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Arterial blood gas interpretation

Identifies the primary acid-base disorder from pH, PaCO₂ and bicarbonate, calculates expected compensation and flags mixed disorders.

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Method · Limits of application

Classical compensation/Winter 1967, Berend 2014 scheme; Henderson–Hasselbalch 6.1/0.03; not Stewart

Arterial blood gas analysis uses pH, PaCO₂ and bicarbonate to describe patterns and approximate compensation; an apparently normal pH can coexist with a mixed disorder. This interface does not accept sodium, chloride or albumin and does not calculate the anion gap or identify every metabolic cause. The formulas assume a physiological context and sufficient time for compensation. Variants exist between sources: local compensation for chronic respiratory acidosis uses 3.5, whereas the Berend 2014 table describes 4–5 per 10 mmHg; the origin of this local variant must be checked before complete equivalence is claimed.

Conditions of use

Check the population, units, inclusion and exclusion criteria, and version in the original source. A result alone does not establish a diagnosis, discharge decision or prescription.

Documented parameters

pH
PaCO₂ · mmHg
HCO₃⁻ · mEq/L

6/6 reference cases checked. Numerical tests are not clinical validation.

Sources and documentation

Documented formula

Transcribed from the source or a recorded revision; this is not a clinical recommendation.

Acidemia: pH < 7.35; alkalemia: pH > 7.45. The primary disorder explains the pH direction. Expected compensation:

Metabolic acidosis (Winter): PaCO₂ = 1.5 × HCO₃⁻ + 8 ± 2.
Metabolic alkalosis: PaCO₂ = 40 + 0.7 × (HCO₃⁻ − 24) ± 2.
Respiratory acidosis: HCO₃⁻ rises 1 mEq/L per 10 mmHg PaCO₂ (acute) or 3.5 mEq/L per 10 mmHg (chronic).
Respiratory alkalosis: HCO₃⁻ falls 2 mEq/L per 10 mmHg (acute) or 4 mEq/L per 10 mmHg (chronic).

A value outside expected compensation indicates a second disorder. Consistency of the three values is checked with Henderson–Hasselbalch: pH = 6.1 + log[HCO₃⁻ ÷ (0.03 × PaCO₂)].

References

Identifier: gasometria-arterial

Original clinical content: Brazilian Portuguese.

Method version

Classical compensation/Winter 1967, Berend 2014 scheme; Henderson–Hasselbalch 6.1/0.03; not Stewart

gasometria-arterial@native-2026-10-03+73acdbaba6b8

Source for the active edition

The bibliographic edition identifies the source. By itself, it proves neither full conformity of the formula nor clinical approval.

Synthetic cases checked (6)

Synthetic cases for checking the implementation, with no patient data.

Case 1

reference-001

Inputs

pH: 7.4
PaCO₂: 40 mmHg
HCO₃⁻: 24 mEq/L

{
  "ph": 7.4,
  "paco2": 40,
  "hco3": 24
}

Expected result

{
  "level": "low",
  "verdict": "sem distúrbio"
}

Actual result

{
  "primary": "normal",
  "phcalc": 7.401029995663981
}

Case 2

reference-002

Inputs

pH: 7.29
PaCO₂: 26 mmHg
HCO₃⁻: 12 mEq/L

{
  "ph": 7.29,
  "paco2": 26,
  "hco3": 12
}

Expected result

{
  "exp": 26,
  "mixed": 0
}

Actual result

{
  "exp": 26,
  "phcalc": 7.287086643357144,
  "mixed": 0,
  "primary": "acidose metabólica"
}

Case 3

reference-003

Inputs

pH: 7.15
PaCO₂: 36 mmHg
HCO₃⁻: 12 mEq/L

{
  "ph": 7.15,
  "paco2": 36,
  "hco3": 12
}

Expected result

{
  "exp": 26,
  "mixed": 1
}

Actual result

{
  "exp": 26,
  "phcalc": 7.145757490560674,
  "mixed": 1,
  "primary": "acidose metabólica"
}

Case 4

reference-004

Inputs

pH: 7.26
PaCO₂: 60 mmHg
HCO₃⁻: 26 mEq/L

{
  "ph": 7.26,
  "paco2": 60,
  "hco3": 26
}

Expected result

{
  "expAguda": 26,
  "expCronica": 31
}

Actual result

{
  "expAguda": 26,
  "expCronica": 31,
  "phcalc": 7.259700842867511,
  "mixed": 0,
  "primary": "acidose respiratória"
}

Case 5

reference-005

Inputs

pH: 7.48
PaCO₂: 47 mmHg
HCO₃⁻: 34 mEq/L

{
  "ph": 7.48,
  "paco2": 47,
  "hco3": 34
}

Expected result

{
  "exp": 47
}

Actual result

{
  "exp": 47,
  "phcalc": 7.482259804386874,
  "mixed": 0,
  "primary": "alcalose metabólica"
}

Case 6

reference-006

Inputs

pH: 7.4
PaCO₂: 60 mmHg
HCO₃⁻: 36 mEq/L

{
  "ph": 7.4,
  "paco2": 60,
  "hco3": 36
}

Expected result

{
  "level": "mid",
  "verdict": "pH normal"
}

Actual result

{
  "primary": "misto ou compensado",
  "phcalc": 7.401029995663981
}

Code and reproducibility

This tool’s code on GitHub

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Sources, version and reproduction instructions

The code tests are technical checks. Clinical approval and professional translation review are recorded separately.

Relationship with cancer research

General context — relationship to be defined

A resource for general clinical contexts. This edition does not assign a specific oncological relationship; selecting it for a study requires a justified question, population and purpose.