🏠 Study Hub 🖼️ Infographics
Nursing Field Notes / Respiratory + Labs · ABG SERIES 3 OF 3 · Pathophysiology
🫁 RESPIRATORY + LABS SET NG-092 ABG · The Method NG-138 ABG · Compensation Practice NG-173 ABG · Answer Key NG-132 Anatomy of Breathing NG-170 Key Terms & Lung Sounds 🧪 By condition 🩺 Bedside tests

ABG Compensation Answers ✅

All four gases, the route each one takes through the decision tree — and what they mean for the patient

NG-173 LABS · ACID–BASE ADHD-friendly visual edition

This is the answer key — but not a list of answers. Each of the four gases from NG-138 is drawn as a lit-up route through the decision tree, so you can see exactly where the reasoning turned. Then: where each disorder comes from, what to do about it, the mixed-disorder trap, and the oxygenation half of the gas that everyone forgets. The method is on NG-092.

📄 Simple Nursing original — opens in Drive →

1️⃣ 7.32 · 55 · 42Respiratory acidosis, PARTIALLY compensated. All three numbers abnormal.
2️⃣ 7.55 · 49 · 35Metabolic alkalosis, PARTIALLY compensated. The high CO₂ is the rescue, not the cause.
3️⃣ 7.37 · 52 · 32Respiratory acidosis, FULLY compensated. Normal pH on the acid side of 7.40.
4️⃣ 7.43 · 43 · 33Metabolic alkalosis, FULLY compensated. Normal pH on the alkaline side of 7.40.
✅

PART 1 · THE FOUR ANSWERS

EVERY TURN SHOWN

Follow the gold route with your finger. Where it lights up is where you had to make a decision. All reference values on this page (pH 7.35–7.45, PaCO₂ 35–45 mmHg, HCO₃⁻ 22–26 mEq/L) are typical adult ranges and vary by lab — read the range printed on your own report.

🧭 First, the trick that unlocks questions 3 and 4

THE 7.40 TRICK — naming a gas whose pH is normal Magnified view of the normal window only (7.35–7.45) · the rest of the scale is off-screen 7.40 — the true midpoint 7.35 7.45 ACIDIC HALF a compensated gas landing here started as an ACIDOSIS ALKALINE HALF a compensated gas landing here started as an ALKALOSIS Q3 · pH 7.37 PaCO₂ 52 (acid) → respiratory acidosis, fully compensated Q4 · pH 7.43 HCO₃⁻ 33 (base) → metabolic alkalosis, fully compensated ⭐ Rule — compensation drags the pH TOWARD 7.40 and stops — it never crosses to the other side. So whichever half the pH landed in tells you what the original disorder must have been.

Two of the four gases come back with a normal pH. The half of the normal window the pH lands in tells you what the original disorder was, because compensation never overshoots 7.40.

🧠 Below 7.40 it was an acidosis. Above 7.40 it was an alkalosis.

1️⃣ Question 1 — pH 7.32 · PaCO₂ 55 · HCO₃⁻ 42

QUESTION 1 — the decision path, filled in pH 7.32 · PaCO₂ 55 mmHg · HCO₃⁻ 42 mEq/L — read left to right KEY ✓ bright = the route this gas took dim = the options it did not take STEP 1 WHICH WAY IS THE pH? STEP 2 WHICH PARTNER MATCHES? STEP 3 HOW FAR DID THE RESCUE GET? THE ANSWER ACIDOSIS pH < 7.35 ✓ pH 7.32 — below 7.35 NORMAL pH 7.35 – 7.45 ALKALOSIS pH > 7.45 RESPIRATORY PaCO₂ matches the pH ✓ PaCO₂ 55 — high = acid METABOLIC HCO₃⁻ matches the pH UNCOMPENSATED rescuer still normal PARTIALLY COMP. pH still out of range ✓ pH is still 7.32 FULLY COMPENSATED pH back in range RESPIRATORY ACIDOSIS PARTIALLY COMPENSATED all three values abnormal WHY — in one line per step Step 1 · pH 7.32 is below 7.35 → acidosis. Step 2 · PaCO₂ 55 is above 45, and a high CO₂ is acidic — it agrees with the pH, so the lungs are the culprit. Step 3 · HCO₃⁻ 42 is far above 26 (base), so the kidneys ARE rescuing — but the pH has not made it back inside 7.35–7.45.

