Answer: The 2010 American Heart Association Guidelines (Berg et al Part 5: Adult Basic Life Support Circulation 2010) state the following in terms of initial rescuer sequence:
A change in the 2010 AHA Guidelines for CPR and ECC is to recommend the initiation of compressions before ventilations. While no published human or animal evidence demonstrates that starting CPR with 30 compressions rather than 2 ventilations leads to improved outcomes, it is clear that blood flow depends on chest compressions. Therefore, delays in, and interruptions of, chest compressions should be minimized throughout the entire resuscitation. Moreover, chest compressions can be started almost immediately, while positioning the head, achieving a seal for mouth-to-mouth rescue breathing, and getting a bag-mask apparatus for rescue breathing all take time. Beginning CPR with 30 compressions rather than 2 ventilations leads to a shorter delay to first compression (Class IIb, LOE C).
Once chest compressions have been started, a trained rescuer should deliver rescue breaths by mouth-to-mouth or bag-mask to provide oxygenation and ventilation, as follows:
- Deliver each rescue breath over 1 second (Class IIa, LOE C).
- Give a sufficient tidal volume to produce visible chest rise (Class IIa, LOE C).
- Use a compression to ventilation ratio of 30 chest compressions to 2 ventilations.
The SWORBHP Medical Council advises that given the above, ventilations are required via a BVM after 30 compressions to achieve the recommended 30:2 compression ratio. You are absolutely correct that the priorities are good compressions and defibrillation. Paramedics should however work as a team on scene to apply the defibrillator as early as possible and ideally the defibrillator will be ready to analyze by the time the 30 compressions are complete.
However, to answer your specific question, if the defibrillator is not ready to analyze once the 30 compressions have been completed, interrupting compressions to provide 2 ventilations as per the recommended 30:2 ratio is acceptable.