To the Editor,
In their challenging study conducted on 39 patients undergoing one-lung ventilation (OLV), Moreault et al. have succeeded in “highlighting the need to better understand the physiology of lung collapse during OLV”.1 My letter addresses but one of the many thought-provoking volume and airway pressure findings: following the initiation of OLV and before pleural opening, the volume of “gaseous influx” into the non-ventilated lung from a measuring ambient air reservoir was greater when it occurred via the narrow-bore internal channel of a bronchial blocker (BB) than via the wide lumen of a double lumen endotracheal tube (DL-ETT) (contrary to one of the researchers’ two hypotheses).1 This totally unexpected finding could conceivably be a consequence of the “tidal gas movement” that will have been occurring via the DL-ETT lumen,2 but not to any meaningful degree via the long narrow-bore internal channel of the BB. “Paradoxical ventilation” occurs in association with the “tidal gas movement” and has been shown (as a single picture “saying a thousand words”) to be necessarily associated with an influx of ambient nitrogen into the non-ventilated lung.3 This could well have resulted in an earlier initiation of hypoxic pulmonary vasoconstriction in the non-ventilated lung in the studies with the wide-bore DL-ETT, with a consequent reduction in pulmonary blood flow that resulted in a lesser ongoing “gaseous influx” than might otherwise have occurred.
Whether or not this particular explanation is correct, one important message should be clear from the Moreault et al. study: after OLV is initiated and until the pleura is opened, ambient air (with slowly diffusing nitrogen) will certainly enter the non-ventilated lung if its airway is left non-occluded (open to air), regardless of whether the non-occluded airway is the lumen of a DL-ETT or the narrow-bore internal channel of a BB. Thus, if prompt lung collapse is desired, the open airway should either be connected to an ambient pressure oxygen source2,3 or, as has previously been described,4,5 occluded as soon as the patient is placed in the lateral position and OLV is initiated.4,5
With regard to the latter option, further studies will determine whether the appreciable reduction in airway pressure that occurs with intentional unilateral airway occlusion1 might prove to be, in some patients at least, an added risk of OLV. Further studies will also determine which of the two above-mentioned options will be the more efficient at facilitating the non-ventilated lung’s prompt collapse.
References
Moreault O, Couture EJ, Provencher S, et al. Double-lumen endotracheal tubes and bronchial blockers exhibit similar lung collapse physiology during lung isolation. Can J Anesth 2021. https://doi.org/10.1007/s12630-021-01938-y.
Pfitzner J, Peacock MJ, McAleer PT. Gas movement in the nonventilated lung at the onset of single-lung ventilation for video-assisted thoracoscopy. Anaesthesia 1999; 54: 437-43.
Pfitzner J. The role of an ambient pressure oxygen source during one-lung ventilation for thoracoscopic surgery. Anaesth Intensive Care 2016; 44: 20-7.
Bussières JS, Somma J, Del Castillo JL, et al. Bronchial blocker versus left double-lumen endotracheal tube in video-assisted thoracoscopic surgery: a randomized-controlled trial examining time and quality of lung deflation. Can J Anesth 2016; 63: 818-27.
Zhang Y, Yan W, Fan Z, et al. Preemptive one lung ventilation enhances lung collapse during thoracoscopic surgery: a randomized controlled trial. Thorac Cancer 2019; 10: 1448-52.
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This submission was handled by Dr. Stephan K.W. Schwarz, Editor-in-Chief, Canadian Journal of Anesthesia/Journal canadien d’anesthésie.
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This letter is accompanied by a reply. Please see Can J Anesth 2021; this issue.
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Pfitzner, J. The need to better understand the physiology of lung collapse during one-lung ventilation. Can J Anesth/J Can Anesth 68, 1452–1453 (2021). https://doi.org/10.1007/s12630-021-02040-z
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DOI: https://doi.org/10.1007/s12630-021-02040-z