How to survive on a raftAn excercise in applied physiology

Mattijn Buwaldaanaesthesiologist-intensivist

Le Radeau De La Meduse Theodore Gericault

Ik ga op reis en neem mee….

Problems

• Heat

• Cold

• Dehydration

• Starvation

• Mental condition

• Hostile marine

animals

Thermoregulation

Fluid balance

Heat balance

Metabolism

•Resting state 100 watt

•Exercise 1500 watt

External heat

Heat loss

Core body

370 C

Hypothermia :

Mild 350 - 320

Moderate 310- 280

Severe < 280

Heat exhaustion

Heat stroke

Heat exchange

External heat

•Radiation

•Conduction

•Convection

Heat loss

•Radiation

•Conduction

•Convection

•Evaporation

Radiation

• All heat objects emit thermal

radiation

• Infra red spectrum

• No medium required

• No radiation in water

• Radiating surface area 50-95%

• Difference between mean

surface temp of two objects

• Reflection or absorption

Boundery layer

• Air or water layer close

to the skin

• Provide isolation when

stagnant

• The thicker the layer the

more isolation

• In air:

• Wind chill factor!

• Max > 15 km/h

• In water:

• Max > 1.8 km/h

• Max conductive heat loss

during swimming

Thermoneutral temperature

In Air

• 26-30 C

• Naked person

• no sweating or

shivering

• Still air (no flow)

In Water

• 35-35.5 C

• Naked person

• no sweating or

shivering

• Still water

Water vs AirThermal conductivity x 24

Volume specific heat capacity x 3500

Thermoregulation

• Skin

– Cold > heat

– Very close to skin surface

• Muscle

– Anticipation of heat production?

• Hypothalamus (brain)

– More heat then cold receptors

– More sensitive to change then skin receptors

Temperature receptors

Thermoregulation

• Vasoconstriction

• Piloerection

• Heat production

Cold response

Thermoregulation

• Peripheral shutdown (vasoconstriction)

– Max perfusion = 3 - 4 L/min

– Min perfussion = 0.02 L/min

– 99% shutdown!

• Subcutaneous fat insulation

• Unperfused muscle

• Skin temperature decrease and approximates

environmental temperature

vasoconstriction

Thermoregulation

• Skin blood flow regulation

• 3 functionally different regions

• Extremities (hands, feet, ears, lips, nose)

– Extreme vasoconstriction

• Trunk and upper limbs

– Moderate vasoconstriction

• Head and brow

– Scalp constant blood flow

– Heat loss!!

Vasoconstriction

Scalp > 50% body

heat loss in cold

environment

Core vs peripheral temperature

Thermoregulation

• “Goose bumps”

• Increased boundary layer

• Strongest on forearms

• Dysfunctional in hairless humans

• Pre-humans living in East Africa 4.4 million years ago inhabited savannas

piloerection

Thermoregulation

• Increased muscle tone (stiffness)

• Shivering

– Motor units 10-20/sec out of phase

– But alternating with opposing muscle

– No external work only heat production

– Can co exist with voluntary exercise (to a degree)

– Max heat production = basal x 6

– Shivering stops when:

• Glucose runs out (starvation, alcohol)

• Hypoxia, hypercapnia

• < 30 C (spasticity)

Heat production

Thermoregulation

• Peripheral vasodilation

– Bypasses the subcutaneous fat isolation layer

– Decreased core-skin gradient

vasodilation

Thermoregulation

• Humans: 2.5 x 106 sweat glands

• Skin cooling can inhibit sweating

• Acclimatization: more and less saltsweat

• Max 2 liter/hour!

• Each liter evaporated sweat removes576 kcal of heat

• Droplets don’t cool!

• Sweating does not help in a fullyhumidified environment

Sweating

Behavioral thermoregulation

• Naked body thermoneutral temperature

– in air: 26-30 C

– in water: 35 C

• Physiological thermoregulation is limited and time

dependent

• Proper clothing can get you anywhere on the planet!

Behavioral thermoregulation

• Goal = thermoneutral skin temp 26-30 C

• Clothing reduces:

– Radiant heat loss (proportional to layers of clothing)

– Conductive heat loss (boundary layer of air)

– Convective heat loss is minimized (proper size)

– Insensible evaporation continues (even in the cold)!!

