Heat-Related Illness and Rhabdomyolysis
Heat stress is the sum of the heat generated in the body (metabolic heat) plus the heat
gained from the environment (environmental heat) minus the heat lost from the body to the
environment [NIOSH 2013]. Many bodily responses to heat stress are desirable and beneficial;
however, at some stage of heat stress, the body’s compensatory measures cannot maintain
internal body temperature at the level required for normal functioning. As a result, the risk of
HRI and accidents occurring as a result of HRI-related impaired mental status increase.
The body’s response to heat stress is called heat strain. Heat strain is dependent upon
a number of factors and cannot be predicted on the basis of environmental heat stress
measurements alone. As a result of working in a hot environment, HRI may develop. HRI
includes disorders such as:
●● Heat stroke – An acute medical emergency arising during exposure to heat resulting
in an excessive rise in body temperature and failure of the temperature regulating
mechanism. It is characterized by a change in mental status, which can range from
confusion or bizarre behavior to seizures and loss of consciousness. It is often preceded
by signs and symptoms of heat exhaustion as described below. Body temperature may
be in excess of 106°F, but there is no specific temperature used to make the diagnosis.
Heat stroke can be fatal if not immediately treated.
●● Heat exhaustion – A heat-related illness characterized by muscular weakness, distress,nausea, vomiting, dizziness, pale clammy skin, and fainting; usually associated with lack of heat acclimatization and physical fitness, poor health status, and inadequate
water intake.
●● Heat rash – Skin irritation that occurs most often in hot environments and causes skin
to become red and itchy. The rash usually appears in areas where clothing is restrictive.
●● Heat cramps – Muscle pains or spasms that can happen during prolonged work or
exercise in high temperatures.
Rhabdomyolysis, or muscle tissue breakdown, is the result of any process that causes injury
to or death of muscle tissue. When muscle cells die, their contents of electrolytes and proteins
are released into the bloodstream, which can result in potentially life-threatening conditions
affecting the heart and kidneys [Khan 2009]. There is a well-known association between
heat stroke and rhabdomyolysis [Department of the Army and Air Force 2003; Bontempo
and Kaji 2010; O’Connor and Duester 2011; ACGIH 2014]. Rhabdomyolysis and acute
kidney failure often occur together in people with exertional heat stroke [Bontempo and Kaji
2010]. Rhabdomyolysis is serious; up to 8% of documented rhabdomyolysis cases are fatal
[Cervellin et al. 2010]. Muscle tissue can be damaged by overheating, overexertion, crush
injury, some medications or supplements, or certain medical conditions. More information
about heat stress, heat strain, and rhabdomyolysis is in Appendix A.