Neurological Emergencies - part 5 ppt

Active treatment isnormally instituted if ICP exceeds 25 mmHg for more than fiveminutes, although a treatment threshold of 15–20 mmHg hasbeen suggested to improve outcome.10 In the very

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37 Robson DJ, Blow C, Gaines P, Flanagan RJ, Henry JA Accumulation of

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38 Giroud M, Gras D, Escousse A, Dumas R, Venaud G Use of injectable

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39 Stecker MM, Kramer TH, Raps EC, O’Meeghan R, Dulaney E, Skaar DJ Treatment of refractory status epilepticus with propofol: clinical and

pharmacokinetic findings Epilepsia 1998;39:18–26.

40 Treiman DM Pharmacokinetics and clinical use of benzodiazepines in

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Antiepileptic drugs New York: Raven Press, 1995;705–24.

42 Remy C, Jourdil N, Villemain D, Favel P, Genton P Intrarectal diazepam

in epileptic adults Epilepsia 1992;33:353–8

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44 Kumar A, Bleck TP Intravenous midazolam for the treatment of refractory

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47 Scott RC, Besag FM, Boyd SG, Berry D, Neville BG Buccal absorption of

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49 Crawford TO, Mitchell WG, Snodgrass SR Lorazepam in childhood status

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50 Shaner DM, McCurdy SA, Herring MO, Gabor AJ Treatment of status epilepticus: a prospective comparison of diazepam and phenytoin versus

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51 Crawford TO, Mitchell WG, Fishman LS, Snodgrass SR Very-high-dose

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52 Krishnamurthy KB, Drislane FW Relapse and survival after barbiturate

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55 Cloyd JC, Gumnit RJ, McLain-LWJ Status epilepticus The role of

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56 Leppik IE, Patrick BK, Cranford RE Treatment of acute seizures and status

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57 Ramsay RE, DeToledo J Intravenous administration of fosphenytoin:

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58 Browne TR Fosphenytoin (Cerebyx) Clin Neuropharmacol 1997;20:1–12.

59 Wood PR, Browne GP, Pugh S Propofol infusion for the treatment of

status epilepticus Lancet 1988;i:480–1.

60 Mackenzie SJ, Kapadia F, Grant IS Propofol infusion for control of status

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61 De-Riu PL, Petruzzi V, Testa C, et al Propofol anticonvulsant activity in

experimental epileptic status Br J Anaesth 1992;69:177–81.

62 Rasmussen PA, Yang Y, Rutecki PA Propofol inhibits epileptiform activity

in rat hippocampal slices Epilepsy Res 1996;25:169–75.

63 Brown LA, Levin GM Role of propofol in refractory status epilepticus.

Ann Pharmacother 1998;32:1053–9

64 Hewitt PB, Chu DLK, Polkey CE, Binnie CD Effect of propofol on the electrocorticogram in epileptic patients undergoing cortical resection.

Br J Anaesth 1999;82:199–202.

65 Sneyd JR Propofol and epilepsy Br J Anaesth 1999;82:168–9.

66 Hanna JP, Ramundo ML Rhabdomyolysis and hypoxia associated with

prolonged propofol infusion in children Neurology 1998;50:301–3.

67 Holtkamp M, Tong X, Walker MC Propofol in subanesthetic doses

terminates status epilepticus in a rodent model Ann Neurol 2001;49:

260–3.

68 Young GB, Blume WT, Bolton CF, Warren KG Anesthetic barbiturates in

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69 Partinen M, Kovanen J, Nilsson E Status epilepticus treated by barbiturate anaesthesia with continuous monitoring of cerebral function.

