Alterations in Fluid and Electrolyte Balance

Functions of Water in the Body - Total Body water

Nutrient and waste transport in blood
Skin structure and resilience
Digestion
Temperature maintenance
Lubrication of joints and membranes
Chemical reactions
IgA function

Total Body Water

60% of body weight in adults
2/3 intracellular
1/3 extracellular
Interstitial
Plasma
Other

Composition of the ECF, Plasma, and Interstitial Fluids

Large amounts of sodium and chloride
Moderate amounts of bicarbonate
Small quantities of potassium, magnesium, calcium, and phosphorus

Composition of the ICF

Almost no calcium
Small amounts of sodium, chloride, bicarbonate, and phosphorus
Moderate amounts of magnesium
Large amounts of potassium

Body Water Intake

Intake of 2000 - 2500 mls
Liquid
Water in food
Oxidation

Body Water Output

Output of 2000 - 2500 mls
Urine
Feces
Lungs
Skin

Total Body Water Variants

TBW varies with age
Infants = 75%
Adults = 60%
Elderly = 50%
TBW varies with body composition
More fat = lower % water

Mechanisms Controlling Fluid and Electrolyte Movement

Diffusion
Active transport
Osmosis
Measurement of osmolality
Osmotic movement of fluids

Diffusion

Constant movement of molecules across cell membranes is required to maintain homeostasis.
Diffusion refers to the movement of particles along a concentration gradient.

Active Transport

Na+ moves out of cell and K+ moves in by sodium/potassium pump (energy dependent)

Osmosis

Water moves by osmosis
Water pulled to area of higher particle concentration
Osmotically active particles
Na+, Cl-, urea, glucose

Tonicity

The tension that osmotic pressure exerts on a cell
Isotonic
Hypertonic
Hypotonic

Hydrostatic pressure

pushing force exerted by fluid

Osmotic pressure

pulling force of particles (colloidal osmotic pressure, colloidal oncotic pressure)

Exchange Across Cell Membranes- Difference between Osmotic and Hydrostatic Pressure

Hydrostatic pressure varies throughout the capillaries
Osmotic pressure is relatively stable
Difference between the two pressures determines the direction of fluid movement

Lymphatic channels

Absorb proteins, fats, plasma and cells from the interstitial fluid and return to the circulatory system.
Blockage causes increased interstitial osmotic pressure.

Thirst

early symptom of volume deficit
Release of ADH when serum osmolality increases

Homeostatic Regulation of Fluid Balance

Release of aldosterone when blood volume decreases
Natriuretic peptides released when atria are streched

Edema

Palpable swelling by expansion of the interstitial fluid volume
Can occur in any body tissue
Most common in the feet and lower legs
Can be life-threatening in the brain, lungs, or larynx

Causes of Edema

Increased capillary hydrostatic pressure
Decreased capillary osmotic pressure
Increased capillary permeability
Obstruction of lymphatic flow

Third Spacing

(1st space = normal fluid distribution; 2nd space = edema)
Loss of fluid into a non-functional space
Ascites
Pleural effusion
Ileus
Pericardial effusion

Isotonic Fluid Volume Disorders

Also called
Extracellular fluid volume disorders
Saline imbalances
Because sodium is confined to the extracellular compartment, loss or gain of saline does not affect the intracellular compartment

Volume deficit- Isotonic Disorders

Volume deficit
Loss of sodium-containing fluid from the body
Causes - see Table 39.4, p. 1035
Manifestations
Thirst
Weight loss
Hypotension
Dizziness
Oliguria

Volume Excess- Isotonic Disorders

Abnormal increase in sodium- containing fluid
Causes - see Table 39.5, p. 1036
Manifestations
Weight gain
Edema
Neck vein distention
Dyspnea, crackles

Disorders of Na+ Concentration

Abnormal osmolality
Abnormal sodium concentration
Also called water imbalance
Normal serum sodium
concentration: 135 - 145 mEq/L

Water excess: Hyponatremia

Serum Na+ < 135mEq/L
Causes - see Table 39.6, p. 1038
Result: cellular swelling

Manifestations of Water Excess

Headache, lethargy, confusion, seizures, coma
Nausea, vomiting, anorexia, diarrhea
Muscle cramps, weakness, fatigue

Water deficit: Hypernatremia

Serum Na+ > 145mEq/L
Causes - see Table 39.7, p. 1040
Result: cellular shriveling

Manifestations of Water Deficit

Confusion, lethargy, seizures, coma
Thirst
Dry, flushed skin
Tachycardia, hypotension

Dehydration

Combination of ECV deficit and hypernatremia

Causes of Dehydration

Vomiting and diarrhea
Excessive sweating
Untreated diabetes mellitus
No access to water
Lack of thirst in elderly

Dehydration Manifestations

Sudden weight loss
Hypotension
Dizziness
Sunken fontanels (infants)
Thirst
Decreased skin turgor
Dry mouth
Lethargy, confusion

Potassium Balance

Normal level 3.5 - 5.0 mEq/L
Source - dietary
Excreted through kidneys, skin, gi tract
Predominates in ICF

Hypokalemia

Serum K+ < 3.5
Affects resting potential of cells
Low potassium makes muscles less reactive causing::::
Cardiac dysrhythmias
Anorexia, vomiting, ileus
Weakness, paralysis, CNS depression
Polyuria, thirst

Hypokalemia Causes

Vomiting, diarrhea, gastric suction
NPO status, fasting
Alkalosis, rapid correction of acidosis
Certain diuretics, renal failure
Cushing syndrome, corticosteroids

Hyperkalemia

Serum K+ > 5.0
Affects resting potential of cells
Muscles may be unable to contract resulting in
Dysrhythmias, cardiac arrest
Weakness, flaccid paralysis
Nausea, vomiting, diarrhea

Hyperkalemia Causes

Renal failure
Certain diuretics
IV infusion, blood transfusion
Acidosis
Major tissue injury or chemotherapy

Calcium Balance

Normal level 9 - 11 mg/dl
99% of calcium is in bone
1% in blood
40% bound to plasma protein
Essential for blood clotting

Hypocalcemia

Serum Ca++ < 9
Affects threshold potential of cells
Low calcium makes muscles more reactive causing
Neuromuscular irritability
Trousseau & Chvostek signs
Hyperactive reflexes
Tetany
Seizures
Cardiac dysrhythmias, hypotension

Hypocalcemia Causes

Insufficient intake, low albumin
Chronic diarrhea
Hypoparathyroidism, high phosphate
Alkalosis
Pancreatitis, renal failure
Cancer chemotherapy

Hypercalcemia

Serum Ca++ > 11
Affects threshold potential of cells
Neural excitability is decreased and kidneys cannot concentrate urine
Nausea, vomiting, constipation
Polyuria, polydipsia
Muscle weakness and atrophy
Osteoporosis
Hypertension, dysrhythmias, cardiac arr

Hypercalcemia Causes

Hyperparathyroidism
Malignant tumors
High calcium ingestion
Prolonged immobility
Excessive Vitamin D

Phosphate

intracellular anion
Inverse relationship to calcium
Important in energy production

Magnesium

ICF cation
S&S similar to calcium

Chloride

ECF anion
Important in pH regulation
HCl acid in stomach

Electrolyte Summary

Cardiac dysrhythmias
Hyper- or hypo- kalemia
Weakness, poor muscle tone
Hyperkalemia
Hypokalemia
Hypercalcemia
Hypermagnesemia
Twitchy, crampy muscles
Hypocalcemia
Hypomagnesemia