An ambulatory infusion system and a method of operating including a disposable infusion cartridge having a collapsible reservoir and a substantially rigid shell disposed over the collapsible reservoir having an interior volume, a pump device, a pressure sensor in communication with the interior volume and a processor. The method includes actuating the pressure sensor to take pressure measurements at regular time intervals periodically assessing a preselected number of the pressure measurements with statistical analysis to identify statistical measures associated with the pressure measurements and using the statistical measures to assess the status of the flexible reservoir and the pump device.
