Development and application of a simplified liquid ventilator

A new paradigm for lung-conservative total liquid ventilation

Background

Total liquid ventilation (TLV) of the lungs could provide radically new benefits in critically ill patients requiring lung lavage or ultra-fast cooling after cardiac arrest. It consists in an initial filling of the lungs with perfluorocarbons and subsequent tidal ventilation using a dedicated liquid ventilator. Here, we propose a new paradigm for a lung-conservative TLV using pulmonary volumes of perfluorocarbons below functional residual capacity (FRC).

Methods and findings

Using a dedicated technology, we showed that perfluorocarbon end-expiratory volumes could be maintained below expected FRC and lead to better respiratory recovery, preserved lung structure and accelerated evaporation of liquid residues as compared to complete lung filling in piglets. Such TLV below FRC prevented volutrauma through preservation of alveolar recruitment reserve. When used with temperature-controlled perfluorocarbons, this lung-conservative approach provided neuroprotective ultra-fast cooling in a model of hypoxic-ischemic encephalopathy. The scale-up and automating of the technology confirmed that incomplete initial lung filling during TLV was beneficial in human adult-sized pigs, despite larger size and maturity of the lungs. Our results were confirmed in aged non-human primates, confirming the safety of this lung-conservative approach.

Interpretation

This study demonstrated that TLV with an accurate control of perfluorocarbon volume below FRC could provide the full potential of TLV in an innovative and safe manner. This constitutes a new paradigm through the tidal liquid ventilation of incompletely filled lungs, which strongly differs from the previously known TLV approach, opening promising perspectives for a safer clinical translation.

Fund

ANR (COOLIVENT), FRM (DBS20140930781), SATT IdfInnov (project 273).

A Feedback Controller for the Maintenance of FRC during Tidal Liquid Ventilation: Theory, Implementation, and Testing

The necessity of controlling functional residual capacity (FRC) during tidal liquid ventilation has been recognized since the first description of this respiratory support technique by Kylstra et al in 1962. We developed a microcomputer feedback system that adjusts the inspired tidal volume (Vt,i) of a liquid ventilator based on the end-expiratory quasi-static alveolar pressure (Pa,ee), in order to maintain a stable FRC. The system consists of three subunits: (1) a tracheal pressure catheter to estimate breath by breath FRC changes, derived from Pa,ee changes, and (2) a roller pump interfaced with (3) a personal computer in which a closed-loop control is implemented. The regulator sets the actual Pa,ee against the corresponding desired value. Any discrepancy is offset by changes in Vt,i and the required change in pump velocity is communicated to the roller pump. The size of any change in pump velocity is determined to both the observed and target or desired Pa,ee (i.e., the error) and the (calibration) pressure-volume curve.

To evaluate the efficacy of the controller, a set of laboratory bench tests were conducted under steady state and transient conditions. Closed-loop control was effective in keeping FRC and Pa,ee near the desired level, with an acceptable oscillatory behaviour. The feedback controller successfully compensated for transient disturbances of PFC liquid balance. The steady state stability was confirmed during a five hour period of liquid ventilation in five preterm lambs.

Perfluorochemical Liquid Ventilation: From the Animal Laboratory to the Intensive Care Unit

Perfluorochemical or perfluorocarbon liquids have an enormous gas-carrying capacity. During tidal liquid ventilation the respiratory medium of both functional residual capacity and tidal volume is replaced by neat perfluorocarbon liquid. Tidal liquid ventilation is characterized by convective and diffusive limitations, but offers the advantage of preserved functional residual capacity, high compliance and improved ventilation-perfusion matching. During partial liquid ventilation only the functional residual capacity is replaced by perfluorocarbon liquid. Both tidal and partial liquid ventilation improve gas exchange and lung mechanics in hyaline membrane disease, adult respiratory distress models and meconium aspiration. Compared to gas ventilation, there is less histologic evidence of barotrauma after liquid ventilation. Cardio-pulmonary interaction, inherent to the high density of liquid, and long term safety need further study. However, extrapolating from animal data, and taking into account promising human pilot studies, liquid ventilation has the desired properties to occupy an important place in the therapy of restrictive lung disease in man.

Safety and efficacy of perflubron-induced lung growth in neonates with congenital diaphragmatic hernia: Results of a prospective randomized trial

BACKGROUND

Mechanical transduction has been shown to promote fetal lung growth. We examined the safety and efficacy of perflubron-induced lung growth (PILG) in neonates with congenital diaphragmatic hernia (CDH) requiring extracorporeal membrane oxygenation (ECMO).

METHODS

Infants with left-sided CDH requiring ECMO were eligible. Exclusion criteria included active air leak, intracranial hemorrhage, major congenital anomalies, and oxygenation index >25 for 24hours. Perflubron was instilled endotracheally and continuous positive airway pressure was applied without ventilation. Survival to discharge was the primary outcome. Daily chest radiographs were used to quantify lung size (the secondary outcome). Midway through the study our institutional practice shifted toward earlier repair of CDH.

RESULTS

Eight infants were randomized to each arm. In the conventional-ventilation arm, six survived to discharge (75%). In the perflubron arm, four survived (50%); the others succumbed to suprasystemic pulmonary hypertension. No adverse events related to perflubron occurred. Within the perflubron group, 4/8 patients had "late repair" (15-19days of life [DOL]) and 4 had "early repair" (2-3 DOL). "Early repair" patients had similar total lung growth, but accelerated growth and shorter ECMO runs.

CONCLUSION

PILG is safe in CDH and doubles the total lung size on average (accelerated with early repair). Despite amelioration of pulmonary hypoplasia with PILG, pulmonary hypertension persists.

