Gen Surg: Fluids and Electrolytes

Respiratory Alkalosis

Primary disturbance → increased pH, decreased PCO2. Compensation is reflected in a decreased HCO3 reabsorption rate

-Sx: lightheadedness, confusion, peripheral/circumoral paresthesias, cramps, syncope

-Acute causes: pain, anxiety, hypoxemia, sepsis, seizures, drugs, hypocalcemia

-Chronic causes: PE during pregnancy, liver failure, hyperthyroidism, brainstem tumor

-Tx: treat underlying cause, discourage paper bag breathing

Respiratory Acidosis

Primary disturbance → decreased pH, increased PCO2. Compensation is reflected in an increased HCO3 reabsorption rate

-Sx: headache, confusion, anxiety, drowsiness, tremor, blunted DTRs, myoclonic jerks, asterixis

-Acute causes: pneumonia, pulmonary edema, CNS depression

-Chronic causes: airway obstruction, respiratory muscle weakness

BiPAP

What is the treatment of choice for acute respiratory acidosis, in order to blow off CO2?

Metabolic Alkalosis

Primary disturbance → increased pH, increased HCO3. Compensation is reflected in an increased PCO2 due to hypoventilation

-Can be due to vomiting, NG suction, mineralocorticoid excess

NS

What fluid should be given to patients in metabolic alkalosis?

Metabolic Acidosis

Primary disturbance → decreased pH and HCO3, compensation reflected in decreased PCO2 due to hyperventilation

-High Anion Gap causes: methanol, uremia, ketoacidosis, propylene glycol, iron, lactic acidosis, ethylene glycol, salicylates

-Non Gap causes: GI HCO3 loss, renal tubular acidosis

Hyperphosphatemia

Serum PO4 > 4.5 mg/dL, with advanced CKD being the most common cause

-Sx: generally asymptomatic

-Dx: PO4 > 4.5, QT prolongation on EKG

IV calcium gluconate

What is the treatment of choice for symptomatic hypocalcemia, as a result of hyperphosphatemia?

Hypophosphatemia

Serum PO4 < 2.5

-Sx: weakness, paresthesias, encephalopathy, decreased contractility, respiratory failure, bone pain

-Dx: PO4 < 2.5, urine PO4 < 100

Phosphate

What is the treatment of choice for hypophosphatemia, with PO form > 1 mg/dL and IV if < 1 mg?

Hypermagnesemia

Serum Mg > 2.6, almost always due to advanced CKD and chronic intake of Mg-containing drugs like antacids/laxatives

-Sx: muscle weakness, decreased DTRs, confusion, flaccid paralysis, ileus, hypotension, respiratory muscle paralysis, complete heart block, cardiac arrest

-Dx: Mg > 2.6, wide QRS/prolonged PR/prolonged QT on EKG

Calcium Chloride

What can be given to patients with hypermagnesemia, due to its ability to antagonize Mg?

Hypomagnesemia

Serum Mg < 1.8, which causes decreased K and Ca

-Sx: tremors, cramps, confusion, increased DTRs, weakness, HTN, tachycardia, Torsades de Pointes

-Dx: decreased Mg, wide QRS/prolonged PR/ventricular arrhythmias/Torsades on EKG

-Tx: IV magnesium sulfate

Hypercalcemia

Serum Ca > 10.5 and ionized Ca > 5.2, with hyperparathyroidism and malignancy being the most common causes

-Sx: nephrolithiasis, anorexia, N/V, constipation, bone pain, osteopenia/osteoporosis, anxiety, lethargy, cognitive changes

-Dx: 24 urine Ca > 200 points to hyperparathyroidism as a cause, shortened QT on EKG

Cinacalcet

What can be given in hypercalcemia in order to suppress PTH secretion?

Hypocalcemia

Serum Ca < 8.5, which is MCC by hypoalbuminemia and CKD

-Sx: carpopedal spasm, cramps, perioral paresthesias, positive Chvostek sign and Trousseau sign

-Dx: prolonged QT on EKG

-Tx: Calcium + Vitamin D

Hyperkalemia

Serum K > 5.2, with hemolysis and CKD being the most common causes

-Meds like ACE/ARB, spironolactone, trimethoprim, tacrolimus can also cause

-Sx: arrhythmias (AV blocks, VFIB, cardiac arrest), N/V/D, muscle weakness, flaccid paralysis, paresthesias, decreased DTRs

-Dx: labs, EKG shows peaked T waves and QRS widening

-Tx: calcium gluconate

Hypokalemia

Serum K < 3.5, seen largely in alcoholics and those on loop diuretics

-Sx: muscle weakness, cramps, decreased DTRs, constipation, ileus, hyperglycemia, polyuria, cardiac arrhythmias, hypotension, arrest, rhabdomyolysis

-Dx: labs, 24 hr urinary K, EKG shows flat/inverted T waves or U waves

-Tx: K + Mg

Dextrose

What type of fluids should be avoided in a patient with hypokalemia?

-Stimulates insulin release and shifts K intracellularly

Hypernatremia

Sodium > 145, always hyperosmolar

-Sx: lethargy, weakness, irritability, delirium, seizures, coma

-Dx: labs

-Tx: fluids

Hyponatremia

Low serum sodium

-Tx: fluids (NS)

Osmotic demyelination syndrome

What do you run the risk of if you rapidly correct low sodium?

Hypervolemia

Volume overload, which can be isotonic, hypotonic, or hypertonic

-Sx: tachypnea, orthopnea, weight gain, pulmonary edema, crackles, rales, ascites, pleural effusion, increased JVD, peripheral edema, oliguria

-Dx: mainly clinical, CXR, ECHO

-Tx: Na and H2O restriction, loop diuretics, dialysis

Hypovolemia

Volume depletion secondary to loss of sodium and water from the extracellular fluid, resulting in compromised tissue perfusion

-Sx: lack of energy, easy fatigability, thirst, muscle cramps, postural dizziness, oliguria

-Dx: urine, BUN/Cr

-Tx: IV fluid boluses

Crystalloids

Aqueous solutions with varying concentrations of electrolytes, MC used fluids in hospital setting. Increases intravascular volume

-Types: isotonic, hypotonic, hypertonic

Colloids

Solutions that contain larger molecular weight solutes like albumin, which mostly remain confined to intravascular compartment

-Natural: albumin, FFP

-Artificial: gelatins, dextrans, hydroxyethyl starch

Isotonic

Are the following crystalloids isotonic, hypotonic, or hypertonic?

-Normal saline, LR, plasma-lyte A

Hypotonic

Are the following crystalloids isotonic, hypotonic, or hypertonic?

-Half normal saline, D5W

Hypertonic

Are the following crystalloids isotonic, hypotonic, or hypertonic?

-3% NaCl, 5% NaCl, D50W

NS

What isotonic crystalloid is being described?

-No net H2O shift

-Used primarily for fluid resuscitation, maintenance fluids, mild hyponatremia, early DKA, shock, blood transfusions, metabolic alkalosis, hypercalcemia, TBI

-Risks: fluid overload → caution in HF, edema, renal failure, metabolic acidosis, hypernatremia

LR

What isotonic crystalloid is being described?

-Balanced solution that helps combat acidosis

-Used for hypovolemia due to third spacing, burns, fistula drainage, trauma, diarrhea, hemorrhage, pancreatitis

-Risks: fluid overload, liver failure, hyperkalemia, incompatible with transfusions

Cerebral Edema

What is the biggest risk associated with using hypotonic crystalloids?