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Pediatric Respiratory Acidosis Workup

  • Author: Mithilesh K Lal, MBBS, MD, MRCP, FRCPCH; Chief Editor: Timothy E Corden, MD  more...
Updated: Jun 05, 2014

Laboratory Studies

Failure to consider a mixed acidosis can lead to missed therapies and diagnosis. Always critically analyze acid-base values by assessing the pH, the arterial partial pressure of carbon dioxide (Pa CO2), and the bicarbonate (HCO3) concentration.

Diagnosis of respiratory acidosis is established with arterial blood gas values. Insight into the underlying cause and etiopathologic mechanisms requires further investigations, as detailed below. The serum HCO3 level and pH can be helpful in distinguishing acute hypercapnia from chronic hypercapnia. If the pH is greater than 7.45, elevated Pa CO2 may compensate for metabolic alkalosis and not a primary process.

In the setting of acute respiratory acidosis, pH decreases by 0.08 for every 10-mm Hg increase in Pa CO2. The HCO3 concentration increases by 1 mEq/L for every 10-mm Hg increase in Pa CO2. If Pa CO2 increases acutely to 80 mm Hg, the pH is 7.12, and the HCO3 value is 28 mEq/L.

In the setting of chronic respiratory acidosis, pH decreases 0.03 for every 10-mm Hg increase in Pa CO2. HCO3 concentration equals 24 mmol/L ± 4 for every 10-mm Hg increase in Pa CO2 greater than 40 mm Hg. For example, if the Pa CO2 is 80 mm Hg, the pH is 7.28, and the HCO3 value is 40 mEq/L ± 4.

The HCO3 -resorption process is efficient. If a patient with chronic hypercapnia has a pH higher than 7.20, a superimposed acute-on-chronic respiratory acidosis or a concomitant metabolic acidosis is most likely occurring as well.

A toxicology screen for narcotics, benzodiazepines, alcohol, or tricyclic antidepressants should be performed if indicated. Electrolyte assessment is indicated for abnormalities associated with muscle weakness (eg, hypophosphatemia, hypokalemia, hypomagnesemia, and hypocalcemia).


Radiography, CT, and MRI

Chest radiography findings may help in the diagnosis.

Computed tomography (CT) of the chest is indicated if the history and physical findings suggest primary pulmonary disease. CT angiography may be indicated to rule out pulmonary embolus.

CT scanning or MRI of the brain is indicated if the history and physical findings suggest signs of an intracranial process. MRI of the spine may be indicated by the history and physical findings.


Other Tests

Additional studies that may be considered include the following:

  • Pulmonary function tests, including spirometry, if the child can cooperate
  • Electromyography (EMG), if indicated to evaluate neuromuscular disease
  • Polysomnography (sleep study) to evaluate for obstructive or central sleep apnea, if indicated
Contributor Information and Disclosures

Mithilesh K Lal, MBBS, MD, MRCP, FRCPCH MRCP, MRCPCH, FRCPCH, Consultant Neonatologist, James Cook University Hospital, UK

Mithilesh K Lal, MBBS, MD, MRCP, FRCPCH is a member of the following medical societies: British Medical Association, Royal College of Physicians, Royal College of Paediatrics and Child Health, British Association of Perinatal Medicine, American Pediatric Society, Society for Pediatric Research, Neonatal Society, Nepal Medical Association

Disclosure: Nothing to disclose.


Ronald Litman, DO Professor of Anesthesiology and Pediatrics, University of Pennsylvania School of Medicine

Ronald Litman, DO is a member of the following medical societies: American Academy of Pediatrics, American Society of Anesthesiologists, Society for Pediatric Anesthesia

Disclosure: Nothing to disclose.

Margaret A Priestley, MD Associate Professor of Clinical Anesthesiology and Critical Care, Perelman School of Medicine at the University of Pennsylvania; Clinical Director, Pediatric Intensive Care Unit, The Children's Hospital of Philadelphia

Margaret A Priestley, MD is a member of the following medical societies: American Academy of Pediatrics, American Medical Association, Society of Critical Care Medicine

Disclosure: Nothing to disclose.

Chief Editor

Timothy E Corden, MD Associate Professor of Pediatrics, Co-Director, Policy Core, Injury Research Center, Medical College of Wisconsin; Associate Director, PICU, Children's Hospital of Wisconsin

Timothy E Corden, MD is a member of the following medical societies: American Academy of Pediatrics, Phi Beta Kappa, Society of Critical Care Medicine, Wisconsin Medical Society

Disclosure: Nothing to disclose.


G Patricia Cantwell, MD, FCCM Professor of Clinical Pediatrics, University of Miami, Leonard M Miller School of Medicine; Chief, Division of Pediatric Critical Care Medicine, Medical Manager, Urban Search & Rescue, South Florida TF-2, Medical Director, Holtz Children's Hospital Palliative Care Team, Medical Director, Tilli Kids – Pediatric Initiative of Hospice Care of SE Florida, Director, Pediatric Critical Care Transport, Holtz Children's Hospital/Jackson Memorial Hospital

G Patricia Cantwell, MD, FCCM is a member of the following medical societies: American Academy of Hospice and Palliative Medicine, American Academy of Pediatrics, American Heart Association, American Trauma Society, National Association of EMS Physicians, Society of Critical Care Medicine, and Wilderness Medical Society

Disclosure: Nothing to disclose.

Barry J Evans, MD Assistant Professor of Pediatrics, Temple University Medical School; Director of Pediatric Critical Care and Pulmonology, Associate Chair for Pediatric Education, Temple University Children's Medical Center

Barry J Evans, MD is a member of the following medical societies: American Academy of Pediatrics, American College of Chest Physicians, American Thoracic Society, and Society of Critical Care Medicine

Disclosure: Nothing to disclose.

Mary L Windle, PharmD Adjunct Associate Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Nothing to disclose.

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