title: Age and mortality after injury: is the association linear?
abstract: BACKGROUND
  Multiple studies have demonstrated a linear association between advancing age and mortality after injury. An inflection point, or an age at which outcomes begin to differ, has not been previously described. We hypothesized that the relationship between age and mortality after injury is non-linear and an inflection point exists.
  
  
  METHODS
  We performed a retrospective cohort analysis at our urban level I center from 2007 through 2009. All patients aged 65 years and older with the admission diagnosis of injury were included. Non-parametric logistic regression was used to identify the functional form between mortality and age. Multivariate logistic regression was utilized to explore the association between age and mortality. Age 65 years was used as the reference. Significance was defined as p < 0.05.
  
  
  RESULTS
  A total of 1,107 patients were included in the analysis. One-third required intensive care unit (ICU) admission and 48 % had traumatic brain injury. 229 patients (20.6 %) were 84 years of age or older. The overall mortality was 7.2 %. Our model indicates that mortality is a quadratic function of age. After controlling for confounders, age is associated with mortality with a regression coefficient of 1.08 for the linear term (p = 0.02) and a regression coefficient of -0.006 for the quadratic term (p = 0.03). The model identified 84.4 years of age as the inflection point at which mortality rates begin to decline.
  
  
  CONCLUSIONS
  The risk of death after injury varies linearly with age until 84 years. After 84 years of age, the mortality rates decline. These findings may reflect the varying severity of comorbidities and differences in baseline functional status in elderly trauma patients. Specifically, a proportion of our injured patient population less than 84 years old may be more frail, contributing to increased mortality after trauma, whereas a larger proportion of our injured patients over 84 years old, by virtue of reaching this advanced age, may, in fact, be less frail, contributing to less risk of death.
authors.affiliation: Division of Trauma, Critical Care, Burn and Emergency Surgery, Department of Surgery, University of Arizona College of Medicine, 1501 N. Campbell Ave., Room 5411, P.O. Box 245063, Tucson, AZ, 85727, USA.
authors.forename: R S
authors.initials: RS
authors.lastname: Friese
authors.affiliation: Division of Trauma, Critical Care, Burn and Emergency Surgery, Department of Surgery, University of Arizona College of Medicine, 1501 N. Campbell Ave., Room 5411, P.O. Box 245063, Tucson, AZ, 85727, USA.
authors.forename: J
authors.initials: J
authors.lastname: Wynne
authors.affiliation: Division of Trauma, Critical Care, Burn and Emergency Surgery, Department of Surgery, University of Arizona College of Medicine, 1501 N. Campbell Ave., Room 5411, P.O. Box 245063, Tucson, AZ, 85727, USA. bjoseph@surgery.arizona.edu.
authors.forename: B
authors.initials: B
authors.lastname: Joseph
authors.affiliation: Division of Trauma, Critical Care, Burn and Emergency Surgery, Department of Surgery, University of Arizona College of Medicine, 1501 N. Campbell Ave., Room 5411, P.O. Box 245063, Tucson, AZ, 85727, USA.
authors.forename: A
authors.initials: A
authors.lastname: Hashmi
authors.affiliation: Division of Trauma, Critical Care, Burn and Emergency Surgery, Department of Surgery, University of Arizona College of Medicine, 1501 N. Campbell Ave., Room 5411, P.O. Box 245063, Tucson, AZ, 85727, USA.
authors.forename: C
authors.initials: C
authors.lastname: Diven
authors.affiliation: Division of Trauma, Critical Care, Burn and Emergency Surgery, Department of Surgery, University of Arizona College of Medicine, 1501 N. Campbell Ave., Room 5411, P.O. Box 245063, Tucson, AZ, 85727, USA.
authors.forename: V
authors.initials: V
authors.lastname: Pandit
