Bracing to cool the literal burn-out| MEDICUS 2023 Issue 4

Bracing to cool the literal burn-out

By Dr Chua Li Min, Science writer

Credit: iStock.com / justhavealook

Singapore’s lush garden city landscape is enticing—from the cool comfort of an air-conditioned space. For as soon as we step out into the hot and humid climate, we look eagerly for the nearest sheltered route or reach for an umbrella to protect us from the scorching sun; seeking any escape from the sticky embrace. The year-round heat is part and parcel of life near the equator. Forever seeking refuge in air-conditioned buildings and homes, we can even convince ourselves that we are used to the heat. But are we clinging to a false sense of security that could spell bigger trouble as our planet’s mercury continues to trend upwards?

“We are behaviourally heat acclimatised, not physiologically. That means we are not as acclimatised to the actual temperature as we think we are,” said National University of Singapore (NUS) Associate Professor Jason Lee.

With climate change driving the rise of more frequent and more extreme weather events around the world, Singapore is bracing for new record temperatures of 40 degrees Celsius by 2045—a trend that is alarming doctors and research scientists here.

“The heat creeps in on you subtly, and you can’t feel its impact on your body until it’s much too late,” cautioned Clinical Associate Professor Mark Leong from the SingHealth Duke-NUS Emergency Medicine Academic Clinical Programme.

And while awareness spikes after a heat-related death, continued vigilance is only part of the solution for Lee: “While we need to stay vigilant to the dangers of heat, it would be beneficial for us in the long run if we learn how to use heat correctly to induce positive physiological adaptations to optimise health and performance.”

Professor Mark Leong, an emergency medicine physician, treats patients coming in with heat injuries at the Singapore General Hospital’s emergency department

When the heat is just too much

“Heat injuries can strike anybody,” said Leong, who is a practising emergency medicine physician at one of Singapore’s busiest emergency rooms. As ambient temperature rises, so does our body’s core temperature. Once that breaches the optimum range for cellular processes to keep running, critical enzymes and proteins start to malfunction and “that’s when the problem starts,” added Leong.

In a bid to bring down the core temperature, the body starts to lose water by sweating. “The loss in body fluids results in dehydration, which also affects our kidneys. Then when our muscles start breaking down, these by-products block the kidney tubules, worsening the injury. The effects are systemic across many organs, ranging from the brain to heart,” explained Leong.

While these events unfold unseen, they first translate into symptoms of physical exhaustion.

A snapshot at the organs that are affected in the body under heat stress // Sources: Mark Leong, Ignasius Jappar, Critical Care

“We know for a fact, that very young children and very old persons are at higher risk.”
Prof Mark Leong

“But things move along and become heat cramps. Then when things go downhill, it becomes heat exhaustion, and then the worst outcome will be a heat stroke. When you get heat stroke, it is very serious,” said Leong, who is also Deputy Chair of the SingHealth Duke-NUS Emergency Medicine Academic Clinical Programme. When the body suffers a heat stroke, its core temperature may go as high as 41 degrees Celsius, a temperature that can trigger body-wide organ failure; hot enough for “your mental state to be altered causing you to lose consciousness,” added Leong.

A prolonged assault of such high internal temperatures can also trigger heart muscle injuries and heart attacks that may have serious long-term health implications, explained Clinical Assistant Professor Ignasius Jappar (Class of 2012) from the SingHealth Duke-NUS Cardiovascular Sciences Academic Clinical Programme.

That is why Leong and his colleagues at the emergency department act swiftly to cool patients with heat injuries. This involves replenishing the levels of fluids and electrolytes in the body, as well as removing excess heat by using cooling pads or suits.

Why some of us are more vulnerable

“We know for a fact, that very young children and very old persons are at higher risk. And they are at risk because of different reasons,” said Leong. For young children, this includes being unable to seek help when they are in distress.

Equally at risk of non-exertional heat stroke are the elderly, whose physiology causes them to lose heat less effectively.

One reason is their blunted thirst response, which means that elderly people end up drinking less water because “they just don’t feel thirsty as often as a normal active, younger adult”, explained Leong.

Ignasius added: “They also sweat a little bit less because of reduced sweat production. Their hearts will have to work harder under the heat stress, putting them at a higher risk of a heart attack.”

On top of that, some of the medications that they take also predispose them to heat disorders. “These drugs compromise certain physiological functions which hinder the body’s ability to lose heat,” said Lee, referring to a paper his group published in Pharmacological Reviews in June.

It is an issue that Ignasius is acutely aware of. Many of his patients at the National Heart Centre Singapore are prescribed beta-blockers for heart failure, but the very same drug also prevents effective heat loss from the body. “They affect the ability of the heart to increase cardiac output—that is one. Two, they also tend to reduce sweating,” he explained.

Assistant Professor Ignasius Jappar advises his patients who are on medications that may predispose them to heat disorders to avoid exposure to extreme heat and to manage their intake of fluids

“The other medication that we use very frequently in heart failure patients is a class called diuretics. Diuretics promote the loss of water and some minerals through urine, which can cause dehydration. When patients are relatively dehydrated, they are also at a higher risk of developing poor response to heat stress,” added Ignasius.

His advice to patients?

