Fluid and Electrolytes Lecture: Unit 4

Composition and Clinical Structure of Body Fluids

Total body water (TBW) represents the complete volume of fluid present in the human body. This fluid is categorized primarily into two compartments: intracellular fluid (ICF), which exists inside the cells, and extracellular fluid (ECF). The extracellular compartment is further subdivided into interstitial fluid, which surrounds the cells; intravascular fluid, or plasma within the blood vessels; and transcellular fluid, which includes specialized fluids like cerebrospinal fluid or synovial fluid.

Fluids contain solutes, which are categorized as crystalloids or colloids. Crystalloids consist of small particles and are easily dissolved, while colloids are larger particles such as proteins that do not settle and are unable to pass through certain membranes. These substances can also be distinguished based on their electrical properties as electrolytes, which carry an electrical charge and conduct electricity, or nonelectrolytes, which do not carry a charge. Common cations, which are positively charged electrolytes, include sodium ($Na^+$), magnesium ($Mg^{2+}$), potassium ($K^+$), calcium ($Ca^{2+}$), and hydrogen ($H^+$). Major anions, which are negatively charged electrolytes, include chloride ($Cl^-$), bicarbonate ($HCO_3^-$), and phosphate ($PO_4^{3-}$). Fluids and electrolytes move to maintain homeostasis, which is the internal stability of the body.

Mechanisms of Fluid and Electrolyte Movement

Fluids shift back and forth through cell walls and vessel walls via several distinct processes. Osmosis is the primary movement of fluid across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration. Diffusion involves the movement of solutes or particles from an area of higher concentration to an area of lower concentration. Filtration is the process through which fluid and solutes move together across a membrane from a compartment of higher pressure to one of lower pressure. Active transport is a movement mechanism that requires energy to move electrolytes across cell membranes against a concentration gradient.

Key terminology regarding fluid movement includes osmotic pressure, which is the power of a solution to draw water across a semipermeable membrane. Oncoic pressure, specifically referred to as colloid osmotic pressure, is the osmotic pressure exerted by proteins like albumin in the plasma. Osmolality and osmolarity are measures of the concentration of solutes in the body fluids. Tonicity describes the osmotic pressure of two solutions and how that pressure influences the movement of water across the cell membrane.

Classifications of Fluid Tonicity and Volume States

Tonicity is used to describe the relationship between particles and fluid. Isotonic fluids have an equal concentration of particles and fluid compared to the internal environment of cells. Hypotonic fluids contain fewer particles relative to the fluid volume, causing water to move into cells. Hypertonic fluids contain more particles than fluid, causing water to move out of cells.

Clinical volume states are described similarly. An isotonic state indicates that fluid and particles are in equal balance. Hypervolemia refers to a state where there is more fluid relative to particles (fluid volume excess). Hypovolemia describes a state where there is less fluid relative to particles (fluid volume deficit). While simple fluid volume excess and deficit typically refer to isotonic imbalances, hypertonic and hypotonic imbalances also occur. Advanced conditions, such as cirrhosis, can lead to simultaneous fluid volume excess in some compartments while maintaining a deficit in others, often presenting with symptoms like edema.

Sodium Homeostasis ($Na^+$) and Imbalances

The normal range for serum sodium is $135-145\,mEq/L$. Sodium serves as the primary determinant of serum osmolality. Hyponatremia occurs when the serum sodium level is less than $135\,mEq/L$, often resulting in serum osmolality less than $290\,mOsm/kg$. Signs and symptoms include confusion, lethargy, weakness, muscle cramping, seizures, anorexia, nausea, and vomiting. Nursing interventions involve administering intravenous fluids containing sodium, encouraging the consumption of high-sodium foods, and monitoring vital signs, intake and output (I&O), and laboratory results. In severe cases, hypertonic IV saline solutions may be ordered. Dietary sources of sodium include breads, cheeses, chips, processed meats like lunch meat, hot dogs, bacon, and ham, as well as commercially canned foods and table salt.

Hypernatremia is defined by a serum sodium level greater than $145\,mEq/L$, frequently resulting in serum osmolality greater than $290\,mOsm/kg$. Clinical manifestations include thirst, dry and sticky mucous membranes, weakness, elevated temperature, and severe psychological symptoms such as confusion, irritability, decreased level of consciousness (LOC), hallucinations, and seizures. Nursing management focuses on increasing water intake, Implementing sodium-restricted diets, and administering hypotonic IV solutions as ordered. Vital signs, LOC, and lab values must be monitored closely.

