Blood test findings

Hypothermia is most commonly diagnosed by measuring the core body temperature using specialized low-reading rectal thermometers or rectal thermistor probes. Other tests may be required for confirmation or further evaluation.

• Hematology
• Complete blood count (CBC) may reveal elevated hemoglobin due to hemoconcentration
• Clinical coagulopathies are usually present in hypothermic patients, as certain enzymes involved in coagulation pathways are temperature dependent. In such patients, rewarming the specimen to 37°C usually will yield normal results
• Since white blood cell (WBC) count is not an accurate indicator of infection, the decision of whether a bacterial infection might be present, especially in high risk individuals such as elderly patients, Immunocompromised patients, and neonates should in no way be influenced by the WBC count
• Platelet counts drop with reduction in temperature, but normalize following rewarming
• Arterial blood gas (ABG) analysis
• ABG analysis may reveal metabolic acidosis along with either respiratory acidosis or alkalosis. It is probably appropriate to make clinical decisions based upon temperature uncorrected values on ABG or VBG
• Serum chemistry
• Electrolyte levels, particularly potassium levels, should be monitored regularly, as they tend to rapidly fluctuate during resuscitation due to fluids administered, potential renal failure and other major acid-base changes that can occur as tissue reperfusion occurs
• Serum glucose levels need to be monitored as hypoglycemia can commonly occur and may require treatment
• Assessment of serum creatine kinase, both initially and serially, is indicated to evaluate for rhabdomyolysis
• Assessment of creatinine, both initially and serially, is indicated to evaluate for acute renal failure (usually secondary to rhabdomyolysis) or acute tubular necrosis
• Elevated levels of liver enzymes and serum amylase or lipase suggest pancreatitis or hepatic impairment
• In avalanche victims, an initial serum potassium of >12 meq/L (mmol/L) in a buried patient in cardiac arrest portends to unlikely survival

Other laboratory test findings

• Blood culture may be indicated in some cases to evaluate for bacteremia
• Urinalysis and urine culture can be used to evaluate for presence of urinary tract infection

Radiographic findings

• A head computed tomography (CT) may be useful in the evaluation of altered mental status when causes such as stroke, head trauma, or mass occupying lesion are being considered
• A chest x-ray can be useful in the evaluation of aspiration pneumonia or pulmonary edema

Other diagnostic test findings

• Electrocardiogram (ECG)
• Various electrocardiographic changes may be observed in hypothermic patients
• Arrhythmias
• Asystole
• Atrial fibrillation/flutter - including with slow ventricular response
• Bradycardia
• Ventricular fibrillation
• Inverted T wave
• J waves (Osbome waves) which appear at junction of QRS and ST interval
• Prolongation of PR, QRS and/or QT intervals

General treatment items

• ABC's must be actively managed along with the priorities laid out below
• Initial management of hypothermia relates to severity of symptoms and degree of hypothermia. Severely hypothermic patients may require aggressive invasive rewarming, whereas, mildly hypothermic patients may be adequately treated with external rewarming
• Patients with severe hypothermia often require active internal rewarming or extracorporeal warming. Such patients require continuous monitoring, may require intubation, CPR and other advanced critical care maneuvers
• Alert, shivering hypothermic patients generally only require removal from adverse environment and passive rewarming with insulation (blankets)
• Wet clothing should be promptly removed and the patient should insulated at minimum, and may benefit from external rewarming blankets (e.g. such as a Bair Hugger which is a warmed forced air cover)
• The healthcare provider should be aware of the potential of "after-drop," which is the situation in which the patient's core temperature further cools after being removed from the adverse environment. This relates to return of blood from the periphery and is a risk to be monitored for in all patients. Significant worsening in clinical condition can occur due to after-drop. By providing internal core rewarming prior to external warming, this risk can be minimized
• Bedside glucose should be assessed and hypoglycemia treated, as glycogen stores are often depleted. Initial treatment will usually consist of 25-50 grams of IV dextrose (50-100 mL of 50% dextrose) followed by an infusion of lower concentrations of dextrose mixed with the bolus IV fluids or administered separately with serial monitoring of glucose
• Aggressive fluid resuscitation using warmed (40-42°C) hypotonic crystalloid solutions is a routine part of therapy in moderate to severe hypothermia, as most patients have had cold diuresis and will be significantly dehydrated (and may also have rhabdomyolysis)
• Oxygen is recommended, and where available, warmed and humidified
• Rough handling or nasogastric tube insertion should be avoided as movement may trigger ventricular fibrillation; however, life-saving interventions such as intubation, CPR, or administration of pressor agents are often necessary and should be performed as gently as possible
• Thiamine may be indicated in those with any indication of heavy chronic ethanol use (or if any suspicion thereof)
• Patients with a history of adrenal insufficiency may be treated with corticosteroids (may also be indicated in patients who fail to normalize their temperature after appropriate warming)
• Patients with suspected infection should be given appropriate antibiotics
• Careful consideration of whether an underlying medical, traumatic or toxicologic issue is present which led to the patient becoming hypothermic is required as this will require concomitant treatment in addition to the hypothermia

