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Tipton and colleagues at the University of Portsmouth and the Brighton and Sussex University Hospital NHS Trust published this narrative review in Experimental Physiology in 2017. It was the first review to treat both the risks and the uses of cold water in one paper. The evidence for each area of application is graded using an adapted version of the SIGN criteria. The modality is cold water immersion, largely in open water, not sauna.
The authors describe four phases with distinct risks: cold shock in the first 3 minutes, superficial neuromuscular cooling from 3 minutes, core cooling from 30 minutes and circulatory collapse around rescue. Cold shock, a gasp and uncontrollable hyperventilation driven by cold receptors in the skin, is described as the most dangerous. It begins in water at 25 degrees, where it can still be consciously suppressed, and in the laboratory the breathing response peaked between 15 and 10 degrees without rising further at 5 degrees. Hypothermia, defined as a core temperature below 35 degrees, is not the main cause of death. A UK report from 1977 placed about 55 percent of open-water deaths within 3 metres of safety and 42 percent within 2 metres. For 2012, around 372,000 immersion deaths are estimated worldwide, 42 an hour and 7 percent of all deaths from unintentional injury.
The review has no data or meta-analysis of its own, and its evidence grading remains the authors' judgement. The death statistics come from field reports of different decades, the authors consider the global figure an underestimate, and all of them describe involuntary immersion in open water, not supervised use of a plunge pool.
On the therapeutic side, the authors find the evidence uneven: most areas have a plausible rationale, while in some the evidence goes no further than anecdote and speculation.