Liquid ventilation

Mammals have lungs to breathe air and they have no gills to breath liquids. When the surface tension at the air-liquid interface of the lung increases, as in acute lung injury, scientists started to think about filling the lung with fluid instead of air to reduce the surface tension and facilitate ventilation. Liquid ventilation (LV) is a technique of mechanical ventilation in which the lungs are insufflated with an oxygenated perfluorochemical liquid rather than an oxygen-containing gas mixture. The use of perfluorochemicals, rather than nitrogen, as the inert carrier of oxygen and carbon dioxide offers a number of theoretical advantages for the treatment of acute lung injury. In addition, there are non-respiratory applications with expanding potential including pulmonary drug delivery and radiographic imaging. The potential for multiple clinical applications for liquid-assisted ventilation will be clarified and optimized in future.

Measurements of Evaporated Perfluorocarbon during Partial Liquid Ventilation by a Zeolite Absorber

During partial liquid ventilation (PLV) the knowledge of the quantity of exhaled perfluorocarbon (PFC) allows a continuous substitution of the PFC loss to achieve a constant PFC level in the lungs. The aim of our in vitro study was to determine the PFC loss in the mixed expired gas by an absorber and to investigate the effect of the evaporated PFC on ventilatory measurements.

METHOD

To simulate the PFC loss during PLV, a heated flask was rinsed with a constant airflow of 4 L min(-1) and PFC was infused by different speeds (5, 10, 20 mL h(-1)). An absorber filled with PFC selective zeolites was connected with the flask to measure the PFC in the gas. The evaporated PFC volume and the PFC concentration were determined from the weight gain of the absorber measured by an electronic scale. The PFC-dependent volume error of the CO2SMO plus neonatal pneumotachograph was measured by manual movements of a syringe with volumes of 10 and 28 mL with a rate of 30 min(-1).

RESULTS

Under steady state conditions there was a strong correlation (r2 = 0.999) between the infusion speed of PFC and the calculated PFC flow rate. The PFC flow rate was slightly underestimated by 4.3% (p < 0.01). However, this bias was independent from PFC infusion rate. The evaporated PFC volume was precisely measured with errors < 1%. The volume error of the CO2SMO-Plus pneumotachograph increased with increasing PFC content for both tidal volumes (p < 0.01). However for PFC flow rates up to 20 mL/h the error of the measured tidal volumes was < 5%.

CONCLUSIONS

PFC selective zeolites can be used to quantify accurately the evaporated PFC volume during PLV. With increasing PFC concentrations in the exhaled air the measurement errors of ventilatory parameters have to be taken into account.

Effects of respiratory rate and tidal volume on gas exchange in total liquid ventilation

Using a rabbit model of total liquid ventilation (TLV), and in a corresponding theoretical model, we compared nine tidal volume-respiratory rate combinations to identify a ventilator strategy to maximize gas exchange, while avoiding choked flow, during TLV. Nine different ventilation strategies were tested in each animal (n = 12): low [LR = 2.5 breath/min (bpm)], medium (MR = 5 bpm), or high (HR = 7.5 bpm) respiratory rates were combined with a low (LV = 10 ml/kg), medium (MV = 15 ml/kg), or high (HV = 20 ml/kg) tidal volumes. Blood gases and partial pressures, perfluorocarbon gas content, and airway pressures were measured for each combination. Choked flow occurred in all high respiratory rate-high volume animals, 71% of high respiratory rate-medium volume (HRMV) animals, and 50% of medium respiratory rate-high volume (MRHV) animals but in no other combinations. Medium respiratory rate-medium volume (MRMV) resulted in the highest gas exchange of the combinations that did not induce choke. The HRMV and MRHV animals that did not choke had similar or higher gas exchange than MRMV. The theory predicted this behavior, along with spatial and temporal variations in alveolar gas partial pressures. Of the combinations that did not induce choked flow, MRMV provided the highest gas exchange. Alveolar gas transport is diffusion dominated and rapid during gas ventilation but is convection dominated and slow during TLV. Consequently, the usual alveolar gas equation is not applicable for TLV.

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.

Pulmonary applications of perfluorochemical liquids: ventilation and beyond

In this review of liquid ventilation, concepts and applications are presented that summarise the pulmonary applications of perfluorochemical liquids. Beginning with the question of whether this alternative form of respiratory support is needed and ending with lessons learned from clinical trials, the various methods of liquid assisted ventilation are compared and contrasted, evidence for mechanoprotective and cytoprotective attributes of intrapulmonary perfluorochemical liquid are presented and alternative intrapulmonary applications, including their use as vehicles for drugs, for thermal control and as imaging agents are presented.

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.

New approaches to managing congenital diaphragmatic hernia

A number of new techniques have been studied for managing newborns with congenital diaphragmatic hernia and respiratory insufficiency. Among these have been the techniques of delayed approach to the repair of the diaphragmatic hernia; permissive hypercapnia; nitric oxide and surfactant administration; intratracheal pulmonary ventilation; liquid ventilation; perfluorocarbon-induced lung growth; and lung transplantation. These interventions are at various stages of development and evaluation of effectiveness. All, however, are being explored in the hopes of improving outcome in patients with congenital diaphragmatic hernia who continue to have significant morbidity and mortality in the newborn period.

Liquid ventilation: an adjunct for respiratory management

Although significant advances in respiratory care have reduced mortality of patients with respiratory failure, morbidity persists, often resulting from iatrogenic mechanisms. Mechanical ventilation with gas has been shown to initiate as well as exacerbate underlying lung injury, resulting in progressive structural damage and release of inflammatory mediators within the lung. Alternative means to support pulmonary gas exchange while preserving lung structure and function are therefore required. Perfluorochemical (PFC) liquids are currently used clinically in a number of ways, such as intravascular PFC emulsions for volume expansion/oxygen carrying/angiography and intracavitary neat PFC liquid for image contrast enhancement or vitreous fluid replacement. As a novel approach to replace gas as the respiratory medium, liquid assisted ventilation (LAV) with PFC liquids has been investigated as an alternative respiratory modality for over 30 years. Currently, there are several theoretical and practical applications of LAV in the immature or mature lung at risk for acute respiratory distress and injury associated with mechanical ventilation.