Three abnormal numbers is the signature of partial compensation: the culprit is out of range, the rescuer is out of range, and the pH still hasn't made it home.

Respiratory acidosis · partially compensated

🧠 The dramatic HCO₃⁻ of 42 is the rescuer, not the problem. It argues with the pH.

🩺 Question 1 — the patient behind the numbers

A CO₂ retainer who is losing ground. The kidneys have had days to bank bicarbonate (HCO₃⁻ 42 is a long-term adaptation), but the CO₂ has now climbed faster than they can keep up.

  • Think COPD with an acute exacerbation on top of chronic retention, or a chronic retainer who has been over-sedated.
  • Watch for drowsiness, confusion, headache, flushed skin, asterixis — CO₂ narcosis.
  • Priorities: improve ventilation — position upright, treat the reversible cause (bronchospasm, secretions, infection, sedation), escalate for possible non-invasive ventilation.
  • Never assume a sleepy CO₂ retainer is “settled for the night.”
🧠 Partial compensation + a deteriorating patient = the rescue is losing. Escalate.

2️⃣ Question 2 — pH 7.55 · PaCO₂ 49 · HCO₃⁻ 35

QUESTION 2 — the decision path, filled in pH 7.55 · PaCO₂ 49 mmHg · HCO₃⁻ 35 mEq/L — read left to right KEY ✓ bright = the route this gas took dim = the options it did not take STEP 1 WHICH WAY IS THE pH? STEP 2 WHICH PARTNER MATCHES? STEP 3 HOW FAR DID THE RESCUE GET? THE ANSWER ACIDOSIS pH < 7.35 NORMAL pH 7.35 – 7.45 ALKALOSIS pH > 7.45 ✓ pH 7.55 — above 7.45 RESPIRATORY PaCO₂ matches the pH METABOLIC HCO₃⁻ matches the pH ✓ HCO₃⁻ 35 — high = base UNCOMPENSATED rescuer still normal PARTIALLY COMP. pH still out of range ✓ pH is still 7.55 FULLY COMPENSATED pH back in range METABOLIC ALKALOSIS PARTIALLY COMPENSATED all three values abnormal WHY — in one line per step Step 1 · pH 7.55 is above 7.45 → alkalosis. Step 2 · PaCO₂ 49 is high, which is ACID — the wrong direction, so no match. HCO₃⁻ 35 is high, which is BASE — that agrees, so the kidneys / metabolism are the culprit. Step 3 · That high CO₂ is the lungs hypoventilating on purpose to hold acid in — a rescue — but the pH is still far outside the range.

The step-2 turn is the whole question here. The first abnormal partner you meet (PaCO₂ 49) is not the culprit — it points the wrong way.

Metabolic alkalosis · partially compensated

🧠 Don't grab the first abnormal number. Grab the one that AGREES with the pH.

🩺 Question 2 — the patient behind the numbers

Base gained, or acid lost. Something has been taking hydrogen ions out of this patient.

  • Classic causes: protracted vomiting, nasogastric suction, over-use of antacids or bicarbonate, loop and thiazide diuretics, hypokalemia.
  • Expect the alkalosis picture: tingling, muscle cramps, twitchiness, tetany, arrhythmias — alkalosis lowers ionized calcium and drives potassium into cells.
  • Priorities: stop the loss (antiemetics, review the NG suction and diuretics), replace fluid and electrolytes as prescribed, and check potassium, chloride and calcium.
  • The high CO₂ is deliberate hypoventilation. Do not “correct” it — it is the only help this patient has.
🧠 Vomit and suction throw acid away. What's left behind is base.

