Fluid and Electrolytes

Fluid and Electrolyte: Chapter 6

Water is very important to all of us, why?
Essential for homeostasis
Medium where metabolic reactions take place
Transportation system for the body, carries nutrients, wastes
Facilitates movements of body parts, lungs, joints

60% adults body weight
70% infant
Females higher fat, lower water
Elders and obese lower %

Ideally water taken in should = water eliminated

Fluid distribution:
ICF – Intracellular, inside the cells
Extracellular – outside the cells

Extracellular fluid includes
Intravascular (IVF) or blood
Interstitial (ISF) intercellular fluid
Cerebrospinal fluid (CSF) constantly being produced, reabsorbed
Transcellular fluids – in joints, cavities
Up to 8 liters in 24 hours present in stomach, small intestine, later reabsorbed in the large intestine

Obtain fluid through solid food and liquids
Eliminate through urine, feces, perspiration, and exhaled air

Control mechanisms:
Thirst – hypothalamus, osmoreceptor cells sense internal environment
Antidiuretic hormone (ADH) controls the amount of fluid leaving the body by promoting reabsorption of water into the blood from the kidneys
Aldosterone reabsorption of sodium and water
Atrial natriuretic peptide (ANP) reduces workload on heart by regulating fluid, sodium and potassium

Water moves throughout the body primarily by filtration and osmosis

Edema – excessive fluid visible or hidden, usually worse in dependent areas, prolonged edema interferes with venous return, arterial circulation, cell function

Edema: 4 causes:
1. Increased capillary hydrostatic pressure - ^ BP…what does this do…if the blood pressure in the venous system is high it can force fluid back into tissues ex. Pulmonary edema
Other causes – hypervolemia, increased blood volume, associated with kidney failure, pregnancy, congestive heart failure, administration of excessive fluids

2. Loss of plasma proteins (albumin) – kidney disease, malnutrition (less protein synthesis) can cause the loss of proteins which generally stay in capillaries these proteins keep fluids with them, so less proteins = greater loss of fluids from the capillaries

3. Edema from obstruction of the lymphatic circulation, lymphedema

4. Increased capillary permeability from inflammatory response or infection, histamines and other chemicals released during tissue injury

Effects of edema:
Increase body weight
Functional impairment – joint, lungs, heart
Pain from pressure on nerves, crerbral edema, visceral edema
Impaired circulation – fatigue, poor healing
Difficult to get proper measurements, dental, casts
Edematous tissue very susceptible to breakdown

Insufficient intake, excessive loss or combination
Ex. Vomiting causes fluid to shift from vascular compartment to replace digestive fluids, if this continues hypovolemia, eventually fluid is loss from cells which decreases function

*Mild deficit 2% body weight loss
*Moderate deficit 5% loss in body weight
*Severe deficit decrease 8%

Dehydration is more serious for elderly and infants due to the lack of reserves. Also infants’ greater insensible water losses through proportionally larger body surface area but also greater need for water due to higher metabolic rate. Vascular department can deplete quickly leading to hypovolemia affecting heart, brain, kidneys. S&S decreased # wet diapers, lethargy and dry mucous membranes.

Water loss may also indicate loss of electrolytes example, sweat = water and sodium chloride

*Isotonic dehydration proportionate loss of fluid and electrolytes,
*Hypotonic loss of more electrolytes than water
*Hypertonic loss of more fluid than electrolytes

Causes of dehydration:
Vomiting and diarrhea, gastric suctioning or drainage can result in loss of electrolytes, nutrients, glucose and water.
Excessive sweating loss of sodium and water
Diabetic ketoacidosis loss of fluid, electrolytes and glucose in urine
Insufficient water intake elderly, unconscious
Use of concentrated formula in attempt to provide extra nutrition

Dry mucous membranes, decreased skin turgor, dry skin, no tears
Lower BP, higher weak pulse, fatigue
Increased hematocrit (^ red blood cells in proportion to water
Decreasing mental function as brain cells lose water and decrease function

Body attempts to compensate
Increasing thirst
Increasing heart rate
Constricting cutaneous blood vessels pale cool skin
Production of less urine

What is ‘Third Spacing’?

When fluid shifts out of vessels into body cavity or tissue and is no longer available as circulating fluid examples – peritonitis – until the cause is removed fluid remains in the third space. Weighing will not indicate labs such as hematocrit and electrolytes do.

