Noninvasive monitoring of gas in the lungs and intestines of newborn infants using diode lasers: feasibility study

Abstract

Preterm newborn infants have a high morbidity rate. The most frequently affected organs where free gas is involved are the lungs and intestines. In respiratory distress syndrome, both hyperexpanded and atelectatic (collapsed) areas occur, and in necrotizing enterocolitis, intramural gas may appear in the intestine. Today, these conditions are diagnosed with x-ray radiography. A bed-side, rapid, nonintrusive, and gas-specific technique for in vivo gas sensing would improve diagnosis. We report the use of noninvasive laser spectroscopy, for the first time, to assess gas content in the lungs and intestines of three full-term infants. Water vapor and oxygen were studied with two low-power diode lasers, illuminating the skin and detecting light a few centimeters away. Water vapor was easily detected in the intestines and was also observed in the lungs. The relatively thick chest walls of the infants prevented detection of the weaker oxygen signal in this study. However, results from a previous phantom study, together with scaling of the results presented here to the typical chest-wall thickness of preterm infants, suggest that oxygen also should be detectable in their lungs.

Diode laser spectroscopy for noninvasive monitoring of oxygen in the lungs of newborn infants

“…In our pilot study (21), water vapor was detected in the lungs of three infants, but no oxygen, even though obviously present during the measurements, probably due to the fact that the Articles oxygen absorption is much weaker than that of water vapor. For this reason, the power of the diode laser (at 760 nm) detecting oxygen was now increased to around 30 mW.…”

“…Our results show that the revised system is capable of detecting oxygen, the gas of main interest, in the lungs of infants ranging from <3,000 g up to almost 4,000 g. However, further technical developments are clearly needed for a more stable and robust performance, where oxygen would be detectable at all relevant locations. According to the findings in our pilot study (21), the geometry chosen for measurements was in the midclavicular line between the collar bone and the nipple bilateral. Three different positions following this line were used (Figure 3) showing similar signal intensities.…”

“…A detailed description of the basic system is published (21). It enables quantification of gas constituents in cavities surrounded by solid materials from gas absorption imprints in light transmitted through the cavity.…”

“…Light emitted from this laser was coupled through a 2-m multimode 600-µm fiber (Thorlabs, Newton, New Jersey) into a probe. This probe comprised a highly reflecting polytetrafluoroethylene plate (thickness 6 mm, diameter 15 mm) with threaded connectors for optical fibers from the 30 mW oxygen (Toptica, Munich, Germany) and 4 mW water vapor (Nanoplus, Gerbrunn, Germany) lasers, as well as for a small reference photodiode (21). All emitting fiber tips were covered with thin transparent light-diffusing material (polypropylene).…”

“…We could detect both oxygen gas and water vapor in a feasibility in vitro study of the optical GASMAS technique applied on a wild boar lung phantom, covered with gelatin layers with scattering particles and absorbing ink to resemble the chest of a small infant (20). In a pilot in vivo study, we showed that water vapor was detectable with GASMAS in the lungs and in the gastrointestinal tract of three full-term infants weighing 4,000-5,000 g (21). Since absorption lines for oxygen are much weaker than those for water vapor, and since thoracic tissue layers covering the lungs are thicker in larger than in smaller infants, penetration of light into the lungs was probably too low to enable detection of intrapulmonary oxygen gas in that study.…”