monitoring the brain: what’s worthwhile?

Tony Figaji MBChB, MMed, FCS, PhDHead of Pediatric NeurosurgeryRed Cross Children’s HospitalUniversity of Cape Town

•Neurocritical care is underdeveloped•Pediatric neurocritical care is even worse•Secondary brain injury is underappreciated

•The brain is complex•Children are physiologically different•Individual and temporal heterogeneity•Many different causes for raised ICP, standard Rx•Surrogate markers of brain health used•Direct measures of brain physiology?

Brain tissue oxygen tensionNear-infrared spectroscopyJugular venous saturationContinuous EEGMicrodialysisTCD / autoregulationContinuous CBFPhysiological imaging

1. Classic cellular oedema

2. Hyperemia

3. Vasospasm

4. Subclinical seizures

5. Impaired autoregulation

GCS 4ICP = 35

GCS 4ICP = 35

GCS 4ICP = 35

GCS 4ICP = 35

GCS 4ICP = 35

BrO2 lowCBF↓/N

BrO2 high, FV / CBF high

BrO2 low, FV high/ LR↑

BrO2 low, EEG typical

BrO2 passive,ARI low

Examined associations with outcome in multivariate model: clinical, physiological, radiological

Adjusted Odds Ratio for poor outcome:PbtO2<10 for >2 hoursOR 10.8 (1.4-82.4)PbtO2<5 for >1 hour OR 27.4 (1.9-391)

Strongest independent predictor of outcomeMortality for series = 9.6%

Low BrO2 is associated with poor outcome

Childs Nerv Syst. 2009 Oct;25(10):1325-3

It is not a surrogate marker of something else

It is not predicted by measures of initial injury severity

0

10

20

30

40

50

60

70

80

90

< 20 mmHg < 15 mmHg < 10 mmHg < 5 mmHg

%ofpts

Brain hypoxia/ischemia is common despite observing current thresholds for treatment based on available evidence

Figaji et al, Neurosurgery. 2008 Jul;63(1):83-91

BrO2

ICP

N=75 children9452 hrs monitoring

ICP

PbtO2

MAP

BrO2

decompressive craniectomy

Can evaluate the effects of intervention

Figaji et al, Acta Neurochir Suppl. 2008;102:77-80

ICP

PbtO2

MAP

ICM+

Increase in blood pressure

Pressure autoregulation, intracranial pressure and brain tissue oxygenation in children with severe traumatic brain injuryFigaji et al. J Neurosurg Peds, 2009;4:420-8

PbtO2 : 28.7 ± 6.8 mmHg

CPP : 64 ± 15 mmHg

FiO2 : 46 ± 12%

PbtO2 : 33.3 ± 11.8 mmHg

CPP : 70 ± 13 mmHg

FiO2 : 47 ± 13%

P=0.002

P=0.021

P= 0.474

Account for CPP change:

Co-efficient 0.3356, P=0.001

4 hour period post-RBCTBaseline values

The effect of blood transfusion on brain oxygenation in childrenwith severe traumatic brain injuryFigaji et al. Pediatric Crit Care Med 2009

Blood transfusion

ICP

PbtO2

↑FiO2 ↓FiO2

Increase in PaO2

34 patients, 291 TCD studies

Mean Flow Velocity (MCA):

95 (79-115) range 32-180cm/s

Figaji et al, Surgical Neurology 2009; 72:389-394

Patients are different

Yes

No

•Depends on correct application and interpretation•Intervention misapplied can have equally hazardous effects•The treatment may be worse than the problem

•Gives us more information•Lets us know when patients are getting into trouble before an established problem•Helps interpret the underlying pathophysiological problem•Helps us titrate therapy appropriately•Probably reduces secondary injury