HEAT STRESS

Keep An Eye on Medications

• By Marc Barrera
• Jul 01, 2009

The chances are great that a large percentage of the workforce is taking some kind of drugs. The reasons for medications can vary widely, whether for treating allergies, high blood pressure, infections, or a host of other maladies.

"There are a huge number of drugs, when you come down to it," said Dr. Robert McLellan, M.D., MPH, FACOEM, past president of the American College of Occupational and Environmental Medicine (ACOEM) and section chief of Occupational and Environmental Medicine at Dartmouth-Hitchcock Medical Center, Occupational Medicine. "Because of the prevalence of some of the conditions that these are used to treat, you can recognize that there's actually a pretty fair percentage of who may potentially be taking these drugs."

A prominent danger of the proliferation of these medications is especially present for workers subjected to grueling temperatures. Many of these workers may be unaware of the effects some of these medications can have in increasing their risk for heat stress.

To better understand the effects that medicines can have on heat stress, McLellan said, it is important to think about how the body produces and manages heat. "There's obviously an external heat load--what you're exposed to. Then there's the amount of heat that an individual worker actually generates by the work that they're doing and how active they are," he said. "But the other important piece is the capacity of an individual in other aspects of the environment to remove heat. It's on this issue of the ability to remove heat from your body that these various drugs are affecting."

To Robert R. Orford, immediate past president of ACOEM and consultant in Preventive Medicine for Mayo Clinic, the two drugs that have the most worrisome ramifications for workers are antihistamines and beta blockers. Many antihistamines are available without prescription, so effects may be unknown to the worker taking them, having had little or no consultation or warning about possible symptoms.

Antihistamines dry up the mucus membranes to ease symptoms such as a runny nose. In the process, they make it harder for the body to cool itself. "One of the things antihistamines do is stop the body from sweating in a before-normal way," Orford said. "People have allergies, and obviously many plant species cause allergies. So if a person works out where they're exposed to ragweed--or whatever their particular allergen might be--they might be popping antihistamines for that."

Beta blockers are commonly prescribed for the treatment of high blood pressure, control of arrhythmias (rapid heart beat), or to steady tremors. Part of their danger lies in the fact that many of the things beta blockers "block" are also mechanisms the body uses to cool itself. "Heat stress normally would increase your heart rate," Orford said. "Well, beta blockers would stop your heart rate from going faster. The faster your heart rate goes, then the more you're going to have the blood going around your skin so that you get that convection going off and getting rid of the heat that way. The beta blockers also reduce dilation of blood vessels, which would inhibit the body's ability to radiate heat."

At the same time, beta blockers can suppress some symptoms of heat stress or delay the appearance of such symptoms, which in turn would keep the worker unaware of his or her worsening condition. For example, one characteristic of heat stroke is the victim's skin turning red or beginning to appear flushed. Also, someone experiencing it tends to develop a rapid heart beat and rapid breathing. "It's not the symptoms that are the problem. It's the body temperature that's the problem," said Orford. "If you're in that situation with a beta blocker, your co-workers don't know you're on beta blockers, and you're looking okay, they're not going to do anything until you actually start having a real seizure or go into a coma or something like that."

The 'Cry Wolf' Effect
Diuretics are drugs commonly used to treat high blood pressure. Often called "water pills," these drugs present two immediate problems: the increased possibility of mimicking heat stress symptoms and the increased possibility of dehydration.

Possible diuretic side effects include dizziness, lightheadedness, fainting, muscle cramps, weakness, and red and itchy skin rash. Because these side effects are similar to heat stress symptoms, workers on blood pressure medications must take extra care to avoid dismissing heat stress symptoms as merely an effect of their medication. Whatever the cause for these symptoms may be, workers should seek medical attention immediately.

Diuretic drugs also cause the kidneys to remove excess fluids and sodium through urination, which can lead to dehydration. In itself, dehydration brings many problems and complications a worker should take care to avoid. Drinking plenty of fluids and electrolytes is recommended. But an additional problem associated with dehydration, regardless of drug type, is drug potency.

"When dehydration occurs, your blood volume contracts and any medicines you are taking become more concentrated, so you are going to potentially enhance their effects," said Dr. David A. Calhoun, M.D., professor of medicine at the Vascular Biology and Hypertension Program Sleep/Wake Disorders Center at the University of Alabama at Birmingham. "If the blood pressure medicine becomes concentrated, you could have more of an effect and risk having too low of a blood pressure."

Psychiatric drugs also can present symptoms similar to heat stress and can elevate a person's temperature, making that worker even more susceptible to heat stress. "These are drugs that are typically used to treat psychiatric conditions that can cause this malignant hypothermia," McLellan said. "In addition to that, some of these drugs can cause the vague symptoms, some of the early symptoms, of feeling dizzy, lightheaded, or thirsty, et cetera."

Photosensitivity

Although not directly related to heat stress, another important factor to consider when taking certain medications is potential adverse reactions after exposure to the sun. These reactions fall into two general types: phototoxic and photoallergic.

Phototoxic reactions give the appearance of sunburn and typically clear up once the drug is discontinued and gone from the body. Antibiotics fall under this category. One example is tetracycline, which is commonly prescribed to treat several types of infections, including those in the respiratory tract, urinary tract, and skin. In addition to its photosensitivity properties, the antibiotic has a side effects of diarrhea, which increases a worker's chances of dehydration. Included in the phototoxic group are antihistamines, cancer chemotherapy drugs, diuretics, diabetic drugs, and psychiatric drugs.

With photoallergic reactions, ultraviolet exposure can change the structure of a drug, causing an immune system's allergic response and inflammation of the skin in the sun-exposed areas, usually resembling eczema. Even after the drug has cleared the body, these symptoms can return with future sun exposure. Included in this group are sunscreen, painkillers, fragrances, and cancer chemotherapy drugs.

Solutions
Safety may collide with privacy concerns when an employer wants to know which medications a worker may be taking. Thus, the burden of ensuring a worker's safety falls largely on that worker.

"There's absolutely no way under HIPAA that you would want employers to know who's on medication. They just would not allow it," Orford said. "So it really is incumbent on the workers themselves to be aware of these."

Although employers are required to varying degrees to educate workers about heat risks and provide them adequate shade and water, McLellan stressed the importance of the workers taking steps to educate themselves. "It's important to have a visit with a doctor who knows about these issues, because it's hard purely from a self-care perspective to necessarily identify them," he said. "Also, in a good occupational medicine program, workers that would be potentially at risk for being put in a heat stress situation should be identified by management and the industrial hygiene safety management people, and they should be evaluated." Workers who don't have the benefit of such comprehensive programs should educate themselves about how generally to deal with heat with information that is easily available from OSHA and NIOSH, McLellan said.

Another useful tool McLellan recommends is the Cardiac Stress Test. "It's commonly done to check to see if you've got problems with your heart, and basically what happens is you're put onto a treadmill, and while you're on the treadmill your heart is monitored by an EKG kind of device," he said. "Based on how fast the conveyor is going and the elevation, it will increase your workload. That workload is measured in METs (metabolic equivalents), which is basically a measure of physical work by a human being."

According to McLellan, NIOSH studied this approach and came up with a way to identify people at risk for heat stress. "It's been shown that people who are able to exercise up to 10 METs have a much, much, much lower risk of adverse effects from heat stress than if they're unable to do that," he said. "It's a tool that we tend to use in the nuclear industry, in particular, where there're a lot of hot environments and people have to be fully suited up."