How noisy are anaesthesia and intensive care medicine? Quantification of the patients' stress.

The minimum and maximum sound pressure levels (Lmin, Lmax) were measured, and the energy equivalent sound pressure level (Leq) and the impulse rated Leq (LAlm) were ascertained in the surgical intensive care unit and the anaesthetic and recovery room. Frequency analyses were also made of the noise from various pieces of equipment. The LAlm was never below 60 dB(A)--the wake-up threshold in man--comprising strong narrow-band impulses with Lmax more than 100 dB(A) primarily from instrument alarms. When several instruments were alerted at the same time, a broad-band noise resulted which was based on their various spectral peaks. Whilst the maximum sound level of the technical equipment was high, it was surpassed by avoidable background noise caused by the staff (e.g. falling bucket lid: 94.7 dB(A)). No relationship was found between acoustic parameters and intended type of anaesthesia or surgery. Sound level was low in dangerous situations and high during routine work.