title: Which factors influence spontaneous state transitions during resuscitation?
abstract: BACKGROUND
  The clinical state (i.e. ventricular fibrillation/tachycardia: VF/VT, asystole: ASY, pulseless electrical activity: PEA, or return of spontaneous circulation, ROSC) during cardiopulmonary resuscitation determines patient management. We investigate how spontaneous transitions (i.e. not forced by DC shock) between these states are influenced by factors like age, gender, bystander CPR, CPR quality, proportion of time spent in a state, or the number of state transitions.
  
  
  METHODS
  Detailed recordings from CPR attempts in 304 out-of-hospital cardiac arrests in Akershus (Norway), Stockholm (Sweden), and London (UK) were obtained from modified Heartstart 4000 defibrillators. Spontaneous state transitions were studied using a non-parametric intensity regression method that can handle dynamic factors like the state history properly.
  
  
  RESULTS
  The initial state tended to preserve itself, as did cumulative time in any state. Recent DC shock, bystander CPR, location, response time, gender, compression depth, and ventilation rate were important for some transitions. More ventilation during PEA might possibly avert development to ASY and favour ROSC; otherwise observed variations in CPR quality had little impact.
  
  
  CONCLUSIONS
  Using a novel intensity regression approach we studied the influence of various factors on spontaneous (i.e. non-shock) state transitions during CPR. State development was largely determined by the initial state, the proportion of time spent in a state, and the transition frequency; all probably reflecting the underlying aetiology.
authors.affiliation: Department of Mathematics and Natural Sciences, Faculty of Science and Technology, University of Stavanger, N-4036 Stavanger, Norway. jan.t.kvaloy@uis.no
authors.forename: Jan Terje
authors.initials: JT
authors.lastname: Kvaløy
authors.forename: Eirik
authors.initials: E
authors.lastname: Skogvoll
authors.forename: Trygve
authors.initials: T
authors.lastname: Eftestøl
authors.forename: Kenneth
authors.initials: K
authors.lastname: Gundersen
authors.forename: Jo
authors.initials: J
authors.lastname: Kramer-Johansen
authors.forename: Theresa Mariero
authors.initials: TM
authors.lastname: Olasveengen
authors.forename: Petter Andreas
authors.initials: PA
authors.lastname: Steen
mesh_terms: D000367:Age Factors; D016887:Cardiopulmonary Resuscitation / Q000379:methods*; D006323:Heart Arrest / Q000453:epidemiology / Q000209:etiology / Q000628:therapy*; D006439:Hemodynamics / Q000502:physiology*; D006801:Humans; D015994:Incidence; D008390:Markov Chains; D015233:Models, Statistical; D012307:Risk Factors; D016896:Treatment Outcome