Comparison of Static Airway Pressures During Total Liquid Ventilation While Applying Different Expiratory Modes and Time Patterns

To compare pump driven (active) and gravity-siphon (passive) expiration modes during perfluorocarbon total liquid ventilation (TLV), a liquid ventilator was developed capable of providing either expiration mode. In a prospective, controlled laboratory study, 90 rabbits (3.2 +/- 0.1 kg) were anesthetized, tracheotomized, killed. After prefill with 12 ml/kg perflubron and TLV for 90 minutes (tidal volume 12 ml/kg, I:E ratio 1:2), randomly using passive (height 40 or 80 cm) or active expiration, respiratory rates were 4, 8, or 12/min. Static peak inspiratory and end-expiratory intratracheal pressures were measured at 5 minute intervals. Peak inspiratory and end-expiratory were constant in active groups, and increases in all 40 cm and 80 cm passive groups were significant. Differences between groups were significant for expiratory mode but not for respiratory rates. Only passive groups showed significant increases in body weight after TLV. Percentage of fluorothoraces was 10% using active and 85% using passive expiration. Based upon the stability of intrapulmonary pressures and volumes and a reduced rate of fluorothoraces, active expiration is more efficient than passive drainage during TLV.

Long-Term Tidal Liquid Ventilation in Premature Lambs: Physiologic, Biochemical and Histological Correlates

Chronic lung disease in infants continues to be problematic. Tidal liquid ventilation (TLV) improves lung mechanics and provides effective gas exchange. We hypothesized that premature lambs could be supported safely with TLV and evaluated 9 preterm lambs (132 days gestation) on TLV up to 72 h. Results (mean +/- SEM): pH 7.36 +/- 0.003, PaCO2 44 +/- 0.34 mm Hg, PaO2 170 +/- 4.8 mm Hg, compliance=1.65 +/- 0.24 ml/cm H2O/kg, mean arterial blood pressure=53 +/- 0.08 mm Hg, heart rate=189 +/- 1.5 bpm. Blood perflubron levels were 6.0 +/- 0.24 microg/ml over 24 h. Tissue perflubron levels increased from 81 +/- 7.0 microg/g at 24 h to 108 +/- 15 microg/g at 72 h (p<0.05). There was a difference in perflubron concentrations as a function of tissue (p<0.001) that correlated to lipid levels (r2=0.93, p<0.01). These data demonstrate that TLV is both safe and effective up to 72 h in premature lambs.

Effect of ventilatory variables on gas exchange and hemodynamics during total liquid ventilation in a rat model

OBJECTIVES

To investigate the settings necessary to achieve maximum gas exchange and pulmonary function while minimizing effects on cardiovascular hemodynamics during total liquid ventilation with a pressure-limited, time-cycled ventilator in a rat model.

DESIGN

Prospective, randomized controlled animal study.

SETTING

A university research laboratory.

SUBJECTS

Male Sprague-Dawley rats (n = 48).

INTERVENTIONS

All animals had a tracheostomy tube designed for total liquid ventilation placed under anesthesia. The carotid artery was cannulated for blood pressure monitoring and for assessing blood gas data.

MEASUREMENTS AND MAIN RESULTS

Forty 492 +/- 33 g rats were assigned to one of four inspiratory/expiratory ratio groups (inspiratory/expiratory ratio of 1:2, 1:2.5, 1:3, and 1:4). Total liquid ventilation was performed with a pressure-limited, time-cycled total liquid ventilator. Outcome measures were evaluated as a function of respiratory rate and included tidal volume, maximal alveolar ventilation, inspiratory and expiratory mean arterial pressures, the difference of mean arterial pressure between the inspiratory and expiratory phase, static end-inspiratory/expiratory pressures, Paco(2), Pao(2), tidal volume + approximate expiratory reserve volume, and lung volume-induced suppression of mean arterial pressure. Maximal alveolar ventilation increased and decreased in parabolic fashion as a function of respiratory rate and was maximal at rates of 4.3-6.8 breaths/min and high inspiratory/expiratory ratios that corroborated with optimal levels of Pao(2) and Paco(2). Lung overdistention occurred at high respiratory rates and high inspiratory/expiratory ratios. Deleterious effects were observed on the difference of mean arterial pressure between the inspiratory and expiratory phase during total liquid ventilation at low respiratory rates, apparently due to increased tidal volume, and on suppression of mean arterial pressure at high inspiratory/expiratory ratios and high respiratory rate apparently due to "auto-positive end-expiratory pressure." These effects were minimized in this model at respiratory rates >/=5.7 and </=6.8 breaths/min and inspiratory/expiratory ratios </=1:2.5. These settings were successfully tested in eight additional animals.

CONCLUSION

These data demonstrate the feasibility of performing total liquid ventilation in rodents. A balance must be identified where gas exchange is optimal yet hemodynamics are least affected. In the specific system studied, an inspiratory/expiratory ratio of 1:2.5 and respiratory rate of 6.8 breaths/min appeared to provide optimal gas exchange while minimizing the effects on hemodynamics.

A prospective, randomized pilot trial of perfluorocarbon-induced lung growth in newborns with congenital diaphragmatic hernia

BACKGROUND/PURPOSE

Initial laboratory and clinical data suggest that partial liquid ventilation (PLV) can enhance pulmonary function and that lung growth can be induced via distension of the newborn lung using perfluorocarbon in patients with congenital diaphragmatic hernia (CDH). The authors, therefore, performed a prospective, randomized pilot study evaluating PLV and perfluorocarbon-induced lung growth (PILG) in newborns with CDH on extracorporeal life support (ECLS) at 6 medical centers.

