Zoll received a warning letter from the Food and Drug Administration citing quality concerns and problems with how the firm handles complaints.
The warning letter focused on MRI compatibility problems with some of Zoll’s portable ventilators. It also cited concerns with automated external defibrillators and electrodes used with the company’s defibrillators.
Zoll, a subsidiary of Asahi Kasei that makes ventilators, defibrillators and other medical devices, received the warning letter on April 30, and the FDA posted the letter on Tuesday. The warning followed an inspection of Zoll’s facility in Chelmsford, Massachusetts, where the company is headquartered, between February and April 2025.
The FDA uses warning letters to flag significant violations after an inspection.
Some of the concerns raised by the agency were related to Zoll’s 731 series ventilators, portable devices that can be used in hospitals and during transport. The FDA said ventilator failures related to the MRI nonconformances caused malfunctions and shutdowns that led to the stoppage of ventilatory support and the need for alternative means of ventilation.
In one case, Zoll waited several months to report an incident to the FDA that suggested the ventilator malfunctioned while operating near an MRI, according to the letter. The FDA also said that Zoll documented 27 complaints related to the device defect, but an investigator found 50 complaints between 2016 and 2024.
Zoll recalled the devices in 2024, updating the instructions for use to specify how far the ventilators should be placed from MRI machines to avoid failure.
The FDA also documented missing device validation with Zoll’s Z Vent Ventilator, another portable device. The ventilator is intended to be compatible with MRI machines of 1.5-Tesla or 3-Tesla strength, but was only tested with 3-Tesla scanners, according to the warning letter.
The device’s labeling did not specify where the ventilator should be placed when using a 1.5T MRI machine. Zoll received a complaint in 2024 where a customer reported image quality discrepancies when the ventilator was used with a 1.5T MRI, according to the warning letter.
Other quality issues mentioned in the letter include Zoll’s handling of complaints related to a feature with its AccuVent Sensor not working. The sensor is used with some of Zoll’s ventilators to provide feedback on volume, breath rate and other metrics.
The FDA also raised concerns about Zoll’s handling of a finding that one of its defibrillation electrodes had burnt tin under the electrode gel. Zoll did not open a corrective and preventive action because it was the first instance of the problem, despite concerns that it could burn a patient.
