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Reduction of noise in the neonatal intensive care unit using sound-activated noise meters
  1. D Wang1,
  2. C Aubertin1,
  3. N Barrowman2,
  4. K Moreau2,
  5. S Dunn1,3,
  6. J Harrold1,2,3
  1. 1Children's Hospital of Eastern Ontario, Ottawa, Ontario, Canada
  2. 2Children's Hospital of Eastern Ontario Research Institute, Ottawa, Ontario, Canada
  3. 3University of Ottawa, Ottawa, Ontario, Canada
  1. Correspondence to Dr D Wang, Department of Pediatrics, Children's Hospital of Eastern Ontario, 401 Smyth Road, Ottawa, Ontario, Canada K1H 8L1; dwang{at}cheo.on.ca

Abstract

Objectives To determine if sound-activated noise meters providing direct audit and visual feedback can reduce sound levels in a level 3 neonatal intensive care unit (NICU).

Design/methods Sound levels (in dB) were compared between a 2-month period with noise meters present but without visual signal fluctuation and a subsequent 2 months with the noise meters providing direct audit and visual feedback.

Results There was a significant increase in the percentage of time the sound level in the NICU was below 50 dB across all patient care areas (9.9%, 8.9% and 7.3%). This improvement was not observed in the desk area where there are no admitted patients. There was no change in the percentage of time the NICU was below 45 or 55 dB.

Conclusions Sound-activated noise meters seem effective in reducing sound levels in patient care areas. Conversations may have moved to non-patient care areas preventing a similar change there.

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Excessive or undesirable sounds (noise) can be detrimental to newborns with both short-term1 ,2 and long-term consequences.3 ,4

Recommendations for sound levels in neonatal intensive care unit (NICU) patient rooms include an Leq (equivalent steady sound) of 45 dB, L10 (exceeded <10% of the time) of 50 dB and Lmax (highest decibel lasting ≥0.05 s) of 65 dB.5 Studies show that NICU sound levels generally exceed recommendations.W1–W4

One important modifiable contributor to an adverse sound environment is staff conversation.W5 W6 Studies examining NICU sound reduction methods have largely focused on educationW7 W8 and, to a lesser extent, use of sound-activated noise meters. Previously, we combined a targeted noise reduction policy with noise meters to reduce sound levels in a level 3 NICU.W9 High baseline sound levels due to factors such as the heating, ventilation and air conditioning (HVAC) system prevented the noise meters from functioning as intended. We hypothesise that direct audit and visual feedback, resulting from resetting the noise meter threshold to distinguish between quiet and noisy periods in our unit, will reduce sound levels in a level 3 NICU.

Methods

Study design

This study took place in a level 3 NICU in Ontario, Canada. Sound level data were measured using SoundEar noise meters with visual feedback capabilities. At sound levels above the set threshold, the meter turns red; ≤5 dB below threshold, it turns yellow and at sound levels >5 dB below threshold, it is green.

The noise meter thresholds were initially set at 45 dB. The meters were visible to all staff but continually showed ‘red’. After 2 months of recording sound data with the noise meters visible and red, the thresholds were reset to 50 dB (found to discriminate between quiet and noisy periods in our NICU). Data were collected for 2 months with the 50 dB threshold.

Data collection

Our NICU setup was described in detail in a previous publication.W9 One noise meter was placed in each patient area (pod) and a fourth in the central desk area. Sound levels were measured every second and 5-min Leq values were recorded by the noise meters. Similar to our previous study, data representing unit activity and other sources of sound were also collected.W9

Analysis

Data were exported from the noise meters using proprietary software (SoundLog V.1.3.4) and analysed with R programming language V.3.0.1. Sound levels were summarised graphically using time series plots. Means and SDs of sound levels were computed by transforming Leq values into linear measurements of sound pressure and back transforming to dB. Autocorrelation and partial autocorrelation plots assessed the effectiveness of using the mean sound level within each shift to reduce autocorrelation between successive measurements. Mean sound levels were adjusted for measures of activity using linear models.W10 Within each shift, the percentage of mean sound level measurements below each of 45, 50 and 55 dB was computed. Similar models were used to perform adjusted comparisons of the mean percentage of measurements below each threshold. Tukey's method for pairwise comparisons of means was used to adjust for multiple comparisons.W11 Residuals from the linear models were examined visually to verify that autocorrelation was not significant. Due to some residual autocorrelation, a single-shift lag term and, when necessary, a double-shift lag term was included in the model.