METHODS

Patients were selected randomly using a permuted block design to PLV/PILG (n = 8) or conventional mechanical ventilation (CMV/control, n = 5). Patients in the PILG group received daily doses which filled the lungs with perflubron for up to 7 days and were placed on continuous positive airway pressure of 5 to 8 cm H2O. CMV patients were treated with standard mechanical ventilation while on extracorporeal membrane oxygenation (ECMO).

RESULTS

A total of 13 patients were evaluated in this study. All 3 patients enrolled without being on ECLS rapidly transitioned to ECLS. The study, therefore, effectively evaluated PILG (n = 8) versus standard ventilation (control, n = 5) on ECLS. Mean (+/- SE) gestational age was 37 +/- 1 weeks and weight was 3.1 +/- 0.1 kg. Time on ECMO was 9.8 +/- 2.3 days in the PILG and 14.5 +/- 3.5 days (P =.58) in the control group. Survival rate in the PILG group was 6 of 8 (75%), whereas survival rate was 2 of 5 (40%) in the control group (P =.50). The number of days free from the ventilator in the first 28 days (VFD) was 6.3 +/- 3.3 days with PILG and 4.6 +/- 4.6 days with control (P =.9). Causes of death in the PILG group included sepsis and renal failure in one patient and pulmonary hypertension in the other. There were no safety issues, and the deaths in the PILG group did not appear to be related to the administration of perflubron.

CONCLUSIONS

These data show that PILG can be performed safely. The survival rate, VFD, and time on ECMO data, although not conclusive, are encouraging and indicate the need for a definitive trial of this novel intervention in these neonates with high mortality.

Development of a time-cycled volume-controlled pressure-limited respirator and lung mechanics system for total liquid ventilation

Total liquid ventilation can support gas exchange in animal models of lung injury. Clinical application awaits further technical improvements and performance verification. Our aim was to develop a liquid ventilator, able to deliver accurate tidal volumes, and a computerized system for measuring lung mechanics. The computer-assisted, piston-driven respirator controlled ventilatory parameters that were displayed and modified on a real-time basis. Pressure and temperature transducers along with a lineal displacement controller provided the necessary signals to calculate lung mechanics. Ten newborn lambs (<6 days old) with respiratory failure induced by lung lavage, were monitored using the system. Electromechanical, hydraulic, and data acquisition/analysis components of the ventilator were developed and tested in animals with respiratory failure. All pulmonary signals were collected synchronized in time, displayed in real-time, and archived on digital media. The total mean error (due to transducers, analog-to-digital conversion, amplifiers, etc.) was less than 5% compared with calibrated signals. Components (tubing, pistons, etc.) in contact with exchange fluids were developed so that they could be readily switched, a feature that will be important in clinical settings. Improvements in gas exchange and lung mechanics were observed during liquid ventilation, without impairment of cardiovascular profiles. The total liquid ventilator maintained accurate control of tidal volumes and the sequencing of inspiration/expiration. The computerized system demonstrated its ability to monitor in vivo lung mechanics, providing valuable data for early decision making.

A model of neonatal tidal liquid ventilation mechanics

Tidal liquid ventilation (TLV) with perfluorocarbons (PFC) has been proposed to treat surfactant-deficient lungs of preterm neonates, since it may prevent pulmonary instability by abating saccular surface tension. With a previous model describing gas exchange, we showed that ventilator settings are crucial for CO(2) scavenging during neonatal TLV. The present work is focused on some mechanical aspects of neonatal TLV that were hardly studied, i.e. the distribution of mechanical loads in the lungs, which is expected to differ substantially from gas ventilation. A new computational model is presented, describing pulmonary PFC hydrodynamics, where viscous losses, kinetic energy changes and lung compliance are accounted for. The model was implemented in a software package (LVMech) aimed at calculating pressures (and approximately estimate shear stresses) within the bronchial tree at different ventilator regimes. Simulations were run taking the previous model's outcomes into account. Results show that the pressure decrease due to high saccular compliance may compensate for the increased pressure drops due to PFC viscosity, and keep airway pressure low. Saccules are exposed to pressures remarkably different from those at the airway opening; during expiration negative pressures, which may cause airway collapse, are moderate and appear in the upper airways only. Delivering the fluid with a slightly smoothed square flow wave is convenient with respect to a sine wave. The use of LVMech allows to familiarize with LV treatment management taking the lungs' mechanical load into account, consistently with a proper respiratory support.

The pulmonary and systemic distribution and elimination of perflubron from adult patients treated with partial liquid ventilation

OBJECTIVE

To assess the pulmonary and systemic distribution and elimination of perflubron (C(8)F(17)Br(1); LiquiVent; Alliance Pharmaceutical; San Diego, CA) during and following the period of partial liquid ventilation.

DESIGN

Prospective phase I and II clinical trial.

SETTING

Adult surgical ICU.

PATIENTS

Eighteen adult patients (mean +/- SEM age, 37.9 +/- 3.4 years) with severe respiratory failure, some of whom required extracorporeal life support (72%), and who were managed with partial liquid ventilation with perflubron.

INTERVENTIONS

Perflubron was administered into the trachea, and gas ventilation of the perfluorocarbon-filled lung (partial liquid ventilation) was then performed. Additional doses were administered daily for from 1 to 7 days, with a median cumulative dose of 31 mL/kg (range, 3 to 60 mL/kg).

