Fluids and Electrolytes prelecture

Hyponatremia

Low plasma osmolality → water moves into cells (cerebral swelling) → confusion, headache, nausea, seizures, lethargy

Hypernatremia

High plasma osmolality → water moves out of cells (cellular dehydration) → thirst, dry mucous membranes, confusion, agitation, weakness

Hypokalemia

Hyperpolarizes cell membranes → low muscle and cardiac excitability → muscle weakness, cramps, constipation, arrhythmias (U wave)

Hyperkalemia

Depolarizes membranes too much → Na+ channels inactivate → muscle weakness, paresthesia, cardiac arrest, arrhythmias (peaked T waves, widened QRS)

Hypocalcemia

Increased neuromuscular excitability (Na+ channels opens more easily) → spasms, tetany, seizures, Chvostek/Trousseau signs, prolonged QT

Chvostek/Troussea signs

Facial and hand muscle spasms triggered by hypocalcemia

Hypercalcemia

Decreased neuromuscular excitability → slow smooth muscle contractions (constipation), weakness, fatigue; kidney stones, polyuria from excess

Hypomagnesemia

Lack of neuromuscular and cardiac stability → hyper excitability → muscle cramps, tremor, tetany, arrhythmias, seizures

Hypermagnesemia

Reduces neuromuscular excitability → flaccid paralysis, hypotension, respiratory depression, bradyarrhythmias

Hypophosphatemia

Impaired ATP production → decreased energy for muscles and neurons → muscle weakness, bone pain, confusion, respiratory failure

Hyperphosphatemia

Binds calcium → lowers free calcium → spasms, tetany, cramps, seizures, cardiac conduction delays

Hypochloremia

Increases bicarbonate → alkalosis → neuromuscular instability (weakness, hyperexcitability)

Hyperchloremia

Lowers bicarbonate → acidosis → lethargy, rapid breathing

Respiratory alkalosis

Anxiety/panic, pain, fever, sepsis, pregnancy, high altitudes (breathe faster for O2)

Respiratory acidosis

COPD, asthma, airway obstruction, opioids, neuromuscular weakness

Respiratory compensation for metabolic acidosis

Hyperventilation → expels and lowers PaCO2 (Kussmaul respirations)

Respiratory compensation for metabolic alkalosis

Hypoventilation → retains PaCO2

Metabolic Alkalosis

Loss of metabolic acids with increases in bicarbonate concentrations, causing hypoventilation to keep CO2

What causes metabolic alkalosis?

Hypokalemia, excess bicarbonate (antacids), low acids (vomiting, gastric suction)

Metabolic acidosis

Poisoning (methanol, ethylene, glycol), loss of HCO3, increased acid (DKA, lactic acidosis, renal failure)

Normal HCO3

22-28 mEq/L

Normal BUN

7-20mg/dL

Normal Creatinine

0.7-1.3mg/dL (men); 0.6-1.1 mg/dL (women)

Normal CO2

35-45 mmHg

Normal Chloride

95-105 mEq/L

Normal Magnesium

1.8-2.5 mg/dL

Normal Potassium

3.5-5.0 mEq/L

Normal Sodium

135-145 mEq/L

Normal Phosphorus

2.5-4.5 mg/dL

Normal Calcium

8.5-10.5 mg/dL

Sodium Function

controls water movement, generate AP for nerve, affects BP/volume; ECF+

Potassium Function

sets resting membrane potential, vital for cardiac electrical activity and muscle contraction (ICF+)

Calcium Function

needed for muscle contraction, neurotransmitter release, bone storage

Magnesium Function

suppresses excessive nerve firing, cofactor for ATP, regulates Na/K pump

Chloride Function

acid-base balance, part of HCl in stomach

Phosphate function

part of ATP, DNA/RNA, inverse relationship w/ calcium (phosphate binds to calcium)