Development of lumbar spinal cord and cortical evoked potentials after tibial nerve stimulation in the pre-term newborns: effects of gestational age and other factors.

Pre-term neonates are at increased risk for neurological dysfunction. Several investigators have found scalp recorded somatosensory evoked potential studies (SSEPs) after median nerve stimulation useful in the evaluation of newborn infants with asphyxiation and the effects of other adverse prenatal and perinatal factors. In order to evaluate the entire developing neuraxis, we undertook SSEPs after tibial nerve stimulation (PTN-SSEP) in pre-term neonates. Using bilateral simultaneous stimulation, potentials were recorded from the following sites: PF-spT6 (N5), spL1-spT6 (N16), spC7-Fpz (N27), Cz' (1 cm behind the vertex)-Fpz (P55). In all newborns studied, the N5 and N16 were reliably recorded. The N5 appeared relatively independent of the length of the newborns. The N16 correlated inversely with length. The N27 and P55 were recorded in 52% and 65% of the newborns, respectively. N27 inversely correlated modestly with length. The P55 was independent of most factors and probably reflects variable rates of cerebral myelination, neuronogenesis, varying states of alertness, and possibly subclinical encephalopathies. These results demonstrate the feasibility of obtaining such data in pre-term newborns.