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Review of: Deakin CD, O Neill JF, Tabor T: "Does compression-only cardiopulmonary resuscitation generate adequate passive ventilation during cardiac arrest?" Resuscitation. 75(1):53-59, 2007.
The Science:
Researchers in England were concerned with the potential impact that performing compression-only CPR would have on ventilation. They acknowledge the science supporting the vital importance of uninterrupted chest compression but wondered whether they could measure the amount of air that was moved in and out of an intubated cardiac arrest patient and from that decide whether this amount of passive ventilation was sufficient to oxygenate the lungs.
They studied 17 cardiac arrest victims who had CPR provided mechanically to ensure consistent chest compression. Fourteen of the arrests were witnessed, and 11 had bystander-CPR administered. It's unknown how many of these had any ventilations performed by bystanders prior to EMS arrival. Ten patients were intubated, and three had an LMA inserted by EMS prior to hospital arrival. Four had no form of advanced airway management. All 17 patients died with none regaining ROSC.
Those that were not intubated in the field were intubated in the emergency department (ED), and ventilation measured as well as end-tidal CO2.
They found that the median volume of air moved per compression was 41.5 cc, which is considered to be less than half the calculated dead space in the airway. Maximum end-tidal CO2 was around 10 mmH20.
They concluded that compression-only CPR is limited in its ability to maintain adequate gas exchange.
The Street:
This was the first attempt to study the actual amount of air moved during passive ventilation on human cardiac arrest victims. Despite the authors' conclusion, sufficient data exists to suggest that -- at least in the early phases of cardiac arrest when chest wall compliance is higher -- compression-only CPR results in higher rates of return of spontaneous circulation following defibrillation.
Although I have no question with the validity of the values these researchers found, one has to wonder the significance of them given what we know of these 17 victims. Only four of the patients were in V Fib on arrival by EMS. Seven were in asystole, and the remaining six in pulseless electrical activity (PEA). It could be argued that the asystole and PEA patients suffer from significantly greater acidosis and therefore would have worse chest wall compliance than the relatively "fresh" cardiac arrest victims in V Fib.
Furthermore, many program currently used end-tidal CO2 readings as an indicator to terminate resuscitation because it indicates that regardless of ventilation, there is no ongoing cellular metabolism. Studies have shown values of less than 10 are uniformly fatal.
So, does this study mean was should shun compression-only CPR? I agree with the authors that it's premature to make that conclusion. Larger studies will be required to do that. Clearly, for some patients compression-only CPR appears to work, and we all acknowledge that bystanders have an issue with performing mouth-to-mouth ventilations. The exact role of compression-only CPR remains undefined but at least this study has proven that we can accurately measure the movement of air during this form of CPR.
