Fluid and Electrolyte Balance Quiz

Fluid and Electrolytes

• Fluid and electrolytes are crucial for bodily functions.
• Total body water (TBW) is approximately 60% of total body weight.
• Intracellular fluid (ICF) accounts for 67% of the ECF compartment.
• Extracellular fluid (ECF) comprises 33% of the TBW.

Fluid and Electrolyte Compartments

• Interstitial fluid typically makes up 25% of the ECF.
• Intravascular fluid (plasma) represents 75% of the ECF.
• These compartments have different electrolyte concentrations.

Electrolytes: Hyper vs Hypo

• Hyper refers to excess total body amount of an electrolyte.
• Hypo indicates depleted total body amounts.
• Shifts between compartments can also signify electrolyte imbalances.
• Rate of change in electrolyte concentrations is often more important than absolute concentrations in determining severity.

Sodium

• Total body sodium content varies between 40-50 meq/kg.
• Predominantly found in the extracellular fluid.
• Normal concentration in blood plasma is 140 mmol/L (135-145 mmol/L).
• Intracellular sodium concentration is low (<10-12 mmol/L) compared to extracellular concentrations.

Hyponatremia

• Defined as serum sodium levels below 135 mmol/L.
• Causes include primary water gain, sodium loss exceeding water loss, or issues with body water distribution.
• Symptoms can include nausea, vomiting, anorexia, muscle cramps, confusion, lethargy, and seizures (coma possible with extremely low levels).
• Patients with serum sodium below 120 mmol/L are more likely to exhibit symptoms, especially those who developed the condition gradually.
• Levels below 113 mmol/L significantly increase the risk of seizures.

Pathophysiology - CNS

• Cerebral edema develops in response to rapidly declining serum sodium.
• Severe hyponatremia within 24 hours with serum sodium below 120 mmol/L or rapid decrease in serum sodium of 0.5 mmol/hour or more can lead to muscle twitching, seizures, and coma
• High rates of correction can cause more damage to brain cells.
• Osmotic demyelination syndrome (ODS) is a severe neurological complication arising from rapid correction of hyponatremia.

Osmotic Demyelination Syndrome

• Symptoms include dysarthria, dysphagia, seizures, altered mental status, quadriparesis, and hypotension.
• ODS typically presents 2-6 days after correction of sodium levels.

Pathophysiology - Musculoskeletal System

• Normal muscle tone and function are generally observed in most patients with hyponatremia.
• Muscle cramps/weakness are often seen during strenuous exercise, particularly in cases where water replaces excessive sweating.
• Symptoms typically resolve rapidly following correction of serum sodium levels.

Pathophysiology - Renal System

• Reduced ADH levels can alter the normal handling of sodium.
• Urine sodium levels below 10 mEq/L suggest intact renal handling and contracted effective arterial blood volume.
• Urine sodium levels above 20 mEq/L may indicate intrinsic renal tubular damage or natriuretic response to hypervolemia.

Diagnosis

• Initial diagnosis involves clinical evaluation of ECF volume status and measurement/calculation of plasma osmolality.
• This helps differentiate true hyponatremia (low plasma osmolality) from factitious hyponatremia (normal or increased plasma osmolality).

Hypertonic Hyponatremia

• Large quantities of osmotic solute accumulate in the extracellular fluid space.
• Net fluid shift from intracellular to extracellular space occurs.
• Possible causes include hyperglycemia, mannitol excess, and glycerol therapy.
• Treatment involves reducing ECF hypertonicity and managing the underlying cause.

Isotonic Hyponatremia

• Also called pseudohyponatremia.
• Characterized by normal plasma osmolality.
• High plasma protein or lipid content leads to lower water fraction causing artificially low sodium readings.

Hypotonic Hyponatremia Types

• Categorized into hypovolemic, euvolemic, and hypervolemic subtypes.
• Hyponatremia often leads to fluid overload.

Hypotonic - Hypovolemic

• Characterized by disproportionate loss of sodium and water, potentially due to inadequate oral fluid intake or inadequate fluid replacement during loss of bodily fluids.
• Renal causes could include diuretics, renal diseases and mineralocorticoid deficiencies.
• Extrarenal losses include GI losses (vomiting, diarrhea, fistula, third space loss), and sweating.

Hypotonic - Euvolemic

• Clinically not edematous, but has normal body sodium content despite hyponatremia.
• Often caused by syndrome of inappropriate antidiuretic hormone (SIADH), drug use, physiological stress, or certain diseases.

Hypotonic - Hypervolemic

• Characterized by excessive total body water.
• Often occurs due to cardiac failure, kidney dysfunction, or hepatic disease.
• Manifests as fluid overload via peripheral and pulmonary edema.
• Can't effectively eliminate water and results in sodium retention.
• Treatment involves managing the underlying condition like cirrhosis, CHF or renal disease with salt and water restrictions.