• More layers > more trapped air

• Avoid draught (neck, arms and legs)

• Avoid moisture or getting wet

Behavioral thermoregulation

ambient temperature: 21 C

relative humidity: < 50%

Wind speed: < 0.9 km/h

no exertion

Behavioral thermoregulation

Old sayings….

• “If you want to stay warm in the mountains, stay

slightly cold”

– Minimize sweating to preserve clothing insolation

– Vapour permeable clothings only work when clean

and don’t work when splashed from the outside

• “If you want to keep your hands warm in the cold

wear a hat”

– > 50% heat loss through the head

– A normal core temperature provides warm blood to

perfuse the extremities

Behavioral thermoregulation

Cold environment

• Multiple layers

• Wear a hat

• Protect hands and feet

• Avoid draught

• If dry: vapour permeable

clothing

• Splash: waterproof outer

garment

• Windproof outer garment

• Dark coloured (absorption)

Hot environment

• Loose fitting

• Promote draught

• Light +flexible

• Light coloured (reflection)

What shall I wear?

When thermo regulation fails…

Sea temperature and death rate

Aboard raft < 5 C 5-10 C 10-20 C 20-31 C

% died 50 36 6 6

Man at risk 306 1240 7894 6101

McCance RA, et al. The hazards to men in ships lost at sea, 1940-44. Medical Research

Council, Special Report Series No. 291. HMSO. London

Hypothermia prevention on a raft

• Stay dry

• Put on as much clothing

as possible

• Stay out of the wind

• Prevent conductive heat

loss

• Minimize body surface

ara

• Remove wet clothing

during sun shine

• Use a saturation bag

when shivering and

during the night

Heat preservation in water

Survival time in cold water

Barnett PW field tests of two anti exposure assemblies. 1962 Arctic arospace laboratories report No AAL-TDR-61-56

Survival prediction and SAR times

• SAR time 3-6 x predicted 50% survival time

• 5 C >> 6 h search time

• 20-30 C >> 24 h search time

• Relevant factors:

– Fat or slim

– Physical fitness

– Naked or immersion suit

Stay on your raft!

Cold water immersion

Drowning

Wave splash:

•cooling of head

•frequent micro aspirations

•exhaustion

Cold shock:

•intense vasoconstriction

and tachycardia

•gasp reflex and

hyperventilation

Swim failure

Fast loss of

manual dexterity

Hypothermia

Dehydration

Cold environment

1. Hypothermia

2. Dehydration

3. Starvation

Dessert environment

1. Dehydration

2. Hyperthermia

3. Or nocturnal

hypothermia

4. Starvation

Popular survival literature:

3-3-3 rule: "3 minutes without air, 3 days without water,

and 3 weeks without food.

Fluid balance

Water balance

In 2250 ml

• Metabolism: 500 ml

• Intake: 1750 ml

Out 2250 ml

• Feces: 100 ml

• Skin 500 ml

• Lungs: 500 ml

• Urine: 1150 ml

• Thermoneutral environment

• Resting person

• Healthy person!C6H12O6 + 6 O2 = 6 CO2 + 6 H2O

Insensible

loss

What happens if you drink:

More then 1150 ml?

• Osmolality ↓

• n= 280 mosm/kg

• 1% decrease triggers

osmoreceptors

• Down regulation ADH output

• Collecting ducts less permeable

to H2O

• More diluted urine

Less then 1150 ml

• Osmolality ↑

• 1% increase triggers

osmoreceptors

• Thirst sensation

• More ADH

• More H20 reabsorption

• Less and more concentrated

urine

Dehydration

Max ADH secretion

• Assuming GFR 125 ml/min

• Urine osmolality 1200 mosm/L

• Urine composition:

– Urea 600 mmol/L

– Non urea electrolytes 600 mmol/L

• Urine production 500 ml/day

• Urea and electrolytes need H2O

to be excreted

• Max urinary salt excretion = 20

gram/ liter H2O

Renal failure

• Oliguria < 400 ml/day

• Anuria < 100 ml/day

• Hyperosmolality

• ↑Na

• ↑ Urea

• And many more disurbances

Why ?

