Morphometrics of normal and hypoplastic lungs in preterm lambs with gas and partial liquid ventilation

To test the hypothesis that perfluorochemical (PFC) instillation may reduce the pulmonary trauma commonly associated with conventional gas ventilation, we studied 12 lambs with normal lungs and 10 with pulmonary hypoplasia secondary to congenital diaphragmatic hernia (CDH). We used mechanical ventilation for up to 3.5 h, with and without tracheal instillation of LiquiVent PFC liquid. At the end of experimentation lungs were fixed for morphometrical analysis of their components and pulmonary trauma was evaluated by measurement of the perivascular compression index (PCI = % perivascular emphysema/% vessels). In normal lungs good gas exchange and respiratory mechanics were obtained with all modes of ventilation, with no statistical difference in the index of pulmonary trauma with or without instillation of LiquiVent (P >0.05). In the hypoplastic lungs, tracheal instillation of PFC liquid after 30 min of conventional gas ventilation significantly improved PaCO2 (from 107+/-8 to 55+/-6 mmHg, P <0.05), pH (from 7.00+/-0.03 to 7.29+/-0. 04, P <0.05), compliance (from 0.08+/-0.01 to 0.25+/-0.03 ml/cmH2O . kg, P <0.05), and ventilatory index (from 1,445+/-148 to 794+/-139, P <0.05). Survival was 6/6 animals with PFC ventilation compared to 1/4 with conventional gas ventilation with no more pulmonary trauma (mean PCI 12.6+/-1.8 vs. 11.4+/-4.0%, P >0.05) for a longer mean ventilatory period in the PFC group. We conclude that the PFC liquid technique of ventilation can improve respiratory physiology when conventional gas ventilation alone is proving inefficient. There was no significant difference in pulmonary trauma at morphometrics between gas and partial liquid ventilation.

Partial liquid ventilation in critically ill infants receiving extracorporeal life support. Philadelphia Liquid Ventilation Consortium

OBJECTIVES

To demonstrate that a period of partial liquid ventilation (PLV) with perflubron improves pulmonary function, without adverse events, in a select group of critically ill infants receiving extracorporeal life support (ECLS) with a high likelihood of mortality.

METHODS

This was an open-label, noncontrolled, phase I and II trial of PLV in two infants with congenital diaphragmatic hernia and four infants with acute respiratory distress syndrome (ARDS) who were failing to improve while receiving ECLS. PLV was performed by instilling and maintaining a functional residual capacity of sterile perflubron for 4 to 96 hours.

RESULTS

Four infants were successfully weaned off ECLS for at least 3 days, and two infants (both with ARDS) are long-term survivors after PLV. All infants demonstrated lung recruitment and improved lung compliance, and there were no adverse events related to PLV.

CONCLUSIONS

The study suggests that perflubron PLV is safe, improves lung function, and recruits lung volume in critically ill infants receiving ECLS. PLV therapy for infants with ARDS seems to have a great deal of promise. Based on this and other phase I and II trials, studies of PLV on selected full-term infants before ECLS have been initiated.

Quantitative structure-activity relationships of perfluorinated hetero-hydrocarbons as potential respiratory media. Application to oxygen solubility, partition coefficient, viscosity, vapor pressure, and density

It has been extensively reported that liquid-assisted ventilation, using inert perfluorocarbon liquids (PFCs), can reduce interfacial surface tension and allow for improved ventilation at decreased alveolar pressures. PFCs are bioinert, minimally absorbed, and have no deleterious histologic, cellular, or biochemical effects when used as respiratory media. Although several types of PFCs have been characterized, a select few are considered to be compatible with life. Compatibility is often related to the physicochemical profile inherent to the PFC liquids. It is essential that certain physical properties such as respiratory gas solubility, vapor pressure, density, viscosity, and tissue permeability be within a narrow, acceptable range for a PFC to be considered as a possible candidate for respiratory media. The current study sought to characterize the physicochemical profile of commercially available PFCs. This was accomplished by creating a method for accurate, rapid prediction of a host of unknown physical characteristics of PFCs. The physicochemical properties of 16 perfluorinated hetero-hydrocarbons were catalogued from the literature. The input data were categorized into three major groups: empiric properties, geometric indices, and quantum mechanical descriptors, to generate a database. Algorithms were then developed, one for each dependent variable (FUNCTION), including oxygen solubility, partition coefficient (logP), vapor pressure, viscosity, and density, that related the values of these physical properties of potential breathable PFC liquids to the parameters listed in the database. The general form of the algorithm can be written as follows: FUNCTION = sigma (CiPi/magnitude of Pi) + constant; where the FUNCTIONS are oxygen solubility, logP, vapor pressure, viscosity, and density. Ci is a coefficient that weights the relative contribution of each parameter. Each independent parameter, Pi, was normalized by the average value of the parameter used in the analysis, magnitude of Pi. Residual analysis demonstrated validity with all five equations. This method is expected to assist in the prediction of physical properties of PFC liquids with acceptable accuracy, such that PFC production and selection from currently available liquids can be optimized for each liquid ventilation application.

