Review of Fluids and Electrolytes

Lecture Objectives

  • Describe factors that influence fluid movement between intracellular and extracellular fluid compartments

  • Calculate maintenance fluid requirements based on patient-specific information

  • Recognize common IV fluids utilized in various patients care scenarios

  • Identify common electrolyte abnormalities related to medication administration

  • Recommend appropriate treatment for common fluid and electrolyte abnormalities

Body Fluid Compartments

  • Intracellular Fluid (ICF) - 67%

  • Transcellular Fluid - 3%

  • Extracellular Fluid - 33%

    • Intravascular Space - 25%

    • Interstitial Space - 75%

Fluid Movement Between Extracellular and Intracellular Compartments

  • Osmotic pressure determines water distribution

  • Sodium → Extracellular osmole

    • Holds water in extracellular space

  • Potassium → Intracellular osmole

    • Holds water within the cell

  • Regulation of cell volume maintained by Na+/K+/ATPase

Movement of Fluid Between Plasma and Interstitial Fluid

  • Determined by plasma oncotic and hydrostatic pressure

  • Disruption leads to third spacing/edema

    • Third spacing = accumulation of excess fluid in interstitium (edema) or in fluid spaces (effusion)

    • Due to heart, kidney, or liver failure

    • Excess sodium retention

    • Anasarca = massive amount of generalized edema

Fluid Deficit

  • Causes:

    • Diarrhea, vomiting

    • NG aspiration

    • Excessive, unreplenished urinary losses

    • Excessive insensible losses

      • Fever, burns, fasting

  • Sources of loss

    • Dehydration < 3 days

      • ECF - 80%

      • ICF - 20%

      • Loss from outside cells

    • Dehydration > 3 days

      • ECF - 60%

      • ICF - 40%

      • Loss from inside cell, must save plasma volume

IV Hydration Solutions

Emergent Needs

  • Isotonic fluids without dextrose

    • Normal saline (NS)

    • Lactated ringers (LR)

  • Bolus infusion

    • Adults - 1-2 liters

    • Pediatrics - 20 mL/kg

    • Never more than 2 liters

Appropriate IV Hydration Solutions

  • Adults/pediatric patients - D5NS with or without 20 mEq/L of KCl

  • Neonates - D10 0.2% NaCl or D10 1/4NS

Fluid Overload

  • Causes:

    • Limited renal function, errors in estimating, SIADH

  • Consequences:

    • Cardiovascular and pulmonary

  • Treatment:

    • Fluid restrictions, diuretics, dialysis/hemofiltration

Maintenance IV Fluids (MIVFs)

  • Replaces daily urine, fecal, insensible losses

  • Prevents dehydration, electrolyte disorders, ketoacidosis, protein degradation

  • Holliday-Segar Method:

    • Premature infants: 75-120 mL/kg

    • Term infants: 60-120 mL/kg

    • 3-10 kg: 100 mL/kg

    • 10-20 kg: 1000 mL + 50 mL/kg (for every kg between 10-20)

    • > 20 kg: 1500 mL + 20 mL/kg (for every kg > 20 kg)

  • 4-2-1 Method:

    • < 10 kg: 4 mL/kg/hr

    • 10-20 kg: 40 mL/hr + 2 mL/kg/hr (for every kg between 10-20)

    • > 20 kg: 60 mL/hr + 1 mL/kg/hr (for every kg > 20 kg)

Normal Electrolyte Concentrations

  • Sodium

    • Newborn: 133-145 mEq/L

    • Pediatric: 135-145 mEq/L

    • Adult: 135-145 mEq/L

    • Maintenance of extracellular fluid volume + tonicity

    • Regulation of osmolarity and cell membrane potential

  • Potassium

    • Newborn: 4-6.2 mEq/L

    • Pediatric: 3.4-4.7 mEq/L

    • Adult: 3.5-5.0 mEq/L

    • Determination of resting membrane potential

  • Phosphorous

    • Newborn: 4.2-9 mEq/L

    • Pediatric: 4.5-5.5 mEq/L

    • Adult: 2.5-4.5 mEq/L

Hypokalemia

  • Increased entry into cells → Elevation of extracellular pH → Increased insulin

  • Increased GI losses → Vomiting, NG output, diarrhea, ostomy output

  • Increase urinary losses → Diuretics, metabolic acidosis, hypomagnesemia, medications, polyuria

  • Medication induced:

    • Albuterol, loop and thiazide diuretics, corticosteroids, anti-pseudomonal penicillins, insulin, amphotericin B, caspofungin, antivirals

Hyperkalemia

  • Renal dysfunction

  • Excessive intake

  • Cell lysis

  • Medication-induced:

    • K+ sparing diuretics

    • Heparin

    • Trimethoprim/sulfamethoxazole

    • Potassium penicillin

    • ACEi/ARBs

Pseudo-Hyperkalemia

  • Hemolysis of lab specimen

  • Hemolysis of blood products given

  • Improper blood draw → Contaminated sample

Magnesium

  • Cofactor for many enzyme systems

  • Muscle contractility

  • Nerve conduction

  • Hypermagnesemia

    • Caused by: excess magnesium intake, renal failure

    • Symptoms: respiratory paralysis, AV block, PVC, hypotension

  • Hypomagnesemia

    • Caused by: GI/renal losses

    • Symptoms: nausea, dizziness, depression, weakness, convulsions

    • Medication induced: amphoteracin B, aminoglycosides, loop/thiazide diuretics, cisplatin, cyclosporine, tacrolimus

Calcium

  • Essential for neuromuscular activity, regulation of endocrine secretory activities, blood coagulation, activation of complement system, bone metabolism

  • Hypercalcemia

    • Caused by: cancer, hyperparathyroidism, adrenal insufficiency, immobilization

    • Symptoms: fatigue, weakness, anorexia, cognitive dysfunction, constipation, kidney stones

  • Hypocalcemia

    • Caused by: vitamin D deficiency, hypoparathyroidism, magnesium deficiency

    • Symptoms: osteoporosis, tetany, muscle cramps, memory loss, confusion, prolonged QT interval

Phosphorous

  • Main intracellular anion

  • Important for bone/cell membrane composition, maintenance of normal pH, provision of energy through ATP

  • Hyperphosphatemia

    • Caused by: renal dysfunction

  • Hypophosphatemia

    • Caused by: starvation, alcoholism, burns, DKA, hyperparathyroidism, diarrhea, long term diuretics, long term aluminum antacids, dialysis

Calcium-Phosphorous Relationship

Calcium Deficiency

  • Osteoporosis

  • Severe deficiency

    • Cardiovascular = hypotension, decreased myocardial contractility, prolonged QT interval

    • Neuromuscular = distal extremity paresthesias, muscle cramps, tetany, seizures

Phosphorus Deficiency

  • Neuro: ataxia, confusion, paresthesias

  • Neuromuscular: weakness, myalgia, rhabdomyolysis

  • Cardio/Pulmonary: cardiac/ventilatory failure

  • Hematologic: reduced 2,3-diphosphoglycerate concentration, hemolysis

  • Consequences of refeeding syndrome

Serum Calcium

  • Measures bound/unbound calcium → Dependent on albumin status

  • Corrected Ca2+ = Ca2+ + ((4 - albumin) x 0.8))

  • Biologically active form = ionized Ca2+ - free calcium