title: Cerebral perfusion pressure in head-injured patients: a noninvasive assessment using transcranial Doppler ultrasonography.
abstract: OBJECTIVE
  The authors studied the reliability of a new method for noninvasive assessment of cerebral perfusion pressure (CPP) in head-injured patients in which mean arterial blood pressure (ABP) and transcranial Doppler middle cerebral artery mean and diastolic flow velocities are measured.
  
  
  METHODS
  Cerebral perfusion pressure was estimated (eCPP) over periods of continuous monitoring (20 minutes-2 hours, 421 daily examinations) in 96 head-injured patients (Glasgow Coma Scale score < 13) who were admitted to the intensive care unit. All patients were sedated, paralyzed, and ventilated. The eCPP and the measured CPP (ABP minus intracranial pressure, measured using an intraparenchymal microsensor) were compared. The correlation between eCPP and measured CPP was r=0.73; p < 10(-6). In 71% of the examinations, the estimation error was less than 10 mm Hg and in 84% of the examinations, the error was less than 15 mm Hg. The method had a high positive predictive power (94%) for detecting low CPP (< 60 mm Hg). The eCPP also accurately reflected changes in measured CPP over time (r > 0.8; p < 0.001) in situations such as plateau and B waves of intracranial pressure, arterial hypotension, and refractory intracranial hypertension. A good correlation was found between the average measured CPP and eCPP when day-by-day variability was assessed in a group of 41 patients (r=0.71).
  
  
  CONCLUSIONS
  Noninvasive estimation of CPP by using transcranial Doppler ultrasonography may be of value in situations in which monitoring relative changes in CPP is required without invasive measurement of intracranial pressure.
authors.affiliation: Medical Research Council/Cambridge Centre for Brain Repair, Department of Anaesthesia, Addenbrooke's Hospital, United Kingdom.
authors.forename: M
authors.initials: M
authors.lastname: Czosnyka
authors.forename: B F
authors.initials: BF
authors.lastname: Matta
authors.forename: P
authors.initials: P
authors.lastname: Smielewski
authors.forename: P J
authors.initials: PJ
authors.lastname: Kirkpatrick
authors.forename: J D
authors.initials: JD
authors.lastname: Pickard
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001783:Blood Flow Velocity / Q000502:physiology; D001794:Blood Pressure / Q000502:physiology*; D002536:Cerebral Arteries / Q000000981:diagnostic imaging / Q000503:physiopathology; D002560:Cerebrovascular Circulation / Q000502:physiology*; D002648:Child; D015986:Confounding Factors, Epidemiologic; D006259:Craniocerebral Trauma / Q000000981:diagnostic imaging* / Q000503:physiopathology; D003422:Critical Care; D003971:Diastole; D005260:Female; D015600:Glasgow Coma Scale; D006801:Humans; D007022:Hypotension / Q000000981:diagnostic imaging / Q000503:physiopathology; D019586:Intracranial Hypertension / Q000000981:diagnostic imaging / Q000503:physiopathology; D007427:Intracranial Pressure; D002546:Ischemic Attack, Transient / Q000000981:diagnostic imaging / Q000503:physiopathology; D016013:Likelihood Functions; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D017585:Ultrasonography, Doppler, Transcranial; D014655:Vascular Resistance / Q000502:physiology