self-rescue during accidental cold water immersion: is swimming an option?

Defence Research andDevelopment Canada

Recherche et développementpour la défense Canada Canada

Self-rescue during accidental cold water immersion:is swimming an option?

Michel B. Ducharme & David S. LounsburyHuman Protection and Performance,

Defence R&D Canada – Toronto

Defence R&D Canada – Toronto • R & D pour la défense Canada – Toronto

Background

The problem of accidental cold water immersion…

• drowning is the leading cause of accidental death for recreational activities in Canada (The National Drowning Report, 2003)

• 35 % of drowning occur in cold water (National Drowning Trends Report, 2006)

• BC Fishing Industry: 95 % of drowning occur

in water with a temperature ≤ 15 ºC (Brooks et al, Occupational. Med, 2005)

• 2007 persons died of cold immersion in Canada during 1991-2000 (The National Drowning Report, 2006)


What should a person do upon accidentalimmersion in cold water?

Would you attempt a 300 m swim in 10C wearing a PFD over seasonal clothing?

Result of survey:70% of final year university graduates said “NO”


Background

• public safety information agencies

– cold water swimming distance is only 1/10 of warm

water swimming distance (CRCS, 1983)

– attempting a swim of 100 m in cold water is too risky,

even for PFD-wearers (CRCS, 1995)

– “Do not attempt swimming. It has been shown that a strong swimmer has only a 50/50 chance of reaching shore one-half mile away.” (RLSSC, 1997)

– “If immersion is from a capsized craft: wait for rescue. Don’t try to swim for safety unless you are sure you can make it - you cool faster than you think.” (Ministry of the Environment)


Background

• public safety information agencies

– Cold water can paralyze your muscles instantly

(Transport Canada, 2006)

- If you end up in the water, do everything you can to conserve energy and body heat…Do not swim to keep warm. (Transport Canada, 2006)


Background

• rationale for the recommendations

– Subjects were only able to swim 7 to 12 min in 5°C water (Keatinge et al., 1969)

– moderate intensity swimming (40 - 45 % VO2 MAX) in 10.5 °C water can cause a 35 % in heat loss compared to holding steady (Hayward et al, 1975)

– hypothermia was assumed to be the limiting factor to swimming in cold water (Pugh 1955, Hayward et al, 1975)

– each °C in TEs or TM induces a 5 - 6 % in VO2 MAX (Bergh and Ekblom, 1979)


Background

“the traditional naval advice to cling to wreckage and not to waste energy by swimming is probable correct” (Pugh and Edholm, 1955)

“people are better off if they float still in lifejackets or hang on to wrekage and do not swim about to try to keep warm” (Keatinge, 1972)


In 2006…

“If rescue is unlikely, it may be preferable to swim to safety”(CRCS, 2006)


New evidence (epidemiological studies)

1- More survivors of boating incidents swam for shore thanstayed with the boat (Sawyer and Barss, 1998)

2- 60% of survivors of cold water boating immersions swamfor shore as opposed to only 30% who stayed with the boat(CRCS, 2006)


New evidence (physiological studies)

1- Subjects not wearing PFD could swim on average 55 min in 10°C water (Tipton et al., 1999)

2- Subjects wearing a PFD could swim on average 889 min 14°C water before incapacitation (Wallingford, Ducharme et al, 2000)

3- Subjects wearing a PFD could swim on average 792 min 10°C water before incapacitation, 3 times shorter thanthe 2375 m in 24°C (Kenny, Ducharme et al., 2001; 2002)

4- Subjects wearing a PFD could swim on average 806 m(novice swimmer) and 1439 m (expert swimmer) in 10°Cwater before incapacitation (Lounsbury and Ducharme, 2005)



0

500

1000

1500

2000

2500

3000

0 5 10 15 20 25 30

Water Temperature (°C)

Sw

im D

ista

nce

(m

)

A

B C1

C2

D

E A: Keatinge et al., 1969

B: Kenny et al., 2001

C1: Lounsbury & Ducharme, 2005 (novice swimmers)

C2: Lounsbury & Ducharme, 2005 (expert swimmers)

D: Wallingford et at., 2000

E: Kenny et al., 2001



0

500

1000

1500

2000

2500

3000

0 5 10 15 20 25 30

Water Temperature (°C)

Sw

im D

ista

nce

(m

)

A

B C1

C2

D

E A: Keatinge et al., 1969

B: Kenny et al., 2001

C1: Lounsbury & Ducharme, 2005 (novice swimmers)

C2: Lounsbury & Ducharme, 2005 (expert swimmers)

D: Wallingford et at., 2000

E: Kenny et al., 2001

?