authors.affiliation: Division of Trauma, Critical Care, Burn and Emergency Surgery, Department of Surgery, University of Arizona College of Medicine, 1501 N. Campbell Ave., Room 5411, P.O. Box 245063, Tucson, AZ, 85727, USA.
authors.forename: T
authors.initials: T
authors.lastname: O'Keeffe
authors.affiliation: Division of Trauma, Critical Care, Burn and Emergency Surgery, Department of Surgery, University of Arizona College of Medicine, 1501 N. Campbell Ave., Room 5411, P.O. Box 245063, Tucson, AZ, 85727, USA.
authors.forename: B
authors.initials: B
authors.lastname: Zangbar
authors.affiliation: Division of Trauma, Critical Care, Burn and Emergency Surgery, Department of Surgery, University of Arizona College of Medicine, 1501 N. Campbell Ave., Room 5411, P.O. Box 245063, Tucson, AZ, 85727, USA.
authors.forename: N
authors.initials: N
authors.lastname: Kulvatunyou
authors.affiliation: Division of Trauma, Critical Care, Burn and Emergency Surgery, Department of Surgery, University of Arizona College of Medicine, 1501 N. Campbell Ave., Room 5411, P.O. Box 245063, Tucson, AZ, 85727, USA.
authors.forename: P
authors.initials: P
authors.lastname: Rhee
keywords: Geriatric trauma; Intensive care unit admission and old age; Old age and mortality; Outcome is elderly trauma patients
references.citation: J Trauma Acute Care Surg. 2014 Mar;76(3):894-901
references.pmid: 24553567
references.citation: J Trauma. 2003 Feb;54(2):391-416
references.pmid: 12579072
references.citation: J Trauma. 2011 Mar;70(3):616-21
references.pmid: 21610351
references.citation: J Trauma Acute Care Surg. 2014 Jan;76(1):196-200
references.pmid: 24368379
references.citation: J Trauma. 2001 Oct;51(4):754-6; discussion 756-7
references.pmid: 11586171
references.citation: J Am Geriatr Soc. 2010 Oct;58(10):1843-9
references.pmid: 20831727
references.citation: J Trauma. 1990 Dec;30(12):1476-82
references.pmid: 2258958
references.citation: J Gerontol A Biol Sci Med Sci. 2004 Sep;59(9):M962-5
references.pmid: 15472162
references.citation: Am J Emerg Med. 2010 Feb;28(2):151-8
references.pmid: 20159383
references.citation: J Trauma. 1984 Jul;24(7):565-72
references.pmid: 6748116
references.citation: J Trauma. 1992 Feb;32(2):236-43; discussion 243-4
references.pmid: 1740808
references.citation: J Am Coll Surg. 2003 Apr;196(4):549-55
references.pmid: 12691929
references.citation: Br J Surg. 2002 Oct;89(10):1319-22
references.pmid: 12296905
references.citation: J Trauma. 2003 Jul;55(1):26-32
references.pmid: 12855877
references.citation: J Trauma. 1989 Jun;29(6):757-64; discussion 764-5
references.pmid: 2738973
references.citation: CMAJ. 2005 Aug 30;173(5):489-95
references.pmid: 16129869
references.citation: Am Surg. 2014 Jan;80(1):43-7
references.pmid: 24401514
references.citation: World J Surg. 2006 Jan;30(1):114-8
references.pmid: 16369714
references.citation: Int Surg. 1988 Apr-Jun;73(2):119-22
references.pmid: 3397258
references.citation: J Trauma. 1990 Feb;30(2):129-34; discussion 134-6
references.pmid: 2304107
references.citation: Crit Care Med. 2006 Jun;34(6):1597-601
references.pmid: 16607232
references.citation: J Trauma Acute Care Surg. 2012 Jan;72(1):112-8
references.pmid: 22310124
references.citation: Am Surg. 1998 Sep;64(9):826-31; discussion 831-2
references.pmid: 9731808
references.citation: Am Surg. 2010 Jan;76(1):65-9
references.pmid: 20135942
references.citation: Injury. 2009 Apr;40(4):362-7
references.pmid: 19217104
references.citation: JAMA. 1990 Apr 11;263(14):1942-6
references.pmid: 2313871
references.citation: Ann Surg. 1987 Dec;206(6):738-43
references.pmid: 3689009
references.citation: J Trauma. 2002 Sep;53(3):407-14
references.pmid: 12352472
references.citation: J Surg Res. 2013 Sep;184(1):541-5
references.pmid: 23664534
references.citation: Int J Nurs Pract. 2010 Feb;16(1):14-9
references.pmid: 20158543
references.citation: J Am Coll Surg. 2011 Jul;213(1):37-42; discussion 42-4
references.pmid: 21435921