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Fiberoptic Medical Products, Inc., contracted with CITECH to compare the heating effects of various neonatal phototherapy devices under simulated clinical conditions. Fiberoptic Medical Products provided us with a sample of its Wallaby phototherapy spotlight, and we rented an Air-Shields Micro-Lite, a Healthdyne spotlight (similar to one marketed by Ohmeda), and an Olympic Bili-Lite, Model 66 (two daylight fluorescent tubes, two blue tubes), from local medical equipment rental companies.
The Healthdyne spotlight has two adjustment wheels; one to change the aperture through which light is delivered, and one to introduce a filter. We adjusted these to the no-filter position (the comparable Ohmeda spotlight has no such filters) and a spot of approximately the same size as the Wallaby. We also installed the lamp specified by Ohmeda into the Healthdyne unit. The Micro-Lite and Olympic lights irradiate over larger areas.
We tested each light by positioning it in, on, or over an Air-Shields Isolette Model C550 infant incubator, set to 36°C in the air control mode. We used an aluminum disc, painted matte black, with an embedded thermocouple, to simulate the baby (this simulator design was taken from the International Electrotechnical Commission standard for infant radiant warmers). An automatic data acquisition system sampled the temperature of the disc once per minute. When equilibrium was reached, we turned on the light under test and continued recording the temperatures until a new equilibrium was reached for at least an hour. We then turned the light off and continued recording data to confirm that the original equilibrium temperatures would be repeated. Following the temperature test, we measured the irradiance of the light at the level of the top of the disc and at about 9.5 cm above the mattress (approximately the top surface of a baby), using a Joey dosimeter, provided by Fiberoptic Medical. (Note that the Joey meter measures the irradiance over an area of approximately 20 cm2.)
The two irradiance levels and the temperature rise are listed below for each of the lights:
| Irradiance (baby) | Irradiance (disc) |
Temperature Rise | |
| Wallaby | 45 mW/cm2/nm | 24 mW/cm2/nm | 1.2°C |
| Healthdyne | 34 | 29 | 4.5 |
| Micro-Lite | 27 | 23 | 6.3 |
| Olympic | 8 | 6 | 1.0 |
This shows that the Olympic and Wallaby lights caused far less heating of the test disc than did the Healthdyne and Micro-Lite lights. These results cannot be transferred directly to the clinical situation because of differences between our test disc and an infant (with its own heat production and heat transfer mechanisms).
Fiberoptic Medical Products Wallaby. Model MD-1000, Serial No. 670092. This unit consists of a light source and a moderately flexible fiberoptic light cable. The light source offers two levels of illumination (we tested it on the higher one), and is placed on a shelf or table adjacent to the incubator. The distal end of the fiberoptic cable fits through the hole in the top of the incubator hood, and a locking ring holds it in place to direct the light output towards the center of the mattress. The output is a circle of intense blue-green light about 30 cm in diameter; according to Fiberoptic Medical Products, the light is within the 420-550 nm range.
Air-Shields Micro-Lite. Model PTL68-1, Serial No. VM00054 (lamp module); Model PTT68-1, Serial No. PM00029 (power module). This unit comprises two modules and mounts on the rail system of an Air-Shields Isolette infant incubator. The power module mounts on the lower part of the rail system; it supplies low voltage AC power to the lamp module. The latter mounts near the top of the rail, and is positioned to rest on the top of the incubator hood. The lamp module includes a row of three Type EXZ high-intensity quartz halogen lamps that provide intense, nearly white illumination of the entire mattress, with the center of the mattress being brighter than the outer edges. [Note: Air-Shields provided two modifications of the Micro-Lite (in 1992 and 1993, respectively) to reduce heating of the infant. Our sample included both modifications.]
Healthdyne Phototherapy Spotlight. Model PT1400-2, Serial No. 02153. This is a freestanding unit on a wheeled stand. It uses a single quartz halogen lamp to provide near-white illumination of a round target area. While the Healthdyne unit was widely marketed for many years, it is no longer being sold by that company. Instead, the design was taken over by Ohmeda and modified slightly. Because we were not able to rent an Ohmeda unit, we rented a Healthdyne Spotlight. Both units include a wheel that provides several different spot sizes; the Healthdyne unit includes a second wheel that provides several filters, as well. We fitted it with the same lamp as is used by Ohmeda (Burton No. 0006004PK), which provides a more bluish light than the GE lamp provided with the Healthdyne lamp, and set it to the largest aperture (about 30 cm diameter light pattern at the mattress) and no filter.
Olympic Bili-Lite. Model 66, Serial No. 66-1791. This is a freestanding unit on a wheeled stand. It uses a bank of four fluorescent lamps to provide broad illumination of the entire incubator mattress. The two outer lamps are GE Daylight, No. F20T12-D, while the two inner lamps are GE Blue, No. F20T12-B.