3️⃣ Question 3 — pH 7.37 · PaCO₂ 52 · HCO₃⁻ 32

QUESTION 3 — the decision path, filled in pH 7.37 · PaCO₂ 52 mmHg · HCO₃⁻ 32 mEq/L — read left to right KEY ✓ bright = the route this gas took dim = the options it did not take STEP 1 WHICH WAY IS THE pH? STEP 2 WHICH PARTNER MATCHES? STEP 3 HOW FAR DID THE RESCUE GET? THE ANSWER ACIDOSIS pH < 7.35 NORMAL pH 7.35 – 7.45 ✓ pH 7.37 — normal, acid side ALKALOSIS pH > 7.45 RESPIRATORY PaCO₂ matches the pH ✓ PaCO₂ 52 — high = acid METABOLIC HCO₃⁻ matches the pH UNCOMPENSATED rescuer still normal PARTIALLY COMP. pH still out of range FULLY COMPENSATED pH back in range ✓ pH is back in range RESPIRATORY ACIDOSIS FULLY COMPENSATED the chronic COPD gas WHY — in one line per step Step 1 · pH 7.37 is inside 7.35–7.45, but BOTH partners are abnormal — so keep going. 7.37 is on the acid side of 7.40, so this began as an acidosis. Step 2 · PaCO₂ 52 is high = acid, which agrees with “acidosis” → respiratory. HCO₃⁻ 32 is high = base, the opposite way → that is the rescuer. Step 3 · The pH is back inside the normal range, so the rescue finished the job → fully compensated.

The step-1 box that lights up is NORMAL pH — and the route keeps going anyway. That is the entire lesson of this question.

Respiratory acidosis · fully compensated

🧠 Normal pH + two abnormal partners = fully compensated, never “normal”.

🩺 Question 3 — the patient behind the numbers

This is the textbook chronic COPD gas. The kidneys have had days to bank bicarbonate and have bought back a normal pH.

  • Very likely the patient's baseline. Compare with previous gases before you treat it as new.
  • The patient can look and feel completely well with these numbers.
  • Priorities: treat the underlying disease, not the printout. Keep an eye on their usual oxygen target — check the plan for that individual patient.
  • What matters clinically is the trend: a rising CO₂ with a falling pH from this baseline is an acute-on-chronic deterioration.
🧠 Fully compensated respiratory acidosis = old. Take a history, not fright.

4️⃣ Question 4 — pH 7.43 · PaCO₂ 43 · HCO₃⁻ 33

QUESTION 4 — the decision path, filled in pH 7.43 · PaCO₂ 43 mmHg · HCO₃⁻ 33 mEq/L — read left to right KEY ✓ bright = the route this gas took dim = the options it did not take STEP 1 WHICH WAY IS THE pH? STEP 2 WHICH PARTNER MATCHES? STEP 3 HOW FAR DID THE RESCUE GET? THE ANSWER ACIDOSIS pH < 7.35 NORMAL pH 7.35 – 7.45 ✓ pH 7.43 — normal, base side ALKALOSIS pH > 7.45 RESPIRATORY PaCO₂ matches the pH METABOLIC HCO₃⁻ matches the pH ✓ HCO₃⁻ 33 — high = base UNCOMPENSATED rescuer still normal PARTIALLY COMP. pH still out of range FULLY COMPENSATED pH back in range ✓ pH is back in range METABOLIC ALKALOSIS FULLY COMPENSATED judge the state by the pH WHY — in one line per step Step 1 · pH 7.43 is inside 7.35–7.45 but sits on the ALKALINE side of 7.40 — so this began as an alkalosis. Step 2 · HCO₃⁻ 33 is above 26 = base, which agrees → metabolic alkalosis. PaCO₂ 43 is still (just) inside 35–45. Step 3 · By the rule the question sheet teaches — full compensation means a fully normal pH — this one is fully compensated.

Only one partner is frankly abnormal here. The pH is normal, so the state is judged by the pH — and the side of 7.40 names the disorder.

Metabolic alkalosis · fully compensated

🧠 7.41–7.45 with a high HCO₃⁻ = a compensated metabolic alkalosis.

⚠️ Question 4 — the honest nuance

The compensating PaCO₂ of 43 is sitting at the very top of normal. The lungs are hypoventilating a little, but not enough to push the number out of range.

  • By the rule this course teaches — full compensation = a fully normal pH — the answer is fully compensated.
  • Some references would describe the respiratory response here as incomplete, because the CO₂ has not moved as far as expected. Both descriptions are talking about the same gas.
  • If you are ever unsure on an exam, say what you see: “normal pH on the alkaline side of 7.40 with a high bicarbonate — a compensated metabolic alkalosis.”
🧠 Describe the gas, then name it. Description never loses marks.

