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Sound Environments Surrounding Preterm Infants Within an Occupied Closed Incubator
Journal of Pediatric Nursing (2016) 31, e149–e154
Sound Environments Surrounding Preterm Infants Within an Occupied Closed Incubator Aya Shimizu MSN a,⁎, Hiroya Matsuo PhD b a
Department of Nursing, Graduate School of Health Sciences, Kobe University, Hyogo, Japan Department of International Health, Graduate School of Health Sciences, Kobe University, Hyogo, Japan
b
Received 16 April 2015; revised 18 October 2015; accepted 18 October 2015
Key words: Preterm infants; Sound; Environment; Frequency analysis; Developmental care
Purpose: Preterm infants often exhibit functional disorders due to the stressful environment in the neonatal intensive care unit (NICU). The sound pressure level (SPL) in the NICU is often much higher than the levels recommended by the American Academy of Pediatrics. Our study aims to describe the SPL and sound frequency levels surrounding preterm infants within closed incubators that utilize high frequency oscillation (HFO) or nasal directional positive airway pressure (nasal-DPAP) respiratory settings. Design and Methods: This is a descriptive research study of eight preterm infants (corrected age b 33 weeks) exposed to the equipment when placed in an incubator. The actual noise levels were observed and the results were compared to the recommendations made by neonatal experts. Results: Increased noise levels, which have reported to affect neonates' ability to self-regulate, could increase the risk of developing attention deficit disorder, and may result in tachycardia, bradycardia, increased intracranial pressure, and hypoxia. Conclusion and Practice implications: The care provider should closely assess for adverse effects of higher sound levels generated by different modes of respiratory support and take measures to ensure that preterm infants are protected from exposure to noise exceeding the optimal safe levels. © 2016 Elsevier Inc. All rights reserved.
RECENT ADVANCES IN neonatal medical treatment and nursing have significantly reduced the mortality rate from 55.3% (1980) to 15.2% (2000) in extremely low birth weight infants (500 g to 999 g) and from 20.7% (1980) to 3.8% (2000) in very low birth weight infants in Japan (Horiuchi, Itani, & Ohno, 2002). Some preterm infants survive but develop functional disorders because of the stressful environments in the neonatal intensive care unit (NICU). Several studies have shown that a stressful environment could interfere with the neonates' ability to self-regulate and could increase the risk of developing attention-deficit hyperactivity disorder (ADHD) later in life (Brown, 2009; Schieve et al., 2010). In particular, sudden, ⁎ Corresponding author: Aya Shimizu, MSN. E-mail address: [email protected]. http://dx.doi.org/10.1016/j.pedn.2015.10.011 0882-5963/© 2016 Elsevier Inc. All rights reserved.
jarring, or transient sounds may cause an unstable physiological state, resulting in tachycardia, bradycardia, increased intracranial pressure, and hypoxia (Brown, 2009). Thus, improving the acoustic environment will encourage natural growth and development in neonates. For almost two decades, in America as well as in Japan, the sound pressure level (SPL) in NICUs has remained much higher than the levels recommended by the American Academy of Pediatrics (AAP) (American Academy of Pediatrics, 1997; Graven, 2000; Thomas, 1989; Thomas & Uran, 2007) and the Recommended Standard for Newborn ICU Design (Smith & White, 2001; White, 1999; White, Smith, & Shepley, 2013). According to both guidelines, the hourly equivalent continuous sound level (Leq) should be kept at less than 45 A-weighted decibels (dBa), and the hourly maximum sound level (Lmax) should be maintained at less
e150 than 65 dBa. Most studies that have evaluated SPL have determined that the ventilator equipment, supplemental oxygen therapy, and bed types are the major contributors to noises in the NICU (Berens & Weigle, 1995, 1997; Thomas & Martin, 2000; Byers, Waugh, & Lowman, 2006; Lasky & Williams, 2009; Knutson, 2013; Wang et al., 2014). In addition, the AAP guidelines (1997) do not address the issue of appropriate sound frequency level (SFL). Some studies have shown that the SFL range after birth is possibly higher than that in the womb; sounds are possibly muted in-utero because of the amniotic fluid (Krueger, Horesh, & Crosland, 2012). The SFL was measured both inside and outside the closed incubator and was seen to affect the autonomic nervous system (Kellam & Bhatia, 2008, 2009; Livera et al., 2008). There is, however, a lack of reports that evaluate both SPL and SFL within occupied closed incubators, and determine to what sounds infants are actually being exposed. In this study, we aimed to describe the SPL and SFL in the preterm infants on respiratory support in the following areas a) beside the respirator (outside), b) near the neonate's head inside the incubator with opened windows, and c) near the neonate's head inside the incubator with closed windows.
Methods An observational study was conducted to measure the sounds within closed incubators occupied by preterm infants. The present study was approved by the ethics committee of our university. The recruitment extended from September 2013 to May 2014.
NICU Environment NICU In the present study, the NICU (level-III) consisted of a 21-bed unit in a large general hospital in Osaka, Japan. This study was conducted only in the rooms for infants who were attached to more medical equipment. Medical Equipment Neonates in the NICU were cared for in a closed incubator and respiratory support was provided with a mechanical ventilator. All neonates were placed in the same type of incubator (Atom Infant Incubator V-2100G, Atom Medical, Tokyo, Japan). The mechanical ventilator was selected depending on each infant's respiratory setting requirements. The Dräger Babylog® VN500 (Drägerwerk AG & Co. KGaA, Lübeck, Germany) was used for high frequency oscillation (HFO), and the Infant Flow® SiPAP™ (CareFusion, CA, USA) was used for the nasal directional positive airway pressure (nasal-DPAP) setting.
