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
What does hyponatremia do to intracranial pressure? What does the patient feel?
Increases ICP. Confusion, anorexia, lethargy, N/V, coma, seizures
What can happen if you correct hyponatremia too rapidly?
Central pontine and extra-pontine myelinolysis, which can cause irreversible CNS damage and death. Which is a big bummer.
Limit for increasing sodium to correct hyponatremia
12 mEq/L during first 24 hours, and then even less during subsequent 24 hours
Preferred, conservative method of correcting hyponatremia
Fluid restriction
Signs of hypernatremia (list 8)
Restlessness, twitching, ataxia, seizures, delirium, dry mucous membranes, oliguria, fever.
What can result if you reduce osmolality too rapidly?
convulsions and coma
How does respiratory alkalosis lead to cerebral ischemia?
It shifts the O2 dissociation curve to the left, limiting the ability of Hb to unload O2 at the tissue level.
Pulmonary compensation of metabolic acidosis
hyperventilation
Normal anion gap
10-12 mEq/L
Describe the paradoxical aciduria in the setting of metabolic alkalosis
In the case of chloride responsive metabolic alkalosis (due to ECF volume depletion, vomiting, NG tube suction etc.), the ECF deficit stimulates renal resorption of Na, causing H+ ions to be excreted even further.
When is metabolic alkalosis chloride responsive?
In cases of ECF volume depletion, vomiting, NG tube suction etc.
When is metabolic alkalosis chloride resistant?
Adrenal disorders which increase renal resorption of Na and bicarb, increasing ECF volume, w/ loss of chloride in urine
Normal potassium level
4 mEq/L (range 3.5-5)
First EKG change to look for in hyperkalemia
Peaked T waves
Symptoms of hyperkalemia (list 3)
EKG changes, arrhythmias, N/V/D
Possible artificial causes of a high K lab value (list 3)
Hemolysis in the blood sample (“sample is hemolyzed”), shaking of the clot tube instead of letting it sit, patient on RL infusion
What to do if a patient K level comes back high
Repeat test, do an EKG, stop any sources of K infusion. Still high? Hydrate, consider loop diuretics (e.g. Lasix).
What happens to the ionized fraction of serum calcium in the setting of acidosis?
Increases
What happens to the ionized fraction of serum calcium in the setting of alkalosis?
Decreases
What is it called when you tap on someone’s cheek and their facial muscles spasm, and what does it mean?
Chvostek’s sign, a sign of hypocalcemia
What is it called when you inflate a BP cuff, and the arm spasms?
Trousseau’s sign, a sign of hypocalcemia
What are possible causes of hypocalcemia? List 6
Pancreatitis, massive soft tissue infection, renal failure, pancreatic and small bowel fistulas, hypoparathyroidism, hyperparathyroid patient s/p removal of parathyroid
Symptoms of hypocalcemia (list 8)
Hyperactive tendon reflexes, tremors, Chvostek’s sign, Trousseau’s sign, muscle/abdominal cramps, tetany with carpopedal spasm, convulsions, prolonged Q-T interval.
Treatment for hypocalcemia (2)
Calcium gluconate or calcium chloride
Symptoms of hypercalcemia
“bones, stones, groans, and psychiatric overtones”.
Fatigue, weakness, anorexia, N/V, weight loss, headaches, pain in back and extremities.
3 possible causes of hypercalcemia
Hyperparathyroidism, carcinoma with mets to bone (highest Ca+ levels), granulomatous processes
First treatment for emergency hypercalcemia
Replace volume losses
Magnesium deficiency symptoms
similar to hypocalcemia
Hypermagnesemia does what to deep tendon reflexes
loss of deep tendon reflexes
The use of Succinylcholine for rapid-sequence intubation has the risk of causing what in a trauma patient?
Cardiac arrhythmia due to severe hyperkalemia
