Short Report
Brief Report: Bronzed baby with low peripheral saturation. Is it real?
https://doi.org/10.21203/rs.3.rs-2069862/v1
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Pulse oximetry is used across all medical specialties providing non-invasive and continuous oxygen saturation of haemoglobin. However, potential interferers must be continually scrutinized to ensure its validity and accuracy. An erroneous measurement could lead to unnecessary invasive testing or treatments.
Pulse oximetry is used across all medical specialties providing non-invasive and continuous oxygen saturation of haemoglobin. However, potential interferers must be continually scrutinized to ensure its validity and accuracy. An erroneous measurement could lead to unnecessary invasive testing or treatments.
We report a case of inconsistencies between pulse oximetry saturation (SpO2) and arterial saturation (SaO2) and arterial oxygen partial pressure (PaO2) values in a neonate with bronze baby syndrome (BBS) due to anti-E and anti-Fya haemolytic disease treated with phototherapy.
A male infant delivered at 36 weeks of gestation with a birth weight of 2.425 g; Apgar score was 9/9. The mother was caucasian, G2P0A1C1 and her blood group was A, Rh positive. Maternal blood at 32 weeks of gestation showed the presence of anti-E and anti-Fya antibodies.
Prenatal studies revealed polyhydramnios, duodenal atresia and esophageal atresia with distal tracheoesophageal fistula (type III).
He was admitted to NICU because of respiratory distress due to his congenital malformations and he underwent early surgical intervention.
He presented serum total bilirubin of 6,16 mg/dl at birth. The infant’s blood group was A and Rh positive as his mother but he had a positive direct Coombs’ test due to Anti-E and anti-Fya antibodies. He was treated with intravenous immunoglobulin and intensive phototherapy to control the rising levels of bilirubin. On day 5 the conjugated fraction of bilirubin was noted to be rising and peaked at 8,85 mg/dl at day 10 of age. Progressive gray-brown skin discoloration and dark urine was also noted. Liver function tests were normal.
By day 6 the infant was in spontaneous ventilation, had not respiratory distress, not apnoeas and not carbon dioxide retention; but SpO2 dropped progressively from 94–97% to 83–85%. The chest X-ray was normal and methemoglobinemia was discarded by capillary blood gas test. Increase in inspired oxygen, did not lead to concomitant changes in SpO2. SpO2 were continuously measured by different oximetry devices with high sensitivity and neonatal profile and the sensors were covered to protect them from the phototherapy light. The oximetry sensors employed were: LNCS Neo, RD rainbow SET – 2 Neo, RD SET Newborn Infant/Pediatric, RD rainbow SET Neo and RD SET Blue of Masimo®, but no data was obtained. Nevertheless, we obtained a reliable measurement with SpO₂ Nellcor™ of COVIDEN™ who has wavelengths: red: 650 to 670 nm and infrared: 880 to 910 nm.
To check the correct patient`s oxygenation an arterial blood gas in point of care test was made after 5 minutes of oxygen exposure (FiO2: 1) with an automatic analyzer (ABL90 FLEX PLUS Radiometer Medical ApS, Copenhagen, Denmark). It showed a PaO2 399 mmHg, and a SaO2 of 100%. Intensive phototherapy was discontinued by day 8 of age, although it was reintroduced as simple phototherapy from 9 to 12 days of age. SpO2 values showed progressive normalization from day 8, just after suspension of intensive phototherapy although direct bilirubin persisted in its maximum value. Skin discoloration was resolved over 2 weeks. Oxygen saturation and the evolution of bilirubin values are shown, as well as treatment with phototherapy in Fig. 1.
Pulse oximetry is based on the absorption of red and infrared light by different tissues. This is how, by means of the differences in the absorption of light between oxygenated and deoxygenated hemoglobin, its saturation percentage can be calculated. Currently, there are different neonatal pulse oximetry monitoring sensors, with different wavelengths. Therefore, in this patient, several sensors were tested until a measurable value was obtained.
Being a technology based on the absorption of light, it is subject to various interferences or limitations, such as: Hemoglobin alterations (methemoglobinemia or carboxyhemoglobinemia), dyes and pigments, external light sources or situations of peripheral hypoperfusion. Perhaps, in this case, due to the accumulation of pigments in the skin of the newborn, these could interfere with the SpO2 measurements since they are present in the arterial blood. This could be due to pigments such as bilirubin, biliverdin, or porphyrin having spectral absorbances that may overlap red or infrared frequencies used in pulse oximetry.
In this sense, Ralston AC et al. reported that bilirubin introduces no significant errors in SpO2 measurement. This can be explained by bilirubin’s spectral absorbance, which does not extend to wavelengths of 500nm.1
On the other hand, Bronze baby syndrome (BBS) is an unusual condition developed in neonates with elevated serum levels of unconjugated and conjugated bilirubin treated with phototherapy 2–4. Although the exact etiology of BBS is still unknown, there are possible explanations about why bronze skin colour may occurs. First one is the abnormal accumulation of photo isomers of bilirubin, such as (EZ)-cyclobilirubin. Secondly, the accumulation of copper porphyrins, resulting from erythroid and hepatic hemopoietic hyperactivity, as seen in haemolytic jaundice. Apparently copper porphyrins undergo bilirubin-induced photosensitized chemical modification, which results in photoproducts with generalized absorption in the near-ultraviolet and red spectrum and thus causes brown discoloration that could interfere SpO2 readings5–6 although conflicting results have been obtained in other studies7. And the third is an elevated level of biliverdin, a green pigment of heme catabolism. These three pigments possess the spectral characteristics with absorption in the near ultraviolet and red spectral regions that could interfere SpO2 readings.8
Despite BBS is considered a self-limiting process there is not consensus on stopping or not phototherapy treatment. Although some authors have recommended stopping phototherapy3, most of them recommend continuing phototherapy to decrease bilirubin levels and so the risk of exchange transfusion4.
In our infant SpO2 readings of 83–85% by pulse oximeter were obtained with a SaO2 of 100% in arterial blood gas test so we conclude that SpO2 values underestimated the true SpO2.
Afterwards, SpO2 readings progressively normalized after a period without intensive phototherapy despite the fact that he had the highest total and direct bilirubin values, which would imply that both bilirubin and phototherapy are necessary for the development of pigments. The resolution of gray-brown coloration was also observed over the following days. Our findings and a similar case previously described by Hussain’s8, suggest that the absorbance or transmission of light can be influenced by bilirubin photoproducts because of interference at the wavelengths captured by pulse oximetry sensors.
Thus, FDA’s recent report alert on possible erroneous measurements of the pulse oximeter in alteration of the skin coloration10.
Awareness of the interference of BBS, may help in interpreting SpO2 values correctly, and preventing unnecessary invasive testing or treatments. This issue should be included in the data sheet of the pulse oximetry monitors.
Conflicts of interest
Authors declare no conflicts of interest in relation to the present manuscript
Funding sources
Authors have no funding to declare.
Ethical Approval
As it was a clinical case, the consent of the legal representatives of the minor was obtained and the national and international legal regulations for research and data protection were followed.
Authors' contributions
All authors contributed equally.
No competing interests reported.
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