A. Shimizu, H. Matsuo infants who met the following selection criteria: neonates with a gestational age of less than 28 weeks at birth (estimated by date of confinement, in turn based on fetal ultrasound during pregnancy) and neonates occupying a closed incubator. Parents signed an informed consent document that described the purpose of the study, methods, and expectations before starting the study. After the parents provided consent, the sound scaling was conducted at least twice, at approximately 2-week intervals. However the infants with serious physical problems such as intraventricular hemorrhage or sepsis were not included in the study because the participating hospital had agreed to consider the sentiments of their families. All the neonates were less than 33 weeks of corrected age during the course of the study. This study was conducted during the daytime shift. The nurse in charge or one of the researchers placed a covered microphone to collect data regarding the sound levels a) outside beside the respirator, and near the baby's head both b) inside the incubator with open windows and c) inside the incubator with closed windows. The total recording time was determined depending on the intubation time, as indicated by the chief doctor. Each sound recording was paused during the routine patient care activities. After collection, the recordings were analyzed in a laboratory. Based on the results of frequency analysis, the SPL and SPF were determined.
Subjects Seven families (including one family with twins) agreed to participate in this study. A total of 19 measurement times were scheduled for the 8 preterm infants; however, the dataset of 17 measurement times (HFO, n = 8; nasal-DPAP, n = 9; total measurement duration = 31 h 23 min) was analyzed because the measurement was cancelled twice due to serious physical condition of the infant on observation. The SPL was analyzed with all sound recorded regardless of the microphone location. On the other hand, the SFL was analyzed only with the sound recorded when the windows within the occupied incubators remained closed for continuous 15 minutes, which is the longest duration to analyze the SFL by the sound level meter. Table 1 shows the demographic characteristic comparisons for both the ventilator groups (HFO and nasal-DPAP). The gestational age at birth and corrected age at observation ranged from 22 to 28 weeks and 27 to 32 weeks, respectively. The mean gestational age at birth, corrected age at birth, and infant body weight at observation were significantly different between the HFO group and the nasal-DPAP group, (gestational age at birth: 23.3 ± 1.2 vs. 26.0 ± 2.9 weeks, p b 0.05; corrected age at observation: 29.4 ± 1.9 vs. 31.4 ± 0.7 weeks, p b 0.01; infant body weight at observation: 838.0 ± 191.7 vs. 1052. 8 ± 177.0 g, p b 0.01).
Study Protocol The sound levels were measured after consent was obtained from the parents whose preterm infants were enrolled at 30 weeks of age (corrected age). A nurse manager was recruited to explain this study to the parents of the
Measurements The sound within the closed incubator was recorded by a sound level meter of international standards, the LA-5560 K, which was calibrated by professionals before this study, with
Sound Environments Table 1
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Demographic characteristics. HFO (N = 8) Nasal-DPAP (N = 9)
Characteristics
Mean ± SD
Mean ± SD
Gestational age at 23.3 ± 1.2 26.0 birth (weeks) Birth weight (g) 509.0 ± 45.1 676.6 The number of days 43.0 ± 18.3 39.6 after birth (days) Corrected age at 29.4 ± 1.9 31.4 observation (weeks) Infant weight at 838.0 ± 191.7 1052.8 observation (g)
± 2.9
p-value ⁎
± 226.7 n.s. ± 20.7 n.s. ± 0.7
⁎⁎
± 177.0 ⁎
Note: HFO = high frequency oscillation; nasal-DPAP = nasal directional positive airway pressure. Leven test and t-test; p b 0.05 for all comparison between the 2 groups (HFO and nasal-DPAP). ⁎ b 0.05. ⁎⁎ b 0.01.
mean Leq inside the occupied incubators with closed windows was significantly higher in the nasal-DPAP group than in the HFO group (63.7 ± 3.5 vs. 49.3 ± 1.7 dBa, p b 0.001).
SPL According to Microphone Location in Both Respiratory Support Types In the nasal-DPAP group, the inside Leq with closed windows did not significantly differ across other locations when tested with the microphone. However, in the HFO group, the mean Leq inside occupied incubators with closed windows was significantly lower than when the microphone was beside the respirator (49.3 ± 1.7 vs. 54.2 ± 1.3 dBa, p b 0.05) (Figure 1). Moreover, in the HFO group, the mean Leq inside occupied incubators with closed windows had the smallest standard deviation (SD) of all positions, while the mean Leq inside occupied incubators with opened windows in the nasal-DPAP group had the smallest SD of all microphone locations.
SPL Within Occupied Incubators a sound recording function (LA-0554) (Onosokki Co. Ltd., Yokohama, Japan). Through frequency analysis with an Oscope ver.2 software (Onosokki Co. Ltd.), the SPL in A-weighted slow response mode (dBa) and sound frequency (Hz) were calculated. In the present study, SPL indicated the equivalent sound level (Leq) at 1-minute intervals, maximum sound level (Lmax) at 1-minute intervals, and minimum sound level (Lmin) at 1-minute intervals. Based on previous studies, a value greater than 1 kHz was considered a high-frequency sound for the neonates (Kellam & Bhatia, 2008, 2009; Livera et al., 2008).
The SPL (the Leq calculated and averaged at 1-minute intervals) within occupied closed incubators was calculated for each week of corrected age to identify outliers and compare the distributions (Figure 2). Overall, the Leq inside occupied incubators with closed windows did not correlate with the corrected age at observation in any respiratory
Table 2 setting.
The sound pressure level according to the respiratory
Data Analyses The chi-squared test was used for categorical comparisons of data, and the t-test was used to assess the difference in the means of continuous variables in each respiratory setting (HFO or nasal-DPAP). The correlation was assessed by using Pearson's product–moment correlation coefficient. The differences in Leq means were quantified by using one-way analysis of variance under the three conditions in each respiratory setting (HFO or nasal-DPAP). A p-value less than 0.05 was considered statistically significant; all tests were two-tailed. All statistical analyses were performed on a personal computer with the statistical package SPSS for Windows Ver.22.0 (IBM, Tokyo, Japan). The results of the statistical analysis were verified by an epidemiologist.
