At our hospital, balloon pumps are 1:1. Every hour the nurse is supposed to do an assessment... start at the patient's leg and make sure dressing is CDI, gently palpate the area around it to make sure skin is still soft and there are no signs of a hematoma, then follow the tubing down to the IABP machine to make sure there's no blood in the line. Then we feel radial and dorsalis pedis pulses, along with posterior tibialis pulses (usually with a doppler).
Just a brief answer about how the balloon "knows" to inflate - we generally have patients on "EKG Trigger" in which the machine is reading the EKG and inflates at just the right time. If a patient is having serious dysrhythmias or is asystole and we start chest compressions, the machine can be turned to "pressure trigger" so that it knows when to based on the pressures in the heart.
Correct me if I'm wrong about any of this, I'm a new ICU nurse so I'm just getting familiar with IABPs.