To measure the heating effects of the unit under test, we used an aluminum disc, as specified in IEC 601-2-21 (1994), the international standard for infant radiant warmers. The disc has a diameter of 100 mm and a thickness of 23 mm; it is painted flat black. A radial hole is drilled in the side of the disc, and a thermocouple (we used a T-type thermocouple) is embedded in it. The radiant warmer standard calls for five of these discs, spaced across the mattress, to measure the heating effects (and uniformity) of the warmer under test. Using such a disc to measure radiant heating is not an accurate simulation of the clinical situation because, unlike a baby, the disc does not have its own metabolic heat production, nor does it have the same heat transfer mechanisms of living tissue. Furthermore, its flat black color is likely to absorb and emit more radiant energy than would a baby's skin. Nevertheless, it provides a reasonable way of comparing radiant energy from different sources, as long as one is careful not to equate temperature rise in the disc to the same degree of temperature rise in a baby.
We tested the phototherapy intensity and the heating effects of each lamp, in turn, using an Air-Shields Isolette incubator, Model C550 in the air control mode. The C550 is the latest model of Isolette incubator being widely marketed by Air-Shields; it includes an electronic temperature controller. We used the air control mode, rather than the baby (servo) control mode, because the latter would not function well with our simulator, which lacked its own metabolic heat production capability. In all cases, we set the air temperature to 36°C.
We installed or placed each phototherapy unit in a position typical of its clinical use with the Air-Shields incubator. We placed the test disc in the middle of the mattress, in the center of the illumination pattern from the unit under test. We connected the thermocouple to a Metrosonics automatic data acquisition system that recorded the temperature once per minute. The system had a resolution of 0.1°C. All testing was done in a normal room environment.
The incubator was operated with the phototherapy lamp turned off until the test disc had reached equilibrium. Because of radiation losses from the disc, the equilibrium temperature was about 34°C (about 2° lower than the incubator air temperature). We recorded the equilibrium state for at least one hour, then turned on the phototherapy unit under test and left it on until at least one hour after the disc reached its new equilibrium temperature. Then, we turned off the unit under test and continued to record the disc temperature until it returned to its previous equilibrium value. We noted the maximum temperature rise of the disc with each of the four units tested, and produced graphs of the disc temperature versus time.
To compare the therapeutic light intensity of the units, we used a Joey dosimeter, Model JD-101, provided by Fiberoptic Medical Products. The dosimeter uses a 20 cm2 sensor to calculate the average irradiance across the therapeutic spectrum (420-550 nm); it provides a direct readout, in microwatts per square centimeter per nanometer. We made the measurement by positioning the Joey sensor at the same distance from the light source as the top of the test disc. (It should be noted that the irradiance recorded by any dosimeter does not correlate directly with therapeutic effectiveness, because it does not consider the total area of the baby that is exposed to the light.)
The following table reports the distance between the top of the test disc and the closest part of the light source (e.g., patient end of Wallaby cable, lens of Healthdyne spotlight, front of glass of Micro-Lite and Olympic); the irradiance at that distance; and the maximum temperature rise of the disc:
| Distance To Disc | Irradiance (Disc) |
Irradiance (Baby) | Temperature Rise | |
| Wallaby | 27 cm | 24 mW/cm2/nm | 45 mW/cm2/nm | 1.2°C |
| Healthdyne | 63 | 29 | 34 | 4.5 |
| Micro-Lite | 42 | 23 | 27 | 6.3 |
| Olympic | 44 | 6 | 8 | 1.0 |
It can be seen, from the above data, that the heating effects of the Micro-Lite and Healthdyne lights are substantially greater than those of the Wallaby and Olympic units. Graphs of the temperature rise versus time for each unit are presented in the Appendix to this report; these graphs have been smoothed to eliminate the apparent jitter caused by the 0.1°C resolution of our data acquisition system.
The irradiance of the Olympic Bili-Lite, in the therapeutic range, was much lower than those of the other units, which were similar. Of course, the Olympic Bili-Lite and the Micro-Lite irradiated a much larger area than the other two units, whose irradiation areas were similar (i.e., roughly equal spot sizes).
The results of our testing show that the Air-Shields Micro-Lite and Healthdyne Spotlight (configured similarly to the Ohmeda Spotlight) radiated significantly more heat to our test object than did the Fiberoptic Medical Products Wallaby and the Olympic Bili-Lite. The Wallaby also had significantly higher irradiance than the Bili-Lite, albeit over a smaller area, providing the highest ratio of irradiance-to-heating of all units tested. Because of thermodynamic differences between the test disc and a baby, we can draw no conclusions, from our testing, regarding the extent to which a baby might be overheated by any of these lights. However, the risk of overheating is clearly lower with the Wallaby and the Olympic Bili-Lite than with the Micro-Lite or the Healthdyne/Ohmeda Spotlight. Also, it should be noted that Air-Shields has had two field modifications of the Micro-Lite to reduce the risk of overheating.
