Pulmonary blood flow distribution during partial liquid ventilation

Perflubron Distribution During Transition From Gas to Total Liquid Ventilation

Total liquid ventilation (TLV) using perfluorocarbons has shown promising results for the management of neonatal respiratory distress. However, one important safety consideration for TLV is a better understanding of the early events during the transition to TLV, especially regarding the fate of residual air in the non-dependent-lung regions. Our objective was to assess perflubron distribution during transition to TLV using electrical impedance tomography, complemented by fluoroscopy, in a neonatal lamb model of induced surfactant deficiency. Eight lambs were anesthetized and ventilated in supine position. Surfactant deficit was induced by saline lung lavage. After deflation, lungs were filled with 25 ml/kg perflubron over 18 s, and TLV was initiated. Electrical impedance tomography data was recorded from electrodes placed around the chest, during the first 10 and at 120 min of TLV. Lung perfusion was also assessed using hypertonic saline injection during apnea. In addition, fluoroscopic sequences were recorded during initial lung filling with perfluorocarbons, then at 10 and 60 min of TLV. Twelve lambs were used as controls for histological comparisons. Transition to TLV involved a short period of increased total lung volume (p = 0.01) secondary to recruitment of the dependent lung regions. Histological analysis shows that TLV was protective of these same regions when compared to gas-ventilated lambs (p = 0.03). The non-dependent lung regions filled with perflubron over at least 10 min, without showing signs of overdistention. Tidal volume distribution was more homogenous in TLV than during the preceding gas ventilation. Perflubron filling was associated with a non-significant increase in the anterior distribution of the blood perfusion signal, from 46 ± 17% to 53 ± 6% (p = 0.4). However, combined to the effects on ventilation, TLV had an instantaneous effect on ventilation-perfusion relationship (p = 0.03), suggesting better coupling. Conclusion: transition to TLV requires at least 10 min, and involves air evacuation or dissolution in perflubron, dependent lung recruitment and rapid ventilation-perfusion coupling modifications. During that time interval, the total lung volume transiently increases. Considering the potential deleterious effect of high lung volumes, one must manage this transition phase with care and, we suggest using a real-time monitoring system such as electrical impedance tomography.

Effect of surfactant and partial liquid ventilation treatment on gas exchange and lung mechanics in immature lambs: influence of gestational age

Objectives

Surfactant (SF) and partial liquid ventilation (PLV) improve gas exchange and lung mechanics in neonatal RDS. However, variations in the effects of SF and PLV with degree of lung immaturity have not been thoroughly explored.

Setting

Experimental Neonatal Respiratory Physiology Research Unit, Cruces University Hospital.

Design

Prospective, randomized study using sealed envelopes.

Subjects

36 preterm lambs were exposed (at 125 or 133-days of gestational age) by laparotomy and intubated. Catheters were placed in the jugular vein and carotid artery.

Interventions

All the lambs were assigned to one of three subgroups given: 20 mL/Kg perfluorocarbon and managed with partial liquid ventilation (PLV), surfactant (Curosurf®, 200 mg/kg) or (3) no pulmonary treatment (Controls) for 3 h.

Measurements and Main Results

Cardiovascular parameters, blood gases and pulmonary mechanics were measured. In 125-day gestation lambs, SF treatment partially improved gas exchange and lung mechanics, while PLV produced significant rapid improvements in these parameters. In 133-day lambs, treatments with SF or PLV achieved similarly good responses. Neither surfactant nor PLV significantly affected the cardiovascular parameters.

Conclusion

SF therapy response was more effective in the older gestational age group whereas the effectiveness of PLV therapy was not gestational age dependent.

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.

Phenylephrine-modulated cardiopulmonary blood flow measured with use of X-ray digital subtraction angiography

INTRODUCTION

Cardiopulmonary blood flow is an important indicator of organ function. Limitations in measuring blood flow in live rodents suggest that rapid physiological changes may be overlooked. For instance, relative measurements limit imaging to whole organs or large sections without adequately visualizing vasculature. Additionally, current methods use small samples and invasive techniques that often require killing animals, limiting sampling speed, or both. A recently developed high spatial- and temporal-resolution X-ray digital subtraction angiography (DSA) system visualizes vasculature and measures blood flow in rodents. This study was the first to use this system to measure changes in cardiopulmonary blood flow in rats after administering the vasoconstrictor phenylephrine.

METHODS

Cardiopulmonary blood flow and vascular anatomy were assessed in 11 rats before, during, and after recovery from phenylephrine. After acquiring DSA images at 12 time points, a calibrated non-parametric deconvolution technique using singular value decomposition (SVD) was applied to calculate quantitative aortic blood flow in absolute metrics (mL/min). Trans-pulmonary transit time was calculated as the time interval between maximum signal enhancement in the pulmonary trunk and aorta. Pulmonary blood volume was calculated based on the central volume principle. Statistical analysis compared differences in trans-pulmonary blood volume and pressure, and aortic diameter using paired t-tests on baseline, peak, and late-recovery time points.

RESULTS

Phenylephrine had dramatic qualitative and quantitative effects on vascular anatomy and blood flow. Major vessels distended significantly (aorta, ~1.2-times baseline) and mean arterial blood pressure increased ~2 times. Pulmonary blood volume, flow, pressure, and aortic diameter were not significantly different between baseline and late recovery, but differences were significant between baseline and peak, as well as peak and recovery time points.

DISCUSSION

The DSA system with calibrated SVD technique acquired blood flow measurements every 30s with a high level of regional specificity, thus providing a new option for in vivo functional assessment in small animals.

High-resolution three-dimensional 19F-magnetic resonance imaging of rat lung in situ: evaluation of airway strain in the perfluorocarbon-filled lung

Perfluorocarbons (PFC) are biologically and chemically inert fluids with high oxygen and CO(2) carrying capacities. Their use as liquid intrapulmonary gas carriers during liquid ventilation has been investigated. We established a method of high resolution 3D-(19)F-MRI of the totally PFC-filled lung. The goal of this study was to investigate longitudinal and circumferential airway strain in the setting of increasing airway pressures on 3D-(19)F-MR images of the PFC-filled lung. Sixteen female Wistar rats were euthanized and the liquid perfluorocarbon FC-84 instilled into their lungs. 3D-(19)F-MRI was performed at various intrapulmonary pressures. Measurements of bronchial length and cross-sectional area were obtained from transversal 2D images for each pressure range. Changes in bronchial area were used to determine circumferential strain, while longitudinal strain was calculated from changes in bronchial length. Our method of 3D-(19)F-MRI allowed clear visualization of the great bronchi. Longitudinal strain increased significantly up to 31.1 cmH(2)O. The greatest strain could be found in the range of low airway pressures. Circumferential strain increased strongly with the initial pressure rise, but showed no significant changes above 10.4 cmH(2)O. Longitudinal strain was generally higher in distal airways, while circumferential strain showed no difference. Analysis of mechanical characteristics showed that longitudinal and circumferential airway expansion occurred in an anisotropic fashion. Whereas longitudinal strain still increased with higher pressures, circumferential strain quickly reached a 'strain limit'. Longitudinal strain was higher in distal bronchi, as dense PFCs gravitate to dependent, in this case to dorso-basal parts of the lung, acting as liquid positive end expiratory pressure.