Partial liquid ventilation with perflubron in premature infants with severe respiratory distress syndrome. The LiquiVent Study Group

BACKGROUND

The intratracheal administration of a perfluorocarbon liquid during continuous positive-pressure ventilation (partial liquid ventilation) improves lung function in animals with surfactant deficiency. Whether partial liquid ventilation is effective in the treatment of infants with severe respiratory distress syndrome is not known.

METHODS

We studied the efficacy of partial liquid ventilation with perflubron in 13 premature infants with severe respiratory distress syndrome in whom conventional treatment, including surfactant therapy, had failed. Partial liquid ventilation was initiated by instilling perflubron during conventional mechanical ventilation to a volume approximating the functional residual capacity. Infants were considered to have completed the study if they received partial liquid ventilation for at least 24 hours.

RESULTS

Ten infants received partial liquid ventilation for 24 to 76 hours. In the other three infants, partial liquid ventilation was discontinued within four hours in favor of high-frequency ventilation, which was not permitted by the protocol, and the data from these infants were excluded from the analysis. Within one hour after the instillation of perflubron, the arterial oxygen tension increased by 138 percent and the dynamic compliance increased by 61 percent; the mean (+/- SD) oxygenation index was reduced from 49 +/- 60 to 17 +/- 16. Chest radiographs showed symmetric filling, with patchy clearing during the return from partial liquid to gas ventilation. There were no adverse events clearly attributable to partial liquid ventilation. Infants were weaned from partial liquid to gas ventilation without complications. Eight infants survived to 36 weeks' corrected gestational age.

CONCLUSIONS

Partial liquid ventilation leads to clinical improvement and survival in some infants with severe respiratory distress syndrome who are not predicted to survive.

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.

Liquid assisted ventilation: an alternative ventilatory strategy for acute meconium aspiration injury

Evidence of surfactant inactivation by meconium has led to the use of exogenous surfactant therapy in the management of meconium aspiration syndrome (MAS). Liquid assisted ventilation has been shown to improve the cardiopulmonary function in lungs with high surface tension. We compared exogenous surfactant therapy with liquid assisted ventilation in the management of experimental acute meconium aspiration injury. Thirty-two newborn lambs were ventilated at peak inspiratory pressures of 13-16 cm H2O, positive end expiratory pressure of 3-4 cm H2O, fractional inspired oxygen concentration (FiO2) of 1.0, and a respiratory frequency range between 30 and 35 breaths/min. Baseline arterial blood gases, pulmonary function, and arterial blood pressure measurements were taken. All lambs were given 2-3 ml/kg of an unfiltered 25% meconium solution. Lambs were then randomized into either gas-ventilated meconium control, or one of three treatment groups: 1) surfactant; 2) partial liquid ventilation (PLV); or 3) total liquid ventilation (TLV) for 4 hours after meconium injury. All treated groups demonstrated a significant increase in arterial oxygenation (P < 0.05); surfactant and PLV-treated lambs demonstrated significantly decreased arterial PCO2 (P < 0.05). Compliance in all groups increased compared with injury values; compliance of the TLV group increased more than in all other treatment groups (P < 0.05). In addition, lung histology of the TLV group demonstrated clear, intact alveolar epithelium and homogeneously expanded alveoli, while no such improvement was evident in the other groups. These data suggest roles for both exogenous surfactant therapy and liquid assisted ventilation techniques in the management of MAS.

Pulmonary administration of vasoactive substances by perfluorochemical ventilation

OBJECTIVES

Therapeutic management of respiratory distress syndrome, pneumonia, and pulmonary hypertension includes delivery of biologically active agents to the neonatal lung. However, mechanical abnormalities of the lung, intrapulmonary shunting, ventilation-perfusion mismatching, and elevated surface tension impede effective systemic or intratracheal delivery of agents to the lung during conventional gas ventilation. The objective of this study was to test the hypothesis that perfluorochemical (PFC) liquid ventilation can be used for pulmonary administration of vasoactive drugs (PAD) and to compare these responses to those elicited with intravascular (IV) administration during tidal liquid ventilation.

