Monro-Kellie 2.0

PresentatieMDO17-08-2016L.L.A.Bisschops

Thedynamic vascular andveneuspathophysiological components ofICP

Wilson, Journal of Cerebral Blood Flow &Metabolism, 2016

1783‘Science ofICP’

AlexanderMonro1733-1817

Monro described theskull asarigid structurecontaining incompressible brain andstated thatthevolumeofblood mustremain constantunless:‘wateror other matteriseffused orsecreted from theblood-vessels’inwhich case‘aquantity ofblood,equal inbulktotheeffusedmatterwill be pressed outofthecranium’.

1824‘Science ofICP’Confirmation ofMonro’s doctrineinhuman andanimal studies:cerebral (inparticular,venous)blood volumewassimilar no matterwhat thecause ofdeath (hanging,exsanguination)was.

GeorgeKellie1720-1779

ATLSCourseManual 9thedition

Cushing doctrine:sum ofvolumeofthebrain,blood andCSFisconstant.

This description fails toexplain theimportance ofvolumeflow

Thedynamic components ofICP

StaticMonro-Kellie doctrine:Equal weighting toblood andCSFmisses thedynamic reality.

Averagemalebrain volume1473ml(brain/CSF/blood)Intracranial blood volume:100-130mlCSFvolume:75ml

Slowandsteady production ofCSF (≈0.35ml/min)Substantial,continuous blood inflow andoutflow(≈700ml/min,14%ofCO)

Thedynamic components ofICPNormal ICP≈5-15mmHg

- Greatly influenced by orthostatic postition(ICPcan be negativewhen standingup).

- Generally similar tocerebral venouspressures (if no distalobstruction).

Dynamic components:Arterial influence on ICPVenous influence on ICPExtracranial causes ofcerebral venous hypertension

Thedynamic components ofICPArterial influence on ICP

CPP=MAP- ICPICP=MAP- CPP;implies no venous involvementGuidelines:MAP>80-90,RRsyst >90mmHgHowever:Cerebral Blood Flow resulting fromanyMAPwill differ betweenindividuals (autoregulation,PaCO2)

‘static’viewoffactorsregulating ICP,andfocuson arterial inflow alone,ledtoneglect ofimportantinfluence ofcerebral veins

Thedynamic components ofICPVenous influence on ICP

CorticalDeeper (anterior)Central(thalamic)

Nomuscular wall:vulnerable tocompression

Thedynamic components ofICPArole forveinsinfluencing ICP

Failure for (intra- andextracranial)venous efferent flow toprecisely matcharterial afferent flow yields immediate anddramaticchanges inintracranialvolumeandpressure.

asCBF↑,venous drainage↑,with limited venous distension IVPwill riseupstream,andthus ICP(similar toMonro-Kellie doctrine).

Causes ofraised cerebral venouspressure

Diffusecompression ofthevenous system

Concurrentacutesubdural removementandsplenectomy

Relative venous outflow restriction

Intracraniallyisolateddiffuse

Extracranially

ConclusionBalance between cerebral inflow andoutflow isvital

Restrictions inoutflow can be assignificantasmass accumulation within thecranium

Concentration ofinterestinICP/CPP,neglect for venous side

ICPisafunction ofvenous outflow:acombination ofintra-cerebral resistance,andcervical,thoracic andabdominal pressures

If no resistance tovenous outflow:ICP=0.IVfluids to‘maintain CPP’increaseCVPandcanworsen ICP