Selective effect of mannitol-induced hyperosmolality on brain interstitial fluid and water content in white matter

Monitoring and intraoperative management of elevated intracranial pressure and decompressive craniectomy

Elevated intracranial pressure can be caused by a variety of underlying conditions. Several physiologic and pharmacologic factors have a significant impact on intracranial hypertension, mostly caused by changes on cerebral blood volume, flow, and oxygenation. There are many therapies that can be used to decrease intracranial pressure ranging from pharmacologic to the surgical decompressive removal of the calvarium. Special consideration is made for the anesthetic management of these patients perioperatively.

Monitoring and intraoperative management of elevated intracranial pressure and decompressive craniectomy

There are numerous clinical scenarios wherein a critically ill patient may present with neurologic dysfunction. In a general sense these scenarios often involve ischemia, trauma, or neuroexcitation. Each of these may include a period of decreased cerebral perfusion pressure, usually due to elevated intracranial pressure (ICP), eventually compromising cerebral blood flow sufficiently to produce permanent neuronal loss, infarction, and possibly brain death. Elevated ICP is thus a common pathway for neural demise and it may arise from a variety of causes, many of which may result in a neurosurgical procedure intended to ameliorate the impact or etiology of elevated ICP.

Effects of Mannitol Bolus Administration on Intracranial Pressure, Cerebral Extracellular Metabolites, and Tissue Oxygenation in Severely Head-Injured Patients

BACKGROUND

Osmotic agents are widely used to lower elevated intracranial pressure (ICP). However, little data are available regarding cerebral oxygenation and metabolism in the traumatized brains studied under clinical conditions. The present prospective, open-labeled clinical study was designed to investigate whether administration of mannitol, with the aim of reducing moderate intracranial hypertension, improves cerebral metabolism and oxygenation in patients after severe traumatic brain injury (TBI).

METHODS

Multimodal cerebral monitoring (MCM), consisting of intraparenchymal ICP, tissue oxygenation (ptiO2), and micro dialysis measurements was initiated in six male TBI patients (mean age 45 years; Glasgow Coma Scale score <9). A total of 14 mannitol boli (20%, 0.5g/kg, 20 minutes infusion time) were administered to treat ICP exceeding 20 mm Hg (2.7 kPa). Temporal alterations determined by MCM after mannitol infusions were recorded for 120 minutes. Microdialysates were assayed immediately for extracellular glucose, lactate, pyruvate, and glutamate concentrations.

RESULTS

Elevated ICP was successfully treated in all cases. This effect was maximal 40 minutes after start of infusion (25 +/- 6 mm Hg [3.3 +/- 0.8 kPa] to 17 +/- 3 mm Hg [2.3 +/- 0.4 kPa], p < 0.05) and lasted up to 100 minutes. Cerebral ptiO2 remained unaffected (21 +/- 5 mm Hg [2.8 +/- 0.7 kPa] to 23 +/- 6 mm Hg [3.1 +/- 0.8 kPa], n.s.). Microdialysate concentrations of all analytes rose unspecifically by 10% to 40% from baseline, reaching maximum concentrations 40 to 60 minutes after start of the infusion.

CONCLUSIONS

Mannitol efficiently reduces increased ICP. At an ICP of up to 30 mm Hg [4 kPa] it does not affect cerebral oxygenation. Unspecific increases of extracellular fluid metabolites can be explained by transient osmotic dehydration. Additional mechanisms, such as increased cerebral perfusion and blood volume, might explain an accelerated return to baseline.

Effect of seizures and diuretics on the osmolality of the cerebrospinal fluid

There was a significant increase in the osmolality of the cerebrospinal fluid (CSF) of the anesthetized rats after treatment with 80 mg/kg (but not 39 mg/kg) furosemide and 1 g/kg of mannitol, but not during seizures induced by kainic acid. Furosemide (10 mg/kg) blocked seizure activity by kainic acid, while mannitol (1 g/kg) did not. The results suggest that the antiepileptic effect of furosemide is due to a direct CNS effect not related to a change in CSF osmolality.

Autoradiographic patterns of brain interstitial fluid flow after collagenase-induced haemorrhage in rat

Cerebral oedema accompanies intracerebral haemorrhage. We induced intracranial bleeding by the intracerebral injection of bacterial collagenase. There was oedema observed both at the haematoma site in the caudate/putamen and bilaterally in the hippocampal regions. To determine the role of vasogenic oedema spread from the site of injury, we studied by autoradiography the distribution of extracellular markers injected along with the collagenase. Both 14C-dextran (m.w. 70,000) and 14C-sucrose (m.w. 341) spread away from the injection site into both hippocampal regions in a similar pattern, suggesting bulk flow. Vasogenic oedema secondary to a haemorrhagic lesion in the caudate/putamen is an important cause of the oedema observed in both hippocampal regions in our model.