Background

Respiratory alkalosis is one of many acid-base disorders found among critically ill patients. It is detected by arterial blood gas (ABG) analysis and electrolyte levels. To diagnose respiratory alkalosis or assess the severity of the condition, the physician must understand clinical acid-base balance. Alkalosis, by definition, is a pathologic state that causes or tends to cause an increase in blood pH. Hence, one can have an alkalosis with normal pH if compensation has occurred; alkalemia is defined as a blood pH above 7.45. The term respiratory in respiratory alkalosis refers to the primary respiratory mechanism responsible for the change.^[1]

Pathophysiology

Hypocapnia (low PCO₂) develops whenever CO₂ elimination by the lungs exceeds tissue production. One or more of three basic categories usually underlie respiratory alkalosis: hypoxia, pulmonary diseases, and CNS disorders^[2](see image below).

Schematic presentation of pathophysiology of hyperventilation.

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Compensation

In respiratory acid-base disturbances, changes in ventilation, and hence PCO₂, represent the primary disturbance, and compensation occurs by alterations in plasma bicarbonate.

In chronic respiratory alkalosis, increased urinary bicarbonate excretion resists the pH change caused by hypocapnia. This renal compensation begins within several hours and takes several days for the maximal response.

In acute respiratory alkalosis, an initial small decrease may occur in plasma bicarbonate concentration because of chemical mass action.^[3]Hypocapnia leads to increased formation of carbonic acid, to lowered plasma hydrogen ion concentration (alkalemia), and to concomitant reduced plasma bicarbonate concentration. This is quantitatively less profound than renal compensation and is not related to change in bicarbonate excretion.^[4]

Formulas for estimating appropriate compensation in simple respiratory alkalosis (limit of compensation is [HCO₃^-] of approximately 15) include the following:

Acute alkalosis - Change in pH = (change in PCO₂) X 0.08
Chronic alkalosis - Change in pH = (change in PCO₂) X 0.003

Clinical Presentation

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Media Gallery

Acid-base nomogram shows confidence bands for simple acid-base disturbances. Conversion factor is 1 torr = 0.13 kPa.
Schematic presentation of pathophysiology of hyperventilation.

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Author

Mary C Mancini, MD, PhD, MMM

Mary C Mancini, MD, PhD, MMM is a member of the following medical societies: American Association for Thoracic Surgery, American College of Surgeons, American Surgical Association, Phi Beta Kappa, Society of Thoracic Surgeons

Disclosure: Nothing to disclose.

Coauthor(s)

Girish G Deshpande, MD, MBBS, FAAP Associate Professor of Pediatrics, Interim Director and Division Chief of Critical Care Medicine, Department of Pediatrics, University of Illinois College of Medicine at Peoria; Consulting Staff, Division of Critical Care Medicine, Children's Hospital of Illinois at OSF St Francis Medical Center

Girish G Deshpande, MD, MBBS, FAAP is a member of the following medical societies: American Academy of Pediatrics

Disclosure: Nothing to disclose.

Specialty Editor Board

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.

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, Society of Critical Care Medicine

Disclosure: Nothing to disclose.

Chief Editor

Michael R Bye, MD Professor of Clinical Pediatrics, State University of New York at Buffalo School of Medicine; Attending Physician, Pediatric Pulmonary Division, Women's and Children's Hospital of Buffalo

Michael R Bye, MD is a member of the following medical societies: American Academy of Pediatrics, American College of Chest Physicians, American Thoracic Society

Disclosure: Nothing to disclose.

Additional Contributors

G Patricia Cantwell, MD, FCCM Professor of Clinical Pediatrics, Chief, Division of Pediatric Critical Care Medicine, University of Miami Leonard M Miller School of Medicine/ Holtz Children's Hospital, Jackson Memorial Medical Center; Medical Director, Palliative Care Team, Holtz Children's Hospital; Medical Manager, FEMA, South Florida Urban Search and Rescue, Task Force 2

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, Wilderness Medical Society

Disclosure: Nothing to disclose.

Sections Pediatric Respiratory Alkalosis
Overview
Presentation
DDx
Workup
Treatment
Media Gallery
References

Pediatric Respiratory Alkalosis

Background

Pathophysiology

Compensation

References

Tables

Contributor Information and Disclosures

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