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70 Orlowski JP, Erenberg G, Lueders H, Cruse RP Hypothermia and

barbiturate coma for refractory status epilepticus Crit Care Med 1984;

to the family and community Similarly, 20 per 100 000 peryear are admitted with intracerebral haematoma and 10–12 per

100 000 per annum with subarachnoid haemorrhage Theaverage regional neurosurgical unit serving a population oftwo million will manage 200 patients per annum with braintumours, some 15 patients with a cerebral abscess, and 100patients with hydrocephalus.3 In comatose children theincidence of raised intracranial pressure was 53% of those withhead injuries, 23% with anoxic-ischaemic damage, 66% withmeningitis, 57% with encephalitis, 100% with mass lesions,and 80% with hydrocephalus.4There is a considerable risk inall such patients of secondary brain damage with long termsevere disability if raised intracranial pressure is not recognisedand managed appropriately

Box 7.1 Some common causes of raised intracranial

Cerebral venous thrombosis

Major cerebral infarct

Hypertensive encephalopathy (malignant hypertension, eclampsia) Hydrocephalus

Congenital or acquired

Obstructive or communicating

Craniocerebral dispropor tion

Brain “tumour” (cysts; benign or malignant tumours)

Resting intracranial pressure represents that equilibriumpressure at which cerebrospinal fluid (CSF) production andabsorption are in balance and is associated with an equivalentequilibrium volume of CSF CSF is actively secreted by thechoroid plexus at about 0·35 ml/min and production remainsconstant provided cerebral perfusion pressure is adequate CSFabsorption is a passive process through the arachnoidgranulations and increases with rising CSF pressure:

CSF pressure = Resistance to CSF outflow × CSF outflow rate

+ sagittal sinus pressure

According to the above formula (known as the Davson’sequation), the mean intracranial pressure (ICP) explainedsolely by CSF circulation, is proportional to the resistance toCSF outflow, CSF production rate, and sagittal sinus pressure

Marmarou et al.5 proposed a modification to this formula,stating that average ICP can be expressed by two components:CSF circulatory and vasogenic Thus, the Davson formula can

to complete Davson’s formula Its contribution to total ICPcan be as large as 60% in pathological circumstances

The “four-lump” concept describes most simply the causes

of raised intracranial pressure: the mass, CSF accumulation,vascular congestion, and cerebral oedema (Box 7.2).7–9

The description of a patient with raised ICP as havingcerebral congestion, vasogenic oedema, etc can only be aworking approximation, albeit useful, until our rather crudemethods of assessment are refined In adults the normal ICPunder resting conditions is between 0 and 10 mmHg, with

15 mmHg being the upper limit of normal Active treatment isnormally instituted if ICP exceeds 25 mmHg for more than fiveminutes, although a treatment threshold of 15–20 mmHg hasbeen suggested to improve outcome.10 In the very young, theupper limit of normal ICP is up to 5 mmHg.4,11Small increases

in mass may be compensated for by reduction in CSF volumeand cerebral blood volume but, once such mechanisms areexhausted, ICP rises with increasing pulse pressure and withthe appearance of spontaneous waves (plateau and B waves).12

There is an exponential relationship between increase involume of an intracranial mass and the increase in ICP, at leastwithin the clinically significant range This relationship isalso helpful in understanding the most specific fluctuatingcomponent of ICP: the pulse amplitude (Figure 7.1a) It isderived from pulsation of arterial blood pressure but thechange of its shape can be considerable Classically, the pulsewaveform of ICP can be depicted using the pressure–volume

Box 7.2 Mechanisms of raised intracranial pressure

Increase in brain volume as a result of increased water content.

1 Vasogenic – vessel damage (tumour, abscess, contusion)

2 Cytotoxic – cell membrane pump failure (hypoxaemia, ischaemia, toxins)

3 Hydrostatic – high vascular transmural pressure (loss of autoregulation; post intracranial decompression)

4 Hypoosmolar – hyponatremia

5 Interstitial – high CSF pressure (hydrocephalus)

D: Vascular (congestive) brain swelling

Increased cerebral blood volume

Ar terial vasodilatation (active, passive)

Venous congestion/obstruction

curve with the pulsating changes in cerebral blood volumedrawn along the x (volume) axis13 (Figure 7.1b) The curvehas three major zones:14 in the initial range ICP changesproportionally to the change of intracerebral volume This is azone of good compensatory reserve Then, ICP starts toincrease exponentially when intracerebral volume expandsfurther This is a zone of poor compensatory reserve and can beseen in clinical practice most often whenever there is anydifficulty in managing a cerebrospinal volume-evolvingprocess (head injury, poor grade subarachnoid haemorrhage,acute hydrocephalus, etc.) Finally, at very high ICP, when adecrease in cerebral perfusion pressure is too deep to secure anyfurther arterial dilatation (that is, vessels are maximally dilated),the pressure–volume curve bends to the right (Figure 7.1b).Entering this zone represents the transition of thecerebrovascular bed from the state of active dilatation topassive collapse When the transmural pressure furtherdecreases, the additional compensatory reserve is gained atthe expense of reduction of arterial blood volume andderangement of the autoregulatory cerebrovascular response.