Results SPL According to Respiratory Support Type The mean of all sound pressure indicators (Leq, Lmax, and Lmin) was louder in the nasal-DPAP group than in the HFO group under all three circumstances (beside the respirator, inside the incubator with opened windows, and inside the incubator with closed windows) (Table 2). The
Beside respirator Leq (dBa) Lmax (dBa) Lmin (dBa) Inside with opened windows Leq (dBa) Lmax (dBa) Lmin (dBa) Inside with closed windows Leq (dBa) Lmax (dBa) Lmin (dBa)
HFO
Nasal-DPAP
Mean ± SD
Mean ± SD
p-value
(HFO N = 5, nasal-DPAP N = 6) ⁎ 54.2 ± 1.3 64.0 ± 8.5 ⁎ 57.3 ± 4.4 67.2 ± 8.1 ⁎ 49.1 ± 2.5 60.7 ± 8.3 (HFO N = 7, nasal-DPAP N = 7) 52.6 ± 4.5 63.9 ± 2.7 56.5 ± 6.1 67.9 ± 2.3 47.9 ± 2.3 61.2 ± 2.7 (HFO N = 8, nasal-DPAP N = 49.3 ± 1.7 51.8 ± 2.0 47.4 ± 1.5
63.7 ± 3.5 65.1 ± 3.7 62.3 ± 3.4
⁎⁎⁎ ⁎⁎⁎ ⁎⁎⁎ 9) ⁎⁎⁎ ⁎⁎⁎ ⁎⁎⁎
Note: HFO = high frequency oscillation; nasal-DPAP = nasal directional positive airway pressure. Leven test and t-test; p b 0.05 for all comparison between 2 groups (HFO and nasal-DPAP). n.s. = not significant. ⁎ b 0.05. ⁎⁎⁎ b 0.001.
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A. Shimizu, H. Matsuo
Figure 1 Sound pressure level according to microphone location in both respiratory support types. HFO = high frequency oscillation; nasal-DPAP = nasal directional positive airway pressure.
group. In the HFO group, the mean Leq was approximately 50 dBa; however, the mean Leq in the nasal-DPAP group was approximately 60 dBa or greater.
SFL Within Occupied Incubators The SFL within occupied incubators with closed windows differed according to the respiratory support type (Figure 3). In the HFO group, the mean SPL profile was bimodal, and most frequency bands were less than 40 dB. In the nasal-DPAP group, the peak sound frequency ranged from 2.5 kHz to 8 kHz, and each sound pressure was maintained at approximately 45 dB or more. The SPL in each frequency range was significantly higher in the nasal-DPAP group than in the HFO group (250 Hz: p b 0.05; more than 500 Hz: p b 0.001).
believed that a multifaceted sound scale is necessary for improving the acoustic environment, according to the AAP guidelines (American Academy of Pediatrics, 1997; Graven, 2000; Thomas, 1989; Thomas & Uran, 2007) and Recommended Standard for Newborn ICU Design (Smith & White, 2001; White, 1999; White et al., 2013). The identification of sound properties would enable care providers to evaluate the effects of sound on infants and subsequently take the appropriate measures for infants in various environments (Shahheidari & Homer, 2012). To the best of our knowledge, this study is the first to evaluate sounds surrounding preterm infants in closed incubators in terms of both SPL and SFL at the same time.
The SPL Within the Occupied Incubator
Discussion Providing evidence-based developmental care for promoting development and preventing morbidity in preterm infants has been a difficult mission for health care providers (Symington & Pinelli, 2006). Because the property of sound involves not only SPL but also SFL (Gray, 2000), we initially
Figure 2 Sound pressure level according to respiratory support type. HFO = high frequency oscillation; nasal-DPAP = nasal directional positive airway pressure.* b 0.05.
The present study showed that the SPL and the corrected age at observation (weeks) were not correlated, even though Saunders identified a correlation between these two
Figure 3 Sound frequency level within incubators. HFO = high frequency oscillation; nasal-DPAP = nasal directional positive airway pressure.
Sound Environments parameters (Saunders, 1995). The SPL was, however, affected by respiratory settings (HFO or nasal-DPAP) and varied significantly according to the mean gestational age at birth, corrected age at birth, and infant body weight at observation. Noninvasive respiratory management has recently been implemented for preterm infants to prevent pneumomediastinum, and nasal-DPAP, rather than HFO, is being used in smaller infants (Waskosky & Huey, 2014). Our results showed that the nasal-DPAP setting is louder than the HFO setting. In fact, the nasal-DPAP sound level in the present study failed to meet the AAP (1997) and Recommended Standard for Newborn ICU Design recommendations for appropriate noise levels. In addition, in the nasal-DPAP setting, there was no significant difference in the SPL whether the microphone was outside the incubator, near the neonate's head inside the incubator with opened windows, or near the neonate's head inside the incubator with closed windows. On the other hand, in the HFO setting, the SPL near the neonate's head inside the incubator with closed windows was significantly lower than the SPL beside the respirator (outside), although it was not lower than inside the incubator with open windows. In cases of noninvasive respiratory management such as nasal-DPAP, the SPL inside occupied incubators with closed windows may depend on internal, rather than external, sound sources.
