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Hypothermia
1. Hypothermia
David Caro, MD
University of Florida
Emergency Medicine
2. Introduction
Definition
Etiology
Epidemiology
Physiology
Impact on organ systems
3. Introduction (cont’d)
Response of organ systems
Identification
Treatment modalities
Sequelae
Review
4. Physiology
The hypothalamus is your
temperature control center
Core and peripheral receptors
provide temperature information
Various responses help maintain
temperature homeostasis
Cut heat loss; generate heat!
5. Physiology – Heat
Generation
Basal Metabolic Rate = 40-60
Kcal/m2
Movement, shivering can increase
the BMR 2 to 5 x normal
6. Physiology: The physics
of temperature
homeostasis
4 ways heat is lost
Radiation (65%)
Evaporation (25%)
Convection (5-10%)
Conduction (2-5%) (except in
immersion; cold water conductivity
32 times that of air)
7. Physiology
Our body responds to decreased
temperature by attempting to:
Decrease heat loss
Vasoconstriction
Behavior modification
Increase heat production
Shivering
Am J Physiol 1997 Feb;272(2 Pt
2):R557-62
8. Hypothermia-Definition
A core body temperature below
96.8oF
Mild hypothermia = 92 – 96.8oF
Moderate = 88 – 92oF
Severe = < 88oF
“They’re not dead until they’re
warm and dead.” One case report
of recovery after accidental 15.2oC
(59.4F) hypothermia.
9. Hypothermia –
Morbidity/Mortality
Mild hypothermia – very little
Moderate – one study showed a
mortality rate of 21% for moderate
hypothermia
10. Clinical features
Mild: shivering, loss of fine motor
control
Moderate: lethargy, confusion
Severe: pupillary dilation, coma,
cardiovascular irritability and
eventual collapse
14. Etiology
Increased Heat Loss
Exposure (cont’d)
Immersion
Significant risk begins in water colder than
25 C (72 F). The water temperature of
Lake Huron is approximately 4.6 C (40 F)
in May and is highest in August at 19 C
(66 F).
Hypothermia can occur rapidly during
cold-water immersion (one hour or less
when water temperature is below 45oF).
Core temp drops 0.3C in 20 min when
immersed in 22C (Am J Phys Med
Rehabil 1999 Jan-Feb; 78(1):33-8.
17. Impact on Organ
Systems
Respiratory
Altitude will decrease pO2
Temperature of inspired air
decreased
Airwarmed + humidified by
oral/nasal mucosa prior to hitting
lower airways
Expired air rich in warm water –
heat lost
18. Impact on organ
systems
Hemoglobin increasingly binds O2
as temperature drops
(oxyhemoglobin dissociation curve)
Hypoxia may occur due to
decrease offloading of oxygen
(Cardiovasc Surg 1999
Jun;7(4):425-31
19. Organ System Response
Acid-base balance
11/18 with decompensated
metabolic acidosis (Coll Antropol
1999 Dec;23(2):683-90
Most texts recommend not
correcting for temperature when
evaluating ABGs
20.
21. Impact on Organ
Systems
Cardiac
Repolarization becomes abnormal
with decreasing temperature
Osborn Wave – lead V3 or V4
Increasing cardiac irritability with
decreasing temperature
QT prolongation (0.45-0.688 vs.
0.343-0.444; Coll Antropol 1999
Dec; 23(2):683-90)
22. Osborn Wave
86% of hypothermic patients (Acad
Emerg Med 1999 Nov;
6(11):1121-6)
Voltage gradient due to action
potential notch in epicardium;
epicardium activated later, which
manifests as notching or J-point
elevation (Circulation 1996 Jan
15;93(2):372-9)
23.
24. Impact on Organ
systems
Cardiac
Mild: Tachycardia, hypertension,
increased CO
Moderate: Bradycardia,
Arrhythmias
Severe: Arrhythmias, hypotension,
decreased cardiac output
Below 30C, ventricular fibrillation
risk increases
25. Impact on Organ
Systems
Neurologic
Decreasing metabolic activity of
neurons; therefore, decreased O2
requirement
Linear decrease in CNS function
as temperature decreases
Neuron function stops below 20C
26. Organ System Response
Neurologic
Decline in mental status
Mild confusion
Delirium
Coma
Peripheral anesthesia
Ataxia
27. Impact on Organ
Systems
Renal
Hypothermia impairs renal
concentrating abilities
“Cold-induced diuresis”
Potential rhabdomyolysis → ATN
28. Impact on Organ
Systems
Gastrointestinal
Pancreatitis ± pancreatic necrosis
can develop due to HT
29. Impact on Organ
Systems
Hematologic
Hemoconcentration
Increased blood viscosity
Decreased flow in capillaries
Potential for thrombosis
Potential for DIC
30. Impact on Organ
Systems
Musculoskeletal
Temperature extremes can cause
crystallization of blood in
capillaries of extremities
Cutaneous vasoconstriction occurs
in response to lower ambient
temperature
32. Frostbite
Grade as burns
1st degree
Erythema, edema, burning
Swelling for ten days or more
Desquamation
Parathesias, aching, and necrosis
of the pressure points of the foot
Increased sensitivity to cold,
hyperhydrosis
33. Frostbite
Grading
Second degree
progresses to blister formation,
anesthesia, and deep color change
34. Frostbite
Third degree
involvesfull skin thickness and
extends into the subcutaneous
tissue
Subfascial pressure increases;
compartment syndromes are
common
35. Frostbite
4th degree
Destruction of entire thickness
Cyanotic, insensitive; hemorrhagic
blister formation.
