A nurse reports that the PCA pump ran satisfactorily for over an hour "on demand" but then stopped delivering medication for two hours. What is the most likely cause?

The situation described indicates that the PCA (Patient-Controlled Analgesia) pump operated correctly for a period of time but then ceased delivering medication, which suggests that the device itself is functioning properly. When the pump is set to deliver medication "on demand," it incorporates a lockout interval during which the patient cannot receive additional doses until a specified time has passed. If the patient attempts to request medication during this lockout period, the pump will not deliver any medication, leading to the scenario where it seems like the pump has stopped working when, in fact, it's adhering to its programmed safety features.

Understanding the lockout mechanism is crucial in PCA pumps; it prevents overmedication by limiting the frequency of doses, protecting patient safety. Therefore, if this interval was exceeded, the pump would remain inactive until the lockout period ended, explaining the two-hour cessation in medication delivery.