If the patient should begin to grow stronger and start to resist the flow of the ventilator, you should be alerted so that the settings can be adjusted. There should be an input flow and output flow measurement that shows you just how much oxygen is going into and out of the patient at all times. If the patient seems to be having trouble with the flow, you should be able to adjust it on the actual medical respiratory ventilator. Most medical respiratory ventilators will actually have an alarm that will let you know when the patient is 'taking over' the breathing naturally. By changing the inflow or the outflow as necessary, the patient can feel comfortable as the machine helps them breathe while also getting the proper amount of oxygen into their bloodstream. Ideally, the battery for medical respiratory ventilators should last as long as eight hours or until a new power source can be found. If the home's power supply should suddenly be cut or the hospital's generators fail, you need to know that your patient will still be able to breathe until the power is restored. In most cases, this will never be a problem, but try to find a battery system that is as efficient as possible to ensure that you aren't compromising the health of the patient. At the very least, the battery should be able to last until the patient can get to a hospital with a powered up ventilator system.