📋 All four answers on one line each

QpHPaCO₂HCO₃⁻ Primary problemCompensation
17.32 ↓55 ↑ acid42 ↑ base Respiratory acidosisPartial
27.55 ↑49 ↑ acid35 ↑ base Metabolic alkalosisPartial
37.37 (n)52 ↑ acid32 ↑ base Respiratory acidosisFull
47.43 (n)43 (n)33 ↑ base Metabolic alkalosisFull

In every one of the four, the culprit is the partner that agrees with the pH.

🧠 Two respiratory, two metabolic · two partial, two full. The set covers the whole grid.
🗺️

PART 2 · WHERE THEY COME FROM

CAUSES + WHAT YOU DO

Naming the gas is half the job. The other half is knowing which organ to go and look at.

🗺️ The cause map — organs on the left, causes on the right

WHERE EACH DISORDER COMES FROM LEFT: anterior view of the trunk, organs numbered · RIGHT: the causes, tagged with those numbers anterior view · skin and ribs removed 1 lungs 2 stomach 3 pancreas 4 kidneys 5 intestine 6 muscle RESPIRATORY ACIDOSIS CO₂ ↑ — not breathing enough 1 COPD, asthma attack, airway obstruction 1 pneumonia, atelectasis, chest trauma 1 opioids, sedatives, anesthesia (they slow the drive) 1 neuromuscular weakness — Guillain-Barré, myasthenia 1 head injury depressing the brainstem RESPIRATORY ALKALOSIS CO₂ ↓ — breathing too much 1 anxiety or panic, pain, fever 1 early sepsis, pulmonary embolism 1 hypoxia of any cause, high altitude 1 over-set mechanical ventilation METABOLIC ACIDOSIS HCO₃⁻ ↓ — acid gained or base lost 3 diabetic ketoacidosis — ketoacids build up 6 lactic acidosis — shock, sepsis, cardiac arrest 4 kidney failure — acid cannot be excreted 5 severe or prolonged diarrhea — bicarbonate poured out • certain poisonings (salicylates, toxic alcohols) METABOLIC ALKALOSIS HCO₃⁻ ↑ — base gained or acid lost 2 vomiting — stomach acid thrown away 2 nasogastric suction — the same loss, by tube 2 excess antacids or bicarbonate 4 loop and thiazide diuretics 4 hypokalemia 🧠 One sorting question: “Breathing problem, or chemistry problem?” Breathing → respiratory.

Every acid–base disorder starts somewhere physical. Match the number on the cause to the numbered organ on the body.

SEE ALSO Airway and alveolar anatomy is drawn in full on NG-004 Anatomy of the Lungs; the mechanics of the breath itself are on NG-132 Anatomy of Breathing.
🧠 “Breathing problem or chemistry problem?” One question sorts almost every case.

🚨 Respiratory acidosis — what you actually do

Answer first: make them ventilate. This is a CO₂ problem, not simply an oxygen problem.

  • Sit upright, wake them, coach deep breathing and coughing, incentive spirometer.
  • Clear the airway — suction secretions, treat bronchospasm as prescribed.
  • Treat pain so they can take a full breath; review sedation and opioids.
  • Escalate early for non-invasive ventilation if the CO₂ is climbing and the patient is tiring.
  • Monitor level of consciousness — a falling LOC with a rising CO₂ is an emergency.
🧠 Move air, not just oxygen.

💨 Respiratory alkalosis — what you actually do

Answer first: find out why they are breathing so hard.

  • Rule out the dangerous causes first — hypoxia, pulmonary embolism, sepsis, pain, fever — before you call it anxiety.
  • If it is anxiety: stay with them, coach slow breathing, reduce stimulation.
  • If they are ventilated: the settings may be doing it — report the gas.
  • Expect and manage the symptoms: tingling, dizziness, carpopedal spasm.
🧠 Hyperventilation is a symptom. Treat the reason, not the rate.

