Incubator-based Sound Attenuation: Active Noise Control In A Simulated Clinical Environment

Abstract

Objective: Noise in the neonatal intensive care unit can be detrimental to the health of the hospitalized infant. Means of reducing that noise include staff training, warning lights, and ear coverings, all of which have had limited success. Single family rooms, while an improvement, also expose the hospitalized infant to the same device alarms and mechanical noises found in open bay units.

Methods: We evaluated a non-contact incubator-based active noise control device (Neoasis™, Invictus Medical, San Antonio, Texas) in a simulated neonatal intensive care unit (NICU) setting to determine whether it could effectively reduce the noise exposure of infants within an incubator. In the NICU simulation center, we generated a series of clinically appropriate sound sequences with bedside medical devices such as a patient monitor and fluid infusion devices, hospital air handling systems, and device mechanical sounds. A microphone-equipped infant mannequin was oriented within an incubator. Measurements were made with the microphones with the Neoasis™ deactivated and activated.

Results: The active noise control device decreased sound pressure levels for certain alarm sounds by as much as 14.4 dB (a 5.2-fold reduction in sound pressure) at the alarm tone's primary frequency. Frequencies below the 2 kHz octave band were more effectively attenuated than frequencies at or above the 2 kHz octave band. Background noise levels below 40 dBA were essentially not impacted by the active noise control device.

Conclusions: The active noise control device further reduces noise inside infant incubators. Device safety and potential health benefits of the quieter environment should be verified in a clinical setting.

Fig 1. Schematic of the Neoasis™ elements.

The Neoasis™ comprises a residual noise sensor, two speakers positioned inside the incubator, an outside noise sensor affixed to the outside of the incubator, and a control unit to which the other items are connected.

Fig 2. Test mannequin showing microphone placement.

Holes were cut in the head of an infant mannequin, permitting the tip of each microphone to emerge from the molded auditory canal. The number written on the cheek of the mannequin indicates the calibration number of that microphone.

Fig 3. Noise attenuation for noise sequence 1 for both ears and seven octave bands.

The unattenuated SPL is indicaterd by the square mark and the attenuated SPL is indicated by the bar at the top of the column. Measurements for the left and right ears are indicated by the letters “L” and “R,” respectively. The shaded region on the lower portion of the graph indicates the level of the AAP guideline recommendations. The vertical shaded regions indicate each octave band.

Fig 4. Amount of attenuation for all instances when the original SPL is above 40 dBA.

The seven octave bands are shown on the x-axis and the A-weighted SPL is shown on the Y-axis. The results for the right and left ears are shown, labelled “R” and “L.” The square represents the unattenuated sound and the top of the gray bar represents the attenuation achieved by the Neoasis™ system. The test sequence used comprised a high priority patient monitor alarm, a bubble CPAP device operating, and hospital environmental noise.

Fig 5. Typical sound levels on the dBA scale.

Figure adapted from OSHA Technical Manual [25].