Concealed Air Leak Associated with Large Tidal Volumes in Partial Liquid Ventilation

Abstract

Current ventilator strategies aim at maintaining an open lung and limiting both peak inspiratory pressures and tidal volumes to avoid alveolar distension. Perfluorocarbons, as well as being excellent solvents for oxygen and carbon dioxide, have the unique properties of being able to recruit dependent lung regions and improve pulmonary mechanics. Optimal ventilator strategies for partial liquid ventilation (PLV) have not yet been clearly defined. In the surfactant-depleted rabbit model, an approach involving a large tidal volume (VT) (15 ml/kg) and lung filled to FRC with perfluorocarbon (PFC) was compared with strategies involving a moderate VT (9 ml/kg) and partially filled lung (6 ml/kg), a moderate VT (9 ml/kg) and lung filled to FRC with PFC, and a large VT (15 ml/kg) and partially filled lung (6 ml/kg). PEEP was maintained at 5 cm H2O except in the moderate VT, partial-filling group, in which a PEEP of 9 cm H2O was used to maintain the rabbits for the duration of the experiment. Oxygenation was satisfactory in all groups, and peak inspiratory pressures were not significantly different. However, five of the 13 animals in the large-VT, PFC-filled lung group died of a pneumothorax prior to completion of the experiment. Of the eight animals in this group surviving the experiment, two had radiographic evidence of pneumothoraces, with an additional three animals having autopsy evidence of air leak. Of the 22 animals in the other groups, all survived with the exception of a single rabbit in the large VT, partial-filling group, which had both radiographic and autopsy evidence of air leak. We conclude that there is a significant risk of barotrauma in a PLV strategy in which a large VT is used in association with a lung filled to FRC with perfluorocarbon. Adequate gas exchange can be achieved with alternative ventilation strategies in combination with PLV.

Liquid-assisted ventilation: An alternative respiratory modality

“…Recent studies indicate that improvement in pulmonary gas exchange and mechanics and reduction in barotrauma during PLV is favored by surfactant pretreatment, higher PFC doses, higher breathing frequencies (within the conventional range), and smaller tidal volumes to prevent overdistension, optimize PFC distribution, and minimize exposure of the alveolarcapillary membrane to a gas-liquid interface. [128][129][130]132 Maintenance of a therapeutic PFC liquid volume following initial instillation in the lungs is dependent on the rate of PFC elimination during gas ventilation, which is influenced by many factors, including time, PFC physical properties, gas to liquid contact, ventilation strategy, lung pathophysiology, repositioning of the subject, and the administration of supplemental PFC doses to the lungs (see Uptake, Biodistribution, and Elimination of PFC During LAV). Lung protection is enhanced by replacing PFC liquid at the measured loss rate.…”

“…During this time, preclinical studies have indicated that frequencies within the conventional range can be maintained during instillation and barotrauma is significantly reduced when using low pressures and low tidal volumes and high-frequency strategies. 128,132 Clinical information to date is inconclusive. However, we experienced that 1) inspiratory pressures may need to be decreased to avoid overdistention as lung compliance improves; 2) expiratory pressures may need to be increased to facilitate distal migration of the liquid into the lung; and 3) inspired oxygen may need to be increased briefly to overcome initial diffusional limitations associated with a liquid respiratory medium.…”

“…However, recent preclinical studies indicate that higher levels of end-expiratory distending pressure, lower tidal volumes, and higher frequencies may protect the lung from air leak, particularly in the gas-filled nondependent regions. 128,132 Evaluation of extrapulmonary gas or PFC leak is similar to that during conventional gas ventilation (i.e., acute changes in vital signs, gas exchange, chest volume, positive transillumination). Assessment of interstitial gas or PFC by plain film radiography is complicated by the radiopacity of the PFC liquid and can be facilitated by CT. Auscultation can be utilized to assess symmetry of ventilation between lungs, and cardiac sounds can be appreciated.…”

Partial Liquid Ventilation with Low-Dose Perfluorochemical and High-Frequency Oscillation Improves Oxygenation and Lung Compliance in a Rabbit Model of Surfactant Depletion

“…Overdosing of PFC may increase the risk of pneumothorax because of the static pressure of PFC and high MAP [29] . Baden et al [30] reported that a larger volume of PFC (30 ml/kg) did not produce marked improvements in oxygenation in a piglet model of ARDS.…”

Partial Liquid Ventilation^TM with Low Dose of Perflubron and a Low Stretch Ventilation Strategy Improves Oxygenation in a Rabbit Model of Surfactant Depletion

“…Current ventilator strategies in PLV have tended to use larger tidal volumes and near FRC doses of PFB, with the recommendation of at least a low level of PEEP (5 cm H 2 O) to avoid the high airway pressures caused by slow moving liquid in central airways [8]. Recently, Cox et al [13] reported a significant risk of barotrauma in a surfactant-depleted rabbit model in which a large tidal volume (15 ml/kg) was used in association with a lung filled to FRC with PFB.…”