🚨 Metabolic acidosis — what you actually do

  • Find the acid. Blood glucose and ketones (DKA), lactate and perfusion (shock, sepsis), renal function, and a stool history (diarrhea).
  • Restore perfusion — fluids as prescribed; a poorly perfused patient keeps making lactate.
  • Insulin and fluids for DKA per protocol; replace ongoing GI losses.
  • Watch the potassium and the cardiac monitor — acidosis drives K⁺ out of cells, and correcting the acidosis drives it back in.
  • Leave the Kussmaul breathing alone. It is the only compensation they have.
🧠 Perfuse, treat the cause, watch the K⁺.

🤢 Metabolic alkalosis — what you actually do

  • Stop the loss: antiemetics as prescribed, review nasogastric suction, review diuretics and antacid use.
  • Replace fluid and electrolytes as prescribed — this is very often a volume and chloride problem.
  • Correct the potassium. Hypokalemia both causes and maintains a metabolic alkalosis.
  • Monitor for tetany, cramps and arrhythmias; keep the patient on a monitor if the potassium is low.
🧠 Vomiting is not just fluid loss — it is acid loss.

🧠 The pattern that names most cases before you see a gas

The storyPredict this gas
Post-op, sleepy, had opioidsRespiratory acidosis
Panicking, tingling fingers, fast deep breathsRespiratory alkalosis
New diabetic, thirsty, fruity breath, deep sighing breathingMetabolic acidosis (DKA)
Vomiting for three days, or on continuous NG suctionMetabolic alkalosis
Long-standing COPD, comfortable, normal pHFully compensated respiratory acidosis
Profound shock or a cardiac arrestMixed acidosis (respiratory + metabolic)
🧠 Read the story before you read the numbers. The gas usually confirms what you already suspected.
🚨

PART 3 · THE HARDER CASES

MIXED, EXPECTED, OXYGEN

Three things that turn an easy ABG question into a hard one.

🚨 Compensated vs mixed — the two-second check

COMPENSATED vs MIXED — read the two partner arrows Schematic · look only at where PaCO₂ and HCO₃⁻ sit, acid side or base side COMPENSATED the two partners sit on OPPOSITE sides PaCO₂ ACID SIDE BASE SIDE PaCO₂ 55 — high, acid HCO₃⁻ ACID SIDE BASE SIDE HCO₃⁻ 34 — high, base One is rescuing the other → the pH is defended Example: pH 7.36 · PaCO₂ 55 · HCO₃⁻ 34 MIXED / COMBINED the two partners sit on the SAME side PaCO₂ ACID SIDE BASE SIDE PaCO₂ 60 — high, acid HCO₃⁻ ACID SIDE BASE SIDE HCO₃⁻ 14 — low, ALSO acid Nobody is rescuing — the pH collapses Example: pH 7.10 · PaCO₂ 60 · HCO₃⁻ 14 Cardiac arrest, severe sepsis, opioid overdose in shock ⭐ The two-second check — put a finger on PaCO₂ and a finger on HCO₃⁻. Opposite sides = compensation. Same side = a mixed disorder, and the patient is in real trouble. Escalate, do not chart and wait.

Put a finger on PaCO₂ and a finger on HCO₃⁻. Opposite sides means someone is rescuing. Same side means nobody is, and the pH falls off a cliff.

🧠 Opposite = rescue. Same = disaster.

🚨 Mixed disorders — when to worry

  • Both partners abnormal in the same acid–base direction = a combined disorder.
  • The commonest one you will meet: cardiac arrest — the patient is not ventilating (CO₂ up) and is not perfusing (lactate up, HCO₃⁻ down).
  • Also seen in severe sepsis, in opioid overdose with shock, and in a patient with COPD who develops a severe metabolic acidosis.
  • Recognize it by the severity of the pH — mixed disorders produce the most extreme pH values you will ever see.

Never label a mixed picture “partially compensated”. Nothing is compensating.

🧠 Two problems pushing the same way = a resuscitation, not a lab result.

⭐ “Is the compensation about right?”

You are not usually asked to calculate this at this stage, but the reasoning is worth having.

  • Compensation should be in the right direction and roughly proportional to the problem.
  • A large primary problem with only a tiny partner change suggests the rescuing organ cannot respond — for example, kidneys that are failing, or lungs too weak to hyperventilate.
  • Compensation in the wrong direction is not compensation at all — it is a second disorder.
  • If your course teaches specific expected-compensation formulas, use theirs; they vary between texts.
🧠 Right direction, sensible size. Anything else means a second problem.