The SFL Within the Occupied Incubator Overall, sound within the incubator was louder in the nasal-DPAP group than the HFO group, with particularly striking differences in the high-frequency range. Considering that high SFL is uncomfortable even for adults, the effect of SFLs on infants early after birth merits even greater concern, as they were not exposed to such sounds while in the womb. In addition, the sound study group recommended SFL for pregnant women to protect the fetus (Graven, 2000). Preterm infants' inability to cope with high SFL may affect their development; thus, while the AAP does not offer SFLrelated recommendations, some appropriate limits should be considered.
Measures to Reduce Noise Exceeding Optimal Levels This study showed that the nasal-DPAP generated loud sounds. The present study pointed out that a reasonably loud sound level could be assumed due to the high sound pressure at the high-frequency range, even though previous studies noted that this was caused only by the SPL of tangent sound such as higher Leq and Lmax and longer L10 (Byers et al., 2006; Lasky & Williams, 2009). Furthermore, we demonstrated that the main sound source in the nasal-DPAP group originated inside the incubator, since the internal SPL with closed windows was not significantly lower than the external SPL. Although most nurses already strive to reduce the level of sound outside the incubators by using incubator covers and avoiding conversation, these measures may be insufficient for reducing SPL in
e153 the nasal-DPAP setting. Thus, we should consider alternatives for reducing ambient noise; a) use of sound absorbing materials inside the incubator to help reduce noise level; b) reduce the mechanical noise generated by the equipment through improved equipment design; c) and better isolation of the noise generating equipment from the incubator. In addition, we propose maintaining optimal SPL and SFL that should depend on the characteristics of the sound and be maintained through regular measurements to prevent infants being exposed to loud sounds (Almadhoob & Ohlsson, 2015). We should also include individual measurements and education for health care providers to gain knowledge regarding the current research (Philbin, Robertson, & Hall, 1999; Philbin & Klass, 2000; Philbin & Gray, 2002).
Limitations This study had some limitations. Even though the number of participants was almost significantly different between HFO and nasal-DPAP, the small sample size at the hospital caused sample selection bias. Even though the number of participants included in this study was low at this hospital, we could not involve patients from another hospital, since the expensive equipment for sound scaling was not easily portable. In addition, the evaluation to scale sounds in NICU was based on the AAP guidelines (1997), which is the most popular among medical care providers worldwide; however, it might be advisable to be updated after evaluating infants' behaviors or physical reactions within the occupied incubators, which is the topic of our ongoing study.
Conclusion Our results showed that noise levels affect neonates' ability to self-regulate, can increase the risk of attention deficit disorder, and may result in tachycardia, bradycardia, increased intracranial pressure, and hypoxia. The care provider should carefully assess for adverse effects of higher sound levels such as SPL and SFL generated by different respiration support equipment and take measures to ensure that preterm infants are not exposed to noise exceeding the optimal safe levels.
Acknowledgments The authors would like to thank the neonates, their parents, and the medical staff members for their cooperation. This study was funded by the Japan Society for the Promotion of Science (JSPS) KAKENHI (26861921), Grant-in-Aid for Young Scientists (B). The funding source had no role in study design; in the collection, analysis and interpretation of data; in the writing of the report; and in the decision to submit the article for publication.
References Almadhoob, A., & Ohlsson, A. (2015). Sound reduction management in the neonatal intensive care unit for preterm or very low birth weight infants. Cochrane Database of Systematic Reviews, 1, CD010333.
e154 American Academy of Pediatrics (1997). Committee on environmental health, noise: A hazard for the fetus and newborn. Pediatrics, 100, 724–727. Berens, R. J., & Weigle, C. G. (1995). Noise measurements during highfrequency oscillatory and conventional mechanical ventilation. Chest, 108, 1026–1029. Berens, R. J., & Weigle, C. G. (1997). Noise analysis of three newborn infant isolettes. Journal of perinatology: official journal of the California Perinatal Association, 17, 351–354. Brown, G. (2009). NICU noise and the preterm infant. Neonatal Network, 28, 165–173. Byers, J. F., Waugh, W. R., & Lowman, L. B. (2006). Sound level exposure of high-risk infants in different environmental conditions. Neonatal Network, 25, 25–32. Graven, S. N. (2000). Sound and the developing infant in the NICU: Conclusions and recommendations for care. Journal of Perinatology, 20, S88–S93. Gray, L. (2000). Properties of sound. Journal of Perinatology, 20, S6–S11. Horiuchi, T., Itani, Y., & Ohno, T. (2002). Studies on the states of care for high risk neonates and neonatal mortality in our country (year 2000). The Journal of the Japan Pediatric Society, 106, 603–613. Kellam, B., & Bhatia, J. (2008). Sound spectral analysis in the intensive care nursery: Measuring high-frequency sound. Journal of Pediatric Nursing, 23, 317–323. Kellam, B., & Bhatia, J. (2009). Effectiveness of an acoustical product in reducing high-frequency sound within unoccupied incubators. Journal of Pediatric Nursing, 24, 338–343. Knutson, A. J. (2013). Acceptable noise levels for neonates in the neonatal intensive care unit, Washington University School of Medicine Program in Audiology and Communication Sciences. (Retrieved from http://digitalcommons.wustl.edu/cgi/viewcontent.cgi?article= 1643&context=pacs_capstones,2015/06/20). Krueger, C., Horesh, E., & Crosland, B. A. (2012). Safe sound exposure in the fetus and preterm infant. Journal of obstetric, gynecologic, and neonatal nursing : JOGNN/NAACOG, 41, 166–170. Lasky, R. E., & Williams, A. L. (2009). Noise and light exposures for extremely low birth weight newborns during their stay in the neonatal intensive care unit. Pediatrics, 123, 540–546. Livera, M. D., Priya, B., Ramesh, A., Suman, R. V., Slirakshmi, M., Nagapoornima, A. G., & Ramakrishnam', M. D. (2008). Spectral analysis of noise in the neonatal intensive care unit. Indian Journal of Pediatrics, 75, 217–222. Philbin, M. K., & Gray, L. (2002). Changing levels of quiet in an intensive care nursery. Journal of Perinatology, 22, 455–460.
