Not Always Top 5 - Hypoxia on One Lung
Ask the surgeons to stop. Gently re-inflate top lung and ventilate BOTH lungs with 100% O2*
THEN, to prevent recurrence:
Deliver O2 to top lung: Low flow O2 catheter or CPAP circuit (see above)
PEEP to bottom lung
Propofol infusion
Clamp the pulmonary artery
PS - *Sometimes the surgeon will be in the middle of something that cannot be stopped to allow re-inflation of the top lung. This is one of the reasons why it's so important to communicate across the drapes in thoracics.
The trick here is to re-establish safe oxygenation first. Then you can fiddle around to try and prevent further episodes of hypoxia.
Don't forget the usual system for working out the cause of hypoxia: It's either the machine, the tube, or the patient. In thoracics it is usually the patient. Never the tube if you use a Robert Shaw, and always the tube if you use a Broncho-Cath
The reason to choose top lung CPAP before bottom lung PEEP is that PEEP on the bottom lung can actually worsen the shunt. PEEP on the bottom lung does 2 things: Increases FRC and raises PVR. The effect on PaO2 is variable and depends on the balance of the two variables. In diseased lung FRC is usually the predominant effect. In healthy lung it's usually PVR. This is one of the reasons that good pre-op spirometry is a risk factor for hypoxia in one lung ventilation. 5cm CPAP rarely gets in the way of the surgical field.
Propofol does not inhibit hypoxic pulmonary vasoconstriction (HPV), so theoretically there may be some benefit in using propofol. But the evidence for this is not really there. Volatiles only inhibit HPV significantly over 1 MAC.
Thoracics is seriously the best fun to be had in the operating theatre!
Picture: CPAP circuit on top lung with pressure at about 5cmH2O. If you don't have one of these, just use an airway suction catheter taped to oxygen tubing. You also have to tape over the proximal opening to stop the oxygen leaking out. Don't pass the tip of the catheter beyond the lumen of the double lumen tube or you risk injuring the trachea/bronchus.