Originally published in The Ottawa Citizen July 2, 2003
Original Title: Sweat Shops

The effects of this current heat wave and high humidity levels are particularly dangerous for children and the elderly. Children have parents who oversee their well-being and protection from the elements. Many elderly people on the other hand do not have this level of care. They remain confined to their residences, nursing homes or apartments, some without the benefit of air conditioning.

What specific difficulties are encountered with age as it relates to heat regulation? The normal response to heat overload is a ramping-up of the body’s heat dissipation mechanisms.

Normally, heart rate increases to deliver more blood to the blood vessels on the skin surface where heat dissipates. The skin will lose heat through the processes of evaporation of sweat, air convection, heat conduction and radiation. These processes are less efficient with the current weather conditions.

The elderly have a decreased thirst response. They are at risk of not replenishing water lost through sweating. With this week’s temperatures it is not unreasonable to assume a loss of a litre of sweat every one or two hours. This rate increases with physical exertion or activity.

Many elderly people are on some type of medication that can increase the risk of heat stroke and dehydration. Diuretics such as hydrochlorothiazide and furosemide (Lasix) are commonly used to treat hypertension and congestive heart failure among other disorders. They promote salt and water loss through their affect on the kidneys.

Alcoholic and caffeinated beverages also have diuretic properties. The use of laxatives, especially the harsher agents can augment fluid loss.

They will rapidly dehydrate should they not adequately replace their fluid loss. Their blood volume will contract because of the water loss. Less blood will flow to the skin surface reducing heat transfer to the skin surface. A reduction of sweating ability compounds the problem.

With age, blood vessels do not dilate efficiently (vasodilatory response).Heart medications such as beta-blockers and certain calcium channel blockers can reduce heart rate and blood pressure reducing the capacity to circulate blood. The elderly’s maximum heart rate is much less compared to a younger adult further reducing blood flow to the skin. This also reduces the body’ ability to dissipate heat from the skin surface.

The elderly tend to be less fit and are not as mobile as younger folks. Some are bedridden or so incapacitated that they have difficultly replenishing their fluid supply. It can be difficult to get to the kitchen.

Since many of the elderly remain indoors, it is difficult to know who needs help. If you suspect someone is at risk, please check up on them. If you live in a non air-conditioned apartment complex and are uncomfortable from the heat be very aware of your risk. Knock on your elderly neighbour’s door to ensure they are safe.

This week’s temperatures and humidex will cause heat gain via heat radiation into the body. Humidity interferes with sweat evaporation. The end result can be swelling, heat cramps, fainting, heat exhaustion and heat stroke.

General recommendations for prevention include:

* Stay in air conditioning if possible.
* Drink lots of water before, during and after any outdoor activity.
* Avoid drinks with caffeine or alcohol. They are diuretics that will increase fluid loss via urination.
* Take a lot of rest breaks if you must go outdoors in hot weather.
* Avoid direct sunlight and stay in the shade when you can.
* Wear light-coloured, loose-fitting, open-weave clothes.
* Change wet clothes.
* Try to schedule activities early in the morning or late in the evening.
* Avoid heavy outdoor activity between 10 a.m. and 6 p.m., when the sun is hottest.

Source: American Family Physician

Please contact your doctor if you have questions about your medication use during this heat wave.