Human long nephron

The spinifex hopping-mouse

• It does not need to drink. The seeds, insects and

roots that it eats provide enough water to live on.

• It has no sweat glands.

• Its droppings are almost completely dry.

• Its kidneys waste very little water. 9400 mosm/l

• Mothers produce very concentrated milk (and drink

the urine of their young).

DehydrationContinued insensible H20 loss 1000 ml/day

Or more in a tropical climate

Circulation:

•Hemoconcentration

•Tachycardia

•Hypotension

Kidney:

•Needs H2O to excrete Na+

•Renal failure

•Hyper Na+ > 170 mmol/l

CNS:

•Hyperactive deep tendon reflexes

•Muscular weakness

•Seizures

•Lethargy

•Confusion/ delirium

•Coma

Water restriction and survival

Daily H2O

ration

Men at risk Men who died % of men who

died

“none” 143 57 40

“some” 896 135 15

“0-110 ml 684 165 24

110-220 ml 1314 96 7

220-330 ml 523 7 1

“plenty” 56 1 2

121 life-craft voyages involving 3616 men

Critical volume of potable

water = 100 - 200 ml/dagMcCance RA, et al. The hazards to men in ships lost at sea, 1940-44. Medical Research

Council, Special Report Series No. 291. HMSO. London

Water management

• Don’t drink in the first 24 hours!

– Use your body’s reserve

– Much of the water drunk will be excreted!

• Restrict intake to 500 ml/day

• If water supply is plentiful: 1000 ml/day

• Optimize the use of shade and convective cooling

• Wetting clothing and exposed skin with seawater

• Don’t eat protein if low on water

• Stay horizontal when cooling off in the sea!

Conservation

Urea excretion:

3 ml water for

every gram prot.

The great temptation

Day after day, day after day,

We stuck, nor breath nor motion;

As idle as a painted ship

Upon a painted ocean.

Water, water, everywhere,

And all the boards did shrink;

Water, water, everywhere,

Nor any drop to drink.

The Rime of the Ancient Mariner

Samuel Taylor Coleridge (1772 - 1834)

Seawater

Seawater

Drinking seawater

No. of Life

craft

No. Of men

at risk

No. Men

who died

Seawater

group

29 997 387 = 38.8 %

Non seawater 134 3994 133 = 3.3 %

McCance RA, et al. The hazards to men in ships lost at sea, 1940-44. Medical Research

Council, Special Report Series No. 291. HMSO. London

Seawater enemas

• “busted myth”

• Causes osmotic diarrhea

• Ascelerates dehydration

• Colon is incapable of concentrating seawater!

• What could help is an enema with unpalatable

water

Other trics

• Fish lymph

– same salinity as plasma

– Squeezing fish takes a lot of energy

• Fish eyes and spinal fluid

• Turtle blood

– Same salinity

– 50 ml blood per kg

Solar still

Reverse Osmosis

Katadyn Survivor 35 Desalinator

The most widely-used emergency desalinator

•Produces up to 4.5 litres per hour.

•20 strokes/ minute

•Produces enough water for multiple person liferafts.

•Widely used by US and international military forces,

voyagers, sea kayakers, and other adventurers.

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Starvation…….

Is not the main concern!

Food

Daily

requirements

Kcal

2400

Carbohydrates 370 gram 63 %

Fats 65 gram 25 %

Protein 70 gram 12 %

StorageEnergy

content

70 kg human

Total body

content (kg)

Energy per

gram (Kcal/g)

Total body energy

content

Kcal %

Carbohydrates 0.5 4 2.000 1

Fats 14 9 126.000 78

Protein 9.5 4 38.000 21

Glycogen:

• 450 gram in muscle

• 100 gram in liver

• 1500-2500 Kcal in total

• Easy accessible energy

• Depleted after 24 h fasting

Fat:

• Huge amount

• Not easy accessible!

• Has to be metabolized

Starvation

• Complete starvation >> death in 30-60 days

• Hugh variation in human energy storage!

• Survival rations offer 500 - 800 kcal/day

Recommended Survival literature

0736002154 00065512540801670446