When evaluating a heart-lung machine (HLM), buyers must focus on the precision of the roller pumps, the integration of safety sensors, and the modularity of the system. Ensure the device features high-resolution flow meters and bubble detectors with an automatic shut-off response time of less than 0.1 seconds. The system should support pulsatile and non-pulsatile flow modes to accommodate different surgical requirements. Additionally, verify the battery backup duration, which should ideally provide at least 90 to 120 minutes of autonomous operation in case of power failure.