Potassium Homeostasis ($K^+$) and Imbalances

The normal serum range for potassium is $3.5-5.0\,mEq/L$. Hypokalemia occurs when the serum potassium level falls below $3.5\,mEq/L$. Symptoms include a weak and irregular pulse, fatigue, lethargy, anorexia, nausea, vomiting, muscle weakness, cramping, decreased peristalsis, hypoactive bowel sounds, paresthesia, and cardiac dysrhythmias. Nursing interventions include cardiac monitoring, monitoring vital signs (especially heart rate and rhythm), and administering potassium supplements or IV fluids containing potassium. Safety warning: Potassium must never be administered via IV bolus or IV push. High-potassium foods include fish (excluding shellfish), whole grains, nuts, broccoli, cabbage, carrots, potatoes with skins, bananas, cantaloupe, oranges, and nectarines.

Hyperkalemia is defined as a serum potassium level greater than $5.0\,mEq/L$. Signs and symptoms include anxiety, irritability, confusion, muscle weakness, flaccid paralysis, paresthesia, gastrointestinal hyperactivity, diarrhea, abdominal cramping, and life-threatening cardiac dysrhythmias, bradycardia, heart block, or cardiac arrest. Nursing management involves cardiac monitoring, limiting potassium-rich foods, and the administration of Kayexalate. In acute settings, glucose and insulin may be administered to move potassium back into the cells. Dialysis may be required in severe cases.

Calcium Homeostasis ($Ca^{2+}$) and Imbalances

The normal serum range for calcium is $9-10.5\,mg/dL$. Hypocalcemia is defined as a serum calcium level below $9\,mg/dL$. Signs and symptoms include confusion, anxiety, hyperactive reflexes, cardiac dysrhythmias, and muscle cramps that can progress to tetany and seizures. Specific clinical signs include positive Trousseau’s and Chvostek’s signs, as well as numbness and tingling of the extremities. Nursing actions include monitoring the heart rate and rhythm via a cardiac monitor, initiating fall and seizure precautions, and administering calcium and Vitamin D. Dietary sources of calcium include dark green leafy vegetables, canned salmon, soy products, and milk.

Hypercalcemia occurs when the serum calcium level is greater than $10.5\,mg/dL$. Clinical manifestations include lethargy, stupor, coma, depressed deep muscle strength and tone, dysrhythmias, anorexia, nausea, vomiting, constipation, pathological fractures, and the development of kidney stones. Nursing interventions focus on cardiac monitoring, encouraging increased fluid intake, increasing client activity including active range of motion (ROM), and restricting high-calcium foods.

Magnesium Homeostasis ($Mg^{2+}$) and Imbalances

The normal serum range for magnesium is $1.5-2.5\,mEq/L$. Hypomagnesemia is a level below $1.5\,mEq/L$. It presents as neuromuscular irritability with tremors, disorientation, vertigo, confusion, increased reflexes, and convulsions. Similar to hypocalcemia, it may present with positive Trousseau’s and Chvostek’s signs. Cardiovascular signs include tachycardia and elevated blood pressure. Respiratory difficulties, anorexia, and dysphagia (difficulty swallowing) are also common. Nursing interventions include cardiac monitoring, assessing mental status and LOC, assessing swallowing ability before providing food or medicine, administering magnesium, and implementing seizure precautions. Clients should be advised to avoid alcohol. Dietary sources include cereal grains, nuts, dried fruit, legumes, green leafy vegetables, dairy, meat, fish, and chocolate.

Hypermagnesemia is a level greater than $2.5\,mEq/L$. Symptoms include a warm, flushed appearance, peripheral vasodilation, nausea, vomiting, drowsiness, lethargy, generalized weakness, and decreased deep tendon reflexes. Critical signs include hypotension, dysrhythmias (especially bradycardia and heart block), and respiratory depression or arrest. Nursing care includes assessing vital signs, heart rhythm, and mental status. Nurses should encourage increased oral intake, increase IV fluids, and may administer loop diuretics or provide respiratory support. Dialysis is used for severe cases, and a low-magnesium diet should be maintained.

Physical Assessment and Diagnostic Indicators

Assessment of fluid and electrolyte status begins with a health history focused on recent changes in fluid intake, diet, and lifestyle habits. Vital signs require close attention, specifically for prolonged fever, tachycardia, changes in respiration, and alterations in blood pressure.

Intake and output (I&O) measurement is critical. Oral intake includes all fluids and foods that become liquid at room temperature. Output includes all body fluids and drainage that can be measured. Documentation should occur every shift, and totals are added to calculate 24-hour balances to identify trends over subsequent days. Weight monitoring is a precise indicator of fluid status; a change of $1\,kg$ ($2.2\,lb$) is equivalent to $1\,L$ ($1000\,mL$) of fluid.

Edema is graded on a $4+$ scale based on the depth of the indentation in millimeters:

• $1+$: Slight indentation ($2\,mm$) that returns to normal fairly quickly.

• $2+$: Deeper indentation ($4\,mm$) that lasts longer.

• $3+$: Obvious indentation ($6\,mm$) that lasts for several seconds.

• $4+$: Deep indentation ($8\,mm$) that remains for several minutes.