METHODS

Cardiovascular responses of 16 preterm and neonatal lambs to randomized doses of acetylcholine, epinephrine, and priscoline were studied. Physiologic gas exchanged and acid-base balance were maintained using previously described tidal liquid ventilation techniques. In subgroups of animals, the distribution pattern of carbon 1- and choline 14-labeled dipalmitoylphosphatidylcholine (14C-DPPC) in saline and the responses to priscoline after hypoxia-induced pulmonary hypertension and hypoxemia administered during liquid ventilation were studied.

RESULTS

Dose-response curves for PAD and IV administration demonstrated progressive, dose-dependent, cholinergic responses to acetylcholine (decreased mean systemic arterial pressure [MAP] and heart rate), sympathomimetic responses to epinephrine (increased MAP and heart rate), and alpha-adrenergic blockade responses to priscoline (decreased MAP and mean pulmonary arterial pressure). Compared with IV administration, PAD of priscoline resulted in a significantly greater decrease in pulmonary relative to systemic arterial pressure; this response was potentiated by hypoxia, reduced pulmonary pressures to near normal values, and improved oxygenation. The 14C-DPPC in saline was distributed relatively homogeneously throughout the lung by PAD, with 80% of the lung pieces receiving amounts of 14C-DPPC with +/-20% of the mean value.

CONCLUSIONS

This study demonstrates that vasoactive agents can be delivered to the lung directly by PAD during PFC liquid ventilation. The inherent advantages of this method relate to the physical properties of PFC liquid ventilation as a vehicle (respiratory gas solubility, low surface tension-enhancing distribution, and inertness precluding interaction) and physiological properties of the lung as an exchanger.

Liquid ventilation: a comprehensive overview

Despite advances in neonatology, some infants do not respond to current pharmacologic and ventilatory techniques. Others suffer chronic lung disease, require prolonged ventilatory support, and experience significant morbidity during infancy due to the elevated inflation pressures used to treat their respiratory problems. Over the past 30 years, results of studies in premature animals as well as clinical trials have demonstrated that ventilation with oxygenated perfluorochemical (PFC) fluids provides effective gas exchange and improved lung mechanics. PFC fluids are biologically inert, have a high gas solubility and a low surface tension, and are nonbiotransformable. With liquid ventilation, alveolar pressures are low because the high surface tension of the gas-lung interface in eliminated. Potential neonatal applications include surfactant deficiency, persistent pulmonary hypertension, meconium aspiration, diaphragmatic hernia, pneumonia, and a vehicle for drug delivery. In order to develop a nursing care plan for the liquid-ventilated infant, nurses need knowledge of the physiologic changes involved in liquid ventilation, as well as its mechanics.

Comparison of natural surfactant and brief liquid ventilation rescue treatment in very immature lambs. Clinical and physiological correlates

We studied the effect of rescue therapy with modified porcine surfactant (Curosurf) or brief perfluorocarbon liquid ventilation on pulmonary gas exchange, mechanics and structure in very immature lambs. Both rescue strategies produced an improvement in arterial oxygenation and were able to support CO2 elimination. Histology showed unevenly inflated lungs in all but tidal-liquid-ventilated lambs. We speculate that due to immature lung architecture and relatively high permeability, previous exposure to gas ventilation impeded full effectiveness of both rescue modalities, perhaps prophylactic surfactant or liquid ventilation could be a better alternative.

Liquid ventilation in premature lambs: uptake, biodistribution and elimination of perfluorodecalin liquid

Perfluorochemical (PFC) liquids are biologically inert and nonbiotransformable substances that, when used as breathing medium, may be transported across the lung epithelium in small quantities, distributed throughout the body, and ultimately vapourized through the lungs and transpired through the skin. To further evaluate the uptake, biodistribution and elimination of a PFC liquid (perfluorodecalin) in the neonatal population, arterial blood, tissue and expired gas samples were obtained from preterm lambs (105-114 days gestation). Two groups of premature lambs were studied: Group I (n = 4) lambs were liquid ventilated from birth for 1 h and killed without exposure to gas ventilation (GV) and Group II (n = 5) lambs were liquid ventilated for 1 h followed by up to 2 h of GV. Samples were analysed by electron-capture gas chromatography and data were expressed in nl of PFC/ml of blood or gas and nl of PFC/gm tissue. During liquid ventilation and subsequent GV, PFC blood levels significantly increased (P < 0.001) from baseline control levels (0.007 +/- 0.001 SE nl PFC/ml blood) to a high of 2.95 +/- 1.03 SE nl PFC/ml blood. Perfluorochemical levels measured in expired gas (Group II) demonstrated a rapid decrease as a function of time of GV. Tissue levels of PFC indicated that uptake of PFC in Group I was significantly different (P < 0.001) than baseline levels and organ dependent; the highest levels were in the lungs (221 +/- 26.2 SE nl PFC/g tissue) and the lowest in the liver (2.24 +/- 1.6 SE nl PFC/g tissue). Comparison of tissue levels of PFC between groups indicated a 34.8% mean decrease across organs in Group II compared with Group I. These data indicate that PFC uptake and elimination is organ dependent and that PFC liquids can be eliminated through the lungs upon return to GV. Sustained PFC blood levels may be related to residual PFC in the organs and lung as well as regional variation in ventilation-perfusion matching upon return to GV.

