Despite the current election cycle and massive denial of climate change by the MAGA party – the average temperature of the Earth is getting much higher. The ten warmest years on record are the last 10 years (see graph above). That is corresponding with the expected melting of glacial ice, increasing sea surface temperatures, and higher sea levels. It is equally obvious that the necessary measures to reduce carbon dioxide in the atmosphere are not being taken. We can therefore expect future generations to experience the burden of excessive heat, unstable weather patterns, flooding, crop shortages, and all of the economic and international instability that will occur. I don’t think it is a stretch to see this as potentially catastrophic to civilization.
Of all those weather related phenomena – extreme heat and
humidity are the number one
cause of death. Mortality due to
heat stroke is increasing every year. This was the first year that I heard frequent
stories about hikers perishing from the heat.
The CDC estimates that about 1200 people a year die from extreme heat
and they have a web
page dedicated to providing resources about this public health threat. The
EPA has a site that looks at heat
related deaths over the past 20 years and although they are higher – they
discuss the issue of variable reporting, largely due to inconsistent criteria
about what is called a heat related death.
There is a good chance that heat related deaths are underreported and
attributed to other causes.
Modern reviews of heat stroke and heat related illnesses
(1-3) suggest that there are two conditions that are clear emergencies and
varieties of heat stroke – classic heat stroke and exertional heat stroke.
Classic heat stroke develops in people exposed to heat who may be predisposed
because of chronic illness, medications, and an environment that is excessively
hot. These patients are typically
elderly. Exertional heat stroke occurs
when heat is generated by muscle exertion in hot weather and that leads to
excessive body temperature. In both cases emergency cooling is a critical
treatment along with fluid volume replacement if that is an issue. Heat stroke is a multisystem inflammatory
disease that leads to a combination of autonomic, cardiovascular, and metabolic
responses that can lead to organ failure and death. Mortality is high - 80% in classic heat
stroke and 33% in exertional heat stroke (3) if there is no immediate
treatment. The issue of immediate
treatment is problematic because heat stroke can cause compromised mental
status including loss of consciousness – further exposing the person to
prolonged heat exposure. Preexisting
cognitive compromise complicates both recognition of heat related illness and
getting timely care.
The issue of heat, humidity, and heat dissipation from the
human body is an exercise in physical chemistry. Evaporative cooling is one of the ways that
mammals cool their bodies to maintain a stable body temperature. In humans the other way is skin surface
vasodilatation and heat transfer from blood.
Every time water changes phase (solid -> liquid -> gas) there is
an energy requirement that is termed enthalpy in physical chemistry. The
enthalpy or heat of transition from liquid to gas is 40.67 kJ/mol. That means that we can calculate the amount
of water necessary to maintain cooling at an amount of energy production. The
relevant variables include how much energy the person is expending, ambient air
temperature, and the relative humidity since the last two affect the amount of
water that can transition to the gaseous phase.
All these variables can be considered form a meteorological
viewpoint using the concepts of heat
index and wet bulb global temperature. On this prototype site you can chose
either value, click on your location on the map (it scrolls), and get the heat
index or WBGT. As an example, two days
ago the temperature at my location went firmly into the danger zone as
indicated by this tracing that I downloaded at the time. Suggested activity
levels and precautions are available on the site for the WBGT values on the
curve over the course of the day.
Another way to look at WBGT is that it is the temperature where
evaporative cooling starts to fail and that is the measure of danger.
WBGT was recently assessed looking at wet-bulb temperature
adaptability thresholds in health young research subjects (4). Under experimental conditions they looked at
subjects under moderate metabolic load and determined the critical wet-bulb
temp beyond which the heat stress could no longer be compensated for. The researchers looked at the proposed
critical wet bulb temp of 35ºC (95 Fº)(threshold wet bulb temp) and discovered
that it could be considerably lower and that it was unlikely that a single critical
temperature for all conditions could be found.
