Frequently Asked Questions
Chapter 34: Fluid, Electrolyte, and Acid-Bade Balance

What is the relationship between the amount of hydrogen ions in the blood and the blood pH?

When the blood pH is below 7.35 (and the blood is more acidic), the hydrogen ions are increased. When the blood pH is above 7.45 (and the blood is more alkaline), the hydrogen ions are decreased.

What are the causes and characteristics of sodium imbalances?

Hypernatremia (serum Na>145 mEq/L) is caused by high sodium intake, low water intake, severe GI loss, excessive perspiration, salt-water drowning, IV solutions high in sodium, hypertonic saline abortions, bladder irrigation, problems with elimination, and hemostatic dysfunction. When ECF sodium is high, the kidneys conserve chloride and water. Hyponatremia low (serum K<3.5 mEq/L) is caused by nutrition and metabolic problems, advanced renal disorders, excessive diuretics, and the syndrome of inappropriate antidiuretic hormone (SIADH). When ECF sodium is low, water moves out of vascular space and into the interstitial and intracellular spaces, causing edema.

What are the causes and characteristics of potassium imbalances?

Hypokalemia (serum K <3.5 mEq/L) is caused by poor nutrition, gastrointestinal loss, hyperaldosteronism, tissue injury or surgery, and similar conditions. Hypokalemia causes gastrointestinal disturbances, cognitive and sensory changes, muscle weakness, and electrocardiogram changes. Hyperkalemia (serum K >5.3 mEq/L) is caused by excessive supplemental potassium, renal failure, excessive potassium-sparing diuretics, Addison’s disease, and disruptions in skin or cellular integrity. Hyperkalemia causes abdominal cramps, nausea, diarrhea, muscular weaknesses, oliguria or anuria, cardiac dysrhythmias, and electrocardiogram changes.

What are the causes and characteristics of calcium imbalances?

Hypocalcemia (serum calcium <4.5 mEq/L) is caused by inadequate intake of calcium, hypothyroidism, diarrhea, wound drainage, steroid therapy, and similar conditions. Hypocalcemia causes anxiety, irritability, tingling and numbness of fingers, tetany, convulsions, abdominal and muscle spasms, and pathologic fractures, and is accompanied by an elevated serum phosphorus and a prolonged prothrombin time. Hypercalcemia (serum calcium >5.5 mEq/L) is caused by excessive movement of calcium out of the bones, overconsumption of milk and dietary salts, over activity of parathyroid glands, renal impairment, thiazide diuretics, and steroid therapy. The signs and symptoms of hypercalcemia are depression and lethargy, decreased muscle tone and reflexes, osteoporosis or osteomalacia, pathologic fractures, heart block and cardiac arrest, gastrointestinal problems, urinary calculi and polyuria.

What are the causes and characteristics of magnesium imbalances?

Hypomagnesemia is caused by prolonged malnutrition and alcoholism, vomiting, gastric suction, severe renal disease, thiazide diuretics, aldosterone excess, and polyuria. Hypomagnesemia causes cognitive and sensory problems, increased tendon reflexes, positive Chvostek’s and Trousseau’s signs, elevated blood pressure and pulse, dysrhythmias, and electrocardiogram changes. Hypermagnesemia (serum magnesium >2.5 mEq/L) is caused by excessive intake of solutions containing phosphates, hypoparathyroidism, laxatives containing phosphate, and renal insufficiency. Hypermagnesemia causes tetany, muscle weaknesses and paralyses, tachycardia, electrocardiogram changes, and gastrointestinal disturbances.

What are the causes and characteristics of phosphate imbalances?

Hypophosphatemia (serum phosphate <1.7 mEq/L) is caused by chronic malnutrition or alcoholism, prolonged use of IV solutions that are low in phosphorus, acid-base imbalances, excess parathyroid hormone, and overuse of aluminum-containing antacids. Hypophosphatemia causes cognitive and sensory problems, muscle weakness and other mobility problems, hypoxia, hyperventilation, possible bleeding, weak pulse, possible infection, anorexia, and dysphagia. It is accompanied by reduced white blood cells and platelets, plus elevated cardiac isoenzymes. Hyperphosphatemia is caused by excessive intake of phosphates and hypoparathyroidism, along with renal insufficiency. Hyperphosphatemia is characterized by tetany, muscle weakness, flaccid paralysis, circumoral paraesthesia, hyperreflexia, electrocardiogram changes, and gastrointestinal upset.

What are the causes and characteristics of chloride imbalances?

Hypochloremia is a decrease in chloride in the ECF. Hypochloremia is caused by gastrointestinal fluid loss and causes muscle twitching and slow, shallow breathing. Hyperchloremia is an increase in the level of chloride in the ECF and causes muscle weakness; deep, rapid breathing; lethargy; and unconsciousness.

How do the acid-base disturbances (respiratory acidosis, respiratory alkalosis, metabolic acidosis, and metabolic alkalosis) differ?

Respiratory acidosis (carbonic acid excess) is an acid-base disturbance characterized by a blood pH below 7.35, arterial carbon dioxide pressure greater than 45 mm Hg, and an excess of carbonic acid. Respiratory acidosis is caused by hypoventilation or depressed ventilation. Respiratory acidosis causes disorientation, weakness, stupor, flushed and warm skin and mucous membranes, dyspnea, tachycardia, and dysrhythmias.

Respiratory alkalosis (carbonic acid deficit) is characterized by decreased hydrogen ion concentration (blood pH above 7.45) and an arterial carbon dioxide pressure less than 35 mm Hg. Respiratory alkalosis is caused by hyperventilation (excessive exhalation of carbon dioxide, leading to hypocapnia (decreased arterial dioxide concentration). Respiratory alkalosis causes hyperactive reflexes, sweating, rapid and shallow breathing, and palpitations.

Metabolic acidosis (bicarbonate deficit) is characterized by an increased hydrogen ion concentration (blood pH below 7.35) or a decrease in bicarbonate concentration. It can be caused by a loss of base such as the loss of bicarbonate and sodium ions from the small intestines with chronic diarrhea, or a gain in metabolic acids cased by diabetic ketoacidosis, renal failure, anerobic metabolism, or drug overdose. Metabolic acidosis causes disorientation and shift of hydrogen and sodium ions into the cell. Potassium then moves into the extracellular fluid, causing ventricular fibrillation and death.

Metabolic alkalosis (bicarbonate excess) is characterized by a blood pH above 7.45. It is caused by excess ingestions of antacids or sodium bicarbonate or a loss of metabolic acids through vomiting, nasogastric suctioning, low potassium or chloride, increased aldosterone, or administration of steroids or diuretics. Symptoms are irritability confusion, tetany, hypertonic muscles and reflexes, depressed respirations, and vomiting.

What are the Chvostek’s and Trousseau’s signs and what do they mean?

Chvostek’s sign and Trousseau’s sign are tests for neuromuscular irritability. Chvostek’s sign is elicited by tapping the facial nerve 2 cm anterior to the earlobe. A positive response is ipsilateral (same side) twitching of the facial muscles. Trousseau’s sign is elicited by placing a blood pressure cuff on the arm, inflating the cuff slightly above the systolic pressure, leaving the cuff inflated 2 to 3 minutes, and deflating. A carpal spasm is a positive response. A positive Chvostek’s sign and Trousseau’s sign indicate hypocalcemia or hypomagnesemia.