3 - Fluids and Electrolytes

4 Questions

How is total body fluid distributed?

60% intracellular fluid

40% extracellular fluid

Of extracellular fluid → 75% is interstitial fluid and 25% is intravascular fluid

What substances are found in body fluids?

Water, glucose, lipids, creatinine, and urea

Cations (+) → Sodium, potassium, magnesium, calcium

Anions (−) → Chloride, bicarbonate, phosphate

How does water move between body fluid compartments?

Water is an uncharged molecule that can cross cell membranes

Movement is regulated by osmotic pressure

It moves toward the area with the higher osmolar concentration → more dissolved particles

Osmolarity?

Number of osmoles in a particular volume of solvent

Accounts for total volume, including solutes and water

Units → mOsm/L

Osmolality?

Number of osmoles in a particular weight of solvent

Accounts only for water content

Units → mOsm/kg

What is normal plasma osmolality?

275-295 mOsm/kg

Tonicity?

Concentration of non-permeable solutes in a solution

Higher concentrations → pull water out of cells

Lower concentrations → push water into cells

Hypertonic?

Solute concentration of intravenous fluid is higher than intracellular fluid

Fluid moves out of the cell

Isotonic?

Solute concentration of intravenous fluids equal to intracellular fluid

No overall net movement of water

Hypotonic?

Solute concentration of intravenous fluids less than intracellular fluids

Fluid moves into the cell

Examples of fluid disorders?

Dehydration

Hypovolemia

Hypervolemia

ELectrolyte imbalances

What causes dehydration?

Diarrhea

Vomiting

Excessive sweating

Fever

Inadequate fluid intake

Diuretic use

Hypovolemia?

Significant decrease in volume

Caused by → bleeding, severe dehydration, burns

Can lead to either hemorrhagic (blood loss) shock or distributive (sepsis) shock!!

Fluid resuscitation?

The practice of →

Restoring the intravascular volume

Improving tissue perfusion to prevent end organ damage

Correcting hemodynamic instability

What characteristics should we look for when choosing a fluid for resuscitation?

Remains in the intravascular space

Predictably increases blood volume and restores hemodynamics

Causes minimal electrolyte changes

Readily available and inexpensive

Adult fluid resuscitation?

Estimated around 30-35ml/kg/day

Or around 1500 mL/m²

Pediatric fluid resuscitation for <10kg?

At least 100 mL/kg/day

Pediatric fluid resuscitation for 10-20kg?

100 mL/kg/day plus an additional 50mL/kg/day

Pediatric fluid resuscitation for >20kg?

100 ml/kg/day, and 50ml/kg/day AND an additional 20 ml/day/day

What is the 4-2-1 rule for maintenance fluids?

Calculates hourly maintenance fluid requirements for PEDs →

First 10 kg → 4 mL/kg/hr

Next 10 kg → 2 mL/kg/hr

Each kg over 20 kg → 1 mL/kg/hr

What are the fluid resuscitation guidelines for special populations?

Sepsis → 30 mL/kg fluid bolus over the first 3 hours

Burn patients → Use the Parkland formula to calculate fluid requirements

Examples of crystalloid fluids for fluid resuscitation?

0.9% Normal saline (NS)

Lactated Ringers (LR)

Plasma-lyte

Examples of colloid fluids for fluid resuscitation?

Blood

Albumin

Hetastarch

Dextran

Blood?

Colloid

Typing required

Potential disease transmission

Increases oxygen carrying capacity

Product of choice → during hemorrhagic shock

Albumin?

Colloid

No blood typing

Must be treated like a blood product

Potential disease transmission

Hetastarch and Dextran?

Colloids

Risk of kidney injury

Increased bleeding risk

Normal sodium range?

135-145 mEq/L

Hypernatremia?

>145 mEq/L

Hyponatremia?

<135 mEq/L

Severe hyponatremia?

<125 mEq/L

Causes of hypernatremia?

Insensible water loss → lungs, skin

GI water loss

Fever

Burns

Arginine vasopressin disorder (diabetes insipidus) → either AVP-Deficiency or AVP-Resistance

How is hypernatremia treated?

Correct elevated sodium slowly to avoid complications

If hypovolemic → restore intravascular volume first

Then give hypotonic fluids → D5W or 0.45% NS to replace free water

Arginine vasopressin deficiency disorder (AVP-D) treatment?

Desmopressin (DDAVP) 5-10 mcg up to twice daily intranasally

Max dose 40 mcg/day

Arginine vasopressin resistance disorder (AVP-R) treatment?

Sodium restriction → 2000 mg/day

Thiazide diuretics

Hyponatremia symptoms?

Nausea

Headache

Fatigue

Hyponatremia treatment?

Treat underlying cause

Max correction rate generally 8-10 mEq/L per 24 hours to → reduce the risk of osmotic demyelination syndrome

Isotonic hyponatremia / pseudohyponatremia ?

Osmotic substances in the blood that make the sodium “look” low on the lab

Causes include → hyperlipidemia, hyperproteinemia, hypertriglyceridemia

Hypertonic hyponatremia ?

Osmotic substances in the blood that pull water into the bloodstream and dilute sodium

Causes include → hyperglycemia, mannitol infusions

Hypotonic hyponatremia?

Low serum tonicity causing water to move into cells

Types include → hypovolemic, euvolemic, hypervolemic hyponatremia

Hypovolemic hyponatremia?

Loss of sodium and water, with proportionally greater sodium loss

Causes include → diarrhea, vomiting, blood loss, diuretic use

Treatment → replace lost volume with NS

Hypervolemic hyponatremia ?