• Bradycardia is common in hypothermia, careful evaluation of carotid pulse for a minimum of 30-60 seconds is recommended before considering the patient to have no cardiac output and start CPR. Doppler or echocardiography, if available can be useful
• Chest compression may be complicated by a frozen thorax
• Defibrillation for ventricular fibrillation, at maximum joules is indicated up to 3 times in patients 30°C; however, if unsuccessful, withhold further attempts as defibrillation until the patient is >30°C
• Do not administer standard cardiac arrest ACLS type drugs until the patient is >30°C
• Patients whose temperatures are between 30-35°C can have standard ACLS drugs, but the interval between doses should be doubled. Once body temperature is >35°C, normal intervals between doses can be utilized
• Other dysrhythmias, such as atrial fibrillation, usually resolve spontaneously with rewarming

• Active or passive rewarming techniques may be used based on the severity of hypothermia, urgency of clinical situation, and other patient factors
• Passive rewarming
• Passive rewarming, also known as spontaneous rewarming, involves prevention of further heat loss by keeping the patient dry, protected from wind, and covered with blankets to permit thermogenesis and help reestablish normal temperature
• The rewarming technique is very slow with an average temperature increase of 0.38 °C per hour
• This is appropriate for all patients, and is generally the only therapy needed for alert and shivering patients with hypothermia
• Active rewarming
• Active rewarming may be either external (surface rewarming) or internal (central rewarming)
• Surface rewarming
• Technique involves direct heat application to the body surface in presence of intact circulation
• Forced-air warming systems (eg, Bair Hugger® Therapy) uses a specialized blanket that circulates warm air around the patient's body
• Surface rewarming can lead to complications such as "after-drop" which results from the return of cold blood from peripheral to central circulation. After-drop is associated with significant mortality
• Other complications include rewarming acidosis due to movement of peripherally accumulated lactic acid to central circulation, and rewarming shock due to venous pooling during peripheral vasodilation
• Central rewarming
• Among invasive rewarming techniques, the simplest is infusion of warmed IV fluids heated to 40-43°C with a microwave or blood warmer along with administration of warmed humidified oxygen at 40°C (104°F). Combined methods increase the core temperature by 1°C to 2°C/hour
• Extracorporeal blood warming is the most efficient, and includes arteriovenous or venovenous rewarming, warm hemodialysis, or cardiopulmonary bypass. This method increases core temperature by 1°C to 2°C (3.6°F) every 5 minutes. This technique is preferred in patients with cardiac arrest - it is however only available at tertiary centers. Extracorporeal membrane oxygenation (ECMO) may be a preferred rewarming procedure as it reduces the risk of cardiorespiratory failure, which is common with severe hypothermia
• When extracorporeal blood warming is not available, central rewarming can also be achieved through warm lavage of body cavities (e.g., gastric lavage, peritoneal cavity, chest through thoracostomy tubes, and bladder). Such techniques, when properly employed; often using multiple sites for lavage when necessary with 40°C warmed saline is capable of warming rates of 1-4°C per hour

Medications indicated with specific doses

• Dextrose [IV]
• Adult Dosing
• Pediatric Dosing
• Thiamine [IM/IV]
• Adult Dosing

