Maturation of median nerve somatosensory evoked potentials (SEP) in healthy term and preterm infants

Objectives: To provide normal values of median nerve somatosensory evoked potentials (SEP) in healthy term and preterm infants.

Material and Methods: Our prospective study included 31 healthy preterm and term infants (postconceptional age: 33–41 wks). SEP were performed at the median chronological age of 13d. Cortical responses were recorded at C 3'/C 4' against Fz (international 10–20 system) and nuchal responses from the second cervical vertebra against a frontolateral electrode (stimulation: 1.1Hz, 100µs). A 1–3000Hz filter bandpass was used. At least two (median: four) recordings were performed. The median number of stimuli was 128. We analysed cortical latency (N20), nuchal latency (N13) and central conduction time (CCT; N13-N20). Grouped by postconceptional age (A1: 33–35 wks, n=10; A2: 36–37 wks, n=11, A3: 38–41 wks, n=10) mean latencies were calculated. In addition, the influence of weight and chronological age was tested.

Results: (mean±SD): Latencies and postconceptional age were significantly related (p<0,001). In contrast, there was no correlation between chronological age and latencies in any of the three age groups. As to weight, no significant influence on latencies was noted in preterm infants (A1, A2). However, in term babies (A3) a negative correlation between central latencies and weight (p<0,01) was found. No significant difference in mean latencies (ms) could be shown between A1 (N13/N20/CCT: 11,9±1,0/55,9±8,8/44,1±8,6) and A2 (11,0±0,6/54,7±8,1/43,8±8,1). Latencies of term babies (A3: 10,1±0,5/38,9±4,7/28,2±4,5) were significantly shorter (p<0,005) than those of preterm infants (A1, A2).

Conclusions: SEP analysis is a practicable and non-invasive diagnostic tool in preterm and term newborns during early postnatal period. Latencies significantly decreased during the preterm period indicating gradual maturation. The most important factor determining maturation was gestational age. Considering variable measurement standards in literature, our data emphasise the necessity of standardised own reference values.