Anaesthesia may help fight influenza, says study

Common anaesthetics used during surgeries may help combat viral and bacterial infections in the lung, including influenza and pneumonia, researchers including one of Indian-origin have found. In use for more than a century, inhaled anaesthetics like nitrous oxide and halothane have made modern surgery possible. 

Now, in experiments in mice, researchers have found that certain so-called "volatile" anaesthetics - commonly used during surgeries - may also possess powerful effects on the immune system that can combat viral and bacterial infections in the lung, including influenza and pneumonia. Researchers built their experiments on previous work showing that children with upper viral respiratory tract infections who were exposed to the anaesthetic halothane during minor surgical procedures had significantly less respiratory symptoms and a shorter duration of symptoms compared with children who did not receive halothane.

To examine just how some inhaled anaesthetic drugs affect viral and bacterial infections, Krishnan Chakravarthy, faculty member at the Johns Hopkins Institute of Nanobiotechnology and Paul Knight, a professor of anesthesiology at the University of Buffalo School of Medicine and Biomedical Sciences, along with others, exposed mice to both influenza virus and Streptococcus pneumoniae bacteria.

The team discovered that giving the animals volatile anaesthetics, such as halothane, led to decreased bacterial burden and lung injury following infection. The researchers report that the anaesthetics augmented the anti-bacterial immune response after influenza viral infection by blocking chemical signalling that involves type I interferon, a group of proteins that help regulate the activity of the immune system.

Using a combination of genetic, molecular and knockout animal techniques, the researchers found that animals exposed to halothane had 450-fold less viable bacteria compared with non-halothane exposed animals with respect to the initial inoculum dose, and astoundingly, treatment made it as if the animals were never infected with a prior influenza virus. The investigators report that symptoms of piloerection (involuntary bristling of hairs of the skin), hunched posture, impaired gait, laboured breathing, lethargy, and weight loss (equal to or greater than 10 per cent of body weight at the time of infection) were significantly less in mice exposed to halothane and then infected with flu and S pneumonia.

Similar results, they said, were seen in mice bred to lack the receptor for type I interferon and not exposed to halothane before infection. "Given that these drugs are the most common anaesthetics used in the operating room, there is a serious need to understand how they work and how we can use their immune effects to our advantage," said Chakravarthy.

The findings, he said, suggest that volatile anaesthetics may someday be helpful for combating seasonal and pandemic influenza, particularly when there are flu vaccine shortages or limitations.