25

150 120 90 60 30 0

0

0

0 52·5

37·5

12·5 17·5

(a)

Pulse amplitude of ICP does not change with ICP in the firstzone, then grows linearly with ICP in the second zone In the thirdzone it starts to decrease with a further increase in ICP (Figure 7.2).When monitored continuously, mean ICP presents anumber of stereotypic patterns (Figure 7.3) The first eight

ICP

“Critical”

ICP

Good compensatory reserve

Deranged cerebrovascular reactivity

Figure 7.1 (a) Examples of ICP pulse waves Peak-to-peak amplitude increases with increasing mean ICP (upper panel) Three distinctive

“peaks” can be sometimes recorded (lower panel) (b) In a simple model, pulse amplitude of ICP (expressed along the y-axis on the right side of the panel) results from pulsatile changes in cerebral blood volume (expressed along the x-axis) transformed by the pressure–volume curve This curve has three zones: a flat zone, expressing good compensatory reserve, an exponential zone, depicting poor compensatory reserve, and

a flat zone again, seen at very high ICP (above the “critical” ICP)

depicting derangement of normal cerebrovascular responses The pulse amplitude of ICP is low and does not depend on mean ICP in the first zone The pulse amplitude increases linearly with mean ICP in the zone

of poor compensatory reserve In the third zone, the pulse amplitude starts to decrease with rising ICP.

Adapted from Miller et al 2

and Bingham et al 21

; based on data from Lofgren et al 14 and Avezaat et al 30

(b)

panels (a–h) are representative for acute cases, such as headinjury Long term monitoring in other, non-acute cases, such

as chronic hydrocephalus, produces specific but usuallydifferent patterns (Figure 7.3i,j):

1 Low and stable ICP (below 20 mmHg) – this pattern isspecific for uncomplicated patients following head injury

or during the first hours after trauma before ICP increasesfurther (Figure 7.3a)

2 High and stable ICP (above 20 mmHg) – the mostcommon picture following head injury (Figure 7.3b).

3 Vasogenic waves — B waves (Figure 7.3c), plateau waves(Figure 7.3d), or waves related to changes in arterialpressure and hyperaemic events (Figure 7.3e–g)

4 Refractory intracranial hypertension (Figure 7.3h) whichusually leads to the death of the patient unless radicalmeasures are taken (for example, surgical decompression)

5 Overnight recording of ICP in patients suffering fromhydrocephalus with cyclically increased activity of Bwaves (Figure 7.3i) and benign intracranial hypertension(Figure 7.3j)

Spontaneous waves of intracranial pressure are usuallyassociated with cerebrovascular dilatation Cerebral blood volumeincreases during plateau waves (intracranial pressure > 50 mmHgfor more than five minutes) and may be the result in some cases

of inappropriate autoregulatory vasodilatation, described byRosner and Becker15 as the so-called vasodilatatory cascade Anincrease in cerebral blood volume causes an increase in ICP, adecrease in cerebral perfusion pressure, leading to vasodilatation,and a further increase in cerebral blood volume, etc., until thesystem reaches the state of maximal vasodilatation Plateau wavesare observed in patients with preserved cerebral autoregulationbut reduced pressure volume compensatory reserve Very highincreases in ICP when associated with a reduction in cerebralperfusion pressure may dramatically decrease cerebral blood flow(Figure 7.4, p 200).16

Transcranial Doppler examinations reveal that middlecerebral artery flow velocity increases at the same rate as Bwaves (0·5–2/min) of intracranial pressure (Figure 7.5, p 201).17