🫁 The oxygenation half of the gas — the bit everyone forgets

THE OTHER HALF OF THE GAS — oxygenation Oxyhemoglobin dissociation curve · PaO₂ against SaO₂ · typical adult, varies with age and altitude 0 20 40 60 80 100 0% 20% 40% 60% 80% 100% PaO₂ (mmHg) SaO₂ — oxygen saturation of hemoglobin PaO₂ 60 ≈ SaO₂ 90% the edge of the cliff — below this, saturation falls fast SAFE PLATEAU PaO₂ 80–100 · SaO₂ 95–100% right shift ▶ ◀ left shift THE STEEP PART below PaO₂ 60 a small extra drop costs a LOT of saturation WHY THE CURVE SHIFTS RIGHT shift Hb lets GO of O₂ more easily • ↑ CO₂ • ↑ H⁺ (acidosis) • ↑ temperature • ↑ 2,3-DPG LEFT shift Hb HOLDS ON to O₂ • the opposite of all four above • (alkalosis, cold, low CO₂) 🧠 MEMORY HOOK Hard-working muscle is hot, acidic and full of CO₂ — so the curve shifts RIGHT exactly where oxygen is needed most. READING THE OXYGEN NUMBERS • PaO₂ 80–100 mmHg and SaO₂ 95–100% are typical adult reference values — they vary with age and altitude. • The acid–base answer and the oxygenation answer are SEPARATE questions — answer both. • Because of the plateau, saturation barely changes between PaO₂ 80 and 100 — but below 60 it falls off a cliff. • Always record what oxygen the patient was on. A “normal” PaO₂ on 15 L/min is not reassuring.

Acid–base and oxygenation are two separate questions on the same printout. The flat top of the curve is why a saturation of 95% and one of 99% are almost the same thing — and why 88% is not.

SEE ALSO Hypoxia, oxygen delivery devices and target saturations are covered on NG-006 Hypoxia & O₂ Devices.
🧠 60 and 90 travel together — PaO₂ 60 mmHg ≈ SaO₂ 90%, and that is the edge.

✅ Hypoxemia vs hypoxia — not the same word

  • Hypoxemia = low oxygen in the blood — that is what PaO₂ and SaO₂ measure.
  • Hypoxia = not enough oxygen reaching the tissues. You can be hypoxic with a normal PaO₂ (severe anemia, shock, carbon monoxide poisoning, cyanide).
  • So a normal-looking oxygen number does not prove the tissues are being oxygenated.
  • The earliest clinical sign of hypoxia is usually restlessness and anxiety — long before cyanosis.
🧠 -emia is in the blood. Hypoxia is in the cells.

⚠️ Things that make an ABG lie

  • Air bubbles left in the syringe — they change the gas values.
  • Delay in getting the sample to the lab — follow local policy on transport and icing.
  • Venous blood drawn by mistake — the picture looks falsely acidotic with a high CO₂.
  • No record of the oxygen the patient was on — the PaO₂ becomes uninterpretable.
  • Comparing to the wrong baseline — a chronic retainer's “abnormal” gas may be their normal.
🧠 No bubbles · straight to the lab · write down the FiO₂.
🎯

PART 4 · FINAL DRILL

PROVE IT

If you can do these ten without the tree, you can do them in an exam.

