Liquid ventilation: Gas exchange, perfluorochemical uptake, and biodistribution in an acute lung injury

Administration of Drugs/Gene Products to the Respiratory System: A Historical Perspective of the Use of Inert Liquids

The present review is a historical perspective of methodology and applications using inert liquids for respiratory support and as a vehicle to deliver biological agents to the respiratory system. As such, the background of using oxygenated inert liquids (considered a drug when used in the lungs) opposed to an oxygen-nitrogen gas mixture for respiratory support is presented. The properties of these inert liquids and the mechanisms of gas exchange and lung function alterations using this technology are described. In addition, published preclinical and clinical trial results are discussed with respect to treatment modalities for respiratory diseases. Finally, this forward-looking review provides a comprehensive overview of potential methods for administration of drugs/gene products to the respiratory system and potential biomedical applications.

An Unsettled Promise: The Newborn Piglet Model of Neonatal Acute Respiratory Distress Syndrome (NARDS). Physiologic Data and Systematic Review

Despite great advances in mechanical ventilation and surfactant administration for the newborn infant with life-threatening respiratory failure no specific therapies are currently established to tackle major pro-inflammatory pathways. The susceptibility of the newborn infant with neonatal acute respiratory distress syndrome (NARDS) to exogenous surfactant is linked with a suppression of most of the immunologic responses by the innate immune system, however, additional corticosteroids applied in any severe pediatric lung disease with inflammatory background do not reduce morbidity or mortality and may even cause harm. Thus, the neonatal piglet model of acute lung injury serves as an excellent model to study respiratory failure and is the preferred animal model for reasons of availability, body size, similarities of porcine and human lung, robustness, and costs. In addition, similarities to the human toll-like receptor 4, the existence of intraalveolar macrophages, the sensitivity to lipopolysaccharide, and the production of nitric oxide make the piglet indispensable in anti-inflammatory research. Here we present the physiologic and immunologic data of newborn piglets from three trials involving acute lung injury secondary to repeated airway lavage (and others), mechanical ventilation, and a specific anti-inflammatory intervention via the intratracheal route using surfactant as a carrier substance. The physiologic data from many organ systems of the newborn piglet—but with preference on the lung—are presented here differentiating between baseline data from the uninjured piglet, the impact of acute lung injury on various parameters (24 h), and the follow up data after 72 h of mechanical ventilation. Data from the control group and the intervention groups are listed separately or combined. A systematic review of the newborn piglet meconium aspiration model and the repeated airway lavage model is finally presented. While many studies assessed lung injury scores, leukocyte infiltration, and protein/cytokine concentrations in bronchoalveolar fluid, a systematic approach to tackle major upstream pro-inflammatory pathways of the innate immune system is still in the fledgling stages. For the sake of newborn infants with life-threatening NARDS the newborn piglet model still is an unsettled promise offering many options to conquer neonatal physiology/immunology and to establish potent treatment modalities.

Establishment of a total liquid ventilation system using saline-based oxygen micro/nano-bubble dispersions in rats

Micro/nano-bubbles are practical nanomaterials designed to increase the gas content in liquids. We attempted to use oxygen micro/nano-bubble dispersions as an oxygen-rich liquid as a means for total liquid ventilation. To determine the oxygen content in the bubble dispersion, a new method based on a spectrophotometric change between oxy- and deoxy-hemoglobin was established. The oxygen micro/nano-bubble dispersion was supplied to an experimental total ventilation liquid in anesthetic rats. Though the amount of dissolving oxygen was as low as 6 mg/L in physiological saline, the oxygen content in the oxygen micro/nano-bubble dispersion was increased to 45 mg/L. The positive correlation between the oxygen content and the life-saving time under liquid ventilation clearly indicates that the life-saving time is prolonged by increasing the oxygen content in the oxygen micro/nano-bubble dispersion. This is the first report indicating that the oxygen micro/nano-bubbles containing a sufficient amount of oxygen are useful in producing oxygen-rich liquid for the process of liquid ventilation.

Perfluorodecalin lavage of a longstanding lung atelectasis in a child with spinal muscle atrophy

OBJECTIVE

Persistent lung atelectasis is difficult to treat and perfluorochemical (PFC) liquid may be an option for bronchioalveolar lavage (BAL).

