Accidental hypothermia

Background

1. Definition: Core Temp <35C (95F)
2. Severity:
   1. Mild hypothermia: 32-35C (90-95F)
   2. Moderate hypothermia: 28-32C (82-90F)
   3. Severe hypothermia: <28C (82F)
3. Immersion in any water colder than 16-21C (60.8-69.8F) can lead to severe hypothermia

DDx

1. Accidental (environmental) exposure
2. Metabolic disorders
   1. Hypoglycemia
   2. Hypothyroidism
   3. Hypoadrenalism
   4. Hypopituitarism
3. Hypothalamic and CNS
   1. Head trauma
   2. Tumor
   3. Stroke
   4. Wernicke encephalopathy
4. Drugs
   1. Ethanol
   2. Sedatives-hypnotics
5. Sepsis
6. Dermal disease
   1. Burns
   2. Exfoliative dermatitis
7. Acute incapacitating illness
8. Massive fluid or blood resuscitation

Diagnosis

ECG

1. Dysrhythmias a/w temp <30C (86F)
2. Typical sequence is sinus brady > a fib w/ slow ventricular response > v-fib > asystole
3. Other ECG findings:
   1. Osborn (J) wave
   2. T-wave inversions
   3. PR, QRS, QT prolongation
   4. Muscle tremor artifact
4. AV block
   1. PVCs

Cold-induced bronchorrhea, along with a depression of cough and gag reflexes, makes aspiration pneumonia a common complication

The combination of hemoconcentration, cold-induced increase in blood viscosity, and poor circulation may lead to intravascular thrombosis and embolic complications. Disseminated intravascular coagulation may occur because of the release of tissue thromboplastins into the blood stream, especially when circulation is restored during rewarming. Because cold inhibits both platelet function and the enzymatic reactions of the coagulation cascade, hypothermic patients are prone to bleeding.

Treatment

General

1. Handle pt gently
   1. V-fib may be induced by rough handling of pt due to irritable myocardium
2. O2
   1. Hypothermia causes leftward shift of oxyhemoglobin dissociation curve
3. IVF
   1. Reasons:
      1. Hypothermia > impaired renal concentrating ability > cold diuresis
      2. Pts are prone to rhabdo
      3. Intravascular volume is lost due to extravascular shift
4. CPR
   1. Only perform if pt truly does not have a pulse (unnecessary CRP may lead to V-fib)
   2. Spend 30-45s attempting to detect respiratory activity and pulse before starting CPR
5. Dysrhythmias
   1. Rewarming is treatment of choice
      1. Most dysrhythmias (e.g. sinus brady, a-fib/flutter) require no other therapy
      2. Activity of antiarrhythmics is unpredictable in hypothermia
      3. Hypothermic heart is relatively resistant to atropine, pacing, and countershock
   2. V-fib
      1. May be refractory to therapy until pt is rewarmed
      2. Attempt a single defibrillation attempt
         1. If unsuccessful continue CPR and attempt defibrillation again once temp >30C (86F)

Rewarming

1. Passive
   1. Techniques
      1. Removal from cold environment
      2. Insulation
   2. Consider in pt w/ mild hypothermia who is able to generate intrinsic heat
2. Active External
   1. Techniques
      1. Warm water immersion
      2. Heating blankets
      3. Radiant heat
      4. Forced air
   2. Rewarm trunk BEFORE the extremities
      1. Otherwise may lead to hypotension, core temperature afterdrop
   3. May be ineffective in pts w/ poor perfusion or in cardiac arrest
   4. Consider in:
      1. Moderate-severe hypothermia
      2. Mild hypothermia in pt who is unstable or cannot generate intrinsic heat
      3. Failure to respond to passive external rewarming
3. Active Internal
   1. Techniques
      1. Heated IV fluids
         1. If central line is placed avoid irritating the heart
      2. GI tract lavage
      3. Bladder lavage
      4. Pleural lavage
      5. Peritoneal lavage
   2. Consider alone or along with active external warming in:
      1. Severe hypothermia
      2. Moderate hypothermia which fails to respond to less aggressive measures

Because a number of hypothermic patients are thiamine-depleted alcoholics (and because Wernicke disease may cause hypothermia), consider giving IV thiamine, 100 milligrams. Between 50 and 100 mL of 50% glucose should be administered if a test-strip serum glucose measurement is low or if a rapid glucose test is unavailable

thorough search for infection is indicated.

Hydrocortisone (100 milligrams) should be given to the patient who has a history of adrenal suppression or insufficiency or is in myxedema coma. Routine corticosteroid therapy is not necessary.

In severe hypothermia or hypothermia secondary to an underlying illness, patients may fail to rewarm passively; active rewarming is then indicated. Active rewarming is also indicated for patients with cardiovascular compromise.

IV fluids and blood should also be warmed to 40°C (104°F) before administration, especially in patients receiving massive volume resuscitation. Commercial fluid warmers allow the temperature of infused fluids to be precisely controlled.

Both inhalation rewarming and administration of heated fluids should be used in all patients, because these are simple techniques without complications, as long as the temperature is controlled.

lavage with warmed saline is simple, and patients can be lavaged with large volumes of warm fluid over a short time. However, the obtunded hypothermic patient may develop pulmonary aspiration if lavaged with an unprotected airway. The urinary bladder can also be lavaged with warm saline solution through a urinary drainage catheter.

Pleural lavage using thoracostomy tubes has provided effective rewarming in animal studies and a few human cases.15 Lavaging the left thoracic cavity delivers heated fluid in close proximity to the heart, which potentially allows rapid cardiac warming. Two thoracostomy tubes (for fluid inflow and outflow) generally have been employed. If this technique is chosen, care must be taken to monitor the net fluid infusion, because increased intrathoracic pressure and tension hydrothorax may complicate the procedure. The risk of precipitating dysrhythmias during chest tube insertion is unknown.

Approach to Rewarming Patients with mild hypothermia, who are still in the excitation stage, generally improve spontaneously, as long as endogenous heat production mechanisms are functional. At temperatures of >30°C (>86°F), the incidence of dysrhythmias is low, and rapid rewarming is rarely necessary.

By far the most important consideration in the selection of rewarming techniques is the patient's cardiovascular status; a secondary consideration is the presenting temperature. Some feel that patients with a stable cardiac rhythm (including sinus bradycardia and atrial fibrillation) and stable vital signs do not need rapid rewarming, even if the temperature is very low. They recommend passive rewarming and noninvasive rewarming modalities (e.g., forced-air rewarming, administration of warm moist oxygen, and use of warm IV fluids) in this setting. Others argue that profoundly hypothermic patients, even if currently in "stable" condition, are at risk of developing life-threatening dysrhythmias. They recommend rapid rewarming until the temperature has reached 30°C to 32°C (86.0°F to 89.6°F) to minimize the time period during which dysrhythmias may develop. The relative merits of each approach have not been studied.

Patients with cardiovascular insufficiency or instability, including persistent hypotension and life-threatening dysrhythmias, need to be rewarmed rapidly.

Unless there is strong evidence that the patient is incapable of survival, resuscitative efforts should be continued until core temperature is at least 30°C to 32°C (86.0°F to 89.6°F).

Source

Tintinalli