Fluids and Electrolytes - 4 Nursing CEs

Author: Kristi Hudson RN MSN CCRN

Written: 12/23/05

Updated: September 11, 2009

Course Description:

This course is designed to gain a better understanding of the care and management of the patient with fluid and electrolyte disorders/imbalances. Focus will be placed on the composition of body fluids, fluid compartments and factors that affect movement of water and solutes. The regulation of vascular volume and extracellular fluid osmolality will also be presented. Nursing assessment as well as laboratory assessment for patients with fluid and electrolyte imbalance (sodium, potassium, calcium phosphorus and magnesium) will also be explored. Common clinical conditions associated with fluid and electrolyte disorders will be the final focus of this course.

Course Objectives:

Upon completion of this course the student will be able to:

• Describe the composition of body fluids
• Differentiate between the fluid compartments of the body
• Explain the factors that affect movement of fluids and water
• Describe the regulation of vascular volume
• Discuss proper nursing assessment for patients with fluid and electrolyte imbalance
• Have a better understanding of laboratory assessment of fluid and electrolyte imbalance
• State normal lab values for sodium, potassium, calcium, phosphorus and magnesium
• State common causes of sodium, potassium, calcium, phosphorus and magnesium imbalances
• List 3 signs and symptoms for patients with hyponatremia and hypernatremia
• List 3 signs and symptoms for patients with hypocalcemia and hypercalcemia
• Discuss the affect that gastrointestinal disorders can have on fluid and electrolyte imbalances
• Describe the affect that hepatic failure has on fluid and electrolyte imbalances

Composition of Body Fluids:

All body fluids are dilute solutions that are made up of water and dissolved substances known as solutes. Water is the major component of the human body (males approx. 60% and females approx. 50%). The following are factors that affect body water:

• Fat Cells – Fat cells contain very little water so the more fat cells a person has, the less water they have.
• Age – As a rule, body water decreases with age and with muscle mass decline.
• Female Gender – Because of increased body fat, women are inclined to have less water mass (approx. 10% less).

Solutes:

In addition to water the body contains solutes that are either electrolytes or non-electrolyte substances. Electrolytes are substances that dissociate or separate in solution and conduct electrical current. This current dissociates into either negative (anions) or positive (cations), which are measured by their capacity to combine with each other.

• Cations – In the extracellular space Sodium (Na+) is the primary cation where as potassium (K+) is the primary cation in the intracellular space. A system known as the sodium/potassium pump which exists in the wall of the cell is responsible for releasing these electrolytes.
• Anions – The primary anions in the extracellular space are chloride (Cl-) and bicarbonate (HCO-3) where as the primary intracellular anion is phosphorus (PO3/4- ).

Non-electrolyte substances such as glucose and urea do not dissociate in solution and are measured by weight. Other clinically important non-electrolyte substances include creatinine and bilirubin.

Fluid Compartments:

• Extracellular Fluid (ECF) – This is fluid found outside of the cells and the amount of ECF decreases with age. In the newborn for example, approximately ½ of the body fluid is contained in the ECF. By the time the infant has reached one year old; the ECF has decreased to approximately 1/3 of the total volume. In an average 70 kg adult the ECF is approximately 15 liters of total volume. ECF can further be divided into the following:
  • Interstitial Fluid – This is the fluid that surrounds the cells and equals approximately 11 to 12 liters of fluid in adults (Lymph fluid is included in interstitial fluid).
  • Intravascular Fluid – This is the fluid contained within the blood vessels (plasma volume). The average adult blood volume is approximately 5 to 6 liters or which approximately 3 liters is plasma. The remaining 2 or 3 liters of volume consists of red blood cells and erythrocytes (which transport oxygen and important body buffers).
  • Transcellular Fluid – This is fluid contained within specialized cavities of the body and is also considered to be part of the ECF. Examples of trancellular fluid include:
    • Cerebral Spinal Fluid
    • Pericardial Fluid
    • Pleural Fluid
    • Synovial Fluid
    • Intraocular Fluid
    • Digestive Secretions

Intracellular Fluid (ICF) – This is the fluid that is contained within the cell. In adults it is approximately 2/3’s of the body’s fluid (27 liters). The ICF also known as “cellular soup” is comprised mostly of potassium, organic anions, proteins and other small cations and anions.

Note: The 60-40-20 rule is that in total 60% of our body weight is water with 40% of that being intracellular with the remaining 20% being extracellular.

