Methods and systems for delivering a total quantity of pharmaceutical gas to a patient. The methods and systems provide one of a low amount and high amount of pharmaceutical gas to a patient. The selection of the high amount or low amount may be determined by comparing the amount per unit of time of pharmaceutical gas delivered to the patient over the past number of breaths to the required quantity of pharmaceutical gas per unit of time. Upon completion of delivering the total quantity of pharmaceutical gas to the patient, the system can terminate, continue, activate and alarm, etc.