dexamethasone is rapidly eliminated, the short half-life (about 3 hours) indicating that dosage intervals should be kept small. As yet, however, its therapeutic efficacy has not been clearly demonstrated. Therefore, an association between pharmacokinetics and pharmacodynamics cannot be established. Osmotic diuretics are the most widely used agents for reduction of intracranial pressure. Pharmacokinetics show a very close relationship to changes in serum osmolality, but there are large variations in the clearance. For the use of osmotics, the blood-brain barrier must be intact. Osmotic diuretics may lead to intracerebral oedema or to acute renal failure as serum osmolality increases. Considering the pharmacokinetics of each drug, and the dynamics of intracerebral pressure and osmolality, an intermittent, individually titrated dosage should be administered, with simultaneous monitoring of intracranial pressure. Frusemide (furosemide) can be used as an adjunct, to enhance the effect of osmotic diuretics. Its pharmacokinetics are limited by renal function, depending on age as well as on the extent of renal impairment. Altered renal elimination of concomitantly administered drugs, and electrolyte imbalances should be anticipated when diuretics are used. Barbiturates are certain to decrease intracranial pressure in humans by an as yet unknown mechanism. Their administration is recommended for patients that do not respond to conventional therapy. As barbiturates can result in deep coma, knowledge of their pharmacokinetics is of great importance for recovery. Following single doses, pentobarbitone has a relatively long elimination half-life (about 22 hours). However, after repeated administration for several days, its elimination may be enhanced due to autoinduction. Thiopentone kinetics are characterised by distribution and redistribution into deep peripheral compartments. Administration of high and frequent doses leads to considerably delayed recovery. This is not true for methohexitone, which shows comparable pharmacokinetics after single and multiple dose administration. Elimination depends on liver blood flow. Thus, recovery from methohexitone-coma is rapid. Rapid elimination is also an important characteristic of etomidate and alphaxalone/alphadolone, two non-barbiturate hypnotics.(ABSTRACT TRUNCATED AT 400 WORDS)

Comparison of the effects of hypertonic glycerol and urea on brain edema, energy metabolism and blood flow following cerebral microembolism in the rat. Deleterious effect of glycerol treatment

Cerebral microembolism was performed in rats by injecting radioactive calibrated 50 mu microspheres into the left internal carotid artery. The use of radioactive microspheres as embolic agents enabled the number of microspheres to be determined in each cerebral hemisphere. Edema was assessed 24 h after embolization by measuring brain water, sodium, and potassium content. Equiosmolal doses (40 mmol/kg) of glycerol or urea were injected i.p. at various times before sacrifice. Both treatments caused similar changes in water and electrolyte content, brain dehydration being maximal 30 min after urea and 2 h after glycerol injection. Cerebral energy metabolism and regional blood flow were evaluated at the times of maximal brain dehydration. Urea treatment resulted in an improvement of the cerebral circulation whereas glycerol treatment led to a deterioration of cerebral blood flow which cannot be explained by failure to reduce edema and the consequent microcirculatory impairment. Urea treatment had no marked effect on cerebral energy metabolism whereas glycerol injection resulted in an important increase in brain lactate level which may be relevant to the impairment of cerebral reperfusion. These results point out that administration of a metabolized solute like glycerol may exert deleterious effects on the ischemic brain.

Effect of furosemide (lasix) on acute severe experimental cerebral edema

The effect of furosemide (Lasix) therapy on a standardized experimental cerebral edema, induced in rats by applying a cooling stamp to the right side of the skull over the right coronal suture by means of a stereotactic instrument, was examined. The hemispherically separated water and electrolyte contents of the brain were analyzed after 24 h. Following furosemide therapy, the behavior of these edema parameters was compared statistically with dexamethasone, glycerol and albumin. An increase of the water and sodium content, and a decrease of potassium was observed 24 h after the trauma, especially in the right hemisphere. Furosemide did not improve either the water content or the electrolyte balance. By contrast, the administration of dexamethasone, glycerol and albumin was followed by a significant improvement of the edema. In experiments with cats, the course of the edema and the effect of furosemide on the cold brain injury of the right hemisphere were observed by measuring the intracranial pressure (ICP) values, and by continuous monitoring of the EEG. The ventricular CSF pressure and epidural pressures were also recorded. The electrical brain activity was continuously compared with the course of the ICP by means of computer analysis. In addition, the blood osmolality and diuresis were monitored. The ICP increased rapidly after the trauma, establishing considerable pressure gradients, and the EEG power intensities decreased markedly on the right side. Histologically, there was an extended edema of the white matter of both hemispheres. The ICP was not lowered by single injections or high dose infusions of furosemide, and the EEG power intensities also did not improve. Infusions of large volumes of furosemide even resulted in an increase of ICP, but infusion of 40% sorbitol effected a rapid decrease of ICP and EEG recovery over the left hemisphere. Sorbitol infusion also caused a marked rise in the blood osmolality, whereas furosemide had no such effect. The results raise considerable doubts as to the propriety of the exclusive use of furosemide for cases of acute cerebral edema with raised ICP. The diuretic effect is insufficient to establish an osmotic gradient, and its general dehydrating effect does not acutely influence the ICP. The absence of effect on the experimental tissue edema would not appear to commend furosemide as basic therapy for cases of traumatic cerebral edema.