Acid-base balance and fluid electrolyte homeostasis

1. Big picture

In surgery, acid–base, fluid, and electrolyte disorders are not theoretical physiology. They directly influence whether the patient can survive anesthesia, whether shock is improving, whether bowel obstruction is causing dangerous dehydration, whether pancreatitis needs aggressive resuscitation, and whether postoperative complications are developing.

The surgical logic is:

Fluid loss / bleeding / sepsis / obstruction / vomiting / fistula
→ disturbed volume + electrolytes + acid–base status
→ impaired perfusion, arrhythmia, renal failure, ileus, shock
→ correct before, during, and after surgery

The examiner usually wants you to answer three practical questions:

1. Is the patient hypovolemic, overloaded, or euvolemic?
2. Is there a dangerous electrolyte abnormality, especially potassium?
3. Is the acid–base disorder a marker of shock, sepsis, respiratory failure, vomiting, renal failure, or gastrointestinal loss?

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