MEASUREMENTS AND MAIN RESULTS

Patient blood samples were evaluated by gas chromatography for serum perflubron levels. Sequential lateral and anteroposterior radiographs were assessed, using a 5-point rating scale, for the degree of perflubron fill following the final dose. Samples of expired gas were collected, and the rate of loss of perflubron in the expired gas was measured by gas chromatography. Mean serum perflubron levels increased to 0.16 +/- 0.05 mg/dL at 24 h following administration of the initial dose. A mean maximum level of 0.26 +/- 0.05 mg/dL of perflubron was present in the serum 24 h following the administration of the last dose. This level slowly trended downward to 0.18 +/- 0.06 mg/dL over the ensuing 7 days (p = 0.281). Perflubron elimination via expired gas occurred at a mean rate of 9.4 +/- 3.0 mL/h at 1 h, and 1.0 +/- 0.4 mL/h at 48 h after the last dose (p = 0.012). By radiologic evaluation, perflubron was eliminated from the lungs progressively from 4.2 +/- 0.2 at the time of administration of the last dose, to 2.8 +/- 0.3 at 4 days later (p < 0.001). Perflubron tended to distribute and remain for longer periods in the dependent regions of the lung when compared to the nondependent regions (96-h perflubron fill score: posterior, 3.8 +/- 0.5; anterior, 1.9 +/- 0.4; p = 0.004).

CONCLUSIONS

Perflubron is eliminated at a maximum rate of 9.4 +/- 3.0 mL/h by evaporative loss from the airways and is retained in greater amounts in the dependent lung regions when compared to the nondependent lung regions. There is a low but measurable maximum blood concentration of 0.26 +/- 0.05 mg/dL in patients after perflubron administration, which did not decrease significantly after cessation of partial liquid ventilation.

Development and application of a double-piston configured, total-liquid ventilatory support device

OBJECTIVE

Perfluorocarbon liquid ventilation has been shown to enhance pulmonary mechanics and gas exchange in the setting of respiratory failure. To optimize the total liquid ventilation process, we developed a volume-limited, time-cycled liquid ventilatory support, consisting of an electrically actuated, microprocessor-controlled, double-cylinder, piston pump with two separate limbs for active inspiration and expiration.

DESIGN

Prospective, controlled, animal laboratory study, involving sequential application of conventional gas ventilation, partial ventilation (PLV), and total liquid ventilation (TLV).

SETTING

Research facility at a university medical center.

SUBJECTS

A total of 12 normal adult New Zealand rabbits weighing 3.25+/-0.1 kg.

INTERVENTIONS

Anesthestized rabbits were supported with gas ventilation for 30 mins (respiratory rate, 20 cycles/min; peak inspiratory pressure, 15 cm H2O; end-expiratory pressure, 5 cm H2O), then PLV was established with perflubron (12 mL/kg). After 15 mins, TLV was instituted (tidal volume, 18 mL/kg; respiratory rate, 7 cycles/min; inspiratory/expiratory ratio, 1:2 cycles/min). After 4 hrs of TLV, PLV was re-established.

MEASUREMENTS AND MAIN RESULTS

Of 12 animals, nine survived the 4-hr TLV period. During TLV, mean values +/- SEM were as follows: PaO2, 363+/-30 torr; PaCO2, 39+/-1.5 torr; pH, 7.39+/-0.01; static peak inspiratory pressure, 13.2+/-0.2 cm H2O; static endexpiratory pressure, 5.5+/-0.1 cm H2O. No significant changes were observed. When compared with gas ventilation and PLV, significant increases occurred in mean arterial pressure (62.4+/-3.5 torr vs. 74.0+/-1.2 torr) and central venous pressure (5.6+/-0.7 cm H2O vs. 7.8+/-0.2 cm H2O) (p < .05).

CONCLUSIONS

Total liquid ventilation can be performed successfully utilizing piston pumps with active expiration. Considering the enhanced flow profiles, this device configuration provides advantages over others.

Neutrophil accumulation is reduced during partial liquid ventilation

OBJECTIVE

This study evaluates the ability of perflubron to inhibit pulmonary neutrophil accumulation during partial liquid ventilation (PLV) in the setting of acute lung injury.

DESIGN

Randomized, controlled, nonblinded study.

SETTING

Research laboratory at a university.

SUBJECTS

Male, Sprague-Dawley rats (n = 120, 506 +/- 42 g).

INTERVENTIONS

Animals were divided into eight groups (n = 15 in each group, of which n = 12 for myeloperoxidase content and n = 3 for histologic neutrophil counting): a) GV-CVF group, animals received gas ventilation (GV) with the induction of lung injury using cobra venom factor (CVF); b) PLV-CVF group, animals received partial liquid ventilation before the induction of lung injury; c) PEEP-CVF group, animals received positive end-expiratory pressure (PEEP) before the administration of cobra venom factor; d) CVF-PLV group, animals received partial liquid ventilation after cobra venom factor; e) CVF-PEEP group, animals received PEEP after cobra venom factor; f) PLV only group, animals received partial liquid ventilation only; g) GV only group, animals received gas ventilation only; and h) NVSBA group, nonventilated spontaneous breathing animals.

MEASUREMENTS AND MAIN RESULTS

After the experimental period, total lung myeloperoxidase content was significantly decreased in the PLV-CVF (0.29 +/- 0.08, p = .02) and PEEP-CVF (0.34 +/- 0.04, p = .01) groups when compared with the GV-CVF group (0.62 +/- 0.07). When compared with the GV-CVF group, a trend toward a reduction in myeloperoxidase was observed in the CVF-PLV (0.42 +/- 0.05, p = .07) and the CVF-PEEP (0.39 +/- 0.06, p = .07) groups. When compared with the cobra venom factor only group (GV-CVF 47 +/- 2 neutrophils/high-power field), reductions in neutrophil count were observed in all groups (neutrophils/high-power field): PLV-CVF (20 +/- 2, p = .009); PEEP-CVF (24 +/- 1, p = .01); CVF-PLV (30 +/- 2, p = .03); and CVF-PEEP (37 +/- 1, p = .04).

CONCLUSION

These data suggest that both partial liquid ventilation and PEEP result in a reduction in neutrophil accumulation in the setting of acute lung injury.