The average swimming duration in all studies was about 45-50 min before incapacitation, irrelevant to the swimming ability

Swimming failure develops before incapacitating hypothermia

Swimming failure is likely primarily related to muscle fatigueof the arms as a consequence of muscle cooling rather thanhypothermia


Recommendations for self-rescue

1- Upon falling into water (cold shock):- focus on keeping the head above water- do not swim until regaining control of breathing

2- Ask yourself: “Am I likely to be rescued soon?”- <10% body fat: 2-3 hours- 15-20% body fat: 4-5 hours- >30% body fat: several hours- Yes: use HELP posture

3- No: swimming is an option- look around for the nearest source of safety- try to assess if you can swim the distance based on

your ability to swim and level of fitness- can you swim the required distance within 45-50 min?


Recommendations for self-rescue

4- Once you have made your decision, hold on to it, as your judgment will become impaired with time

5- Try to swim with an even and sustained pace


Swimming distance in cold water

Km

m

Fat, fit, good swimmer

Thin, unfit, bad swimmer

Average fatness, fit, novice

Average fatness, fit, expert


The Defence Research

and Development Branch

provides Science and

Technology leadership

in the advancement and

maintenance of Canada’s

defence and security

capabilities.


Objective of the study

To compare two self-rescue strategies (e.g. swimming vs. preserving heat) for their thermal performance during immersion in cold water.


Hypothesis of the study

- Swimming will induce a higher body heat loss as compared to HELP

- Swimming will not induce a higher change in body heat content as compared to HELP


Methods - Subjects

• 15 subjects between 18 to 55 years of age

• either gender

• attempts made to recruit across a wide range of body sizes and somatotypes

• classified by swimming skill into “novice” or “expert” categories


Methods - Subject Characteristics

• Novice (n=7)

Age = 31.7 years

Height = 1.73 m

Mass = 69.8 kg

BMI = 23.0 kg/m2

BSA = 1.82 m2

BSA:mass = 0.027 m

%BF-SkF = 17.4

%BF-UWW = 13.7

VO2 MAX Trd = 42.1* mL/kg/min

VO2 MAX Arm = 20.4 mL/kg/min

Aqua Quest Level = 7*

• Expert (n=8)

Age = 31.0 years

Height = 1.74 m

Mass = 74.4 kg

BMI = 24.5 kg/m2

BSA = 1.89 m2

BSA:mass = 0.026 m

%BF-SkF = 15.0

%BF-UWW = 13.3

VO2 MAX Trd = 52.1* mL/kg/min

VO2 MAX Arm = 24.6 mL/kg/min

Aqua Quest Level = 11*

Total Subject Pool (n=15)

* - NOV vs. EXP (p<0.05)


Methods - Design

0 3 45? 120time (min)

Trial 1: Passive Cooling (PC)

Trial 2: Free Swimming (FS)

HELP

HELP Free Swimming HELP

TRec (°C)37 34

Nov.

Exp.

Nov.

Exp.HELPHeat EscapeLessing Position

Coldshock


Methods: Flume set-up

- Twater: 10.0 ± 0.1 °C- Speed: 0.2 to 0.8 m/s- Tair: ~20 °C- Clothing: cotton pants, short-sleeved T-shirt, sweat shirt, socks, shoes, PFD.


Methods: Flume calibration

x

y

z

10 cm depth

30 cm depth

50 cm depth

20 cmlat. dev.

40 cmlat. dev.

flow178 cmlength

(Range: 0.1 to 1.0 m/s)


Methods - Measurements

Continuous

• Swimming Performance

– Speed (flume)

– Technique (video)

• Thermal

– Rectal Temperature

– Skin Temperature

– Heat Flow

• Heart Rate

Discrete

• Oxygen Uptake

• Electromyography

• Grip Strength

• Visuoperceptual

• Decision Making

• Psychophysical

– Thermal Comfort

– Rating of Perceived Exertion


Methods - Dressing Procedures

EMG

HR

BeltTSk and HF

Rectal probe

Dressed subject


Results - Rectal Temperature

34.0

34.5

35.0

35.5

36.0

36.5

37.0

37.5

38.0

0 10 20 30 40 50 60 70 80

Time (min)

Re

cta

l T

em

pe

ratu

re (

°C)

PC

FS

* x

n=15 n=14 n=13 n=8 n=6 n=5 n=4

Symbols: x - PC significantly different from FS, * - main effect of time first becomes significant.


Results - Skin Temperature

10.0

15.0

20.0

25.0

30.0

35.0

0 10 20 30 40 50 60 70 80

Time (min)

Sk

in T

em

pe

ratu

re (

°C)

PC

FS

*

n=15 n=14 n=13 n=8 n=6 n=5 n=4

x

Symbols: x - PC significantly different from FS, * - main effect of time first becomes significant.


