Hypothermia

1
Hypothermia

• Hyperthermia

2
Hypothermia

• Core temperature lt35 C
• Causes
• Exposure to low environmental or water temps
• Alcohol intoxification
• A primary neurological insult (stroke)
• Thermoregulatory compromise (spinal cord injury)
• Predisposing factors (hypothyroid/hypopituitarism)
  
• Drugs that alter cold perception, cause
  vasodilation, or inhibit heat generation
  (barbiturates)
• Induced hypothermia during cardiac or neurosurgery

3
Hypothermia, cont.

• Progressive effects
• Confusion and lethargy
• Myocardial irritability
• Ventricular fibrillation, anuria, fixed pupils,
  coma
• Respiratory arrest
• asystole

4
Clinical features of hypothermia

• Respiratory
• lt33 C respiratory depression
• lt20 C respirations cease
• Renal
• Initial diuresismay cause hypovolemia on
  rewarming
• CNS
• 33-35 confusion
• lt30 coma
• lt20 EEG activity stopsmuscle rigidity
• EKG
• Late QRS widening
• J wave at lt33 C
• Long PR intervals
• Long QT interval

5
Clinical features, cont

• Cardiac effects
• Purkinje fibers lose conduction advantage,
  resulting in arrhythmias
• lt33 bradycardia, atrial fib, cardiac failure
• lt28 spontaneous v fib
• lt20 asystole
• Blood sugar effects
• Initially high blood sugar due to low insulin
  secretion and peripheral resistance
• Later hypoglycemia
• Metabolic effects
• BMR falls by 6 per degree C
• lt30 shivering stops
• pH falsely low
• Left shift of oxyHb curve
• Metabolic acidosis

6
Clinical features, cont

• Other effects
• Infection risk increased
• Impaired clotting
• DIC
• Venous thrombosis
• Hypothyroidism, hypopituitarism, hypoadrenalism
  all predispose a patient to hypothermia

7
Management of hypothermia

• Oxygen therapy
• Prevention of further heat loss
• Treatment of underlying cause
• Rough handling and tracheal intubation may
  precipitate life-threatening arrhythmias that may
  be resistant to therapy
• CPR is performed as normal, but cardioversion is
  ineffective until the core temp has increased gt30

8
Rewarming the Patient

• Caution is requiredyou cant re-warm too quickly
• If the temp is gt33, then generally passive
  external warming is all that is needed
• Warm room temp
• Lots of covers
• Warming blankets (active external warming) are
  controversial peripheral vasodilation from the
  blanket could decrease organ perfusion and
  increase mortality
• Internal rewarming is used if the hypothermia is
  severe (lt33)
• Warm IV fluids
• Warm inhaled gas
• Warm gastric, bladder, or pleural lavage
• Hemodialysis or peritoneal lavage
• Cardiopulmonary bypass

9
Hyperthermia

• Core temperature gt37.5C
• Potentially lethal if gt40 C
• Associated with increased metabolic rate,
  increased CO2 production, metabolic acidosis
• Sweating and vasodilation cause a relative
  hypovolemia
• Epilepsy, neurological impairment, acute renal
  failure, rhabdomyolysis, and myocardial ischemia
  may follow

10
Causes of hyperthermia

• Infection/pyrogens
• Sepsis, burns, transfusion reactions, allergy
• Increased heat production
• Muscular activity, exercise, seizures, rigidity,
  agitation
• Drug related salicylates, thyroxine,
  sympathomimetics, tricyclic antidepressants,
  serotonin reuptake inhibitors, cocaine,
  amphetamines
• Hypothalamus injury (stroke)
• Disease related malignancy, vasculitis,
  arthritis
• Endocrine hyperthyroidism, phaeochromocytoma
• Reduced heat loss
• Cooling failure
• Heat stroke
• Drug related (anticholinergics)
• Malignant hyperthermia
• Neuroleptic malignant syndrome

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Causes, cont

• Heat stroke
• Affects the elderly and pt with thermoregulatory
  disorders
• Inability to dissipate heat during hot weather
• Extreme exercise, confined garments, and hot
  environments are potential causes
• Malignant hyperthermia
• A rare autosomal dominant trait that causes
  excessive muscle heat production due to altered
  calcium kinetics
• Muscle rigidity, sudden hyperpyrexia,
  tachycardia, metabolic acidosis, and hypercapnia
  may occur during or shortly after anesthetic
  administrationcommon with succinylcholine

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Management of hyperthermia

• Stopping precipitating drugs, fluid replacement,
  correction of hyperkalemia, renal replacement
  therapy, and seizure prophylaxis
• Cooling
• Exposure, wetting, and fans
• Ice packs to the axilla and groin
• Cold IV fluids
• Iced gastric or peritoneal lavage
• Hemofiltration
• Cardiopulmonary bypass
• Drug therapy
• Dantrolene a muscle relaxant that uncouples
  actin and myosin
• Other muscle relaxants
• Anticholinergics
• Mannitol reduces myoglobin-induced renal damage