Gettysburg Medical News
 The Clinical View
 by P.E. Hoffsten, M.D.
 06 July 2005

HOW MUCH WATER DO YOU NEED?

            I have previously written several columns regarding water balance in the human body.  But patients continue to come to the clinic with water overload, the associated dropsy, the associated shortness of breath, and stating that they are drinking eight glasses of water a day. They state that is what they were taught in Junior High School.  For some people, that much water is poisonous.  In the past month, I have had to hospitalize two individuals with heart failure because they wanted to continue drinking large amounts of water to “flush their kidneys”.  That idea just doesn’t work.

            To gain perspective on the right amount of water to use each day, imagine our ancestors living in the jungle or the desert.  There weren’t any flush toilets, there was no running water in the sink and the idea of watering the lawn hadn’t occurred to them yet.  They were simply trying to stay alive.  If a drought occurred and the watering holes dried up, they had a major crisis.  Now imagine what a gift it would if these people had the ability to conserve water.  The human body is equipped with a series of hormones that are released when the body begins to get dehydrated.  These hormones are carried to the kidneys and tell the kidneys to conserve water and salt because it looks like the body is running out.  In this situation, the kidneys are capable of maintaining balance while excreting just a pint of urine per day.  The body’s waste products can  all be concentrated down into that small volume and excreted on a daily basis without accumulation of waste products.

            These hormones, mentioned above, are released by a sensing mechanism in the heart.  As the amount of blood that the heart pumps decreases and causes dehydration. These hormones are released in increasing amounts telling the kidney to conserve water and salt.  Because of the excellence of these mechanisms, we are here today because our ancestors survived the droughts.

            Today, we have flush toilets, running water in the sink, and spend a lot of time watering the lawn or crops.  Thus, dehydration of a life-threatening degree is unusual.

            But another problem has become very common.  This is called heart failure.  When a person develops heart failure, the heart doesn’t pump as much blood as it normally would because the heart has gotten weak.  While this is very different than the dehydration that our ancestors experienced, the message from the heart to the kidneys is exactly the same.  The heart tells the kidneys that there is not much blood getting pumped and misinterprets the situation to represent dehydration.  Therefore, the kidneys are told to save salt and save water.  But of course, this is the wrong strategy for a person with heart failure because it leads to edema (dropsy) and accumulation of water in the lungs making the person short of breath.  To treat this problem, we give patients “water pills” such as furosemide (Lasix) or hydrochlorothiazide (HCTZ).  These two water pills prevent the kidneys from retaining salt in water that the heart is telling the kidneys to do.  This lets the persons extra water get urinated out.

            Now comes the problem.  Imagine a person who has heart failure and is drinking eight glasses of water per day.  This amounts to four pounds of water.  If a person accumulates half of that a day, in a weeks time they gained 14 pounds.  That is a lot of weight to be carrying around in one’s legs or one’s lungs.  To compound the problem, the person has already learned that the water pills, that they are taking, makes them urinate more. This means getting up and making more trips to the bathroom and this has little recreational value.  Therefore, the person stops taking the water pills because it makes them urinate so much. As long as they drink eight glasses of water a day, the fluid builds up and builds up and builds up.  As an additional concern, when a person drinks these large amounts of water, they rarely take in the amount of salt that would balance that water intake. Thus, the salt in their body gets diluted out and the person feels weak and very tired.  I think of this whole constellation of events as “water poisoning”.

            How do you fix this problem?  There are several steps to take as listed below:

            1.  Limit fluid intake to those beverages that have recreational value or fluid value.  Drinking water by itself in a person with heart failure is unnecessary and actually poisonous.

            2.  The tendency for people whose salt in their body has be diluted out is to become thirstier yet. Recognize this problem and resist drinking the large amount of water this impulse brings.

            3.  Use the water pills to drain the extra water from the body.  Believe it or not, this will cut down on the thirst.

            4.  There are medications that can be prescribed through your local clinics called ARB’s (angiotensin receptor blockers) and ACE-I’s (angiotensin converting enzyme inhibitors).  These two families of blood pressure and heart failure drugs decrease the thirst that the person has and allows the heart to recompensate.

            5.  Recognize that travel and stress independently lead to secretion of water-retaining hormones.  It is very common for individuals who travel across country sitting in a car or airplane to develop ankle swelling on arrival at the new destination.  This may occur even in those individuals who do not have heart failure but can be a major problem in those that do.  For patients with heart failure, it is highly recommended that there be intermittent days of rest, such as the first or second day of arrival and on the first and second day on return home.

            To re-iterate the message of this column, it is very unusual that an adult needs to drink eight glasses of water a day no matter what.  For patients with heart problems, this can be poisonous.  Young individuals working in the sun and hot environments need fluids. Our elderly population which are protected by air conditioned homes, do not need eight glasses of water a day.