Combined gas ventilation and perfluorochemical tracheal instillation as an alternative treatment for lethal congenital diaphragmatic hernia in lambs

Tracheal instillation of perfluorochemical liquid (PFC) lowers surface tension in the lung and thus might reduce barotrauma commonly associated with conventional gas ventilation (GV) in highly immature and hypoplastic lungs. It could be a promising alternative treatment for congenital diaphragmatic hernia (CDH) when GV alone is proving inefficient. The authors compared data for eight newborn lambs with surgically induced CDH. The animals had GV and were studied (in 2 groups) for up to 3.5 hours. Group 1 (GV, n = 4) had gas ventilation only. In group 2 (PFC, n = 4), after 30 minutes of GV, 10 to 12 mL/kg of warmed, oxygenated PFC liquid (LiquiVent) was instilled into the lung via the trachea under pressure-volume curve monitoring. Arterial pressure, blood chemistry, and pulmonary mechanics were evaluated serially; histological analysis was performed. One preassigned animal in group 1 died after 15 minutes. After 30 minutes of life, the cardiopulmonary profile of survivors was indicative of severe respiratory distress (Pao2 < 72 mm Hg with FIO2 at 1.0, PaCO2 > 90 mm Hg, compliance < 0.10 mL/cm H2O/kg) and not different between groups; the severity of pulmonary hypoplasia was further confirmed postmortem; the ratio of lung weight to body weight was 41% of that observed in control lambs, in both gas-only and combined gas/PFC-ventilated animals, compared with their respective controls. After instillation of PFC, there were dramatic improvements in acid-base status and pulmonary compliance in group 2. Survival at 3.5 hours also was markedly different (4 of 4 PFC animals and 1 of 3 GV animals).(ABSTRACT TRUNCATED AT 250 WORDS)

Use of liquid ventilation with perflubron during extracorporeal membrane oxygenation: chest radiographic appearances

PURPOSE

To assess the effectiveness of performing liquid ventilation with perflubron in neonates with severe respiratory failure or pulmonary hypertension who receive extracorporeal membrane oxygenation (ECMO) life support.

MATERIALS AND METHODS

We studied an infant (aged 1 month) and a neonate with respiratory failure who underwent ECMO and liquid ventilation with perflubron, which was slowly instilled via an endotracheal tube (in the infant, 40 mL for more than 1 hour; in the neonate, 28 mL within 1 hour).

RESULTS

The infant survived termination of ECMO support and has been breathing room air since 6 months of age. The neonate died soon after ECMO support was withdrawn.

CONCLUSION

A minority of neonates or infants with severe respiratory failure or pulmonary hypertension do not respond adequately to treatment with ECMO and are almost certain to die with termination of ECMO support. Liquid ventilation with perflubron offers a potential salvage therapy in this patient population. In addition, perflubron is a good contrast agent to use in the evaluation of neonatal pulmonary abnormalities.

Liquid ventilation improves pulmonary function, gas exchange, and lung injury in a model of respiratory failure

OBJECTIVE

The authors evaluated gas exchange, pulmonary function, and lung histology during perfluorocarbon liquid ventilation (LV) when compared with gas ventilation (GV) in the setting of severe respiratory failure.

BACKGROUND

The efficacy of LV in the setting of respiratory failure has been evaluated in premature animals with surfactant deficiency. However, very little work has been performed in evaluating the efficacy of LV in older animal models of the adult respiratory distress syndrome (ARDS).

