How to survive in a raft An exercise in applied physiology

Mattijn Buwalda

anaesthesiologist-intensivist

Le Radeau De La Meduse Theodore Gericault

Ik ga op reis en neem mee….

Problems

• Cold

• Heat

• 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

36-37o C

Hypothermia :

Mild 35o– 32o

Moderate 31o- 28o

Severe < 28o Heat exhaustion

Heat stroke

Heat exchange (in air)

External heat

•Radiation

•Conduction

•Convection

Heat loss

•Radiation

•Conduction

•Convection

•Evaporation

Conduction

In air

• direct contact between

skin and object

• 26 mW/M2/k

• standing human: minimal

conductive heat loss

In water

• 630 mW/M2/k

• Thermal conductivity x 24!

Radiation

• All heat objects emit or absorb

thermal radiation

• Difference between mean surface

temp of two objects

• Infra red spectrum

• No medium required (space)

• No radiation in water

• Radiating surface area 50-95%

Convection

Boundary layer

• Air or water layer close to the

skin

• Provides insulation when

stagnant

• The thicker the layer the more

insulation

In air:

• Wind chill factor!

• Max > 15 km/h

In water:

• Max > 1.8 km/h

• Max conductive heat loss

during swimming

Evaporation

• Each liter evaporated sweat

removes 576 kcal of heat!

• = 2419 J

• Droplets don’t cool!

• Sweating does not help in a fully humidified environment

Thermoneutral zone

In Air

• 26-30 o C

• naked person

• no sweating or

shivering

• still air (no wind)

In Water

• 35-35.5 o C

• naked person

• no sweating or shivering

• stagnant water

Water vs Air Thermal conductivity x 24

Volume specific heat capacity x 3500

Thermo

neutral zone

Thermoregulatory

zone

Thermoregulatory

zone

vasoconstriction

piloerection

shivering

vasodilation

sweating

26

C

30

C

Air temperature

core: 36o C

skin: 33o C

Thermoregulation

• Skin

– cold receptors > heat receptors

– very close to skin surface (fast

response)

• Hypothalamus (brain)

– more heat then cold receptors

– more sensitive to change

compared to skin receptors

Temperature receptors

•skin perfusion

•piloerection

•shivering

•sweating

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 decreases 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 neck

– 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 5 = 500 watt

– Shivering stops when:

• Glucose runs out (starvation, alcohol)

• Hypoxia, hypercapnia

• < 30o C (spasticity)

Heat production

• We want an ambient thermoneutral temperature!

• Preferably with as little clothes as possible

• We lost most of our insulation and body hair

• Heat thermoregulation >>> cold thermoregulation

• We are still naked apes living in the African savanna’s

Behavioral thermoregulation

• Naked body thermoneutral temperature

– in air: 26-30o C

– in water: 35o C

• Physiological thermoregulation is limited and time

dependent

• Proper clothing can get you anywhere on the planet!

Behavioral thermoregulation

• Goal = thermoneutral inner 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)

• More layers > more trapped air

• Avoid draught (neck, arms and legs)

• Avoid moisture or getting wet

• How much clothes?

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

• “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 < 5o C 5-10o C 10-20o C 20-31o 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 in a raft

• Stay dry

• Put on as much clothing

as possible

• Stay out of the wind

• Prevent conductive heat

loss (raft floor)

• Minimize body surface

ara

• Remove wet clothing

during sun shine

• Use a saturation bag

when shivering and

during the night

Saturation bag

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

• SAR time 3-6 x predicted

50% survival time

• 5 C >> 6 h search time

• 20-30o C >> 24 h search

time

• Relevant factors:

– Fat or slim

– Physical fitness

– Naked or immersion suit

Stay in 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

Renal failure

• Oliguria < 400 ml/day

• Anuria < 100 ml/day

• Hyperosmolality

• ↑Na

• ↑ Urea

• And many more disurbances

• Urea and electrolytes need H2O to be excreted

• Max urinary salt excretion = 20 gram/ liter H2O

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).

Dehydration Continued 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/dag 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

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

• 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

fresh 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.

$1,995.00 - Survivor 35 Desalinator

Osmotic desalination

• 500 ml in 5 hours

• Filters 97% of the

salt in seawater

Starvation…….

Is not the main concern!

Thank you for listening!

mattijnb@gmail.com