Archive for the ‘Environmental Emergencies’ Category

LIGHTNING – THE BEAUTY AND THE BEAST

February 17, 2007

Lightning #3: Lightning-Related Injury

Injury can be caused by:

Direct effects of electricity on the nervous system.
Heat that is caused by the resistance of the current across or through the body.
Concussive effect of the shock wave of thunder.
Explosive force on other objects can hurl debris.  Water – steam expands 1700x’s.

Lightning-related injuries:

Minor: 

Confusion  – Amnesia ( hours to days )
Temporary deafness – Temporary blindness – Temporary loss of consciousness
Cutaneous burns – Contusions – minor blunt trauma & injuries
Paresthesias – Muscular pain
Tympanic membrane rupture
Mild transient hypertension
Cognitive damage to learning, thinking, or memory

Moderate: Temporary – to – permanent

Eyes – cataracts
Disoriented  – combative – comatose
Motor paralysis
Mottled skin
Diminished or absent pulses – Hypotension
Fractures – Spinal shock – spinal fractures
Temporary cardiopulmonary standstill or Respiratory arrest – can lead to cardiac arrest
Seizures
1st and 2nd degree thermal burns
Ruptured tympanic membrane – Hemotympanum – may indicate basilar skull fracture

Severe:

Cardiac arrest – asystole, ventricular fibrillation
Direct brain damage
Hematologic disorders – DIC
Basilar skull fracture

For more detailed information about lightning and lightning-related injuries see the Wilderness Medicine Newsletter, Lightning – Beauty & the Beast, July/August 2003.

This blog is powered by the Wilderness Medicine Newsletter, now celebrating 20 years of publication. The WMN is published and distributed online six times each year by TMC Books, and subscriptions cost as little as $10 per year. To find out more, or to subscribe online, click here.

Heat Loss Through the Head and Hypothermia

February 14, 2007

The rate of heat loss, at rest, with exercise, and with hypothermia

Since there has been a fair amount of interest regarding Myth #2 in the Wilderness Medicine Newsletter – Frozen Mythbusters, Nov/Dec 2004 – the topic deserves more discussion.

MYTH #2 states.  “If your feet are cold, cover your head because you can lose up to 75% of your body heat through your head alone.

The problem is that the head is only about 10% of the body surface area.  Thus, the head would have to lose about 40 times as much heat per square inch or centimeter compared to the rest of the body.
 
Gordon had heard this statement one too many times and finally decided to see if this was indeed true.  So he took several test subjects, all volunteers, of course, (you have to wonder what problem they caused at the university), wired them to monitor their core temperatures, and discovered that we do indeed lose heat through any exposed part of the body and the amount of heat we lose depends on the amount of exposed surface area.  The rate of heat loss is relatively the same for any exposed part of the body not simply the head. You do not lose heat significantly faster through the scalp than any other portion of the body with the same surface area. 

It is still a good idea to put on a hat (a hood really – what insulation does a baseball hat have?) if your feet are cold.  But what is BUSTED is that there is nothing peculiar or unique about the head. The idea that we lose heat faster through out scalp, because of the constant blood supply to the brain, is simply a myth. (One that I personally have believed for many years.)”

UPDATE & DISCUSSION
 
#1 Heat loss via the head at rest, during exercise, and with hypothermia:

I did have the opportunity to speak with Dr. Murray Hamlet about this topic, and we hope this additional information will help to clarify heat loss in the hypothermia patient.

The cerebral blood flow is supplied via the carotid and vertebral arteries (4 in total) and is constant. The blood flow to the brain does not change as the demand for oxygen is constant. As a result, when you look at total heat loss, the head accounts for about 7% of the heat lost. 

The cerebral blood flow does, however, vary based on cardiac output – the harder your heart beats, the greater the blood flow to the brain.  And as you increase the blood flow to the brain, you also increase the percentage of heat loss.  As it turns out, when you begin to exercise, there is increased cerebral blood flow. This increases the percentage of heat lost through the head to about 50% of total body heat loss.  But as the person continues to exercise, the muscles demand more oxygen which increases blood flow. To ensure thermoregulation and maintain normal core temperature (exercises increases body heat), the skin vasodilates which increases blood flow to the skin to cool the blood. The net result is a decrease in the total blood flow to the brain and a decrease in percentage of total body heat lost through the head to about 10%.  Once sweating begins, the percent lost through the scalp returns to 7%.

In Gordon’s research his test subjects were at rest in cool water, and the researchers were comparing the rate of heat lost by monitoring core temperature through different body parts and quantities of skin exposed.  At rest, they found that the rate of heat loss only depended upon the amount of skin surface area exposed, and the percentage of heat lost through the head was the same as the rest of the body.