Results

There was a reduction in sound levels during the 2-month period with the meters providing direct audit and visual feedback (post) compared with the meters being present but continually red (pre). This was most evident comparing the percentage of time the sound level was below certain thresholds (table 1). There was a statistically significant increase in the percentage of levels below 50 dB in all patient care areas. There was no significant difference in the percentage of levels below 45 or 55 dB.

Table 1

Change in percentage of adjusted mean sound level measurements below 45, 50 and 55 dB after implementation of immediate direct audit and visual feedback

Unadjusted mean sound levels (Leq) for each NICU area are listed in table 2. Mean sound levels adjusted for unit activity were also compared preintervention and postintervention (see online supplementary table S3). There was minimal change in the adjusted mean sound levels.

Table 2

Unadjusted mean sound levels by location predirect and postdirect audit and visual feedback

Discussion

Overall, there was no significant change in mean sound levels with direct audit and visual feedback using noise meters. Changes in mean sound levels may be difficult to achieve as there is a high sound floor due to un-modifiable factors (eg, HVAC system).

There was a statistically significant increase in the proportion of adjusted mean sound measurements <50 dB postinitiation of direct audit and visual feedback in all patient areas (increase of 7.3%–9.9%). A sound level of 50 dB is the recommended L10, meaning sound levels should be below this >90% of the time. Even with the improvement, sound measurements were below 50 dB <50% of the time. There was no significant increase in adjusted mean sound levels below 45 dB, likely related to the elevated sound floor preventing lower sound levels from being achieved. A difference was not seen at 55 dB likely due to high rates of sound levels below this preintervention. The desk area did not experience significant change at any threshold. This could be due to movement of conversations out of patient care areas. Staff may also be less aware of the noise meters in non-patient care areas.

Our results are similar to the small number of available studies in the literature. Chang et alW12 used a much higher meter threshold of 65 dB but found that mean sound levels decreased almost 2 dB in incubators and the percentage of time below 58 dB increased by 28% in incubators and 4% in radiant beds. No adjustments were made in that study for measures of unit acuity. In a similar study, Jousselme et al introduced a noise meter in a paediatric intensive care unit and evaluated its effects.W13 They also assessed for a difference in effect if the device is turned on or off. They found mean sound levels decreased by 2 dB with the meter present. However, no adjustments were made to the results for unit acuity. They noted no difference in sound levels whether the device was functioning or not which is in contrast to our results where a reduction in sound levels was found once the thresholds on the noise meters were adjusted and the meters were able to provide feedback.

Since the noise meter output is 5-min Leq, peak sound levels (Lmax) were not measured in this study. Short-lived loud noises are important as they may wake babies. The noise meters turn red in response to short loud sounds and can alert staff; however, it was not possible to assess for decreased Lmax or frequency of short loud noises. Additionally, sound levels were not measured at the neonate's ear; however, the majority of patients are nursed in open beds with overhead warmers making room measures relevant.

Future directions include investigating the long-term efficacy of the noise meters to determine whether the effect diminishes over time.

Conclusions

Noise meters providing direct audit and visual feedback are effective in reducing sound levels in patient care areas compared with having the meters present but not visually distinguishing between quieter and noisier periods. This effect was most noticeable when examining the percentage of time the measured sound levels were below a threshold of 50 dB. Conversations may have moved to non-patient care areas, preventing a similar change there. Overall adjusted mean sound levels did not change significantly which may be related to high background noise. Sound-activated noise meters should be considered in NICUs as part of the effort to provide an appropriate sound environment for fragile infants. Thresholds on the meters should be individualised to reflect the intrinsic background sound level of the unit.

References

Supplementary materials

  • Supplementary Data

    This web only file has been produced by the BMJ Publishing Group from an electronic file supplied by the author(s) and has not been edited for content.

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Footnotes

  • Contributors DW developed the protocol for the study, entered data, drafted and revised the manuscript. CA developed the protocol for the study and revised the manuscript. NB performed all data analysis and revised the manuscript. KM provided input on the study protocol and revised the manuscript. JH conceptualised and developed the protocol for the study and revised the manuscript. SD provided input on the study protocol and revised the manuscript.

  • Funding This study was supported by a resident research grant from the Children's Hospital of Eastern Ontario Research Institute.

  • Competing interests None.

  • Ethics approval Children's Hospital of Eastern Ontario Research Institute.

  • Provenance and peer review Not commissioned; externally peer reviewed.