Effect of artificial surfactant on pulmonary function in preterm and full-term 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.

Effects of perfluorocarbons on surfactant exocytosis and membrane properties in isolated alveolar type II cells

Background

Perfluorocarbons (PFC) are used to improve gas exchange in diseased lungs. PFC have been shown to affect various cell types. Thus, effects on alveolar type II (ATII) cells and surfactant metabolism can be expected, data, however, are controversial.

Objective

The study was performed to test two hypotheses: (I) the effects of PFC on surfactant exocytosis depend on their respective vapor pressures; (II) different pathways of surfactant exocytosis are affected differently by PFC.

Methods

Isolated ATII cells were exposed to two PFC with different vapor pressures and spontaneous surfactant exocytosis was measured. Furthermore, surfactant exocytosis was stimulated by either ATP, PMA or Ionomycin. The effects of PFC on cell morphology, cellular viability, endocytosis, membrane permeability and fluidity were determined.

Results

The spontaneous exocytosis was reduced by PFC, however, the ATP and PMA stimulated exocytosis was slightly increased by PFC with high vapor pressure. In contrast, Ionomycin-induced exocytosis was decreased by PFC with low vapor pressure. Cellular uptake of FM 1-43 - a marker of membrane integrity - was increased. However, membrane fluidity, endocytosis and viability were not affected by PFC incubation.

Conclusions

We conclude that PFC effects can be explained by modest, unspecific interactions with the plasma membrane rather than by specific interactions with intracellular targets.

Alterations of alveolar type II cells and intraalveolar surfactant after bronchoalveolar lavage and perfluorocarbon ventilation. An electron microscopical and stereological study in the rat lung

Background

Repeated bronchoalveolar lavage (BAL) has been used in animals to induce surfactant depletion and to study therapeutical interventions of subsequent respiratory insufficiency. Intratracheal administration of surface active agents such as perfluorocarbons (PFC) can prevent the alveolar collapse in surfactant depleted lungs. However, it is not known how BAL or subsequent PFC administration affect the intracellular and intraalveolar surfactant pool.

Methods

Male wistar rats were surfactant depleted by BAL and treated for 1 hour by conventional mechanical ventilation (Lavaged-Gas, n = 5) or partial liquid ventilation with PF 5080 (Lavaged-PF5080, n = 5). For control, 10 healthy animals with gas (Healthy-Gas, n = 5) or PF5080 filled lungs (Healthy-PF5080, n = 5) were studied. A design-based stereological approach was used for quantification of lung parenchyma and the intracellular and intraalveolar surfactant pool at the light and electron microscopic level.

Results

Compared to Healthy-lungs, Lavaged-animals had more type II cells with lamellar bodies in the process of secretion and freshly secreted lamellar body-like surfactant forms in the alveoli. The fraction of alveolar epithelial surface area covered with surfactant and total intraalveolar surfactant content were significantly smaller in Lavaged-animals. Compared with Gas-filled lungs, both PF5080-groups had a significantly higher total lung volume, but no other differences.

Conclusion

After BAL-induced alveolar surfactant depletion the amount of intracellularly stored surfactant is about half as high as in healthy animals. In lavaged animals short time liquid ventilation with PF5080 did not alter intra- or extracellular surfactant content or subtype composition.

Fluorocarbons facilitate lung recruitment

OBJECTIVE

"Open the lung and keep it open" is increasingly accepted as a fundamental principle for mechanical ventilation. However, it is sometimes very difficult, or impossible, to recruit the diseased lung. We questioned whether one could facilitate recruitment by using a low dose of fluorocarbon in a model previously shown to be non-recruitable by conventional sustained inflation maneuvers.

DESIGN AND SETTING

Experimental prospective study in a university laboratory.

