Fluid and Acid-Base Balance Overview

Osmosis

Movement of fluids from an area of low concentration of solutes (lots of water) to an area of high concentration of solutes (less water)

Diffusion

Movement of particles from an area of high concentration to low concentration

Hydration

Water balance is regulated by thirst perception and the antidiuretic hormone (ADH)

ADH

Antidiuretic Hormone (also called arginine vasopressin) released from pituitary gland when there is an increase in osmolality or decrease in circulating blood volume; increases water absorption

Dehydration

Water deficit - both sodium and water loss

ICF

Intracellular Fluid - Fluid INSIDE of the cell; Potassium (K+) is the primary electrolyte inside of the cell

ECF

Extracellular Fluid - Fluid OUTSIDE of the cell; Sodium (Na+) is the primary electrolyte outside of the cell

Interstitial Fluid

Fluid that surrounds the outside of cells

Intravascular Fluid

Fluid located inside the blood vessels; contains blood cells & electrolytes

Homeostasis

Osmatic equilibrium between compartments

Osmolality

Natural body concentration of solutes

Tonicity

Concentration of IV fluid

Isotonic

Equal concentration; Example: saline solution for body

Hypertonic

Lower osmolality than the body

Hypotonic

Higher osmolality than the body

RAAS

Renin-Angiotensin-Aldosterone System

Renin

Released by the kidney due to low blood pressure

Aldosterone

Hormone that tells the kidneys to reabsorb sodium and water

Angiotensin II

Activated by renin and causes vasoconstriction

Electrolytes

Play a role in the movement of fluid and the process of osmosis

Signs and Symptoms of Dehydration

Low blood pressure, weak pulse, and postural hypotension; Elevated hematocrit and serum sodium levels; Headache, dry skin, and dry mucous membranes

Treatment for Dehydration

Oral fluids and hypotonic saline solution (5% dextrose in water)

Isotonic Alterations

Lose everything (water & sodium) together.

Isotonic fluid loss (FVD)

Loss of total body water (TBW) with proportional change in concentration of electrolytes.

Examples of Isotonic fluid loss

Dehydration & hypovolemia.

Isotonic fluid excess (FVE)

Gain of total body water (TBW) with proportional change in concentration of electrolytes.

Hypertonic Alterations

Related to water loss or sodium gain.

Water deficit

Dehydration - both sodium and water loss.

Manifestations of water deficit

Low blood pressure, weak pulse, postural hypotension.

Treatment for water deficit

Oral fluids, hypotonic saline solution (5% dextrose in water).

Hypernatremia

Serum sodium >145 mEq/L.

Effects of hypernatremia

Water movement from ICF to ECF leading to intracellular dehydration.

Manifestations of hypernatremia

Intracellular dehydration, seizures, muscle twitching, hyperreflexia.

Treatment for hypernatremia

Isotonic salt-free fluids.

Hypotonic Alterations

Free water excess that dilutes sodium.

Hyponatremia

Decreases the ECF osmotic pressure leading to water moving into the cell.

Water excess

Compulsive water drinking leading to water intoxication.

Manifestations of water excess

Cerebral edema, pulmonary edema, cellular edema.

Treatment for water excess

Fluid restriction; may need hypertonic saline solution.

FVD - Fluid Volume Deficit

Causes include fluids shifting in response to concentration of solutes in other compartments.

Signs & Symptoms of FVD

Low BP / Hypotension & Orthostatic Hypotension, compensatory tachycardia, dizziness, dry mouth, thirst, cool clammy skin.

Management of FVD

Fluid restriction, sodium restriction, hypertonic fluids, diuretics.

FVE - Fluid Volume Excess

Causes include fluids shifting in response to the concentration of solutes in other compartments.

Signs & Symptoms of FVE

High BP, bounding pulse, pulmonary congestion, shortness of breath (SOB), jugular vein distention (JVD), later edema.

Common examples of Isotonic fluids

0.9 NS, Lactated Ringers (RS), D5W (Dextrose 5%).

Examples of Hypotonic fluids

0.45% NS, 0.25% NS.

Examples of Hypertonic fluids

D5/0.45 NS, D5% 0.9% NS, Hypertonic Saline (HS) 3% or 5%.

Effects of administering hypo, iso and hypertonic fluids

Do they stay in the veins and arteries? Do they move into the cell? Do they cause fluid to move out of the cell?

Isotonic

No fluid shift; fluid is the same as natural body concentration (same osmolality & tonicity).

Hypotonic

Fluid moves from vascular space into the cells; used for dehydration.

Hypertonic

Fluid moves from cells into the vascular space.

Edema

Accumulation of fluid in interstitium.

Causes of Edema

Hypertonic alterations, increased capillary hydrostatic pressure, decreased plasma oncotic pressure, increased capillary permeability, lymphatic obstruction.

Venous obstruction

A cause of increased capillary hydrostatic pressure leading to edema.

Decreased plasma oncotic pressure

Caused by loss or diminished production of albumin.

Increased capillary permeability

Caused by inflammation and immune response.

Lymphatic obstruction

Can lead to lymphedema.

Manifestations of Edema

Localized vs generalized, dependent edema, pitting edema, 'third space', swelling and puffiness, tight-fitting clothes and shoes, weight gain.

Treatment for Edema

Treat fluid imbalance, elevate edematous limbs, use compression stockings or devices, avoid prolonged standing, restrict salt intake, take diuretic agents.

