Phototherapy Lights: What a Pediatrician need to know Dr Anu Thukral & Dr Ashok Deorari
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Phototherapy involves exposure of the skin of the jaundiced baby to visible blue light of wavelength 400 – 520 nm generated by artificial light sources. It is used to prevent and treat hyperbilirubinemia that is caused by hemolysis, ineffective clearance of bilirubin, or both and dramatically reduces the need for exchange transfusion. Detoxification begins immediately by the production of configurational and structural photo-isomers of bilirubin in the skin and this precedes the fall in serum bilirubin. Special lamps emitting light predominantly in the blue to blue-green wavelengths are the most effective.
Mechanism of Phototherapy
Phototherapy converts bilirubin in skin and subcutaneous tissues into water-solubleless lipophilic, presumably non-toxic, photo-products25 that are water solubleexcreted through the intestine and in the urine. For phototherapy to be effective bilirubin needs to be present in skin, hence there is no role for prophylactic phototherapy.
The reactions that occur during phototherapy are:
(a) Configurational isomerization:The normal Z-isomers of bilirubin are is converted into yellow E-isomers. (Z and E are chemical terms, akin to the terms cis and trans, that denote the stereochemistry of double bonds). Although this reaction is instantaneous upon exposure to light, the clearance of E-isomers is slow. These photoisomers revert to native bilirubin in bile. Depending on the light dosage and spectral quality up to After exposure of 8-12 hrs of phototherapy, this constitutes about 25% of total serumbilirubin (TSB) , may be converted to the presumably less toxic E-isomers within a few hours.
(b) Structural isomerization: This is an a relatively slow, but irreversible reaction where thewhereby bilirubin is converted into another yellow isomer, lumirubin, which is excreted rapidly. The formation of lumirubin is directly proportional to the dose of phototherapy.
(c) Photo-oxidation: This is an even slower minor reaction where which leads to colorless water-soluble photo-products that are excreted in urine.
The efficacy of phototherapy depends upon
(a) The level of bilirubin at initiation of phototherapy – the higher the bilirubin level, the more rapid the decrease in bilirubin.
(b) Body surface area (BSA) exposed to light.1 .
(c)The dose of light (measured as irradiance x duration of treatment x% BSA treated). Increasing the surface area exposed can be achieved by using a light source above and below the infant or by placing reflecting material around the inside of the bassinette or incubator.2,3
Indications for Phototherapy
Each institution must create its own guidelines. Some general guidelines are:
1. For term and late preterm infants, follow the guidelines of the American Academy of Pediatrics . 4
2. For very low birth weight babies, phototherapy is indicated at a bilirubin level (in mg/dL) equal to 1% of the body weight (e.g. 10 mg/dl (170 mol/L) in a 1000 gm baby. Exchange blood transfusion is warranted when the TB level is 5 mg/dl (85 mol/L) higher than the phototherapy level. However, the overall clinical situation also needs to be considered.
3. Acidosis, asphyxia, hypoglycemia or sepsis make the blood brain barrier more porous and the brain more susceptible to bilirubin induced damage. When these conditions are present, consider initiating phototherapy at lower TB as per AAP guidelines. 4
Effective Use of Phototherapy
Phototherapy light sourcesunits Emitted light should be filtered to remove Harmful harmful infra-red and ultraviolet radiation. should be filtered Light should be focused on the baby. Mobile units are preferred because they can be used for babies nursed in cots, incubators or radiant warmers. The height should be adjustable, while a few units may be tilted on axis. Phototherapy lights may be mounted on the radiant warmers themselves. A standard locally fabricated phototherapy unit should consist of 6 to 8, white fluorescent tubes (20 or 40 watts), preferably of the day light variety, if blue or special blue tubes are not available locally.
(a) Halogen spotlights: Spotlight phototherapy units were available in the market generally use a 150 Watt, 21V halogen bulb with a specially coated reflector which absorbs infrared wave length. A fan continuously cools the hot bulb. Options for varying aperture diameter and different filters are available. Positioning of the light on the baby is critically important in maximizing the spotlight’s effectiveness.. But never gained popularity as the surface area of exposure was limited despite they emit a relatively high level of irradiance compared with the conventional fluorescent tubes. Light of relatively narrow spectrum is emitted when a high voltage excites a mixture of halogens. They have a 150 watt, 21V halogen bulb with a specially coated reflector which absorbs infrared waves. A fan continuously cools the heated bulb. Options for varying aperture diameter and different filters are available. Positioning of the light on baby is critically important in determining the spotlight’s effectiveness. They are most effective when delivered fromlocated directly above the infant at a distance of 45-50 cm. Directing the light from the side of the crib or allowing the circle of light to move off the infant’s largest surface area e.g. abdomen, significantly reduces the dose delivered.
