It is of utmost importance that a patient is able to rest and sleep, but a Swedish study, conducted in a neurological intensive care unit, shows that is easier said than done.
Measurements were made over five days and showed average LAeq values of 53-58 dB, depending on time of day. But analysing equivalent sound pressure levels is not enough. It is also essential to analyse the occurrence and length of restorative periods, i.e. quieter periods where the noise levels is not assumed to disturb the patient’s sleep. The study shows that restorative periods last for only about 10 minutes, which means that a resting or sleeping patient will be disturbed several times an hour.
Read more about the study: Characterizing noise and perceived work environment in a neurological intensive care unit.
In this study a restorative period was defined as “LAeq below 50 dB for more than 5 min”. The length of restorative periods was only 9 minutes during the days and 13 minutes during the nights. A LAeq of 50 dB may not be ideal for resting or sleeping, but this definition was used since there were no 5 min periods of time below 45 dB LAeq during the entire measurement week. A similar analysis was conducted for LAFMax. The mean restorative length was defined as “LAFMax below 55 dBA for more than 5 min”. The level of 55 dB was chosen because there were no 5 min periods of time below 50 dB LAFMax during the entire measurement week. The measurements showed that mean restorative length (LAFMax <55 dBA) was only 10 and 8 min for the day and night, respectively. These figures can be compared to previous research that has shown that sleep disturbance can occur from traffic noise at levels from 45 dB LAFMax. Questionnaires answered by the staff shows that most of them felt that noise may negatively affect them in their daily work environment and that noise contributed to the development of ICU syndrome in patients. ICU syndrome is an emotional state, manifested by a variety of psychological reactions, including fear, anxiety, depression, hallucinations, and delirium. ICU syndrome can occur when a patient spend several days in an ICU. Stressors include, for example, loss of day-night orientation, disturbing sounds, isolation and sleep deprivation. Compared to previous studies, this study provides a more thorough description of intensive care noise and the behaviour of noise over time. This aids in understanding how the sound environment may be disruptive to occupants.