ICP waveforms & monitoring

Dr. Joe M Das

• Physiology• Waveforms• Monitoring

Physiology

Vintracranial vault=Vbrain+Vblood +Vcsf

• “compliance reflects the ability of the intracranial system to compensate for increases in volume without subsequent increases in ICP. When compliance is decreased, even small increases in intracranial volume result in large increases in ICP.”

Normal ICP

• It is difficult to establish a universal “normal value” for ICP as it depends on age, body posture and clinical conditions.

• The upper limit of normal ICP – 15 mm Hg(5 – 10 mm Hg)

• Physiologic increase – Coughing, sneezing – 30-50 mm Hg

• ICP = CSF pressure – The pressure that must be exerted against a needle introduced into the CSF space to just prevent escape of fluid

ICP waveforms

ICP monitoring waveforms

Flow of 3 upstrokes in one wave.

P1 = (Percussion wave) represents arterial pulsationP2 = (Tidal wave) represents intracranial complianceP3 = (Dicrotic wave) represents venous pulsation

In normal ICP waveform P1 should have highest upstroke, P2 in between and P3 should show lowest upstroke.

On eyeballing the monitor, if P2 is higher than P1 - it indicates intracranial hypertension.

Related to • Cardiac cycle : within individual waves• Respiratory cycle : between consecutive waves

• ICP waveform – pulsatile• Baseline is referred to as ICP• Magnitude of baseline, amplitude &

periodicity of pulsatile components• Earliest sign of ↑ ICP – Changes in pulsatile

components

Flat

• EVD clogged / kinked• Patient expired

↑⁄↓ amplitude

• Increasing CSF volume (or decreased)

• If a large volume of CSF is drained off, the waveform will decrease in amplitude.

• Missing bone flap

Prominent P1 wave

• The systolic BP is too high

Diminished P1 wave

• If the systolic BP is too low, P1 decreases and eventually disappears, leaving only P2.

• P2 and P3 are not changed by this.

Prominent P2 wave

• The mass lesion is increasing in volume

• The intracranial compliance has decreased

• An inspiratory breath hold (as ICP will also rise)

Diminished P2 and P3 waves

• Hyperventilation

Rounded ICP waveform

• ICP critically high

Lundberg waves

Nils Lundberg

Lundberg A wave

Lundberg A waves

• Increases of ICP sustained for several minutes and then return spontaneously to baseline, which is slightly higher than the preceding one.

• Results from ↑ cerebrovascular volume due to vasodilatation (Lundberg)

• Results from normal compensatory response to decreases in CPP. Hence give vasopressors. (Rosner) – But may enhance lesion size & edema

4 phases:1. Drift phase : ↓ CPP → vasodilatation2. Plateau phase : Vasodilatation → ↑ ICP3. Ischemic response phase : ↓ CPP → Cerebral

ischemia → Brainstem vasomotor centres → Cushing response

4. Resolution phase : Cushing response → Restores CPP

Lundberg B wave

Lundberg B waves

• Short elevations of modest nature (10 – 20 mm Hg)• 0.5 – 2 Hz• Relate to vasodilatation secondary to respiratory

fluctuations in PaCO2

• Seen in ventilated patients (?)• Secondary to intracranial vasomotor waves,

causing variations in CBF• Reflects ↑ ICP in a qualitative manner

Lundberg C waves

Lundberg C wave

Lundberg C waves

• More rapid sinusoidal fluctuation (0.1 Hz)• Corresponds to Traube-Hering-Meyer

fluctuations in arterial pressure brought about by oscillations in baroreceptor and chemoreceptor reflex control systems

• Sometimes seen in normal ICP waveform• High amplitude – pre-terminal, seen on top of

A waves

ICP monitoring

Why look at ICP waveform analysis?

“…provides information about intracranial dynamics that can help identify individuals who have decreased adaptive capacity and are at risk for increases in ICP and decreases in CPP, which may contribute to secondary brain injury and have a negative impact on neurologic outcome.”

C.J Kirkness et. al; J Neurosci Nurs. 2000 Oct; 32(5):271-7.