METHODS

A stable model of lung injury was induced in 12 young sheep weighing 16.4 +/- 3.0 kg using right atrial injection of 0.07 mL/kg of oleic acid followed by saline pulmonary lavage and bijugular venovenous extracorporeal life support (ECLS). For the first 30 minutes on ECLS, all animals were ventilated with gas. Animals were then ventilated with either 15 mL/kg gas (GV, n = 6) or perflubron ([PFC], LV, n = 6) over the ensuing 2.5 hours. Subsequently, ECLS was discontinued in five of the GV animals and five of the LV animals, and GV or LV continued for 1 hour or until death.

MAIN FINDINGS

Physiologic shunt (Qps/Qt) was significantly reduced in the LV animals when compared with the GV animals (LV = 31 +/- 10%; GV = 93 +/- 4%; p < 0.001) after 3 hours of ECLS. At the same time point, pulmonary compliance (CT) was significantly increased in the LV group when compared with the GV group (LV = 1.04 +/- 0.19 mL/cm H2O/kg; GV = 0.41 +/- 0.02 mL/cm H2O/kg; p < 0.001). In addition, the ECLS flow rate required to maintain the PaO2 in the 50- to 80-mm Hg range was substantially and significantly lower in the LV group when compared with that of the GV group (LV = 14 +/- 5 mL/kg/min; GV = 87 +/- 15 mL/kg/min; p < 0.001). All of the GV animals died after discontinuation of ECLS, whereas all the LV animals demonstrated effective gas exchange without extracorporeal support for 1 hour (p < 0.01). Lung biopsy light microscopy demonstrated a marked reduction in alveolar hemorrhage, lung fluid accumulation, and inflammatory infiltration in the LV group when compared with the GV animals.

CONCLUSION

In a model of severe respiratory failure, LV improves pulmonary gas exchange and compliance with an associated reduction in alveolar hemorrhage, edema, and inflammatory infiltrate.

Development and application of a simplified liquid ventilator

OBJECTIVE

Perfluorocarbon liquid ventilation has been shown to have advantages over conventional gas ventilation in premature newborn and lung-injured animals. To simplify the process of liquid ventilation, we adapted an extra-corporeal life-support circuit as a time-cycled, volume-limited liquid ventilator.

DESIGN

Laboratory study that involved sequential application of gas and liquid ventilation in normal cats and in lung-injured sheep.

SETTING

A research laboratory at a university medical center.

SUBJECTS

Eight normal cats weighing 2.7 to 3.8 kg (mean 3.1 +/- 0.5), and four lung-injured young sheep weighing 10.4 to 22.5 kg (mean 15.9 +/- 5.0).

INTERVENTIONS

Normal cats were supported with traditional gas ventilation for 1 hr (respiratory rate 20 breaths/min, peak inspiratory pressure 12 cm H2O, positive end-expiratory pressure 4 cm H2O, and FIO2 1.0). The lungs were then filled with perfluorocarbon (30 mL/kg) and tidal volume liquid ventilation was instituted, utilizing a newly developed liquid ventilation device. Liquid ventilatory settings were 4 secs for inspiration time, 8 secs for expiration time, 5 breaths/min for respiratory rate, and 15 to 20 mL/kg for tidal volume. Liquid ventilation utilizing this device was also applied to sheep after induction of severe lung injury by right atrial injection of 0.07 mL/kg of oleic acid, followed by saline pulmonary lavage. Extracorporeal life support was instituted to provide a stable model of lung injury. For the first 30 mins of extracorporeal support, all animals were ventilated with gas. Animals were then ventilated with 15 mL/kg of perfluorocarbon over the ensuing 2.5 hrs.

MEASUREMENTS AND MAIN RESULTS

In normal cats, mean PaO2 values after 1 hr of liquid or gas ventilation were 275 +/- 90 (SD) torr (36.7 +/- 10.4 kPa) in the liquid-ventilated animals and 332 +/- 78 torr (44.3 +/- 10.4 kPa) in the gas-ventilated animals (NS). Mean PaCO2 values were 40.5 +/- 5.7 torr (5.39 +/- 0.31 kPa) in the liquid-ventilated animals and 37.6 +/- 2.3 torr (5.01 +/- 0.31 kPa) in the gas-ventilated animals (NS). Mean arterial pH values were 7.35 +/- 0.07 in the liquid-ventilated animals and 7.34 +/- 0.04 in the gas-ventilated animals (NS). No significant changes in heart rate, mean arterial pressure, lung compliance, or right atrial venous oxygen saturation were observed during liquid ventilation when compared with gas ventilation. In the lung-injured sheep, an increase in physiologic shunt from 15 +/- 7% to 66 +/- 9% was observed with induction of lung injury during gas ventilation. Liquid ventilation resulted in a significant reduction in physiologic shunt to 31 +/- 10% (p < .001). In addition, the extracorporeal blood flow rate required to maintain the PaO2 in the 50 to 80 torr (6.7 to 10.7 kPa) range was substantially and significantly (p < .001) lower during liquid ventilation than during gas ventilation (liquid ventilation 15 +/- 5 vs. gas ventilation 87 +/- 15 mL/min/kg).

