Evaluation Of Respiratory Acidosis - Differential Diagnosis Of Symptoms

Evaluation of respiratory acidosisView PDF Menu Close

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Log in or subscribe to access all of BMJ Best PracticeLast reviewed: 23 Jan 2026Last updated: 27 Jan 2026

Summary

Respiratory acidosis occurs when acute, acute-on-chronic, or chronic derangements of the respiratory system lead to inefficient carbon dioxide clearance and pathologic accumulation of carbon dioxide.

When alveolar gas exchange units are unable to sufficiently excrete carbon dioxide, this leads to an increase in arterial carbon dioxide levels above the normal range of 35 to 45 mmHg (4.7-6.0 kPa). With the increase in carbon dioxide, hydrogen ions accumulate, causing the arterial pH to fall below the normal range (i.e., <7.35).[1]British Thoracic Society. BTS guideline for oxygen use in adults in healthcare and emergency settings. May 2017 [internet publication]. https://www.brit-thoracic.org.uk/quality-improvement/guidelines/emergency-oxygen

Acute respiratory acidosis is usually secondary to acute respiratory failure.

In acute respiratory failure, there is insufficient buffering capacity to handle the dramatic increase in arterial and venous carbon dioxide. In chronic derangements, however, carbon dioxide is processed by carbonic anhydrase to bicarbonate (the Hamburger shift). This leads to chloride excretion (with ammonium) by the kidney, and the pH gradually rises.[2]Alfaro V, Torras R, Ibáñez J, et al. A physical-chemical analysis of the acid-base response to chronic obstructive pulmonary disease. Can J Physiol Pharmacol. 1996;74:1229-1235. http://www.ncbi.nlm.nih.gov/pubmed/9028582?tool=bestpractice.com

Common pathophysiologic mechanisms in the development of respiratory acidosis include:

• Alveolar hypoventilation

  • Central alveolar hypoventilation

  • Neuromuscular disorders

• Increase of dead space ventilation (V/Q mismatching)

• Overproduction of carbon dioxide

The consequences of failing to recognize acute respiratory failure include marked hypoxemia, hyperkalemia, cardiovascular instability, and cardiac arrest.

Differentials

Common

• COPD
• Multilobar pneumonia
• Foreign body aspiration
• Drug use (narcotics, alcohol, sedatives, anesthetics)
• Oxygen therapy in COPD
• CNS infarction or hemorrhage
• Head trauma
• CNS infection
• Hypoventilation syndrome in obesity
• Pleural effusion
• Pneumothorax
• Obesity
• Kyphoscoliosis
• Hypokalemia
• Hypophosphatemia
• Inadequate mechanical ventilation

Full details

Uncommon

• Cardiogenic pulmonary edema
• Acute lung injury/acute respiratory distress syndrome
• Pulmonary fibrosis
• Status asthmaticus
• Laryngospasm
• Angioedema
• Primary alveolar hypoventilation
• Empyema
• Hemothorax
• Flail chest
• Scleroderma
• Ankylosing spondylitis
• Fibrothorax
• Hypothyroidism
• Paralytic agents and organophosphates
• High cord trauma/lesions (above C4)
• Guillain-Barre syndrome
• Multiple sclerosis
• Myasthenia gravis
• Muscular dystrophy
• Amyotrophic lateral sclerosis
• Polymyositis and dermatomyositis
• Phrenic nerve trauma
• Tetanus
• Botulism
• Poliomyelitis
• Sepsis
• Fever/malignant hyperthermia
• Insufflation of CO₂ into body cavity (e.g., laparoscopic surgery)

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Contributors

Authors

VIEW ALLAuthors

Rajiv Dhand, MD

Professor of Medicine

Department of Medicine

University of Tennessee Graduate School of Medicine

Knoxville

TN

Disclosures

RD declares that he has received grants/contracts from Mylan/Theravance and Viatris. RD receives royalties from UpToDate and Taylor and Francis. RD has been a consultant for Verona Pharma and is a member of the American Association for Respiratory Care Clinical Practice Guidelines for Aerosol Therapy. RD has received drugs from Theravance and Viatris for research in clinical trials.

Ghassan Jamal Wadi, MBBS

Pulmonary and Critical care fellow

Department of Medicine

University of Tennessee Graduate School of Medicine

Knoxville

TN

Disclosures

GJW declares that he has no competing interests.

Acknowledgements

Dr Rajiv Dhand and Dr Ghassan Jamal Wadi would like to gratefully acknowledge Dr M. Bradley Drummond and Dr Eddy Fan, previous contributors to this topic.

Disclosures

MBD declares that he has no competing interests. EF has received fees from MC3 Cardiopulmonary and ALung Technologies, Baxter, Getinge, Inspire, Vasomune, and Zoll Medical.

Peer reviewers

VIEW ALLPeer reviewers

Guy Soo Hoo, MD, MPH

Director

Intensive Care Unit

West Los Angeles VA Healthcare Center

Clinical Professor of Medicine

Geffen School of Medicine

UCLA

Los Angeles

CA

Disclosures

GSH declares that he has no competing interests.

Harman Paintal, MBBS

Division of Pulmonary and Critical Care Medicine

Veterans Affairs Palo Alto Health Care System (VAPAHCS)

Palo Alto

CA

Disclosures

HP declares that he has no competing interests.

Patrick J. Neligan, MA, MB BCh, FCARCSI, FJFICM

Consultant in Anaesthesia and Intensive Care

Galway University Hospitals

Senior Lecturer in Anaesthesia

National University of Ireland

Galway Department of Anaesthesia and Intensive Care

University College Hospitals

Galway

Ireland

Disclosures

Not disclosed.

Peer reviewer acknowledgements

BMJ Best Practice topics are updated on a rolling basis in line with developments in evidence and guidance. The peer reviewers listed here have reviewed the content at least once during the history of the topic.

Disclosures

Peer reviewer affiliations and disclosures pertain to the time of the review.

References

Our in-house evidence and editorial teams collaborate with international expert contributors and peer reviewers to ensure that we provide access to the most clinically relevant information possible.

Key articles

British Thoracic Society. BTS guideline for oxygen use in adults in healthcare and emergency settings. May 2017 [internet publication].Full text

British Thoracic Society. BTS/ICS guideline for the ventilatory management of acute hypercapnic respiratory failure in adults. Mar 2016 [internet publication].Full text

​Global Initiative for Chronic Obstructive Lung Disease. Global strategy for prevention, diagnosis and management of COPD: 2026 report. 2025 [internet publication].Full text

Reference articles

A full list of sources referenced in this topic is available to users with access to all of BMJ Best Practice.

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