INTRACRANIAL PRESSURE (ICP) MONITORING
ICP monitoring is used to measure the pressure within the brain and to evaluate cerebral compliance so
that changes can be detected early and effects of various medical and nursing interventions can be
evaluated. The traditional clinical signs of increased ICP (decreasing level of consciousness, increased
systolic BP and widening pulse pressure, bradycardia, and slow irregular respirations) do not actually
reflect early increases in ICP and in fact may occur too late for intervention and treatment to be
ICP monitoring also provides the necessary data to calculate cerebral perfusion pressure (CPP); this is
measured by subtracting mean ICP from the mean arterial blood pressure. Adequate cerebral
circulation is ensured if the CPP remains approximately 70 to 90 mm Hg.
A pressure transducer set-up is connected, using sterile normal saline (without preservative) to provide
a fluid column between the cerebrospinal fluid (CSF) within the ventricles and the transducer. The
pressure is transmitted to a monitor, and the pressure waveform and digital readings are displayed. A
continuous flush device is not used on any ICP monitoring system because it may contribute to further
Complications include CNS infection.
The Monroe-Kellie hypothesis states that the volume of the intracranium is equal to the volume of the
brain plus the volume of the blood within the brain plus the volume of the CSF within the brain.
Therefore any condition that results in an increase in the volume of one or more of these will increase
the ICP, unless there is a concomitant decrease in one or more of the components.
The intraventricular catheter is placed via a burr hole into the lateral ventricle of the nondominant
hemisphere. When ICP is severely elevated, CSF can be drained using this type of system. This is the
most invasive method of monitoring ICP, yet it is also the most accurate because the catheter is placed
directly into the ventricle.
The subarachnoid screw or bolt is inserted into the subarachnoid space. This system is unreliable in
patients with elevated ICP because the device becomes obstructed by brain tissue.
The epidural sensor is a transducer placed between the skull and dura. It is less invasive than the
intraventricular catheter and the subarachnoid screw, so it may be less accurate. Once it is placed,
recalibration is not necessary. Drainage of CSF cannot be performed with this system.
The fiberoptic transducer-tipped catheter can be placed in the ventricle, subarachnoid or subdural
spaces, or parenchyma (Figure 6-39). With ventricular placement, CSF can be drained. Once it is
placed, it cannot be recalibrated.
Figure 6-39 Fiberoptic techniques for intracranial pressure (ICP) monitoring. (Courtesy Integra
Neurosciences, Camino, San Diego.)
0 to 15 mm Hg
Significance of Abnormal Values
Consistently elevated ICP suggests that the compensatory mechanisms of cerebral autoregulation
(arterial constriction and dilation) have failed. Patients usually become symptomatic with an ICP of 20
to 25 mm Hg, and a sustained ICP >60 mm Hg is usually fatal. Factors that increase ICP include the
Hypercapnia (PaCO2 >42 mm Hg)
Hypoxia (PaO2 <50 mm Hg)
Excessive fluid intake
Head, neck, and extreme hip flexion
Head rotation of 90 degrees to either side
Valsalva maneuver (straining, coughing)
Continuous activity without adequate rest
In addition, arousal from sleep, rapid eye movement (REM) sleep, emotional upset, and noxious
stimuli such as suctioning are known to increase ICP.
PATIENT CARE MANAGEMENT
For insertion, the patient is placed in a supine position with the head of the bed elevated 30 to 45
degrees. A twist drill is used to insert the device. Strict aseptic technique is essential, as is a sterile
environment, during the procedure.
The ICP waveform should be continuously displayed on the monitor, and alarms should be set to
coincide with the patient's clinical status. The ICP should be monitored and recorded as ordered, and
the mean arterial blood pressure should be monitored to determine CPP.
It is imperative that strict aseptic technique be maintained during the care of the insertion site and
pressure line and during dressing changes. Assess for signs of infection, drainage, swelling, or
irritation. The site must be kept clean and dry and should be covered with an occlusive dressing at all
The patient should be positioned with the head of the bed elevated 15 to 30 degrees (unless
contraindicated) and maintained in a neutral position with minimal hip and knee flexion to facilitate
venous drainage from the brain and prevent further increases in ICP.
Additional measures to prevent sustained intracranial hypertension should be taken: prevent
hypothermia and hyperthermia, keep PaCO2 at 28 to 30 mm Hg, instruct the patient to avoid a Valsalva
maneuver, and restrict fluids as ordered.
Obtaining Accurate Measurements
1. Zero the transducer by opening the transducer to air and adjusting the monitor to read zero; this
eliminates the pressure contributions from the atmosphere, and only pressures within the chamber
being monitored will be measured. Check with the manufacturer's recommendations for routine
zeroing. Epidural sensors and fiberoptic devices are zeroed only before insertion.
2. Level the air reference port of the transducer to the level of the foramen of Monro (Figure 6-40)
with each position change or a change in waveform and after any manipulation of the system. Epidural
and fiberoptic devices do not require leveling after insertion.
3. Check the fluid-filled systems frequently for air because this will alter readings.
4. Obtain ICP readings at end-expiration to avoid the effects of thoracic pressures on the cerebral
The ICP waveform (Figure 6-41) is very similar in appearance to that of the CVP. Because the
ventricles of the brain are relatively low-pressure chambers, the waveform has small systolic and
diastolic fluctuations and thus the mean is monitored. The waveform consists of at least three peaks
(Figure 6-41), although additional peaks may be present in some individuals. An increase in ICP will
cause an increase in all waveform components initially; as ICP progresses, there is an elevation of P2.
A P2 equal to or higher than P1 suggests decreased compliance, which may precede an actual increase
in ICP. This signifies that compensatory mechanisms are failing and that a small increase in the
volume can increase ICP significantly.
The intraventricular catheter and subarachnoid screw may develop a damped waveform as a result of
tissue, blood, or debris blocking the transmission of the pressure. The line is irrigated only when
ordered by a physician (Table 6-5). Air bubbles may cause a damped waveform in fluid-coupled
The ICP monitoring device is removed by a physician. A wrench is required for the bolt. Sterile
technique is used to prevent contamination of the insertion site. A sterile dressing is applied to the site
for at least 24 hours; after this, the site is left open to air. If there is evidence of a CSF leak, additional
sutures may be required.
Risk factors that influence infection rate include the insertion environment and technique, type of
device used, duration of monitoring, and patient factors such as age and state of immunosuppression.
• The entire pressure transducer set-up must remain a closed system to prevent contamination.
Strict aseptic technique must be followed during insertion of the device and while manipulating the
pressure line and changing dressings.
Figure 6-40 Location of foramen of Monro for transducer placement. Map an imaginary equilateral
triangle from the external auditory meatus (1) to the outer canthus of the eye (2) to behind the hairline
(3). Point 3 is the location of the foramen of Monro.
Figure 6-41 Intracranial pressure (ICP) waveform.
Table 6-5 TROUBLESHOOTING INTRACRANIAL PRESSURE (ICP) MONITORING LINES