A. Shimizu, H. Matsuo Philbin, M. K., & Klaas, P. (2000). Evaluating studies of the behavioral effects of sound on newborns. Journal of Perinatology, 20, S61–S67. Philbin, M. K., Robertson, A., & Hall, J. W., III (1999). Recommended permissible noise criteria for occupied, newly constructed or renovated hospital nurseries. The Sound Study Group of the National Resource Center. Journal of Perinatology, 19, 559–563. Saunders, A. N. (1995). Incubator noise: A method to decrease decibels. Pediatric Nursing, 21, 265–268. Schieve, L. A., Baio, J., Rice, C. E., Durkin, M., Kirby, R. S., DrewsBotsch, C., & Cunniff, C. M. (2010). Risk for cognitive deficit in a population-based sample of U.S. children with autism spectrum disorders: Variation by perinatal health factors. Disability and Health Journal, 3, 202–212. Shahheidari, M., & Homer, C. (2012). Impact of the design of neonatal intensive care units on neonates, staff, and families: A systematic literature review. The Journal of Perinatal & Neonatal Nursing, 26, 260–266. Smith, J., & White, R. (2001). Nurturing design. A look at recommended newborn ICU standards. Health Facility Management, 14, 28–31. Symington, A., & Pinelli, J. (2006). Developmental care for promoting development and preventing morbidity in preterm infants. Cochrane Database of Systematic Reviews, 2, CD001814. Thomas, K. A. (1989). How the NICU environment sounds to a preterm infant, MCN. American Journal of Maternity and Children Nursing, 14, 249–251. Thomas, K. A., & Martin, P. A. (2000). NICU sound environment and the potential problems for caregivers. Journal of Perinatology, 20, S94–S99. Thomas, K. A., & Uran, A. (2007). How the NICU environment sounds to a preterm infant: Update. MCN. American Journal of Maternity and Children Nursing, 32, 250–253. Wang, D., Aubertin, C., Barrowman, N., Moreau, K., Dunn, S., & Harrold, J. (2014). Reduction of noise in the neonatal intensive care unit using soundactivated noise meters. Archives of disease in childhood. Fetal and neonatal edition, 99, 515–516. Waskosky, A., & Huey, T. K. (2014). Quality improvement project: Implementing guidelines supporting noninvasive respiratory management for premature infants. Neonatal Network, 33, 245–253. White, R. D. (1999). Recommended standards for newborn ICU design. Committee to establish recommended standards for newborn ICU design. Journal of Perinatology, 19, S1–S12. White, R. D., Smith, J. A., & Shepley, M. M. (2013). Recommended standards for newborn ICU design, eighth edition. Journal of Perinatology, 33, S2–S16.
Sound Environments Surrounding Preterm Infants Within an Occupied Closed Incubator Aya Shimizu MSN a,⁎, Hiroya Matsuo PhD b a
Department of Nursing, Graduate School of Health Sciences, Kobe University, Hyogo, Japan Department of International Health, Graduate School of Health Sciences, Kobe University, Hyogo, Japan
b
Received 16 April 2015; revised 18 October 2015; accepted 18 October 2015
Key words: Preterm infants; Sound; Environment; Frequency analysis; Developmental care
Purpose: Preterm infants often exhibit functional disorders due to the stressful environment in the neonatal intensive care unit (NICU). The sound pressure level (SPL) in the NICU is often much higher than the levels recommended by the American Academy of Pediatrics. Our study aims to describe the SPL and sound frequency levels surrounding preterm infants within closed incubators that utilize high frequency oscillation (HFO) or nasal directional positive airway pressure (nasal-DPAP) respiratory settings. Design and Methods: This is a descriptive research study of eight preterm infants (corrected age b 33 weeks) exposed to the equipment when placed in an incubator. The actual noise levels were observed and the results were compared to the recommendations made by neonatal experts. Results: Increased noise levels, which have reported to affect neonates' ability to self-regulate, could increase the risk of developing attention deficit disorder, and may result in tachycardia, bradycardia, increased intracranial pressure, and hypoxia. Conclusion and Practice implications: The care provider should closely assess for adverse effects of higher sound levels generated by different modes of respiratory support and take measures to ensure that preterm infants are protected from exposure to noise exceeding the optimal safe levels. © 2016 Elsevier Inc. All rights reserved.
RECENT ADVANCES IN neonatal medical treatment and nursing have significantly reduced the mortality rate from 55.3% (1980) to 15.2% (2000) in extremely low birth weight infants (500 g to 999 g) and from 20.7% (1980) to 3.8% (2000) in very low birth weight infants in Japan (Horiuchi, Itani, & Ohno, 2002). Some preterm infants survive but develop functional disorders because of the stressful environments in the neonatal intensive care unit (NICU). Several studies have shown that a stressful environment could interfere with the neonates' ability to self-regulate and could increase the risk of developing attention-deficit hyperactivity disorder (ADHD) later in life (Brown, 2009; Schieve et al., 2010). In particular, sudden, ⁎ Corresponding author: Aya Shimizu, MSN. E-mail address: [email protected]. http://dx.doi.org/10.1016/j.pedn.2015.10.011 0882-5963/© 2016 Elsevier Inc. All rights reserved.
