Investigating Noise Exposure to Newborn Infants From Respiratory Support: Methodological Considerations

Background and objective Excessive noise in the neonatal intensive care unit (NICU) may lead to serious long-term effects on hearing and sensory development in newborns. As such, the maximum allowed noise level is 45 A-weighted decibels (dBA). Studies regarding noise exposure to ventilated preterm infants show inconsistent results; however, these studies also vary considerably in their methodology in terms of noise ascertainment. We hypothesized that the study methodology can significantly influence data quality when measuring noise levels. In this study, we aimed to investigate whether the variations in ventilator noise levels in NICUs could be a result of methodological differences in study designs. Methods A ventilator circuit was set up using nasal continuous positive airway pressure (nCPAP) and high-frequency (HF) modes with nasal prongs. Noise levels were measured using a commercially calibrated noise meter. Three different scenarios were tested: (1) measurements were taken at different angles (0° to 180°), with 180° facing the end of the nasal prongs, without a mannequin, with the membrane/orifice of the noise meter placed 2 mm laterally from the prongs; (2) noise levels were measured at 180° at distances of 0-20 mm from the nasal prongs; (3) measurements were taken in the oral cavity of a life-size intubation mannequin of a newborn baby. Results Overall, the noise levels produced at different settings varied significantly, ranging from 45.7 dB to 82.2 dB. The average environmental background noise was 44.4 dB. Noise levels typically increased as the angle increased, with the highest noise level recorded at 180° for both HF and nCPAP modes, at 58.4 dB and 58.2 dB, respectively. Noise levels recorded at HF were slightly higher than nCPAP values. Furthermore, with regard to distance, the highest mean value, 82.2 dB, was recorded with the noise meter approximately 3 mm from the nasal prongs, and the lowest mean value, 47.6 dB, was recorded at ~20 mm. During trials with the mannequin, the lowest value, 50.1 dB, was recorded at the entrance of the mouth with slightly higher values being recorded within the oral cavity. Conclusion The results indicate that small changes in experimental settings, such as positioning and distance from the nasal prongs, can greatly influence noise levels, particularly above the recommended levels for neonates. These differences may be attributed to wind-generated noise. In summary, some study results are potentially influenced more by the study design than the device type or ventilator setting. We recommend further research and detailed reporting in the NICU to gain deeper insights into the topic.