🎯 Ten gases — cover, answer, check

1 · pH 7.28 · PaCO₂ 58 · HCO₃⁻ 25 pH acid · CO₂ high = acid (match, lungs) · HCO₃⁻ normal. Respiratory acidosis, uncompensated.
2 · pH 7.52 · PaCO₂ 28 · HCO₃⁻ 23 pH base · CO₂ low = base (match, lungs) · HCO₃⁻ normal. Respiratory alkalosis, uncompensated.
3 · pH 7.30 · PaCO₂ 30 · HCO₃⁻ 16 pH acid · CO₂ low = base (no match) · HCO₃⁻ low = acid (match, metabolic). The low CO₂ is the lungs helping. pH still abnormal. Metabolic acidosis, partially compensated.
4 · pH 7.38 · PaCO₂ 60 · HCO₃⁻ 35 pH normal on the acid side of 7.40 · CO₂ high = acid (match) · HCO₃⁻ high = the rescuer. Respiratory acidosis, fully compensated — the chronic COPD picture.
5 · pH 7.48 · PaCO₂ 42 · HCO₃⁻ 32 pH base · CO₂ normal · HCO₃⁻ high = base (match, metabolic). Metabolic alkalosis, uncompensated.
6 · pH 7.12 · PaCO₂ 62 · HCO₃⁻ 15 pH severely acid · CO₂ high = acid and HCO₃⁻ low = acid. Both partners on the same side. Mixed (combined) respiratory and metabolic acidosis — a resuscitation picture.
7 · pH 7.41 · PaCO₂ 30 · HCO₃⁻ 19 pH normal on the alkaline side of 7.40 · CO₂ low = base (match) · HCO₃⁻ low = the kidneys dumping base to help. Respiratory alkalosis, fully compensated — think chronic hyperventilation or altitude.
8 · pH 7.20 · PaCO₂ 38 · HCO₃⁻ 12 in a new diabetic pH acid · CO₂ normal · HCO₃⁻ very low = acid (match, metabolic). Metabolic acidosis, uncompensated — consistent with DKA. Expect Kussmaul respirations to start and the CO₂ to fall on the next gas.
9 · pH 7.34 · PaCO₂ 50 · HCO₃⁻ 30 · PaO₂ 55 on room air Acid–base: pH acid · CO₂ high = acid (match) · HCO₃⁻ high = rescuer, pH still low → respiratory acidosis, partially compensated. Separately, PaO₂ 55 is hypoxemia — below the 60 mmHg cliff. Both problems need reporting.
10 · pH 7.40 · PaCO₂ 40 · HCO₃⁻ 24 Everything inside its reference range. A genuinely normal ABG.

⭐ The 30-second script for any ABG

1
“The pH is ___ — that's an acidosis / alkalosis (or normal, on the ___ side of 7.40).”
2
“The ___ agrees with it, so this is respiratory / metabolic.”
3
“The ___ has moved the other way, so it is uncompensated / partially / fully compensated.”
4
“Oxygenation: PaO₂ ___ on ___ oxygen — that's adequate / hypoxemic.”
🧠 Four sentences. Say them in that order and you cannot leave anything out.

✅ What to hand over, every time

  • The values and the oxygen they were on.
  • The name of the disorder and the compensation state.
  • Whether it is new or their baseline — quote the previous gas if there is one.
  • What the patient looks like: level of consciousness, work of breathing, observations.
  • What you have already done and what you are asking for.
🧠 Numbers · name · trend · patient · ask.

🔗 The ABG series — all three pages, in order

PageWhat it gives you
NG-092 · ABG Answers (1 of 3) THE METHOD — the 3-step read, ROME, the decision tree, the pH scale, which organ fixes what, and three fully worked uncompensated gases.
NG-138 · Compensation Questions (2 of 3) PRACTICE — what compensation actually is, uncompensated vs partial vs full, and four compensation gases plotted for you to answer before you peek.
NG-173 · Compensation Answers (3 of 3) ANSWER KEY — the filled-in decision path for all four gases, plus the causes of each disorder, the expected-compensation check, oxygenation, and the traps.
🧠 Method → Practice → Key. Do them in that order and the fourth ABG stops being scary.
✅ Q1 & Q2 = PARTIALAll three numbers abnormal. 7.32/55/42 resp acidosis · 7.55/49/35 metabolic alkalosis.
✅ Q3 & Q4 = FULLpH normal, partner(s) abnormal. 7.37/52/32 resp acidosis · 7.43/43/33 metabolic alkalosis.
🧭 THE 7.40 TRICKNormal pH? Below 7.40 it was an acidosis; above it was an alkalosis. Compensation never overshoots.
🔍 CULPRIT vs RESCUERThe culprit agrees with the pH. The rescuer argues with it. Name the culprit, never the rescuer.
🚨 SAME SIDE = MIXEDBoth partners acid, or both base? That is a combined disorder — arrest, severe sepsis, shock. Escalate.
🫁 DON'T FORGET THE O₂PaO₂ 80–100 · SaO₂ 95–100% (typical adult, varies by lab). PaO₂ 60 ≈ SaO₂ 90% — the cliff edge.