Systems and methods for compensating long term sensitivity drift of electrochemical gas sensors exposed to nitric oxide

Inventors

Tolmie, Craig R. • Milsap, Jeff • Acker, Jaron M.

Assignees

Mallinckrodt Pharma IP Trading DAC • Therakos Inc • INO Therapeutics LLC • Mallinckrodt Critical Care Finance Inc

Abstract

Systems and methods for compensating long term sensitivity drift of catalytic type electrochemical gas sensors used in systems for delivering therapeutic nitric oxide (NO) gas to a patient by compensating for drift that may be specific to the sensors. In at least some instances, the long term sensitivity drift of catalytic type electrochemical gas sensors can be addressed using calibration schedules, which can factor in the absolute change in set dose of NO being delivered to the patient that can drive one or more baseline calibrations. The calibration schedules can reduce the amount of times the sensor goes offline. Systems and methods may factor in actions occurring at the delivery system and/or aspects of the surrounding environment, prior to performing a baseline calibration, and may postpone the calibration and/or rejected using the sensor's output for the calibration.

Core Innovation

The patent describes compensating for therapeutic gas sensor drift in a therapeutic gas delivery system by storing a correlation of sensor output voltages and concentrations of therapeutic gas on a non-transitory memory. The system delivers a dosage of therapeutic gas and monitors the delivery via a therapeutic gas sensor, and the stored correlation is updated by performing a calibration that includes exposing the therapeutic gas sensor to gas having a zero concentration of the therapeutic gas and adjusting the correlation according to the sensor output voltage detected during calibration.

For nitric oxide, the patent further specifies a correlation that includes a baseline current and a slope stored in non-transitory memory. Nitric oxide is delivered to a breathing circuit and monitored via a nitric oxide sensor, while the system stores a calibration schedule. Calibration is performed according to the schedule by exposing the nitric oxide sensor to a gas having a zero concentration of nitric oxide, and the correlation is adjusted by a current offset measured during the calibration.

The patent also describes a nitric oxide delivery system including a system controller, non-transitory memory, and a sampling system configured to monitor nitric oxide concentration in the breathing circuit via a sampling line. A calibration schedule and a calibration line defined by a baseline current and a slope are stored, and the calibration line is adjusted according to a current measured by the nitric oxide sensor during calibration after exposing the nitric oxide sensor to a gas having a zero concentration of nitric oxide.

The described drift compensation is intended to address long term sensitivity drift of catalytic-type electrochemical nitric oxide gas sensors used during therapeutic NO delivery, including drift challenges arising from atypical continuous exposure and localized sensor effects. The patent addresses these issues by using scheduled baseline calibrations and by applying logic for postponement or rejection of calibration based on alarm activity, user interaction, interfering gases or out-of-range sensor output, and timing controls to reduce periods when the sensor is offline.

Claims Coverage

The independent claims include three inventive methods for therapeutic gas sensor drift, nitric oxide sensor drift in general, and nitric oxide sensor drift in a nitric oxide delivery system. Across these claims, the inventive features focus on storing and updating voltage-to-concentration or current-based calibration relationships using scheduled zero-concentration exposures in a therapeutic gas delivery or nitric oxide delivery system, including breathing circuit monitoring and correlation adjustment.

Taken together, the independent claims cover drift compensation by storing a sensor output-to-concentration correlation or a calibration line defined by baseline current and slope, monitoring therapeutic gas or nitric oxide delivery in a breathing circuit, and updating the stored correlation or calibration line based on current or voltage readings obtained during calibration with exposure to zero-concentration gas, optionally using a calibration schedule.

Stated Advantages

Documented Applications