Factors That Affect Movement of Water and Solutes:

Membranes – Each of the fluid compartments are separated by specific permeable membranes that allow the movement of water and some solutes (not plasma proteins for example because they are large molecules). Because permeability is selective; the composition of each compartment (ECF, ICF) maintains its own unique composition. Specific semi-permeable membranes include:

• Cell Membranes – these membranes separate intracellular fluid from interstitial fluid, and are composed of lipids and proteins.
• Capillary Membranes – these membranes separate intravascular fluid from interstitial fluid.
• Epithelial Membranes – these membranes separate interstitial fluid and intravascular fluid from transcellular fluid.

The Transport Process:

In addition to the use of membranes (permeable and semi-permeable); the movement of water and solutes are determined by the following processes:

Diffusion – This is the random movement of particles in all directions from an area of high concentration to low concentration. One example of diffusion is the movement of oxygen from the alveoli of the lungs into the blood stream. Another example of diffusions occurs when cations follow anions and vice versa. Substances may diffuse across the cell wall (which is composed of lipids and proteins) under the following conditions:

• The substance is small enough to pass through the protein pores (water, urea).
• The substance is lipid soluble (oxygen and carbon dioxide).
• The substance is transported by a “carrier substance” (Fore example, because glucose is such a large molecule it must combine on the outside of the cell with a carrier substance to be moved into the cell).

Factors that increase diffusion include:

• Increased temperature
• Increased concentration of solutes
• Decreased size or weight of solutes
• Increased surface area available for diffusion
• Decreased distance across which the solute mass must diffuse

Active Transport – The need for active transport (energy) is also a requirement for simple diffusion. Active transport also relies on the availability of carrier substances. Important solutes that require active transport to move in and out of the cells are:

• Sodium
• Potassium
• Hydrogen
• Glucose
• Amino-Acids

Filtration – This is the movement of water and solutes from an area of high hydrostatic pressure to an area of low hydrostatic pressure. Hydrostatic pressure is the pressure that is created by the “weight” of fluid. It is filtration for example, that allows the kidneys to filter plasma (approximately 180 liters per day).

Osmosis – This is the movement of water across a semi-permeable membrane from an area of lower solute concentration to an area of higher solute concentration. Osmosis can occur on either side of the membrane when changes in concentration occur. The following are terms that are associated with osmosis:

• Osmotic Pressure (the amount of hydrostatic pressure required to stop the osmotic flow of water)
• Oncotic Pressure (the osmotic pressure exerted by colloids which are proteins such as albumin)
• Osmotic Diuresis (increased urine output caused by substances such as Mannitol, glucose or contrast medium)
• Osmolality (the ratio of solutes to water)

Regulation of Vascular Volume:

In an attempt to maximize the environment for the body’s cells, the extracellular fluid volume (ECF) is continually being regulated by a combination of renal, metabolic and neurological functions. Though “the total content of sodium” in the ECF determines the ECF volume, there are other regulatory properties that alter and modify the ECF as the body changes. The following are examples of the body’s fluid volume regulatory systems:

The Sympathetic Nervous System (SNS) – The SNS provides the initial compensatory response to rapid and short term changes in the ECF. Changes in stretch that are sensed by volume receptors for example lead to changes in sympathetic tone (i.e. cardiac output, arterial resistance and release of renin by the kidneys).

Renin-Angiotensin – Renin is released from the kidneys in response to decreased renal perfusion. Here is the process:

• Renin acts on Angiotensin to produce Angiotensin 1
• Angiotensin 1 is converted by an enzyme to Angiotensin 2 which is a potent vasoconstrictor
• Angiotensin 2 stimulates the release of Aldosterone
• Aldosterone is a mineralcorticoid hormone released by the adrenal cortex and acts to increase reabsorption of sodium
• The reabsorption of sodium leads to water retention making Aldosterone a potent and important volume regulator

Natriuretic Peptides – These peptides are hormones that influence fluid volume and cardiovascular function through increased excretion of sodium, direct vasodilation and opposing the Renin-Angiotensin process. The following three natriuretic peptides have been identified:

• Type A – produced by the atrial myocardium
• Type B – produced by the ventricular myocardium
• Type C – produced by the vascular endothelium

Note: Type A and B peptides are released in response to increased pressure in the myocardium while Type C peptide is released in response to vascular bed changes.