ANIMALS AND INTERVENTIONS

Nine saline-lavaged rabbits subjected to prolonged large tidal volume mechanical ventilation to establish significant lung injury were randomly allocated to two groups: control [High Frequency Oscillation (HFO) alone: n=4] or 1 ml/kg fluorocarbon (FC) treated (HFO/FC: n=5) for 2+1 h (experiment 1). An additional four similarly prepared animals were treated by single-lung instillation of 0.5 ml/kg dose of fluorocarbon and underwent serial computerized tomography scans at a series of predetermined step-wise pressure increase in both lungs (experiment 2).

MEASUREMENTS AND RESULTS

In experiment 1 there was a very significant improvement in oxygenation in HFO/FC group (PaO(2) increased from 108 mmHg to 424+/-81 mmHg; P<0.05) while there was no significant change in the control group. In experiment 2 lung volumes were determined using three-dimensional reconstruction. The lung having fluorocarbon showed a 2.4-fold increase in lung volume at inflation pressure of 15 cmH(2)O compared to the lung without fluorocarbon.

CONCLUSIONS

We propose that the low equilibrium surface tension and positive spreading coefficient of fluorocarbon facilitates lung recruitment by ungluing adherent surfaces in this model of lung injury.

Comparative randomized study: administration of natural and synthetic surfactant to premature newborns with respiratory distress syndrome

BACKGROUND

The respiratory distress syndrome (RDS) in premature newborns has been etiologically correlated to immature lungs and specifically with surfactant deficiency. Exogenous administration of surfactant is nowadays considered to be the treatment of choice. In this paper we attempt a comparison of clinical results from the administration of natural Alveofact and synthetic Exosurf surfactants in premature newborns with respiratory distress syndrome.

METHODS

The study subjects were 92 premature newborns who had been hospitalized in the Department of Neonatology, of the University of Crete. A total of 42 subjects received synthetic surfactant and 50 subjects received natural surfactant. The surfactant was administered in one to three doses, depending on respiratory support requirements.

RESULTS

The time of administration was a little longer for the natural surfactant group. The duration of mechanical ventilatory support, requiring oxygen, the duration of hospitalization and the percentage of increase of arterial alveolar partial pressure oxygen ratio (a/APO2) were slightly higher for the synthetic surfactant group. The mortality rate during the neonatal period (28th day) was higher for the synthetic surfactant group than for the natural surfactant group (38.1 vs 24%). A similar tendency was noticed also as regards to complications, e.g. pneumothorax (11.2 vs 5.2%; relative risk (RR) 0.27) intraventricular hemorrhage (34.6 vs 21.1%; RR 0.61), septicemia (11.5 vs 5.2%; RR 0.46) and bronchopulmonary dysplasia (12.5 vs 2.8%; RR 0.22).

CONCLUSION

The use of natural surfactant seems to offer more advantages in comparison with its synthetic counterpart.

Small dose of exogenous surfactant combined with partial liquid ventilation in experimental acute lung injury: effects on gas exchange, haemodynamics, lung mechanics, and lung pathology

