The Overuse of Diuretics in the Older Patient

INTRODUCTION

Diuretics are used everyday in the hospital and especially in older patients. Many older adults have health issues, like heart failure, that causes their bodies to retain more fluid than it should. This leads to edema, which can have adverse effects on the body. Diuretics are often used to help the body expel some of the excessive amounts of fluid, but if used in excess, diuretics can cause their own problems. This paper will examine the normal fluid and electrolyte status of older adults and then go into the different shifts and clinical manifestations that take place when diuretics are overused.

NORMAL FLUID AND ELECTROLYTE STATUS OF OLDER ADULTS

In an older adults maintaining fluid and electrolyte balance is important. Notable differences in older adults’ ability to regulate fluids and electrolytes relate to a lower body water percentage and decreased kidney function. When people age their body’s water percentage decreases and this happens for multiple reasons. One of those reasons is that older people’s thirst decreases so they take in less water. In the kidney, the creatinine clearance decreases indicating a decreased glomerular filtration rate. There is also a decrease in renal plasma flow. The kidney also gets smaller and weighs less as people age. This means homeostasis can be lost because of either a build-up or loss of electrolytes. The two most common electrolyte and fluid problems in the elderly are dysnatremias, which are abnormal levels of sodium. This can be caused by an older adult’s inability to concentrate or dilute their urine. Finally, assuming there is no adverse pathology occuring, older adults’ electrolyte levels should be in the normal ranges when they are maintaining homeostasis (Allison & Lobo, 2004).

FLUID SHIFTS

Older adults face many health issues. A common symptom of many of these issues is fluid overload. For example, when there is heart failure and the heart is not able to pump fluids as efficiently, there can be fluid overload, which may lead to edema or other fluid concerns. To correct this fluid imbalance, many geriatric patients are prescribed diuretics. Diuretics in the simplest explanation, increase urination and decrease the amount of fluid in the body; however, when taken in excess, diuretics can cause new issues. The primary fluid issues caused by excessive diuretic use is dehydration and hypovolemia (Burchum & Rosenthal, 2016). Here is an examination of the different types of diuretics, how they work, and how they affect the fluids in the body.

Most patients are prescribed thiazide diuretics first. This class of diuretics work in the distal convoluted tubules in the nephrons in the kidneys. A thiazide’s primary effect is that it blocks three to five percent of sodium reabsorption in the distal convoluted tubule. Without a thiazide diuretic, sodium is normally reabsorbed in the distal convoluted tubule and, because water follows sodium, water is also reabsorbed. When a patient takes a thiazide diuretic, there is a decrease in sodium reabsorption and therefore a decrease in water reabsorption, which leads to an increase in fluid output in the form of increased urination. This ultimately leads to less fluid in the body (Akbari & Khorasani-Zadeh, 2019) .

The most effective class of diuretics are loop diuretics. The are considered the most effective because loop diuretics lead to the highest level of fluid loss. As the name suggests, loop diuretics act on the loop of Henle. Specifically, loop diuretics tend to work on the ascending portion of the loop and block the reabsorption of sodium and chloride. Loop diuretics block all reabsorption in this portion of the loop. Normally about twenty percent of sodium and chloride reabsorption happen in this portion of the nephron so blocking this reabsorption significantly decreases the amount of fluid that is reabsorbed. This strength of diuretic is only used when there is a substantial fluid overload and weaker diuretics will not work. The amount of fluid that is not reabsorbed leads to an increased urinary output and this leads to less fluid being present in the body, which could lead to dehydration or hypovolemia if used in excess (Burchum & Rosenthal, 2016).

A third class of diuretics are osmotic diuretics. Currently, there is only one approved osmotic diuretic in the United States and that is mannitol. Mannitol differs in its mechanism from other diuretics. Mannitol is a sugar based drug that has a six-carbon structure and is filtered by the glomerulus, but is not absorbed like other solutes in the tubules. This means that when mannitol is present, the solute concentration of the fluid traveling through the nephron is higher, leading to a higher osmotic pressure that prevents water from being reabsorbed. The more mannitol a patient has in their system, the smaller the amount of water that is reabsorbed and the greater the fluid output (Burchum & Rosenthal, 2016).

Mannitol clearly works different than the other diuretics and it is used for a different purpose. The other diuretics are administered when there is a fluid overload, and it is necessary for the body to expel fluids. In contrast, mannitol is used when the body is already in a state of hypovolemia, hypotension, or dehydration. In order to prevent complete kidney failure, urination is necessary. In these low fluid situations, the amount of fluid going through the kidney is so small that all the sodium and chloride is reabsorbed (even with the use of other diuretics) and with it the water is also reabsorbed and there is no urine and that leads to kidney failure. By administering mannitol intravenously, the sugar provides enough solute so that all the water cannot be reabsorbed and urine flow continues preserving kidney function (Burchum & Rosenthal, 2016).

Close monitoring of fluid balance is required when administering mannitol because it can leave the bloodstream at any capillary bed besides for those in the brain. This means that mannitol could leave and with it water would follow causing edema. It is especially important to monitor this when administering mannitol for someone who is already experiencing pulmonary edema because mannitol could exacerbate this condition (Burchum & Rosenthal, 2016).