CASE REPORT

A 4-year-old girl with spinal muscle atrophy was admitted in respiratory failure. On admission, the X-ray confirmed the persistence of total right-sided lung atelectasis, which had been present for 14 months. She was endotracheally intubated and ventilated from the day of admission. BAL with normal saline was performed twice without improvement. Following failed extubation and being dependent on continuous respiratory support, a trial of BAL using PFC liquid (Perfluorodecalin HP) was carried out. The PFC was delivered through the endotracheal tube on three consecutive days. A loading dose of 3 ml/kg was administered, followed by a varying dose in order to more effectively lavage the lungs. She tolerated the procedure well the first 2 days, although there were no clinical signs of improvement in the atelectasis. Intentionally, higher inflation pressures were applied after PFC instillation on day 3. Chest X-ray then showed hazy infiltrates on her left lung and she required more ventilatory support. However, lung infiltrates cleared over the next 3 days. A tracheotomy was done 6 days after the last PFC instillation. She had a slow recovery and was successfully decanulated. Clinical improvement of lung function was seen including less need of BiPAP and oxygen. A chest CT scan showed then functional lung tissue appearing in the previous total atelectatic right lung.

CONCLUSION

Lavage with PFC can safely be performed with a therapeutic effect in a child with unilateral total lung atelectasis.

Optimal expiratory volume profile in tidal liquid ventilation under steady state conditions, based on a symmetrical lung model

Liquid-assisted ventilation (LAV) using perfluorochemicals (PFC) offers clear theoretical advantages over gas ventilation. During tidal liquid ventilation (TLV) the residual capacity of the lungs is filled with PFC and a liquid ventilator is necessary to inhale and exhale the tidal volume of PFC. However, during the expiration phase, a flow limitation (choked flow) can be observed, which compromises minute ventilation and consequently the gas exchange. The hypothesis of the presented works is that the choked flow can be avoided by profiling the expiratory volume. To validate this concept, an elastic symmetrical lung numerical model, used to characterize forced expiration in gas ventilation, was transposed to TLV. The parameters of the developed numerical model were fitted from experimental data obtained on a newborn lamb. The results obtained demonstrate that general observations made with gas ventilation still hold, however, in TLV: flow limitation in the central airways is the result of a coupling between viscous pressure losses and airway compliance, and the flow limiting segment is located in the central airways. Using the model results, an optimal theoretical expiratory profile seems to be exponential as first approximation, and its time constant is dependent on the chocked flow mechanism and not on the product of resistance by compliance. This optimal profile is used to compute the maximal minute ventilation allowable with an acceptable risk of collapse. Also, the sensitivity of minute ventilation to different parameter variations were analyzed and practical recommendations are proposed.

Multicenter comparative study of conventional mechanical gas ventilation to tidal liquid ventilation in oleic acid injured sheep

We performed a multicenter study to test the hypothesis that tidal liquid ventilation (TLV) would improve cardiopulmonary, lung histomorphological, and inflammatory profiles compared with conventional mechanical gas ventilation (CMV). Sheep were studied using the same volume-controlled, pressure-limited ventilator systems, protocols, and treatment strategies in three independent laboratories. Following baseline measurements, oleic acid lung injury was induced and animals were randomized to 4 hours of CMV or TLV targeted to "best PaO2" and PaCO2 35 to 60 mm Hg. The following were significantly higher (p < 0.01) during TLV than CMV: PaO2, venous oxygen saturation, respiratory compliance, cardiac output, stroke volume, oxygen delivery, ventilatory efficiency index; alveolar area, lung % gas exchange space, and expansion index. The following were lower (p < 0.01) during TLV compared with CMV: inspiratory and expiratory pause pressures, mean airway pressure, minute ventilation, physiologic shunt, plasma lactate, lung interleukin-6, interleukin-8, myeloperoxidase, and composite total injury score. No significant laboratories by treatment group interactions were found. In summary, TLV resulted in improved cardiopulmonary physiology at lower ventilatory requirements with more favorable histological and inflammatory profiles than CMV. As such, TLV offers a feasible ventilatory alternative as a lung protective strategy in this model of acute lung injury.

