|June 2015 | Archive|
Preparing for the Summer Heat
Rosemary Laird, MD, MHSA, AGSF
Every summer as temperatures and humidity indices rise, I have a more than a few flashbacks to the summer of 1995, specifically the month of July. As the chief resident for the department of internal medicine at University of Chicago Hospital, I was steeling myself for the challenges of welcoming and supervising the newest cadre of recently degreed medical interns to our urban home on Chicago’s south side. Little did I know how quickly we would be tested beyond anything we could have anticipated.
In his book, Heat Wave: A Social Autopsy of Disaster in Chicago, Eric Klinenberg sets the scene:
“On Thursday, July 13, 1995, Chicagoans awoke to a blistering day on which the temperature would reach 106 degrees. The heat index, which measures how the temperature actually feels on the body, would hit 126 degrees by the time the day was over. Meteorologists had been warning residents about a two-day heat wave, but these temperatures did not end that quickly. When the heat wave broke a week later, city streets had buckled; the records for electrical use were shattered; and power grids had failed, leaving residents without electricity for up to two days. And by July 20, more than 700 people had perished—more than twice the number who died in the Chicago Fire of 1871 and 20 times the number of those struck by Hurricane Andrew in 1992—in the great Chicago heat wave, one of the deadliest in American history.”
Klinenberg’s book presents a comprehensive analysis of the numerous social factors that played a role in the catastrophe. It’s an intelligent and important analysis that highlights the interconnectivity of an elder’s health status and social status. It is a powerful example of the fact that anyone aiming to provide quality health care to an elder necessarily must know the world in which an elder lives.
Two of the critical medical issues that created morbidity and mortality in the heat wave were dehydration and hyperthermia. Elderly patients are at increased risk for both conditions. Here are some key points to keep in mind.
Recall from Physiology 101 the term “homeostasis.” It’s occurring when the body’s physiologic checks and balances are functioning properly to keep all systems operational and appropriate in relation to each other. Circulating blood volumes are normal, keeping blood pressure normal so arterial tone is normal, and all are appropriately responsive. A key and nearly universal change in the aging process is the diminution of the abilities of homeostatic processes, termed homeostenosis. Imagine any process being just a bit slower, less reactive, less able to respond in a timely fashion to a normal physiologic change, and far less able to respond to a large perturbation of normal function.
Warm Weather Concerns
Here’s a time when its important to think like a geriatrician and imagine the body’s processes affected by homeostenosis.
Dehydration provides an easy model. Lower circulating volume leads to decreased cardiac output.
In the young, decreased cardiac output leads to a compensatory increase in heart rate to normalize cardiac output. Young folks may be dehydrated, but their homeostatic processes have worked.
Now take the same level of dehydration in a body 50 years older. In the aged, the heart rate response is not as robust, so there can be a clinically significant drop in cardiac output. If an aged individual stands up quickly, there is likely to be a sensation of dizziness or perhaps a fall due to cerebral hypotension to which the aged carotid vasoresponsive tone of the carotid arteries cannot respond as quickly.
Now add hyperthermia. In Chicago that July, ambient temperatures reached levels higher than 100 degrees. Typically, as the body temperature rises, thirst increases. The aged experience a decreased thirst response even when core temperature climbs. At baseline, many elderly eat less from day to day, at the same time, consuming less water. Add to that poor baseline a limited thirst response when there’s a need to drink, and you can understand why the elderly become dehydrated so quickly. It was the combined and additive effects of dehydration and hyperthermia that led to the extraordinarily high death rates in the Chicago heat wave.
Fortunately for most of our patients, the risk of death from either dehydration or hyperthermia is low. But as the summer heat begins, dehydration and hyperthermia pose risks for the elderly.
For older adults, the recommendation of eight 8-oz glasses of water per day is appropriate. However, it’s up to physicians to modify this, as needed, for the few patients who need fluid restriction. Keep in mind that someone on diuretics need not necessarily limitfree water. And they are at increased risk of dehydration because control of their chronic illness is requiring a relative dehydration, ie, the use of diuretics, for clinical stability. It’s a fine line, and often these patients can do well with an agreed-upon “dry weight” and plan for a daily weight check to allow proper diuretic dosing and plan for free fluid intake.
Be mindful that many older adults will purposely decease their fluid intake due to urinary frequency and incontinence or mobility issues that create difficulty in getting to the bathroom. They are literally dehydrating themselves and risking falls and prerenal azotemia among other things. For patients with this concern I often advise they pick a time during the day when they will be home and can get to the bathroom every hour if necessary. Then drink. The fluid is good for them as is the exercise.
Consider making the following a part of your summertime routine. Ask your staff to regularly inquire about patients’ water intake during vital signs checks. This is especially important if they identify any older adults who are losing weight. Individuals who don’t eat usually don’t get adequate water. Anyone who isn’t drinking at least four glasses of water per day should be brought to your attention. All patients can receive a handout as they leave the office.
In the elderly, another physiologic process that is blunted is the response to elevated body temperature. Due to homeostensosis, the usual mechanisms for detecting and regulating heat are less active and less effective. Core temperature can rise without triggering aggressive perspiration or sending a message to get a drink of cold water. Chronic illnesses and their medications can further complicate thermoregulation as well. Remedies for hyperthermia are squarely focused on prevention. Raising awareness of the risk is key.
Consider a patient education handout on this topic as well. A reputable resource for patient handout materials comes from the American Geriatrics Society Health In Aging Foundation (www.healthinaging.org/files/documents/tipsheets/hot_weather_safety.pdf).
Drink water to your health. Fluid is important to your health because about 60% of the body is made up of water. All systems in the body rely on water to function properly. The lack of adequate water in your system it is called dehydration. Not having enough water in your body can reduce your energy and make you feel tired. You may also feel dizzy when you stand up, and dehydration can harm your kidney function.
Fluid/water will do the following:
How to Maintain Hydration
How to Drink More Water Every Day