Fluid and Electrolytes

Electrolyte Imbalances:
Sodium – Na+ primary cation (positively charged) in the extracellular fluid
Diffusion occurs between vascular and interstitial fluids. Transport is controlled by the sodium-potassium pump. Actively secreted in body fluids. Ingested and then expelled in urine, feces and sweat. Levels are primarily controlled by aldosterone. Vital in the maintanence of extracellular fluid volume and essential for nerve impulses and muscle contraction.

Hyponatremia – below 135 mEq per liter

Excessive sweating, vomiting, diarrhea
Use of diuretic drugs combined with low salt diet
Hormonal imbalances, insufficient aldosterone, adrenal insufficiency, excess ADH
Early chronic renal failure
Excessive water intake

Impair nerve conduction – fatigue, muscle cramps, weakness, nausea, vomiting, anorexia, headache, confusion
Decreased osmotic pressure may cause a fluid shift into cells, hypovolemia, v BP

Hypernatremia – more than 145 mEq/liter
Excess sodium intake without proportionate water intake or loss of water larger and faster than loss of water.

Inadequate amounts of ADH (diabetes insipidus)
Loss of thirst mechanism
Watery diarrhea
Prolonged periods of rapid respirations

Fluid shift out of cells
Weakness, agitation
Firm subcutaneous tissues
Increased thrist
Decreased urine output
^ BP

Potassium K+ major intracellular cation thus serum levels are low – 3.5-5mEq/L
Intracellular concentration 160 mEq/L. It is difficult to assess total body potassium by measuring the serum level.

Available: Bananas, citrus fruits, tomatoes, lentils, potassium chloride tablets may be taken. Insulin helps move potassium into cells.

*The acid base balance influences potassium movement

Hypokalemia: less than 3.5 mEq/L

Excessive losses from body – diarrhea, diuretic drugs
Excessive aldosterone or glucocorticoids (Cushings)
Treatment of ketoacidosis with insulin
Decreased dietary intake, alcoholism, eating disorders, starvation

Cardiac arrhythmias, cardiac arrest,
Anorexia, nausea, constipation,
Fatigue, muscle twitch, weakness, leg cramps,
Shallow respirations, paresthesias, postural hypotension,
Polyuria, nocturia,
Elevated serum pH 7.45

Hyperkalemia: greater than 5 mEq/L

Renal failure
Deficit of aldosterone
Use of potassium sparing diuretics
Leakage of intracellular potassium into extracellular fluids via severe burns
Displacement of potassium by prolonged or severe acidosis

Arrhythmias, cardiac arrest,
Nausea, diarrhea,
Muscle weakness, Paralysis, paresthesias,
Decreased serum pH 7.3

Ca++ extracellular cation, ingested in food primarily milk, excreted in urine and feces

Hypocalcemia less than 4 mEq/L

Deficient serum albumin
Increased serum pH

Hypercalcemia greater than 5mEq/L

Uncontrolled release of calcium ions from bones due to neoplasms
Immobility leading to demineralization
Increased intake of calcium
Milk-alkali syndrome – increased milk and antacids intake

Depressed neuromuscular activity, muscle weakness, lethargy, stupor, personality changes,
Anorexia, nausea
Interference with ADH, decreased absorption of water, polyuria, thirst
Kidney stones
Arrhythmias, increased blood pressure

Magnesium -

Normal Labs

Acid-Base balance

Normal pH 7.35-7.45

Death can result from a pH below 6.8 or above 7.8


A pH less than 7.35 decreases cell enzyme activity and depresses the CNS

Mechanisms to control pH
  1. Buffer pairs respond to pH changes
  2. Respiratory system can affect carbon dioxide (carbonic acid)
  3. Kidneys can modify excretion of acids and production of bicarbonate

Buffer systems:
A buffer is a combination of alkaline salts and weak acids

Buffer systems pairs:
Sodium bicarbonate – carbonic acid system
Phosphate system
Hemoglobin system
Protein system

Respiratory system

Renal system

Acid-Base Imbalance





Acid Base Balance


Gould, B. E., & Dyer, R. M. (2011). Pathophysiology for the health professions (4 ed.). St. Louis, Missouri: Saunders Elsevier.

Story, L. (2012). Pathophysiology: A practical approach. Sudbury, MA: Jones & Bartlett Learning .



Fluid and electrolytes by Sarah Varney

Acid Base balance by Sarah Varney