What does the colour of the tongue tells us in the delivery room?

In this issue of Acta Paediatrica, Dawson et al. describe an observational study that presents the hypothesis that the colour of a newborn infant’s colour could help medical staff to decide whether they need oxygen supplementation in the delivery room (1). They suggest that if the tongue is blue then oxygen saturation (SpO2) would be less than 70% and oxygen supplementation would be indicated. On the contrary, a pink tongue would indicate adequate oxygenation. In this prospective study, a total of 70 babies less than 28 weeks of gestational age and born by Caesarean section were studied. Once the pulse oximeter showed reliable readings, medical staff blinded for SpO2 were asked to assess if the baby’s tongue was pink or not at different time intervals between the second and tenth minutes after birth. SpO2 was simultaneously recorded. The results showed that the tongue test lacked sensitivity, although it was very specific with a positive predictive value of 61% and a negative predictive value of 84%. Moreover, neither the lighting in the delivery room or the infant’s ethnicity influenced the final results. Interestingly, medical staff reported a pink tongue at a wide range of SpO2 measurements, from 48% to 78%. The authors concluded that determining the tongue’s colour was specific but insensitive when it came to assessing an SpO2 of less than 70% and initiate oxygen supplementation (1). There are several aspects of the Dawson et al. study that should be discussed further (1). The argument that central cyanosis can be detecting by inspecting a newborn infant’s tongue in the first minutes after birth is based on the fact that there are still many births occurring in settings where pulse oximetry is not readily available in the delivery room. It is notable that heart rate is only briefly mentioned in this study as a guide for assessing the newborn’s clinical status, despite the fact that it is probably the most relevant clinical sign when evaluating a newborn’s response to resuscitation. Furthermore, heart rate has a strong predictive value, as it allows for the early identification of babies at risk of a poor prognosis (2). Interestingly, Kamlin et al. demonstrated that assessing heart rate by pulse palpation and, or, auscultation was inaccurate and underestimated electrocardiogram heart rate (3). However, close monitoring of the progress of the heart rate by auscultation in a critical situation would be more feasible, and perhaps more reliable, for assessing an infant’s response to resuscitation than changes in the colour of their tongue. Another interesting point refers to the type of birth. Babies in this study were born by Caesarean section, which causes a delay in postnatal adaptation, with lower Apgar scores, a slower rise and a lower final SpO2 (4). In addition, the incidence of cyanosis in the delivery room in scheduled Caesarean sections is infrequent in developed countries where pregnancies and deliveries are closely monitored. Therefore, the number of babies recruited in this study seems insufficient to prove the suitability of the tongue’s colour as an indication of hypoxia and further studies with an adequate power calculation should be undertaken. Finally, although the eligible babies had a gestational age of less than 28 weeks, the mean gestational age of the recruited infants was 38 weeks and preterm babies seemed to be under represented. The time needed to achieve stable oxygen saturation is around 85–90%, and it is inversely proportional to gestational age. As a result, many very preterm babies will need up to 8 to 10 min to reach an SpO2 plateau (5). This circumstance should be taken into consideration when establishing the time at which the tongue’s colour should be assessed in future studies, and these studies should obviously have a higher representation of preterm infants. Virginia Apgar was probably the first physician in modern medicine who considered a newborn infant’s colour as a valuable sign when assessing postnatal adaptation in the delivery room. The Apgar score rated pink colour at 1 and 5 min as two points and this is equivalent to the scores for more relevant parameters, such as heart rate or tone (6). For decades, medical staff have supplemented newborn infants with 100% oxygen immediately after birth to achieve a reassuring pink colour, which reflects adequate oxygenation. However, in the 1990s, researchers in the field of resuscitation started to seek objectivity in the assessment of clinical variables in the delivery room and prospective randomised or quasi-randomised controlled studies were carried out. In addition, oxygen supplementation during resuscitation was randomised and blinded for the first time in 2001. The results of these studies provided information that the use of higher concentrations of oxygen upon reoxygenation could be deleterious