Non-conventional respiratory support modalities applicable in the older child. High frequency ventilation and liquid ventilation

HFV, LV, and several other novel therapies offer promise to adults and children that the mortality associated with respiratory failure may be affected. Although there are several forms of HFV, HFOV is presently gaining favor in the treatment of severe respiratory failure and has generally supplanted HFJV in pediatric critical care. HFOV has the advantage of having an active expiratory phase, which helps to minimize air trapping and better modulate mean lung volume. Ventilators with sufficient power to perform HFOV in adults are currently under investigation, although there is a growing experience in using current ventilators in larger patients. To date, however, demonstration of lowered mortality with HFOV is lacking although intermediate outcome indicators are improved. PLV also offers promise in the treatment of ARF through its drastic ability to improve oxygenation, ventilation, and compliance in many lung injury models. Human trials are presently underway, but the optimal delivery of this novel therapy still necessitates extensive investigation. TLV is likely even more removed from general clinical application given the necessity of developing a new generation of ventilators for the delivery of liquid tidal volumes. How these and other modalities may piece together to improve the condition of our patients who have respiratory failure remains to be seen, but certainly, present and future investigation will be intriguing for years to come.

Partial liquid ventilation decreases albumin leak in the setting of acute lung injury

PURPOSE

This study evaluated the ability of partial liquid ventilation (PLV, gas ventilation of the perfluorocarbon-filled lungs) to reduce the amount of lung albumin leak present in the setting of acute lung injury.

MATERIALS AND METHODS

An experimental controlled, randomized design was used. All studies were performed in the liquid ventilation laboratories at the University of Michigan Medical Center. Twenty-five Sprague-Dawley male rats 500+/-50 g were divided into five experimental groups: (1) CVF only (n=5), animals were cobra venom factor (CVF) lung injured; (2) PLV-CVF (n=5) animals received perflubron and PLV before CVF lung injury; (3) CVF-PLV (n=5) animals received PLV after CVF lung injury; (4) PLV only (n=5) animals underwent partial liquid ventilation without lung injury; and (5) Gas only (n=5) animals underwent gas ventilation without lung injury. In all groups iodinated bovine serum albumin (125I-BSA) was delivered by intravenous injection along with CVF or a saline placebo.

RESULTS

When the CVF animals were compared with all other groups, a decrease in albumin leak was observed for all groups when compared with the CVF only controls (P < .001 by ANOVA; CVF only=1.22+/-0.12 versus PLV-CVF=0.46+/-0.08, P < .001; CVF-PLV=0.70+/-0.25, P < .001; PLV only=0.22+/-0.01, P < .001; Gas only=0.17+/-0.02, P < .001).

CONCLUSIONS

These data suggest that intratracheal instillation of perfluorocarbon before or after induction of lung injury results in a reduction in pulmonary albumin leak.

Computer tomographic assessment of perfluorocarbon and gas distribution during partial liquid ventilation for acute respiratory failure

The average in vivo chest computed tomographic (CT) attenuation number (air = -1,000, soft tissue = 0, perflubron = +2,300 Hounsfield units [HU]) of 10 ventrodorsal-oriented lung segments was calculated to assess the distribution of gas and perflubron in 14 oleic acid lung-injured adult sheep during partial liquid ventilation (PLV, n = 7) or gas ventilation (GV, n = 7). Partial liquid ventilation was associated with a significant decrease in shunt fraction (PLV = 40 +/- 12%, GV = 76 +/- 12%, p = 0.004). Computed tomographic attenuation data during expiration (HUexp) demonstrated minimal gas aeration in GV animals in the dependent (segments 6-10) lung zones (HUexp = -562 +/- 108 for segments 1-5, HUexp = -165 +/- 104 for segments 6-10, p = 0.015). During PLV, perflubron was predominantly distributed to the dependent lung regions (HUexp = 579 +/- 338 for segments 1-5, HUexp = 790 +/- 149 for segments 6-10, p = 0.04). The ratio of the inspiratory to expiratory HU (HUinsp/exp) was greater in dependent than nondependent regions (mean HUinsp/exp segments 1-5 = 0.56, segments 6-10 = 0.81, p = 0.01), indicating that during inspiration relatively more gas than perflubron was distributed to the nondependent lung regions. We conclude that during PLV in this lung injury model, (1) gas exchange is improved when compared with gas ventilation, (2) perflubron is distributed predominantly to the dependent regions of the lung, and (3) although gas is distributed throughout the lung with each inspiration, more gas than perflubron goes to the nondependent lung regions.

Effects of partial liquid ventilation on lung injury in a model of acute respiratory failure: a histologic and morphometric analysis

OBJECTIVE

To compare the histopathologic changes observed in a sheep model of oleic acid-induced acute respiratory failure during partial liquid ventilation with perflubron with gas ventilation.

DESIGN

Randomized, controlled study.

SETTING

Animal laboratory and pathology laboratories of a university hospital.

SUBJECTS

Fourteen healthy adult sheep, weighing 64.9 +/- 6.4 kg.

INTERVENTIONS

Lung injury was induced with oleic acid (0.15 mL/kg). A tracheostomy tube was inserted, along with systemic and pulmonary artery monitoring catheters. Animals were randomized to undergo either partial liquid ventilation (n = 7) or gas ventilation (n = 7). Animals underwent euthanasia at the end of the 90-min study period, after which the endotracheal tube was clamped with the lungs in expiratory hold at a positive end-expiratory pressure of 5 cm H2O. En bloc excision of the heart and lungs was performed by thoracotomy. Perfusion of the isolated lung vasculature with 2.5% paraformaldehyde and 0.25% glutaraldehyde in a 0.1-M phosphate buffer was performed. Histologic analysis followed.