CONCLUSIONS

Liquid ventilation can be performed successfully utilizing this simple adaptation of an extracorporeal life-support circuit. This modification to an existing extracorporeal circuit may allow other centers to apply this new investigational method of ventilation in the laboratory or clinical setting.

Brain-stem auditory evoked responses to hypercarbia in preterm infants

To determine the effect of acute hypercarbia on brain-stem function in preterm neonates, we compared brain-stem auditory evoked responses (BAERs) during 8% CO2 breathing to those elicited during room air breathing in 12 healthy preterm infants during the first week of life. End-tidal CO2 (ETpCO2), respiratory rate and depth were monitored throughout the protocol. Absolute wave latencies and interpeak intervals of the BAERs were analyzed from duplicate trials. During 8% CO2 breathing, ETpCO2, respiratory rate and depth of respiration increased significantly (P < 0.05). The absolute latency of wave V was prolonged (P < 0.025) in the hypercarbic state as compared to baseline. Interpeak interval III-V was also prolonged (P < 0.025). Values of absolute peak latencies I and III were unaffected by the hypercarbic state. These data demonstrate that elevations in pCO2 which elicit ventilatory responses also effect the BAER. The specific effects on ventilatory pattern, peak V latency and interpeak interval III-V indicate brain-stem responsiveness and alterations in the more central components of the auditory pathway. These findings raise important considerations regarding the influence of hypercarbia on brain-stem function in preterm infants and the clinical management of such infants with abnormalities of gas exchange.

High frequency jet ventilation: intraoperative application in infants

The potential advantages of the intraoperative use of high frequency jet ventilation (HFJV) when compared with conventional ventilation (CV) include the maintenance of adequate gas exchange and lung function with a relatively motionless surgical field. To determine the pulmonary response to HFJV ventilation in infants during cardiac surgery, we evaluated lung function in nine infants supported with CV and HFJV during a Blalock-Taussig shunt procedure. Infants were randomized to each mode of ventilation with inspiratory and expiratory pressures and FiO2 held constant. Heart rate, blood pressure, arterial blood gases, pulmonary mechanics (lung compliance and resistance), and functional residual capacity (FRC) were compared after 10 minutes of stabilization of each ventilation mode, with the infants in the thoracotomy position and the surgical field adequately exposed. Pulmonary mechanics were measured using esophageal manometry and pneumotachography, and FRC by helium dilution. There was no difference in vital signs, pulmonary mechanics, FRC, or PaO2 on HFJV ventilation when compared with CV. Arterial PaCO2 was lower with a lower mean airway pressure on HFJV when compared with CV. The surgical team subjectively observed a diminished need for lung manipulation and improved ease of access to the surgical field with HFJV. These results indicate that the use of HFJV during closed-heart cardiac surgical procedures in infants provides similar cardiopulmonary stability and some potentially important clinical benefits when compared with CV.

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.

Neonatal endotracheal tubes: variation in airway resistance with different perfluorochemical liquids

To evaluate the effect of the physical properties of density and viscosity on airway resistance, three perfluorochemical fluids (PFCs) were used: FC-75, Liquivent, and APF-140. Using two different endotracheal tubes (ETT) (3.0mm ID and 4.0mm internal diameter (ID)), the three fluids were studied at steady state flow conditions over a range that approximated peak flow required for liquid ventilation of neonatal lambs (0.005-0.02 l/sec). The slope of airway resistance (Raw)-flow curves and absolute values of Raw for the 3 PFC liquids were higher for the 3.0 ETT compared to the 4.0 ETT. The 3.0 ETT demonstrated resistance changes that were dependent on flow, density and viscosity. The 4.0 ETT showed a resistance-flow relationship that was relatively less dependent on flow, density and viscosity.

Utility of a perfluorochemical liquid for pulmonary diagnostic imaging

The use of neat perfluorochemical liquid (PFC) as an alternative respiratory medium has gained increasing attention for assessment and treatment of the immature or injured lung. In vitro and in vivo plain film and computed tomographic (CT) studies were performed on small and large animals to evaluate the use of perfluorooctylbromide (perflubron) as a bronchographic contrast agent and to quantitate the distribution and elimination of this fluid from the lung following total liquid ventilation or during gas breathing after tracheal instillation of small quantities of this liquid. The results demonstrate the utility of a highly radiopaque PFC liquid in combination with diagnostic imaging techniques to visualize small airways anatomy, identify regional and gravity dependent differences in distribution/elimination of the fluid, ventilation, and track PFC liquid following therapeutic application.

