Which of the following best describes chest compression fraction?

The term "chest compression fraction" refers specifically to the proportion of time during a resuscitation attempt that effective chest compressions are being delivered. A high chest compression fraction indicates that most of the resuscitation time is spent actively compressing the chest rather than waiting for other actions, such as ventilations or analyzing an arrhythmia. This is crucial because maintaining a high compression fraction is associated with improved outcomes in cardiac arrest situations; it ensures continuous blood flow to vital organs.

The other choices do not accurately define chest compression fraction. For example, the total number of compressions completed does not provide information about how much time was spent on those compressions relative to other activities. Similarly, the number of ventilations administered or the average depth of compressions are important metrics in assessing the quality of CPR but do not reflect the efficiency of time management during resuscitation efforts. Thus, option B succinctly captures the essence of what chest compression fraction represents in the context of Basic Life Support.