Non-nutritive sucking in the neonate

Abstract

Non-nutritive sucking (NNS) by the newborn infant is a fundamental behaviour and is one of the first coordinated muscular activities in the foetus. A new specially designed computer-based method for automatic analysis of the NNS pattern in neonates has been produced. It records, identifies, analyses and quantifies the pressure signals obtained from a pressure transducer inside a pacifier when the infants suck. Validation of the system was carried out with four independent methods: EMG, visual identification, control of the automatic treatment and comparison of inter-observer results. A high degree of correspondence is shown.The automatic method was applied in 249 infants. A rhythmic NNS pattern of alternating sucking and pauses was elicited in 507 out of 529 recordings. The chance of achieving a recording without regular sucking activity is higher in younger neonates, but no limit in age or maturation is shown for NNS ability. The most immature, recorded at post-menstrual age (PMA) 26 weeks, provided an NNS pattern. Neither were the chances of no sucking increased in clinical stable sick pre-term infants, in those who developed sequelae nor in those exposed to pethidine (meperidine) in utero. The quantification of the NNS pattern showed significant variations between different groups. In healthy full-term infants the one-day-olds demonstrated a lower frequency of their sucking, a greater variability in sucking pattern and longer duration of their bursts compared with the 3-day-olds. Pethidine-exposed babies sucked with lower sucking frequency and with a tendency to less stable rhythm. In healthy pre-term neonates a gradual change of their NNS was seen. Post-menstrual age (PMA) was the dominant predictor of the result but gender, state of activity and weight also influenced it to some extent. The sucking activity, sucking frequency, amplitude and burst duration all increased with maturation, while the variability of the sucking frequency and the duration of the intervals between bursts declined. At term conceptional age pre-terms sucked with higher frequency and lower amplitude than full-term infants. The role of PMA as the dominant predictor for the NNS pattern is diminished in pre-term infants with risk factors. Follow-up of a subgroup revealed fewer sucking bursts per minute, slower sucking frequency and a greater variability of the frequency and amplitude in those who developed sequelae. Conclusions: NNS is in neonates a basic rhythmic motor behaviour that is present even in those born early pre-term. The pattern of bursts of sucking and pauses is robust and present in the vast majority of all neonates. Several variables, with maturation as the most important, are found to affect the rhythm. It appears as a pre-programmed rhythm generator, primarily modulated by maturation in healthy infants regulates their NNS behaviour. This modulation is affected by known risk associated events, in the infants who later develop sequelae and in those exposed to pethidine.Quantification of the NNS pattern in infants may be a valuable future component of their evaluation.