Fluid and Electrolytes
NCLEX™ Review

Electrolytes are charged chemicals or ions that live in the blood to provide the body a variety of important functions. The main function of electrolytes are to serve as messengers delivering signals from cells to cells, nerves to nerves, and even organs to organs. When electrolytes reach specific concentrations in the body, they can trigger a variety of systemic functions including muscle contractions and action potentials in the nerves. For this reason, it is imperative that electrolytes stay within a specific concentration in the blood for the body to function correctly.

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Two key concepts to know for the NCLEX™ exam regarding electrolytes are therapeutic range and homeostasis. Therapeutic range is defined as the range of concentration for which the drug is most effective and least toxic. For electrolytes, it is important to monitor the concentration of ions like sodium or potassium in the blood when patients are taking medications that may alter these values (e.g. potassium retention with ACE inhibitors, sodium loss with loop diuretics).

Homeostasis on the other hand describes the state of equilibrium or balance that is maintained by a self-regulated process in the body. Homeostasis is a vast and complicated concept that helps to explain how the body functions in a variety of ways. In a healthy human the body does an excellent job at maintaining these levels of electrolytes without any outside intervention. When the body experiences trauma, sickness, or even drug toxicities electrolyte levels might become imbalances which can lead to serious consequences and further worsen their condition.

Causes of Fluid and Electrolytes Imbalances

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Electrolyte depletion can occur as a result of a variety of complications often resulting from sickness. Since electrolytes are generally excreted from the body in the urine or feces – conditions affecting the amount of excretion can affect electrolyte concentrations consequently. Excessive vomiting stemming from illnesses such as infection can lead to over excretion of water and the ions within it. Excessive defecation as diarrhea or stoma drainage (via colostomy or ileostomy) can lead to substantial reductions in electrolytes. Excess urination due to diseases like diabetes or UTI infection can lead to over voiding of ions like sodium, potassium, or calcium. Finally, excessive sweating (diaphoresis) as a result of heat exhaustion, fever, or severe burns can also lead to significant electrolyte imbalance.

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It is also important to note that a variety of medicines and supplements can affect the concentration of ions in the blood. Examples includes diuretics which work by excreting ions to draw out water and reduce blood pressure – therefore overdose of certain blood pressure medications can lead to this result. Laxatives are another important class of medications that can lead to over excretion of electrolytes in the same way that diarrhea does. Insulin overdose can lead to reduction of potassium levels as well as blood sugars which can be potentially very dangerous. Finally, antipsychotics such as quetiapine or Risperdal can lead to imbalances of ions like sodium and potassium. For this reason, it is always imperative to check electrolyte labs prior to initiating new therapies in order to prevent long-term complications.

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Signs, Symptoms and Clinical Manifestations of Fluid and Electrolytes Imbalances

Potassium Imbalance

Potassium is a vital ion for the body specifically when it comes to the function of the heart. A normal potassium level is usually considered to be something around 3.5-5.0 mEq/L – however it is important to note that hospitals may vary in what they consider to be the normal therapeutic range. Typical signs and symptoms of potassium imbalances may include irregular heartbeats and spasms or weakness in the muscles.

Sodium Imbalance

Sodium plays a crucial role in the function of practically every organ in the body. Normal sodium levels are usually measured as 135-145 mEq/L. A key function of sodium for the body involves the movement of water in and out of the body as sodium draws water in and out of the tissues. As a result, sodium can regulate blood pressure and fluid retention. Other functions includes maintaining pH or the acidity in the blood as it can help buffer against acids and bases that are consumed. Symptoms of sodium imbalances may include weight gain or loss, weakness and fatigue, and high or low blood pressure.

Magnesium Imbalance

Magnesium is less commonly monitored compared to the other electrolytes, yet it still provides several important functions for the body. Magnesium plays a role in protein synthesis, nerve function, and blood sugar control. Magnesium can also stimulate the parathyroid hormone which regulates calcium levels in the blood. It is necessary for both the absorption of calcium and vitamin D. The normal range of magnesium is 1.3-2.1 mg/dL.

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Calcium Imbalance

Calcium is very famously regarded as the electrolyte that is vital for the growth and structural integrity of the bones, but it has several other important functions as well including muscle contraction and blood pressure dilation. Calcium can also fill in for magnesium when magnesium levels fall. Magnesium is regulated by the parathyroid hormone which stimulates the release of calcium into the blood, calcitonin hormone which puts calcium into the bone, and calcitriol which controls the release of calcitonin. Normal values for calcium are 9.0-10.5 mg/dL.

Phosphate Imbalance

Phosphate is important for bone and teeth formation as well as tissue repair. It is regulated by the parathyroid hormone like calcium and can fluctuate based on calcium levels. Normal values for phosphate are 3.0-4.5 mEq/L.

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Chloride Imbalance

Chloride is often not considered by clinicians when it comes to electrolyte monitoring but can be important to measure in the event of serious conditions as it is important for maintaining the pH levels of the blood. Chloride can also contribute to fluctuations in blood volume and blood pressure – in parts since it usually is consumed alongside sodium. The normal level for chloride is 98-106 mEq/L.

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Pharmacological and Nursing Interventions

When a patient presents with electrolyte imbalances the primary intervention is simply to replace or increase the elimination of these ions. Common pharmacological interventions includes intravenous fluid replacement containing various levels of electrolytes. The best-known example is simply IV saline which can come in various concentrations and should be used based on the measured concentration. For example, hypertonic saline may be used when sodium levels are used instead of normal saline which is 0.9% saline in water (representing approximately the concentration of sodium in the blood). Another example is lactated ringers which contains multiple electrolytes used in cases of more severe depletion.

It is critical to also understand certain food sources that patients can be counseled on to either avoid or increase their consumption of to manage their electrolyte imbalances. Patients who are low in potassium, calcium, magnesium, or phosphate can be advised to increase their consumption of green leafy vegetables. Patients low in potassium specifically may be advised to increase their consumption of fruit and avocados. On the other hand, if they are experiencing hyperkalemia, they should be advised to avoid sodium substitutes as potassium is generally used in these cases to replace sodium in patients who need to have sodium restriction. Magnesium and calcium may be replaced with foods like almonds and dairy products like yogurt or milk. Phosphate is unique in the since that it is usually found in sources like meat, poultry, fish, and beans.

Lastly it is important to understand that the key concept for electrolyte levels involves the concentration of these ions in the blood compared to the total amount of the chemicals in the body. As a result, variation in either the levels of electrolytes or the amount of fluid in the body can yield significant consequences.

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Hemodilution is defined as a decreased concentration of electrolytes resulting from a gain of fluids or due to loss of ions via hemorrhage (bleeding). All lab values in this case will be low as the volume of blood is higher than the number of electrolytes. Examples of conditions that can cause this condition includes volume overload as a result of renal failure or heart failure.

Hemoconcentration is the opposite concept which is the result of fluid loss and dehydration. Reduced fluid leads to a relative increased concentration of electrolytes compared to the volume of blood. These patients will present with high lab values of electrolytes and are at an increased risk of serious complications such as seizures and arrythmias.


Electrolyte imbalances can often be difficult to diagnosis and treat while leading to many different complications. It is imperative to carefully monitor patients for signs and symptoms of these imbalances as a result. Additionally, it is always important to screen patients for risk factors that may alter electrolyte levels such as new medications, illness, or traumatic events. Understanding electrolytes will be crucial for your success on the NCLEX™ exam as well as your career as patients in severe states will often present with these conditions.