NCLEX-RN Flashcards: Fluid and Electrolyte Balance, Acid-Base, IV Therapy

Hyperkalemia, defined as serum potassium above 5.0 milliequivalents per liter, is dangerous because it affects cardiac conduction. Signs include tall peaked T waves on electrocardiogram, muscle weakness progressing to flaccid paralysis, decreased deep tendon reflexes, nausea, diarrhea, and paresthesias. Severe hyperkalemia above 6.5 can cause widened QRS complex, absent P waves, sine wave pattern, and fatal cardiac arrest. Causes include renal failure, potassium-sparing diuretics, ACE inhibitors, tissue destruction, and acidosis.

Hypokalemia, defined as serum potassium below 3.5 milliequivalents per liter, causes muscle weakness, leg cramps, fatigue, constipation and decreased bowel sounds from smooth muscle weakness, flattened T waves and the appearance of U waves on electrocardiogram, and cardiac arrhythmias. Severe hypokalemia can cause respiratory muscle weakness and cardiac arrest. Common causes include loop and thiazide diuretics, vomiting, nasogastric suctioning, and diarrhea. Hypokalemia also increases sensitivity to digoxin toxicity. Treatment includes oral or intravenous potassium replacement.

Arterial blood gas interpretation follows a systematic three-step approach. First, look at the pH: below 7.35 is acidosis, above 7.45 is alkalosis. Second, check the PaCO2 which is respiratory: if it moves in the opposite direction of the pH, the respiratory system is the cause. Normal PaCO2 is 35 to 45. Third, check the bicarbonate which is metabolic: if it moves in the same direction as the pH, the metabolic system is the cause. Normal bicarbonate is 22 to 26. Then determine if compensation is occurring by checking whether the other system is trying to normalize the pH.

Metabolic acidosis occurs when bicarbonate is low, either from excessive acid production or bicarbonate loss. Common causes include diabetic ketoacidosis, lactic acidosis from tissue hypoxia, renal failure, severe diarrhea which loses bicarbonate, and salicylate overdose. The body compensates through respiratory mechanisms: the lungs increase rate and depth of breathing, called Kussmaul respirations, to blow off carbon dioxide and raise the pH. Lab findings show pH below 7.35, bicarbonate below 22, and compensatory PaCO2 below 35 as the lungs work to correct the imbalance.

Respiratory alkalosis results from hyperventilation that blows off too much carbon dioxide, raising blood pH above 7.45. Common causes include anxiety and panic attacks, pain, fever, early sepsis, high altitude, and mechanical ventilation set too fast. Signs and symptoms include lightheadedness, dizziness, numbness and tingling in the fingers and around the mouth, muscle spasms, and confusion. The kidneys compensate by excreting more bicarbonate, but renal compensation takes hours to days.

Fluid volume overload, or hypervolemia, presents with weight gain of more than one kilogram in 24 hours, peripheral edema, distended neck veins also called jugular venous distention, elevated blood pressure, bounding pulse, crackles or rales in the lungs from pulmonary congestion, dyspnea, orthopnea, decreased hematocrit from hemodilution, and decreased serum sodium from dilution. Common causes include heart failure, renal failure, excessive intravenous fluid administration, and excessive sodium intake.

Fluid volume deficit, or hypovolemia, presents with weight loss, decreased skin turgor with tenting, dry mucous membranes, concentrated urine with elevated specific gravity, decreased urine output below 30 milliliters per hour, tachycardia, hypotension, orthostatic blood pressure changes, flat neck veins, elevated hematocrit from hemoconcentration, and elevated blood urea nitrogen. Common causes include vomiting, diarrhea, hemorrhage, excessive diuretic use, burns, and insufficient fluid intake.

Normal serum sodium is 136 to 145 milliequivalents per liter. Hyponatremia, below 136, is the most common electrolyte imbalance in hospitalized patients. Causes include excessive water intake, syndrome of inappropriate antidiuretic hormone also called SIADH, heart failure, cirrhosis, diuretic use, vomiting, and diarrhea. Signs include confusion, headache, nausea, lethargy, seizures, and in severe cases brain herniation from cerebral edema. Severe hyponatremia below 120 is a medical emergency. Treatment depends on the cause and chronicity.

Intravenous potassium must never be given by rapid bolus push because a sudden surge of potassium into the bloodstream can cause fatal cardiac arrhythmias including ventricular fibrillation and cardiac arrest. Potassium must always be diluted and infused slowly, typically no faster than 10 milliequivalents per hour through a peripheral line or 20 milliequivalents per hour through a central line with cardiac monitoring. The infusion site must be monitored because potassium is a vesicant that causes severe pain and tissue damage if it infiltrates. ---