Gradients of intracranial pressure may develop whenherniation occurs – transtentorial, subfalcine, and foramenmagnum Blockage to the free flow of CSF between intracranialcompartments leads to a much greater and more rapid rise inintracranial pressure in the compartment harbouring theprimary pathology and hence to the final common sequence oftranstentorial and foramen magnum coning When intracranialpressure equals arterial blood pressure, angiographic pseudo-occlusion occurs and reverberation, systolic spikes, or no flowmay be seen on transcranial Doppler sonography (Figure 7.6,

p 201) Patients will often satisfy the formal clinical criteria for

80 60

Time [min] 0

105

90 75 60

Time [min]

0 ABP

[mmHg]

(c)

80 60 40 20 120 90 60 30 0

100

75 50

Time [hours] 3 4

(h)

(j)

Figure 7.3 Typical recordings of intracranial pressure.

(a) Low and stable ICP.

(b) Increased and stable ICP after head injur y.

(c) B waves (after head trauma).

(d) Plateau wave after head injur y.

(e–g) Waves of ICP different from plateau commonly recorded after head injur y: (e) increases in ICP due to rapid increases in ar terial blood pressure;

(f) changes in ICP caused by constriction/dilatation of vascular bed, due to variation in ar terial pressure;

(g) longer increase in ICP associated with an increase in blood flow (monitored using TCD- FV).

(h) Intracranial hyper tension – refractor y (after head injur y).

(i) Overnight recording in normal pressure hydrocephalus Baseline pressure is specifically low with increased vasogenic dynamics observed as periods of

increasing pulse amplitude (AMP) and magnitude of B waves.

(j) Overnight monitoring in benign intracranial hyper tension Baseline pressure is elevated with moderate dynamics and gradually increasing magnitude of B waves

brain stem death, for which transcranial Doppler examination

is not a substitute.18,19When ICP rises uncontrollably, it is oftencalled “refractory intracranial hypertension” Mean ICP mayincrease to well above 80 mmHg, probably due to rapid brainswelling over a period of a few hours Pulse amplitude of ICP iscommonly secondarily reduced with activation of a Cushingresponse and a gradual rise of mean arterial pressure Themoment of brain stem herniation is commonly marked by arapid decrease in mean arterial pressure, a rise in a heart rate,and a terminal decrease in cerebral perfusion pressure tonegative values (Figure 7.7)

Cerebral perfusion pressure (CPP) is commonly defined asmean arterial blood pressure minus mean intracranial

80 ICP

Time [min]

0 0

Figure 7.4 Rare occurrence of ver y deep plateau wave, when blood flow velocity (FVx) decreased by more than 60% of baseline Notice the decrease in hear t rate (HR) and hyperaemic increase in flow velocity after the ICP wave subsided.

From Obrist et al 20

pressure Mean intracranial pressure closely approximates tomean cerebral venous pressure The lower limit of CPP whichwill permit autoregulation, when intracranial pressure israised, is about 40 mmHg There is a paradox, however: thelevel of cerebral perfusion pressure below which outcome aftersevere head injury and associated parameters deteriorate is ofthe order of 60–65 mmHg (mean arterial pressure < 80 mmHg;

ICP >20 mmHg) Conventionally any elevation of ICPrequires treatment if CPP is below 60 mmHg in adults for overfive minutes This paradox may partly reflect the “split brain”problem: autoregulation of cerebral blood flow to changes inCPP and the response to changes in arterial carbon dioxide

tension (PacO2) may be impaired focally, leaving intactreactivity in other areas of the brain If vasospasm is present,

an even higher perfusion pressure may be required to provideadequate levels of cerebral blood flow

Total cerebral blood flow may be increased or decreased inareas with absent reactivity Hyperaemia is non-nutritional

