In our study population the incidence of SCFN in cooled neonates with HIE was 2.8 % which is consistent with previous reports [6, 9]. Overlooking the past forty years, approximately 20 articles (mostly case reports) have been published on SCFN occurring in context with HIE in neonates (Additional file 2: Table S1). Most of the studies investigated non cooled neonates with HIE and SCFN.
Certain maternal risk factors such as maternal diabetes mellitus, hypertension, preeclampsia, seizures, thyroid dysfunction or illicit drug consumption have been mentioned in the literature [7, 8, 10]. None of them were found in our study population nor could we find the known neonatal risk factors such as meconium aspiration, hypoglycemia or macrosomia [7, 8, 10]. In our study none of the analyzed perinatal and neonatal characteristics showed statistical significance between neonates with and without SCFN (Table 1). We may have been unable to confirm the risk factors described by Mahé et al. and Burden et al., as they analyzed non-cooled neonates in contrast to our neonates who underwent TH [7, 8]. Additionally our sample size might be too small to detect an association of the known risk factors.
In line with the proposed pathophysiology of SCFN one might expect SCFN to occur in neonates with more severe HIE independently of cooling. However, in our study population there was no significant difference of the Sarnat and Thompson Score, Apgar Score or metabolic parameters within the first hour of life between both groups [11, 12].
Certain body areas with bony protuberances are most susceptible to SCFN [10, 13], namely the back and the occipital scalp as seen on Additional file 3: Figure S1 (parental consent was obtained to publish this picture). This is also true in our collective and the question arises whether the occurrence of SCFN correlates to the cooling technique applied. However, our data does not show any association between applied cooling method and the incidence of SCFN. It seems to be a coincidence that no SCFN occurred in the group of passively cooled neonates with HIE.
Nevertheless, as in our study population most neonates with HIE are bedded in supine position with SCFN occurring on the back, regular changing of position is advocated to reduce any damage. Regular mobilization should be routinely integrated in the nursing protocol, if the neonate is stable enough [9, 14].
Our findings support the data of the TOBY Register that moderate hypothermia during 72 h could be an additional risk factor for SCFN, although our sample size is quite small and we investigated only 42 non cooled neonates as a control group . This does not mean that SCFN does not appear in non-cooled neonates with HIE, because birth asphyxia is a risk factor per se.
Of interest, SCFN occurred independently of the percentage of measured temperatures within the target temperature range during TH. Compared to the findings that severe hypothermia (core temperature below 28.0 °C) is a described risk factor for developing SCFN , overcooling below 33.0 °C (but above 31.5 °C) did not emerge as a risk factor in our study population.
SCFN can still occur after discharge from hospital. This is one of the reasons why SCFN might be well unrecognized and thus undiagnosed. Therefore, it is important to inform the parents and the outpatient paediatricians of the nature of SCFN.
As we analyzed the data of the National Asphyxia and Cooling Register we describe the incidence of SCFN during hospitalization. After discharge all neonates were regularly followed by an outpatient paediatrician one week after discharge, at the age of one, two and four months. However they are not followed by the initial care takers.
Numbers of SCFN in our study population are small and conclusions are difficult to draw. Firm conclusions cannot be supported by this data, but they show a tendency.
Furthermore the SCFN were evaluated with a retrospective questionnaire which entails certain limitations. In the future as soon as SCFN is diagnosed a real time questionnaire needs to be obtained. A national register therefore permits to follow a trend and is important to discover adverse events and to improve patient management.