jarring, or transient sounds may cause an unstable physiological state, resulting in tachycardia, bradycardia, increased intracranial pressure, and hypoxia (Brown, 2009). Thus, improving the acoustic environment will encourage natural growth and development in neonates. For almost two decades, in America as well as in Japan, the sound pressure level (SPL) in NICUs has remained much higher than the levels recommended by the American Academy of Pediatrics (AAP) (American Academy of Pediatrics, 1997; Graven, 2000; Thomas, 1989; Thomas & Uran, 2007) and the Recommended Standard for Newborn ICU Design (Smith & White, 2001; White, 1999; White, Smith, & Shepley, 2013). According to both guidelines, the hourly equivalent continuous sound level (Leq) should be kept at less than 45 A-weighted decibels (dBa), and the hourly maximum sound level (Lmax) should be maintained at less
e150 than 65 dBa. Most studies that have evaluated SPL have determined that the ventilator equipment, supplemental oxygen therapy, and bed types are the major contributors to noises in the NICU (Berens & Weigle, 1995, 1997; Thomas & Martin, 2000; Byers, Waugh, & Lowman, 2006; Lasky & Williams, 2009; Knutson, 2013; Wang et al., 2014). In addition, the AAP guidelines (1997) do not address the issue of appropriate sound frequency level (SFL). Some studies have shown that the SFL range after birth is possibly higher than that in the womb; sounds are possibly muted in-utero because of the amniotic fluid (Krueger, Horesh, & Crosland, 2012). The SFL was measured both inside and outside the closed incubator and was seen to affect the autonomic nervous system (Kellam & Bhatia, 2008, 2009; Livera et al., 2008). There is, however, a lack of reports that evaluate both SPL and SFL within occupied closed incubators, and determine to what sounds infants are actually being exposed. In this study, we aimed to describe the SPL and SFL in the preterm infants on respiratory support in the following areas a) beside the respirator (outside), b) near the neonate's head inside the incubator with opened windows, and c) near the neonate's head inside the incubator with closed windows.
Methods An observational study was conducted to measure the sounds within closed incubators occupied by preterm infants. The present study was approved by the ethics committee of our university. The recruitment extended from September 2013 to May 2014.
NICU Environment NICU In the present study, the NICU (level-III) consisted of a 21-bed unit in a large general hospital in Osaka, Japan. This study was conducted only in the rooms for infants who were attached to more medical equipment. Medical Equipment Neonates in the NICU were cared for in a closed incubator and respiratory support was provided with a mechanical ventilator. All neonates were placed in the same type of incubator (Atom Infant Incubator V-2100G, Atom Medical, Tokyo, Japan). The mechanical ventilator was selected depending on each infant's respiratory setting requirements. The Dräger Babylog® VN500 (Drägerwerk AG & Co. KGaA, Lübeck, Germany) was used for high frequency oscillation (HFO), and the Infant Flow® SiPAP™ (CareFusion, CA, USA) was used for the nasal directional positive airway pressure (nasal-DPAP) setting.
A. Shimizu, H. Matsuo infants who met the following selection criteria: neonates with a gestational age of less than 28 weeks at birth (estimated by date of confinement, in turn based on fetal ultrasound during pregnancy) and neonates occupying a closed incubator. Parents signed an informed consent document that described the purpose of the study, methods, and expectations before starting the study. After the parents provided consent, the sound scaling was conducted at least twice, at approximately 2-week intervals. However the infants with serious physical problems such as intraventricular hemorrhage or sepsis were not included in the study because the participating hospital had agreed to consider the sentiments of their families. All the neonates were less than 33 weeks of corrected age during the course of the study. This study was conducted during the daytime shift. The nurse in charge or one of the researchers placed a covered microphone to collect data regarding the sound levels a) outside beside the respirator, and near the baby's head both b) inside the incubator with open windows and c) inside the incubator with closed windows. The total recording time was determined depending on the intubation time, as indicated by the chief doctor. Each sound recording was paused during the routine patient care activities. After collection, the recordings were analyzed in a laboratory. Based on the results of frequency analysis, the SPL and SPF were determined.
Subjects Seven families (including one family with twins) agreed to participate in this study. A total of 19 measurement times were scheduled for the 8 preterm infants; however, the dataset of 17 measurement times (HFO, n = 8; nasal-DPAP, n = 9; total measurement duration = 31 h 23 min) was analyzed because the measurement was cancelled twice due to serious physical condition of the infant on observation. The SPL was analyzed with all sound recorded regardless of the microphone location. On the other hand, the SFL was analyzed only with the sound recorded when the windows within the occupied incubators remained closed for continuous 15 minutes, which is the longest duration to analyze the SFL by the sound level meter. Table 1 shows the demographic characteristic comparisons for both the ventilator groups (HFO and nasal-DPAP). The gestational age at birth and corrected age at observation ranged from 22 to 28 weeks and 27 to 32 weeks, respectively. The mean gestational age at birth, corrected age at birth, and infant body weight at observation were significantly different between the HFO group and the nasal-DPAP group, (gestational age at birth: 23.3 ± 1.2 vs. 26.0 ± 2.9 weeks, p b 0.05; corrected age at observation: 29.4 ± 1.9 vs. 31.4 ± 0.7 weeks, p b 0.01; infant body weight at observation: 838.0 ± 191.7 vs. 1052. 8 ± 177.0 g, p b 0.01).