A Prototype of Volume-Controlled Tidal Liquid Ventilator Using Independent Piston Pumps

Liquid ventilation using perfluorochemicals (PFC) offers clear theoretical advantages over gas ventilation, such as decreased lung damage, recruitment of collapsed lung regions, and lavage of inflammatory debris. We present a total liquid ventilator designed to ventilate patients with completely filled lungs with a tidal volume of PFC liquid. The two independent piston pumps are volume controlled and pressure limited. Measurable pumping errors are corrected by a programmed supervisor module, which modifies the inserted or withdrawn volume. Pump independence also allows easy functional residual capacity modifications during ventilation. The bubble gas exchanger is divided into two sections such that the PFC exiting the lungs is not in contact with the PFC entering the lungs. The heating system is incorporated into the metallic base of the gas exchanger, and a heat-sink-type condenser is placed on top of the exchanger to retrieve PFC vapors. The prototype was tested on 5 healthy term newborn lambs (<5 days old). The results demonstrate the efficiency and safety of the prototype in maintaining adequate gas exchange, normal acido-basis equilibrium, and cardiovascular stability during a short, 2-hour total liquid ventilator. Airway pressure, lung volume, and ventilation scheme were maintained in the targeted range.

Total Liquid Ventilation Reduces Lung Injury in Piglets After Cardiopulmonary Bypass

BACKGROUND

Cardiopulmonary bypass may cause lung injury that does not respond to traditional therapies. Total liquid ventilation has been developed as an alternative ventilatory strategy for severe lung injury. The aim of this study is to investigate the effect of total liquid ventilation on lung injury in piglets after cardiopulmonary bypass.

METHODS

After exposure to 60 minutes of cardiac arrest and weaning from cardiopulmonary bypass, 12 piglets (4.2 +/- 0.3 kg) were randomly treated with conventional gas ventilation (control group) or total liquid ventilation (study group) for 240 minutes. Samples for blood gas analysis were collected before, and at 30-minute intervals after, cardiopulmonary bypass. The degree of lung injury was quantified by histologic examination. The inflammatory cells and the levels of interleukin-6, interleukin-8, and myeloperoxidase in bronchoalveolar lavage were analyzed.

RESULTS

Neutrophil and macrophage count in bronchoalveolar lavage were significantly decreased in the study group (52.4 +/- 6.82 vs 0.46 +/- 0.11 10(4)/mL; 58.33 +/- 0.88 vs 4.37 +/- 0.90 10(5)/mL; p < 0.001, respectively). The inflammation score and the total lung injury score were also reduced in the study group (4.39 +/- 1.14 vs 2.61 +/- 1.09; 11.06 +/- 1.66 vs 6.94 +/- 1.43; p < 0.05, respectively). The concentrations of interleukin-6 and myeloperoxidase in bronchoalveolar lavage were significantly reduced in the study group (81.32 +/- 15.23 vs 53.55 +/- 15.48 pg/mL, 75.00 +/- 9.19 vs 50.00 +/- 7.37 u/mL; p < 0.05, respectively), whereas the interleukin-8 levels were similar between both groups (551.63 +/- 119.34 vs 563.68 +/- 137.14 pg/mL, p > 0.05).

CONCLUSIONS

Total liquid ventilation with FC-77 (3M, St. Paul, MN) reduces biochemical and histologic lung injury in piglets after cardiopulmonary bypass.

Intrapulmonary perfluorooctyl bromide instillation in fetal rabbits

BACKGROUND

Instilling perfluorooctyl bromide (PFOB) into the fetal lung may lead to alveolar distension.

OBJECTIVE

The aim of the study was to evaluate the safety of PFOB instillation into fetal lungs and to determine the radiographic distribution and tissue concentration of PFOB in New Zealand white rabbits.

METHODS

Sibling fetuses of pregnant (day 27) New Zealand white rabbits were randomized to intratracheal instillation of 1 mL PFOB with tracheal ligation, instillation without ligation, and unmanipulated controls. The maternal animals were killed directly after instillation, at 3 or 6 hours (n = 10 each). For each study cohort, we determined fetal lung/body weight (FLBW) ratios, the radiographic distribution of PFOB, as well as pulmonary PFOB and water content by tissue distillation. PFOB concentrations in maternal and fetal tissues were assessed by gas chromatography.

RESULTS

The relative amount of fetal lung PFOB recovered by fractional distillation was highest in ligated (25%) and lower in unligated lungs (9%). Extrapulmonary PFOB was found in the fetal brain (2.0 +/- 0.7 ppm), but not in any other fetal or maternal tissues. Mean FLBW ratios were highest in ligated fetuses, followed by unligated fetuses and controls. PFOB partially displaced fetal lung water. PFOB was visible in the lungs of all treated fetuses. Fetal survival between manipulated and unmanipulated fetuses did not differ.

