Fluid, Electrolyte, and Acid-Base Regulation

What does homeostasis mean?

A steady, balanced state; the body constantly adjusts to stay in a safe range

What is the nurse's role in homeostasis problems?

Notice when the body drifts out of range and help bring it back

What are the four parts of this chapter?

1) Fluids and electrolytes 2) Rehydration and IV therapy 3) Blood transfusions 4) Acid-base balance (pH, lungs, kidneys, ABGs)

Electrolyte

A mineral in the body that carries an electrical charge; found in blood, urine, tissues and other body fluids

What are the common electrolytes?

Potassium, sodium, calcium, magnesium

Why do electrolytes matter for nerves, muscles and the heart?

These organs run on tiny electrical signals, and electrolytes carry those signals

What blood tests check electrolytes?

Metabolic panels: BMP (basic metabolic panel) and CMP (complete metabolic panel)

What does a BMP look at?

Electrolytes, fluid balance, kidney function and glucose

What does the CMP add to the BMP?

Extra information on protein and liver function

Which tests are on both the BMP and CMP?

BUN, CO2, creatinine, glucose, chloride, potassium, sodium, calcium

Which tests are only on the CMP?

Liver enzymes (ALP, ALT, AST), total bilirubin, total protein, albumin

BUN and creatinine tell you about which organ?

Kidney function

What does the CO2 on a metabolic panel measure?

Blood bicarbonate level

Memory trick for BMP vs CMP

Basic = the basics (electrolytes, kidneys, sugar); Complete = the basics plus liver and protein tests

List the five jobs of electrolytes.

1) Keep the right amount of water in the body

2) Help balance blood pH

3) Move nutrients into cells

4) Move wastes out of cells

5) Keep muscles, heart, nerves and brain working

What percent of an adult's body weight is water?

About 50-60%

What percent of an infant's or young child's body weight is water?

About 65-80%

Why are babies at higher risk for fluid problems?

Their bodies are mostly water and they cannot tell you they are thirsty, so even small losses matter more

What is the main route of water loss?

Urine (kidneys)

What can add large water losses?

Vomiting, severe diarrhea and heavy sweating

What can too little body water cause?

Tachycardia, tachypnea, confusion, headache, kidney stones and other problems

Osmolality

A measure of how many dissolved particles (solutes) are in a liquid compared with the water;

how concentrated the fluid is

What is the most commonly used lab test for fluid status?

Serum osmolality

Expected serum osmolality

285-295 mOsm/kg

Expected urine osmolality (random sample)

50-1,200 mOsm/kg

Less water in the blood causes what change in osmolality and hydration?

More concentrated, higher osmolality, decreased hydration

Higher osmolality means the client is

Drier (dehydrated); the blood is more concentrated

What do serum and urine osmolality help assess?

Serum: fluid status. Urine: kidney function and hydration

Name the three fluid compartments.

Intracellular, interstitial, intravascular

Intracellular space

Fluid inside the cells;

about 67% (two-thirds) of body water

Interstitial space

Fluid between cells, outside blood vessels (part of the extracellular space);

about 25% of body water

Intravascular space

Fluid inside the blood vessels and heart (part of the extracellular space);

about 8% of body water

What is the extracellular space?

The interstitial and intravascular spaces together (everything outside the cells)

Osmosis

Movement of water across a semipermeable membrane toward the side with more solutes (fewer water molecules) to even out concentration

Semipermeable membrane

A barrier that lets water through but not most solutes

Memory phrase that explains IV fluids, sodium problems and swelling

Water follows salt

What are the three main tools the body uses to balance water?

1) Thirst response

2) ADH

3) Osmosis

How does the thirst response work?

The lamina terminalis (near the hypothalamus) senses concentrated blood and triggers thirst; thirst stops when there is plenty of water

ADH stands for

Antidiuretic hormone (also called vasopressin)

Where is ADH released from, and what triggers it?

Posterior pituitary, on signal from the hypothalamus when osmolality rises

What does ADH do at the kidneys?

Tells the collecting ducts to hold on to water, so urine decreases and fluid volume increases

Explain ADH in one chain.

Blood too concentrated, brain releases ADH, kidneys keep water, less urine and more body fluid, blood becomes less concentrated

What do the kidneys do for fluid balance?

Filter blood, remove waste and extra fluid as urine, and return needed water and electrolytes to the blood

Sensible fluid loss

Loss you can see or measure: sweat, urine, liquid stool

Insensible fluid loss

Hard-to-measure loss:

• breathing,

• skin

• water in formed stool

A client loses fluid through breathing and the skin. This is what type of loss?

Insensible

List risk factors for fluid and electrolyte imbalance.

Dehydration, hypovolemia or overhydration; certain medications; heart, kidney or liver disorders; incorrect IV fluids or feedings; heavy sweating, vomiting, diarrhea

Expected potassium range

3.5-5 mEq/L

Expected sodium range

136-145 mEq/L

Expected calcium range (total)

9-10.5 mg/dL

Expected magnesium range

1.3-2.1 mEq/L

What is the nurse's job with an abnormal lab?

