Clinical Correlation

An anatomic shunt is a passage between two natural channels such as blood vessels. There can be shunted and non-shunted areas of the lung or the heart. An alveolar-venous fistula is also a shunt in which there is an abnormal passage between the alveoli and the venous circulation, when the exchange should be between capillaries and alveoli.

focal - present in one small area atelectasis - partial or complete lung collapse due to obstruction of the airway diffuse - present over a large area

Case Scenario 9-3 Acute Respiratory Failure: Pain Medication Made Things Worse Follow-Up

The patient with a history of cigarette smoking and COPD now exhibits long-term carbon dioxide retention, hypoxia, and worsening of respiratory acidosis with incomplete compensation. This is termed acute-on-chronic carbon dioxide retention. The drug testing and patient history revealed excessive intake of OxyContin, a synthetic narcotic, for chronic upper back pain. This medication was causing acute respiratory distress.

Treatment options need to take into consideration that nonshunted areas in the lung do not compensate for shunted portions on 100% O2. From your understanding of the O2 dissociation curve, you realize that, once equilibration has been reached with hemoglobin saturation, more O2 can only be added as dissolved O2, and this is usually insignificant. The shunted areas then will actually add a venous admixture to the saturated blood in the nonshunted areas, prolonging hypoxia. Further and frequent blood gas monitoring will be necessary while respiratory treatments are given.

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