Severe pain on rewarming
Dry gangrene can progress quickly
with mummification.
The line of demarcation becomes
obvious at 20-36 days and extends
into the bone in 60 or more days.
36. Trenchfoot
Caused by prolonged exposure of the
feet to cool, wet conditions.
The skin is initially reddened with
numbness, tingling pain, and itching then
becomes pale and mottled and finally
dark purple, grey or blue.
If circulation is impaired for more than 6
hours there will be permanent damage to
tissue.
If circulation is impaired for more than 24
hours the victim may lose the entire foot.
37. Hypothermia
Identification
Thermometry
Most thermometers’ lower
temperature limit is 93oF
A special low-temperature-reading
thermometer is necessary to read
temperatures lower than 93
38. Evaluation
ABCDEs are the priority
Handle patients gently
Begin passive rewarming
immediately
Cautious ACLS care (coming up)
39. Evaluation
History is essential
Environment/exposure
PMH
Medications
Exam – be complete!
Rectal temperature!
Vital signs
44. Treatment Modalities –
moderate hypothermia
ABCs – every patient
Airway, Breathing – warm,
humidified air by ETT or NRBfm
Circulation – IV access; warmed
crystalloid
All of the above
Bear Hugger
45. Treatment Modalities –
Severe Hypothermia
All of the above
Invasive modalities
NG, foley lavage
Pleural, peritoneal lavage
Dialysis or Cardiac bypass
46. Treatment Modalities
How effective are they?
Reflective Foil – 0.3C/hr Ann Emerg Med
2000 Apr; 35(40):337-45
Warmed IVF – 1.0C/hr J Clin Anesth
1998 Aug;10(5):380-5.
Warm IVF, Warm/humdified oxygen,
blankets – 1.4 C/hr Ann Emerg Med
1996 Apr;27(4):479-84
Bear-Hugger – 0.7C/hr Ann Emerg Med
2000 Apr; 35(40):337-45; IVF/humidified
O2/BH – 2.4C/hr Ann Emerg Med 1996
Apr 27(4):479-84
47. Treatment Ideas
Aviat Space Environ Med 1992
Dec;63(12):1070-6
Total immersion in 42C bath – 10.2C/hr
Blankets – 0.2C/hr
J Appl Physiol 1998 Nov;85(5):867-8
Subatmospheric pressure to limbs while
applying warm-water blanket increased
rewarming 10-fold over WWB alone
(13.6C/hr vs. 1.4C/hr)
49. Afterdrop
Paradoxical drop in core temp
during rewarming
Due to influx of cold blood from
periphery
Can precipitate arrhythmias
50. Treatment of sequelae
Ventricular fibrillation
Cold heart very irritable
Will not respond to multiple rounds
of drugs
Shock – 3 times, then wait until
warm
Bretylium your drug of choice
(ACLS Guidelines)
51. Treatment of sequelae
Renal Failure
Rhabdomyolysis : force fluids;
alkalinization
Cold-diuresis : fluids, watch
electrolytes
52. Treatment of sequelae
Frostbite
Narcotics!
Warm water immersion – warm,
wet heat is best.
Do NOT warm then allow to
refreeze. Better to keep frozen
until definitive care is available.
53. Treatment of sequelae -
Afterdrop
Try to avoid – aggressive
rewarming
Expect arrhythmias, be prepared to
treat
54. Hypothermia
Summary
Physiology plays a HUGE role
Etiology
Treatment
History is key
Rectal temp with low-reading
thermometer
Treat temperature aggressively,
but handle patient gently
Watch for afterdrop!
55. Text References
Ann Emerg Med 1993 Feb;22(2
Pt 2):370-7
Wilderness Medicine – Auerbach
Rosen’s Principles of
Emergency Medicine