Exertional heat illnesses and overhydration is a threat for anyone who works in hot conditions, but they are preventable.
While most of what we know about heat illnesses is derived from sports and military medicine, this knowledge cannot always be successfully and directly applied to the average Australian worker.
New ?keep it simple? guidelines for the prevention of exertional heat illness and the management of hydration at work are urgently required.
With extreme climatic conditions, and the knowledge that we live in one of the hottest countries on earth, exertional heat illness is very important for heavy industry. It affects workers during high intensity or long duration exertion and results in the need for (sudden)withdrawal from that exertion or more serious collapse during or soon after work.
EXERTIONAL HEAT STRESS
Exertional heat illness includes three major conditions: exertional muscle cramping, exertional heat exhaustion, or exertional heatstroke – commonly known as Exertional Heat Stress (EHS).
While certain individuals are more prone to collapse from exhaustion in the heat (eg those not acclimatised, using personal protective equipment, using certain medications, already dehydrated, or recently ill), EHS can affect seemingly healthy workers, even when the environment is cool.
EHS is defined as a core body temperature greater than 400C, accompanied by symptoms of organ system failure, most frequently central nervous system dysfunction. Early recognition and rapid cooling can reduce the morbidity and mortality of EHS, which is in fact a medical emergency.
The clinical changes associated with EHS can be subtle and easy to miss if supervisors, first aiders, health and safety personnel, medical personnel, and workers do not maintain acute awareness and monitor at risk workers closely.
Fatigue and exhaustion during exercise occur more rapidly as heat stress increases and are the most common causes of withdrawal from activity in hot conditions.
When a worker collapses from exhaustion in hot conditions, the term ?exertional heat exhaustion? is often applied. In some cases, high core temperature is the only discernible difference between severe heat exhaustion and EHS in on site evaluations. EHS, if not managed immediately, can lead to death.
On the other hand, exertional heat exhaustion will generally resolve with good symptomatic care and oral fluid support. Exertional muscle cramping can occur with exhaustive work in any temperature range, but appears to be more prevalent in hot and humid conditions. Muscle cramping usually responds to rest and replacement of fluid and salt (sodium).
Prevention strategies are essential to reducing the incidence of all three heat illnesses – EHS, exertional heat exhaustion, and exertional muscle cramping.
LOW SALT LEVELS AND OTHER CHRONIC DISEASES
There is currently a dangerous triple dogma in the Australian workplace that:
1. Collapse during or after prolonged hot work is caused by environmental heat exhaustion.
2. EHS is caused by dehydration.
3. EHS is prevented by copious fluid ingestion.
These misconceptions are strengthened by the lack of appreciation that ?too much fluid can hurt?.
It is well known that hyponatraemia (low salt levels) can and does occur in anyone with ready access to fluid – especially if the worker has been encouraged to ?force fluids? to prevent heat illness.
If the worker?s temperature is less than 400C at the time of collapse, then the worker does not have an exertional heat illness – another cause(s) must be sought, and low body salt is one of the most serious. Therefore, hydration strategies are a vital element of any prevention programme and we need to understand the role of water, electrolyte replacement fluids, sports drinks, energy drinks, soft drinks and alcohol.
But before we do that, there are major differences between what we know about elite athletes and military personnel, and the typical Australian worker.
In Australia, the workforce is beset by chronic diseases like diabetes, heart and kidney disease, nervous system diseases, asthma and arthritis. More than 660,000 older Australians cannot work due to illness and millions more Australian workers have advanced risk factors for chronic diseases at an early age.
It is noteworthy that:
? High blood pressure affects one in four Australians (50 per cent of whom do not have blood pressure managed to targeted treatment levels).
? Diabetes affects 7.6 per cent of Australians over 25 years (50 per cent of whom do not know they have it).
? Kidney disease can affect up to one in seven Australians, whose ability to tolerate fluid and salt changes in the body with heat is seriously disturbed.
? 19.5 per cent of Australians aged over 14 years smoke daily.
? 2.6 million adult Australians aged over 25 years are obese.
Public and occupational health researchers have suggested government should actively seek to turn around the rise in Australia of obesity – a prime risk factor for most of the chronic problems listed above.
In addition it is well documented that:
? Australian employees don?t exercise enough.
? Australians have poor dietary habits.
? Australians are overweight.
? More than half of the Australian workforce is stressed.
? Most are in the medium to high risk area in participating in risk behaviours.
? More than half don?t get enough sleep.
? One fifth of all workers have experienced a significant medical condition in the last three months.
Therefore, in managing a complex health issue such as exertional heat illness in the workplace these other health risks must be acknowledged.
POSSIBLE MANAGEMENT SOLUTIONS
So what can employers do?
1. They can know and understand their workers? strengths and weaknesses in regards to their health. Pre-employment screening for heart disease, diabetes and kidney disease may be the only way of protecting some workers.
2. They can educate workers about heat illness and prevention, eg emphasising the need to manage personal health and not to come to work sick or dehydrated.
3. They can screen workers who must work in extreme heat before they commence work, particularly for pre-existing dehydration. Monitoring core temperature with a simple tympanic thermometer, and the specific gravity (concentration) of the urine are easy to perform and will prevent workers starting hot work inappropriately. Any worker with a core temperature over 38.50C must stop work for rest, cooling and rehydration.
4. They can encourage the use of replacement fluids that work together to avoid dehydration – water and electrolyte replacement fluids such as Hydralyte will help avoid serious dehydration.
5. Electrolyte replacement drinks must be palatable, relatively low in sugar and relatively high in sodium (salt) but must be ingested in limited quantities to avoid overuse. One such success story is the use of electrolyte replacement in icy pole form. It is palatable, portable, avoids overuse, and encourages concomitant use of water.
6. Employers must avoid at all costs use of high sugar fluids such as sports drinks and soft drinks, and high caffeinated drinks including tea, coffee and energy drinks. Carbonated drinks should never be used in the management of exertional heat illness.
It is with this knowledge that we eagerly await new evidence-based guidelines for the management of exertional heat illness which it is hoped will provide a simple road map to ensure the safety of all those who work in extreme environments.
Dr Barry Gilbert MBBS MPH FAFPHM FSIA FAIM is a specialist in public health medicine and a vocationally registered general medical practitioner, with expertise in managing the specific health risks of safety-critical and emergency service personnel.