💓 Savvy NurseOpen the app

🫀 Physiological Adaptation · Lesson 3 of 10 · 7 min

ABGs in Three Steps: ROME

🧪 pH 7.28, PaCO2 58, HCO3 25. Most students stare at it. Three steps and the word ROME turn it into 'respiratory acidosis, uncompensated, hypoventilating client' in under ten seconds.

💡 Key idea

pH decides acid or base. ROME decides respiratory or metabolic. The third value decides compensation.

🧠 Why it matters

Normals: pH 7.35 to 7.45; PaCO2 35 to 45 mmHg; HCO3 22 to 26 mEq/L; PaO2 80 to 100 mmHg. STEP 1: pH below 7.35 is acidosis, above 7.45 is alkalosis. STEP 2: find the matching cause. ROME: Respiratory Opposite, Metabolic Equal. If the pH and PaCO2 move in OPPOSITE directions, the problem is respiratory; if the pH and HCO3 move in the SAME direction, it is metabolic. STEP 3: check compensation. If the other value is also abnormal and the pH is back in range, it is fully compensated; abnormal with the pH still out of range is partial; the other value normal means uncompensated. RESPIRATORY ACIDOSIS: hypoventilation from COPD, opioid overdose, atelectasis; improve ventilation. RESPIRATORY ALKALOSIS: hyperventilation from anxiety, pain, early salicylate overdose; slow the breathing. METABOLIC ACIDOSIS: diabetic ketoacidosis, kidney failure, diarrhea, lactic acidosis from shock; look for deep rapid Kussmaul respirations as compensation. METABOLIC ALKALOSIS: vomiting, nasogastric suction, excess antacids, diuretics; often with hypokalemia.

🏥 In the real world

🧮 pH 7.28, PaCO2 58, HCO3 25. Step 1: pH low, acidosis. Step 2: PaCO2 high while pH is low, opposite directions, so respiratory. Step 3: HCO3 normal, so uncompensated. The client is probably hypoventilating, and the nurse checks the last opioid dose and the respiratory rate before anything else.

📌 Takeaways

  • pH 7.35–7.45, PaCO2 35–45, HCO3 22–26
  • Respiratory Opposite, Metabolic Equal
  • Kussmaul breathing is the lungs compensating for metabolic acidosis

📖 Terms in this lesson

ROME: Respiratory opposite, metabolic equal: the shortcut for telling whether an acid-base problem is respiratory or metabolic.

Kussmaul respirations: Deep, rapid breathing that blows off carbon dioxide to compensate for metabolic acidosis, classic in DKA.

ROME (ABG interpretation): Respiratory Opposite (pH and PaCO2 move in opposite directions), Metabolic Equal (pH and HCO3 move together): the two-step check for naming any acid-base imbalance.

Arterial pH: Normal 7.35 to 7.45; below 7.35 is acidosis and above 7.45 alkalosis, and below about 7.2 or above 7.6 is critical, at which point the heart, brain and drugs all stop working normally.

PaCO2: Normal 35 to 45 mmHg, the respiratory side of ROME; high means hypoventilation (respiratory acidosis, as in COPD or opioids), low means hyperventilation or compensation, and below 20 or above about 60 to 70 is critical.

HCO3 (bicarbonate on an ABG): Normal 22 to 26 mEq/L, the metabolic side of ROME; it moves the same direction as pH in metabolic problems (low in DKA, high with vomiting) and shifts to compensate for respiratory ones.

PaO2: Normal 80 to 100 mmHg; below 80 is hypoxemia, below 60 usually means the client needs supplemental oxygen or more support, and below about 40 is critical.

SaO2 / SpO2 (oxygen saturation): Normal 95 to 100%; 88 to 92% is the accepted target in COPD to avoid blunting the drive to breathe, and below 90% in anyone else means give oxygen and find the cause.

Sodium bicarbonate: An IV base for severe metabolic acidosis, hyperkalemia and tricyclic overdose; it is incompatible with calcium (precipitate), so flush the line before and after, watch the blood gas for overshoot into alkalosis and the potassium for a fall, and expect sodium and fluid load.

✅ Test yourself

ABG results: pH 7.50, PaCO2 29, HCO3 24. How should the nurse interpret these values?
  1. Respiratory acidosis
  2. Respiratory alkalosis, uncompensated
  3. Metabolic acidosis, compensated
  4. Metabolic alkalosis

Answer: B · Respiratory alkalosis, uncompensated

High pH with a low PaCO2 (opposite directions) is respiratory alkalosis; the normal bicarbonate shows no compensation.

A client with diabetic ketoacidosis has deep, rapid respirations. What do these respirations represent?
  1. Respiratory acidosis from hypoventilation
  2. Anxiety-driven hyperventilation
  3. Fluid overload causing pulmonary edema
  4. Compensation for metabolic acidosis

Answer: D · Compensation for metabolic acidosis

Kussmaul respirations lower PaCO2 to offset the metabolic acid load.

ABG results: pH 7.30, PaCO2 40, HCO3 16. Which condition is consistent with these values?
  1. Severe vomiting
  2. Opioid overdose
  3. Hyperventilation from pain
  4. Kidney failure

Answer: D · Kidney failure

Low pH with low bicarbonate (same direction) is metabolic acidosis; kidney failure retains acids. Vomiting causes alkalosis; opioids cause respiratory acidosis.

Start this lesson free →

NCLEX-style questions, XP and streaks in the app. No sign-up needed.

More in Physiological Adaptation

🔗 Related lessons