MEASUREMENTS AND MAIN RESULTS

Gas exchange increased markedly in the animals that underwent partial liquid ventilation compared with the gas-ventilated animals (PaO2 at 90 mins: gas ventilation-treatment group, 40 +/- 8 torr [5.3 +/- 1.1 kPa]; partial liquid ventilation-treatment group, 108 +/- 60 torr [14.4 +/- 8.0 kPa]; p = .004). Lung histologic analysis demonstrated a better overall diffuse alveolar damage score (partial liquid ventilation-treatment group, 12.4 +/- 1.4; gas ventilation-treatment group, 15.0 +/- 1.7; p = .01). In the partial liquid ventilation-treatment group, we observed an increase in mean alveolar diameter (partial liquid ventilation-treatment group, 82.4 +/- 2.9 microm; gas ventilation-treatment group, 67.7 x 3.9 microm; p = .0022) and a decrease in the number of alveoli per high-power field (partial liquid ventilation-treatment group, 25.7 +/- 0.9, gas ventilation-treatment group, 31.4 +/- 2.5; p = .0022), in septal wall thickness (partial liquid ventilation-treatment group, 6.0 +/- 0.6 microm; gas ventilation-treatment group, 8.3 +/- 1.0 microm; p = .0033), and in mean capillary diameter (partial liquid ventilation-treatment group, 13.0 +/- 0.8 microm; gas ventilation-treatment group, 19.9 +/- 1.4 microm; p = .0022).

CONCLUSIONS

Partial liquid ventilation is associated with notable improvement in gas exchange and with a reduction in the histologic and morphologic changes observed in an oleic acid model of acute lung injury.

Demonstration of a method to characterize and develop airway access devices for total liquid ventilation

Devices are being developed to carry out perfluorocarbon total liquid ventilation (TLV) in adult-sized animals or patients. A limiting factor in the clinical application of TLV lies in the ability to administer adequate tidal volumes of oxygenated perfluorocarbon through airway access devices. A single number, the M-number, is demonstrated in this paper as a systematic method for ranking the flow characteristics of currently available airway access devices, such as endotracheal or tracheostomy tubes, and for designing new airway access devices exclusively for TLV. The M-number of several commonly used endotracheal and tracheostomy tubes is determined as a demonstration of the use of the M-number. Two nomograms are presented based on the M-number, and a description for their use in the clinical and laboratory settings is given.

Physiologic, biochemical, and histologic correlates associated with tidal liquid ventilation

Tidal liquid ventilation (TLV) with perfluorochemical fluid (PFC) has been successfully used experimentally for up to 4 h. However, no studies of prolonged TLV have been reported. We hypothesized that full-term newborn lambs can safely and effectively be liquid-ventilated for up to 24 h. To test this hypothesis, 17 lambs were liquid-ventilated; 7 for 4 h, 5 for 12 h, and 5 for 24 h. Arterial blood samples were obtained for PFC uptake, lipid analysis, and blood gas measurements. Tissues were obtained for histologic and biochemical analysis. Arterial blood gas and mean arterial blood pressure were as follows (mean +/- SEM): pH 7.48 +/- 0.04; PaCO2 30.6 +/- 2.8; PaO2 424 +/- 17; mean arterial pressure 76 +/- 16 mm Hg. PFC blood levels increased rapidly to a mean of 5.2 +/- 3.9 microg/mL. PFC tissue levels increased significantly (p < 0.01) from 260 +/- 45 microg/g at 4 h to 400 +/- 140 microg/g at 12 h. There was no further increase in PFC tissue levels by 24 h (456 +/- 181 microg/g). There was a significant difference in PFC concentration as a function of tissue (p < 0.01). Furthermore, there was a significant correlation (r = 0.88; p < 0.01) between the amount of PFC and lipid in blood and tissue. Microscopic examination of the lungs demonstrated no evidence of barotrauma. These data demonstrate that prolonged TLV can be safe and efficacious for up to 24 h in full-term newborn lambs.

Gas Exchange during Gas and Liquid Ventilation

Liquid Ventilation with perfluorochemicals (PFC) violates many of our long-held assumptions about how the lung functions. However, the technique has been so successful in animal models of lung disease that it is currently being tested in clinical trials for the treatment of infant and acute (“adult”) respiratory distress syndrome in newborns, children, and adults. A common feature of both infant and acute respiratory distress syndromes is an inability of the lung's surfactant system to adequately lower surface tension, leading to regions of atelectasis. Liquid ventilation with PFC appears to ameliorate the disease process by lowering interfacial tension in the lung, opening regions of atelectasis, and improving gas exchange. To understand how gas exchange is successful during liquid ventilation requires careful re-evaluation of the assumptions underlying our current models of gas exchange physiology during normal gas ventilation. These assumptions must then be examined in light of the alterations in pulmonary physiology during liquid ventilation.

Evaluation of gas exchange, pulmonary compliance, and lung injury during total and partial liquid ventilation in the acute respiratory distress syndrome

OBJECTIVE

To investigate whether pulmonary compliance and gas exchange will be sustained during "total" perfluorocarbon liquid ventilation followed by "partial" perfluorocarbon liquid ventilation when compared with gas ventilation in the setting of the acute respiratory distress syndrome (ARDS).

STUDY DESIGN

A prospective, controlled, laboratory study.

SETTING

A university research laboratory.

SUBJECTS

Ten sheep, weighing 12.7 to 25.0 kg.

INTERVENTIONS

Lung injury was induced in ten young sheep, utilizing a right atrial injection of 0.07 mL/kg of oleic acid followed by saline pulmonary lavage. Bijugular venovenous extracorporeal life support access, a pulmonary artery catheter, and a carotid artery catheter were placed. When the alveolar-arterial O2 gradient was >/= 600 torr and PaO2 </= 50 torr (</= 6.7 kPa) with an FIO2 of 1.0, extracorporeal life support was instituted. For the first 30 mins on extracorporeal life support, all animals were ventilated with gas. Animals were then ventilated with equal tidal volumes of 15 mL/kg during gas ventilation (n=5) over the ensuing 2.5 hrs, or with total liquid ventilation for 1 hr, followed by partial liquid ventilation for 1.5 hrs (total/partial liquid ventilation, n=5).

