Impacts of Hypothermia

1. Impacts of Hypothermia Cindy Fehr Malaspina University-College BSN Nursing Program Nursing 335 – Fall 2005

2. Hypothermia • Body functions best at core temp 36.4°C – 37.5 °C (97.5 °F – 99.5 °F) • When core temp < 95 °F, body loses heat faster than can produce it • Causes every organ system to be under stress & potential for permanent disability or death increases • Hypothermia defined as temperature < 96.8 °F or 36 °C at two sites (e.g. rectum & esophagus)

3. Hypothermia Classification • Primary hypothermia • Occurring with accidental excessive or prolonged exposure to cold • Secondary hypothermia • Due to failure of thermoregulation by the body

4. Hypothermia Classification cont. • Mild Hypothermia • 86.9 - 95 °F or 35 - 32 °C • Moderate Hypothermia • 82.4 - 89.6 °F or 28 - 32 °C • Severe Hypothermia • Less than 82 °F or 28 °C

5. Normal Body Response • Activation of SNS • Norepinephrine released to  muscle tone & shivering   thermogenesis • Peripheral BV constrict to conserve heat & shunt blood from skin to core • If core temp continues to fall, adaptive mechanisms fail and vasodilation occurs  heat loss from core to periphery

6. Factors Increasing Risk • Extremes of Age • Very young and old have less sq for insulation, insufficient heat generation mechanisms (shivering), inadequate behavioral responses (less recognition of cold environment and what to do) • Traumatic Injury or Pathologic Condition of CNS • E.g. Stroke: can disrupt hypothalamic response • ⅔ bleeding trauma arrive hypothermic to ED • Assessment & treatment procedures tend to worsen hypothermia  lack of clothing, open body cavities, fluid replacement, meds (muscle relaxants, sedatives, anesthetics, opioids)

7. Factors Increasing Risk cont. • Endocrine Disorder • E.g. hypothyroidism:  metabolic rate, heat production, behavioral responses • Alcohol Consumption • Dilates BV,  heat loss,  thermogenesis, impair behavioral responses • Outdoor Occupations, Activities •  exposure

8. Factors Increasing Risk cont. • Medications • E.g. phenothiazines, benzodiazepines  centrally mediated vasoconstriction • Anaesthetics can block shivering • Other Disorders • E.g. hepatic failure, sepsis, burns  disrupt thermoregulation

9. Effects of Hypothermia • Depends of severity of hypothermia, underlying cause, other co-morbid factors (age, underlying disease process & chronic health challenges) • Affects every organ system • Neurologic Effects • Each 1°C  in temp = 6-7%  in cerebral blood flow • Confusion, hallucinations, maladaptive behaviors, impaired judgment,  drowsiness, ataxia, dysarthria, amnesia • < 82.4 °F or 28 °C induces coma

10. Effects of Hypothermia cont. • Cardiovascular Effects • Normally SNS stimulates peripheral vasoconstriction, HTN, tachycardia, CO • Cooling of body temperature  HR,  CO,  risk arrhythmias (ventricular fibrillation or asystole) • V fib and asystole can spontaneously occur temp <25°C • In event of cardiac arrest  response to defibrillation, pacemaker stimulation, cardioactive drugs, metabolism of drugs  active core rewarming must be priority treatment • Metabolic acidosis from impaired O2 delivery to tissues d/t peripheral vasoconstriction  cellular metabolism from aerobic to anaerobic, serum lactate levels   metabolic acidosis (pH 7.30) • DIC risk  slows clotting (impairs platelet aggregation & adherence), reduces production of clotting factors; acidosis also affects normal platelet function

11. Effects of Hypothermia cont. • Respiratory Effects • Mild hypothermia  tachypnea • Moderate to severe hypothermia  progressive  RR & volume of ventilation, bronchospasm, loss of protective airway reflexes • Can lead to pulmonary edema and apnea in severe cases • Respiratory acidosis from marked respiratory depression &  LOC  retaining CO2 • Respiratory arrest with core temp <24 °C

12. Effects of Hypothermia cont. • Renal Effects • Peripheral vasoconstriction  large fluid shifts to central circulation  triggers “cold diuresis” in attempt to remove excess fluid and  dehydration • With progressive hypothermia   renal blood flow, oliguria, anuria • GI Effects •  liver metabolism of drugs & elimination of toxins  bleeding • GI smooth muscle movement slows  paralytic ileus

13. Interventions for Hypothermia • keep flat  prevent worsening hypotension • No sudden/rough movements, excessive activity  prevent lethal arrhythmia • Passive External Rewarming • Tx for mild hypothermia • Relies on patient’s metabolism to rewarm body • Remove wet clothing, sheets • Applying dry blankets or insulating material (extra layers, sleeping bag, hypothermia blanket); especially head cover • Increase room temperature

14. Interventions for Hypothermia cont. • Active External Rewarming • Tx for moderate hypothermia • Forced warm air, fluid-circulating heat blanket, radiant heat source, heating pads • Core Rewarming • Tx for severe hypothermia • Invasive • Inhalation of warm, humidified O2 • warmed IV NS • warmed gastric, colonic, mediastinal, closed throacic or peritoneal lavage • Extracorporeal rewarming with hemodyalysis • Cardiopulmonary bypass