tailieunhanh - Anaesthetists and the physiology of basic: Part 2

(BQ) Continued part 1, part 2 of the document Anaesthetists and the physiology of basic has contents: Cerebrospinal fluid, cerebral blood flow, skeletal muscle, cardiac muscle, the electrocardiogram, autonomic nervous system, immune system, resting membrane potential, and other contents. Invite you to refer. | Section 4 Neurophysiology Chapter 46 Intracranial pressure and head injury What is intracranial pressure How is it measured The ICP is simply the hydrostatic pressure within the skull but reflects the pressure of the CSF and brain parenchyma. At rest in a normal supine adult ICP is 5-15 mmHg ICP varies throughout the cardiac and respiratory cycles. Even in a normal brain coughing straining and sneezing can transiently increase ICP to as high as 50 mmHg. Unfortunately ICP cannot be estimated only invasively measured. ICP may be measured by a variety of devices each with their advantages and disadvantages By an EVD a catheter inserted into the lateral ventricle which is considered the gold standard for measuring ICP. In addition to ICP measurement an EVD can be used to remove CSF for diagnostic and therapeutic purposes to reduce ICP - see later and for the administration of intrathecal medication. However to measure ICP the EVD must be clamped that is CSF cannot be simultaneously drained. An EVD may be surgically challenging to insert especially if the ventricles are small or displaced. Also EVDs are frequently complicated by blockage and are associated with an infection risk of up to 5 . Intraparenchymal probe a fibre-optic-tipped catheter placed within the brain parenchyma through a small burr hole. An intraparenchymal probe is much easier to insert than an EVD and can be used in situations where the ventricles are compressed or displaced. Measurement of ICP using an intraparenchymal probe is almost as accurate as an EVD and infection rates are substantially lower. However there are concerns about the accuracy of intraparenchymal catheters used for prolonged periods the catheter is zeroed at the time of insertion and cannot be recalibrated in vivo. However drift has been shown to be as little as 1 mmHg after 5 days use. An intraparenchymal probe only measures the pressure of the brain parenchyma in which it is located which may not represent global ICP. .