Fluid, Electrolyte & Acid-Base

The patient's blood pressure looks fine lying down — but the moment they stand, it drops 20 mmHg. That orthostatic shift is your earliest warning of fluid volume deficit before labs ever change.

A local IV infiltration is annoying — but a systemic IV complication like air embolism, sepsis, or speed shock can kill your patient in minutes. Recognizing the difference drives your response.

The patient's labs say they're dehydrated, their weight says they're retaining fluid, and the IV is running wide open. Welcome to third-spacing — where fluid is present but useless.

Hanging a hypertonic IV pulls fluid out of cells and into the bloodstream — powerful for cerebral edema, but one wrong move risks fatal volume overload or vein destruction.

Hanging a bag of 0.45% NS seems gentle — until fluid rushes into cells and a patient with increased intracranial pressure herniates. Knowing when hypotonic solutions help versus harm is non-negotiable.

The patient gained 2 kg overnight with no dietary change — that's 2 liters of retained fluid, and the lungs are next in line to show it.

The IV site looks swollen and the patient says it burns — but is it infiltration, extravasation, or phlebitis? Your next action depends entirely on which one.

A potassium of 6.8 mEq/L with peaked T waves means the heart could stop in minutes. The treatment sequence you choose — and the order you choose it in — determines whether it does.

Phosphorus and calcium are locked in an inverse relationship — when one rises, the other falls. Missing this seesaw means missing the real danger hiding behind the lab value.

A post-thyroidectomy patient reports tingling around their mouth and fingertips. The vitals look stable — but neuromuscular crisis is minutes away if you miss the calcium connection.

A patient's potassium keeps dropping despite aggressive replacement — the hidden culprit might be a magnesium level no one checked. You can't fix one without the other.

Magnesium excess sedates everything — reflexes, breathing, and the heart. The first clinical clue disappears before the lethal ones arrive, and missing it costs time you don't have.

A confused postoperative patient with a sodium of 128 mEq/L doesn't need more fluids — they likely need less. Correcting hyponatremia too fast can be more dangerous than the imbalance itself.

The confused elderly patient who "just stopped drinking water" after hip surgery may not have a neuro problem — they may have a sodium of 152 mEq/L that nobody checked.

The patient's ECG shows a new U wave and flattened T waves — but the cardiac monitor won't alarm for these subtle changes. Knowing what hypokalemia looks like before it becomes lethal is your job.

The patient with cancer who becomes confused and constipated isn't just uncomfortable — a calcium level above 10.5 mg/dL can silently progress to cardiac arrest.

The patient who's been vomiting for three days doesn't just need fluids — their pH is climbing because they're losing acid they can't replace. Knowing why changes everything you do next.

When pH looks deceptively normal but the patient is crashing, two opposing acid-base problems may be canceling each other out — and you need to catch both.

An ABG result sits in front of you with four numbers. If you don't know the systematic order for reading them, you'll misclassify the disorder every time.

The pH reads 7.37 and you think everything's fine — but the CO₂ is 58 and the bicarb is 34. The body is hiding a serious problem. Can you see it?

When pH drops and bicarbonate is the culprit, the cause matters as much as the numbers — because DKA and renal failure demand very different nursing responses.

When CO₂ climbs because the lungs can't blow it off, pH drops fast — but the cause determines whether you grab a bronchodilator or call a rapid response for impending respiratory failure.

The anxious post-op patient breathing 28 times per minute has a pH of 7.52 — but the real danger isn't the anxiety. It's what the alkalosis does to calcium and potassium.