Dietary and activity restriction

• Adequate fluid intake and consumption of energy-rich foods are essential to prevent dehydration and malnutrition to allow the body to produce appropriate heat
• Alcohol consumption should be avoided, especially in excess when exposure to a cold environment is possible, as it causes vasodilation which promotes hypothermia
• In patients who are alert and shivering, exercise, if tolerated is usually more efficient at rewarming that shivering, but close observation for after-drop is required as this is a risk
• Use of warm liquids is permitted if patient is fully conscious and able to swallow

Disposition

• Admission criteria
• Moderate and severely hypothermic patients require hospitalization, often to an intensive care unit
• Patients with mild hypothermia (>32°C) with no comorbidities who are successfully rewarmed with no complications may be discharged if entirely well after 8-12 hours of observation
• Discharge criteria
• Patients with mild hypothermia may be discharged as above
• Patients with more significant hypothermia will require stabilization and observation in hospital and only once well for 1-2 days with serial observations, and persistent stable vital signs, no evidence of complications, and clinically well, may discharge be appropriate
• Evaluation of the condition that led to the initial presentation with hypothermia is required to decrease additional presentations for the same (e.g. poor social situation, homelessness, alcoholism, underlying medical condition)

Monitoring

• Cardiac rhythm, glucose and electrolyte levels, renal function, creatine kinase levels, urinary output, and arterial blood gases should be monitored during a hypothermic episode
• Patients should be evaluated for presence of underlying comorbidities after the hypothermic episode

Complications

• Abnormal erythropoiesis
• After-drop
• Cardiac arrest
• Cardiac arrhythmias
• Coagulopathy
• Death
• Heart failure
• Hyperkalemia
• Hypoglycemia
• Liver dysfunction
• Myocardial ischemia/infarction
• Neurological dysfunction
• Pancreatitis
• Renal failure
• Wound infection and delayed healing

Prevention

• Preventive measures for accidental outdoor hypothermia include
• Abstinence from alcohol, as it causes vasodilation, increases likelihood of poor judgment and trauma
• Adequate fluid intake to prevent dehydration
• Avoiding overexertion
• Identifying risk factors and early signs of hypothermia
• Use of adequate protective clothing that is multi-layered, windproof, insulated, and permits evaporation
• Use of warm fluids when in a cold environment
• Indoor hypothermia can be prevented by maintaining appropriate indoor ambient temperature (~75°F) and humidity (40% to 50%)
• Elderly individuals and their caregivers in the U.S. may seek financial assistance for heating expenses through government initiatives such as Low Income Home Energy Assistance Program (LIHEAP)
• Perioperative hypothermia can be effectively prevented using strategies such as preoperative evaluation of at-risk patients, decreasing skin exposure, providing sufficient bed linen during transfers, and patient education regarding significance of keeping warm

Prognosis

• The prognosis depends on the severity of hypothermia, and the presence of comorbidities such as extremes of age, heart disease or alcoholism. The overall mortality rate is approximately 40% for moderate-severe hypothermia, and exceeds 50% with comorbidities
• Patient survival may significantly relate to clinical status and underlying comorbidities rather than the rewarming technique
• Documented cases demonstrate favorable outcomes in severe cases, such as successful resuscitation from hypothermia at temperatures as low as 14.2°C (57.6 °F) in an infant and 13.7°C (56.7°F) in an adult
• A case report in a patient who was severely hypothermic detailed successful resuscitation after 6.5 hours of CPR
• Severe hyperkalemia, shock, and infection are indicators of poor prognosis
• Prognostic factors associated with outcomes in hypothermia include
• Age
• Need for mechanical ventilation
• Need for vasopressor drugs
• Rewarming time
• Serum bicarbonate concentration
• Simplified Acute Physiology Score (SAPS II) score
• Systolic blood pressure

Pregnancy/pediatric effects on the condition

• Pregnant women are at a high risk of developing hypothermia due to pregnancy-induced vasodilation, anesthesia, medications, and blood loss with rapid fluid replenishment during parturition
• Hypothermia during pregnancy may lead to complications such as hypotension, arrhythmias, augmented oxygen uptake, respiratory depression, and disseminated intravascular coagulation (DIC)
• Maternal hypothermia be associated with a decreased fetal heart rate, which returns to normal following rewarming

Synonym

• Systemic cold injury

ICD-9-CM

• 991.6 Hypothermia

ICD-10-CM

• T68 Hypothermia

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