A ventilator system and method can deliver artificial respirations to a person receiving cardiopulmonary resuscitation. The system and method may provide intermittent breath delivery (e.g., with interruptions), so that activation of the device gives a specific predetermined number of breaths, interspersed with a set time period of no breath. This pattern may be by default, manually triggered where one activation gives a set number of breaths followed by a pause until the next activation for breath (one activation gives one breath cycle), or one activation results in continuous cycle of intermittent breaths). In some embodiments, a signaling mechanism may deliver signals to a rescuer relating to timing of chest compressions of the person. The timing of the chest compressions for the signals may be based on a time of delivery of the artificial respirations. In certain embodiments, different sized masks each include a gas flow restrictor which is unique for the size of mask. The ventilator system may assess the size of the mask based on a pressure differential created by the unique gas flow restrictor.