Chapter 30A - Cold Emergencies Flashcards
What structure controls body temperature?
The hypothalamus controls thermoregulation - it directs vasodilation to dissipate heat, or vasoconstriction to conserve it - it stimulates shivering to generate heat, and swearing to shed heat.
Describe how the body generates heat
Heat is produced
- by cellular activity - basal metabolic rate
- by muscle activity (exercise, shivering)
- environmental heat is added
- drugs (metabolic stimulants such as amphetamines
Describe how the body deals with a heat increase, & what problem it creates, or what problem we must observe for:
When the body generates or picks up environmental heat faster than it can get rid of it, it will try to dump heat first by radiation, causing vasodilation of vessels at the surface of the skin. The patients appears redder than usual, and because the skin has the heat sensor, they also “feel” warmer. If that is not enough to correct the overheating, the body will then start to sweat, using evaporation to assist cooling. This causes the skin to become cool and wet. The skin color may become pale at this point due to some surface vasoconstriction brought about by cooling. A significant problem that produces symptoms in the patient is the vasodilation causes the central, vital organs to receive less blood because it is being sent to the surface. As the sweating progresses, there is a loss of body water, leading to hypovolemia. Both contribute to symptoms similar shock.
Describe how the body deals with a heat decrease and what problems it creates, or what problems we must observe for:
When the body loses heat faster than it can make it, it will try to conserve heat first by stopping radiation loss, causing vasoconstriction of vessels at the surface of the skin. The patient appears paler than usual, and because the skin had the heat sensor, they also “feel” cooler. This causes the skin to become cool. The skin color will become pale at this point due to surface vasoconstriction. The benefit here is that cold blood is trapped at the surface, leaving the body’s warm blood for the vital organs. However, there will be a “cold diuresis” as the surface constricts, blood moved into vital organs - the kidneys detect this increase in blood volume and mistakenly eliminates it as urine.
Patients who have been hypothermic for some period of time are usually hypovolemic from this “cold diuresis” and are also usually in need of urinating.
There is also created a phenomenon called “shell vs. core blood” where at the surface of the skin there is a shell of very cold blood, even when the core has a fairly normal temperature. The core can be badly affected if this very cold “shell” blood suddenly is returned to the heart before it is warmed.
If the vasoconstriction is not enough to correct the heat loss, the body will then start to shiver, using skeletal muscular activity to generate heat. This creates a huge increase in oxygen consumption.
Radiation
Heat is radiated from a warm source to the cooler environment = right off the surface of the skin. The rate of loss is proportional to the temperature difference at the skin surface. Stops when ambient exceeds 86 F
Stop it by covering the skin, especially the head
Convection
Heat is lost through movement of surrounding air currents carrying away warm air from the skin, bringing in cooler air
Stop it by covering the patient with a blanket to stop drafts
Conduction
Heat is lost to objects (like the ground) through direct contact. Rate of loss depends on the thermal conductivity of the object (may be 10-32 times that of radiation and convection)
Stop it by insulating the patient from cold objects - remember this loss is mostly down to the surface they are lying on.
Evaporation
Heat is loss as liquid absorbs heat and then dissipates heat to the surrounding air. Rate of loss is 240x that of radiation and convection. Virtually stops when ambient humidity exceeds 65%
Stop by getting patients skin clothing dry
Respiration
Heat is warning up cold inhaled air, and then exhaling warm air. Rate of loss is a function of ambient temperature (it rarely is more than 5% and cannot be recovered or prevented. At 5 F it may amount to 15% of body heat loss = still not very significant)
Get patient in Warm room
99F - 95F S/S
Body attempts to maintain temperature by constricting, increasing metabolic rate, pulse & BP rise, muscle tone rises - as you near 94F, shivering hits maximum
You are really just “cold” not hypothermic yet. Tympanic and rectal are most accurate, oral may at least show a “minimum” temperature.
94F = mild hypothermic
94-91 s/s
Hypothermia begins -
amnesia (forget tasks) Dysarthria Poor judgement Maladaptive (stupid) behavior Normal BP Tachycardia Hyperventilation
Around 91F, cold diuresis, ataxia, and apathy develop
Stupor
25% decreases in oxygen consumption
Shivering stops
86F - 83F s/s
Progressive decrease in level of consciousness, pulse and respiration
A-fib or other dysrhythmias
Pupils dilate
Paradoxical undressing
CPR or violent shaking can set off v-fib
Drugs and defibrillation won’t work below 86F
82F - 80F s/s
Loss of reflexes
Lack of voluntary movement
Pulse, respirations very low (both half of normal)
BP may be undetectable due to decreased pumping and peripheral vasoconstriction
Decreased v-fib threshold
50% decrease in oxygen consumption
Check pulse for 30-45 seconds
80F - 78F s/s
Death likely - severe acid-base imbalance
No reflexes no response to pain.
Death usually due to v-fib
