An eggy whiff could be the scent of things to come in operating theatres if the promise of recent research is realised. US researchers have found that hydrogen sulfide (H₂S) gas can send mice into a hibernation-like state. Driving tissues or even the body into suspended animation could improve the outcome of many surgical interventions, they suggest. 

The response of mice to small concentrations of H₂S is striking. Metabolism slows down immediately, and after six hours' exposure, CO₂ output and oxygen consumption crash to 10 per cent of normal levels, report Mark Roth and colleagues at the University of Washington in Seattle. Breathing rate also drops from 120 to under 10 breaths per minute and core-body temperature falls to just a couple of degrees above ambient, they note. Crucially, the mice seemed to return to normal after the experiment.   

H₂S is a specific, potent and reversible inhibitor of cytochrome c oxidase, the last enzymecomplex in the energy-generating mito-chondrial electron transport chain. Consequently, Roth reasoned that inhibition of this complex might reduce metabolic rate in mammals. 

This is certainly a logical hypothesis, says Hannah Carey, a physiologist at the University of Wisconsin School of Veterinary Medicine. There is no evidence that inhibition of cytochrome c oxidase is a mechanism that natural hibernators use to slow their metabolism, but this needs to be explored, she says. 

This discovery could be of great medical benefit, says Roth's team. 'Lowering metabolic demand in this way could be used to reduce physiological damage resulting from trauma,' they report. However, surgeons will be pleased to note that the characteristic odour of the hospital is not about to be replaced by one of rotten eggs. 'Most operating rooms do a good job of scavenging volatile anaesthetics and could do the same with H₂S,' says Roth. Henry Nicholls