Lung lavage with oxygenated perfluorochemical liquid in acute lung injury

OBJECTIVE

To investigate the effects of lung lavage with oxygenated liquid perfluorochemical on gas exchange, lung mechanics, and cardiac function in animals with acute lung injury.

DESIGN

Prospective, randomized, controlled trial.

SETTING

Animal laboratory.

SUBJECTS

Eight adult cats (2 to 4 kg, random sex).

INTERVENTIONS

Two insults were combined to cause lung injury: oleic acid infusion and saline whole-lung wash. Animals were assigned to either the control or treatment group which consisted of a perfluorochemical liquid (Rimar 101) lavage. Perfluorochemical liquid lavage was performed three times at hourly intervals after lung injury. Three other cats with identical injury but no perfluorochemical liquid lavage served as control animals. All cats were ventilated with an FIO2 of 0.95 and positive end-expiratory pressure of 2 cm H2O continuously.

MEASUREMENTS AND MAIN RESULTS

Arterial blood gas tensions and pH, dynamic pulmonary compliance were measured at 15-min intervals. Cardiac index was assessed hourly, and lung fluid was collected after each of the three perfluorochemical liquid lavages. Arterial oxygen tension and pulmonary compliance deteriorated abruptly after lung injury in all cats, and improved significantly (p < .001, two-way analysis of variance) 15 mins after perfluorochemical liquid lavage. These parameters gradually returned to their baseline over 60 mins. Arterial blood pressure and cardiac index decreased after injury in all cats, and were not significantly changed after perfluorochemical liquid lavage. Hemorrhagic fluid was recovered from distal airways by perfluorochemical liquid lavage, despite prior suctioning of the airway.

CONCLUSIONS

Perfluorochemical liquid lavage removes pulmonary edema fluid and improves gas exchange and the mechanical properties of the lung, after acute severe lung injury.

Operative creation of left to right cardiac shunts: pulmonary functional sequelae

The creation of left to right cardiac shunts in neonates is frequently complicated by pulmonary morbidity in the immediate postoperative course. To elucidate the pattern, severity, and cause of lung dysfunction, pulmonary function testing was performed preoperatively and 1, 3, and 7 days postoperatively on 7 neonates undergoing Blalock-Taussig shunting. Pulmonary mechanics (compliance, conductance) were determined with esophageal manometry and pneumotachography, and functional residual capacity was measured by the helium dilution technique. The infants had pulmonary function preoperatively that was similar to that of healthy term neonatal controls. Significant decreases in compliance, conductance, and functional residual capacity were found on the first postoperative day (57%, 21%, and 53% of predicted, respectively). Alterations in conductance were more severe than those in compliance, but both were low through postoperative day 3. Functional residual capacity was the least affected parameter and recovered by postoperative day 3. All parameters were normal by postoperative day 7. These data indicate that shunting is associated with pulmonary morbidity through the third postoperative day that affects the airways more than the lung parenchyma. Pulmonary function studies of these infants may clarify the etiology of pulmonary dysfunction and have an impact on therapeutic strategies used in neonates undergoing cardiac operations.

Oxygen consumption and carbon dioxide production during liquid ventilation

Liquid ventilation with perfluorocarbon (PFCV) has advantages over conventional gas ventilation (GV) in premature and lung-injured newborn animals. Indirect calorimetric measurement of both oxygen consumption (VO2) and carbon dioxide production (VCO2) during PFCV has not been previously performed. In addition, comparison to indirect calorimetric measurement of VO2 and VCO2 during GV has not been evaluated. Ten fasted normal cats weighing 2.6 to 3.9 kg were anesthetized with pentobarbital and pancuronium. Tracheostomy was performed. Gas exchange was measured across the native lung during GV and across the membrane lung of the liquid ventilator during PFCV. VO2 was measured using a modification of a previously described, indirect, closed-circuit, volumetric technique. VCO2 was analyzed by capnographic assay of the mixed-expired closed-circuit air. The VCO2/VO2 ratio (RQ) was calculated. There was no change in VO2, VCO2, or RQ during PFCV when compared with GV (VO2: GV = 5.7 +/- 0.3 mL/kg/min, PFCV = 5.6 +/- 0.5 mL/kg/min [P = NS]; VCO2: GV = 4.9 +/- 1.1 mL/kg/min, PFCV = 4.8 +/- 0.9 mL/kg/min [P = NS]; RQ: GV = 0.85 +/- 0.21, PFCV = 0.86 +/- 0.21 [P = NS]). During GV the PaO2 was higher than during PFCV (PaO2: GV = 335 +/- 70 mm Hg, PFCV = 267 +/- 83 mm Hg [P = .04]), as is expected because of the relative reduction in the inspiratory PiO2 of the perfluorocarbon during liquid ventilation.(ABSTRACT TRUNCATED AT 250 WORDS)

