Required section · Section 4 of 6

Guided case: respiratory acidosis with an unresolved edge

In worksheet order, pH 7.28 establishes acidemia and PaCO2 60 mmHg is the respiratory acidifying direction. Calculated HCO3 is 27 mmol/L and moves as compensation. The primary pattern is respiratory acidosis.

PaCO2 is 20 mmHg above the 40 mmHg working target. The several-day history supports comparison with chronic HCO3 about 30 to 32 mmol/L, while an acute expectation is about 26. Observed HCO3 27 sits between these patterns, supporting evolving compensation or a possible second process rather than proof of either.

The potassium-excluded anion gap is Na − (Cl + HCO3−) = 138 − (96 + 27) = 15 mmol/L. Albumin is 4.0 g/dL and lactate is 1.1 mmol/L arterial; apply local intervals and policy to both. Communicate a method-aware respiratory-acidosis pattern and the remaining uncertainty without diagnosing disease.

Calculation: Na − (Cl + HCO3−) = 138 − (96 + 27) = anion gap 15 mmol/L. Compare with the reporting laboratory's interval; the 8–12 band shown is a commonly taught example. — Figure 1Guided-case anion-gap calculation with potassium excluded.

Chart shows HCO3 24 working target, acute expected 26, observed 27, and chronic expected range 30 to 32 mmol/L. — Figure 2Observed bicarbonate compared with acute and chronic expectations.

Guided arterial result set.
Result	Value	Status
pH	7.28	low
PaCO2	60 mmHg	high
HCO3	27 mmol/L	high, calculated
Na / Cl	138 / 96 mmol/L	measured ISE
Albumin	4.0 g/dL	no correction under 4.0 convention
Lactate	1.1 mmol/L	arterial example below 1.5

Respiratory-acidosis expectations at PaCO2 60 mmHg.
Pattern	Expected HCO3	Timing
Acute	about 26 mmol/L	minutes
Chronic	about 30-32 mmol/L	days
Guided case	27 mmol/L	several-day admission

Knowledge checks

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Knowledge check 1

Compared with stated chronic expectation, observed HCO3 27 is:

Choose one option.

Below the 30-32 mmol/L chronic range.

Within chronic range.

Proof of a second metabolic acidosis.

Knowledge check 2

What evidence helps resolve possible mixed physiology?

Choose at least 2 options.

Prior gases and timing

Local gap interval and albumin policy

Specimen review

One diagnosis from the gas alone

Section status

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