“luxury perfusion” where cerebral blood flow is in excess ofthe brain’s metabolic requirements20 and accompanied byearly filling of veins on angiography and “red veins” atoperation Cerebral vasodilators such as carbon dioxide willdilate “normal” arterioles, increase intracranial pressure, andmay run the risk of reducing flow to damaged areas of brain(intracerebral “steal”) Inverse “steal” is one reason for thetreatment of raised intracranial pressure by hyperventilation:

an acute reduction of PacO2vasoconstricts normal cerebralarterioles, thereby directing blood to focally abnormal areas.Normally, cerebral blood flow is coupled to cerebral oxidativemetabolism via multiple mechanisms involving local

concentrations of hydrogen ions, potassium, and adenosine, forexample Status epilepticus leads to gross cerebral vasodilatationand intracranial hypertension as a result of greatly increasedcerebral metabolism and local release of endogenousvasodilator agents Depression of cerebral energy metabolism byanaesthesia and hypothermia may reduce cerebral blood flowand intracranial pressure where there is a large area of the brainwith reasonable electrical activity21 and where normalflow–metabolism coupling mechanisms are intact as indicated

by a reasonable cerebral blood flow carbon dioxide reactivity.22

There is a complex interaction between the properties ofthe CSF and the cerebral circulations that may be modelled(Figure 7.8).23–25 The relative contributions of abnormalities ofCSF absorption and cerebral blood volume may be approximated

by calculating the proportion of CSF pressure attributable to CSFoutflow resistance and venous pressure from Davson’s equation.Phenomena such as the interaction of autoregulation to

changing CPP with PacO2may be quantified.26

Monitoring techniques

Clinical features

In the non-trauma patient, there may or may not be a clearhistory of novel headache, vomiting, and visual disturbancesuggestive of papilloedema (blurring of vision, obscuration) or asixth cranial nerve palsy (lateral diplopia) The absence ofpapilloedema does not exclude raised ICP in patients with acute

or chronic problems: disc swelling was found in only 4% ofhead-injured patients, 50% of whom had raised ICP onmonitoring.8 Even in the twenty-first century, it is regrettablethat a clear history of raised ICP may be misinterpreted until thefinal denouement of disturbance of consciousness and pupillaryabnormality or apnoea presents Some patients have learnt tocontrol their intracranial hypertension by hyperventilating,only to be dismissed as hysterics Only slowly has the danger oflumbar puncture in the differential diagnosis of neurologicalpatients been appreciated by the non-expert Many of the latersigns of raised ICP are the result of herniation: monitoringshould detect raised ICP at an earlier stage and hence treatmentshould be started before irreversible damage occurs

CT scanning

CT scanning may reveal not only a mass, hydrocephalus, orcerebral oedema, but also evidence of diffuse brain swellingsuch as absent perimesencephalic cisterns, compressed thirdventricle, and midline shift

ICP

CVR

CVR

Capillaries and small veins Arterioles

Figure 7.8 Hydrodynamic model of cerebral blood flow (CBF) and

CSF circulation with the electrically equivalent circuit (for details, see Ursino 25 ).

Pa= internal carotid artery blood pressure; P v = cerebral venous

pressure; Pss= sagittal sinus blood pressure; ICP = intracranial

pressure; If= CSF formation rate; CVR = resistance of cerebral arterial bed; Rb= resistance of bridging veins; R CSF = resistance to CSF

reabsorption; Ca= compliance of cerebral arterial bed; C v = compliance

of cerebral venous bed; Ci= compliance of lumbar CSF compartment

Invasive methods of intracranial pressure

monitoring including infusion tests

The gold standard of ICP monitoring, which was firstintroduced before 1951,12,27still remains the measurement ofintraventricular fluid pressure either directly or via a CSFreservoir, with the opportunity to exclude zero drift Subduralfluid filled catheters are reasonably accurate below 30 mmHg.Risk of infection, epilepsy, and haemorrhage is less withsubdural than with intraventricular catheters, but even thelatter should be less than 5% overall Catheter tip transducersare useful particularly for waveform analysis, whether placedintraventricularly, subdurally, or intracerebrally Ventricularcatheters permit the therapeutic drainage of CSF in cases ofventricular dilatation

In more chronic conditions of ventricular dilatation, whereICP is not greatly raised, obstruction to CSF absorption may beconfirmed by CSF infusion tests (ventricular or lumbar) takingcare to adapt the technique to the site of any obstruction.28–30

