An Unresponsive 38-Year-Old Man

Lars Grimm, MD, MHS; Malkeet Gupta, MS, MD; Joshua M. Kosowsky, MD

Disclosures

March 15, 2016

Discussion

The patient in this case had severe hypothermia, which was diagnosed on the basis of the core body temperature reading obtained using the rectal temperature probe.

Figure 2.

The patient's ECG demonstrated classic abnormalities associated with hypothermia; the most notable was profound sinus bradycardia. In addition, all leads showed the classic Osborne waves (also known as "J waves"), which were seen at the junction of the QRS complex and the ST segment (Figure 2) and are thought to represent alterations in the initial phase of ventricular repolarization.

Classically, Osborne waves are not thought to affect the ST segment; however, an ECG must be interpreted within the appropriate clinical context. In this case, the patient was found intoxicated, outdoors in near-freezing temperatures, and with a low core body temperature; as such, the apparent elevations of the ST segments should not be misinterpreted as evidence of myocardial injury. Other possible ECG findings of hypothermia that were not seen on this tracing include atrial and ventricular dysrhythmia, as well as prolongation of the PR, QRS, and QT intervals.[1]

The incidence of hypothermia is difficult to assess because many cases are not treated in medical centers. Between 1979 and 1998, hypothermia was listed as the cause of death for 13,970 people in the United States, an average of roughly 700 people per year.[2] More cases occur in urban settings as a result of the higher incidence of alcoholism, illicit drug use, mental illness, and homelessness. One half of all deaths involve patients older than 65 years of age, with an overall male-to-female ratio of 2.5:1.

Regions of the United States with colder temperatures or with greater day-to-night swings in temperature, as is found at high elevations or in deserts, report a higher incidence of hypothermia. The greatest number of cases are reported in Alaska, New Mexico, North Dakota, and Montana.

Patients at the highest risk have impaired cognition, inadequate shelter or clothing, or immobility. A smaller, secondary group of individuals at risk are those who venture into the wilderness for work or pleasure and are unprepared or experience an accident. The rapid increase in the popularity of outdoor sporting is causing the size of this secondary group to grow steadily.[3]

Body heat is lost via four different mechanisms. Radiation is heat loss from infrared emissions, usually in noninsulated areas of the body. Conduction is heat loss from direct contact, which is the primary means of heat loss in water immersion. Convection removes warmed air from around the body, resulting in increased heat loss during windy conditions. Evaporation cools the body via the removal of warmed water and is prevalent in dry, cold, windy environments.

Radiation accounts for 55%-65% of heat loss, conduction and convection each account for an additional 15% loss, and evaporation accounts for the remainder; however, these percentages are highly dependent on the local conditions. In this patient, convection could be expected to play a larger share because of the windy conditions.[3]

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