Fluids and Electrolytes Flashcards
Rule of thumb for relationship between hypernatremia and water loss
Every 3 mEq/L that the serum sodium concentration is above 140 represents roughly 1 L of water lost.
What can be used to replete fluids in cases of slow-onset hypernatremia, so that volume is repleted quickly but tonicity is only nudged in the right direction?
D5 1/2 Normal Saline
What can be used to replete fluids in cases of rapid-onset hypernatremia?
More dilute fluids, like D5 1/3 NS or D5W
Two scenarios resulting in hyponatremia, and how to treat them.
1) retaining water due to elevated ADH. Treat with water restriction.
2) losing isotonic fluids (e.g. via GI), forcing them to retain water. Treat with NS or RL (consider hypertonic solution, as in 3% or 5%)
Two routes to lose potassium, resulting in slow-onset hypokalemia
K is lost from the GI (all GI fluids are high in K) or in the urine (due to loop diuretics or elevated aldosterone).
Safe “Speed limit” of potassium repletion.
10 mEq/hr
Scenarios of slow hyperkalemia vs. fast hyperkalemia
Slow = failure of kidney to excrete potassium (renal failure, aldosterone antagonists like spironolactone). Fast = potassium dumped into extracellular space (like crush injuries, dead tissue, acidosis).
Four methods of treatment for hyperkalemia
Hemodialysis, “pushing” K back into cells with 50% dextrose and insulin, NG suction, or cell membrane stabilization with IV calcium gluconate. Calcium gluconate is the fastest method.
What is an “anion gap” and what can it mean
Serum sodium exceeds by more than 10 or 15 the sum of chloride and bicarbonate. Suggests acids are piling up in the blood (as opposed to loss of buffers)
Three routes of developing metabolic acidosis
1) Excessive production of fixed acids (diabetic ketoacidosis, lactic acidosis).
2) Loss of buffers (loss of bicarb-rich fluid in GI)
3) Inability of kidney to excrete fixed acids (renal failure).
Temporary treatment that helps in cases of metabolic acidosis
Bicarb administration
Two routes of developing metabolic alkalosis
loss of gastric acid juice, or excessive admin of bicarbonate
Tx for metabolic alkalosis
KCl admin (5-10 mEq/hr), allows kidney to correct problem
Respiratory acidosis: cause, lab values, tx
Caused by impaired ventilation. Blood PCO2 is high, pH is low (<7.4). Tx by improving ventilation.
Respiratory alkalosis: cause, lab values, tx
Excessive ventilation. Blood PCO2 is low, pH is high (>7.4). Tx by reducing ventilation.
Metabolic acidosis lab values
pH is low (<7.4), bicarb is low (<25), and there is a base deficit.
Metabolic alkalosis lab values
pH is high (>7.4), bicarb is high (>25), and there is a base excess.
5 signs of volume deficit
TACHYCARDIA, hypotension, decreased urine output, depressed CNS, decreased skin turgor
In a resuscitated hypovolemic post-op patient, aim for this urine output
30-50 cc/hr
Best single measurement to estimate volume status
Pulmonary capillary wedge pressure (PCWP); estimates the pressure in the left atrium of the heart
Working normal Sodium concentration of plasma
140 (range 135-145)
Effect of elevated glucose level on the sodium concentration
Elevated glucose lowers sodium concentration, by drawing water out of cells via osmosis
Calculation to correct plasma Na concentration when glucose is elevated
Na falls 2 mEq/L for each 100mg/100cc that glucose is above normal (normal being 100).
Example; A patient has Na = 125, and glucose=600. Glucose is 500 above normal, so sodium is artificially 10 mEq/L low. Real sodium after correction will be 135.
Level of hyponatremia that begins to be symptomatic
<120 mEq/L
