How could you improve oxygenation during single-lung ventilation?
Answer:
When hypoxia occurs during single-lung ventilation, the goal is to optimize the match between ventilation and perfusion on the dependent lung or increase the amount of oxygen in the shunted blood of the collapsed lung.
Ventilated Lung
Optimize ventilation.
Use 100% oxygen.
Check the position of the DLT with a fiberoptic bronchoscope.
Ventilate manually to determine whether higher or lower tidal volumes or inspiratory pressures are beneficial.
Set minute ventilation to maintain PaCO2 at 40 mmHg (hypocapnia may inhibit HPV in the nondependent lung, whereas hyperventilation may increase airway pressure and promote blood flow to the nonventilated lung).
Apply 5 cm H2O of PEEP. It may be beneficial if larger tidal volumes delivered manually improved arterial saturation (i.e., recruitable alveoli). Alternatively, if tidal volumes are too large, adding PEEP may overdistend alveoli that are already open and compress blood vessels, diverting blood to the nonventilated lung and worsening the shunt.
Use two-lung ventilation intermittently.
Increase perfusion.
Selective vasodilators (inhaled nitric oxide, inhaled PGI2)
Collapsed Lung
Oxygenate shunt blood: A variety of approaches have been described but must be carefully considered for minimally invasive procedures because most involve some degree of lung reexpansion and therefore may affect surgical visualization.
Insufflate oxygen continuously: A flow of about 3 L per minute allowed to freely circulate will often increase arterial oxygen saturation 3% to 4%.
Intermittent single breath with oxygen
Partially reexpand the nonventilated lung and then keep the lumen side closed.
Apply continuous CPAP.
Differential CPAP to the collapsed lung and PEEP to the ventilated lung has been described but is rarely necessary and generally impractical for minimally invasive procedures.
High-frequency ventilation to the nonventilated lung
Decrease the shunt.
Use medications to augment HPV (phenylephrine, norepinephrine, almitrine).
Temporary clamp lobar vessels or the pulmonary artery of the nonventilated lung (rarely necessary).
Possible hypoventilation, in compliance with protective lung strategy and the ERAS guidelines will increase the need for the aforementioned maneuvers to maintain the saturation and the PaCO2 within acceptable ranges.
Reference(s):
- Batchelor TJP, Rasburn NJ, Abdelnour-Bertchtold E, et al. Guidelines for enhanced recovery after lung surgery: recommendations of the Enhanced Recovery after Surgery (ERAS®) Society and the European Society of Thoracic Surgeons (ESTS). Eur J Cardiothoracic Surg. 2019;1(55):91-115.
- Gropper MA, Cohen NH, Eriksson LI, et al, eds. Miller’s Anesthesia. 9th ed. Philadelphia, PA: Elsevier; 2020:1663-1700.