Research at the Army Research in Environmental Medicine labs showed that there was a temporary increase in heat loss through the scalp that returned to the baseline of 7% as the subjects continued to exercise.

Now, what about hypothermia and heat loss through the head? 
If the hypothermia victim is not shivering, they are at rest, and the heat loss through the head remains about 7%.  But, this is important, if they are shivering, the percent of heat loss via the scalp can increase to upwards of 55%, so protecting the head well is a very important part of treating the hypothermia patient.  And as you can imagine, the primary defense against the cold and hypothermia is vasoconstriction of the peripheral circulation, this shunts blood to the core, reduces circulation to the skin, and increases the percent of heat loss through the scalp.

The difference is that the shivering hypothermia patient is indeed exercising, but they do not vasodilate the peripheral circulation; the shivering muscles increase metabolic demand and cardiac demand so the patients do increase their cardiac output; therefore, they do increase cerebral circulation; therefore, they do increase the percent of blood loss through their head.

Treatment of the hypothermia victim:
Remove from the cold.
Get them dry and keep them dry.
Insulate from the ground.
Hypothermia wrap:
Re-insulate with dry insulation.
Cover and protect the head from further heat loss.
Cover and protect the hands and feet from frostbite.
 Surround with a windproof and waterproof layer.
If conscious, feed warm, sweet liquids.
If unconscious, evacuate and handle very gently to prevent ventricular fibrillation.

#2 How does being in water change the equation?

Life-preserver, personal flotation device (PFD), research has shown that when in the water, if your head and neck are wet, you cool faster.  This is why modern PFD’s hold the person in the water with their head and neck out of the water; even if unconscious, to decrease the rate of heat loss into the water.

#3 What difference does hair on your head or facial hair make?

None. 
In order for hair or fur to provide a protective thermal barrier, it has to be much denser than what we humans grow and it has to be in layers of different types of fur to provide a thermal barrier.  Beards are great, but they do not keep you any warmer. And bald is beautiful.

We at the Wilderness Medicine Newsletter appreciate the comments and discussion.
 

LIGHTNING – THE BEAUTY AND THE BEAST

February 14, 2007

Lightning #2 – The Physics of Lightning

The Physics of Lightning:
Direct current electricity.  ( DC, not AC like the current that feeds our houses.)
Very high voltage and high amperage: can exceed 100 million volts, 100,000 amps.
Very hot, 50,000C, hotter than the surface of the sun.
Very short duration – instantaneous; milliseconds.
Produces Ozone, O3, that protects the earth from the deadly effects of ultraviolet light.
Electricity travels over the surface of objects, unless there is an internal conductor.
Internal conductors – nerves & blood vessels (contain an electrolyte solution).

Formation of lightning:
Vertical acceleration of moist air, forms ice crystals, causes charge separation.
Areas of positively and negatively charged atoms occur throughout the cloud head.
Electrical discharge to stabilize charges created in cumulonimbus clouds.
The base is negatively charged with a positive shadow forming on earth.
Typically, lightning occurs under and along the leading edge of the cumulonimbus cloud.
It can occur as far as 10 miles away, a strike “out of the blue.”
Can travel horizontally over 60 miles; the longest recorded to date was at 118 miles long.

Lightning strike can be: 
Direct strike or streamer current.
Splash or surface arc.    
Step voltage or ground current.
The principle is don’t be a conductor!

For more detailed information about lightning and lightning-related injuries see the Wilderness Medicine Newsletter, Lightning – Beauty & the Beast, July/August 2003.

This blog is powered by the Wilderness Medicine Newsletter, now celebrating 20 years of publication. The WMN is published and distributed online six times each year by TMC Books, and subscriptions cost as little as $10 per year. To find out more, or to subscribe online, click here.

LIGHTNING – THE BEAUTY AND THE BEAST

February 10, 2007

Lightning #1 – Lightning Statistics

Severe weather is interesting yet frightening, beautiful yet destructive, and always fascinating. It makes great news and never fails to attract our attention.  With this in mind, we thought it would be a good idea to address an aspect of severe and potentially life-threatening weather, thunderstorms.

Lightning strikes the USA approximately 100 times per second or 20 – 30 million cloud-to-ground lightning flashes per year.

Death caused by lightning is second only to floods for weather-related deaths, according to the National Weather Service, with an average of approximately 100 deaths per year over the past 40 years. 

Lightning strikes have a 10% – 20% mortality rate with a 70% – 80% morbidity rate. 

The odds of being struck by lightning in a year are 1/700,000 or a lifetime prevalence of 1/3000. 

