Cerebral perfusion pressure and risk of brain hypoxia in severe head injury: a prospective observational study.
BACKGROUND
Higher and lower cerebral perfusion pressure (CPP) thresholds have been proposed to improve brain tissue oxygen pressure (PtiO2) and outcome. We study the distribution of hypoxic PtiO2 samples at different CPP thresholds, using prospective multimodality monitoring in patients with severe traumatic brain injury.


METHODS
This is a prospective observational study of 22 severely head injured patients admitted to a neurosurgical critical care unit from whom multimodality data was collected during standard management directed at improving intracranial pressure, CPP and PtiO2. Local PtiO2 was continuously measured in uninjured areas and snapshot samples were collected hourly and analyzed in relation to simultaneous CPP. Other variables that influence tissue oxygen availability, mainly arterial oxygen saturation, end tidal carbon dioxide, body temperature and effective hemoglobin, were also monitored to keep them stable in order to avoid non-ischemic hypoxia.


RESULTS
Our main results indicate that half of PtiO2 samples were at risk of hypoxia (defined by a PtiO2 equal to or less than 15 mmHg) when CPP was below 60 mmHg, and that this percentage decreased to 25% and 10% when CPP was between 60 and 70 mmHg and above 70 mmHg, respectively (p < 0.01).


CONCLUSIONS
Our study indicates that the risk of brain tissue hypoxia in severely head injured patients could be really high when CPP is below the normally recommended threshold of 60 mmHg, is still elevated when CPP is slightly over it, but decreases at CPP values above it.
Marín-Caballos
Antonio J
AJ
Servicio de Cuidados Críticos y Urgencias, Hospitales Universitarios Virgen Del Rocío, Avda Manuel Siurot s/n, Seville, 41013, Spain. antmarin@terra.es
Murillo-Cabezas
Francisco
F
Cayuela-Domínguez
Aurelio
A
Domínguez-Roldán
Jose M
JM
Rincón-Ferrari
M Dolores
MD
Valencia-Anguita
Julio
J
Flores-Cordero
Juan M
JM
Muñoz-Sánchez
M Angeles
MA
D000328:Adult; D001794:Blood Pressure; D006259:Craniocerebral Trauma / Q000150:complications* / Q000378:metabolism / Q000503:physiopathology*; D003422:Critical Care / Q000379:methods; D016638:Critical Illness; D005260:Female; D006801:Humans; D002534:Hypoxia, Brain / Q000209:etiology* / Q000378:metabolism / Q000503:physiopathology*; D008297:Male; D010100:Oxygen / Q000378:metabolism; D011446:Prospective Studies; D012016:Reference Values; D018570:Risk Assessment / Q000379:methods; D012307:Risk Factors; D013687:Telencephalon / Q000098:blood supply* / Q000378:metabolism
D010100:Oxygen