Clinical Pearls & Morning Reports

Posted by Carla Rothaus

Published October 12, 2022


What are urban heat islands?

In the past 20 years, there has been a 54% increase in heat-related mortality among persons older than 65 years of age, and more than one third of all global warm-season heat-related deaths are attributable to climate change. Read the NEJM Clinical Practice Article here.

Clinical Pearls

Q: Name some of the conditions that may worsen during periods of high temperature.

A: Beyond traditionally recognized heat-related illnesses, many diseases are “heat sensitive,” meaning that they are exacerbated or triggered by exposure to heat. Multiple studies have shown increases in the occurrence and exacerbations of a wide range of conditions during periods of high temperature, including ischemic heart disease, cardiac dysrhythmias, ischemic stroke, asthma and chronic obstructive pulmonary disease, respiratory tract infections, hyperglycemia, kidney failure, neuropsychiatric disorders (e.g., psychosis, suicides, homicides, anxiety, and depression), and adverse birth outcomes, such as preterm delivery and small-for-gestational-age infants.

Q: What are urban heat islands?

A: Urban heat islands are areas of high building density, which absorbs and then re-emits heat from the sun, resulting in “islands” of higher temperatures; temperatures in these areas can be 1° to 7°F (0.6° to 3.9°C) hotter, on average, than outlying areas and have much higher nighttime temperatures, as a result of re-radiation of heat from the surrounding environment. In the United States, the residents of urban heat islands are disproportionately low-income Black communities and other underrepresented racial and ethnic groups because of historically racist zoning practices (i.e., “redlining”).

Morning Report Questions 

Q: How common are heat-related deaths outside of heat-wave alert periods?

A: In many communities, climate change is increasing the frequency, duration, and severity of extreme heat hazards, resulting in larger and longer population exposures; meanwhile, adaptation measures, especially among the most vulnerable communities and persons, are not keeping pace. Although early-warning systems and other public health measures undertaken during heat waves may provide some protection, there is emerging evidence that, at least in some regions, most deaths due to heat may occur outside of traditionally defined heat waves. For example, the evaluation of the Heatwave Plan for England concluded that more than 90% of deaths in many parts of the country have been occurring outside of heat-wave alert periods. A similar study across 22 U.S. states showed that a heat-attributable health burden starts to occur at moderately hot heat-index values, which in some regions are below alert ranges.

Q: What are the characteristic phases of heat stroke?

A: Heat stroke is characterized by the triad of hyperthermia, neurologic abnormalities, and recent exposure to hot weather (classic), physical exertion (exertional), or both. Tachycardia, tachypnea, and hypotension are common. Sweating is typical of exertional heat stroke, whereas in cases of classic heat stroke, the skin is often hot and dry. A change in mental status (e.g., confusion or delirium) best differentiates heat stroke from heat exhaustion and other milder forms of heat-related illness. Early manifestations include behavioral changes, confusion, delirium, dizziness, weakness, agitation, combativeness, slurred speech, nausea, and vomiting. Seizures and sphincter incontinence may occur in severe cases. Heat stroke characteristically manifests in three phases: a hyperthermic–neurologic acute phase, a hematologic–enzymatic phase (characterized by inflammation and coagulopathy and peaking at 24 to 48 hours after onset), and a late hepatic–renal phase (characterized by organ failure and occurring 96 hours or longer after onset).

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