Surviving in the Wild - Justin Hensley
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You don’t have to be Bear Grylls to stay alive in the wild. Remember the rule of three - you can live 3 minutes without air, 3 hours without shelter, 3 days without water and 3 weeks without food. The two biggest killers in the wild are cold and heat. Justin discusses the physiology of our body’s responses to cold and heat and the pathophysiology of hypo- and hyperthermia. He also talks about the simple of ways of preventing cold and heat injury, including staying dry, adding layers, drink any water you can get your hands on - just not sea water. Lastly - don’t panic.
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Surviving in the Wild - Justin Hensley
- 1. Physiology of Survival Justin Hensley, MD @EBMgoneWILD
- 15. aborigines
- 23. Mild 32-35°C Moderate 28-32°C Severe 20-28°C Profound <20°C
- 28. Heat-sweat
- 29. Heat Exhaustion 38-41°C Heat Stroke >41.1°C
- 30. Heat
- 34. ( ) 280mOsm/L 350mOsm/L 42L - 42L x 42L - 42L x 280mOsm/L 295mOsm/L = Water deficit = 2.1L deficit Normal Measured TBW - TBW x = 7 days max survival 8.4L deficit 1.2L/day min = 8.4L deficit ( ) ( )
- 35. Water
- 36. Saltwater
Editor's Notes
- November 2006-The Kim family had been in Seattle and Portland visiting friends and family over Thanksgiving. They were heading home to San Francisco, but were stopping overnight in Gold Beach. They started driving at 9p, and later that evening it started snowing.
- They missed the turnoff for their main highway, and took a later turnoff for Bear Camp Road. This road was 40 miles of single track hairpin turns, white knuckle driving in the summer, much less the winter. They stopped due to conditions, waiting until morning. Didn’t drive back due to fear of running out of gas.
- On day 7, James went searching for help. He thought a town was a few miles away. On day 9, Kati and the children were found by helicopter after she used a signal mirror. James was found 2 days later, face up in 3 feet of water. He was 1 mile from the car, but had walked more than 14 miles in a circular route.
- James was a senior editor at CNET, frequently blogging. He was not prepared for a large winter hike. The car was not prepared either. Even on I-5, tire chains are recommended, and more serious gear for the minor roads. No food or blankets in the car. Had not told anyone their route. New signs put up to prevent future incidents.
- Staying alive until you are found or find your way out More killed on single day hikes than long expeditions It’s not Gilligan’s Island.
- When we talk about survival, we often refer to the rule of 3s.
- 3 minutes without air, but I’m not going to discuss air here.
- 3 hours without shelter
- 3 days without water
- You can live for 3 weeks without eating, but the urges of hunger are emotional, and as strong as fight or flight. Food is a big stress. Hunger can make people do stupid things, even kill. However, don’t worry about eating for short term survival.
- Moving on to shelter, this is basically to keep our temps normal. Humans are tropical animals, who have adapted to cold environments with clothing. We do better in heat than in cold. Temp controlled by preoptic anterior hypothalamus to within 1C of 37C, and any deviation from that results in either hypothermia or hyperthermia, with concomitant medical syndromes. Coldest ever was in Antarctica, -89.2C, at Vostok Station, 1983. Siberia not far behind in the -60C range.
- As depicted in this chart, Napoleon lost 653,000 of 680,000 troops going to Moscow and back, many from hypothermia.
- Chilled starts at 25C when naked. Light clothing allows you to go to 0C, as long as no wind. Shivering is done to increase heat. It does this 3-5x over basal metabolic rate. This is limited by glycogen though, which only lasts a few hours. Physical exertion can increase metabolic rate 15x. Certain cofactors can influence basal metabolic rate. Thiamine, iron, copper, iodine, zinc deficiency can all change you. Most of these influence thyroid hormone synthesis.
- Australian aborigines, Kalahari Bushmen of South Africa, and the Arctic Inuit all have blunted shivering and BMR increases. This likely conserves energy over heat.
- To keep core warm, blood to extremities shut down. Skin gets pale because of vasoconstriction, until about 10C skin temp. Then you get alternating vasodilation and constriction, causing red skin (cheeks, nose). Once it gets too low, they’re sacrificed. Ears, fingers, nose, toes.
- Where does the heat go? Radiation accounts for 60% in still air. Wavelength is 10 micrometers which is infrared.
- Conduction is heat flowing from higher temps to lower temps. Convection is movement of heat by molecules changing locations. We also lose heat from evaporation, but that’s more important in high temp environments.
- Wind drastically increases convective heat losses.
- Water conducts and convects 20-25x more than air, don’t fall in it. 15C you have a couple hours, 5C you have 30 minutes.1912 Titanic-water temp 0C, Carpathia there within 2 hours of sinking (only 58 miles away), but nobody outside of lifeboats was found alive. Everyone else who was in water more than momentarily died. You die of cold, not of drowning. Cold water can instantly kill, especially those with long QT. Sudden disappearance syndrome
- Jack never had a chance.
- Heat loss worse if you move. Don’t swim unless it is very short. Heat escape lessening position, get as much out of the water as possible.