(b) Florescent lamp devices: These have optimized blue light emission at 400-520 nm wavelengths. The Special blue fluorescent are labeled must F20T12/BB or TL 20W/52 to be special phototherapy lights. Regular blue fluorescent tubes (F20T12/B) deliver much less irradiance. If possible, the irradiance should be measured at regular time intervals to ensure that an adequate dose is being delivered. Fluorescent tubes lose about 35-40% of blue light irradiance after 1200 hours of use.7 Directing the light from the side of the infant significantly reduces the dose delivered. These lights can provide an irradiance of >25-30 W/cm2/nm in the 400-520 nm range when placed closely, thus making phototherapy maximally effective particularly when the greatest body surface area is exposed.
(c) Fiber-optic pads: These latest phototherapy units devices use plastic fiber-optic light guides to deliver light from a halogen lamp to illuminate a blanket or pad which is wrapped around or placed under the baby. These devices deliver light in the 400 to 550 nm spectral band. The pad is cool and can be placed in direct contact with the baby. They can be used as an auxiliary light source to increase the surface area exposed 6or as the sole source of phototherapy, particularly in preterm infants. 3In recent models, the halogen light source has been replaced by high intensity high power LED bulbs.
(d) Compact fluorescent tubes: These are compact short (approx. 5 to 7 inch) double folded tubes (9-18 Watts) that emit blue or white light. Several (6-8) are of 18 or 13 watts Osram / Phillips bulbs which are cool white or blue 6 to 8 in number housed in a panel with reflectors . As they do not produce much heat the distance to baby can be relatively short thus increasing the irradiance delivered. Most of them produce an irradiance of 20 -30 W/cm2/nm when placed close to the baby and can be used in combination with overhead lights t o increase the surface area of exposure.
(e) Light emitting diodes (LED): Blue LED devices emit a narrow spectrum that overlaps the absorption spectrum of bilirubin. They are power-efficient, portable devices with low heat production that can be kept close to the baby. They are durable, and long lasting with low power consumption.8,9,109-12
Maintenance tips for phototherapy units
If possible, use a spectroradiometer (calibrated for 430-490 nm waveband) to measure the irradiance flux and replace the tubes or halogen light sources with new bulbs if the irradiance has fallen below 10-12uW/cm2/nm or to two thirds of its original value. to two thirds of its original value. It is not necessary to measure irradiance before each use of phototherapy; but it is important to perform periodic checks of phototherapy units to make sure that an adequate irradiance is being delivered. Note that irradiance meter are designed to measure specific light source for precise bandwidth.
If a spectroradiometer f is not available, halogen bulbs and fluorescent tubes should be changed every 1200 hours or 6 months of intermittent use, whichever is earlier, or when fluorescent bulbs flicker or tube ends blacken. Maintaining a logbook for duration of use or built-in timer in the device is useful. Keep bulbs and reflectors dust free and do not cover the unit with cloth, charts or files as this will prevent circulation of air and heat the bulbs.
Conflict of interest: None
|1.||Protect the eyes with eye patches.|
|2.||Keep the baby naked with a small nappy to cover the genitalia.|
|3.||After switching on the unit check that all tubes/bulbs are on.|
|4.||Place the baby as close to the lights as the manufacturers’ instructions allow. Use white cloth or aluminum foil to reflect light back onto the baby, making sure not to impede the air flow that cools the bulbs.|
|5.||Do not place anything on the phototherapy unit (this may block air vents or light and items may fall on the baby).|
|6.||Encourage frequent breastfeeding. Unless there is evidence of dehydration, supplementing breastfeeding or providing IV fluids is unnecessary.|
|7.||Change position supine to prone after each feed to expose the maximum surface area of baby to phototherapy.|
|8.||Keep diaper area dry and clean.|
|9.||Phototherapy does not have to be continuous and can be interrupted for feeding, clinical procedures, and to allow maternal bonding.|
|10.||Monitor temperature every 4 hours and weight every 24 hours.|
|11.||Measure plasma/serum bilirubin frequently ~ every 12 hours. Visual assessment of jaundice during phototherapy is unreliable.|
|12.||Change tube lights every 6 months (or usage time >1200 hrs) whichever is earlier; or if tube ends blacken or if tubes flicker.|