Effects of head-down tilt on intrapulmonary shunt fraction and oxygenation during one-lung ventilation in the lateral decubitus position

Objective: During one-lung ventilation, surgical positions significantly affect deterioration of oxygenation, and the lateral decubitus position is superior in preventing dangerous hypoxemia compared with the supine position. However, additional head-down tilt causes more compression of the dependent ventilated lung by the abdominal contents and may result in dangerous hypoxemia, as occurs in the supine position. Therefore, we evaluated the effect of head-down tilt on intrapulmonary shunt and oxygenation during one-lung ventilation in the lateral decubitus position. Methods: Thirty-four patients requiring one-lung ventilation were randomly allocated to the control group (n = 17) or the head-down tilt group (n = 17). Hemodynamic and respiratory variables were measured 15 minutes after one-lung ventilation in the lateral decubitus position (baseline), 5 and 10 minutes after a 10-degree head-down tilt (T5 and T10, respectively), and 10 minutes after the patient was returned to a horizontal position (T20) in the head-down tilt group. Measurements were done at the same time points in the control group without head-down tilting. Results: In the head-down tilt group, cardiac filling pressures were increased after head-down tilt without any changes in cardiac index. Percent change of shunt to baseline value was significantly increased at T10 and T20 in the head-down tilt group. Percent change of arterial oxygen tension to baseline value was significantly decreased at T5, T10, and T20 in the head-down tilt group, whereas it was decreased only at T20 in the control group. Conclusion: Head-down tilt during one-lung ventilation in the lateral decubitus position caused a significant increase in shunt and a decrease in percent change of arterial oxygen tension, without causing dangerous hypoxemia.