title: Unwitnessed out-of-hospital cardiac arrest: is resuscitation worthwhile?
abstract: OBJECTIVE
  To determine the epidemiology of unwitnessed out-of-hospital cardiac arrest and the factors associated with survival after resuscitation using the Utstein style data collection.
  
  
  METHODS
  We conducted a prospective cohort study in a 525,000-population city served by a single EMS system comprising a tiered response with physicians in the field. We studied consecutive unwitnessed out-of-hospital cardiac arrests that occurred between January 1, 1994, and December 31, 1995. We determined survival from cardiac arrest to discharge from hospital and the factors associated with survival.
  
  
  RESULTS
  Of the 809 patients for whom resuscitation was considered, 205 (25.3%) had sustained unwitnessed arrests. Cardiac origin of arrest was verified in 52% of cases. The most common noncardiac causes of arrest were trauma, intoxication, near-drowning, and hanging. In 150 patients (73.2%) the presenting rhythm was asystole, in 28 (13.6%) it was pulseless electrical activity, and in 27 (13.2%) it was ventricular fibrillation. Resuscitation was attempted in 162 cases, 59 (36.4%) of whom demonstrated return of spontaneous circulation; 45 (27.8%) were hospitalized alive, and 8 (4.9%) were discharged. The survivors represented 6.7% of all out-of-hospital cardiac arrest survivors during the study period. Survival was most likely if patients presented with pulseless electrical activity; none of the patients with asystole of cardiac origin survived. Sex (P = .032), age (inverse relationship, P = .0004), scene of collapse (P = .042), and interval from call receipt to arrival of first responders (P = .004) were associated with survival. In a logistic-regression model, near-drowning remained an independent factor of survival (odds ratio, 15.5; 95% confidence interval, 1.2 to 200). A routine priority dispatching protocol differentiated cardiac arrest patients with survival potential from those who already had irreversible signs of death.
  
  
  CONCLUSIONS
  This survey shows that survival after unwitnessed out-of-hospital cardiac arrest is unlikely with an initial response of basic life support alone. Withdrawal of resuscitation should be considered if an adult victim of unwitnessed cardiac arrest is found in asystole and the arrest is of obvious cardiac origin.
authors.affiliation: Helsinki City Emergency Medical Services, Helsinki, Finland.
authors.forename: M
authors.initials: M
authors.lastname: Kuisma
authors.forename: K
authors.initials: K
authors.lastname: Jaara
mesh_terms: D000293:Adolescent; D000328:Adult; D000465:Algorithms; D016887:Cardiopulmonary Resuscitation; D002648:Child; D005260:Female; D005387:Finland / Q000453:epidemiology; D006323:Heart Arrest / Q000401:mortality*; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D015701:Near Drowning / Q000401:mortality; D011379:Prognosis; D011446:Prospective Studies; D012307:Risk Factors