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Hyponatremia is a condition in which the _____ is hyperosmolar relative to the _____.

ICF, ECF

What is the most common cause of hyponatremia?

Excess total body water

NOT deficiency of sodium

What is the most important regulator of sodium?

Antidiuretic Hormone

What types of patient will hyponatremia be seen?

CHF, cirrhosis, drug, water intoxication

What is an important adverse effect of hyponatremia?

Cerebral edema

Signs and symptoms of hyponatremia

HTN, Bradycardia, confusion, agitation, headache, seizures, N/V, muscle cramps, weakness

Rapid treatment of chronic hyponatremia can result in ____________.

Myelinolysis (dissolving of myelin sheaths around nerves)

Who is are greatest risk for myelinolysis?

Hyponatremic >48 hours, lives transplant, etoh

What should be used to increase sodium levels and at what rate?

Infuse 3% saline at 1-2 ml/kg/hr and sodium level should be increased by no more than 1-2 meq/L/hr
If patient is clinically stable, sodium administration should not exceed 10-15 mmol/L in 24 hours

What sodium level is generally considered safe for patient undergoing general anesthesia?

>130 meq/L

Intraoperative cerebral edema caused by hyponatremia can be manifested by what signs?

Decrease in MAC, postop agitation/confusion/somnolence

What is the most common cause of hypernatremia with a normal total body sodium content?

Diabetes Insipidus

Rapid hypernatremia results in shrinking of the brain and increased traction on intracranial veins/sinuses which can ultimately lead to what?

Intracranial hemorrhage

Rapid correction of hypernatremia can lead to what?

Cerebral edema

Signs and symptoms of hypernatremia

Lethargy, mental status changes, peripheral edema, muscular rigidity and tremor, expanded intravascular volume

How do you correct hypernatremia?

Hydration

If a patient has acute hypernatremia, what type of solution can be given rapidly?

Hypotonic

If a patient has chronic hypernatremia accompanied by volume depletion, correct first with what? Followed by what?

Isotonic crystalloids followed by hypotonic solutions

At what rate should the sodium level be lowered in hypernatremia?

1-2 meq/hr

Hypernatremia increases or decreases the MAC for inhalation in animal studies?

Increases

At what sodium level should elective surgery be postponed?

>150meq/L

What is responsible for the resting membrane potential of the cell?

Potassium

Causes of hypokalemia

GI loss, renal loss, poor K intake, redistribution of K from ECF to ICF, diuretics, beta adrenergic stimulation, insulin, alkalosis (low PCO2, albuterol inhalers), PCN, aminoglycides, corticosteriods, hyperaldosterone, gastric suctioning, anorexia, alcoholism

Surgical stress may decrease serum K by how much?

0.5 meq/L

Signs and Symptoms of Hypokalemia

ST depression, widened QRS, flattened T waves, ectopy, weakness, confusion

Hypokalemic patients on digoxin are at an increased or decreased risk for dig toxicity?

Increased

Intraoperative management of a patient with hypokalemia

1. Administer IV K if arrhythmias develop
2. Avoid hyperventilation
3. Avoid use of glucose in solutions
4. Be aware of increased sensitivity to NMBA's

Causes of hyperkalemia

Acidosis, hemolysis, tissue necrosis, rhabdomyolysis, renal failure, potassium sparing diuretics, hypoaldosteronism, NSAIDS, beta-blockers, ACE inhibitors

Movement of K out of the cells can be seen in what instances?

Administration of sux, acidosis, cell lysis following chemotherapy, hemolysis, rhabdomyolysis, massive tissue trauma, hyperosmolality, digitalis overdose, administration of arginine hyperchloride and beta-2 adrenergic blockade, and during episodes of hyperkalemic periodic paralysis

Average increase in plasma K when sux is administered?

0.5 meq/L (can be exaggerated following large burns or severe muscle trauma and in patient with muscle denervation/paralysis)

Signs and symptoms of hyperkalemia

Tall peaked T waves, widened QRS, ventricular arrhythmias, cardiac arrest, muscle weakness, confusion, parathesias

What is the lethal level regarding hyperkalemia?

>6.0 meq/L

Treatment of Hyperkalemia

1. CALCIUM: 5-10mL of 10% calcium gluconate or 3-5 mL of 10% calcium chloride (partially antagonizes the cardiac effects of hyperkalemia--short lived dig toxicity potentiation
2. BICARB: promotes cellular uptake of K
3. BETA-AGONIST: promote cellular uptake
4. IV GLUCOSE AND INSULIN: 30-50g glucose with 10 units of insulin (promotes cellular uptake of K and lowering plasma K but often takes up to 1 hour for peak effect)
5. FUROSEMIDE
6. DIALYSIS

Intraoperative management of a patient with hyperkalemia

1. Watch for arrhythmias
2. Sux and LR (2 meq K) are contraindicated
3. Avoid acidosis (may mildly hyperventilate)
4. Be aware hyperkalemia can accentuate the effects of NMDAs

Ionized Ca accounts for what percentage of Ca in the ECF? Where is the remainder?

50%, 10% bound to anions, 40% bound to albumin

Total serum level are largely dependent on what levels?

Albumin

Causes of hypocalcemia

Hypoparathyroid (may be surgically induced), pancreatitis, malignancy, alkalosis, rhabdomyolysis, renal insufficiency, hypomagnsemia, low albumin due to malnutrition/sepsis/burns, extensive blood transfusions

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