Cerebral hemodynamic response to unpleasant odors in the preterm newborn measured by near-infrared spectroscopy

Newborn infants in intensive care units are exposed to several unfamiliar s mells, mostly related to the nosocomial environment. How the preterm baby p erceives these olfactory stimulations remains unclear. Near-infrared spectr oscopy can be performed noninvasively above the olfactory cortex to monitor changes of cerebral blood flow as an indicator of cortical activation. The aim of this study was to explore by near-infrared spectroscopy how odorous substances routinely used in the neonatal intensive care unit influence bi lateral cortical hemodynamics in the olfactory region of the brains of pret erm infants. Specifically, a detergent (Neomidil) and an adhesive remover ( Remove) have been tested. Twenty preterm neonates of gestational age 30-37 wk (mean 33.7 +/- 2.3 SD) and postconceptional age 32-37.3 wk (mean 35.5 +/ - 2.75 SD) were monitored by near-infrared spectroscopy. Two optode pairs w ere placed above the anterior orbitofrontal gyri, which is involved in olfa ctory processing, on each side of the skull. Fifteen babies were exposed to the smell of a disinfectant and five babies to that of a detergent, both a pplied to small cotton pads. Changes of oxygenated Hb and deoxygenated Hb w ere recorded before, during, and after a 10-s stimulus. In 17 out of 20 bab ies, there was a decrease in oxygenated Hb and total Hb after the exposure to the substances. The decrease was significantly greater in the right side than in the left side. This change was different from that observed in our previous study after exposure to colostrum and the pleasant smell of vanil la, which elicited an increase in blood oxygenation in the same region. The biologic significance of this finding is unknown. We conclude that cortica l hemodynamic modifications occur in the preterm newborn after exposure to preparations commonly used in the neonatal intensive care unit. A lateraliz ation seems to occur in processing unpleasant olfactory cues.