Intracranial Hypertension-Increased Intracranial Pressure

Intracranial Hypertension-Increased Intracranial Pressure -The rigid cranial vault contains brain, (1400 g) blood (75 ml) and cerebrospinal fluid (CSF) (75 ml) which are normally in a state of pressure and volumeequilibrium. Since there is limited space for expansion wit11 in the skull, anincrease of any one of these compartments necessitate a reciprocal change in thevolume of the other. Under normal circumstances there are minor changes in blood or CSF volumes occurring constantly, with changes in intra-thoracic pressure (laughing, sneezing, straining), postural and blood pressure changes with iluctuation in arterial blood gases. slightest increase in the volume triggers compensatory mechanisms in an effort to maintain an adequate blood supply to the brain.

These mechanisms include followings.

Accommodation and Auto Regulation -Accommodation is the mechanism whereby the spatial relationship of the skull’s content is changed or rearranged to acconlmodate an increase in the volume of any of the intracranial contents.

Mechanism of accominodation include decreased cerebral blood flow, displacement of brain tissue and decreased CSF, secondaiy to either increased absorption by the arachnoid villi or translocation of fluid to the cranial or spinal subarachnoid space. This mecha~lisnf~ai ls if the increase in pressure is prolonged or continue.

Autoregulation is the secondary mechanism that further provides a means of compensation via an automatic alteration in the size of the arterioles. The compensation of this mechanism is very teniporary.

Intracranial Pressure (ICP) is the pressure within the intra cranial space. The nornlal ICP is 4 to 14 mnis Hg (50 -2001nms H,O). Rapid rise of ICP (those that take place in less than half an hour) to level; 501nms Hg or more signals a life threatening emergency.

Pathophysiology

Pathologic conditions such as head injury, cerebrovascular accident, inflammatory lesions, brain tumour or intra cranial susgery can influence intra cranial volume-pressure relationships in a negative inannes. Increased ICP may significantly reduce cerebral blood flow and the resultant ischaemia stim~~latzs the vasomotor center, leading to a rise in systemic pressure. The brain is very vulnerable to ischaemia and generally will not recover function if it is subjected to more than 3-5 mts of complete ischaemia.

The concentration of CO, in the blood and brain tissues has a role in the regulation of cerebral blood flow. A rise in PCO, produces dilatation of the cerebral blood vessels, causing increased cerebral blood flow and increased ICP, ‘ while a fall in PCO, has a vasoconstrictor effect. Decreased venous outflow also increase cerebral blood volume, thus raising ICP. Thus, increased ICP is the summation of a number of physiologic process. Increased ICP from any cause affects the cerebral profusion and causes distortion and shift of the braill tissue.

Cerebral oedema and increased ICP are sometimes spoken of as interchangeable entities. However, they are not the same. Cerebral oedema is only one cause of increased ICP. Cerebra1 oedema is an increase it1 the water content in the white matter of the brain, which leads to an increase in tissue volume.

General Measures

• Avoid straining while passing stool
• Prevent coughing
• Reduce environmental stiinuli
• Restsain client as ‘necessary
• Always assume that client can hear
• Monitor intake and output
• Restrict sodium intake