Noise‐induced stress reactions in the infant

Two narrative reviews on physiological effects of sound/noise on newborns treated in the NICU were conducted 10 years apart (Morris 2000; Wachman 2011). The cardiac response to acoustic stimulation depends on behavioural state, history of previous sound exposure, predisposing conditions of the central nervous system, antenatal and perinatal events, postnatal age of the infant and PMA at birth. High intensity noise may cause either bradycardia or tachycardia. In low birth weight infants, both high‐ and low‐frequency sound stimulation result in a 10 mm Hg increase in systolic and diastolic blood pressure above baseline (Morris 2000; Wachman 2011).

Noise may cause apnoea, hypoxaemia, alternation in oxygen saturation and increased oxygen consumption secondary to elevated heart and respiratory rates and may, therefore, decrease the amount of calories available for growth (Morris 2000; Wachman 2011).

The electrical activity of the central nervous system changes in response to acoustic stimulation in the range between 36 dB and 90 dB. Increases in intracranial pressure and electromyographic and behavioural changes have been noted in newborns in response to sudden noise. Excessive sound may influence the neuroendocrine system and may have an indirect effect on immunity (Morris 2000; Wachman 2011).

The stress responses listed above, including bradycardia or tachycardia, increase in systolic and diastolic blood pressure, apnoea, hypoxaemia, alteration in oxygen saturation, increased oxygen consumption and increase in intracranial pressure, could potentially increase the risk for adverse outcomes such as poor growth, abnormal sleep patterns, hearing impairment, bronchopulmonary dysplasia, retinopathy of prematurity, intraventricular haemorrhage, periventricular leukomalacia, and developmental delay. Schell et al noted that animal studies have established that noise is a stressor and that animal growth is inhibited by noise exposure. They suggested that stress affects growth through the endocrine system. Stress from noise activates the hypothalamic‐pituitary‐adrenal axis, and causes growth‐inhibiting effects possibly through the action of corticosteroids. Birth weights among humans have been shown to be reduced in relation to noise exposure (Schell 2006). Perlman states: "Many clinical factors, (i.e. chronic lung disease, recurrent apnoea and bradycardia, transient hyperthyroxinaemia of prematurity, hyperbilirubinaemia, nutritional deficiencies, glucocorticoid exposure), as well as stressful environmental conditions, including infant–provider interaction, constant noise, and bright light, may act in combination to impact on the developing brain, even in the absence of overt haemorrhage and/or ischemia" (Perlman 2001). It thus seems plausible that a reduction in the noise levels that reach a preterm infant while in the NICU might reduce these adverse outcomes.

Noise‐induced stress reactions among staff

Efforts have been made to characterise noise that interferes with communication and work, and that are annoying and distracting for adults (Lasky 1995). Elevated levels of speech are needed to overcome the noisy environment in the NICU, thereby increasing the negative impacts on staff, newborns and their families (Lasky 1995). High noise levels are associated with an increased rate of errors and accidents leading to decreased performance among staff (Hétu 1994; Lasky 1995).

In one meta‐analysis of 31 studies of nurses' job satisfaction, Zangaro 2007 examined the relationships between job satisfaction and autonomy, job stress, and nurse‐physician collaboration among registered nurses working in staff positions. Job satisfaction was most strongly negatively correlated with job stress.

Noise has been recognised as a risk factor for work‐related stress in Her Majesty's Coastguard (Kingdom 2011). Blomkvist 2005 studied the acoustics and psychosocial environment in an intensive coronary critical care unit in Sweden. The aim of the study was to examine the influence of different acoustic conditions on the work environment and the staff in the coronary critical care unit. Psychosocial work environment data from the start and end of each individual shift were obtained from morning, afternoon and night shifts for a one‐week baseline period and for two four‐week periods during which either sound‐reflecting or sound‐absorbing tiles were installed. Reverberation times and speech intelligibility improved during the study period when the ceiling tiles were changed from sound‐reflecting tiles to sound‐absorbing ones of identical appearance. Improved acoustics positively affected the work environment; the afternoon shift staff experienced significantly lower work demands and reported less pressure and strain. The authors concluded that important gains in the psychosocial work environment of health care can be achieved by improving room acoustics. According to the authors: "The study points to the importance of further research on possible effects of acoustics in health care on staff turnover, quality of patient care, and medical errors" (Blomkvist 2005). Poor communication among intensive care unit nurses and doctors has been found to be a common causal factor underlying critical incidents in intensive care (Reader 2007).

