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Pediatric Respiratory Alkalosis Workup

  • Author: Mary C Mancini, MD, PhD, MMM; Chief Editor: Michael R Bye, MD  more...
 
Updated: Jan 16, 2015
 

Laboratory Studies

A simple step-wise approach proves useful for further workup in patients with respiratory alkalosis, such as the following:

  • Step 1: Prove the presence of respiratory alkalosis by an ABG. A PCO 2 less than 35 indicates alveolar hyperventilation. A pH greater than 7.4 is highly suggestive of alkalosis. When both are found, respiratory alkalosis is likely.
  • Step 2: Assess the chronicity of hyperventilation. Reference range HCO 3 - with a pH greater than 7.45 suggests acute hyperventilation, whereas low HCO 3 - with a pH of 7.4-7.45 suggests a chronic partially compensated process.
  • Step 3: An arterial-alveolar oxygen gradient within the reference range and a pH greater than 7.4 is consistent with hyperventilation secondary to direct CNS stimulation, with normal lung function.
  • Step 4: Arterial pH less than 7.4 is usually observed with alveolar hyperventilation as compensation for metabolic acidosis (overcompensation for metabolic acidosis is very rare).
  • Step 5: Respiratory alkalosis is likely with hypoxemia with alveolar hyperventilation. However, determining if the alkalosis is caused by the hypoxia or if the hypoxia and the alkalosis are caused by the underlying pulmonary disease is difficult.

Measurement of arterial pH, HCO3-, and PCO2 are crucial. Transcutaneous or end-tidal PCO2 may be used in place of arterial PCO2; however, transcutaneous PCO2 requires normal skin perfusion, and end-tidal pCO2 is useful only in the presence of normal lung function and when no other acid-base disturbance is suspected. Furthermore, the noninvasive tests do not measure the pH.

A detailed history and careful physical examination should indicate an underlying disorder.

Standard nomograms (see image below) help diagnose simple acid-base disorders, despite the following limitations:

Acid-base nomogram shows confidence bands for simp Acid-base nomogram shows confidence bands for simple acid-base disturbances. Conversion factor is 1 torr = 0.13 kPa.

See the list below:

  • They describe acid-base status in children with a steady-state condition. Hence, nomograms are not helpful for patients with rapidly changing status.
  • Nomograms lose precision at extremes.
  • Values falling in respiratory alkalosis may overlap with other mixed disorders and ultimately require clinical judgment.

Hyperventilation syndrome is often considered a diagnosis of exclusion. Physicians must consider other causes before making the diagnosis. However, in the typical patient with a normal alveolar-arterial oxygen gradient with an acute stress, the diagnosis can be made with confidence.

Drug screening may be helpful.

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Imaging Studies

Chest radiography may be indicated.

Ventilation/perfusion imaging, helical chest CT imaging, or CT angiography may be performed if pulmonary embolism is suspected.

CT imaging or MRI of the brain may be indicated if CNS pathology is suspected.

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Contributor Information and Disclosures
Author

Mary C Mancini, MD, PhD, MMM Professor and Chief of Cardiothoracic Surgery, Department of Surgery, Louisiana State University School of Medicine in Shreveport

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, Society of Thoracic Surgeons, Phi Beta Kappa

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.

References
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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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