The demand valve is designed to resuscitate a non-breathing patient, or to provide assisted breathing with 100% oxygen on a conscious patient. To use for resuscitation, the caregiver simply presses the button on the demand valve, to inflate the lungs. When the button is released, the gases are expelled from the lungs through the exhalation (non-rebreathing) valve. For the demand function, the patient simply needs to hold the mask to his mouth and breathe. When the patient initiates a breath, the demand valve will sense the negative pressure and assist the breath with 100% oxygen.