Recognize it, report it to the provider (a PN reports to the RN or provider), and anticipate ordered treatments

Diffusion

Passive movement of solutes from high to low concentration until even; needs no energy

Active transport

Cell uses energy (ATP) to move solutes from low to high concentration, against the natural direction

Best example of active transport

The sodium-potassium pump

Memory trick for diffusion vs active transport

Diffusion = rolling downhill (free); active transport = pushing a boulder uphill (costs energy)

What does the ending -emia mean?

In the blood

Hypo- vs hyper-

Hypo- = too low; hyper- = too high

Hypokalemia / hyponatremia / hypocalcemia / hypomagnesemia mean

Low potassium / low sodium / low calcium / low magnesium in the blood

Kalium is Latin for

Potassium

Dehydration vs hypovolemia (NCLEX favorite)

Dehydration = water loss without sodium loss.

Hypovolemia = loss of water AND electrolytes (or blood)

A client has vomiting and diarrhea and loses both water and electrolytes. This is

Hypovolemia

Potassium: where is it found and what does it do?

Largest intracellular electrolyte; sends electrical impulses through nerves and muscles; especially important for the heart's electrical system

How does potassium enter and leave the body?

In through food, drinks and supplements; out mainly through the kidneys, with a little lost in sweat and stool

Recommended daily potassium intake

3,400 mg for adult men; 2,600 mg for adult women

Hypokalemia is defined as

Potassium below 3.5 mEq/L

Critical potassium value for hypokalemia

Less than 3 mEq/L in adults; less than 2.5 mEq/L in newborns

Most common cause of hypokalemia

Potassium loss through the kidneys or GI tract

Which diuretics waste potassium?

Loop, thiazide and osmotic diuretics

Other medications that cause hypokalemia

Amphotericin B, high-dose penicillin, theophylline

GI causes of hypokalemia

Prolonged vomiting or diarrhea, chronic laxative use, bowel diversion, gastric suction

Other causes of hypokalemia

Cardiac conditions, metabolic alkalosis, low intake, heavy alcohol use, chronic kidney disease, DKA, heavy sweating, folic acid deficiency

Signs of mild hypokalemia (3-3.5 mEq/L)

May have no symptoms

Signs of hypokalemia below 3 mEq/L

• Muscle weakness,

• cardiac arrhythmias,

• constipation,

• fatigue

Signs of severe hypokalemia (below 2.5 mEq/L)

Respiratory paralysis and failure, paralytic ileus, hypotension, tetany, rhabdomyolysis, dangerous heart rhythms

Paralytic ileus

The intestines stop moving

Rhabdomyolysis

Muscle breakdown that can harm the kidneys

Memory trick for low potassium

Everything goes weak and slow: weak muscles, tired, constipated, irregular heartbeat (like a dying phone battery)

A client on furosemide reports leg weakness and constipation. Which lab value do you suspect?

Hypokalemia (loop diuretics waste potassium)

How is hypokalemia diagnosed?

BMP or CMP; ECG to check the heart rhythm

Treatment of hypokalemia

Treat the cause; oral or IV potassium supplements; potassium-rich foods; add oral potassium or switch to a potassium-sparing diuretic if diuretics caused it; repeat BMP/CMP to confirm recovery

How should oral potassium be given?

With or after a meal, because it can upset the stomach

IV potassium is what type of medication?

A high-alert medication; given incorrectly it can seriously harm or kill a client

IV potassium must be diluted in

100-1,000 mL of a compatible solution; NEVER given straight from the vial

Maximum IV potassium concentration

Should not exceed 40 mEq/L unless treating severe hypokalemia

Monitoring for a client receiving IV potassium

Continuous ECG monitoring and periodic potassium level rechecks

IV potassium rate in the book

Listed as 10-20 mEq/min, which looks like a typo (most references use mEq per HOUR). Check your instructor, drug reference and facility policy

NCLEX: The nurse is preparing IV potassium. Which action is correct?

Verify it is diluted, use an infusion pump, and have the client on a cardiac monitor. NEVER IV push undiluted potassium

Potassium-rich food: highest vegetable

Baked potato (900 mg, 1 medium)

Potassium-rich food: highest fruit juice

Prune juice (689 mg, 1 cup)

Potassium-rich food: highest dairy

Plain nonfat yogurt (625 mg, 1 cup)

Potassium-rich food: highest fruit

Banana (451 mg, 1 medium)

Potassium-rich food: highest fish

Salmon (400 mg, 3 oz)

Other high-potassium foods

White beans (502 mg, 1/2 cup), sweet potato (500 mg), spinach (419 mg, 1/2 cup), avocado (364 mg, 1/2 cup)

Hyperkalemia is defined as

Potassium above 5 mEq/L

Critical potassium value for hyperkalemia

Above 6.1 mEq/L (above 8.0 in newborns); severe/life-threatening above 7 mEq/L

Most common cause of hyperkalemia

Renal (kidney) failure; kidneys cannot remove potassium

Other causes of hyperkalemia

Dehydration, diabetes mellitus, trauma, burns, excess potassium intake, transfused packed red blood cells, acidosis, sepsis

Medications most linked to hyperkalemia

Potassium-sparing diuretics, NSAIDs, ACE inhibitors

Signs of hyperkalemia

Mild: usually none. Higher: life-threatening dysrhythmias, muscle weakness or paralysis; severe untreated: paralysis, heart failure, death