Fluid, Electrolyte & Acid-Base · Topic 11 of 23
Metabolic Alkalosis
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.
Metabolic alkalosis: read the gas in three calls
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A textbook metabolic alkalosis with no patient attached yet. Read it in three calls, then load a patient.
Make the three calls first. What to look for, what to do and what to expect ordered fill in for the disorder you find.
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Metabolic alkalosis
Acid lost or base gained. The HCO₃⁻ climbs, the pH climbs with it — and potassium almost always falls alongside.
NG suction or vomiting removes stomach acid → the blood turns alkaline (pH up) — and K⁺ drops.
mEq/L · normal 22 – 26 · with a pH above 7.45 (normal 7.35 – 7.45)
Almost always comes with it and keeps it going · report K⁺ below 3.0 mEq/L
0.9% normal saline replaces the chloride the kidneys need · replace potassium (IV KCl)
What causes it
Watch forClassic exam cause: vomiting or NG suction — stomach acid lost
Vomiting causes alkalosis (stomach acid lost) · diarrhea causes acidosis (bicarbonate lost). Diuretics also shrink the fluid volume, which keeps the bicarbonate high.
What you'll see
SignsLabs & diagnostics
CheckHCO₃⁻ above 26 with pH above 7.45
Red flags
Act nowTreatment: replace what was lost
Chloride + K⁺Put back the chloride and the potassium
For vomiting or diuretics — replaces the chloride the kidneys need to excrete bicarbonate.
Not D5W or 0.45% salineLow K⁺ keeps the alkalosis going — replace it.
Report K⁺ below 3.0Avoid sodium bicarbonate; stop the cause when ordered.
Saline won't correct it — treat the cause and replace K⁺.
More detail
Nursing priorities
In orderMetabolic or respiratory alkalosis?
ROME — Respiratory Opposite, Metabolic Equal
| pH | pH above 7.45 |
|---|---|
| PaCO₂ | High (above 45) — the lungs slow down |
| HCO₃⁻ | High HCO₃⁻ (above 26) — the cause |
| Which way | HCO₃⁻ moves the same way as the pH (Metabolic Equal) |
| Breathing | Slow, shallow breathing — compensation |
| Potassium | Low K⁺ — almost always; report below 3.0 |
| Classic causes | Vomiting, NG suction, diuretics |
| Fix | 0.9% normal saline + potassium chloride |
Teach your patient
DischargeMetabolic alkalosis: stomach acid lost — and low potassium comes with it. Fix it with saline plus potassium, never bicarbonate.
Sources · OpenStax Medical-Surgical Nursing 10.4 and 10.3, OpenStax Fundamentals of Nursing 20.2, Open RN Nursing Fundamentals 15.5, Merck Manual Professional on metabolic alkalosis and acid-base disorders, and Sood et al., interpretation of arterial blood gas (2010). Stomach drawn from Servier Medical Art: stomach (CC BY 4.0). Typical adult values — follow your protocol.
Metabolic Alkalosis
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.
Metabolic alkalosis occurs when pH rises above 7.45 due to excess bicarbonate (HCO₃⁻ above 26 mEq/L) or loss of hydrogen ions. The two most testable causes are prolonged vomiting or nasogastric suctioning (loss of hydrochloric acid from the stomach) and overuse of loop or thiazide diuretics (which cause chloride and potassium wasting). Both mechanisms create a chloride-responsive alkalosis — the kidneys want to excrete the excess bicarb but can't without adequate chloride. This is why normal saline, not D5W, is the cornerstone IV fluid. Hypokalemia almost always accompanies metabolic alkalosis because the kidneys trade potassium for hydrogen ions trying to correct pH, and low potassium itself perpetuates the alkalosis. Expected ABG pattern: pH above 7.45, HCO₃⁻ above 26, with respiratory compensation showing a rising PaCO₂ (the body hypoventilates to retain CO₂ and lower pH). Signs include confusion, muscle twitching, tingling, hypoventilation, and possible seizures. Nursing priorities: replace chloride and potassium, monitor I&O closely, assess respiratory rate and depth for compensatory shallow breathing, and address the underlying cause.
Key Distinctions
Don't confuse the slow, shallow breathing of compensatory hypoventilation in metabolic alkalosis with respiratory depression from opioids — the mechanism and intervention differ entirely. Students commonly mistake metabolic alkalosis symptoms (tingling, muscle twitching) for hypocalcemia; both can coexist, but the primary driver here is elevated pH. Chloride-responsive alkalosis (vomiting, NG suction, diuretics) corrects with saline; chloride-resistant alkalosis (Cushing's, hyperaldosteronism) does not.
Clinical Pearl
Vomiting steals acid, diuretics steal chloride and potassium — all roads to metabolic alkalosis run through what the body loses, not what it gains.
Knowledge Check
3 quick questions on the must-knows for this topic.
Which problem is a classic cause of metabolic alkalosis?
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Go further
- SimulatorAcid–Base & ABG SimulatorBuild a gas. Watch compensation happen. Move CO₂ or bicarbonate, then read the gas in three calls: pH, cause, compensation.
- SimulatorFluid & Electrolyte SimulatorChange one lab. Watch the whole patient respond. Sodium, potassium, calcium, magnesium, pH and volume, all linked — with a live ECG and an IV pole where every bag runs.
- GuideRespiratory vs Metabolic Acidosis and Alkalosis: The 4 Disorders With Causes, Findings and What the Nurse DoesTwo organs, two directions. Respiratory disorders are CO₂ problems that belong to the lungs and happen in minutes; metabolic disorders show up in the bicarbonate and come from everywhere else. Each of the four with its causes, what you see, what the nurse does and what the provider orders — in a table, then patient by patient, with each one loaded in a live gas.
- GuideABG NCLEX Questions: The 6 Patterns the Exam Keeps TestingThe NCLEX rarely asks you to name a gas. It asks what the gas means and what the nurse does. Name the gas with the normal-pH trap, which patient is at risk, what the nurse does first, what the provider will order, the electrolyte that moves with the pH, and the finding that means it is getting worse — with a live gas for the anticipate-the-order pattern.
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