OLV: Hypoxemia Predictors

There are several factors that have been demonstrated to predict hypoxemia during one-lung ventilation during thoracic surgery. These include:

1. A relatively high percentage of ventilation or perfusion to the operative lung as seen on pre-operative ventilation/perfusion scan
2. Hypoxemia during two-lung ventilation (especially intraoperatively in the lateral position)
3. A right-sided thoracotomy
4. Normal spirometry or restrictive lung disease as seen on pre-operative PFT’s, and the supine position during one-lung ventilation.

The most important of these factors is hypoxemia during two-lung ventilation.

If the operative lung has less perfusion on V/Q scan preoperatively, initiation of one-lung ventilation with the non-operative lung is less likely to cause desaturation. A left-sided thoracotomy is less likely to cause hypoxemia as compared to right-sided thoracotomy due to the 10% decrease in size of the left lung as compared to the right, resulting in less shunt when collapsed. Patients with obstructive lung disease are less likely to develop hypoxemia during one-lung ventilation and the severity of their airflow limitation correlates inversely to PaO₂. In contrast to the supine position, the lateral position utilizes gravity to encourage a shift in blood flow towards the dependent ventilated lung, which acts to improve the degree of shunt that naturally occurs during one-lung ventilation.