- Mild-chilled, tired, argumentative, reduced dexterity, almost always denied Moderate -Violent shivering, gross incoordination (walking), slurred speech, apathy, uncooperative Severe- Cannot shiver anymore, cannot walk, bradycardia (HR30 at 28), paradoxical undressing Profound-Shallow breathing, nearly pulseless (1-2x per minute), arrhythymias below 28C, usually no activity by 20C
- Lowest temp ever was 13.7C. She fell into a waterfall, was under the flow for 70 minutes. She survived. Children probably do better because they cool fast Wilderness survival tip-warm them up, any means possible. Remove wet clothing. Give warm fluids orally. Put them next to a fire. Get in a sleeping bag with them. Make a hypothermia wrap. Prevention is key. Layer your clothes. Make air pockets with straw, pine boughs, or whatever inside your shirt. Cover overexertion layer dry (COLD). Shelter yourself from wind and rain. Stay out of the water.
- We generate heat as a natural byproduct of cellular metabolism. This is great if you live somewhere colder than 37C. Hottest air temp on earth reliably recorded 53.9C, death valley, in 1960, 1998, 2005, 2007, and 2013. Ground temp of 93.9C measured at Furnace Creek in Death Valley in 1972. Most people don’t live in places that hot, but some do.
- In January of 1775, Charles Blagden (then secretary of the Royal Society of London) went into a room at 105C. He took a dog, a steak, and some eggs. He lasted 12 minutes, felt fatigued, and had a heart rate of 136 upon leaving. The dog was in a basket to protect her feet. She lasted 30 minutes with no ill effects, but started panting at 10 minutes. The eggs were cooked hard at 20 minutes. The steak was “overdone” at 33 minutes. Instantly he thought it would useful for medical conditions.
- As mentioned before, we lose heat by radiation, conduction, convection, and evaporation. Above 37C, only evaporation works to decrease body temp. Sweating increases temp loss by 20x, but at the expense of 2.5L/hr. 3 million sweat glands. Women glow, men sweat, is observation of actual phenomenon. Women sweat less. Doesn’t have to be sweat. Simply getting damp by any means works. See elephants spraying themselves with water. Australian animals lick themselves, because Australia. Once humidity over 75%, sweat doesn’t evaporate and instead drips off. All it does is dehydrate you then.
- We stay at 37C, muscles under load hit 41C easily. Heat exhaustion-heavy sweating, rapid breathing, rapid pulse. Core temp 41.1=heat stroke, Key finding-altered mental status. Doesn’t matter if it’s exertional or classic heatstroke. Old people sweat less, can’t move into cool, etc
- Survival tips, when hot rest. Walk at night, rest during the heat of the day. Don’t get naked. Clothing actually protects you from the sun and hot air. Loose fitting is better. If someone is experiencing hyperthermia, you want to cool them down. Put them in the shade, pour water over them, take off any excess clothing.
- Humans are 50-70% water, and it’s different for everybody. While you can die of water intoxication, you’re more likely to die of dehydration. Children and the elderly at higher risk.
- We need water for 3 reasons. First, water is needed because kidneys need water to excrete byproducts of metabolism. Our kidneys produce urine only about as concentrated as seawater. Minimum urine output is ~0.5L/d. Second, the system is leaky. Skin is a poor vapor barrier, losing 0.4L/d in comfortable conditions, and >1L in hot weather and low humidity. This is why people who die in deserts become mummies. Insensible water losses from respiratory tract also range from 200-1.5L/d. Sweat losses go up to 2.5L/hr. Third, we don’t store water in the body. We aren’t camels, which stores upwards of 50L in the alimentary tract and circulation. Humans can only hold 2-3L.
- Thus, the absolute minimum we need per day is ~1.2L (500 Urine, 400 skin, 200 resp). This is without sweating. Unrealistic when surviving. Resting in tropical sun still makes you lose 4.8L/day. You also decrease UOP to decrease loss. Max concentration is 1200 mOsm/L, slightly less than 4x more concentrated.
- Water deficit is total body water minus the product of total body water times normal osmolality divided by measured osmolality. Sensation of thirst regulated by osmolality of plasma. This occurs at 295 mOsm. If we take 60% average TBW by weight, 70kg man has 42L. Doing the math, this is 2.1L deficit. 350mOsm/L, which is limit compatible with life is consistent with 8.4L deficit. 8.4L/1.2L/day minimum results in 7 day estimation of survival.
- Survival tip-Only drink when you get thirsty, otherwise you aren’t maximally concentrating urine. Collect freshwater whenever possible via rain, stills, or whatever. Drink it, unless stagnant. Diarrhea may result in a few days, but you should be found by then. Avoid high protein foods as they break down to urea, which requires water to excrete. Carbohydrates are the best things to eat, as they don’t increase water loss.
- The rime of the ancient mariner “water water everywhere, but not a drop to drink” While sharks made the story of the USS Indianapolis interesting, most likely died after drinking seawater. They weren’t found for 107 hours after torpedos sank the boat. Those who drank seawater developed diarrhea, became delirious or combative, and then swam away to drown. Seawater is 1000mOsm/L, close enough to urine that you cannot gain free water by drinking seawater. Sea mammals can concentrate urine 2x as much as humans, and even they aren’t observed to drink seawater regularly. To make seawater drinkable, it must be diluted to 1 part in 4 (3 parts fresh, 1 part salt) to be safe to drink
- Don’t drink your own urine
- Loneliness Fear Discomfort Those lost rarely backtrack, instead looking towards real or imagined goals. Greatest skill is up to date mental map of environment. Do not “bend the map”
- You can’t stay too long in any Kubler-Ross stage but the last.