A system for oxygenating blood in an extracorporeal circuit, the system comprising: an oxygenator apparatus including: a housing defining a blood inlet port, a blood outlet port and a blood flow path from the blood inlet port to the blood outlet port, a fiber bundle disposed within the housing and including a plurality of gas exchange elements; a first sensor proximate the blood inlet port for generating an inlet pressure measurement; a second sensor proximate the blood outlet port for generating an outlet pressure measurement; a third sensor for generating a blood flow rate measurement; a communication device; and a controller electronically connected to the first, second and third sensors (52, 54, 56) and the communication device, the controller programmed to: determine a first oxygenator apparatus flow impedance at a first point in time as a function of the inlet pressure measurement, the outlet pressure measurement and the blood flow rate measurement, and determine a second oxygenator apparatus flow impedance at a second point in time, the second point in time being after the first point in time prompt the communication device to communicate information indicative of a comparison between the first oxygenator apparatus flow impedance and the second oxygenator apparatus flow impedance. an oxygenator apparatus including: a housing defining a blood inlet port, a blood outlet port and a blood flow path from the blood inlet port to the blood outlet port, a fiber bundle disposed within the housing and including a plurality of gas exchange elements; a housing defining a blood inlet port, a blood outlet port and a blood flow path from the blood inlet port to the blood outlet port, a fiber bundle disposed within the housing and including a plurality of gas exchange elements; a first sensor proximate the blood inlet port for generating an inlet pressure measurement; a second sensor proximate the blood outlet port for generating an outlet pressure measurement; a third sensor for generating a blood flow rate measurement; a communication device; and a controller electronically connected to the first, second and third sensors (52, 54, 56) and the communication device, the controller programmed to: determine a first oxygenator apparatus flow impedance at a first point in time as a function of the inlet pressure measurement, the outlet pressure measurement and the blood flow rate measurement, and determine a second oxygenator apparatus flow impedance at a second point in time, the second point in time being after the first point in time prompt the communication device to communicate information indicative of a comparison between the first oxygenator apparatus flow impedance and the second oxygenator apparatus flow impedance. determine a first oxygenator apparatus flow impedance at a first point in time as a function of the inlet pressure measurement, the outlet pressure measurement and the blood flow rate measurement, and determine a second oxygenator apparatus flow impedance at a second point in time, the second point in time being after the first point in time prompt the communication device to communicate information indicative of a comparison between the first oxygenator apparatus flow impedance and the second oxygenator apparatus flow impedance.