CLIMATE
& HEALTH
Extreme
Heat Is a Clinical Risk Factor Now — Here's What NPs Need to Build Into
Practice
Heat
waves are longer, more frequent, and more intense — and the health effects go
far beyond heat stroke.
|
CLINICAL BOTTOM LINE Heat waves in the US are now
twice as frequent as in the 1980s, and the heat wave season is more than
three times as long as it was in the 1960s. Extreme heat drives measurable
increases in cardiovascular events, kidney injury, respiratory exacerbations,
adverse pregnancy outcomes, and mental health crises — not just classic heat
stroke. Older adults, patients on common cardiovascular and psychiatric
medications, and historically marginalized or low-income communities carry
disproportionate risk. A heat-risk review belongs in routine care for any
patient with cardiovascular, renal, or psychiatric disease, or who is taking
a medication that impairs thermoregulation. |
The Scope of the Problem
Global mean temperature has
already risen 1.1°C since the Industrial Revolution, with projections of
2.5–2.9°C by century's end absent drastic emissions reductions, according to a
2024 New England Journal of Medicine review. In the US, the annual number of
heat waves is now twice what it was in the 1980s, and the heat wave season is
more than three times as long as it was in the 1960s. More than a third of
heat-related deaths across 43 countries between 1991 and 2018 have been
attributed to anthropogenic greenhouse gas emissions.
This isn't an abstract
environmental issue — it's already showing up in emergency department and
hospitalization data. Days in the 95th percentile of local warm-season
temperatures were associated with a 7.8% increase in the relative risk of an ED
visit for any cause in one large US study, and an analysis of roughly 50
million summertime hospitalizations found increased admissions for
cardiovascular, respiratory, diabetes-related, fluid/electrolyte, and renal
causes as the daily maximum heat index rose.
Beyond Heat Stroke: The Full
Range of Health Risks
Heat stroke and heat exhaustion
get the attention, but they represent only a fraction of the overall health
burden. Substantial epidemiologic evidence links both heat waves and single
days of high temperature to a much broader range of outcomes.
|
System |
Associated Risks |
|
Cardiovascular |
Acute MI, arrhythmias, CHF
exacerbation, ischemic stroke |
|
Respiratory |
Asthma and COPD exacerbations |
|
Renal |
Acute kidney injury,
electrolyte imbalance |
|
Pregnancy |
Preterm birth, stillbirth, low
birth weight, congenital heart defects |
|
Mental health |
Increased anxiety, depression,
suicidality, aggression/violence |
Risks scale with both the
absolute temperature and the deviation from local historical norms — a heat
index that would be unremarkable in Phoenix can be dangerous in Seattle,
because populations acclimate to their typical climate. This matters clinically:
don't rely on a single national temperature threshold to gauge risk for a given
patient population.
Why Older Adults Are
Physiologically Disadvantaged
A 2020 narrative review in
Environment International lays out the mechanisms in detail. Maintaining body
temperature during heat exposure depends on cutaneous vasodilation (routing
blood to the skin) and sweating — both of which decline with age. Older adults
show blunted nitric-oxide-dependent vasodilation, reduced cardiac reserve to
support the elevated cardiac output heat stress demands, and attenuated sweat
gland output even though the number of heat-responsive sweat glands is
preserved. The net effect is greater body heat storage and higher core
temperature for the same environmental exposure compared to younger adults.
•
Cardiovascular:
smaller increases in cardiac output during heat stress, endothelial
dysfunction, stiffer central arteries, and impaired baroreflex-mediated blood
pressure regulation.
•
Fluid
regulation: diminished thirst response to dehydration, impaired renal water
conservation, and reduced ability to concentrate urine — all increasing
susceptibility to both hyper- and hyponatremia.
•
Renal:
basal renal blood flow already declines roughly 10% per decade after age 40;
heat-induced renal vasoconstriction combined with dehydration compounds this,
raising acute kidney injury risk.
As much as 90% of heat
wave-associated mortality is attributable to major adverse cardiovascular
events — and critically, the risk is elevated not only in patients with known
cardiovascular disease but in those without it as well.
Medications That Compound Heat
Risk
Many of the medications NPs
prescribe routinely for chronic disease interfere with the body's ability to
dissipate heat, dehydrate patients further, or blunt the cardiovascular
compensation heat stress requires. This is worth a specific medication-reconciliation
pass before summer or ahead of a forecasted heat wave.
|
Medication Class |
Heat-Related Concern |
|
ACE inhibitors / ARBs |
AKI and electrolyte imbalance
risk; blunted thirst; impaired renal autoregulation |
|
Diuretics (thiazide, loop,
spironolactone) |
Dehydration, hypovolemia,
blunted cardiac output increase, hypotension |
|
Beta-blockers |
Blunted chronotropic reserve
limits cardiac output response to heat |
|
Anticholinergics |
Impaired sweating, increased
heat stroke risk, hypotension |
|
Antipsychotics |
Impaired sweating; risk of
drug-induced hyperthermia |
|
Antidepressants (SSRIs,
tricyclics) |
Impaired sweat rate,
hyponatremia risk (SSRIs), limited cardiac output (tricyclics) |
|
NSAIDs |
Nephrotoxic; compounds AKI
risk during heat stress and dehydration |
None of this is a reason to stop
these medications — they treat serious conditions. It's a reason to counsel
patients on hydration, watch electrolytes more closely during heat events, and
have a specific sick-day/heat-day conversation with anyone on this list who
also has cardiovascular, renal, or autonomic disease.
