Most of what you know about hy­pother­mia is wrong

Soundings - - Contents - BY MARIO VIT­TONE

Most of what you know about hy­pother­mia and cold­wa­ter im­mer­sion is likely in­cor­rect. Mario Vit­tone sep­a­rates fact from fic­tion in his lat­est Lifelines col­umn.

Iwas meet­ing with 40 pro­fes­sional mariners to dis­cuss their man- over­board pro­ce­dures. Be­cause they op­er­ated where the wa­ter is cold (less than 60 de­grees most of the year), I asked them my fa­vorite ques­tion: “If you go over­board in Jan­uary wear­ing street clothes when the wa­ter is just above 33 de­grees Fahren­heit, how long un­til you be­come hy­pother­mic?”

Af­ter hear­ing the most com­mon an­swer— five min­utes—from these on-the-wa­ter pros, I told them the truth. Most of what they know about hy­pother­mia is wrong.

You can’t get hy­pother­mic in less than 10 min­utes. The aver­age adult can sur­vive in cold wa­ter for more than an hour. To un­der­stand the dan­gers of cold wa­ter, you have to stop fo­cus­ing on hy­pother­mia. Cold wa­ter kills, but hy­pother­mia is just one cause of fa­tal­i­ties.

Four things hap­pen to the body when it’s im­mersed in cold wa­ter. The first phase is the cold shock re­sponse. It is a stage of in­creased heart rate and blood pressure, un­con­trolled gasp­ing and, some­times, un­con­trolled move­ment. Last­ing any­where from 30 sec­onds to a few min­utes, the cold shock re­sponse can be deadly on its own. In fact, of all the peo­ple who die in cold wa­ter, it is es­ti­mated that 20 per­cent die in the first two min­utes. Some peo­ple panic or swal­low wa­ter in that first un­con­trolled gasp. If they have heart prob­lems, the cold shock may trig­ger a heart at­tack. Sur­viv­ing this stage is about get­ting your breath­ing un­der con­trol and stay­ing calm; you have to re­al­ize that the feel­ing will pass.

The sec­ond stage of cold wa­ter im­mer­sion is called cold in­ca­pac­i­ta­tion. Lack­ing ad­e­quate in­su­la­tion, your body will make its own. Long be­fore your core tem­per­a­ture drops a de­gree, the veins in your ex­trem­i­ties

(those things you swim with) will con­strict. As a re­sult, you’ll lose the abil­ity to con­trol your hands, and the mus­cles in your arms and legs will just flat-out quit work­ing well enough to keep you above wa­ter. If you’re not wear­ing a life jacket, you’re in trou­ble. With­out some form of flota­tion, even the best swim­mer will drown in cold wa­ter, and in less than 30 min­utes. There’s no way around it. More than 50 per­cent of the peo­ple who die in cold wa­ter drown fol­low­ing cold in­ca­pac­i­ta­tion, of­ten with­out ever ex­pe­ri­enc­ing a drop in core tem­per­a­ture.

As for hy­pother­mia, which is the third phase of cold wa­ter im­mer­sion, it can kill. But that only hap­pens in about 15 per­cent of cold wa­ter deaths. You have to have some form of flota­tion to get hy­pother­mia, and it takes much longer than you think. I once spent an hour in 44-de­gree wa­ter wear­ing street clothes, and my core tem­per­a­ture dropped by less than 2 de­grees. I was not clin­i­cally hy­pother­mic. It was un­com­fort­able, to be sure, and I wouldn’t rec­om­mend find­ing your limit, but it prob­a­bly would have taken an­other hour for me to lose con­scious­ness, and an hour af­ter that to cool my core to the point of no re­turn. The body’s ef­forts to keep the core warm— vaso­con­stric­tion and shiv­er­ing—are sur­pris­ingly ef­fec­tive. Shiv­er­ing and blood shunt­ing to the core were so pro­duc­tive for me that 20 min­utes af­ter jump­ing in, I had a fever of 100.2 de­grees. Keep in mind, though, that wa­ter tem­per­a­ture and body fat per­cent­age are im­por­tant fac­tors that de­ter­mine a per­son’s risk for hy­pother­mia.

Over the years, I’ve res­cued a num­ber of peo­ple from cold wa­ter. Once they’re set­tled in the he­li­copter, I en­force a rule: They must lie down and stay down un­til a doc­tor says they can stand. I’ve lost count of the num­ber of sur­vivors I have an­noyed be­cause I wouldn’t let them move. I don’t care how good or warm a per­son feels. The fi­nal phase of cold wa­ter im­mer­sion is cir­cum­res­cue col­lapse. Shortly be­fore, dur­ing or af­ter res­cue—some­times hours af­ter—vic­tims of cold wa­ter im­mer­sion may pass out, ex­pe­ri­ence ven­tric­u­lar fib­ril­la­tion or go into full car­diac ar­rest.

Why does that hap­pen? One of the things that hy­pother­mia af­fects is heart-rate vari­abil­ity. That is the heart’s abil­ity to speed up and slow down. Get­ting up and mov­ing around re­quires your heart to pump more blood; even sit­ting up­right can be tax­ing on the heart. If the heart starts to flut­ter in­stead of pump, down you go. Vic­tims of im­mer­sion hy­pother­mia are lucky to be alive, but they are also frag­ile.

An adult can sur­vive in cold wa­ter for more than an hour.

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