USA Weather-Related Deaths as per the National Weather Service: (over 40 years)
#1  Floods – 150/year
#2  Lightning – 100/year  (500 – 1000 injuries per year)
#3  Tornado –  68/year
#4  Avalanche –  50/year
#5  Hurricane –  16/year

For more detailed information about lightning and lightning-related injuries, see the Wilderness Medicine Newsletter, Lightning – Beauty & the Beast, July/August 2003.

This blog is powered by the Wilderness Medicine Newsletter, now celebrating 20 years of publication. The WMN is published and distributed online six times each year by TMC Books, and subscriptions cost as little as $10 per year. To find out more, or to subscribe online, click here.

Hypothermia & Paradoxical Undressing

February 7, 2007

Hypothermia & Paradoxical Undressing

Recently in the news, there was a tragic event where a family got caught out in deep snow while driving through the mountains. Eventually, the father decided to leave his family in their car and go for help on foot. Unfortunately, through his valient effort, he didn’t survive that cold, harsh winter environment, and died of hypothermia. 

One of the discussions in the news was that even though he succumbed to the cold and hypothermia, at some point he had taken off some of his clothes. This is a phenomenom associated with hypothermia known as paradoxical undressing.

Pathophysiology:
The supposition as to the cause of paradoxical undressing is that the primary defense against the cold and hypothermia is vasoconstriction of the peripheral circulation. This shunts the blood into the warm core and the skin now becomes a more effective layer of insulation. The problem is that vasoconstriction of the smooth muscles in the vasculature requires glucose and energy consumption. Vasodilation, on the other hand, is a passive process that simply requires the smooth muscles that make up the blood vessels to relax. Over time, the vasoconstricted vessels begin to run out of energy (glucose) because of the poor circulation, and they fatigue and relax, thus vasodilating. This now allows the warm core-blood to re-perfuse the skin, causing a sensation of warmth. This results in the hypothermia victim feeling warm, so, they now begin to shed layers, thus the paradoxical undressing. Between the peripheral vasodilation and the loss of layers of protective clothing, their core temperature now begins to plummet and this hastens death from hypothermia.

I spoke with Dr. Murray Hamlet about parodoxical undressing and hypothermia and his experience and expertise with this phenomenom is the same as ours, in that we do not know of any cases where a hypothermia victim that underwent paradoxical undressing survived.

This blog is powered by the Wilderness Medicine Newsletter, now celebrating 20 years of publication. The WMN is published and distributed online six times each year by TMC Books, and subscriptions cost as little as $10 per year. To find out more, or to subscribe online, click here.

Cold-Induced Urticaria

February 4, 2007

There was a recent comment regarding a rash that occurred when a person went into cold water up to their knees that rapidly evolved into full-blown anaphylaxis.  So, it seemed appropriate to take a moment and explain exactly what happened.

There are individuals who are literally allergic to the cold. It happens more commonly from exposure to cold water, but  it can  be caused by cold air.  A close friend and athlete decided to go out for a short run one cold day, when it was about -10 degrees F.   After a short jog he began to develop shortness of breath and tightness in his chest.  He also began to break out with a red, itchy rash on his face.  Fortunately for him, he was right next to the hospital ER, so he intelligently ran in.  He was quickly diagnosed and treated for cold-induced anaphylaxis that required IV Benadryl and epinephrine.

For some strange reason, in these people cold exposure causes their mast cells to degranulate.  This produces an overdose of histamine, which results in vasodilation, hypotension, tachycardia, and bronchoconstriction, causing the symptoms of the rash (urticaria), shortness of breath, wheezing, tightness in the chest, and eventually a loss of their airway.

Symptoms of anaphylaxis, regardless of the cause:
Rash – red, raised, itchy welts (urticaria)
Hypotension
Tachycardia
Dyspnea – wheezing – stridor that can rapidly deteriorate into extreme difficulty breathing and airway obstruction from the bronchoconstriction.

Treatment of Anaphylaxis:
Antihistamine: such as Benadryl (diphenhydramine) 50mg po
If they develop difficulty breathing:Epinephrine 1:1000, 0.3cc IM, that comes in a pre-filled syringe, EpiPen
Oxygen 15lpm by non rebreather, if available
Evacuation to the closest ER

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BAROTRAUMA & DYSBARISMS #9

January 31, 2007

DECOMPRESSION SICKNESS (DCS):

Rapid reduction in ambient pressure, during ascent, causes dissolved gases to come out of
solution and form bubbles of nitrogen, the oxygen is rapidly metabolized in the tissues.

Gas bubbles can: 
– obstruct small blood vessels
– cause changes in blood chemistry
– stretch and damage tissues

Symptoms present within 12 hours.
– 80% within 1 hour of surfacing.
– 95% within 4 hours of surfacing.

