A chest drainage system including a collection device configured to receive fluid from the pleural cavity of a patient. A sensor is included to detect a pressure differential in the fluid. A display is configured to display a trend in occurrences of changes in pressure of the fluid over time in predetermined time increments based on a number of detections of pressure differentials that exceed a predetermined pressure differential during each of the predetermined time increments. The trend is correlative to the percentage of time that the patient is deemed to have an air leak in the pleural cavity in the predetermined time increments. The trend is derived from a ratio of the quantity of respiratory cycles of the patient for which the predetermined pressure differential is detected (QRCleak) in the predetermined time increments to the total quantity of respiratory cycles of the patient in respective predetermined time increments (QRCtotal).