Study Protocol The sound levels were measured after consent was obtained from the parents whose preterm infants were enrolled at 30 weeks of age (corrected age). A nurse manager was recruited to explain this study to the parents of the
Measurements The sound within the closed incubator was recorded by a sound level meter of international standards, the LA-5560 K, which was calibrated by professionals before this study, with
Sound Environments Table 1
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Demographic characteristics. HFO (N = 8) Nasal-DPAP (N = 9)
Characteristics
Mean ± SD
Mean ± SD
Gestational age at 23.3 ± 1.2 26.0 birth (weeks) Birth weight (g) 509.0 ± 45.1 676.6 The number of days 43.0 ± 18.3 39.6 after birth (days) Corrected age at 29.4 ± 1.9 31.4 observation (weeks) Infant weight at 838.0 ± 191.7 1052.8 observation (g)
± 2.9
p-value ⁎
± 226.7 n.s. ± 20.7 n.s. ± 0.7
⁎⁎
± 177.0 ⁎
Note: HFO = high frequency oscillation; nasal-DPAP = nasal directional positive airway pressure. Leven test and t-test; p b 0.05 for all comparison between the 2 groups (HFO and nasal-DPAP). ⁎ b 0.05. ⁎⁎ b 0.01.
mean Leq inside the occupied incubators with closed windows was significantly higher in the nasal-DPAP group than in the HFO group (63.7 ± 3.5 vs. 49.3 ± 1.7 dBa, p b 0.001).
SPL According to Microphone Location in Both Respiratory Support Types In the nasal-DPAP group, the inside Leq with closed windows did not significantly differ across other locations when tested with the microphone. However, in the HFO group, the mean Leq inside occupied incubators with closed windows was significantly lower than when the microphone was beside the respirator (49.3 ± 1.7 vs. 54.2 ± 1.3 dBa, p b 0.05) (Figure 1). Moreover, in the HFO group, the mean Leq inside occupied incubators with closed windows had the smallest standard deviation (SD) of all positions, while the mean Leq inside occupied incubators with opened windows in the nasal-DPAP group had the smallest SD of all microphone locations.
SPL Within Occupied Incubators a sound recording function (LA-0554) (Onosokki Co. Ltd., Yokohama, Japan). Through frequency analysis with an Oscope ver.2 software (Onosokki Co. Ltd.), the SPL in A-weighted slow response mode (dBa) and sound frequency (Hz) were calculated. In the present study, SPL indicated the equivalent sound level (Leq) at 1-minute intervals, maximum sound level (Lmax) at 1-minute intervals, and minimum sound level (Lmin) at 1-minute intervals. Based on previous studies, a value greater than 1 kHz was considered a high-frequency sound for the neonates (Kellam & Bhatia, 2008, 2009; Livera et al., 2008).
The SPL (the Leq calculated and averaged at 1-minute intervals) within occupied closed incubators was calculated for each week of corrected age to identify outliers and compare the distributions (Figure 2). Overall, the Leq inside occupied incubators with closed windows did not correlate with the corrected age at observation in any respiratory
Table 2 setting.
The sound pressure level according to the respiratory
Data Analyses The chi-squared test was used for categorical comparisons of data, and the t-test was used to assess the difference in the means of continuous variables in each respiratory setting (HFO or nasal-DPAP). The correlation was assessed by using Pearson's product–moment correlation coefficient. The differences in Leq means were quantified by using one-way analysis of variance under the three conditions in each respiratory setting (HFO or nasal-DPAP). A p-value less than 0.05 was considered statistically significant; all tests were two-tailed. All statistical analyses were performed on a personal computer with the statistical package SPSS for Windows Ver.22.0 (IBM, Tokyo, Japan). The results of the statistical analysis were verified by an epidemiologist.
Results SPL According to Respiratory Support Type The mean of all sound pressure indicators (Leq, Lmax, and Lmin) was louder in the nasal-DPAP group than in the HFO group under all three circumstances (beside the respirator, inside the incubator with opened windows, and inside the incubator with closed windows) (Table 2). The
Beside respirator Leq (dBa) Lmax (dBa) Lmin (dBa) Inside with opened windows Leq (dBa) Lmax (dBa) Lmin (dBa) Inside with closed windows Leq (dBa) Lmax (dBa) Lmin (dBa)
HFO
Nasal-DPAP
Mean ± SD
Mean ± SD
p-value
(HFO N = 5, nasal-DPAP N = 6) ⁎ 54.2 ± 1.3 64.0 ± 8.5 ⁎ 57.3 ± 4.4 67.2 ± 8.1 ⁎ 49.1 ± 2.5 60.7 ± 8.3 (HFO N = 7, nasal-DPAP N = 7) 52.6 ± 4.5 63.9 ± 2.7 56.5 ± 6.1 67.9 ± 2.3 47.9 ± 2.3 61.2 ± 2.7 (HFO N = 8, nasal-DPAP N = 49.3 ± 1.7 51.8 ± 2.0 47.4 ± 1.5
63.7 ± 3.5 65.1 ± 3.7 62.3 ± 3.4
⁎⁎⁎ ⁎⁎⁎ ⁎⁎⁎ 9) ⁎⁎⁎ ⁎⁎⁎ ⁎⁎⁎
Note: HFO = high frequency oscillation; nasal-DPAP = nasal directional positive airway pressure. Leven test and t-test; p b 0.05 for all comparison between 2 groups (HFO and nasal-DPAP). n.s. = not significant. ⁎ b 0.05. ⁎⁎⁎ b 0.001.
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A. Shimizu, H. Matsuo
Figure 1 Sound pressure level according to microphone location in both respiratory support types. HFO = high frequency oscillation; nasal-DPAP = nasal directional positive airway pressure.
group. In the HFO group, the mean Leq was approximately 50 dBa; however, the mean Leq in the nasal-DPAP group was approximately 60 dBa or greater.