Irrespective of the reporting issue, public health officials
are concerned about ambient temperatures and the heat island effect of concrete
in large cities where emitting energy can raise the ambient temperature up to
7 degrees hotter than the surrounding area. They have identified high risk populations
including the elderly, people with inadequate housing, and people with no air
conditioning. That last category can rapidly expand whenever weather conditions
effect power transmission and cut electrical power to large populations. We just experienced those conditions in
Minnesota shortly after a burst of peak temperature and humidity conditions.
Many people with chronic mental illnesses are in the
high-risk category. Compromised judgment
whether due to effects on cognition or more focal problems with judgment and
problem solving can lead to potentially fatal situations at either end of the
temperature spectrum. During the recent heat emergency, I witnessed several
people wearing excessive clothing and at the same time expending a lot of
calories. They were in a weather zone
where the National Weather Service (NWS) suggested minimal activity. Chronic
mental illness also creates the risk of no housing or inadequate housing. In
extreme heat – the lack of air conditioning can create an emergency situation
for many people.
At the policy level (5) there have been some approaches to
try to assure the safety of people that might experience exertional health
stroke. They are in the form of mandated
breaks, access to water, and access to air conditioning. They are far from universal and in some cases
there has been political opposition based primarily on anti-science (climate
change, human physiology) ideology and ignorance. It is a reckless approach to
humanity but consistent with gun extremism views held by the same groups.
At the individual level, psychiatrists need to be aware of
their patients’ living conditions and their theoretical susceptibility to heat
related illnesses. That requires an integrated
view of their current health status, medications, cognitive status, functional
capacity, physical activity level, and specific access to air conditioning.
Assertive Community Treatment (ACT) teams will have an advantage is knowing
first hand what the living conditions are. In the past I have worked out a plan
for people to go to an air-conditioned shopping mall depending on the weather
conditions. Some people will find this difficult and could benefit from a visit and prompts from
a case manager. A call list of people who may be at risk could be useful for
case management teams. As more municipal
areas develop cooling shelters – a more formal referral process might be
possible.
In the short term, a focus on the medical and social aspects
of patient care will be necessary to mitigate the potential lethal risks of
heat related illness. It is a necessary role for all physicians as the climate disaster
unfolds.
George Dawson, MD, DFAPA
1: Savioli G, Zanza
C, Longhitano Y, Nardone A, Varesi A, Ceresa IF, Manetti AC, Volonnino G,
Maiese A, La Russa R. Heat-Related Illness in Emergency and Critical Care:
Recommendations for Recognition and Management with Medico-Legal
Considerations. Biomedicines. 2022 Oct 12;10(10):2542. doi:
10.3390/biomedicines10102542. PMID: 36289804; PMCID: PMC9599879.
2: Epstein Y,
Yanovich R. Heatstroke. N Engl J Med. 2019 Jun 20;380(25):2449-2459. doi:
10.1056/NEJMra1810762. PMID: 31216400.
3: Sorensen C, Hess
J. Treatment and Prevention of Heat-Related Illness. N Engl J Med. 2022 Oct
13;387(15):1404-1413. doi: 10.1056/NEJMcp2210623. Epub 2022 Sep 28. PMID:
36170473.
4: Vecellio DJ, Wolf
ST, Cottle RM, Kenney WL. Evaluating the 35°C wet-bulb temperature adaptability
threshold for young, healthy subjects (PSU HEAT Project). J Appl Physiol
(1985). 2022 Feb 1;132(2):340-345. doi: 10.1152/japplphysiol.00738.2021. Epub
2021 Dec 16. PMID: 34913738; PMCID: PMC8799385.
5: Burton A. Energy justice for all: keeping disadvantaged
populations cool in a heating world.
Federation of American Scientists: https://fas.org/publication/energy-justice-keeping-cool/
6: Knochel JP. Heat stroke and related heat stress disorders. Dis Mon. 1989 May;35(5):301-77. PMID: 2653754.
This was the first comprehensive review I read on the topic. I was a subscriber to Disease-a-Month and the Medical Clinics of North America early in my career - based on recommendations from an Internal Medicine resident who I worked with. This remains an excellent review of the topic.
Graphics Credit:
National weather Service (weather.gov) for all except for the North Carolina High School Athletics Association as noted.
