Is There a Best Technique in the Patient With Increased Intracranial Pressure?

INTRODUCTION

The contents of the cranium can be divided into three major constituents. The brain or tissue compartment accounts for approximately 85% of the total intracranial volume, cerebrospinal fluid (CSF) contributes approximately 10%, and the blood in the vasculature contributes approximately 5%. Most of the cerebral blood volume (CBV) resides in the low-pressure venous system, whereas only 15% of the CBV is found in the arteries and 15% in the venous sinuses.

Intracranial pressure (ICP) is maintained within normal limits, even in the presence of a space-occupying lesion, as long as compensatory mechanisms are operational and the pathologic process evolves slowly. Any increase in intracranial volume must be compensated by volume reduction of one of the other compartments to maintain normal ICP. The CSF system has the greatest buffering capacity through displacement of CSF from the cranium to the spinal subarachnoid space. CBV reduction occurs first through compression of the low-pressure venous system, followed by capillary collapse and, lastly, arterial compression, leading to cerebral ischemia. The impact of ICP on outcome lies in its role in determining cerebral perfusion pressure (CPP; CPP = mean arterial pressure [MAP] - ICP). There is evidence, at least in head trauma, that a CPP of less than 50 mm Hg is associated with poor outcome. Nevertheless, an improved outcome does not necessarily result from a higher CPP. For the calculation of CPP, the arterial pressure transducer should be at the level of the ear.

Increased ICP may be caused by changes in the volume of any one or a combination of the intracranial compartments, including hematomas caused by vascular rupture, increases in brain tissue and interstitial volumes caused by tumors, or vasogenic and cytotoxic edema secondary to hypoxia and infection. Increased ICP can also result from obstruction of CSF pathways and alteration of CSF production or reabsorption.

OPTIONS

Management strategies include decisions about the choice of (1) anesthetic drugs, (2) ventilation, (3) hyperosmolar therapy, (4) head and body position, and (5) decompressive craniectomy. The effects are influenced by whether the ICP increase was acute or has developed slowly, which usually allows for some compensation to take place.

EVIDENCE/CONTROVERSIES/AREAS OF UNCERTAINTY/GUIDELINES