A combination of exogenous surfactant and partial liquid ventilation (PLV) with perfluorocarbons should enhance gas exchange, improve respiratory mechanics and reduce tissue damage of the lung in acute lung injury (ALI). We used a small dose of exogenous surfactant with and without PLV in an experimental model of ALI and studied the effects on gas exchange, haemodynamics, lung mechanics, and lung pathology. ALI was induced by repeated lavages (PaO2/FIO2 less than 13 kPa) in 24 anaesthesized, tracheotomized and mechanically ventilated (FIO2 1.0) juvenile pigs. They were treated randomly with either a single intratracheal dose of surfactant (50 mg kg(-1), Curosurf, Serono AG, München, Germany) (SURF-group, n=8), a single intratracheal dose of surfactant (50 mg kg(-1), Curosurf) followed by PLV with 30 ml kg(-1) of perfluorocarbon (PF 5080, 3M, Germany) (SURF-PLV-group, n=8) or no further intervention (controls, n=8). Pulmonary gas exchange, respiratory mechanics, and haemodynamics were measured hourly for a 6 h period. In the SURF-group, the intrapulmonary right-to-left shunt (QS/QT) decreased significantly from mean 51 (SEM 5)% after lavage to 12 (2)%, and PaO2 increased significantly from 8.1 (0.7) to 61.2 (4.7) kPa compared with controls and compared with the SURF-PLV-group (P<0.05). In the SURF-PLV-group, QS/QT decreased significantly from 54 (3)% after induction of ALI to 26 (3)% and PaO2 increased significantly from 7.2 (0.5) to 30.8 (5.0) kPa compared with controls (P<0.05). Static compliance of the respiratory system (C(RS)), significantly improved in the SURF-PLV-group compared with controls (P<0.05). Upon histological examination, the SURF-group revealed the lowest total injury score compared with controls and the SURF-PLV-group (P<0.05). We conclude that in this experimental model of ALI, treatment with a small dose of exogenous surfactant improves pulmonary gas exchange and reduces the lung injury more effectively than the combined treatment of a small dose of exogenous surfactant and PLV.

Delivery and retention of an insulin aerosol produced by a new jet nebulizer

This study describes the delivery and distribution of an aerosol generated by a jet nebulizer (MAXIN) in an experimental animal model. Anesthetised, intubated and ventilated piglets inhaled radiolabeled technetium diethylene-triamine-penta-acetic acid (99mTc-DTPA) through the endotracheal tube. The lungs were excised en bloc and scintigraphed, using a computerized gamma camera to evaluate the pattern of distribution. By nebulizing radiolabeled 125I-insulin and comparing the activity deposited on inspiratory and expiratory electrostatic filters, delivery and retention of nebulized insulin was assessed. The distribution of aerosol in the lungs was very even and reached the most peripheral parts. The delivery of nebulized insulin was calculated to be 88.9 +/- 5.3% and 36.1 +/- 8.8% of the insulin delivered to the respiratory tract was retained. The immediate local effects of insulin aerosol administration on the lungs were evaluated using light microscopy. No adverse effects were observed at histopathologic examination of the lung tissue.

CONCLUSION

This study shows a high penetration of aerosol to the peripheral parts of the lung and efficient delivery of nebulized insulin when using the MAXIN-nebulizer.

Effects of single and multiple doses of perfluorocarbon in comparison with continuous partial liquid ventilation on gas exchange and lung pathology in newborn surfactant-depleted pigs

OBJECTIVE

To compare the efficacy of single, multiple, and continuous application of perfluorocarbon (PFC) FC-77 on gas exchange and lung pathology in a prolonged 24-hr study.

DESIGN

Controlled animal trial.

SETTING

Research laboratory in a university setting.

SUBJECTS

Twenty-one newborn piglets (mean weight 1.94 kg).

INTERVENTIONS

After intubation and instrumentation, the anesthetized animals were randomized in three groups: a) animals receiving one 1-hr session of partial liquid ventilation (PLV) followed by 23 hrs of conventional ventilation (CV), designated as the single PLV (S-PLV) group; b) animals receiving multiple 1-hr sessions of PLV with intermittent CV, designated as the multiple PLV (M-PLV) group; and c) animals receiving continuous PLV over 24 hrs, designated as the continuous PLV (C-PLV) group. After lung injury was induced with repeated saline lavage, specific ventilatory treatment was initiated. The oxygenation index, Pao2/Fio2 ratio, and ventilatory efficacy index were determined before and after lung injury and during the 24-hr course. After 24 hrs, the lungs were removed for histopathologic examination.

MEASUREMENTS AND MAIN RESULTS

Gas exchange variables improved within 60 mins in all groups after the initiation of the specific ventilatory treatment (p < .01). The best outcome was observed in the C-PLV group, which provided a continuously stable gas exchange over the 24-hr period. S-PLV initially improved gas exchange, but after 6 hrs all variables were impaired when compared with C-PLV (p < .01). M-PLV transiently improved gas exchange variables after each PFC application; however, M-PLV was associated with a significant deterioration of all pulmonary variables during the 24-hr course. The lungs of the animals in the M-PLV group demonstrated an increased lung injury score (p < .01) and increased morphometric values (p < .05) when compared with C-PLV.