Regional overdistension identified with electrical impedance tomography in the perflubron-treated lung

Regional lung overdistension occurring during high frequency oscillatory ventilation (HFOV) and partial liquid ventilation (PLV) was investigated in a prospective animal trial using 18 mechanically ventilated Yorkshire swine under general anesthesia. Lung injury was induced with saline lavage and augmented using large tidal volumes. Electrical impedance tomography (EIT) and regional lung histopathology were used to identify regional lung overdistension during HFOV. Lung injury was quantified using a histopathologic lung injury score. The animals were randomized to three groups (n = 6 animals in each group): a control group and two dose groups of perfluorooctyl bromide (PFOB) (PFOB-Lo 1.5 ml kg(-1) and PFOB-Hi 3 ml kg(-1)). The animals were transitioned from conventional ventilation to HFOV, and a slow inflation-deflation maneuver was performed by changing mean airway pressure (Paw) by 5 cmH(2)O every 15 min to a maximum Paw of 40 cmH(2)O. In dependent lung areas, the PFOB-Hi (3 ml kg(-1)) group, in comparison with the control group, was associated with significantly greater alveolar overdistension seen on lung histopathology (P < 0.001 compared to control), a decreased mean impedance (P < 0.05 compared to the control group) and a decreased ventilation-induced impedance change during HFOV (P < 0.05 compared to the control group). We conclude that treatment with PFOB-Hi during HFOV compared to a control group in an animal model of lung injury led to regional overdistension of dependent lung areas, as evidenced by increased alveolar overdistension on lung histopathology, decreased mean lung impedance and decreased HFOV-induced regional lung volume changes as measured by EIT.

Feasibility of lung cancer hyperthermia using breathable perfluorochemical (PFC) liquids. Part I: Convective hyperthermia

Clinical studies have shown that hyperthermia in combination with radiotherapy and/or chemotherapy may be effective in the treatment of advanced cancer. No method of lung hyperthermia, however, has been accepted as standard or superior. This investigation sought to demonstrate in animals the thermal and physiologic feasibility of lung hyperthermia induced using heated breathable perfluorochemical (PFC) liquids, a method termed liquid-filled lung convective hyperthermia (LCHT). The ability to use LCHT is rooted in the development of both PFC liquid ventilation, now in clinical development with the PFC perflubron (LiquiVent), and a PFC blood substitute also in late Phase III trials (Oxygent). As LCHT background, the PFC technologies and biology are first reviewed. The physical properties of a variety of PFCs were evaluated for LCHT and it was concluded that more than one liquid is suitable based on such properties. Using total liquid ventilation type devices, LCHT was shown to deliver successfully localized (lobar) lung heating in sheep, and bilateral whole lung heating and whole-body hyperthermia in rabbits, cats and lambs. During LCHT, lung parenchymal temperatures were uniform (<1 degree C) across heated regions. In addition, based on patterns relating lung tissue temperatures to inspiratory and expiratory PFC liquid temperatures in the endotracheal tube, LCHT may minimize invasive thermometry requirements in the lung. Based on acute experiments, it was concluded that LCHT appears feasible and may simplify lung hyperthermia. It was recommended that potentially synergistic combinations of LCHT with other whole-body hyperthermia or local heating modalities, and with chemotherapeutic lung drug delivery, also be explored in the future.

Gas exchange and lung mechanics during high frequency ventilation in the perflubron-treated lung

OBJECTIVE

To identify the effect of perflubron on gas exchange and lung mechanics during high frequency oscillatory ventilation in an animal model.

DESIGN

Prospective randomized animal trial.

SUBJECTS

Eighteen Yorkshire swine.

INTERVENTIONS

Three groups of six animals each were investigated: control (high frequency oscillatory ventilation alone), low dose perflubron (high frequency oscillatory ventilation plus perfluoro-octyl bromide [PFOB]-Lo, 1.5 mL/kg), and high dose perflubron (high frequency oscillatory ventilation plus PFOB-Hi, 3 mL/kg). Lung injury was induced with repeated saline lavage and amplified for 1 hr using large tidal volumes. Perflubron (Alliance, CA) or a sham dose (room air) was administered with bronchoscopic guidance. The animals were transitioned to high frequency oscillatory ventilation starting at a mean airway pressure of 15 cm H2O. Mean airway pressure was increased (inflation phase) by 5 cm H2O every 15 mins to a maximum mean airway pressure of 40 cm H2O. During the deflation phase, mean airway pressure was reduced by 5 cm H2O every 15 mins to a mean airway pressure of 15 cm H2O.

MEASUREMENTS AND MAIN RESULTS

Oxygenation was improved and pulmonary shunt fraction was reduced for PFOB-Hi compared with the control group only at a mean airway pressure of 15 and 20 cm H2O. At a maximal mean airway pressure of 40 cm H2O, oxygenation was not different between the groups, but pulmonary artery pressures were elevated in both PFOB-groups compared with the control group. During the deflation phase, oxygenation, pulmonary shunt fraction, and pulmonary artery pressures were adversely affected by PFOB-Hi and PFOB-Lo.

CONCLUSIONS

Although PFOB-Hi compared with the control group improved oxygenation and reduced pulmonary shunt fraction only during the first pressure steps of a formal stepwise recruitment maneuver during high frequency oscillatory ventilation, this effect was not sustained during maximal recruitment. During the deflation phase, both PFOB groups were associated with worse gas exchange compared with the control group. PFOB also produced significant pulmonary hypertension in comparison with the control group.

Partial Liquid Ventilation in Adult Patients with Acute Respiratory Distress Syndrome

RATIONALE

Despite recent clinical trials demonstrating improved outcome in acute respiratory distress syndrome (ARDS), mortality remains high. Partial liquid ventilation (PLV) using perfluorocarbons has been shown to improve oxygenation and decrease lung injury in various animal models.

OBJECTIVE

To determine if PLV would have an impact on outcome in patients with ARDS.

METHODS

Patients with ARDS were randomized to (1) conventional mechanical ventilation (CMV; n=107), (2) "low-dose" perfluorocarbon (10 ml/kg; n=99), and (3) "high-dose" perfluorocarbon (20 ml/kg; n=105). Patients in all three groups were ventilated using volume ventilation, Vt <or= 10 ml/kg predicted body weight, rate <or= 25/min, inspiratory-to-expiratory ratio <or= 1:1, Fi(O(2)) >or= 0.5, and positive end-expiratory pressure >or= 13 cm H(2)O.

RESULTS

The 28-d mortality in the CMV group was 15%, versus 26.3% in the low-dose (p=0.06) and 19.1% in the high-dose (p=0.39) PLV groups. There were more ventilator-free days in the CMV group (13.0+/-9.3) compared with both the low-dose (7.4+/-8.5; p<0.001) and high-dose (9.9+/-9.1; p=0.043) groups. There were more pneumothoraces, hypoxic episodes, and hypotensive episodes in the PLV patients.

CONCLUSIONS

PLV at both high and low doses did not improve outcome in ARDS compared with CMV and cannot be recommended for patients with ARDS.