|
CASE FROM PRACTICE An 81-year-old woman with
hypertension (lisinopril, HCTZ) and mild cognitive impairment lives alone in
an un-air-conditioned second-floor apartment. During a 4-day heat advisory,
her daughter calls reporting confusion and reduced oral intake — she "doesn't
feel like drinking water." This profile stacks nearly
every risk factor discussed above: advanced age, two medications that impair
fluid regulation and heat dissipation, cognitive impairment limiting
behavioral thermoregulation (she may not recognize or act on thirst or
overheating), social isolation, and no air conditioning. A same-day BMP,
orthostatic vitals, and a same-day plan for cooling access (a cooling center,
a family member's air-conditioned home) are appropriate — this is not a
wait-and-see situation. |
The Disparities Are Not Fully
Explained by Heat Alone
|
A NOTE ON EQUITY Communities where members of
marginalized racial and ethnic groups and low-income populations live face
disproportionately high heat-related illness risk — and this is not fully
explained by socioeconomic status or air conditioning access alone. Historically redlined
neighborhoods — a discriminatory mortgage-lending practice from the 1930s —
continue to have more paved surface and less green space than other areas,
producing measurably higher ambient temperatures ("urban heat
islands"). Low-income urban communities can run as much as 5°C hotter
than wealthier ones nearby. Contributing factors include
more limited access to care, more frequent occupational heat exposure
(factory work without air conditioning, outdoor labor), and a higher baseline
prevalence of hypertension, diabetes, and kidney disease. For patients in these
circumstances, standard advice ("stay in air conditioning") may not
be actionable — screening for access to a cooling center or a cooler
environment during heat advisories is a more useful clinical question than
assuming air conditioning is available. |
What NPs Can Actually Do
•
Ask
about air conditioning access and living situation for any older or high-risk
patient, especially before summer months — this single question identifies a
major modifiable risk factor.
•
Review
medication lists specifically for heat-interacting drugs (table above) in
patients with cardiovascular, renal, autonomic, or psychiatric disease, and add
heat-specific counseling, not just general "stay hydrated" advice.
•
Identify
socially isolated patients before heat season — they are less likely to have
someone checking on them during a multi-day heat event, which is when risk
accumulates most.
•
Counsel
on individual protective measures: limiting outdoor exposure during peak heat,
loose light-colored clothing, adequate hydration, and cooling devices — while
noting that air conditioning itself has an environmental cost worth naming for
patients who ask.
•
Know
your local cooling center resources and heat-alert systems so you can give
patients a concrete plan, not just a warning, before a forecasted heat wave.
Board & Practice Prep
•
Heat
exhaustion presents with normal mental status; heat stroke involves CNS
dysfunction with core temperature typically ≥40°C — this distinction determines
emergency triage.
•
A
heat wave is generally defined (NOAA) as 2 or more continuous days of unusually
high heat relative to local historical norms — not an absolute temperature
threshold.
•
There
is currently no standardized, universally accepted definition of a
"heat-related death," which complicates surveillance and ICD coding
of indirect heat effects.
•
Heat-induced
hemoconcentration and hypercoagulability contribute to elevated cardiovascular
event risk independent of classic heat illness — worth remembering when a
patient presents with an MI or stroke during a heat event with no other clear
trigger.
•
Mortality
displacement ("harvesting") — where heat-related deaths occur mainly
in already-frail patients who would have died soon regardless — has been
studied and found not to fully explain heat-attributable mortality; the excess
risk is real.
The Takeaway
Extreme heat is no longer a
seasonal inconvenience to mention in passing — it's a modifiable clinical risk
factor with mechanisms as well-characterized as many risk factors NPs already
screen for routinely. Building a heat-risk review into care for older adults,
patients with cardiovascular or renal disease, and anyone on a heat-interacting
medication is a low-cost intervention with a clear evidence base behind it, and
it may prevent the kind of quiet decompensation that too often shows up only
after a multi-day heat event has already done its damage.
References
Bell ML, Gasparrini A, Benjamin GC. Climate change, extreme
heat, and health. N Engl J Med. 2024;390(19):1793-1801.
doi:10.1056/NEJMra2210769
Meade RD, Akerman AP, Notley SR, McGinn R, Poirier P, Gosselin
P, Kenny GP. Physiological factors characterizing heat-vulnerable older adults:
a narrative review. Environ Int. 2020;144:105909.
doi:10.1016/j.envint.2020.105909
