Prehospital blood gas analysis is a new method in out-of-hospital emergency care. In a prospective pilot study we evaluated the feasibility of prehospital compensation of severe acidosis relying on different monitoring systems to evaluate patients oxygen, carbon dioxide or acid-base status, respectively.With the help of arterial blood gas checks taken at the site of the emergency, the acid base status of patients undergoing out of hospital cardiopulmonary resuscitation was analysed. The values derived from the first arterial puncture were used to determine the presence and the type of acidosis. The data of the arterial blood gas checks were set into relation with the time elapsed since the beginning of resuscitation and they were compared with end-tidal CO2.During the observation period 26 blood gas analyses from patients who had out-of-hospital resuscitation because of cardiac arrest were done. Twenty three patients had severe acidosis (pH range 15 mm Hg). In four patients resuscitation was not successful until compensation of an unexpectedly severe acidosis based upon the findings from blood-gas analysis had been performed.Arterial blood gas analysis proved to be helpful in the optimal management of out of hospital cardiac arrest. The incidence of severe acidosis in patients undergoing cardiopulmonary resuscitation was 80%. The probability of developing acidosis was found to increase slightly depending on the time elapsed since the beginning of CPR. The application of a calculated buffering of acidosis with sodium bicarbonate showed a good outcome in selected cases. In emergency patients alternative methods fail to detect severe disturbances of the patients oxygen and/or carbon dioxide status and the acid-base balance. Management of prehospital cardiac arrest could be optimized by the routine use of blood gas analysis.