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Respiratory Alkalosis Workup

  • Author: Ryland P Byrd, Jr, MD; Chief Editor: Zab Mosenifar, MD, FACP, FCCP  more...
 
Updated: Jul 31, 2015
 

Laboratory Studies

An essential laboratory analysis is as follows:

  • Arterial blood gas determination: Alkalemia is documented by the presence of an increased pH level (>7.45) on arterial blood gas determinations. The presence of a decreased PaCO2 level (< 35 mm Hg) indicates a respiratory etiology of the alkalemia.

The following laboratory studies may be helpful:

  • Serum chemistries: Acute respiratory alkalosis causes small changes in electrolyte balances. Minor intracellular shifts of sodium, potassium, and phosphate levels occur. A minor reduction in free calcium occurs due to an increased protein-bound fraction. Compensation for respiratory alkalosis is by increased renal excretion of bicarbonate. In acute respiratory acidosis, the bicarbonate concentration level decreases by 2 mEq/L for each decrease of 10 mm Hg in the PaCO2 level. In chronic respiratory acidosis, the bicarbonate concentration level decreases by 5 mEq/L for each decrease of 10 mm Hg in the PaCO2 level. Plasma bicarbonate levels rarely drop below 12 mm Hg secondary to compensation for primary respiratory alkalosis.
  • Complete blood cell count: An elevation of the WBC count may indicate early sepsis as a possible etiology of respiratory alkalosis. A reduced hematocrit value may indicate severe anemia as the potential cause of respiratory alkalosis.
  • Liver function test: Findings may be abnormal if hepatic failure is the etiology of the respiratory alkalosis.
  • Cultures of blood, sputum, urine, and other sites: These should be considered, depending on information obtained from the history and physical examination and if sepsis or bacteremia are thought to be the cause of the respiratory alkalosis.
  • Thyroid testing: Thyroid-stimulating hormone and thyroxine levels may be indicated to rule out hyperthyroidism.
  • Beta-human chorionic hormone levels may be helpful in ruling out pregnancy.
  • Drug screens and theophylline and salicylate levels may be useful to determine whether drugs or medications are the cause.
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Imaging Studies

Consider the following imaging studies:

  • Chest radiography: Chest radiography should be preformed to help rule out pulmonary disease as a cause of hypocapnia and respiratory alkalosis. Potential etiologies that may be confirmed based on chest radiography findings include pneumonia, pulmonary edema, aspiration pneumonitis, pneumothorax, and interstitial lung disease.
  • Computerized tomography (CT) scanning: CT scanning of the chest may be performed if chest radiography findings are inconclusive or a pulmonary disorder is strongly considered as a differential diagnosis. CT scanning is more sensitive for helping detect disease, and findings may reveal abnormalities not seen on the chest radiograph. Consider spiral CT angiography of the chest if pulmonary embolism is suggested. Consider CT scanning of the brain if a central cause of hyperventilation and respiratory alkalosis is suspected. Specific etiologies that may be diagnosed based on brain CT scan findings include cerebrovascular accident, central nervous system tumor, and central nervous system trauma.
  • Ventilation perfusion scanning: Consider this scan in patients who are unable to undergo an intravenous contrast injection associated with CT scanning to assess the patient for pulmonary embolism.
  • Brain magnetic resonance imaging (MRI): If a central cause of hyperventilation and respiratory alkalosis is suggested and the initial brain CT scan findings are negative or inconclusive, an MRI of the brain can be considered. MRIs may reveal abnormalities not seen on CT scans, particularly lesions of the brain stem. Possible etiologies based on MRIs include cerebrovascular accident, central nervous system tumor, and central nervous system trauma.
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Other Tests

Echocardiography can be preformed to assess myocardial and valvular function. A "bubble" study is helpful when assessing patients for unexplained hypoxemia and right-to-left shunting of blood.

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Procedures

Perform a lumbar puncture if the history and physical examination findings are suggestive of a CNS infectious process. Perform cytologic analysis in patients suggested to have meningeal metastasis.

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Contributor Information and Disclosures
Author

Ryland P Byrd, Jr, MD Professor of Medicine, Division of Pulmonary Disease and Critical Care Medicine, James H Quillen College of Medicine, East Tennessee State University

Ryland P Byrd, Jr, MD is a member of the following medical societies: American College of Chest Physicians, American Thoracic Society

Disclosure: Nothing to disclose.

Specialty Editor Board

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Received salary from Medscape for employment. for: Medscape.

Chief Editor

Zab Mosenifar, MD, FACP, FCCP Geri and Richard Brawerman Chair in Pulmonary and Critical Care Medicine, Professor and Executive Vice Chairman, Department of Medicine, Medical Director, Women's Guild Lung Institute, Cedars Sinai Medical Center, University of California, Los Angeles, David Geffen School of Medicine

Zab Mosenifar, MD, FACP, FCCP is a member of the following medical societies: American College of Chest Physicians, American College of Physicians, American Federation for Medical Research, American Thoracic Society

Disclosure: Nothing to disclose.

Acknowledgements

Gregg T Anders, DO Medical Director, Great Plains Regional Medical Command , Brooke Army Medical Center; Clinical Associate Professor, Department of Internal Medicine, Division of Pulmonary Disease, University of Texas Health Science Center at San Antonio

Disclosure: Nothing to disclose.

Jackie A Hayes, MD, FCCP Clinical Assistant Professor of Medicine, University of Texas Health Science Center at San Antonio; Chief, Pulmonary and Critical Care Medicine, Department of Medicine, Brooke Army Medical Center

Jackie A Hayes is a member of the following medical societies: Alpha Omega Alpha, American College of Chest Physicians, American College of Physicians, and American Thoracic Society

Disclosure: Nothing to disclose.

Oleh Wasyl Hnatiuk, MD Program Director, National Capital Consortium, Pulmonary and Critical Care, Walter Reed Army Medical Center; Associate Professor, Department of Medicine, Uniformed Services University of Health Sciences

Oleh Wasyl Hnatiuk, MD is a member of the following medical societies: American College of Chest Physicians, American College of Physicians, and American Thoracic Society

Disclosure: Nothing to disclose.

April Lambert-Drwiega, DO Fellow, Department of Pulmonology and Critical Care Medicine, East Tennessee State University

April Lambert-Drwiega is a member of the following medical societies: American College of Physicians, American Medical Association, American Osteopathic Association, and Southern Medical Association

Disclosure: Nothing to disclose.

References
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  2. Effros RM, Wesson JA. Acid-Base Balance. Mason RJ, Broaddus VC, Murray JF, Nadel JA, eds. Murray and Nadel's Textbook of Respiratory Medicine. 4th ed. Philadelphia, PA: Elsevier Saunders; 2005. Vol 1: 192-93.

  3. DuBose TD, Jr. Acidosis and Alkalosis. Kasper DL, Braunwald E, Fauci AS, Hauser Sl, Longo DL, Jameson JL,eds. Harrison's Principles of Internal Medicine. 16th. New York, NY: McGraw-Hill; 2005. 270-1.

  4. Phillipson EA, Duffin J. Hypoventilation and Hyperventilation Syndromes. Mason RJ, Broaddus VC, Murray JF, Nadel JA, eds. Murray and Nadel's Textbook of Respiratory Medicine. 4th ed. Philadelphia, PA: Elsevier Saunders; 2005. Vol 2: 2069-70, 2080-84.

  5. Goldman A. Clinical tetany by forced respiration. JAMA. 1922. 78:1193-95.

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  8. Gardner WN. The pathophysiology of hyperventilation disorders. Chest. 1996 Feb. 109(2):516-34. [Medline].

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