The infusion study can be performed via the lumbar CSFspace or via a pre-implanted ventricular access device In bothcases two needles are inserted (22G spinal needles for lumbartests; 25G butterfly needles for ventricular studies) One needle

is connected to a pressure transducer via a stiff saline-filled tubeand the other to an infusion pump mounted on a purpose-builttrolley containing a pressure amplifier and an IBM-compatiblepersonal computer running software written in house After 10minutes of baseline measurement, the infusion of normal saline

at a rate of 1·5 ml/min or 1 ml/min (if the baseline pressure washigher than 15 mmHg) starts and continues until a steady stateICP plateau is achieved (Figure 7.9) If the ICP increases to

40 mmHg, the infusion is interrupted Following cessation ofthe saline infusion, ICP is recorded until it decreases to steadybaseline levels All compensatory parameters are calculatedusing computer-supported methods based on physiologicalmodels of the CSF circulation.30–33 Baseline ICP and RCSFcharacterise static conditions of CSF circulation RCSF iscalculated as the pressure increase during the infusion, divided

by the infusion rate A value below 13 mmHg/(ml/min)characterises normal CSF circulation.28 Above 18 mmHg/(ml/min) the CSF circulation is clearly disturbed.34 Between 13and 18 mmHg/(ml/min) there is a grey zone, when other

compensatory parameters and clinical investigation should beconsidered to make a decision about shunting.33

The cerebrospinal elasticity coefficient (E1) and pulseamplitude of ICP waveform (AMP) express the dynamiccomponents of CSF pressure volume compensation

E1 describes the compliance of the CSF compartmentaccording to the formula:

Compliance of CSF space = Ci = 1/ {E1× (ICP−p0)},

where p0is the unknown reference pressure level, representinghydrostatic difference between the site of ICP measurementand pressure indifferent point of cerebrospinal axis.35,36

Cerebrospinal compliance is inversely proportional to ICP,therefore comparison between different subjects can be madeonly at the same level of the difference: ICP − p0 The elastancecoefficient E1 is independent of ICP, thus this coefficient is

a much more convenient parameter when comparingindividual patients A low value of E1(less 0·2 L/ml) is specificfor a compliant system, whilst a high value indicates decreasedpressure–volume compensatory reserve

Time [min]

10 AMP

21 mmHg/(m/min)

The pulse amplitude of ICP (AMP) increases proportionallywhen the mean ICP rises The proportionality ratio (theAMP/P index) characterises both elastance of the cerebrospinalspace and the transmission of arterial pulsations to the CSFcompartment.30

Finally, the production of CSF fluid can be estimated usingDavson’s equation However, the sagittal sinus pressure isunknown and cannot be easily measured without increasingthe invasiveness of the whole procedure Consequently, the Pssand CSF formation are estimated jointly using a non-linearmodel utilising the least square distance method during thecomputerised infusion test.33 It is important to mention thatsuch an “estimate” of CSF production rate approximates CSFabsorption, rather than the actual production rate It is basedupon the assumption that all circulating CSF is reabsorbed viathe arachnoid granulations In cases where significant CSFleakage into brain parenchyma occurs, CSF production may begrossly underestimated

Twenty-four hour intracranial pressure monitoring inpatients with so-called normal pressure hydrocephalus mayreveal a high incidence of B waves during sleep which is a veryhelpful prognostic sign for the outcome following shunting(see also Figure 7.3i).29,36–38 Benign intracranial hypertensionseldom requires more than CSF pressure monitoring through

a lumbar catheter or needle for an hour

Considerable effort continues into the detailed analysis ofthe ICP trace to determine whether it is possible to reveal themechanism of raised ICP and whether autoregulatory reserveremains intact The pulsatile waveform of ICP hypotheticallyincludes information about both transmission of the arterialpulse pressure through the arterial walls and the compliance

of the brain This information is not always clear and demandsspecific computer analysis and critical interpretation, therebyrestricting its use to only a few centres

It has been proposed9 that congestion or vascular brainswelling may be present when the ratio of the amplitudes of thepulse and respiratory components of the ICP trace exceeds two,when there is an increase in the high frequency centroid,39 orwhen there is a high amplitude transfer function for theharmonics from arterial pressure to ICP Such a transfer function

is calculated from the Fourier transform of the digitised signal.40

Continuous multimodality monitoring is required to draw any