Heat related disease

Heat exposure substantially affects human health in both the short and long term.

Process ranges from minor cramps to rash, heat exhaustion, and heat stroke.

Acute heat related illnesses include: heat rash,   heat cramps, heat edema, heat syncope, heat exhaustion, and heat stroke.

Extreme heat exposure increases emergency room visits and hospitalizations: increased visits from any cause with significant increase in heat related illness, renal disease, and mental health disorders.

An analysis of summertime hospitalizations of approximately 50 million people showed increase rates of hospital admissions with coronary vascular disease, respiratory disease, diabetes, fluid and electrolyte disorders and renal failure as increases in daily maximum heat index occurs.

Acute illnesses, along with acute heat affects, such as sunburn and severe burns from contact with hot surfaces, represent only a fraction of the overall health burden attributable to heat exposure.

Mortality increases with heat and heat waves.

The risk of illness and death from cardiovascular events – acute, myocardial infarction, arrhythmias, exacerbation of congestive heart failure, and stroke, respiratory conditions of asthma and chronic obstructive pulmonary disease, and kidney disease increase with elevated temperatures.

These risks agreed with exposure to find particulate air pollution.

Heat related disease is the most common cause of severe weather fatalities in the United States.

Climate change is causing an increase in the average temperature and is increasing the frequency, duration, and intensity of extreme heat events, resulting in unprecedented levels of heat exposure.

The past seven years have been the hottest on record.

In the past 20 years there has been a 54% increase in heat related mortality among persons older than 65 years, and  more than 1/3 of all global warm season heat related deaths are attributed to climate change.

Extreme heat is linked to increased adverse pregnancy outcomes: preterm, birth, stillbirths, low, birth, weight, and congenital defects.

Heat exposure is linked to increased anxiety, depression, suicidality, and aggressive behavior and violence.

0.02 deaths per 100,000 workers annually.

Between 1992 and 2019 more than 900 US workers died in almost 80,000 were seriously injured because of extreme heat exposure.

Humans thermoregulate through behavioral and autonomic mechanisms such as vasodilatation and sweating to maintain core internal temperature of approximately 37°C.

Metabolic activity generates a heat load, and  exogenous  heat from the environment adds to the total heat burden that must be managed.

Higher humidity levels exacerbate the challenges of dissipating heat.

Under heat loads resulting from exogenous heat, endogenous heat, or both, the thermoregulatory ability may become strained or overwhelmed resulting in a spectrum of heat related processes.

Heat related diseases range from non-threatening processes like heat exhaustion, heat syncope, heat edema, heat cramps, and heat rash to life-threatening heat stroke.

Deaths occur in agriculture, fishing, forestry and hunting industries.

Farm workers are the front line in terms of increased risk of heat related injuries.

The risk of dying for farm workers due to heat exposure is 20 times higher than in all US civilian workers.

Crop workers have an annual fatality rate of 0.39 deaths per 100,000.

Typical deaths occur among male crop workers aged 24-54 years.

Heat related disease is a leading cause of death and disability among US high school athletes.

High temperatures lead to rising core body temperatures and heat stress, heat exhaustion, cramps, heat stroke, or death.

Estimated average annual number of heat associated time-loss illnesses of 9237 among US high school athletes.

5,946 persons treated in US EDs each year for heat illness sustained while participating in a sport or recreational activity, for estimated annual rate of 2 visits per 100,000 population-72.5% males, 35.6% aged 15-19 years, and 7.1% required hospitalization.

Most frequent in summer months.

Without prompt management can result in organ failure, brain damage and mortality.

All cases are preventable.

People with chronic conditions like obesity or diabetes or a greater risk of heat related illness.
Pregnant women are at higher risk because of heat related disease.

Heat stress and dehydration have been linked with acute kidney injury and US farmworkers.

Associated with dehydration, nausea, vomiting, headache, dizziness and altered mental status.

clinical manifestations of heat related illnesses vary by severity of the process.

Heat stroke is characterized by the triad of hyperthermia, neurologic abnormalities, and recent exposure to hot weather, physical exertion, or both.

Can lead to multiple organ system dysfunction from direct effects of heat and the body’ inflammatory response.

Associated with altered mental status, renal failure, coagulopathy, cardiovascular collapse, and an inflammatory response.

Older adults are more vulnerable to heat related complications.

Older patients are at greater risk based on social and behavioral factors, increased likelihood of being alone, being homebound, or taking medications that interfere with fluid balance.

Many illnesses are heat sensitive meaning that they are exacerbated or triggered by exposure to heat: ischemic heart disease, cardiac arrhythmias, ischemic stroke, asthma, COPD, respiratory tract infections, hyperglycemia, kidney failure, neuropsychiatric disorders, and adverse birth outcomes.

The  risk of heat related illness results through a combination of individual susceptibility, endogenous and exogenous heat exposure, and sociocultural factors that affect the ability to adapt.

Older individuals, young children, infants, pregnant women, persons with pre-existing medical conditions,  including obesity, outdoor workers, and athletes are at an increased risk as are persons living in low income households in some communities of color.

Heat related risk vary by individual exposure according to geography, occupation, social isolation, and time spent outdoors or in areas that amplify heat, and in areas with less green space.

Urban heat islands refer to areas of densely built infrastructure which absorbs and then re-emits heat from the sun resulting in islands of higher temperatures which can be 1 to 7°F hotter, on average than outlying areas.

They also have much higher nighttime temperatures as a result of re-radiation heat from the surrounding environment.

In the US these heat islands are disproportionately inhabited by low income Black communities and other underrepresented racial and ethnic groups.

Heat related illness may occur in the absence of a heat wave, and a high index of suspicion is warranted in the context of the suggested symptoms.

Heat exhaustion, on the continuum with heat stroke, can be managed by passive cooling and rehydration in mild cases, and in moderate cases managed with convective cooling, infusion of cold fluids, and close monitoring.

Heat stroke is managed with acute resuscitation measures followed by rapid cooling, reducing the core body temperature to 38 to 39°C, ideally within 30 minutes after presentation.

Heat, indirectly affects health through environmental effects, such as reduction in the quality and quantity of crops and the water supply, and by an increase in ground level ozone.

Both internal and external factors, modify the effects of heat on health.

Being a member of the marginalized, racial or ethnic group, or having lower socioeconomic status is a key factor increasing the risk of adverse health effects.

Adverse health effects of heat risks include extremes of age, social isolation, coexisting morbidities, and medications.

Individuals with cardiac, cerebral vascular, respiratory, or a renal disease, diabetes, dementia, are at increased risk for heat related conditions.

Medications associated with increased risk for heat related conditions include: diuretics, antihypertensive drugs, other cardiovascular medications, some psychotropic agents, and histamines.

Elderly people who have thermal regulatory system abnormalities that are compromised and more likely than the young to have underlying conditions, to use medications that interfere with heat dissipation, have mobility issues that compromise access to hydration or cooling, or live in older housing without air-conditioning.


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