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.

High-frequency oscillatory ventilation: what large-animal studies have taught us!

BACKGROUND

Much of the information on the physiologic effects, mechanisms of gas exchange, and potential utility of high-frequency oscillation (HFO) has been acquired in animal studies. Specifically, large animal data have been useful in assessing adult application because large animals present many of the same concerns and challenges as adults.

OBJECTIVE

To review the literature on HFO testing in large animal models, identifying contributions to the understanding of mechanisms of action and the physiology of HFO.

RESULTS

Large animal studies have clarified the mechanisms of gas exchange during HFO, identified approaches to setting mean airway pressure based on lung mechanics, and identified a potentially better approach to applying partial liquid ventilation.

CONCLUSION

The study of HFO in large animal models has been essential to our understanding of the optimal approach to applying HFO in human studies.

A Mathematical Model of Alveolar Gas Exchange in Partial Liquid Ventilation

In partial liquid ventilation (PLV), perfluorocarbon (PFC) acts as a diffusion barrier to gas transport in the alveolar space since the diffusivities of oxygen and carbon dioxide in this medium are four orders of magnitude lower than in air. Therefore convection in the PFC layer resulting from the oscillatory motions of the alveolar sac during ventilation can significantly affect gas transport. For example, a typical value of the Pe´clet number in air ventilation is Pe∼0.01, whereas in PLV it is Pe∼20. To study the importance of convection, a single terminal alveolar sac is modeled as an oscillating spherical shell with gas, PFC, tissue and capillary blood compartments. Differential equations describing mass conservation within each compartment are derived and solved to obtain time periodic partial pressures. Significant partial pressure gradients in the PFC layer and partial pressure differences between the capillary and gas compartments PC-Pg are found to exist. Because Pe≫1, temporal phase differences are found to exist between PC-Pg and the ventilatory cycle that cannot be adequately described by existing non-convective models of gas exchange in PLV. The mass transfer rate is nearly constant throughout the breath when Pe≫1, but when Pe≪1 nearly 100% of the transport occurs during inspiration. A range of respiratory rates (RR), including those relevant to high frequency oscillation (HFO)+PLV, tidal volumes VT and perfusion rates are studied to determine the effect of heterogeneous distributions of ventilation and perfusion on gas exchange. The largest changes in PCO2 and PCCO2 occur at normal and low perfusion rates respectively as RR and VT are varied. At a given ventilation rate, a low RR-high VT combination results in higher PCO2, lower PCCO2 and lower PC-Pg than a high RR-low VT one.

Measurements of Alveolar pO2 Using 19F-MRI in Partial Liquid Ventilation

RATIONALE AND OBJECTIVES

Partial liquid ventilation using Perfluorcarbon (PFC) is an innovative treatment of acute respiratory distress syndrome. However, the underlying mechanisms are not totally clear. The aim was to investigate the distribution of oxygen partial pressure within the PFC-filled lung (ppO2).

METHODS

Nine pigs underwent partial liquid ventilation, receiving 20 mL PFC/kg bodyweight (bw). Measurements were obtained by a chemical shift selective TurboFLASH sequence at different axial lung levels. ppO2 was calculated from 19F-MRI by nonlinear curve T1-fitting technique after noise correction.

RESULTS

Quantification and distribution of ppO2 was performed successfully. A narrow relationship of the inspiratory O2 fraction and ppO2, as well as a significant ventral-to-dorsal gradient of ppO2 (ventral:dependent lung = 1.9:1) were detected in all subjects and slice positions.

CONCLUSIONS

In vivo measurement of local ppO2 gains new and clinical important insights into the physiology of PLV. The previously unknown ppO2 gradient within PFC fits to distribution of perfusion. Dependent lung regions appear to have limited access to O2 from central airways.

End-expiratory lung volumes and density distribution patterns during partial liquid ventilation in healthy and oleic acid-injured sheep: a computed tomography study

OBJECTIVE

To determine end-expiratory lung volumes (EELVs) and the distribution of gas and perflubron during low- and high-dose partial liquid ventilation (PLV) in healthy and oleic-acid-injured lungs.

DESIGN

A prospective, randomized study.

SETTING

A university medical school laboratory approved for animal research.

SUBJECTS

Adult sheep.

INTERVENTIONS

A total of 18 sheep were randomly divided into two groups (healthy and oleic acid lung injury) and received PLV with perflubron at incremental doses.

MEASUREMENTS AND MAIN RESULTS

Animals were ventilated in a volume-control mode with a positive end-expiratory pressure of 5 cm H2O. Baseline computed tomographic scans of the entire lung were obtained during end-expiratory hold. Thereafter, the animals were randomized to undergo either PLV alone (healthy group) or after oleic acid lung injury was introduced (injury group). In both groups, PLV was induced by instilling 10 mL/kg perflubron into the endotracheal tube over 5 mins (low-dose PLV). At 60 mins after dosing, another set of computed tomographic scans during end-expiratory hold was obtained. Thereafter, another 20 mL/kg perflubron was instilled in both groups (cumulative dose, 30 mL/kg perflubron, high-dose PLV), and computed tomographic scanning was repeated 60 mins later. EELVs were calculated. To study density distribution patterns, the lungs were divided into nine segments, and the mean Hounsfield attenuation number was calculated for each segment. In healthy animals, low-dose PLV did not change EELV (47.5 +/- 8.1 mL/kg vs. 44.5 +/- 6.1 mL/kg at 10 mL/kg perflubron), whereas high-dose PLV significantly increased EELV (58.1 +/- 3.3 mL/kg, p <.01). Oleic acid lung injury significantly reduced EELV (53.9 +/- 7.5 mL/kg vs. 43.9 +/- 8.7 mL/kg, p <.01). Low-dose PLV reestablished baseline EELV (59.8 +/- 10.5 mL/kg), and high-dose PLV resulted in a significant increase in EELV (89.2 +/- 12 mL/kg, p =.003). PLV increased the mean Hounsfield attenuation number along the ventrodorsal axis in the three coronal blocks in a dose-dependent manner. In the oleic acid lung injury group, PLV produced a more homogeneous pattern of density distribution, with the highest Hounsfield attenuation numbers observed in the medial segments.

CONCLUSION

High-dose PLV significantly increased EELV in both states, indicating lung distention. Healthy lungs were filled in a dose-dependent, gravity-governed fashion, showing steep craniocaudal and ventrodorsal gradients. In the oleic acid lung injury model studied, perflubron tended to accumulate on top of the most severely injured dorsal and diaphragmatic parts, rendering effective recruitment by liquid positive end-expiratory pressure in these regions questionable.

Real-time visualization of partial liquid ventilation in a model of acute lung injury

BACKGROUND

To clarify the effects of partial liquid ventilation, we visualized and morphologically analyzed real-time alveolar recruitment in a model of acute lung injury.

