Hypoxemia during a thoracoscopic procedure with one-lung ventilation (OLV) is a common problem that needs to be dealt with by the anesthesia provider. Hypoxemia is commonly defined as oxygen saturation < 90% (Pao2 > 60 mm Hg).
The basic goal during OLV is to maximize pulmonary vascular resistance (PVR) in the nonventilated lung while minimizing PVR in the dependent, ventilated lung. This is achieved by keeping the ventilated lung as close as possible to its FRC while facilitating collapse of the nonventilated lung. Hypoxic pulmonary vasoconstriction (HPV) which is primarily stimulated by low alveolar oxygen tension (Pao2), is a beneficial reflex to this end.
In the event of severe intraoperative hypoxemia the first recommendation is to reinflate the previously nonventilated lung. This will obviously suspend the surgery, so in the case of less severe, gradual hypoxemia the following treatments are suggested:
- Maintain 100% FiO2.
- Check the positioning of the double-lumen tube or bronchial blocker with fiberoptic bronchoscopy.
- Optimize cardiac output (has the IVC been compressed? Would the patient benefit from inotropes/vasopressors?)
- Decrease volatile anesthetics to < 1 MAC.
- Apply a recruitment maneuver to the ventilated lung (this will transiently make the hypoxemia worse).
- Apply PEEP 5 cm H2O to the ventilated lung (except in patients with emphysema).
- Apply CPAP 1-2 cm H2O to the nonventilated lung (apply a recruitment maneuver to this lung immediately before CPAP).
- Partial ventilation techniques of the nonventilated lung: a. Oxygen insufflation b. High-frequency ventilation c. Lobar collapse (using a bronchial blocker)
- Mechanical restriction of the blood flow to the nonventilated lung (i.e. clamp the nonventilated lung PA)
Medical management includes starting prostoglandin E (Flolan) and stopping vasodilators such as nitroglycerin.