What is third spacing?
Fluid accumulation in the interstitium of tissues, as in edema, e.g. loss of fluid into the interstitium and lumen of a paralytic bowel following surgery (think of the intravascular and intracellular spaces as the first two spaces)
When does third-spacing occur postoperatively?
Third-spacing fluid tends to mobilize back into the intravascular space around POD #3 (Note: Beware of fluid overload once the fluid begins to return to the intravascular space); switch to hypotonic fluid and decrease IV rate
What are the classic signs of third spacing?
Tachycardia
Decreased urine output
What is the treatment?
IV hydration w/ isotonic fluids
What is the surgical cause of metabolic acidosis?
Loss of HCO3: diarrhea, ileus, fistula, high-output ileostomy, carbonic anhydrase inhibitors
Increase in acids: lactic acidosis (ischemia), ketoacidosis, renal failure, necrotic tissue
What is the surgical cause of hypochloremic alkalosis?
NGT suction, loss of gastric HCl through vomiting/NGT
What is the surgical cause of metabolic alkalosis?
Vomiting, NG suction, diuretics, alkali ingestion, mineralcorticoid excess
What is the surgical cause of respiratory acidosis?
Hypoventilation (e.g. CNS depression), drugs (e.g. morphine), PTX, pleural effusion, parenchymal lung disease, acute airway obstruction
What is the surgical cause of respiratory alkalosis?
Hyperventilation (e.g. anxiety, pain, fever, wrong ventilator settings)
What is the classic acid-base findings w/ significant vomiting or NGT suctioning?
Hypokalemic hypochloremic metabolic alkalosis
Why hypokalemia w/ NGT suctioning?
Loss in gastric fluid- loss of HCl causes alkalosis, driving K into cells.
What is the treatment for hypokalemic hypochloremic metabolic alkalosis?
IVF, Cl-/K+ replacement
What is paradoxic alkalotic aciduria?
Seen in severe hypokalemic, hypovolemic, hypochloremic metabolic alkalosis w/ paradoxic metabolic alkalosis of serum and acidic urine.
How does paradoxic alkalotic aciduria occur?
H+ is lost in the urine in exchange for Na+ in an attempt to restore volume
With paradoxic alkalotic aciduria, why is H+ preferentially lost?
H+ is exchanged preferentially into the urine instead of K+ b/c of the low concentration of K+
What can be followed to assess fluid status?
Urine output, base deficit, lactic acid, vital signs, weight changes, skin turgor, jugular venous distention (JVD), mucosal membranes, rales (crackles), central venous pressure, PCWP, chest x-ray findings
With hypovolemia, what changes occur in vital signs?
Tachycardia, tachypnea, initial rise in DBP b/c of clamping down (peripheral vasoconstriction) w/ subsequent decrease in both SBP & DBPs.
What are the insensible fluid losses?
Loss of fluid not measured:
Feces- 100-200 mL/24hr
Breathing- 500-700 mL/24hr (increases w/ fever and tachypnea)
Skin- ~300mL/24hr, increased w/ fever, thus insensible fluid loss is not directly measured
How much bile is secreted a day?
~1000 mL/24 hr
How much gastric is secreted a day?
~2000 mL/24 hr
How much pancreatic is secreted a day?
~600 mL/24 hr
How much small intestine is secreted a day?
~3000 mL/24 hr
How much saliva is secreted a day?
~1500 mL/24 hr