METHODS

Male Wistar rats were divided into 3 groups: a group that underwent hydrochloric acid aspiration and mechanical gas ventilation (ALI group, n = 15), a group that underwent acid aspiration and partial liquid ventilation beginning 90 minutes after acid aspiration (PLV group, n = 15), and a group that underwent mechanical ventilation without acid aspiration (control group, n = 5). The number of ventilated alveoli and the diameter of the largest ventilated alveolus in each of 10 high-power fields observed on fluorescence micrographs with a tracer of labeled albumin were determined and averaged from 90 to 210 minutes after acid aspiration.

RESULTS

The number of alveoli in the PLV group significantly increased in comparison to that in the ALI group. The diameter of the largest alveolus in the PLV group decreased from 103.7 +/- 16.3 microm to 76.3 +/- 6.5 microm until the end of the experiment. This diameter was equivalent to that in the control group.

CONCLUSIONS

The excellent alveolar recruitment suggests that liquid ventilation ameliorates ventilator-associated lung injury.

Prospective, randomized, controlled pilot study of partial liquid ventilation in adult acute respiratory distress syndrome

We evaluated the safety and efficacy of partial liquid ventilation (PLV) with perflubron in adult patients with acute lung injury and the acute respiratory distress syndrome (ARDS) in a multicenter, prospective, controlled, randomized exploratory clinical trial. Ninety adult patients with PaO2/FIO2 ratios > 60 and < 300 with ARDS for no more than 24 hours were randomized to receive PLV (n = 65) with administration of perflubron through an endotracheal tube sideport or conventional mechanical ventilation (CMV, n = 25) for a maximum of five days. Although a significant reduction in progression to ARDS was noted among patients with PLV, no significant differences in the number of days free from the ventilator at 28 days (CMV = 6.7 +/- 1.8, PLV = 6.3 +/- 1.0 days, p = 0.85), the incidence of mortality (CMV = 36%, PLV = 42%, p = 0.63), or any pulmonary-related parameter were observed. During a post hoc subgroup analysis, significantly more rapid discontinuation of mechanical ventilation (p = 0.045) and a trend toward an increase in the number of days free from the ventilator at 28 days (CMV = 3.2 +/- 1.9, PLV = 8.0 +/- 2.2 days, p = 0.06) were observed during PLV among those patients under 55 years of age with acute lung injury or ARDS. Episodes of hypoxia, respiratory acidosis, and bradycardia occurred more frequently in the PLV group, but these were transient and self-limited. Further evaluation of PLV is warranted to further define beneficial effects in well-defined groups of patients and also to gain additional information regarding safety.

Effects of perfluorohexane vapor on relative blood flow distribution in an animal model of surfactant-depleted lung injury

OBJECTIVE

To test the hypothesis that treatment with vaporized perfluorocarbon affects the relative pulmonary blood flow distribution in an animal model of surfactant-depleted acute lung injury.

DESIGN

Prospective, randomized, controlled trial.

SETTING

A university research laboratory.

SUBJECTS

Fourteen New Zealand White rabbits (weighing 3.0-4.5 kg).

INTERVENTIONS

The animals were ventilated with an FIO(2) of 1.0 before induction of acute lung injury. Acute lung injury was induced by repeated saline lung lavages. Eight rabbits were randomized to 60 mins of treatment with an inspiratory perfluorohexane vapor concentration of 0.2 in oxygen. To compensate for the reduced FIO(2) during perfluorohexane treatment, FIO(2) was reduced to 0.8 in control animals. Change in relative pulmonary blood flow distribution was assessed by using fluorescent-labeled microspheres.

MEASUREMENTS AND MAIN RESULTS

Microsphere data showed a redistribution of relative pulmonary blood flow attributable to depletion of surfactant. Relative pulmonary blood flow shifted from areas that were initially high-flow to areas that were initially low-flow. During the study period, relative pulmonary blood flow of high-flow areas decreased further in the control group, whereas it increased in the treatment group. This difference was statistically significant between the groups (p =.02) as well as in the treatment group compared with the initial injury (p =.03). Shunt increased in both groups over time (control group, 30% +/- 10% to 63% +/- 20%; treatment group, 37% +/- 20% to 49% +/- 23%), but the changes compared with injury were significantly less in the treatment group (p =.03).

CONCLUSION

Short treatment with perfluorohexane vapor partially reversed the shift of relative pulmonary blood flow from high-flow to low-flow areas attributable to surfactant depletion.

Regional VA, Q, and VA/Q during PLV: effects of nitroprusside and inhaled nitric oxide

Partial liquid ventilation (PLV) with high-specific-weight perfluorocarbon liquids has been shown to improve oxygenation in acute lung injury, possibly by redistributing perfusion from dependent, injured regions to nondependent, less injured regions of the lung. Our hypothesis was that during PLV in normal lungs, a shift in perfusion away from dependent lung zones might, in part, be due to vasoconstriction that could be reversed by infusing sodium nitroprusside (NTP). In addition, delivering inhaled NO during PLV should improve gas exchange by further redistributing blood flow to well-ventilated lung regions. To examine this, we used a single transverse-slice positron emission tomography camera to image regional ventilation and perfusion at the level of the heart apex in six supine mechanically ventilated sheep during five conditions: control, PLV, PLV + NTP, and PLV + NO at 10 and 80 ppm. We found that PLV shifted perfusion from dependent to middle regions, and the dependent region demonstrated marked hypoventilation. The vertical distribution of perfusion changed little when high-dose intravenous NTP was added during PLV, and inhaled NO tended to shift perfusion toward better ventilated middle regions. We conclude that PLV shifts perfusion to the middle regions of the lung because of the high specific weight of perflubron rather than vasoconstriction.

Selective tracheal gas insufflation during partial liquid ventilation improves lung function in an animal model of unilateral acute lung injury

OBJECTIVE

During unilateral lung injury, we hypothesized that we can improve global lung function by applying selective tracheal gas insufflation (TGI) and partial liquid ventilation (PLV) to the injured lung.

DESIGN

Prospective, interventional animal study.

SETTING

Animal laboratory in a university hospital.

SUBJECTS

Adult mixed-breed dogs.

INTERVENTIONS

In six anesthetized dogs, left saline lung lavage was performed until PaO(2)/FiO(2) fell below 100 torr (13.3 kPa). The dogs were then reintubated with a Univent single-lumen endotracheal tube, which incorporates an internal catheter to provide TGI. In a consecutive manner, we studied 1) the application of 10 cm H(2)O of positive end-expiratory pressure (PEEP); 2) instillation of 10 mL/kg of perflubron (Liquivent) to the left lung at a PEEP level of 10 cm H(2)O (PLV+PEEP 10 initial); 3) application of selective TGI (PLV+TGI) while maintaining end-expiratory lung volume (EELV) constant; 4) PLV+TGI at reduced tidal volume (VT); and 5) PLV+PEEP 10 final.