CONCLUSIONS

In surfactant deficient lungs, single and multiple applications of PFC only transiently improved oxygenation. Multiple PFC fillings with intermittent gas ventilation led to a deterioration of gas exchange during the 24-hr study and severe lung damage. Continuous PLV provides the best gas exchange and the most favorable histopathologic outcome.

Surfactant replacement increases compliance in premature lamb lungs during partial liquid ventilation in situ

Treatments available to improve compliance in surfactant-deficient states include exogenous surfactant (ES) and either partial (PLV) or total liquid ventilation (TLV) with perfluorochemical (PFC). Because of the additional air-lung and air-PFC interfaces introduced during PLV compared with TLV, we hypothesized that compliance would be worse during PLV than during TLV. Because surfactant is able to reduce interfacial tension between air and lung as well as between PFC and lung, we further hypothesized that compliance would improve with surfactant treatment before PLV. In excised preterm lamb lungs, we used Survanta for surfactant replacement and perflubron as the PFC. Compliance during PLV was intermediate between TLV and gas inflation, both with and without surfactant. Surfactant improved compliance during PLV, compared with PLV alone. Because of the force-balance equation governing the behavior of immiscible droplets on liquid surfaces, we predict that PFC droplets spread during PLV to cover the alveolar surface in surfactant-deficient lungs during most of lung inflation and deflation but that the PFC would retract into droplets in surfactant-sufficient lungs, except at end inspiration.

Perfluorochemical rescue after surfactant treatment: effect of perflubron dose and ventilatory frequency

To test the hypotheses that perfluorochemical (PFC) liquid rescue after natural surfactant (SF) treatment would improve pulmonary function and histology and that this profile would be influenced by PFC dose or ventilator strategy, anesthetized preterm lambs (n = 31) with respiratory distress were studied using nonpreoxygenated perflubron. All animals received SF at 1 h and were randomized at 2 h as follows and studied to 4 h postnatal age: 1) conventional mechanical gas ventilation (n = 8), 2) 30 ml/kg perflubron with gas ventilation [partial liquid ventilation (PLV)] at 60 breaths/min (n = 8), 3) 10 ml/kg perflubron with PLV at 60 breaths/min (n = 7), and 4) 10 ml/kg perflubron with PLV at 30 breaths/min (n = 8). All animals tolerated instillation without additional cardiopulmonary instability. All perflubron-rescued groups demonstrated sustained improvement in gas exchange, respiratory compliance, and reduction in pressure requirements relative to animals receiving SF alone. Improvement was directly related to perflubron dose and breathing frequency; peak inspiratory pressure required to achieve physiological gas exchange was lower in the higher-dose and -frequency groups, and mean airway pressure was lower in the lower-frequency group. Lung expansion was greater and evidence of barotrauma was less in the higher-dose and -frequency group; regional differences in expansion were not different as a function of dose but were greater in the lower-frequency group. Regional differences in lung perflubron content were reduced in the higher-dose and -frequency groups and greatest in the lower-dose and -frequency group. The results suggest that, whereas PLV of the SF-treated lung improves gas exchange and lung mechanics, the protective benefits of perflubron in the lung may depend on dose and ventilator strategy to optimize PFC distribution and minimize exposure of the alveolar-capillary membrane to a gas-liquid interface.