Epithelial modulation of preterm airway smooth muscle contraction

To determine if epithelium from immature airways can modulate the responsiveness of smooth muscle, we studied paired trachealis muscle strips from preterm sheep. The epithelium was removed from one strip and left undisturbed in the other. Concentration-effect (CE) curves to acetylcholine (ACh), KCl, and isoproterenol were obtained. To evaluate maturational effects, responses to ACh and isoproterenol were studied in trachealis strips from adult airways. Maximal stress (Po) to ACh increased after epithelium removal in preterm (P < 0.05) but not adult strips. Epithelium removal caused a leftward shift of the ACh CE curves in both preterm and adult strips (P < 0.001) and a decrease in the dose required to achieve a one-half maximal response (ED50) in both preterm (P < 0.005) and adult strips (P < 0.05). The magnitude of the change in Po as well as in the ED50 for ACh between preterms and adults was similar. Epithelium removal did not alter either the Po or the CE curves of preterm strips stimulated by KCl. Response to isoproterenol in precontracted strips was enhanced in the presence of an intact epithelium in both groups (P < 0.05). These data demonstrate that preterm airway epithelium is able to modulate the responsiveness of smooth muscle. Additionally, the magnitude of the effect is unchanged with maturation. We speculate that damage of airway epithelium from mechanical ventilation may contribute to the increased incidence of airway hyperreactivity observed in preterm infants.

Effect of exchange transfusion with a red blood cell substitute on neonatal hemodynamics and organ blood flows

The present study was designed to evaluate the effect of a perfluorocarbon erythrocyte substitute on hemodynamics in the newborn lamb. Isovolumic double volume exchange transfusions were performed with perfluorocarbon emulsion (FC-43) on lambs who were ventilated to maintain normal acid base status. Hematocrit, fluorocrit, viscosity, arterial gas tensions, mean arterial pressure, and heart rate were determined before (control) and after (exchange) exchange transfusion. A radiolabeled microsphere technique was used and cardiac output, organ blood flow, organ vascular resistance, and oxygen delivery were calculated. As the hematocrit and viscosity decreased and the fluorocrit increased, there was a significant increase in PaO2 as well as a significant decrease in A-a gradient and oxygen content. There was no significant change in the acid-base status or the hemodynamic profile (heart rate, stroke volume, cardiac output, and mean arterial pressure). Blood flow to the heart and brain showed a significant increase, whereas flow to the cortex of the kidney showed a significant decrease. There was no significant change in flow to the gastrointestinal tract. Organ vascular resistance in the brain significantly decreased, increased in the kidney, and showed no significant change in the heart and gastrointestinal tract. Oxygen delivery significantly decreased in all organs except the heart. These data suggest that perfluorocarbon emulsions can acutely maintain hemodynamic stability in the newborn lamb and that the intrinsic properties of perfluorocarbons allow for the preservation of adequate oxygenation and acid-base status.

High-resolution computed tomographic bronchiolography using perfluoroctylbromide (PFOB): an experimental model

The use of perfluoroctylbromide (PFOB), a liquid ventilatory agent, was evaluated as a computed tomographic contrast agent to visualize small airway anatomy to the level of the centrilobular bronchiole, normally not visible on high-resolution computed tomography (HRCT). A freshly excised neonatal lamb heart-lung preparation was tracheally intubated, suspended in a saline bath, and mechanically ventilated with gas. After obtaining HRCT control images with suspended respiration using continuous positive airway pressure, 30 ml of perfluorocytlbromide was instilled into the trachea and repeat scans were obtained. These images demonstrated PFOB filling and distending the airways to the level of the centrilobular bronchioles and their first order branches. There was only minimal spillage into air spaces, allowing excellent anatomic detail of the bronchiolar structures. A liquid ventilatory agent, PFOB is a superb candidate as a bronchographic contrast agent due to its promotion of gas exchange, low toxicity, low surface tension, radiopacity, and vaporized excretion via the lung. It has great potential to evaluate small airway disease when used in conjunction with HRCT.