Antidiuretic Hormone (ADH) – Produced by the hypothalamus and secreted by the posterior pituitary gland; ADH acts on the collecting ducts of the kidney to increase the reabsorption of water and allow for the excretion of concentrated urine. ADH is primarily regulated by plasma osmolality and ECF volume. Factors that increase the release of ADH include:

• Increased plasma osmolality
• Decreased extracellular fluid volume
• Decreased blood pressure
• Stress and pain
• Medications such as Morphine and Barbiturates
• Surgery and certain anesthetics
• Positive pressure ventilation

Factors that decrease the release of ADH include:

• Decreased plasma osmolality
• Increased extracellular fluid volume
• Increased blood pressure
• Certain medications such as Dilantin

Medications that alter the action of ADH include:

• Lithium (suppresses)
• Demeclocycline (suppresses)
• Methoxyflurane (suppresses)
• Chlorpropamide (enhances)
• Indomethacin (enhances)

Note:  In addition to ADH, thirst also acts to regulate extracellular fluid concentrations and is essentially stimulated by the same factors that stimulate ADH.

Nursing Assessment for Patients at Risk for

Fluid/Electrolyte Imbalances:

Nurses must be diligent in assessing patients for potential or actual fluid volume and electrolyte disturbances. A detailed patient history should include the following dimensions:

• Physiologic – Are there disease processes or disorders that may cause or contribute to a fluid of electrolyte disturbance (diabetes or ulcerative colitis for example)
• Developmental – Is the patient at an increased risk due to age or social situation (an elder who lives alone for example)
• Psychological – Are their behavioral or emotional problems that may increase the risk for fluid and or electrolyte disturbances (anorexia or bulimia)
• Spiritual – Does the patient have specific beliefs or values that affect their ability to comply with treatment or interventions (denial of blood products, religious fasting)
• Sociocultural – Does the patient have cultural, financial or educational factors that are inhibiting them from complying with medical treatment?

Clinical Assessment:

• Daily Weights (one kg of weight represents one liter of fluid)
• Intake (oral fluids, IV fluids, tube feedings, catheter irrigants)
• Output (urine, feces, vomitus, NG and wound drainage and using a rating system excessive sweating)
• Hemodynamic Monitoring (Cardiac Output, CVP, PAP and PAWP)

Vital Signs:

• Elevation of body temperature may lead to increased insensible loss
• Decreased body temperature my result “from” hypovolemia
• Increased respiratory rate and depth my lead to increased insensible loss
• Shortness of breath (crackles, rales, rhonchi) may signal fluid build up
• Increased heart rate may signal fluid volume deficit
• Bounding pulse may signal fluid volume overload
• Weak thready pulse may signal fluid volume deficit
• Irregular heart rate may signal electrolyte imbalance (potassium, calcium or magnesium)
• Elevated blood pressure may signal fluid volume deficit
• Decreased blood pressure may signal fluid volume excess
• Postural changes in blood pressure may signal fluid volume deficit

Integumentary System:

• Flushed dry skin may signal fluid volume deficit
• Changes in skin turgor/increased capillary refill may signal fluid volume deficit
• Edema may signal fluid volume excess
• Increased furrowing of the tongue may signal fluid volume deficit
• Decreased moisture between cheek and gum may signal fluid volume deficit

Cardiovascular System:

• Jugular vein distention may signal fluid volume excess
• Development of an S3 heart tone may signal fluid volume excess
• Dysrhythmias may occur with potassium, calcium or magnesium imbalances

Neurologic System:

• Altered LOC, restlessness and confusion may signal fluid volume deficit
• Positive Trousseau’s sign or positive Chvostek’s signs occur with hypocalcemia and hypomagnesemia
• Neuromuscular irritability can occur with metabolic and respiratory alkalosis

Gastrointestinal System:

• Anorexia, Nausea, Vomiting may occur with either acute fluid volume excess or deficit
• Thirst may be a signal for fluid volume deficit

Laboratory Assessment:

Tests to evaluate fluid status include:

• Serum Osmolality (280 to 300 mOsm/kg)
• Hematocrit (40% to 50% in males and 37% to 47% in females)
• BUN (6 to 20 mg/dL)
• Urine Osmolality (a typical 24 hour specimen is 300 to 900 mOsm/kg. Random urine osmolality is approximately 50 to 1200 mOsm/kg)
• Urine Specific Gravity (1.001 to 1.040)
• Urine Sodium (50 to 130 mEq/L)

Page 2 | Page 3 |