Repeated doses of the perfluorocarbon FC-100 improve lung function of preterm lambs

Intratracheal administration of a single dose of the perfluorocarbon FC-100 improves lung function in surfactant-deficient animals. In this study we compared the response to repeated doses of FC-100 (3 mL/kg 3% solution, n = 5) with that observed after administration of Exosurf (5 mL/kg, n = 5) to mechanically ventilated preterm lambs of 125 d of gestation. The initial dose of FC-100 rapidly increased arterial PO2, decreased arterial PCO2, and improved arterial pH. Also dynamic lung compliance markedly improved with this agent. Administration of an additional dose of FC-100 resulted in relatively similar changes, albeit of lesser magnitude than those observed with the initial dose. In contrast, Exosurf did not improve these variables even after three doses. All lambs treated with FC-100 survived the 6-h study period, whereas one of the five Exosurf-treated lambs survived (p < 0.05). Mean arterial blood pressure and heart rate decreased in those lambs that received FC-100, but not in surviving lambs that received Exosurf. Our data demonstrate that repeated intratracheal administration of the perfluorocarbon FC-100 improves lung function and survival of surfactant-deficient lambs better than the synthetic surfactant Exosurf. We speculate that tensio-active agents with properties different from surfactant, such as FC-100, might improve lung function in preterm neonates with diseases due to surfactant deficiency.

Pulmonary dysfunction in neonatal SP-B-deficient mice

Pulmonary function was assessed in newborn wild-type and homozygous and heterozygous surfactant protein B (SP-B)-deficient mice after birth. SP-B +/+ and SP-B+/- mice became well oxygenated and survived postnatally. Although lung compliance was decreased slightly in the SP-B+/- mice, lung volumes and compliances were decreased markedly in homozygous SP-B-/- mice. They died rapidly after birth, failing to inflate their lungs or oxygenate. SP-B proprotein was absent in the SP-B-/- mice and was reduced in the SP-B+/- mice, as assessed by Western analysis. Surfactant protein A, surfactant proprotein C, surfactant protein D, and surfactant phospholipid content in lungs from SP-B+/- and SP-B-/- mice were not altered. Lung saturated phosphatidylcholine and precursor incorporation into saturated phosphatidylcholine were not influenced by SP-B genotype. Intratracheal administration of perfluorocarbon resulted in lung expansion, oxygenation, and prolonged survival of SP-B-/- mice and in reduced lung compliance in SP-B+/+ and SP-B+/- mice. Lack of SP-B caused respiratory failure at birth, and decreased SP-B protein was associated with reduced lung compliance. These findings demonstrate the critical role of SP-B in perinatal adaptation to air breathing.

Synchronized changing of transinterface pressure, bubble radius and surface tension: a unique feature of lung surfactant

The pulsating bubble surfactometer has been commonly used to measure the minimum surface tension of lung surfactant. The complexity of the original transinterface pressure tracings and its possible physiological meanings remain undefined. In the present study, we compared surface properties between calf lung surfactant extract (CLSE) and Tween 20, a nonionic surfactant, with the pulsating bubble surfactometer. A synchronized change between transinterface pressure (P) and bubble radius (R) was observed when CLSE was tested. Mathematical analysis and computer simulation indicate that this is due to the extremely potent surface tension lowering and adjusting abilities, which allows the surface tension to decrease towards zero at the end of compression and increase towards a high surface tension during re-expansion. In contrast, a time delay between P and R was observed when Tween 20 was assessed. Surface tension adjusting ability was shown only at concentrations below or around the critical micelle concentration (cmc) of Tween 20. Surface tension became unchangeable when concentrations were further increased, suggesting amphipathic molecules were saturated on the interface. The synchronization of transinterface pressure, alveolar radius and surface tension may play an important role in maintaining the pulmonary compliance in vivo. This unique feature, observed at concentrations several orders above the cmc of phospholipids, suggests that the structure of lung surfactant at the air-liquid interface differs from that of Tween 20, a monolayer of free amphipathic molecules.