Excess water relative to sodium, causing low sodium and fluid overload

Causes include → heart failure, cirrhosis, nephrotic syndrome

Treatment → fluid restriction, loop diuretics, vaptans

Euvolemic hyponatremia ?

Low sodium with normal fluid volume

Causes include →

SIAD

Hypothyroidism

Adrenal insufficiency

Cerebral salt wasting

Thiazide use

Excessive water intake

Beer potomania / tea and toast syndrome

Treatment for euvolemic hyponatremia?

Adrenal insufficiency → hydrocortisone

Cerebral salt wasting → 3% NaCl solution and fludrocortisone can be used

Thiazide → Stop thiazide

Primary polydipsia/excessive water intake → limit fluid intake

Beer potomania / Tea and toast syndrome → improve nutrition

Potassium normal range?

3.5-5 mEq/L

Is the most prominent intracellular cation

Hyperkalemia?

>5 mEq/L

Hypokalemia ?

<3.5 mEq/L

Causes of hyperkalemia?

Decreased renal excretion

Increased extracellular potassium

Increased potassium intake

Pseudo-hyperkalemia → hemolysis

EKG changes with hyperkalemia?

Use calcium!!

Stabilizes cardiac cells → does NOT lower potassium

Calcium gluconate: 1–2 g IV over 10 min

Calcium chloride: 1 g IV push

Also use temporizing treatment!!!

Temporizing treatment with hyperkalemia?

Push potassium into the cells intracellularly → temporary lowers K

Use → Insulin + glucose: 10 units regular insulin + 50 g dextrose

Sodium bicarbonate: 50 mEq IV push

Albuterol: 10–20 mg nebulized

Treatment for hyperkalemia after calcium and temporizing treatment?

Potassium removal

Use →

Loop diuretics

Cation exchange resins → sodium polystyrene, sodium zirconium cyclosilicate, patiromer

Dialysis

Causes of hypokalemia?

Increased intracellular shift

Increased GI losses

Increased renal losses

Electrolyte imbalances

Symptoms of hypokalemia?

Fatigues

Muscle weakness / cramping

EKG changes → cardiac arrhythmias

Constipation

Treatment of hypokalemia?

10 mEq KCl = 750 mg; may increase serum K⁺ by ~0.1 mEq/L

IV replacement rates → peripheral line: 10 mEq/hr; central line: 20 mEq/hr

Replacing too much or too quickly can cause dangerous cardiac arrhythmias or death

Magnesium normal range?

1.5-2.2 mg/dL

Hypomagnesemia?

<1.5 mg/dL

Hypermagnesemia?

>2.2 mg/dL

Concerns with hypomagnesemia?

Can cause → neuromuscular problems and cardiovascular problems

Treatment of hypomagnesemia?

Magnesium oxide: oral

Magnesium plus protein: 133 mg tablet, oral

Magnesium sulfate: 1 gm, 2 gm and 4 gm IV bags

What population is often affected by hypermagnesemia?

Chronic kidney disease patients

Over supplementation of pregnant mothers

Symptoms of hypermagnesemia?

Nausea / vomiting

Hypotension

Hyporeflexia

Treatment of hypermagnesemia?

If symptomatic → calcium gluconate

Stop magnesium supplements

Loop diuretics, fluids (NS), or dialysis

Calcium normal range?

8.5-10.5 mg/dL

Ionized caclium normal range?

4.4-5.4 mg/dL

Hypocalcemia?

<8.5 mg/dL

Hypercalcemia?

>10.5 mg/dL

Causes of hypocalcemia?

Vitamin D deficiency

Hypomagnesemia

Hypoparathyroidism

Drug-induced hypocalcemia

Post surgical → hungry bone syndrome

Symptoms of hypocalcemia?

Tetany

Myopathy

Hypoactive reflexes

Hypotension

Impair

Insulin function

Treatment of hypocalcemia?

Oral → calcium citrate, calcium carbonate (tums), calcium carbonate + vitamin D

IV → calcium gluconate, calcium chloride

Causes of hypercalcemia?

Increased bone resorption (cancer)

Increased GI absorption

Increased kidney resorption

Symptoms of hypercalcemia?

Fatigue/weakness

Constipation

Cognitive dysfunction

Polyuria

Severe cases may include → calcium containing kidney stones or acute pancreatitis

Treatment of hypercalcemia?

IV fluids (NS)

Loop diuretics

Calcitonin (4mg/kg IM/SC q12h)

Bisphosphonates

Rank-L inhibitor

Corticosteroids

Cinacalcet

Phosphorus normal range?

2.6-4.5 mg/dL

Hypophosphatemia?

<2.6 mg/dL

Hyperphosphatemia?

>4.5 mg/dL

Causes of hypophosphatemia?

Decreased GI absorption

Increased renal elimination

Cellular shifts (refeeding syndrome)

Symptoms of hypophosphatemia?

Weakness, numbness, irritability, paresthesias

Seizures or coma

Treatment of hypophosphatemia?

Many oral products (Neutra-Phos, K-Phos neutral)

IV phosphate replacement must go → in slowly and need to check a calcium level prior to start of infusion

Causes of hyperphosphatemia?

Chronic kidney disease

Hypoparathyroidism

Symptoms of hyperphosphatemia?

GI disturbances

Calcium-phosphate crystals → urinary tract obstruction

Treatment of hyperphosphatemia?

Sevelamer, lanthanum

Products containing calcium, magnesium, and/or aluminum

Dialysis