MEASUREMENTS AND MAIN RESULTS

An increase in physiologic shunt (gas ventilation = 69 +/- 11%, total/partial liquid ventilation = 71 +/- 3%) and a decrease in static total pulmonary compliance measured at 20 mL/kg inflation volume (gas ventilation = O.48 +/- 0.03 mL/cm H2O/kg, total/partial liquid ventilation = 0.50 +/- 0.17 mL/cm H2O/kg) were observed in both groups with induction of lung injury. Physiologic shunt was significantly reduced during total and partial liquid ventilation when compared with physiologic shunt observed in the gas ventilation animals (gas ventilation = 93 +/- 8%, total liquid ventilation = 45 +/- 11%, p<.001; gas ventilation = 95 +/- 3%, partial liquid ventilation = 61 +/- 12%, p<.001), while static compliance was significantly increased in the total, but not the partial liquid ventilated animals when compared with the gas ventilated group (gas ventilation = 0.43 +/- 0.03 mL/cm H2O/kg, total liquid ventilation = 1.13 +/- 18 mL/cm H2O/kg, p <.001; gas ventilation = 0.41 +/- 0.02 mL/cm H2O/kg, partial liquid ventilation = 0.47 +/- 0.08, p = .151). In addition, the extracorporeal life support flow rate required to maintain adequate oxygenation was significantly lower in the total/partial liquid ventilation group when compared with that of the gas ventilation group (gas ventilation = 89 +/- 7 mL/kg/min, total liquid ventilation = 22 +/- 10 mL/kg/min, p <.001; gas ventilation = 91 +/- 12 mL/kg/min, partial liquid ventilation = 41 +/- 11 mL/kg/min, p < .001). Lung biopsy light microscopy demonstrated a marked reduction in alveolar hemorrhage, lung fluid accumulation, and inflammatory infiltration in the total/partial liquid ventilation animals when compared with the gas ventilation animals.

CONCLUSIONS

In a model of severe ARDS, pulmonary gas exchange is improved during total followed by partial liquid ventilation. Pulmonary compliance is improved during total, but not during partial liquid ventilation. Total followed by partial liquid ventilation was associated with a reduction in alveolar hemorrhage, pulmonary edema, and lung inflammatory infiltration.

Partial liquid ventilation in newborn patients with congenital diaphragmatic hernia

The authors evaluated the safety and efficacy of liquid ventilation with perfluorocarbon in four newborns with congenital diaphragmatic hernia and severe respiratory failure, who were on extracorporeal life support (ECLS). After 2 to 5 days on the ECLS, perflubron was administered into the trachea until the dependent zone of the lung was filled. The first dose was 6 +/- 1 mL/kg (range, 5 to 8 mL/kg). Gas ventilation of the perflubron-filled lung was performed (partial liquid ventilation). The administration of perflubron was repeated daily for 5 to 6 days, with total cumulative doses of 36 +/- 8 mL/kg (range, 26 to 44 mL/kg). A significant increase in PaO(2) (P = .027 by repeated-measures analysis of variance [ANOVA]), a trend toward an increase in arterial oxygen content (P = .052 by repeated-measures ANOVA), and a significant increase in specific static total pulmonary compliance (P = .007 by repeated-measures ANOVA) were observed after administration of the daily dose of perflubron. PaCO(2) data showed a decreasing trend (P = .08 by repeated measures ANOVA). The authors conclude that perflubron can be safely administered into the lungs of newborn patients with congenital diaphragmatic hernia and severe respiratory failure, and it may be associated with improvement in gas exchange and pulmonary compliance.

Initial experience with partial liquid ventilation in pediatric patients with the acute respiratory distress syndrome

OBJECTIVE

Liquid ventilation with perfluorocarbon previously has not been reported in pediatric patients with respiratory failure beyond the neonatal period. We evaluated the technique of partial liquid ventilation in six pediatric patients with the acute respiratory distress syndrome of sufficient severity to require extracorporeal life support (ECLS).

DESIGN

This study was a noncontrolled, phase I/II experimental study with a single group pretest/posttest design.

SETTING

All studies were performed at a tertiary, pediatric referral hospital at the University of Michigan Medical School.

PATIENTS

Six pediatric patients, from 8 wks to 5 1/2 yrs of age, with severe respiratory failure requiring ECLS to support gas exchange.

INTERVENTIONS

After 2 to 9 days on ECLS, perfluorocarbon was administered into the trachea until the dependent zone of each lung was filled. The initial administered was 12.9 +/- 2.3 mL/kg (range 5 to 20). Gas ventilation of the perfluorocarbon-filled lungs (partial liquid ventilation) was then performed. The perfluorocarbon dose was repeated daily for a total of 3 to 7 days, with a cumulative dose of 45.2 +/- 6.1 mL/kg (range 30 to 72.5).

MEASUREMENTS AND MAIN RESULTS

All measurements of native gas exchange were made during brief periods of discontinuation of ECLS and include PaO2 and the alveolar-arterial oxygen gradient, P(A-a)O2. Static pulmonary compliance, corrected for weight, was also measured directly. The mean PaO2 increased from 39 +/- 6 to 92 +/- 29 torr (5.2 +/- 0.8 to 12.2 +/- 3.9 kPa) over the 96 hrs after the initial dose (p = .021 by repeated-measures analysis of variance). The average P(A-a)O2 decreased from 635 +/- 10 to 499 +/- 77 torr (84.7 +/- 1.3 to 66.5 +/- 10.3 kPa) over the same time period (p = .059), while the mean static pulmonary compliance (normalized for patient weight) increased from 0.12 +/- 0.02 to 0.28 +/- 0.08 mL/cm H2O/kg (p = .01). All six patients survived. Complications potentially associated with partial liquid ventilation were limited to pneumothoraces in two of six patients.

CONCLUSIONS

Perfluorocarbon may be safely administered into the lungs of pediatric patients with severe respiratory failure on ECLS and may be associated with improvement in gas exchange and pulmonary compliance.