MEASUREMENTS AND MAIN RESULTS

Application of PLV+PEEP 10 initial did not change gas exchange, lung mechanics, or hemodynamics. PLV+TGI improved PaO(2)/FiO(2) from 189 +/- 13 torr (25.2 +/- 1.7 kPa) to 383 +/- 44 torr (51.1 +/- 5.9 kPa) (p <.01) and decreased PaCO(2) from 55 +/- 5 torr (7.3 +/- 0.7 kPa) to 30 +/- 2 torr (4.0 +/- 0.3 kPa) (p <.01). During ventilation with PLV+TGI, reducing VT from 15 mL/kg to 3.5 mL/kg while keeping EELV constant decreased PaO(2)/FiO(2) to 288 +/- 49 torr (38.4 +/- 6.5 kPa) (not significant) and normalized PaCO(2). At this stage, end-inspiratory plateau pressure decreased from 19.2 +/- 0.7 cm H(2)O to 13.6 +/- 0.7 cm H(2)O (p <.01). At PLV+PEEP 10 final, measurements returned to those observed at previous baseline stage (PLV+PEEP 10 initial).

CONCLUSIONS

During unilateral lung injury, PLV with a moderate PEEP did not improve oxygenation, TGI superimposed on PLV improved gas exchange, and combination of TGI and PLV allowed a 77% reduction in VT without any adverse effect on PaCO(2).

Intratracheal administration of perfluorochemical-gentamicin suspension: a comparison to intravenous administration in normal and injured lungs

Respiratory infections can lead to acute lung injury and perfusion abnormalities. We hypothesized that intratracheal (IT) administration of a perfluorochemical (PFC) gentamicin (G) suspension as compared to intravenous (IV) administration of gentamicin will result in higher lung tissue levels of gentamicin, while maintaining safe serum levels. To test this hypothesis, 21 lambs with normal and acid injured lungs were studied for 4 hr, using 2 different drug delivery methods, IT and IV. Lungs were injured with warm HCl acid in saline lavage, followed by partial liquid ventilation with perflubron (bolus FRC = 20 mL/kg). G at a dose of 5 mg/kg was delivered either IT (G-PFC; 20 mL/kg) or IV (aqueous injection with IT 20 mL/kg PFC alone). Throughout the study, serum G levels, arterial blood gases, respiratory system compliance, and mean arterial blood pressure were measured. Lung tissue G levels were measured at 4 hr and averaged across lobes. Physiologic gas exchange and pulmonary function were maintained throughout the protocol for both the normal and injured lungs. Intravenously administered G resulted in an initial 5-min serum concentration of 43 +/- 2.5 mcg/mL, followed by an exponential decline over the 4-hr protocol to a level of 2.1 +/- 0.23 mcg/mL at hr 4. The intratracheally administered G suspension resulted in a 5-min serum concentration of 1.8 +/- 0.98 mcg/mL and remained relatively constant throughout the protocol, with a 4-hr level of 1.6 +/- 0.29 mcg/mL. With respect to lung tissue G levels, IT administration was significantly more effective in delivering the drug to the normal lungs than IV (31.4 +/- 3.3 mcg/g vs. 4.0 +/- 0.7 mcg/g) 4 hr after administration. In the lung injury group, there was a small but significant difference in lung tissue G levels, with the IT-administered perfluorochemical-G suspension achieving greater levels than the IV-administered G (11.9 +/- 0.52 mcg/g vs. 10.1 +/- 0.8 mcg/g). Additionally, the drug delivered IV and IT in both the normal and injured lung models was homogeneously distributed throughout the lung. These data show that G lung tissue levels in both normal and injured lungs were higher in the IT group when compared to IV administration. The results of this study demonstrate that in normal and injured lungs, homogeneous G lung tissue levels can be more effectively achieved at lower serum levels when delivered IT in a G-PFC suspension as compared to IV administration.

Preserved spontaneous breathing improves cardiac output during partial liquid ventilation

The aim of this study was to examine whether preserved spontaneous breathing (SB) supported by proportional-assist ventilation (PAV) would improve cardiac output (CO) during partial liquid ventilation (PLV) in rabbits with and without lung disease if compared with time-cycled, volume-controlled ventilation (CV) combined with muscle paralysis (MP). PLV was initiated in 17 healthy rabbits and 17 surfactant-depleted rabbits using 12 to 15 ml/kg of perfluorodecaline. Both ventilatory modes, SB+PAV and CV+MP, were applied in random sequence using a crossover design. CO was measured by thermodilution. CO was significantly higher during SB+PAV than during CV+MP: 136 +/- 21 ml/kg x min (mean +/- SD) versus 120 +/- 30 ml/kg x min (p = 0.004) in healthy rabbits, and 147 +/- 19 ml/kg x min versus 111 +/- 13 ml/kg x min (p < 0.0001) in surfactant-depleted rabbits, resulting in an improved oxygen delivery. This difference was mainly caused by a larger stroke volume during SB+PAV, whereas there was little change in heart rate. In surfactant-depleted rabbits, SB+PAV resulted in improved arterial blood pressure and arterial and mixed venous pH and in a higher PaO2 at the same level of PEEP and mean airway pressure. We conclude that during PLV, CO is higher during SB+PAV than during CV+MP, resulting in an improved oxygen delivery. In surfactant-depleted rabbits, improved CO, oxygen delivery, and arterial blood pressure resulted in higher pH, possibly reflecting improved tissue perfusion and oxygenation.

Partial liquid ventilation in severely surfactant-depleted, spontaneously breathing rabbits supported by proportional assist ventilation

OBJECTIVE

We hypothesized that partial liquid ventilation (PLV) would improve oxygenation in nonparalyzed, surfactant-deficient rabbits breathing spontaneously while supported by proportional assist ventilation (PAV). This ventilation mode compensates for low pulmonary compliance and high resistance and thereby facilitates spontaneous breathing.

DESIGN

Randomized trial.

SETTING

University animal research facility.

SUBJECTS

Twenty-six anesthetized New Zealand white rabbits weighing 2592 +/- 237g (mean +/- sd).

INTERVENTIONS

After pulmonary lavage (target Pao2 <100 mm Hg on mechanical ventilation with 6 cm H2O of positive end-expiratory pressure [PEEP] and an Fio2 of 1.0), rabbits were randomized to PAV (PEEP of 8 cm H2O) with or without PLV. PLV rabbits received 25 mL/kg of perfluorocarbon by intratracheal infusion (1 mL/kg/min). Pao2, Paco2, tidal volume, respiratory rate, minute ventilation, mean airway pressure, arterial blood pressure, heart rate, pulmonary compliance, and airway resistance were measured. Evaporated perfluorocarbon was refilled every 30 mins in PLV animals. After 5 hrs, animals were killed and lungs were removed. Lung injury was evaluated using a histologic score.

MAIN RESULTS

Pao2 and compliance were significantly higher in PLV rabbits compared with controls (p <.05, analysis of variance for repeated measures). All other parameters were similar in both groups.

CONCLUSIONS

PLV improved oxygenation and pulmonary compliance in spontaneously breathing, severely surfactant-depleted rabbits supported by PAV. The severity of lung injury by histology was unaffected.

Optimizing intrapulmonary perfluorocarbon distribution: Fluoroscopic comparison of mode of ventilation and body position

OBJECTIVE

Partial liquid ventilation with the perfluorochemical, perflubron, has been shown to improve lung mechanics and enhance gas exchange in the treatment of severe acute lung injury. However, the most effective strategy to provide optimal intrapulmonary distribution of perflubron has not been fully accessed. The objective of this study was to examine the effect of body position (supine vs. rotational) and mode of ventilation (conventional mechanical ventilation [CMV] vs. high-frequency oscillatory ventilation [HFOV]) on perflubron distribution and oxygenation improvement.

