Relationship between intracranial pressure and critical closing pressure in patients with neurotrauma.
BACKGROUND
The driving pressure gradient for cerebral perfusion is the difference between mean arterial pressure (MAP) and critical closing pressure (CCP = zero flow pressure). Therefore, determination of the difference between MAP and CCP should provide an appropriate monitoring of the effective cerebral perfusion pressure (CPP(eff)). Based on this concept, the authors compared conventional measurements of cerebral perfusion pressure by MAP and intracranial pressure (CPP(ICP)) with CPP(eff).


METHODS
Simultaneous synchronized recordings of pressure waveforms of the radial artery and blood flow velocities of the middle cerebral artery were performed in 70 head trauma patients. CCP was calculated from pressure-flow velocity plots by linear extrapolation to zero flow.


RESULTS
Intracranial pressure measured by intraventricular probes and CCP ranged from 3 to 71 and 4 to 70 mmHg, respectively. Linear correlation between ICP and CCP was r = 0.91. CPP(ICP) was 77 +/- 20 mmHg and did not differ from CPP(eff); linear correlation was r = 0.92. However, limits of agreement were only +/- 16.2 mmHg. Therefore, in 51.4% of the patients, CPP(ICP) overestimated CPP(eff) by 19.8 mmHg at most.


CONCLUSIONS
Assuming that CPP(eff) (MAP - CCP) takes into account more determinants of cerebral downstream pressure, in individual cases, the actual gold standard of CPP determination (MAP - ICP) might overestimate the CPP(eff) of therapeutic significance.
Thees
Christof
C
Department of Anesthesia and Intensive Care Medicine, University of Bonn, Bonn, Germany. christof.thees@ukb.uni-bonn.de
Scholz
Martin
M
Schaller M D
Carlo
C
Gass
Annette
A
Pavlidis
Christos
C
Weyland
Andreas
A
Hoeft
Andreas
A
D000293:Adolescent; D000328:Adult; D001794:Blood Pressure / Q000502:physiology; D002552:Cerebral Ventricles / Q000502:physiology; D002560:Cerebrovascular Circulation / Q000502:physiology; D006259:Craniocerebral Trauma / Q000503:physiopathology* / Q000601:surgery*; D005260:Female; D006801:Humans; D007427:Intracranial Pressure / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D020768:Middle Cerebral Artery / Q000502:physiology; D016343:Monitoring, Intraoperative; D019635:Neurosurgical Procedures; D017534:Radial Artery / Q000502:physiology; D012121:Respiration, Artificial