TYPE I  – musculoskeletal limb pain
BENDS = periarticular pain in arms & legs (arms > legs)
pain relieved by direct pressure
pain can be mild, “Niggles,” to severe
skin/lymphatic involvement = pruritus, marbling, rashes

TYPE II – neurological
pain in areas other than the extremities
CNS changes = cord involvement or cerebral
spinal cord DCS = most common form of DCS in divers
paresthesia s – ascending numbness – paraplegia
urinary retention – fecal incontinence – priapism

Cerebral DCS:
classic CVA symptoms
pulmonary manifestations – “CHOKES”
occurs within minutes of surfacing
substernal chest pain – cough – dyspnea
can progress to respiratory failure and shock
labyrinthine or inner ear DCS – “STAGGERS”
vertigo – nausea/vomiting – tinnitus – hearing loss – nystagmus
                 
TREATMENT FOR DCS TYPE I & II:    
RECOMPRESSION
100% oxygen (helps to wash out nitrogen)
IV fluid therapy with crystalloid (hemoconcentration)
diazepam or phenergan for vertigo – nausea – vomiting
should not dive for 6 months after DCS & not until full evaluation

RECOMPRESSION – HYPERBARIC THERAPY
to reduce the size of the bubbles
to promote reabsorption
prevent further bubble production

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BAROTRAUMA & DYSBARISMS #8

January 29, 2007

ARTERAIL GAS EMBOLISM:  (AGE)Most serious of all dive injuries – frequently fatal.
Second only to drowning in fatalities in sport divers.
Ruptured airways allow air bubbles to enter the pulmonary circulation and go to the left side of the heart.
From the left ventricle may migrate to the coronary or cerebral circulation.
Resulting in:
ACUTE MYOCARDIAL INFARCTION (AMI)
CEREBROVASCULAR ACCIDENT (CVA)
AGE usually presents within 10 minutes of the “burst lung”.

SYMPTOMS: 
CVA = neurological symptoms:
change in mood or affect
visual disturbances
hemiplegia or hemiparesis
unconsciousness

AMI = apnea – dyspnea
chest pain – chest pressure
dysrhythmia s – asystole

SUDDEN LOSS OF CONSCIOUSNESS BEFORE SURFACING IS AGE UNTIL PROVEN OTHERWISE

TREATMENT:  RECOMPRESSION!!!
100% O2 while transporting
Transport supine & MONITOR AIRWAY

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BAROTRAUMA & DYSBARISMS #7

January 27, 2007

PNEUMOMEDIASTINUM & INTERSTITIAL EMPHYSEMA:
Ruptured airways allow air to escape into the soft tissues.
Air dissects into the mediastinal – into the pericardium – cephalad into the neck.

SYMPTOMS: 
subcutaneous air & crepitus on compression of the skin – neck
change in voice
dyspnea
pericardial air on x-ray

TREATMENT: 
Interstitial (subcutaneous) emphysema is not dangerous.
100% O2 will hasten recovery.
Must be monitored for other sequela = pericardial tamponade.

PNEUMOTHORX:   (TENSION PNEUMOTHORAX)
Ruptured airways allow air to escape into the pleural space.
Air trapped in the pleural space.

SYMPTOMS: 
Vary from mild to severe dyspnea with cyanosis.

TREATMENT: 
Monitor if mild.
100% O2 in severe cases, may require artificial ventilation.
Chest tube thoracotomy for severe = tension pneumothorax.
Needle thoracotomy in emergency.

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BAROTRAUMA & DYSBARISMS #6

January 25, 2007

ASCENT INJURIES:  “REVERSE SQUEEZE”

ASCENT   = expansion of the gas.     
The volume of gas increases by 2, doubles, every 33 fsw.

This is why it is an absolute rule that people with asthma cannot SCUBA dive!
ASTHMA and SCUBA diving = death
.
During ascent some of the air breathed at depth will get trapped in the alveoli and bronchioles, then during ascent that trapped air will expand and burst the alveoli and bronchioles, resulting in burst lungs and DEATH.

PULMONARY OVERINFLATION:
“Pulmonary Over Pressurization Syndrome” – POPS = “Burst Lung”
Usually occurs with a rapid ascent and breath holding.
Gas in the lung expands rapidly causing alveolar rupture.  (Boyle’s Law)
Alveolar rupture allows air to be forced into other tissues/spaces.
Resulting in escape of air under pressure into the:
Mediastinum = PNEUMOMEDIASTINUM/INTERSTITIAL EMPHYSEMA
Pleural Space = PNEUMOTHORAX
Pulmonary Venous System = ARTERIAL GAS EMBOLISM  (AGE)

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