On about the 3rd post-op day, fluid that moved into the extravascular space begins to move back into the intravascular space. Beware of fluid overload.
What are classic signs of third-spacing?
Decreased urine output
Causes of metabolic acidosis
Loss of bicarb (diarrhea, ileus, fistula, high-output ileostomy, carbonic anhydrase inhibitors)
Gain of acid (ischemia, renal failure, ketoacidosis, necrosis)
What causes hypokalemic hypochloremic alkalosis?
NGT suction or loss of gastric acid (vomiting, NGT)
Why does NGT suctioning cause hypokalemia?
Loss of gastric HCl results in alkalosis. In response, H+ is driven out of the cells, into the interstitium, in exchange for K+. K+ is also lost in the kidneys, in exchange for Na+.
What is paradoxic alkalotic aciduria?
In severe vomiting, there is metabolic alkalosis due to loss of gastric acid, but there is also acidification of the urine, due to loss of H+ in exchange for Na, in an attempt to restore intravascular volume.
What is the most significant cause of insensible fluid loss?
Respiration--500-700 mL are lost, per 24 hours
Respiratory fluid loss increases with fever and tachypnea