What might be done to avoid incurring excessive pressures during PLV
secondary to the mechanism described here? To the extent that the
prevailing pathology is confined to a specific segment of the lungs,
clinicians would be well advised to orient that zone lowermost.
Subsequent introduction of perfluorocarbon will thus tend to
selectively fill the impaired regions of the lung. In the best of
situations, a unilateral disease process would be present, which would
allow for the patient to be placed in the lateral decubitus position.
This would be fortuitous, because the lateral dimension of the lung is
considerably smaller than its vertical dimension. This would, in turn,
result in an attenuated perfluorocarbon-related pressure head in
comparison to that which would be obtained in the erect posture.
Irrespective of the orientation of the patient, the clinical team would
also do well to instill a volume of perfluorocarbon that will rise to a
level that falls short of the entry point(s) of the airway(s) of the
lung(s) that are subject to instillation. Determination of this point
would, of course, be facilitated by the availability of a fluoroscope.
Ensuring that the fluid level does not extend into the affected
bronchus (or bronchi) would obviate the need to subsequently impose
obligatory PEEP in order to enhance the distribution of tidal
ventilation. Finally, the clinical team should consider limiting peak
inspiratory pressure to a level that prevents excessive distention of
the most dependent lung zones. If the fluoroscopically confirmed
vertical dimension of the perfluorocarbon bolus residing in the lung(s)
were, for example, 6 cm, the prevailing end-expiratory pressure at the
base of this fluid column would be (6 × 1.9 =) 11 cm
H2O in the absence of PEEP. This would prompt the clinical
team to restrict inspiratory pressures to ≤ 19 cm H2O, if
30 cm H2O were the selected target for maximum inflation
pressure. The narrowed range of pressures thus imposed might obligate
the clinical team to employ a technique that was developed for the
express purpose of preventing barotrauma-permissive hypercapnia.