DESIGN

Prospective, randomized, animal trial.

SETTING

Research laboratory at a university medical center.

SUBJECTS

Twenty healthy piglets (4.5-6.6 kg).

INTERVENTIONS

Subjects underwent repetitive saline lavage to achieve a uniform degree of lung injury and then were randomized to either CMV or were converted to HFOV. Within each ventilator group, animals were randomized to supine positioning (S) or rotational positioning with alternation between supine and prone position (R) during incremental dosing of three 5-mL/kg doses of perflubron.

MEASUREMENTS AND MAIN RESULTS

Arterial blood gas tensions, hemodynamic variables, and the oxygenation index were recorded after each dose of 5 mL/kg. Lateral cinefluoroscopic images after each dose were digitized for computer analysis of density. A density index was calculated for a 2-cm2 window in three dorsal and three ventral lung regions. Uniformity of distribution was calculated by comparing the mean density among the six regions. Oxygenation improvements were compared between groups. There were no significant differences in hemodynamic variables or gas exchange after lung injury in the four groups. Rotational positioning produced significantly more uniform perflubron distribution during both CMV and HFOV. This effect was independent of the mode of ventilation. The mean ventral density index was affected by rotating position and HFOV mode of ventilation after 10 mL/kg of perflubron, and rotating position was affected only after 15 mL/kg of perflubron. There was a significant reduction in the oxygenation index from baseline to end lavage in both CMV groups, as well as all of the animals that were rotated.

CONCLUSION

Perflubron is more uniformly dispersed when dosed in a rotational fashion with alternation between supine and prone position during incremental dosing. This effect is independent of mode of ventilation. There was no relationship between oxygenation improvements and nondependent perflubron distribution. CMV and rotating dosing both led to a significant decrease in the oxygenation index after a 15 mL/kg dose of perflubron. This information has important impact on the future development of dosing strategies and clinical trial design.

Liquid ventilation

Partial liquid ventilation (PLV) developed considerably in the clinical and experimental fields during the past few years. In addition to improved oxygenation and lung mechanics by perfluorocarbon (PFC) administration, recent animal studies have tried to optimize PLV by evaluating the most appropriate ventilatory mode to use during PLV and by adjusting the best level of positive end-expiratory pressure (PEEP). Other pathophysiological aspects of acute lung injury that may be positively affected by liquid ventilation have been studied, including regional blood flow redistribution, reduction in ventilator-induced lung injury, and antiinflammatory properties of PFC. Although the precise dosing of PFC is debated, evidence from several experimental studies supports the use of smaller doses of PFC because larger doses increase the occurrence of baro- and volutrauma. In the clinical field, after promising data from preliminary studies, an international randomized controlled trial is on the verge of completion.

Partial liquid ventilation for acute respiratory distress syndrome

PLV represents an intriguing alternative paradigm in the approach to the patient with ALI. Within the past decade, substantial information has become available regarding this technique. Clearly, PLV is feasible in patients with ALI and ARDS, and it appears to be safe with respect to short-term effects on hemodynamics and lung physiology, as well as long-term toxicity (although further research in this area is warranted). Although PLV has not yet been proven to be superior to traditional mechanical ventilation for patients with ALI or ARDS, PLV possesses an intriguing combination of physical, physiologic, and biologic effects: "Liquid PEEP" effect--e.g., more effective recruitment of dependent lung zones than achieved by gas ventilation Anti-inflammatory effects Lavage of alveolar debris Mitigation of ventilator-induced lung injury Direct anti-inflammatory effects--e.g., decreased macrophage release of proinflammatory cytokines, etc. Prevention of nosocomial pneumonia Combination with other modalities--e.g., exogenous surfactant replacement, inhaled NO, prone position Enhanced delivery of drugs or gene vectors into the lung. The results of ongoing and future clinical trials will be necessary to establish whether PLV improves clinical outcomes in patients with ALI or ARDS, or specific subgroups of such patients. Significant work also remains to be done to define the optimum dose level of PLV and the most appropriate ventilatory strategies.

Partial liquid ventilation shows dose-dependent increase in oxygenation with PEEP and decreases lung injury associated with mechanical ventilation

PURPOSE

The purpose of this article is to evaluate the effect of positive end-expiratory pressure (PEEP) during partial liquid ventilation (PLV) and to investigate if lung damage associated with mechanical ventilation can be reduced by PLV.

MATERIALS AND METHODS

Twenty-two New-Zealand white rabbits were ventilated in pressure-controlled mode maintaining constant tidal volume (10 mL/kg). Lung injury was induced by repeated saline lavage (PaO2 < 100 mm Hg). Two incremental PEEP steps maneuvers (IPSMs) from 2 to 10 cm H2O in 2 cm H2O steps were performed sequentially. The control group received the first IPSM in the supine position and were turned prone for the second IPSM. In the PLV group (n = 7), 12 mL/kg of perfluorodecalin was instilled after lung injury before the two IPSMs. The early prone group (n = 7) received both IPSMs in the prone position. Parameters of gas exchange, lung mechanics, and hemodynamics as well as pathology were examined.

RESULTS

During the first IPSM, the PLV group showed a significant increase in PaO2 after instillation of perfluorodecalin (P < .05) and then showed a dose-dependent increase in PaO2 with PEER. The control and EP groups showed improvement in PaO2 only at higher PEEP, eventually showing no intergroup differences at PEEP of 10 cm H2O. During the second IPSM only the PLV group retained its ability to increase PaO2 to the level obtained during the first IPSM (P < .05 compared with control and EP groups). During the first IPSM all three groups showed increasing trend in static compliance (Cst) with PEEP peaking at PEEP of 8 cm H2O. During the second IPSM, only the PLV group showed increase in static compliance with PEEP (P < .05 compared with other groups). Lung histology revealed significantly less hyaline membrane formation in the PLV group (P < .05).

CONCLUSION

PLV shows dose-dependent increase in oxygenation with PEEP and may reduce lung damage associated with mechanical ventilation.

Partial liquid ventilation ventilates better than gas ventilation

Partial liquid ventilation (PLV) improves oxygenation in several models of lung injury. However, PLV has only been compared with conventional gas ventilation (GV) with low PEEP. Both PLV and GV can markedly improve oxygenation when PEEP is set above the lower corner pressure (Plc) on the inspiratory pressure-volume (P-V) curve of the total respiratory system. We questioned if the use of PEEP set above the Plc during PLV and GV would result in similar gas exchange. Lung injury was induced in 12 sheep by saline lavage before randomization to PLV (n = 6) or GV (n = 6). Animals in the PLV group were filled with perflubron (22 ml/kg) until a meniscus at the teeth was observed. Both groups were then ventilated with pressure control (FI(O(2)), 1.0; rate, 20/min; I:E, 1:1) and PEEP (1 cm H(2)O above the Plc on the inspiratory P-V curve). Peak inspiratory pressure (PIP) was limited to 35 cm H(2)O. Animals were ventilated for 5 h and then killed for histologic examinations. All 12 animals survived the 5-h ventilation period. After increasing PEEP above Plc, Pa(O(2)) increased significantly (p < 0.01) in both the GV and the PLV groups, but it did not differ significantly between groups (p = 0.86) at any time during the experiment. Pa(CO(2)) and VD/VT in GV increased markedly throughout the experiment after increasing PEEP (p < 0.001), but there was no significant change in Pa(CO(2)) in PLV (p = 0.13). Mean arterial blood pressure, mean pulmonary artery pressure, pulmonary artery occlusion pressure, and central venous pressure, increased and SVR decreased in GV (p < 0.05). The extent and the severity of lung injury in the dependent regions was greater in the GV group (p < 0.05). Both PLV and GV improved oxygenation, but PLV resulted in better ventilation than GV while preserving lung structure when PEEP was set 1 cm H(2)O above the Plc and PIP limited to 35 cm H(2)O.

