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ABG interpretation cheat sheet: the ROME method in four steps

ABG questions follow the same four steps every time: read the pH to name the problem, find which value moved with it, check for compensation, then match the symptoms.

ROME (Respiratory Opposite, Metabolic Equal) does most of the work. The worked examples at the bottom show each pattern.

Built from NurseLingo's RN-written study decks· Updated Oct 2026· Sources

Case/Rule	Read as	Key Clues
ROME rule	Resp Opposite, Metab Equal	CO2 opposite pH = respiratory HCO3 same as pH = metabolic
Step 1: read the pH	Names the problem first	<7.35 = acidosis >7.45 = alkalosis
Step 2: match the mover	Finds the cause	CO2 opposite pH → respiratory HCO3 same as pH → metabolic
Step 3: check compensation	pH near normal, both off	Both off, same direction = compensating Side of 7.40 hints at the original problem
Step 4: match symptoms	Acidosis sedates, alkalosis excites	Acidosis: lethargy, confusion, headache Alkalosis: tingling, tetany, seizures
K+ runs opposite pH	Quick cross-check	Acidosis pushes K+ up Alkalosis pulls K+ down
pH7.28/CO2 52/HCO3 24	Uncompensated resp. acidosis	pH low, CO2 high (opposite)
pH7.30/CO2 40/HCO3 18	Uncompensated metab. acidosis	pH low, HCO3 low (equal)
pH7.32/CO2 55/HCO3 30	Partial comp. resp. acidosis	pH low, CO2 high HCO3 rising to compensate
pH7.36/CO2 50/HCO3 29	Fully comp. resp. acidosis	pH normal (acid side) Both CO2 & HCO3 abnormal
DKA	Metabolic acidosis	Ketones drop pH & HCO3 Kussmaul breathing compensates
Opioid overdose	Respiratory acidosis	Hypoventilation retains CO2 Reverse + support airway

RN pearl: Read pH first, match the mover second; symptoms, K+, and compensation all fall into place from there.

Watch: ABG interpretation explained

▶ ABGs Made Easy for Nursing Students · 9:42 · free on the Nurse Lingo YouTube channel

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Frequently asked questions

What are normal ABG values?

pH 7.35 to 7.45, PaCO2 35 to 45 mmHg, and HCO3 22 to 26 mEq/L. Ranges vary slightly by lab.

What does ROME stand for in ABGs?

Respiratory Opposite, Metabolic Equal. In respiratory problems, the pH and PaCO2 move in opposite directions. In metabolic problems, the pH and HCO3 move in the same direction.

How do you tell if an ABG is compensated?

If PaCO2 and HCO3 are both abnormal and moving in the same direction, the body is compensating. A normal pH means full compensation; an abnormal pH means partial compensation. The side of 7.40 the pH sits on hints at the original problem.

What acid-base imbalance does DKA cause?

Metabolic acidosis. Ketones lower the pH and HCO3, and deep, rapid Kussmaul breathing blows off CO2 to compensate.

Keep studying

⚡ Speed MatchSort drugs, lab values and electrolyte signs NCLEX lab values flashcardsStudy online free Lab values cheat sheetLab values Electrolyte imbalances cheat sheetFluids & electrolytes

Sources

Medical-Surgical Nursing, 10.4 Acid-Base Imbalance, OpenStax
Fundamentals of Nursing, 20.2 Acid-Base Balances, OpenStax
Blood gases, MedlinePlus, U.S. National Library of Medicine

For study only, not medical advice. Ranges and protocols vary by facility; follow your program and facility policies.