• The main indications for ICP monitoring are:– Glasgow Coma Scale (GCS ) < 8– Posturing (extension, flexion)– Bilateral or unilateral pupil dilation (except with

Epidural Hematomas)– CT Scan results showing edema and/or mid-line

shift– Physical assessment /neurological assessment

findings which indicate a need for monitoring

• Contraindications:– Awake patient– Coagulopathy

Methods of ICP measurement

• Technology– external strain gauge– catheter tip (internal) – strain gauge – fibre-optic

• Location– Ventricular (EVD/IVC)– Intraparenchymal– Subarachnoid– Subdural/Extradural– External Fontanelle

External Ventricular Drain

• EVD connected to external strain gauge is the gold standard for measuring ICP

• Tip in foramen of Monro• Extensive history, low cost, reliability,

therapeutic• Success rate of cannulation – 82%

• Malposition: 4 – 20%– Did not have significant clinical sequelae

• Occlusion : By brain matter / blood clots– Flush EVD

• Hemorrhage : 0 – 15% (1.1%)– Most asymptomatic– Intervention in 0.5%

• Infection : 0 – 22% (8.8%)– Risk factors : IVH, SAH, craniotomy, CSF leakage,

systemic infection, depressed skull #– Duration of catheterization & irrigation of catheter– Venue of insertion – No difference– Extended tunneling• Sandalcioglu - <5 vs >5 cm – 83% vs 17%• Leung – No difference

– Prophylactic catheter exchange : No difference

– Prophylactic antibiotics:• Periprocedural vs none – No difference• Periprocedural vs entire duration – No difference• Guidelines for the Management of Severe Traumatic

Brain Injury – No antibiotic prophylaxis– Antibiotic impregnated catheter:• Rifampin + Minocycline (Zabramski) – 9.4 to 1.3%• Cost

When to pull the EVD out?

• CT evidence of resolution of cerebral oedema, and

• Improvement of ICP (consistently under 20-25)

• Or if the EVD is infected.

Fibreoptic ICP monitor

• Catheter tip measures the amount of light reflected off a pressure sensitive diaphragm

• Intraparenchymal Camino ICP monitor– Ease of insertion – Right frontal– Also in the region with pathology– Can be inserted in severely compressed ventricles or those

with midline shift– Low risk of hemorrhage and infection– Zero drift: Recalibration cannot be performed

• 2 mm Hg (first 24 hrs); 1 mm Hg (first 5 days) – Manufacturer• 0.5 – 3.2 mm Hg drift - Actual

Miniature Strain Gauge

• Codman MicroSensor ICP Transducer– Microchip pressure sensor at the tip of a flexible

nylon cable that produces different electricity based on pressure• Intraventricular (Correlation coefficient 0.97 with EVD,

Drift 0.2 mm Hg)• Intraparenchymal (Less accurate)• Subdural space (Not enough studies)

• Spiegelberg Parenchymal Transducer– Air pouch at the tip that is maintained at constant

volume– Pressure transducer located in ICP monitor– Recalibration can be made easily– Good correlation with ICP measured by

ventriculostomy

• Compliance Monitor– Experimental stage– Change in volume per unit change in pressure– Spielberg compliance monitor injects small

amount of air into the air balloon pouch and measures the pressure response to this change in volume

– Inverse relationship between compliance and ICP

• Noninvasive ICP monitoring– CT, clinical examination, monitoring pressure in epidural

space– Optic Nerve Sheath Diameter (ONSD)

• Measured by ultrasound• Critical value is different in different studies

– Venous Opening Pressure (VOP)• Measured by venous ophthalmodynamometry• Requires dilatation of pupil• Performed intermittently – Only screening purpose

– Cochlear fluid pressure, Flow velocity in intracranial arteries, Delay in VEPs

• Pediatric ICP monitoring– ICP monitoring only as an option for treating

patients with severe traumatic brain injury (GCS < 8)

– Similar complication rates as in adults

Summary

• Vintracranial vault = Vbrain+Vblood

+Vcsf

• P1 = (Percussion wave) represents arterial pulsationP2 = (Tidal wave) represents intracranial complianceP3 = (Dicrotic wave) represents venous pulsation

• Lundberg waves– A

• Plateau • Results from ↑ cerebrovascular volume due to

vasodilatation – B

• Secondary to intracranial vasomotor waves, causing variations in CBF• Reflects ↑ ICP in a qualitative manner

– C• Corresponds to Traube-Hering-Meyer fluctuations • Sometimes seen in normal ICP waveform

Summary• ICP monitoring & ICP-directed treatment remains the

cornerstone of neurocritical care• EVD connected to external strain gauge remains the most

reliable, cost-effective and accurate method for monitoring ICP– Allows CSF drainage– Infection and hemorrhage are the main problems

• Intraparenchymal monitors are gaining popularity– Easy to insert, low complication rates– Zero drift, mechanical failure are the problems

• New technologies including the non-invasive ones are emerging

References

• Handbook of Neurosurgery, Mark S Greenberg• Youmans Neurological Surgery, 6th edition•

THANK YOU