The present invention relates to an additive gas delivery apparatus (3) for delivery of additive gas, such as nitric oxide [NO], to a patient (2). The additive gas delivery apparatus comprises a control unit (12) configured to determine if a monitored parameter indicates that a patient (2) is connected to the additive gas delivery apparatus (3), determine if the additive gas delivery apparatus (3) is in a passive state in which it does not deliver additive gas, and activate an alarm if the additive gas delivery apparatus (3) is in said passive state when the monitored parameter indicates that a patient (2) is connected to the additive gas deliver apparatus (3). The alarm serves to notify the user of undesired non-delivery of additive gas, and so serves to improve safety in additive gas delivery systems. The invention also relates to a gas delivery system (1) and a method for monitoring delivery of additive gas to a patient (2).
