Earmuffs During Surgery Cut Post-Op Nausea From 52% to 35%

October 18 — According to New Scientist, nausea and vomiting after surgery are very common, but wearing noise-cancelling headphones during an operation can help prevent this unpleasant side effect. The simple intervention also supports an idea: even when we lose subjective awareness of our surroundings, the brain still processes sound.

Vigi Katlowitz of Baylor College of Medicine in Houston said: “These data are very encouraging and consistent with decades of research — anaesthesia is not a simple on/off switch.”

Nausea and vomiting are common side effects of anaesthetic drugs, and preventive medication is routinely given in clinical practice. Liu Huayue and his team at the First Affiliated Hospital of Soochow University in Suzhou, China, wanted to study a non-drug approach, and presented their findings at the anaesthesiology conference held in San Diego.

The team recruited 192 patients undergoing laparoscopic gynaecological surgery under general anaesthesia. The patients were randomly divided into two groups, and half wore soundproof earmuffs from the start of anaesthesia to the end of surgery; all patients received standard anaesthesia and anti-nausea medication.

Within 48 hours after surgery, 35% of the earmuff group experienced nausea or vomiting, compared with 52% in the group without earmuffs. The researchers also found that patients whose hearing was protected had less severe symptoms: fewer episodes of vomiting and less impact on daily life.

Operating rooms are usually not quiet places. Liu’s team measured an average noise level of 66 decibels in the operating room, roughly the volume of an ordinary conversation.

The mechanism linking sound, nausea and vomiting, and anaesthesia is not yet clear. But anaesthesia affects the nervous system; noise is thought to trigger a stress response that activates the autonomic nervous system. The autonomic nervous system regulates body functions we do not control voluntarily, such as heart rate, and interacts with the nerve pathways in the brainstem responsible for nausea and vomiting.

Liu stressed, however, that the study did not investigate the specific mechanism by which earmuffs reduce nausea and vomiting, and that “suppressing the stress response through soundproofing” remains only a hypothesis.

Even so, the results shed further light on how the brain works under anaesthesia. “Biologically, one can speculate that general anaesthesia only causes loss of consciousness, but does not necessarily completely block the brain’s neural processing of sound,” Liu said.

Liu hopes to carry out a large multicentre clinical trial in the future to measure the link between noise exposure and nervous system activity in patients under general anaesthesia.