Fluid Balance and Electrolytes

Body Fluid Composition

Water + solutes

Function of Body Water

Transports nutrients, removes wastes, transports digestive enzymes, and blood cells

intracellular fluid

inside cell

extracellular fluid

outside cell

insterstitial fluid

fluid between cells

intravascular fluid

fluid inside blood cells

transcellular fluid

fluid found in specialized spaces (CSF)

cell membrane function

acts as a barrier controlling water movement + substances in/out of cell

who is at risks for fluid imbalance?

elderly, infants, obese individuals

why are infants at risk for fluid imbalance?

high body water due to low fat + immature compensatory mechanisms

why are older adults at risk for fluid imbalance?

decreases muscle and fat + reduced compensatory mechanisms

What else can impact those w/ high risk?

diarrhea & vomiting

tonicity

osmotic pressure between two solutions separated by a membrane

what determines tonicity effects"?

solutes that cannot cross the membrane

IV solutions

contain crystalloids + solutes (glucose, salt)

what conditions do IV’s treat

shock, dehydration, electrolyte imbalances

isotonic solutions

same concentration as blood → maintains fluid balance

hypotonic solutions

lower concentration → fluid moves into cells (rehydrate cells)

hypertonic solutions

higher concentration → fluid moves out of cells into bloodstream (increase blood volume + hypernatremia)

cause of edema?

hydrostatic pressure > osmotic pressure (pushing fluid out of vessels)

hypervolemia

excess fluid in blood vessles

causes of hypervolemia

excess sodium + water intake

water intoxication

excess fluid in intracellular space —> lysis

most sensitive cells?

cerebral(brain) cells —> neurological complications

clinical manifestations of fluid excess

edema & swelling, CRACKLES, polyuria, anasarca, peripheral edema, preorbital edema, weight gain

peripheral edema

skin indents with pitting, remains after pressure

preorbital edema

swelling around the eyes

anasarca

generalized edema, skin

Fluid deficit

total body water is insufficent to meet body’s needs

what can fluid deficit lead to?

cell shrinking, hypotension, impaired cellular function & perfusion

causes of fluid deficit(1)

inadequate fluid intake, poor oral intake(stroke/dementia) (1)

causes of fluid deficit(2)

sweating, vomiting, diarrhea, nasogastric suctioning(2)

Clinical manifestations of fluid deficit

thirst, hypotension, tachycardia, dry mucous membrane, decreased skin turgor, oliguria

oliguria

low urine output

electrolytes

minerals with electrical charges found in blood, urine, and body fluids

functions of electrolytes

muscle function, nerve activity, acid-base balance, fluid balance

Sodium (na+)

controls water balance and osmolarity

potassium(k+)

electrical conduction: nervous muscle, cardiac

hyperkalemia

high potassium—> cardiac arrest

dietary sources for potassium

bananas, oranges, raisin, leafy greens, lentils

causes of hyperkalemia

impaired exertion(kidney failure), excess intake, cell lysis

trousseau sign

neuromuscular irritability = low calcoum(hypocalcemia)

positive sign for trousseau

Flexed wrist and metacarpophalangeal joints, Extended interphalangeal joints, Adducted thumb

Chvostek Sign

Facial twitch when tapped → indicates hypocalcemia

normal blood ph

7.35–7.45

Normal PaCO₂

35–45 mmHg

Normal HCO₃⁻

22–26 mEq/L

Buffer System

Uses bicarbonate to neutralize acids quickly

Respiratory Regulation

Controls CO₂ via breathing (fast and short lived)

Renal Regulation

Controls H⁺ and HCO₃⁻ (slow but long-lasting)

Purpose of Compensation

Return pH to normal range

Respiratory Compensation

Adjusts CO₂ when metabolic(kidney) problem occurs

Renal Compensation

Adjusts H⁺/HCO₃⁻ when respiratory problem occurs

Respiratory Acidosis

↑ CO₂ → ↓ pH (caused by hypoventilation)

Respiratory Alkalosis

↓ CO₂ → ↑ pH (caused by hyperventilation)

Metabolic Acidosis

↓ HCO₃⁻ or ↑ acid → ↓ pH (e.g., diarrhea)

Metabolic Alkalosis

↑ HCO₃⁻ or ↓ acid → ↑ pH (e.g., vomiting)

ABGs Measure?

pH, PaCO₂, HCO₃⁻, oxygenation

Purpose of ABGs

Assess acid-base balance

renal compensation?

excreting hydrogen + reabsorbing bicarb

respiratory compensation - acid loss(vomit)

lungs slow breathing (hypoventilation) = retain carbon dioxide = decrease pH

respiratory compensation - base loss(diarrhea)

lungs increase breathing(hyperventilation) = excrete carbon dioxide = increase pH

conditions for respiratory acidosis

asthma exacerbations, pneumonia

conditions for respiratory alkalosis

acute anxiety/panic attacks, pain+fever,

conditions for metabolic acidosis

renal failure, ketoacidosis, decrease tissue perfusion

Respiratory (pH and CO2)

opposite

metabolic acidosis (pH and HCO3-)

match

Question 1

pH: 7.30
PaCO₂: 50 mmHg
HCO₃⁻: 24 mEq/L

Respiratory acidosis
↓ pH, ↑ CO₂ → respiratory problem

pH: 7.48
PaCO₂: 30 mmHg
HCO₃⁻: 24 mEq/L

Respiratory alkalosis
↑ pH, ↓ CO₂

pH: 7.25
PaCO₂: 40 mmHg
HCO₃⁻: 18 mEq/L

Metabolic acidosis
↓ pH, ↓ HCO₃⁻

pH: 7.52
PaCO₂: 40 mmHg
HCO₃⁻: 30 mEq/L

Metabolic alkalosis
➡ pH high and HCO₃⁻ high

pH: 7.28
PaCO₂: 55 mmHg
HCO₃⁻: 26 mEq/L

Respiratory acidosis
➡ pH low and CO₂ high