Non-invasive Tidal Volume Monitoring Using the Linshom Respiratory Monitoring Device

Capnography, Pulmonary Ventilation

Capnography

Many post-operative complications arise from patients who breathe inadequately. Inadequate respiration, whether the result of surgery or the anesthesia, causes a decrease in blood oxygen saturation and an increase in carbon dioxide partial pressure. Both of these surrogate measurements of respiration may pose a challenge to measure. Some administer exogenous oxygen to all patients as they leave the operating room in order to maintain the blood oxygen saturation. This renders the oximeter a less sensitive metric of depressed respiration. In the face of decreased respiration, the carbon dioxide levels continue to increase slowly and often go undetected unless blood gases are measured. Indeed carbon dioxide blood levels are the only metric to detect inadequate ventilation using this surrogate index. Monitoring ventilation is a serious challenge outside of critical care settings. In fact, there are no monitors available that can measure tidal volume or relative tidal volume outside of these settings. Linshom is a novel instrument that tracks relative respiration by measuring the excursions of the temperature swings between inspiration and expiration and normalizing them to the patient's breathing. This monitor may be the first non-invasive monitor to measure relative tidal volume in non-critical care settings. The purpose of this study is to determine whether a non-invasive, temperature-based respiratory instrument can track tidal volume (Vt) in patients. The investigators hypothesize that the Linshom device can accurately and consistently track tidal volume as measured by closed loop mechanical ventilator.

Forty volunteers will be enrolled in this open label, prospective study to determine the correlation between the tidal volumes measured with the Linshom detector and those measured with the mechanical ventilator. after Institutional Review Board (IRB) approval and written informed consent from the volunteers. The Linshom detector, which is comprised of two rapid responding medical-grade thermistors in close proximity to the mouth/nose (sensor) and a thermistor remote to the airway, will be mounted in the continuous positive airway pressure (CPAP) face mask to measure the temperature during breathing. The CPAP will be connected to a Servo-I ventilator (Maquet) with a circuit and disposable filter. The volunteers will be instructed to breathe normal through the CPAP mask on room air. The excursions of the thermistor tracings (from valley to peak) will be recorded by the Linshom device and displayed continuously on a laptop monitor in a waveform. The tidal volume will also be measured by the ventilator and the data downloaded in a Compact Flash card. The temperature profiles from the sensors and the relative tidal volume will be correlated with the tidal volumes measured by the ventilator.

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