Background In Switzerland, right-to-die organisations assist their members with suicide by lethal drugs, usually barbiturates. One organisation, Dignitas, has experimented with oxygen deprivation as an alternative to sodium pentobarbital. Objective To analyse the process of assisted suicide by oxygen deprivation with helium and a common face mask and reservoir bag. Method This study examined four cases of assisted suicide by oxygen deprivation using helium delivered via a face mask. Videos of the deaths were provided by the Zurich police. Dignitas provided protocol and consent information. Results One man and three women were assisted to death by oxygen deprivation. There was wide variation in the time to unconsciousness and the time to death, probably due to the poor mask fit. Swiss law prevented attendants from effectively managing the face mask apparatus. Purposeless movements of the extremities were disconcerting for Dignitas attendants, who are accustomed to assisting suicide with barbiturates. None of the dying individuals attempted self-rescue. Conclusions The dying process of oxygen deprivation with helium is potentially quick and appears painless. It also bypasses the prescribing role of physicians, effectively demedicalising assisted suicide. Oxygen deprivation with a face mask is not acceptable because leaks are difficult to control and it may not eliminate rebreathing. These factors will extend time to unconsciousness and time to death. A hood method could reduce the problem of mask fit. With a hood, a flow rate of helium sufficient to provide continuous washout of expired gases would remedy problems observed with the mask.

The nineteenth-century British philosopher William Hamilton defended his law of the conditioned in part on the strength of its ability to offer a satisfactory theory of causation. He maintained that our belief that every event is the outcome of some cause and the source of some further effect finds its ground, not in the world, but rather in the limitations of our own minds; specifically in our inability to conceive of either absolute commencement of being or its absolute annihilation. While radically unlike modern conceptions of causality, Hamilton's account is better able to defend itself than either its critics or its neglect might suggest, while its modest and negative formulation recommends it to those of a sceptical tendency.