Results - Core Cooling and Heat Loss

Steady State Heat Flow (W/m2)

Passive phase Swimming phase

Mean 234.9a 268.4

SEM 17.6 15.0

a - Swimming Phase vs. Passive Cooling Phase (p<0.001)

0.0070.006SEM

0.0470.037xMean

FSPC

Core cooling rate (ºC/min)

x - FS vs. PC (p<0.001)


Results - Immersion Time

20

75.5

61.5

0

20

40

60

80

100

120

PC FS

Condition

Tim

e (m

in)

x

Symbols: x - PC significantly different from FS

41.5

HELP

Swimming


Results - Swimming Times

47.0

36.7

0

10

20

30

40

50

60

NOV EXP

Swimming Skill

Tim

e (m

in)

NS

Symbols: NS - no significant differencebetween NOV and EXP


Results - Swimming Performance

0.51

0.37

0.00

0.10

0.20

0.30

0.40

0.50

0.60

NOV EXP

Swimming Skill

Sp

eed

(m

/s)

*

806.5

1438.9

0

250

500

750

1000

1250

1500

1750

2000

NOV EXP

Swimming Skill

Dis

tan

ce (

m)

*

Symbols: * - NOV significantly differentfrom EXP


Results - Grip and Body Comfort

24.4

37.0

05

1015

2025

3035

4045

50

PRE POST

Time

Gri

p S

tre

ng

th (

kg

)

*

1

2

3

4

5

6

7

8

-30 -20 -10 0 10 20 30 40 50 60 70

Time (min)

Th

erm

al C

om

fort

Rat

ing

n=15 n=13 n=6 n=5 n=3

a

b

Symbols: * - PRE significantly different from POST

Symbols: a - main effect of time first becomes significant, b - further main effects of time versus a


Results - Cardiovascular Stress

60

80

100

120

140

160

180

200

0 10 20 30 40 50 60 70 80

Time (min)

Hea

rt R

ate

(b/m

in)

PC

FS

*

n=15 n=14 n=13 n=8 n=6 n=5 n=4

x

Symbols: x - PC significantly different from FS, * - main effect of time first becomes significant


Results - Summary

Trial / StrategyVariable PC

"wait for rescue"

FS

"swim for it"

Difference?

Heat Flow

(W/m2)

234.9 268.4 PC < FS

(13 %)

Core Cooling Rate (ºC/min)

0.037 0.047 PC < FS

(21 %)

Functional Time

(min)

75.5 61.5 PC > FS

(19 %)

Grip Strength Loss

(kg)

12.6

(34 % )

12.6

(34 % )

PC = FS

(0 %)

Thermal Comfort

(unitless)

4.0 down to 2.0 4.0 down to 2.0 PC = FS

(0 %)

Swim Distance

(m)

0 1119.8 PC < FS

()


Results – Change in Body Heat Content

resprespsk CEEKCRWMS )(

Rate of change in body heat content (Rate of heat storage)

Work produced

Rate of heat loss

Metabolic heat production


Results – Heat production and heat loss

012345678

0 5 10 15 20 25 30 35 40 45

Swimming failure

Time (min)

Ene

rgy

expe

ndit

ure

(Kca

l/m

in)

0

5

10

15

20

25

30

35

0 5 10 15 20 25 30 35 40

Time (min)

Swimming failure

Hea

t los

s (K

cal/

min

) FS

PC


Results – Cumulative heat production and heat loss

0

100

200

300

400

500

600

700

800

900

1000

0 10 20 30 40 50 60 70 80 90 100 110 120

Time (min)H

eat l

oss

(Kca

l)

N=15 14 13 10 9 8 7 6 3 2 1

FS

PC

559.6 Kcal493.2 Kcal

0

100

200

300

400

500

600

700

800

900

1000

1100

0 10 20 30 40 50 60 70 80 90 100 110 120

Time (min)

Ene

rgy

Exp

endi

ture

(K

cal)

N=15 14 13 10 9 8 7 6 3 2 1

417.0 Kcal

233.8 Kcal


Results – Change in body heat content

Heat storage = Heat production – Work – Heat loss

-259.4 Kcal = 233.8 Kcal – 0 Kcal – 493.2 KcalPC

FS -176.0 Kcal = 417.0 Kcal – 33.4 Kcal – 559.6 Kcal

Zamparo et al, Eur JAP, 2005


Conclusions

– swimming increases body heat loss and core cooling rate compared to HELP

heat loss during swimming returned to HELP levels within 5 minutes of swimming cessation

– NOV swam about 800 m before incapacitation

– EXP swam about 1400 m before incapacitation

– Body heat content is more reduced following HELP than swimming


Recommendations

• Upon accidental immersion into a cold lake, while equipped with a PFD and when land is in sight, one should:

1. Float for 3 minutes to overcome cold shock

2. Locate the nearest source of safety (e.g. land, capsized boat)

3. Assess whether distance is within swimming ability (45 min swim)

4. Choose survival strategy (stick to this decision)

5. Execute strategy. If "await rescue", DONE

6. If "swim for it", attempt to swim (head out) with an even pace, DONE

self-rescue during accidental cold water immersion: is swimming an option?

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