SFL Within Occupied Incubators The SFL within occupied incubators with closed windows differed according to the respiratory support type (Figure 3). In the HFO group, the mean SPL profile was bimodal, and most frequency bands were less than 40 dB. In the nasal-DPAP group, the peak sound frequency ranged from 2.5 kHz to 8 kHz, and each sound pressure was maintained at approximately 45 dB or more. The SPL in each frequency range was significantly higher in the nasal-DPAP group than in the HFO group (250 Hz: p b 0.05; more than 500 Hz: p b 0.001).
believed that a multifaceted sound scale is necessary for improving the acoustic environment, according to the AAP guidelines (American Academy of Pediatrics, 1997; Graven, 2000; Thomas, 1989; Thomas & Uran, 2007) and Recommended Standard for Newborn ICU Design (Smith & White, 2001; White, 1999; White et al., 2013). The identification of sound properties would enable care providers to evaluate the effects of sound on infants and subsequently take the appropriate measures for infants in various environments (Shahheidari & Homer, 2012). To the best of our knowledge, this study is the first to evaluate sounds surrounding preterm infants in closed incubators in terms of both SPL and SFL at the same time.
The SPL Within the Occupied Incubator
Discussion Providing evidence-based developmental care for promoting development and preventing morbidity in preterm infants has been a difficult mission for health care providers (Symington & Pinelli, 2006). Because the property of sound involves not only SPL but also SFL (Gray, 2000), we initially
Figure 2 Sound pressure level according to respiratory support type. HFO = high frequency oscillation; nasal-DPAP = nasal directional positive airway pressure.* b 0.05.
The present study showed that the SPL and the corrected age at observation (weeks) were not correlated, even though Saunders identified a correlation between these two
Figure 3 Sound frequency level within incubators. HFO = high frequency oscillation; nasal-DPAP = nasal directional positive airway pressure.
Sound Environments parameters (Saunders, 1995). The SPL was, however, affected by respiratory settings (HFO or nasal-DPAP) and varied significantly according to the mean gestational age at birth, corrected age at birth, and infant body weight at observation. Noninvasive respiratory management has recently been implemented for preterm infants to prevent pneumomediastinum, and nasal-DPAP, rather than HFO, is being used in smaller infants (Waskosky & Huey, 2014). Our results showed that the nasal-DPAP setting is louder than the HFO setting. In fact, the nasal-DPAP sound level in the present study failed to meet the AAP (1997) and Recommended Standard for Newborn ICU Design recommendations for appropriate noise levels. In addition, in the nasal-DPAP setting, there was no significant difference in the SPL whether the microphone was outside the incubator, near the neonate's head inside the incubator with opened windows, or near the neonate's head inside the incubator with closed windows. On the other hand, in the HFO setting, the SPL near the neonate's head inside the incubator with closed windows was significantly lower than the SPL beside the respirator (outside), although it was not lower than inside the incubator with open windows. In cases of noninvasive respiratory management such as nasal-DPAP, the SPL inside occupied incubators with closed windows may depend on internal, rather than external, sound sources.
The SFL Within the Occupied Incubator Overall, sound within the incubator was louder in the nasal-DPAP group than the HFO group, with particularly striking differences in the high-frequency range. Considering that high SFL is uncomfortable even for adults, the effect of SFLs on infants early after birth merits even greater concern, as they were not exposed to such sounds while in the womb. In addition, the sound study group recommended SFL for pregnant women to protect the fetus (Graven, 2000). Preterm infants' inability to cope with high SFL may affect their development; thus, while the AAP does not offer SFLrelated recommendations, some appropriate limits should be considered.
Measures to Reduce Noise Exceeding Optimal Levels This study showed that the nasal-DPAP generated loud sounds. The present study pointed out that a reasonably loud sound level could be assumed due to the high sound pressure at the high-frequency range, even though previous studies noted that this was caused only by the SPL of tangent sound such as higher Leq and Lmax and longer L10 (Byers et al., 2006; Lasky & Williams, 2009). Furthermore, we demonstrated that the main sound source in the nasal-DPAP group originated inside the incubator, since the internal SPL with closed windows was not significantly lower than the external SPL. Although most nurses already strive to reduce the level of sound outside the incubators by using incubator covers and avoiding conversation, these measures may be insufficient for reducing SPL in
e153 the nasal-DPAP setting. Thus, we should consider alternatives for reducing ambient noise; a) use of sound absorbing materials inside the incubator to help reduce noise level; b) reduce the mechanical noise generated by the equipment through improved equipment design; c) and better isolation of the noise generating equipment from the incubator. In addition, we propose maintaining optimal SPL and SFL that should depend on the characteristics of the sound and be maintained through regular measurements to prevent infants being exposed to loud sounds (Almadhoob & Ohlsson, 2015). We should also include individual measurements and education for health care providers to gain knowledge regarding the current research (Philbin, Robertson, & Hall, 1999; Philbin & Klass, 2000; Philbin & Gray, 2002).
Limitations This study had some limitations. Even though the number of participants was almost significantly different between HFO and nasal-DPAP, the small sample size at the hospital caused sample selection bias. Even though the number of participants included in this study was low at this hospital, we could not involve patients from another hospital, since the expensive equipment for sound scaling was not easily portable. In addition, the evaluation to scale sounds in NICU was based on the AAP guidelines (1997), which is the most popular among medical care providers worldwide; however, it might be advisable to be updated after evaluating infants' behaviors or physical reactions within the occupied incubators, which is the topic of our ongoing study.
Conclusion Our results showed that noise levels affect neonates' ability to self-regulate, can increase the risk of attention deficit disorder, and may result in tachycardia, bradycardia, increased intracranial pressure, and hypoxia. The care provider should carefully assess for adverse effects of higher sound levels such as SPL and SFL generated by different respiration support equipment and take measures to ensure that preterm infants are not exposed to noise exceeding the optimal safe levels.
Acknowledgments The authors would like to thank the neonates, their parents, and the medical staff members for their cooperation. This study was funded by the Japan Society for the Promotion of Science (JSPS) KAKENHI (26861921), Grant-in-Aid for Young Scientists (B). The funding source had no role in study design; in the collection, analysis and interpretation of data; in the writing of the report; and in the decision to submit the article for publication.
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