Severe Hyponatremia Emergency Treatment

• Treat patients with serum sodium below 115 mEq/L with caution & continuous cardiac monitoring.
• Calculate total body sodium deficit (desired plasma sodium – actual plasma sodium * total body water).
• Initially replace deficits with saline, carefully monitoring sodium levels to avoid osmotic demyelination syndrome.
• Correction rates should not exceed 0.5 - 1 mEq/L per hour.
• Faster correction is generally not recommended

Hypernatremia

• Serum sodium concentration exceeding 150 mEq/L.
• Typically caused by deficient fluid intake or increased loss.
• Can develop due to lack of thirst, inability to obtain fluids, or elevated insensible water loss.
• The body attempts to maintain water balance by regulating thirst and urination.

Hypernatremia Symptoms (Acute)

• Acute symptoms appear with serum sodium exceeding 158 mEq/L.
• Neurological symptoms include irritability, increased muscle tone, seizures, coma, and possible death.
• Cellular fluid loss, brain shrinkage, and cerebral blood vessel damage can occur, potential to cause massive brain haemorrhage or multiple smaller hemorrhages and thromboses.
• Associated with electrolyte imbalance, hypocalcemia frequently observed (exact mechanism unclear).

Hypernatremia Osmolality Related Symptoms

• Clinical signs, manifestations of serum osmolality range from restlessness and irritability to tremors, ataxia, hyperreflexia, twitching and spasticity, progressing eventually to seizures and death.

Hypernatremia Causes

• Excessive sodium administration (iatrogenic).
• Inappropriate ingestion of solute-rich fluids or substances.
• Inadequate water intake.
• Inability to obtain water or impaired thirst mechanism.
• Excessive insensible water loss.

Hypernatremia Renal Loss Causes

• Central diabetes insipidus - Inability of kidneys to concentrate urine, resulting in excessive water loss.
• Impaired renal concentrating ability - Inability of kidneys to concentrate urine, resulting in excessive water loss.
• Osmotic diuresis - Excessive water loss due to substances like glucose, urea, or mannitol in the urine that promote osmotic water excretion.

Hypernatremia Skin Loss Causes

• Burns.
• Sweating.

Hypernatremia Treatment

• Prioritize volume repletion using normal saline or lactated Ringer's solution.
• Monitor total body sodium deficit and adjust fluid administration rates appropriately.
• Carefully introduce fluids to rectify imbalance, with rate of change measured in incremental steps, (0.5 – 1 mEq/L) over time and should be closely monitored for adverse neurological effects. Calculate free water deficit and limit correction rate to 10–15 mEq/L / day.

Potassium Overview

• Normal intracellular potassium concentration is typically 100-150 mEq/L.
• Normal extracellular potassium concentration is 3.5-5.0 mEq/L.

Hypokalemia

• Serum potassium levels below 3.5 mEq/L.
• Potential causes include intracellular shifts, increased losses, or decreased intake.

Hypokalemia Symptoms

• Muscle weakness.
• Fatigue.
• Cramps.
• Paresthesias.
• Malaise.
• Hyporeflexia.
• Cardiac arrhythmias.

Hypokalemia Causes

• Various causes, including alkalosis, excessive diuretic use, kidney diseases (renal losses), GI losses (vomiting, diarrhea), and low intake.

Hypokalemia Treatment

• Treatment often involves oral or intravenous potassium supplementation, which depend on the severity, cause, and the patient's overall clinical picture and medical history.
• For severe cases, patients may require IV potassium with continuous cardiac monitoring.
  • Must limit administration rates to 10-20 mEq/ hour, or a maximum of 40 mEq in a single liter of IV solution..

Hyperkalemia

• Serum potassium levels exceeding 5.5 mEq/L.
• Often arises from intracellular shifts, reduced excretion, or excessive intake.

Hyperkalemia Symptoms

• Muscle weakness.
• Paralysis.
• Cardiac arrhythmias (often the most significant symptom).

Hyperkalemia Treatment

• Emergency treatment focuses on stabilizing the membrane and rapidly shifting potassium intracellularly, or removing potassium from the body.
• Initial treatment aims to improve cardiac function and prevent life-threatening arrhythmias.
• Treatment phases include membrane stabilization, intracellular potassium shifting, and potassium removal/excretion.
• Potassium needs to be safely lowered and monitored.

Calcium

• Total body calcium is predominantly stored within bone tissue.
• The body maintains calcium balance for many essential bodily functions.
• Normal daily calcium intake ranges from 800-3000mg

Calcium Properties

• Important calcium functions are heavily dependent on active ion concentrations in the body.
• Factors affecting calcium binding include serum protein levels.
• Significant alterations in blood pH (acidosis/alkalosis) can substantially impact ionized calcium levels.