Page 248 - Critical Care Nursing Demystified

Chapter 5 CARE OF THE PATIENT WITH NEUROLOGICAL NEEDS 233

performed on patients with pacemakers, surgical clips, and prosthetic implants
made of ferrous metal, including life support mechanical ventilators.

Intracranial Pressure (ICP) Monitoring

To maintain a normal ICP, the following three brain components need to be
regulated to maintain a fixed intracranial volume. As long as the total intracra-
nial volume remains the same, ICP remains constant at 0 to 15 mm Hg = nor-
mal. Parts that compose the total intracranial volume are CBF or cerebral blood
flow = 3% to 10%, cerebrospinal fluid circulation = 8% to 12%, and intravascu-
lar plus the volume of semisolid brain tissue, which is more than 80% H O.
2
A constant perfusion pressure to the brain is needed to supply oxygen and nutri-
ents to the cerebral neurons and to prevent excessive pressure leading to brain
herniation. In order to do this, cerebral perfusion pressures need to be monitored
via an intracranial monitoring device. An intracranial monitoring device records the
ICP, which is used to calculate the cerebral perfusion pressure (CPP).
CPP is calculated by taking the mean arterial BP (MAP) minus the ICP. Normal
CPP is between 70 and 90 mm Hg. Let us see an example of this calculation. Downloaded by [ Faculty of Nursing, Chiangmai University 5.62.158.117] at [07/18/16]. Copyright © McGraw-Hill Global Education Holdings, LLC. Not to be redistributed or modified in any way without permission.

H ? How to Do It—Calculation of

w t
t—C
o
o I
l
c
a
o D
Cerebral Perfusion Presure (CPP)
Cerebral Perfusio
1. Take the MAP of 120 mm Hg. .
e the MAP o
1.
ak
120 mm H

g
f
T
2. Record the ICP from the monitor as 80 mm Hg.
2. Rec o r d the ICP f r om the monit or as 80 m
12
0
= 4
0
–
80

MAP – I
3. MAP – ICP = CPP: 120 – 80 = 40
3.
C
:
PP
C
P =
4. Analysis: This is too low of a CPP to sustain life. Nursing action is required! Usu-
ally this involves decreasing the BP since the MAP is high.
NURSING ALERT
According to the Monro-Kellie doctrine, when there is an increase in volume of the
brain, blood, or CSF properties, the pressure within the brain will increase unless one
or more of these components decrease.