(b)(4).Method: the complaint mr290v vented autofeed humidification chambers were returned to fisher & paykel healthcare (f&p) in new zealand where they were visually inspected and analysed.Results: visual inspection of the returned mr290v chambers revealed multiple curved and diagonal cracks were observed towards the base of the chamber dome near the hinge brackets.Further testing showed that the rolled base thickness were found to be within specification.Conclusion: we are unable to determine what may have caused the cracks of the complaint chamber domes.However our investigation indicates that the cracks are most likely due to mechanical stress.The stress source is unknown.The mr290v chambers are designed and tested to conform to iso 5367 breathing tubes intended for use with anaesthetic apparatus and ventilators.Every mr290v chamber is pressure tested following the manufacturing process to check for any leaks present in the chamber dome due to cracks and other causes.Any chamber which fails this test is rejected.In addition, the pressure test is followed by a visual inspection of each chamber.No cracks in the chamber dome are acceptable.Any chamber that fails this inspection is rejected.The subject mr290v chambers would have met the required specification at the time of production.Our user instructions that accompany the mr290v vented autofeed humidification chamber state the following: - "do not soak, wash, sterilize, or reuse this product.Avoid contact with chemicals, cleaning agents, or hand sanitizers." - "ensure appropriate ventilator or flow source alarms are set before connecting breathing set to patient." - "perform a pressure and leak test on the breathing system and check for occlusions before connecting to a patient." - "use of the mr290 above the maximum operating pressure may lead to cracking, water leakage and, on rare occasions, could lead to a loss of ventilation pressure".
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