Abstract
The quantification of visceral organ oxygenation after trauma-related systemic hypovolemia and shock is critical to enable effective resuscitation. In this work, a photoplethysmography-based (PPG) sensor was specifically designed for probing the perfusion and oxygenation condition of intestinal tissue with the ultimate goal to monitor patients post trauma to guide resuscitation. Through Monte Carlo modeling, suitable optofluidic phantoms were determined, the wavelength and separation distance for the sensor was optimized, and sensor performance for the quantification of tissue perfusion and oxygenation was tested on the in-vitro phantom. In particular, the Monte Carlo simulated both a standard block three-layer model and a more realistic model including villi. Measurements were collected on the designed three layer optofluidic phantom and the results taken with the small form factor PPG device showed a marked improvement when using shorter visible wavelengths over the more conventional longer visible wavelengths. Overall, in this work a Monte Carlo model was developed, an optofluidic phantom was built, and a small form factor PPG sensor was developed and characterized using the phantom for perfusion and oxygenation over the visible wavelength range. The results show promise that this small form factor PPG sensor could be used as a future guide to shock-related resuscitation.
Highlights
Trauma is the leading cause of death for people aged 1-44 year(s) in the United States [1]
3.1 Monte Carlo modeling A comparison of the villi and slab models was performed to assess intensity of reflection as a function of tissue and arterial perfusion as well as to assess any differences for the simulated phantom with villi versus a plain slab geometry, using 560 nm as an example
The differences in the two model geometries are negligible with less than 1.5% difference across the entire range of perfusions
Summary
Trauma is the leading cause of death for people aged 1-44 year(s) in the United States [1]. Resuscitation is often guided by systemic indicators such as blood pressure, urine output, and heart rate After these parameters are normalized, up to 85% of patients are still in “compensated shock” with associated tissue acidosis [3]. The compensated shock state can lead to multiple organ dysfunction syndrome (MODS), the leading cause of death in surgical intensive care units [4]. Basic methods used in surgical suites include palpation of intestinal vascular pulses, and injection of fluorescent dyes and subsequent examination for “abnormal” dye distributions. These methods do not provide quantitative results and are not applicable to guide resuscitation from shock. Perfusion and flow measurements coupled with a measure of oxygen consumption to ensure the oxygen supply meets tissue demands may provide a more comprehensive monitoring alternative than measuring just flow
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