Liquid ventilation: an alternative ventilation strategy for management of neonatal respiratory distress

Perfluorochemical (PFC) liquids have great potential for biomedical use and the support of respiration. Currently, there are several commercially available PFC fluids which meet the physiochemical property requirements as well as purity specifications necessary to perform many of the discussed biomedical applications. Moreover, state-of-the-art fluorine chemistry should enable production of new PFC liquids uniquely sculptured relative to the proposed specific application (ie. vehicle for pulmonary delivery of drugs, a diluent for pulmonary lavage, a medium for respiratory gas exchange). In addition to PFC fluid requirements, there have been several techniques reported for liquid assisted ventilation. These methods include total liquid ventilation, liquid lavage, and partial liquid ventilation. The efficacy of these various techniques is under extensive investigation with respect to specific types of lung dysfunction. Liquid ventilation (LV) techniques have the potential to treat lung disease with less risk of barotrauma and provide the means for direct and uniform delivery of pulmonary agents to injured or dysfunctional sites in the lung. For LV to assume a role in clinical medicine it must be shown to be safe and effective with respect to other therapies or in combination with current therapies. Although the use of LV in animal and initial clinical studies has been impressive to date, better documentation of efficacy in human disease will be required. Further controlled multi-center clinical trials are warranted and are currently in progress.

Partial liquid ventilation in premature lambs with respiratory distress syndrome: efficacy and compatibility with exogenous surfactant

OBJECTIVE

To determine the efficacy of partial liquid ventilation (PLV) by means of a medical-grade perfluorochemical liquid, perflubron (LiquiVent), in premature lambs with respiratory distress syndrome (RDS). Further, to determine the compatibility of perflubron with exogenous surfactant both in vitro and in vivo during PLV.

DESIGN

Prospective, randomized, controlled study, with in vitro open comparison.

SUBJECTS

Twenty-two premature lambs with RDS.

INTERVENTIONS

In vitro assays were conducted on three exogenous surfactants before and after combination with perflubron. We studied four groups of lambs, which received one of the following treatment strategies: conventional mechanical ventilation (CMV); surfactant (Exosurf) plus CMV; PLV; or surfactant plus PLV.

MEASUREMENTS AND MAIN RESULTS

In vitro surface tension, measured for three exogenous surfactants, was unchanged in each animal after exposure to perflubron. Lung mechanics and arterial blood gases were serially measured. All animals treated with PLV survived the 5 hours of experiment without complication; several animals treated with CMV died. During CMV, all animals had marked hypoxemia and hypercapnia. During PLV, arterial oxygen tension increased sixfold to sevenfold within minutes of initiation, and this increase was sustained; arterial carbon dioxide tension decreased to within the normal range. Compliance increased fourfold to fivefold during PLV compared with CMV. Tidal volumes were increased during PLV, with lower mean airway pressure. Resistance was similar for both CMV and PLV; there was no difference with surfactant treatment.

CONCLUSIONS

We conclude that PLV with perflubron improves lung mechanics and gas exchange in premature lambs with RDS, that PLV is compatible with exogenous surfactant therapy, and that, as a treatment for RDS in this model, PLV is superior to the surfactant studied.

Perfluorochemical liquid as a respiratory medium

The use of perfluorochemical (PFC) liquids to facilitate or support respiration has been under study for several decades. The low surface tension and high respiratory gas solubility of liquid PFC enable adequate oxygenation and carbon dioxide removal at low insufflation pressures relative to gas ventilation in the immature or injured lung. Because liquid ventilation homogeneously inflates the lung and improves V/Q matching it has been studied as a vehicle for delivering biologically active agents to the lung tissues and systemic circulation. More recently, we have shown the utility of highly opaque PFC liquids as a high resolution computed tomographic (HRCT) bronchographic contrast agent either during LV or gas breathing after tracheal instillation of small quantities of PFC. As a result of extensive experimental work in premature animals as well as lung injury models, liquid PFC ventilation has been recently implemented as an investigational therapy for severe respiratory distress in human infants. This manuscript summarizes the physiological principles and applications of LV as well as the results of initial investigational clinical studies in human neonates with severe respiratory distress.