Avoid exposure to extreme heat, and manage their intake of fluids. “We remind patients to drink more water during very hot days when they are sweating a lot to counteract the water loss.”

Our activities can also put us at risk

Even seemingly healthy individuals are not spared from the effects of the sweltering heat, said Lee, who leads the Heat Resilience and Performance Centre at the NUS Yong Loo Lin School of Medicine.

Whether someone can tolerate heat well depends on their fitness and health, said Lee. “You will see that usually those who are aerobically fit also tolerate heat as well, because the physiological adaptations of someone who is heat resilient is not far from someone who is aerobically fit.”

A military physiologist by training, he is no stranger to heat stress, having worked with soldiers on heat management techniques for more than ten years.

At the Heat Resilience and Performance Centre at the NUS Yong Loo Lin School of Medicine, Associate Professor Jason Lee studies the impact of extreme heat on the human body // Credit: Jason Lee

Through his studies of the effects of extreme heat on the human body, Lee found that attire, the environment as well as the type of work or activity itself can affect someone’s chance of developing heat stress and heat-related injuries.

Citing a recent study of COVID-19 frontline workers, he described how they were at a higher risk of heat stress because of the enhanced personal protective equipment they had to wear, which restricted the body’s ability to shed heat through the evaporation of sweat.

And the list of individuals at risk continues. Firefighters and delivery riders, who spend long hours working outdoors, are similarly vulnerable. “They could suffer from exertional heat stroke if we are not careful,” said Lee, referring to the type of heat stroke that is triggered by the activity, and its intensity.

This type of heat stroke also brings some patients through the doors of the emergency department after a bout of intense physical activity. “We still see spikes in the number of cases, usually during marathons,” observed Leong.

And it is not just the body’s physiology that is affected, but also the mind.

“When people get thermally uncomfortable, they tend to take more risks. This results in the ‘I want to get my job done and get out of off here as soon as possible’ mentality,” said Lee. “That is why having appropriate heat mitigation strategies is important.”

To effectively manage heat stress, Lee recommends the following five strategies: “Get yourself aerobically fit, work towards getting heat-acclimatised, have work rest cycles in place, include cooling strategies in your routine and stay hydrated.”

Five strategies to effectively heat stress // Source: Healthcare

Getting the word out

While having more heat-resilient structures, like buildings and shelters, will help to mitigate the risks, they form only part of the solution as it is not possible to avoid the heat entirely.

That is why increasing awareness at all levels is key when it comes to building a population that is heat-resilient. For this reason, Lee and Leong have been actively lending their insights to government taskforces.

And their efforts to raise awareness around these issues over the past few years have paid off. “The awareness is phenomenal,” recalled Leong, who was head of the Singapore Ministry of Defence’s review panel for heat injury management in 2018. “We came out with a slew of recommendations which were adopted—every single one was adopted.”

Recently, the duo also served as advisors on the Ministry of Health’s Heat Stress Guidelines Expert Panel, leading to the launch of a new heat stress advisory by the Ministry of Sustainability and the Environment and the National Environment Agency.

But more research will have to be undertaken to assess the full effects of heat on people, stressed Lee, who has led projects like HeatSafe that focus on studying occupational heat stress. In Cooling Singapore 2.0, which Lee is also involved in, his team will evaluate the effect of heat on children, non-heat-acclimatised adults and the elderly to establish norms within each group and provide specific thresholds for managing heat stress. He hopes to expand the study to include other populations such as the disabled and pregnant women as well.

“Treat this (the heat stress advisory) as a version one, akin to an awareness creation exercise,” said Lee, who is striving for a much more personalised approach to help people live better with the heat: “Eventually we will have to harness other enablers like wearables or data analytics to come up with a personalised heat stress advisory.”

Duke University launches Heat Policy Innovation Hub

By Karl Leif Bates, Executive director of research communications at Duke University

As summer heat records were shattered around the Northern Hemisphere this year, Duke University launched a new Heat Policy Innovation Hub, the US’ first academic centre to look at how policy solutions to rising temperatures can help save lives.

The group’s research blends Duke’s expertise in medicine, health policy, engineering, the environment, and will focus on planning and preparedness, women’s health, early warning systems rural interventions and healthcare delivery.

“We aim to integrate vulnerability to extreme heat and climate data into electronic medical records to enhance patient safety, empower healthcare provider, and foster resilience in the face of escalating climate extremes,” said hub director Dr Ashley Ward.

The hub will launch collaborative research projects and work toward “actionable solutions” and policies that can make a difference. For example, Duke scholars are working with state and local agencies in North Carolina to develop comprehensive heat action plans that will help local governments prepare for extreme heat events, while its women’s health thrust is particularly concerned with maternal health in the hot and humid southeastern United States, a region with historically poor maternal health outcomes.

“Heat exposure is a systemic burden for women that is magnified by existing inequities,” said Ward. “Women are more likely to live in poor housing, be exposed to unsafe working conditions, lack access to healthcare, experience higher rates of poverty and become victims of domestic violence, the impacts of which are exacerbated by extreme heat.”

Picture of Duke Heat Policy Innovation Hub lead Dr Ashley Ward

Duke Heat Policy Innovation Hub director Ashley Ward talks about some of the collaborative research projects that the hub is doing to boost resilience against the rising heat in US // Credit: Duke