Reduction in sound levels in general in an entire NICU or in a separate part of a NICU

Reductions in sound levels can be achieved in an entire NICU or in an individual patient room by architectural remodelling (Philbin 2002). Interventions include education of caregivers and parents to achieve behavioural changes to decrease sound levels (Philbin 2002; Ramesh 2009). Sound levels can be monitored and electronically recorded for long periods of time using a sound level meter with computing and data storage capabilities (dosimeter) (Philbin 2002). As sound levels vary by location and over 24 hours in a NICU (Ramesh 2009; Matook 2010), it is important that the monitoring is ongoing in various locations of the NICU, including inside the incubators (Pinheiro 2011). Environmental changes in the NICU aimed at reducing the sound levels might even increase decibel levels as described by Brandon et al after installation of motion‐sensing motorised paper towel dispensers and the introduction of a new communication system (Brandon 2007). It is of note that two centres, using primarily human behaviour noise reduction strategies, were unable to demonstrate measurable improvements in sound levels within the occupied open‐unit design NICU (Liu 2010). A single‐family room level 3 NICU is a quieter, less loud environment compared with the open‐unit level 3 NICU when the patient is supported on room air, high flow nasal cannula, bubble continuous positive airway pressure and conventional ventilation. High‐frequency ventilation results in similar measurements to the open‐unit level 3 bedside NICU (Liu 2012). In our experience, the sound levels in the resuscitation area can be very high, especially when several neonates are resuscitated simultaneously. We have not been able to identify any study that measured the sound levels in that area. Any innovative, developmentally sensitive intervention should start at birth in the resuscitation room, where neonates are exposed to excessive noise and light levels and painful/stressful stimuli to body parts (mouth, nose, throat, larynx and hands) represented by large areas in the sensory cortex (Ohlsson 2009). The sensory receptor in the minute cochlea occupies an area of the cortex comparable to that occupied by an area as large as the skin of the whole face. The cortex in this area, measuring about 3 mm in depth, is thicker than in other sensory fields (Fisch 1983).

In a prospective cohort study 136 preterm infants (< 30 weeks PMA) were assigned to a bed space in an open ward or in a private room within the same hospital, based on space and staffing availability (Pineda 2014). The infants remained in the location to which they were first assigned for the whole duration of their hospital stay. The primary outcome was developmental performance at two years of age measured using the Bayley Scales of Infant and Toddler Development, 3rd Edition. Eighty‐six infants returned for testing (83% of survivors). At age two years, infants cared for in private rooms had lower language scores (average difference in Bayley score ‐8.3; 95% CI ‐14.2 to ‐2.4) and a trend toward lower motor scores (average difference in Bayley score ‐6.3; 95% CI ‐11.7 to ‐0.99) compared to infants cared in an open ward. The differences persisted after adjustment for potential confounders (Pineda 2014). The authors concluded that "these findings raise concerns that highlight the need for further research into the potential adverse effects of different amounts of sensory exposure in the NICU environment" (Pineda 2014). In an accompanying editorial in The Journal of Pediatrics, Dr. Jobe wrote: "The optimal types and frequencies of stimulations for development of the very preterm brain are unknown, but isolation of these infants in relatively dark and quiet private rooms may be going in the wrong direction" (Jobe 2014). Commonly recommended interventions as part of the Newborn Individualized Developmental Care and Assessment Program (NIDCAP^®) include incubator covers and lowering of sound levels in the NICU, which have not been shown to be effective in improving developmental outcomes (Ohlsson 2013).

Reduction in sound levels for an individual infant

Reduction in sound levels that reach the individual neonate only can be achieved by the use of earmuffs/earplugs or by the use of sound‐reducing incubator covers. Sound levels in an incubator during actual flight conditions in four common medically configured aircrafts were measured (Sittig 2011). The incubator provided a 6 dB decrease in noise exposure from that in the crew cabin, but the average noise level in the incubator was still close to 80 dB (Sittig 2011).

Initiation and duration of the intervention

Ideally the sound reducing intervention should start at birth and be implemented during resuscitation, during transport from a referring hospital to a NICU and during the stay in a Level III or II unit to at least 34 weeks' PMA, but ideally to 36 weeks' PMA.

Reduction in sound levels in the NICU ‐ effects on nursing staff and parents

As high noise levels are associated with an increased rate of errors and accidents leading to decreased performance among staff (Hétu 1994; Lasky 1995), lowering the noise levels could improve staff performance and parental satisfaction with the care. Voluntary anonymous reporting of medical errors for NICUs is feasible and has the potential of enhancing patient safety (Suresh 2004). Nurses' working experience and satisfaction with care following the implementation of the Newborn Individualized Developmental Care and Assessment Program (NIDCAP^®) has been measured using questionnaires (Westrup 2003).

At least five parent satisfaction questionnaires have been developed (the Parent Feedback Questionnaire, Neonatal Index of Parent Satisfaction, Inpatient Parent Satisfaction‐Children's Hospital Minneapolis, Picker Institute‐Inpatient Neonatal Intensive Care Unit Survey, and the Neonatal Intensive Care Unit‐Parent Satisfaction Form) (Mitchell‐Dicenso 1996; Conner 1999). These instruments have not been fully tested and validated (Conner 1999), but may have been used in studies to be included in this review.