ALTERATIONS IN ACID/BASE BALANCE

Directly, diuretics do not have a lot of influence on the acid/base balance. Diuretics affect fluid balance by increasing urinary output and through that affect the balance of electrolytes. It is the changes in electrolytes that can affect the acid/base balance. As previously discussed, diuretics block the reabsorption of sodium, but this means that the fluid gets to the end of the distal collecting duct with a very high sodium concentration. This high sodium concentration triggers the kidneys to try to reabsorb the sodium (now that the diuretic is not interfering) and in order to absorb that sodium the kidneys release hydrogen, which causes metabolic alkalosis (Luckey & Parsa, 2003).

Another common connection to acid/base imbalances is that diuretics can cause hypokalemia, which is a decrease in potassium levels. A common issue with hypokalemia is metabolic alkalosis. When diuretics block the reabsorption of electrolytes, one of the things the kidneys lose is potassium ions. The kidney responds by trying to conserve its potassium by releasing hydrogen ions. As the potassium exits the cell, hydrogen ions enter the cell and this leads to metabolic alkalosis. The loss of chloride can also lead to metabolic alkalosis. This happens because the body is excreting chloride faster than it is excreting bicarbonate and the build up of bicarbonate can trigger metabolic alkalosis (Willis, 2015).

CLINICAL MANIFESTATIONS

The most common side effects of excessive diuretic use are hypochloremia, hyponatremia, hypovolemia, hypokalemia, hypotension, and dehydration (Burchum & Rosenthal, 2016). Being able to recognize the signs and symptoms of these different conditions will help one recognize when their patient is at risk for the overuse of diuretics. Dehydration and hypovolemia happen because the body is losing an excessive amount of fluids and hypotension often follows. Often all of these conditions go together and will happen concurrently, but the different electrolyte decreases present with some different symptoms that one should be able to recognize .

Most of the problems with diuretics come from the loss of electrolytes. These conditions are hypochloremia, hyponatremia, and hypokalemia and often they will all go together. Diuretics block the reabsorption of fluid by blocking the reabsorption of different solutes. This means that the body is losing sodium, chloride, and potassium at a faster than normal rate and this leads to deficits. Monitoring the lab values can indicate when a patient is heading into deficit. Low levels begin when sodium drops below 135 mEq/L, potassium drops below 3.5 mEq/L, and chloride drops below 95 mEq/L. It is also crucial that one can recognize the signs and symptoms of these different deficits so that they can either stop the use of diuretics or take countermeasures (Willis, 2015).

The first signs of hypokalemia is muscle weakness. This can progress to leg cramps, diminished tendon reflexes, and occasionally these symptoms can impact the respiratory muscles, which will lead to the patient having an elevated heart rate and respiratory rate. If the hypokalemia is not addressed and the condition progresses, severe symptoms can take place. These include the loss of critical muscles which lead to conditions such as cardiac arrest, paralytic ileus, and respiratory arrest. Cardiac problems are one of the main concerns with low potassium levels so monitoring those vital signs will be very important. As a patient starts having cardiac problems, their pulse may weaken and become irregular (Willis, 2015). These are all things that a nurse needs to monitor in order to catch hypokalemia early.

Hyponatremia symptoms will vary based on how quickly the sodium levels are falling and how low they get. At first, there may not be any symptoms, but then as sodium levels continue to decrease the first observable symptoms will often include nausea that is followed by vomiting and possibly anorexia. From there symptoms progress to the neurologic system and include headaches and confusions. The patient may decline in their levels of consciousness and if not addressed can go all the way to a coma (Willis, 2015).

Hypochloremia goes along with hyponatremia and hypokalemia and because of that, shares many of the same signs and symptoms. One of the distinguishing factors is that when a patient hits hypochloremia (often along with the other deficit conditions) they may go into metabolic alkalosis as talked about above. The signs and symptoms that a person is entering this acid base imbalance include twitching, muscle cramps and weakness, fever, and possible irritability or agitation. Patients will also likely exhibit shallow breathing because they will be trying to hold on to their carbon dioxide to correct their imbalance. As the condition reaches dangerous levels a patient may have seizures, enter a coma, display arrhythmias, or go into respiratory arrest (Willis, 2015).

CONCLUSION

In conclusion, diuretics can be a very effective therapy for correcting an overload of fluid in the body; however, the patient should be closely monitored to avoid the complications caused by the overuse of diuretics. By monitoring patients lab values, specifically around electrolyte levels, caregivers can catch electrolyte imbalances early and either stop the use of diuretics if appropriate or start a secondary therapy to counteract the effect of the diuretic.

SUPPORT DRAWINGS

Normal Nephron with Normal Na + and Cl – reabsorption rates

Osmotic Diuretics (Mannitol)	Loop Diuretics	Thiazide Diuretics

REFERENCES

• Akbari, P., & Khorasani-Zadeh, A. (2019, February 04). Thiazide Diuretics. Retrieved July 17, 2019, from https://www.ncbi.nlm.nih.gov/books/NBK532918/
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• Luckey, A. E., MD, & Parsa, C. J., MD. (2003, October 01). Fluid and Electrolytes in the Aged. Retrieved July 17, 2019, from https://jamanetwork.com/journals/jamasurgery/fullarticle/395625
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