title: The association between admission systolic blood pressure and mortality in significant traumatic brain injury: a multi-centre cohort study.
abstract: BACKGROUND
  Low systolic blood pressure (SBP) is an important secondary insult following traumatic brain injury (TBI), but its exact relationship with outcome is not well characterised. Although a SBP of <90 mmHg represents the threshold for hypotension in consensus TBI treatment guidelines, recent studies suggest redefining hypotension at higher levels. This study therefore aimed to fully characterise the association between admission SBP and mortality to further inform resuscitation endpoints.
  
  
  METHODS
  We conducted a multicentre cohort study using data from the largest European trauma registry. Consecutive adult patients with AIS head scores >2 admitted directly to specialist neuroscience centres between 2005 and July 2012 were studied. Multilevel logistic regression models were developed to examine the association between admission SBP and 30 day inpatient mortality. Models were adjusted for confounders including age, severity of injury, and to account for differential quality of hospital care.
  
  
  RESULTS
  5057 patients were included in complete case analyses. Admission SBP demonstrated a smooth u-shaped association with outcome in a bivariate analysis, with increasing mortality at both lower and higher values, and no evidence of any threshold effect. Adjusting for confounding slightly attenuated the association between mortality and SBP at levels <120 mmHg, and abolished the relationship for higher SBP values. Case-mix adjusted odds of death were 1.5 times greater at <120 mmHg, doubled at <100 mmHg, tripled at <90 mmHg, and six times greater at SBP<70 mmHg, p<0.01.
  
  
  CONCLUSIONS
  These findings indicate that TBI studies should model SBP as a continuous variable and may suggest that current TBI treatment guidelines, using a cut-off for hypotension at SBP<90 mmHg, should be reconsidered.
authors.affiliation: Trauma Audit and Research Network, Health Sciences Research Group, Manchester Academic Health Sciences Centre, Mayo Building, Salford Royal Hospital, Eccles Old Road, Salford M6 8HD, UK. Electronic address: gordonwfuller@doctors.net.uk.
authors.forename: Gordon
authors.initials: G
authors.lastname: Fuller
authors.affiliation: Department of Emergency Medicine, University Hospital Bern, Freiburgstr, 3010 Bern, Switzerland.
authors.forename: Rebecca M
authors.initials: RM
authors.lastname: Hasler
authors.affiliation: Institute of Social and Preventive Medicine (ISPM), University of Bern, Finkenhubelweg 11, 3012 Bern, Switzerland.
authors.forename: Nicole
authors.initials: N
authors.lastname: Mealing
authors.affiliation: Trauma Audit and Research Network, Health Sciences Research Group, Manchester Academic Health Sciences Centre, Mayo Building, Salford Royal Hospital, Eccles Old Road, Salford M6 8HD, UK.
authors.forename: Thomas
authors.initials: T
authors.lastname: Lawrence
authors.affiliation: Trauma Audit and Research Network, Health Sciences Research Group, Manchester Academic Health Sciences Centre, Mayo Building, Salford Royal Hospital, Eccles Old Road, Salford M6 8HD, UK.
authors.forename: Maralyn
authors.initials: M
authors.lastname: Woodford
authors.affiliation: Institute of Social and Preventive Medicine (ISPM), University of Bern, Finkenhubelweg 11, 3012 Bern, Switzerland.
authors.forename: Peter
authors.initials: P
authors.lastname: Juni
authors.affiliation: School of Health and Related Research, University of Sheffield, Regent Court, 30 Regent Street, Sheffield S1 4DA, UK.
authors.forename: Fiona
authors.initials: F
authors.lastname: Lecky
mesh_terms: D000328:Adult; D000368:Aged; D001794:Blood Pressure; D001795:Blood Pressure Determination / Q000379:methods; D001930:Brain Injuries / Q000401:mortality* / Q000503:physiopathology; D015331:Cohort Studies; D005060:Europe / Q000453:epidemiology; D005260:Female; D023261:Glasgow Outcome Scale; D017052:Hospital Mortality; D006801:Humans; D006973:Hypertension / Q000401:mortality* / Q000503:physiopathology; D007022:Hypotension / Q000401:mortality* / Q000503:physiopathology; D015601:Injury Severity Score; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D017410:Practice Guidelines as Topic; D011379:Prognosis; D011446:Prospective Studies; D012042:Registries; D016019:Survival Analysis; D014193:Trauma Centers; D014218:Triage
keywords: Craniocerebral trauma; Hypotension; Resuscitation; Systolic blood pressure