Electrolyte balance/imbalance

Identify normal levels, signs of deficit and excess, and treatment.

Sodium (Na+)

Normal Levels: 136-145 mEq/L

Sodium Functions

PRIMARY ECF cation, regulates osmotic forces, maintains fluid volume, allows muscle contractions, contributes to nerve impulses.

Signs of Sodium Deficit (<135 mEq/L)

Causes: Plasma hypoosmality, cellular swelling. Manifestations: Lethargy, headache, confusion, seizures, coma, muscle cramping, memory loss, anorexia.

Treatment for Sodium Deficit

Restrict water intake; depends on underlying disorder.

Signs of Sodium Excess (>145 mEq/L)

Causes: Excess water loss, excess Na admin, diabetes insipidus, heat stroke, hypertonic IV solution. Manifestations: Thirst, elevated temperature, dry & swollen tongue, sticky mucosa, neuro symptoms, restlessness, weakness, fluid retention, hypertension, disorientation.

Treatment for Sodium Excess

Hypotonic solution, encourage fluids, restrict sodium.

Chlorine (Cl)

FOLLOWS SODIUM. Function: Primary ECF anion, provides electroneutrality.

Potassium Normal Levels

3.5-5.0 mEq/L

Potassium Functions

Transmission and conduction of nerve impulses, normal cardiac rhythms, skeletal and smooth muscle contraction, regulates ICF osmolality & deposits glycogen in liver and skeletal muscle cells.

Potassium during pH imbalance - Acidosis

Potassium moves from ICF to ECF in exchange for hydrogen.

Potassium during pH imbalance - Alkalosis

Potassium moves from ECF to ICF in exchange for hydrogen.

Signs of Potassium Deficit (<3.5 mEq/L)

Causes: Decreased intake (starvation), shift from ECF to ICF with increased renal loss, v/d. Manifestations: Decreased neuromuscular excitability, skeletal muscle weakness, smooth muscle atony, cardiac dysrhythmias (flattened/depressed T-wave, prominent U-wave).

Treatment for Potassium Deficit

Replace potassium orally and/or intravenously; dietary sources include bananas, oranges, dried fruits, tomatoes, avocados, dried peas, meats, broccoli, dairy products, meat, whole grains, potato.

Signs of Potassium Excess (>5.0 mEq/L)

Causes: Increased intake, shift from ICF to ECF, decreased renal loss, metabolic acidosis, insulin deficiency, cell trauma. Manifestations: Mild attacks (tingling of lips and fingers, restlessness, intestinal cramping and diarrhea, peaked T-waves on ECG), severe attacks (muscle weakness, loss of muscle tone, paralysis).

Treatment for Potassium Excess

Polystyrene sulfonate (kayexalate); if bowels do not work, limit dietary K+, calcium gluconate + insulin + buffered solution (bicarb), dialysis.

Normal pH

7.35-7.45

Abnormal pH

<6.8 & >7.8

Body Fluid Normal pH - Gastric Juices

1.0-3.0

Body Fluid Normal pH - Urine

5.0-6.0

Body Fluid Normal pH - Blood

7.35-7.45

Body Fluid Normal pH - Cerebrospinal Fluid

7.28-7.32

Body Fluid Normal pH - Pancreatic Fluid & Bile

7.8-8.0

Body Fluid Normal pH - Small Intestine

6.8-7.5

ABG - Arterial Blood Gas

Normal, acidosis, and alkalosis arterial blood pH levels are obtained through ABG sampling.

Acidosis

pH < 7.35

Alkalosis

pH > 7.45

Reading ABGs - CO2

If CO2 matches = Respiratory; High = acid/acidosis.

Reading ABGs - HCO3

If HCO3 matches = Metabolic; High = base/alkalosis.

Systems that help regulate acid-base balance

Bones, Lungs, Kidneys.

Lungs Function in Acid-Base Balance

Lungs can decrease carbonic acid by exhaling carbon dioxide; compensate in minutes to hours by increasing or decreasing ventilation.

Kidneys Function in Acid-Base Balance

Kidneys can reabsorb bicarbonate or regenerate new bicarbonate; compensate in hours to days by producing more acidic or alkaline urine.

Metabolic Acidosis

pH < 7.35, PaCO2: normal, HCO3 < 22mEq/L; causes include lactic acidosis, renal failure, diabetic ketoacidosis, diarrhea, starvation.

Treatment for Metabolic Acidosis

Buffering solution administration (sodium bicarb), treat underlying causes, correct sodium and water deficits.

Metabolic Alkalosis

pH > 7.45, PaCO2: normal, HCO3 > 26 mEq/L; causes include prolonged vomiting or gastric suctioning, excessive bicarbonate intake, hyperaldosteronism with hypokalemia, diuretic therapy.

Treatment for Metabolic Alkalosis

Sodium chloride, potassium, chloride IV (chloride replaces HCO3).

Respiratory Acidosis

pH < 7.35, PaCO2 > 45 mmHg, HCO3: normal; causes include depression of the respiratory center, respiratory muscle paralysis, disorders of the chest wall and lung tissue.

Treatment for Respiratory Acidosis

Restore adequate ventilation; may need mechanical ventilation, oxygen therapy.

Respiratory Alkalosis

pH > 7.45, PaCO2 < 35mmHg, HCO3: normal; causes include high altitudes, hypermetabolic state, early salicylate intoxication, anxiety/panic disorder.

Treatment for Respiratory Alkalosis

Paper bag (treats hypoxemia & hypermetabolic states).