Effect of partial liquid ventilation on pulmonary vascular permeability and edema after experimental acute lung injury

We evaluated the effects of partial liquid ventilation (PLV) with two different dosages of the perfluorocarbon LiquiVent (perflubron) on pulmonary vascular permeability and edema formation after oleic acid (OA)-induced acute lung injury in dogs. We used imaging with positron emission tomography to measure fractional pulmonary blood flow, lung water concentration (LWC), and the pulmonary transcapillary escape rate (PTCER) of (68)Ga-labeled transferrin at 5 and 21 h after lung injury in five dogs undergoing conventional mechanical ventilation (CMV), five dogs undergoing low-dose PLV (perflubron at 10 ml/kg), and four dogs undergoing high dose PLV (perflubron at 30 ml/kg). A positive end-expiratory pressure of 7.5 cm H(2)O was used in all dogs. After OA (0.08 ml/kg)- induced lung injury, there were no significant differences or trends for PTCER or LWC at any time when the PLV groups were compared with the CMV group. However, lung tissue myeloperoxidase activity was significantly lower in the combined PLV group than in the CMV group (p = 0.016). We conclude that after OA-induced lung injury, the addition of PLV to CMV does not directly attenuate pulmonary vascular leak or lung water accumulation. Rather, the benefits of such treatment may be due to modifications of the inflammatory response.

Effects of partial liquid ventilation on regional pulmonary blood flow distribution of isolated rabbit lungs

OBJECTIVE

Partial liquid ventilation with perfluorocarbons may increase alveolar hydrostatic transmural pressure and may result in a redistribution of pulmonary blood flow from dependent to nondependent lung regions. To test this hypothesis under controlled study conditions, we determined intrapulmonary blood flow distributions during gas and perfluorocarbon ventilation in isolated rabbit lungs.

DESIGN

Controlled animal study with an ex vivo isolated lung preparation.

SETTING

Research laboratory for Experimental Anesthesiology at the Heinrich-Heine-University of Düsseldorf.

SUBJECTS

New Zealand White rabbits.

INTERVENTIONS

The lungs were perfused with autologous blood at constant flow (150 mL/min) and ventilated with 5% C(O2) in air (positive end-expiratory pressure, 2 cm H2O; tidal volume, 10 mL/kg body weight; respiratory rate, 30 breaths/ min) without and with perfluorocarbon administered intratracheally (15 mL/kg).

MEASUREMENTS AND MAIN RESULTS

Regional lung perfusion was measured with colored microspheres in apical, central, peripheral, and basal samples before and after bronchial instillation of perfluorocarbons. Compared with gas ventilation, intrapulmonary blood flow during perfluorocarbon ventilation was higher in apical samples (49.4+/-8.6 mL/min/g vs. 38.3+/-6.8 mL/min/g dry weight; p = .03) and lower in basal samples (22.2+/-5.1 mL/min/g vs. 39.9+/-8.2 mL/min/g; p = .04).

CONCLUSIONS

Our findings suggest that during partial liquid ventilation, intrapulmonary blood flow is redistributed toward less-dependent lung regions. (Crit Care Med 2000; 28:1522-1525)

Dynamics of breathing during partial liquid ventilation in spontaneously breathing rabbits supported by elastic and resistive unloading

Partial liquid ventilation (PLV) has been shown to improve gas exchange in paralyzed animals and in humans with lung disease. This study tests the hypothesis that PLV combined with respiratory mechanical unloading results in stable ventilation and gas exchange in spontaneously breathing animals. Ten adult anesthetized, intubated, and spontaneously breathing rabbits received ventilatory support by respiratory mechanical unloading (Fi(O2) 1.0). Minute ventilation, respiratory rate, esophageal pressure, heart rate, and arterial blood pressure were recorded continuously during gas ventilation for 1 h. Next, 30 mL/kg of perfluorocarbon was instilled into the endotracheal tube. Thereafter, data were recorded again for 1 h (PLV). Arterial blood gases were obtained at the end of each period. Variability of recorded data was assessed by calculating coefficients of variation using data obtained each minute. Compared with gas ventilation, minute ventilation was larger during PLV (275 +/- 93 versus 368 +/- 89 mL/kg/min.; p < 0.01). This was because of a higher respiratory rate during PLV (58 +/- 23 versus 74 +/- 18 breaths/min; p < 0.05), while tidal volume was similar. Compared with gas ventilation, Pa(O2) was lower during PLV (61.31 +/- 5.32 versus 47.35 +/- 8.38 kPa; p < 0.05). Pa(CO2), peak esophageal pressure deflections, heart rate, mean arterial blood pressure, and coefficients of variation for minute ventilation, tidal volume, respiratory rate, and peak esophageal pressure were not significantly different between modes. Compliance was decreased and resistance and work of breathing were increased during PLV. We conclude that stable ventilation and gas exchange may be achieved during PLV combined with mechanical unloading in spontaneously breathing animals without lung disease.

The relationship between gas delivery patterns and the lower inflection point of the pressure-volume curve during partial liquid ventilation

STUDY QUESTION

To determine whether a positive end-expiratory pressure (PEEP) level equivalent to the lower inflection point (LIP) could be identified by evaluation of the airway pressure, flow (f1. gif" BORDER="0">), and volume vs time waveforms during partial liquid ventilation (PLV).

DESIGN

Prospective application of PEEP during PLV in a healthy animal model.

SETTING

University hospital animal laboratory.

PARTICIPANTS

Five healthy sheep weighing 30 kg each.

INTERVENTIONS

The sequential application of 0 to 20 cm H(2)O PEEP in 2.5-cm H(2)O steps during PLV with both pressure and volume ventilation.

MEASUREMENTS

Analysis of the pressure, volume, and f1. gif" BORDER="0"> waveforms as PEEP is sequentially increased.

RESULTS

At 0 cm H(2)O PEEP, VT was markedly reduced compared with PEEP VT at > or = 7.5 cm H(2)O (p < 0.05) in pressure control ventilation (PCV), and peak inspiratory pressure minus PEEP was markedly increased compared with PEEP at > or = 5.0 cm H(2)O (p < 0.05) in volume control ventilation. At 10 cm H(2)O PEEP, all waveforms began to stabilize, and no significant differences in any variable assessed were measured at > 12.5 cm H(2)O PEEP.