Skin turgor assessment involves pinching the skin. In normal balance, it returns to normal quickly, while a fluid volume deficit causes the skin to remain "tented." This is less accurate in older adults due to decreased elasticity. Mucous membranes are normally moist and pink; severe deficit causes dry, sticky membranes with tongue furrows and cracked lips.

Factors Influencing Fluid and Electrolyte Balance

Multiple factors impact balance, including age, where infants and elderly individuals are significantly more susceptible to imbalances. Stress causes increased fluid retention and decreased renal excretion. Body weight is a factor because total body fluid is often disproportionate in people who are obese. Surgery affects balance through preoperative NPO (nothing by mouth) status, blood loss, stress, fluid drainage, and postoperative vomiting. Chronic medical conditions such as cardiac, hepatic, renal, and respiratory disorders are secondary causes of ongoing imbalance.

Nursing diagnoses are derived from this data. For example, a diagnosis of fluid imbalance may be supported by nausea, vomiting, output greater than intake, dry mucous membranes, a urine specific gravity of $1.041$, and a urine osmolarity of $1080\,mOsm/kg$. Fluid retention might be diagnosed based on a bounding pulse of $116\,bpm$, labored respirations at $32\,breaths/min$, $3+$ pitting edema, and lung crackles. Dehydration is supported by fluid volume loss, weak pulse, tachycardia, and thirst.

Nursing Planning and Implementation

Goals for clients at risk are centered on returning to or maintaining normal balance, such as achieving moist mucous membranes by a specific time, ensuring no pitting edema within $48\,hours$, or achieving a normal pulse rate. Monitoring involves continuous evaluation of vital signs, I&O, heart rhythm, and daily weights. Blood tests are used to assess the effectiveness of treatments.

When restricting fluid intake, the nurse should provide $50\%$ of the total allowance during the day when the client is most active and consuming meals. This allowance is divided among meals, snacks, and medication administration. Any running IV fluids must be subtracted from the total fluid restriction. Electrolyte restrictions (such as sodium) are classified as mild, moderate, or severe.

For oral replacement, clients should be encouraged to increase fluid intake to offset losses, with at least $50\%$ taken during the day. Caffeine should be avoided. The most common electrolyte supplements are potassium and calcium. Potassium is often needed when using potassium-wasting diuretics, and calcium is needed when there is inadequate vitamin D or milk product intake.

Intravenous Therapy and Site Assessment

Intravenous (IV) fluids are classified as medications and must follow the rights of medication administration. The IV route allows for immediate fluid/electrolyte maintenance or replacement, faster medication onset, and access for nutrition or blood transfusions to reestablish oncotic pressure.

IV solutions include crystalloids, which are classified by tonicity (hypotonic, isotonic, hypertonic). Common types include Normal Saline and Lactated Ringer's. Colloids contain protein or starch and remain in the vascular space to increase circulating volume and oncotic pressure.

Assessing the IV site for infiltration is a critical nursing responsibility. Signs include swelling, tenderness, coolness, firmness, and skin blanching. The infiltration severity scale is as follows:

• 0: No symptoms.

• 1: Skin blanched, edema less than $1\,inch$, cool to touch, possible pain.

• 2: All grade 1 symptoms plus edema of $1-6\,inches$.

• 3: All grade 2 symptoms plus translucent extremity, edema greater than $6\,inches$, mild to moderate pain, and possible numbness.

• 4: All grade 3 symptoms plus tight, leaking skin, deep pitting edema, circulatory impairment, and moderate to severe pain (indicative of extravasation).

If infiltration occurs, the infusion must be stopped immediately, the catheter removed, and the area assessed for extravasation. Nurses should apply thermal applications, elevate the extremity, and outline the area of damage with a marker. If tissues leak, a sterile dressing should be applied.

Questions and Discussion

NGN NCLEX-RN Practice Question: Potassium Imbalance
A nurse is reviewing laboratory results for a client who has been experiencing prolonged vomiting. The client's serum potassium level is $2.9\,mEq/L$. Which four assessment findings should the nurse anticipate?
Correct Findings:

1. Muscle weakness and cramping

2. Decreased peristalsis and hypoactive bowel sounds

3. Weak, irregular pulse

4. Cardiac dysrhythmias
   (Note: Anxiety, irritability, GI hyperactivity, and diarrhea are signs of hyperkalemia, not hypokalemia).

Knowledge Check: Fluid Movement
The nurse identifies that body fluids shift back and forth through cell and vessel walls. Which term best describes this movement of fluid?
Correct Answer: Osmosis.

NGN NCLEX-RN Practice Question: Sodium Assessment and Intervention
A nurse is caring for a client with a serum sodium level of $152\,mEq/L$. The client is experiencing thirst and dry, sticky mucous membranes. Which four nursing interventions are appropriate?
Correct Interventions:

1. Administer hypotonic IV saline solutions as ordered.

2. Monitor vital signs, level of consciousness, and laboratory results.

3. Encourage the client to increase water intake.

4. Implement a sodium-restricted diet.