A 48-year-old female with no significant past medical history presents to the emergency department (ED) with 7 days of dyspnea, fatigue, and 2 days of coughing up frank blood. Chest CT shows a large right pulmonary arteriovenous malformation (PAVM) extending the width of the right middle lobe, which is thought to be the source of bleeding. The patient is admitted to the ICU for monitoring and while in the ICU she has an episode of large volume hemoptysis (more than 300 mL) associated with desaturation to 83%, which improves to 98% with deep suctioning and oxygen delivery via non-rebreather face mask.
The patient is intubated using a 39F left-sided double lumen tube (DLT) and the endobronchial cuff is inflated to isolate her right lung and prevent blood from entering the left lung. Immediately after intubation her vital signs are:
After confirming appropriate tube position with bronchoscopy, leftsided one lung ventilation is initiated. Approximately 10 minutes after start of one lung ventilation, her vital signs are as follows:
Which of the following factors correlates with increased risk of hypoxemia during one lung ventilation?A. Right-sided one lung ventilation
Correct Answer: B
During one lung ventilation while both lungs are perfused only one lung is ventilated. This invariably leads to transpulmonary shunting and impairment in oxygenation. Hypoxemia typically occurs within the first 10 to 30 minutes of initiation of OLV and stabilizes or slightly increases as hypoxic pulmonary vasoconstriction (HPV) increases over the next 2 hours.
A number of factors may be helpful in predicting oxygenation during OLV:
Side of ventilation—The right lung is larger and 10% better perfused than the left lung. Thus, it is not surprising that right-sided OLV is better tolerated than left-sided OLV. The overall mean PaO2 is 100 mm Hg higher during stable right-sided OLV than during left-sided OLV (A).
Baseline Spirometry—Studies consistently show that patients with better spirometric lung function are more likely to desaturate during OLV. This is due to a dramatic increase in shunt fraction on initiation of one lung ventilation. Oxygenation often improves as HPV diverts blood flow to the ventilated lung with decreasing shunt fraction over time.
Typically, patients with an obstructive spirometric pattern tolerate OLV very well. In a chronically diseased lung, perfusion to areas with poor function is decreased because of chronic HPV. Thus, there is a less dramatic change in shunt fraction when OLV is initiated (B).
Baseline PaO2—Abnormally low arterial oxygen tension (PaO2 ) as found by blood gas analysis during two lung ventilation is a reliable indicator of abnormal lung function and a predictor of hypoxemia during OLV. PaO2 levels during two lung ventilation are strongly and positively correlated with PaO2 during OLV (C).
Position—Patient’s position during OLV is a factor in oxygenation. Positioning ventilated lung in the dependent position decreases VQ mismatch as perfusion to the ventilated lung increases because of gravity, whereas blood flow to the nonventilated lung is decreased (D).