CONCLUSIONS

After prenatal intrapulmonary instillation, some PFOB remains in the lung, even if the trachea is not ligated, and may exert distending pressure on the alveoli.

A prototype of a liquid ventilator using a novel hollow-fiber oxygenator in a rabbit model

OBJECTIVE

A functional total liquid ventilator should be simple in design to minimize operating errors and have a low priming volume to minimize the amount of perfluorocarbon needed. Closed system circuits using a membrane oxygenator have partially met these requirements but have high resistance to perfluorocarbon flow and high priming volume. To further this goal, a single piston prototype ventilator with a low priming volume and a new high-efficiency hollow-fiber oxygenator in a circuit with a check valve flow control system was developed.

DESIGN

Prospective, controlled animal laboratory study.

SETTING

Research facility at a university medical center.

SUBJECTS

Seven anesthetized, paralyzed, normal New Zealand rabbits

INTERVENTIONS

The prototype oxygenator, consisting of cross-wound silicone hollow fibers with a surface area of 1.5 m2 with a priming volume of 190 mL, was tested in a bench-top model followed by an in vivo rabbit model. Total liquid ventilation was performed for 3 hrs with 20 mL.kg(-1) initial fill volume, 17.5-20 mL.kg(-1) tidal volume, respiratory rate of 5 breaths/min, inspiratory/expiratory ratio 1:2, and countercurrent sweep gas of 100% oxygen.

MEASUREMENTS AND MAIN RESULTS

Bench top experiments demonstrated 66-81% elimination of CO2 and 0.64-0.76 mL.min(-1) loss of perfluorocarbon across the fibers. No significant changes in PaCO2 and PaO2 were observed. Dynamic airway pressures were in a safe range in which ventilator lung injury or airway closure was unlikely (3.6 +/- 0.5 and -7.8 +/- 0.3 cm H2O, respectively, for mean peak inspiratory pressure and mean end expiratory pressure). No leakage of perfluorocarbon was noted in the new silicone fiber gas exchange device. Estimated in vivo perfluorocarbon loss from the device was 1.2 mL.min(-1).

CONCLUSIONS

These data demonstrate the ability of this novel single-piston, nonporous hollow silicone fiber oxygenator to adequately support gas exchange, allowing successful performance of total liquid ventilation.

Continuous tracheal gas insufflation during partial liquid ventilation in juvenile rabbits with acute lung injury

To examine the hypothesis that combined treatment with tracheal gas insufflation (TGI) and partial liquid ventilation (PLV) may improve pulmonary outcome relative to either treatment alone in acute lung injury (ALI), saline lavage lung injury was induced in 24 anesthetized, ventilated juvenile rabbits that were then randomly assigned to receive ( n = 6/group) 1) conventional mechanical ventilation (CMV) alone, 2) continuous TGI at 0.5 l/min, 3) PLV with perfluorochemical liquid, and 4) combined TGI and PLV (TGI + PLV), and subsequently ventilated with minimized pressures and tidal volume (Vt) to keep arterial Po2 (PaO2) >100 Torr and arterial Pco2 (PaCO2) at 45-60 Torr for 4 h. Gas exchange, lung mechanics, myeloperoxidase, IL-8, and histomorphometry [including expansion index (EI)] were assessed. The CMV group showed no improvement in lung mechanics and gas exchange; all treated groups had significant increases in compliance, PaO2, ventilation efficacy index (VEI), and EI, and decreases in PaCO2, oxygenation index, physiological dead space-to-Vt ratio (Vd/Vt), myeloperoxidase, and IL-8, relative to the CMV group. TGI resulted in lower peak inspiratory pressure, Vt, Vd/Vt, and greater VEI vs. PLV group; PLV resulted in greater compliance, PaO2, and EI vs. TGI. TGI + PLV resulted in decreased peak inspiratory pressure, Vt, Vd/Vt, and increased VEI compared with TGI, improved compliance and EI compared with PLV, and a further increase in PaO2 and oxygenation index and a decrease in PaCO2 vs. either treatment alone. These results indicate that combined treatment of TGI and PLV results in improved pulmonary outcome than either treatment alone in this animal model of ALI.