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Prehosp Emerg Care. 2010 Jan-Mar;14(1):71-7. doi: 10.3109/10903120903349820.

The association between emergency medical services staffing patterns and out-of-hospital cardiac arrest survival.

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Department of Epidemiology, Medical College of Wisconsin, Milwaukee, Wisconsin, USA.



To determine whether the number of advanced life support-trained personnel at the scene of an out-of-hospital cardiac arrest (OHCA) was associated with return of spontaneous circulation (ROSC) or survival to hospital discharge.


A retrospective database review using Utstein-style reporting definitions was conducted in Milwaukee County. All adult (>or= 18 years of age) OHCA cases of presumed cardiac etiology from January 1993 through December 2005 were eligible for inclusion in the study. Cardiac arrests resulting from a drug overdose, suicide, drowning, hypoxia, exsanguination, stroke, or trauma were excluded from the study. Also excluded were cases in which no crew configuration or responding unit was available, cases in which no resuscitation effort was attempted, and cases in which no time data were available. Return of spontaneous circulation and survival to hospital discharge for OHCA patients treated by a crew with two paramedics were compared to those patients treated by crews with three or more paramedics. Multivariable logistic regression was used for the analysis and the results are reported as odds ratios (ORs).


During the study period, there were 10,298 OHCAs of cardiac etiology. Of those, 10,057 (98%) cases had sufficient data to be included in the analysis. There were 4,229 patients treated by two paramedics (9% survived to discharge), 4,459 patients treated by three paramedics (9% survived to discharge), and 1,369 patients treated by four or more paramedics (8% survived to discharge). In the multivariable analysis, when referenced against crews with two paramedics and controlled for factors that have a known correlation with cardiac arrest survival, patients treated by crews with three paramedics (0.83, 95% confidence interval [CI] 0.70 to 0.97, p = 0.02) and crews with four or more paramedics (0.66, 95% CI 0.52 to 0.83, p < 0.01) were associated with reduced survival to hospital discharge. Return of spontaneous circulation was not influenced by the number of paramedics present.


The presence of three or more paramedics at the scene of OHCA was not associated with improved survival to hospital discharge when compared to crews with two paramedics. Additional research is needed to determine the potential cause of this finding.

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