CONCLUSIONS

The application of PEEP during PLV markedly alters airway waveforms. Low PEEP decreases VT in PCV and increases airway pressure in VCV. The PEEP level equal to the LIP during PLV can be grossly estimated from airway waveforms. PEEP at > or = 10 cm H(2)O is needed to normalize gas delivery to functional residual capacity in the uninjured lung that is partially filled with perfluorocarbon.

Does perfluorocarbon deoxygenate during partial liquid ventilation?

Perfluorocarbons accumulate in the dependent regions of the lungs, which may result in regional hypoxia if ventilation with oxygen is insufficient to oxygenate the dependent perfluorocarbon-filled alveoli. In this issue of Critical Care, Max et al present data that demonstrate a decrease in arterial oxygen tension (PaO2) at 30 min compared to that observed at 5 min after administration of FC 3280. These data suggest failure of on-going ventilation/oxygenation to support the initial increase in PaO2 attributed to the oxygen dissolved in the administered perfluorocarbon. Studies such as this one demonstrate that development of the optimal partial liquid ventilation (PLV) technique is ongoing.

Partial liquid ventilation with and without inhaled nitric oxide in a newborn piglet model of meconium aspiration

The object of this study was to determine the effects of partial liquid ventilation (PLV) with and without inhaled nitric oxide (NO) over a 4-h period on lung mechanics, gas exchange, and hemodynamics in an animal model of meconium aspiration syndrome (MAS). Twenty-four fentanyl-anesthetized piglets were instrumented and administered a slurry of human meconium to create a model with hypoxia, hypercarbia, acidosis, and pulmonary hypertension. They were then randomly assigned to conventional ventilation, conventional ventilation plus inhaled NO at 40 ppm, PLV using perfluorodecalin, or PLV plus inhaled NO. The perfluorocarbon was added until a meniscus was visible in the endotracheal tube during expiration. Hemodynamics, lung mechanics, and gas exchange were monitored for 4 h, and then the animals were killed. The conventionally ventilated animals continued to deteriorate, and three of the six died prior to 4 h. All the animals in the remaining groups survived. Oxygenation improved significantly immediately with the start of inhaled NO (from 43.8 SD 10.3 to 62.6 SD 11.7 mm Hg after 30 min) and stayed elevated compared with the control group for the remainder of the study (62.4 SD 21.8 mm Hg at 4 h compared with 44.9 SD 1.6 mm Hg for the control group, p < 0.05). Oxygenation improved more slowly in the PLV alone group, being slightly less than control at 30 min (p = NS) but increasing to 104 SD 34.9 after 4 h (p < 0.01 compared with the control group), at which time it was also greater than inhaled NO alone (p < 0.05). The combined group had an acute increase in oxygenation indistinguishable from the NO alone group and maintained this until the end of the study. Lung compliance was unaffected in the inhaled NO group. In both the liquid ventilation groups the lung compliance improved with the instillation of perfluorodecalin (from 0.46 SD 0.18 to 0.62 SD 0.09 ml/cm H(2)O/kg in the PLV alone group at 1 h, p < 0.05 compared with the control group) and remained stable for the remainder of the study. Cardiac output and pulmonary vascular resistance were not significantly affected by any of the treatments. It was concluded that in this animal model of MAS, inhaled NO led to an acute improvement in gas exchange and prolonged survival compared with conventional therapy. PLV improved lung mechanics, which was maintained over the course of the study. The combination of PLV and inhaled NO produced both effects, acutely improving both gas exchange and lung mechanics. Combined therapy with PLV and inhaled NO may have benefits in the MAS.

The effect of varying inspiratory to expiratory ratio on gas exchange in partial liquid ventilation

BACKGROUND

In partial liquid ventilation (PLV), the nondependent lung was observed to be inflated first and the dependent lung later. The inflational time difference between the lung regions can lead to maldistribution of tidal gas and inefficient gas bubbling in the slow-inflating region during PLV. In this situation, increasing the inspiratory to expiratory (I:E) ratio of the mechanical ventilator would lessen the heterogeneity of regional ventilation and improve gas exchange possibly to a greater degree than in gas ventilation (GV).

DESIGN AND SETTING

Animal study at the Asan Institute for Life Sciences, Seoul, Korea Subjects: Eighteen rabbits (2.6 +/- 0.5 kg) with acute lung injury by saline solution lavage.

INTERVENTIONS

Three I:E ratios were tried in GV and then in PLV. I:E ratios were changed by adjusting pause (1:2, 1:1, and 2:1; group 1) or by adjusting inspiratory flow rate (1:3, 1:1, and 2:1; group 2).

MEASUREMENTS AND RESULTS

With increasing I:E ratio in all animals, PaO(2)/FIO(2) increased (80 +/- 24, 143 +/- 74, and 147 +/- 88 mm Hg; p = 0.001), and PaCO(2) decreased (74 +/- 15, 66 +/- 16, and 66 +/- 15 mm Hg; p = 0.006). The increases of PaO(2)/FIO(2) from 1:2/1:3 to 1:1 (p = 0.006) and from 1:1 to 2:1 (p = 0.036) were both greater in group 1 than in group 2. PaCO(2) decreased with increasing I:E ratio in group 1, but not in group 2. The change of PaO(2)/FIO(2) by varying the I:E ratio was 49 +/- 65% in PLV and 14 +/- 14% in GV (p = 0.003).

CONCLUSIONS

Extending the I:E ratio, especially by adding pause, improved gas exchange in PLV. Oxygenation in PLV was affected by the I:E ratio to a greater degree than in GV.

Respiratory failure: current status of experimental therapies

A number of advances in the treatment of infants and children with respiratory failure have been investigated in the laboratory with translation to clinical practice. Investigators have recognized that application of high ventilating pressures and failure to apply adequate levels of positive end-expiratory pressure (PEEP) can inflict injury to the already failing lung. Other interventions such as prone positioning and application of new ventilating strategies such as proportional assist ventilation (PAV), inverse ratio ventilation (IRV), high frequency ventilation, liquid ventilation, and intratracheal pulmonary ventilation (ITPV), continue to be developed and explored. Administration of inhaled nitric oxide (iNO) may improve pulmonary physiology and gas exchange in patients with respiratory insufficiency. Finally, the technique of extracorporeal life support (ECLS) is being simplified and refined. This report summarizes the status of these advances and describes the basic science and clinical research that brought them to clinical application.

Newer ventilatory strategies

Over the past year a large number of innovations in mechanical ventilation have been evaluated. Three of the most exciting are non-invasive positive pressure ventilation, tracheal gas insufflation and partial liquid ventilation. Non-invasive positive pressure ventilation is now clearly a standard of care in the management of an acute exacerbation of chronic obstructive pulmonary disease. In addition, its use in other clinical settings is being actively explored. Tracheal gas insufflation appears to be a useful adjunct to mechanical ventilation for the management of carbon dioxide but requires manufacturer-designed devices for safe application. The effects of partial liquid ventilation on lung injury have been more clearly defined in the past year as well as approaches to provide gas ventilation during partial liquid ventilation.