An optimal dose of perfluorocarbon for respiratory mechanics in partial liquid ventilation for dependent lung-dominant acute lung injury

Perfluorocarbons: A perspective of theranostic applications and challenges

Perfluorocarbon (PFC) are biocompatible compounds, chemically and biologically inert, and lacks toxicity as oxygen carriers. PFCs nanoemulsions and nanoparticles (NPs) are highly used in diagnostic imaging and enable novel imaging technology in clinical imaging modalities to notice and image pathological and physiological alterations. Therapeutics with PFCs such as the innovative approach to preventing thrombus formation, PFC nanodroplets utilized in ultrasonic medication delivery in arthritis, or PFC-based NPs such as Perfluortributylamine (PFTBA), Pentafluorophenyl (PFP), Perfluorohexan (PFH), Perfluorooctyl bromide (PFOB), and others, recently become renowned for oxygenating tumors and enhancing the effects of anticancer treatments as oxygen carriers for tumor hypoxia. In this review, we will discuss the recent advancements that have been made in PFC's applications in theranostic (therapeutics and diagnostics) as well as assess the benefits and drawbacks of these applications.

Semi-fluorinated alkanes as carriers for drug targeting in acute respiratory failure

Partial liquid ventilation (PLV) with perfluorocarbons may cause pulmonary recruitment in acute lung injury (ALI). Semi-fluorinated alkanes (SFAs) provide biochemical properties similar to perfluorocarbons. Additionally, SFAs are characterized by increased lipophilicity. Therefore, SFA-PLV may be considered for deposition of certain therapeutic drugs into atelectatic lung areas. In this experimental study SFA-PLV was evaluated to demonstrate feasibility, pulmonary recruitment, and efficacy of drug deposition. Feasibility of SFA-PLV was determined in pigs with and without experimental ALI. Animals were randomized to PLV with SFAs up to a cumulative amount of 30 mL x kg⁻¹ or to conventional mechanical ventilation. Pulmonary recruitment effects were determined by analyzing ventilation-perfusion distributions. Efficacy of intrapulmonary drug deposition was evaluated in further experiments by measuring drug serum concentrations in the course of PLV with SFA-dissolved α-tocopherol and ibuprofen. Increasing SFA doses caused progressive reduction of intrapulmonary shunt in animals with ALI, indicating pulmonary recruitment. PLV with SFA-dissolved α-tocopherol had no effect on serum levels of α-tocopherol, whereas PLV with SFA-dissolved ibuprofen caused a rapid increase of serum levels of ibuprofen. The authors conclude that SFA-PLV is feasible and causes pulmonary recruitment in ALI. Effectiveness of drug deposition in the lung obviously depends on the partitioning drugs out of the SFA phase into blood.

Effects of perfluorochemical evaporative properties on oxygenation during partial liquid ventilation

BACKGROUND

The physical-chemical properties of perfluorochemical (PFC) liquids have been shown to influence physiological and cellular responses during partial liquid ventilation (PLV). The aim of this study is to compare the relationship between patho-physiological endpoints and the physical properties of three PFC liquids used in treating acute lung injury.

METHODS

A total of 18 juvenile rabbits were randomized into conventional mechanical ventilation or PLV groups after lung saline lavages. Three PFC liquids, including Flutec perfluoro-1,3,5-trimethylcyclohexane (PP4; vapor pressure, 28.8 mmHg at 37 degrees C), Perfluorodecalin (PFD; vapor pressure, 13.6 mmHg at 37 degrees C), and Perflubron (PFB; vapor pressure, 10.4 mmHg at 37 degrees C) were used for PLV with no replacement for 4 h. A thermal detector was used to measure PFC loss rate. Physiological measurements and evaporative loss rate of PFC were done every 30 min, and lung histology was examined.

RESULTS

The mean evaporative loss rate was significantly higher in the PP4 group (4.75 +/- 0.24 mL/kg per h) than in either the PFD (1.43 +/- 0.11 mL/kg per h) or the PFB (1.18 +/- 0.05 mL/kg per h) group (P < 0.05). The oxygenation of PFD and PFB was maintained good for 4 h, however, the PP4 group showed a fast deterioration since 2 h post-treatment due to fast dropping of the residual PP4 amount in lungs. Histology showed good alveolar integrity in the PFD and PFB groups.

CONCLUSIONS

The effects of PLV are directly influenced by the evaporative property of the PFC liquid. With no replacement over 4 h, PLV effects could be maintained with utilizing a PFC liquid with low, rather than high, vapor pressure. PFC with high vapor pressure has a high loss rate and low residual volume that causes poor maintenance on oxygenation during PLV. Therefore, measuring PFC loss rate is important in future studies and clinical application of PLV.

Cold perfluorochemical-induced hypothermia protects lung integrity in normal rabbits

To test the hypothesis that intrapulmonary perfluorochemical (PFC) liquid may induce hypothermia, and to compare the effects of internal (IC), external (EC), and combined cooling techniques (EC + IC), 14 juvenile rabbits were randomized to EC by a cold blanket (4 degrees C, n = 5), IC by intrapulmonary cold PFC liquid lavage (4 degrees C, n = 5), or combined IC with PFC and EC (n = 4). Arterial blood gas, blood pressure, and lung mechanics were monitored, and lung histology was examined by light microscopy. The results showed that cooling rates and the time needed to be cooled down to 30 degrees C were significantly faster in EC and EC + IC than IC (p < 0.05). Blood gas analysis and cardiopulmonary function were within the normal range in all groups. Histological assessment revealed varied atelectasis in all lung regions in EC, whereas PFC-filled lungs (IC and EC + IC) demonstrated more homogenous expansion and no evidence of atelectasis. The results indicate that intrapulmonary PFC may be an effective technique to induce and/or augment hypothermia while supporting gas exchange, lung volume and pulmonary architecture.

Effects of partial liquid ventilation on lipopolysaccharide-induced inflammatory responses in rats

To determine whether partial liquid ventilation (PLV) modified lung inflammatory response, we analyzed blood cytokine levels and cytokine mRNA expression in the lungs, using a rat model of endotoxemia. Thirty-six rats were allocated into one of four groups. The first group received conventional gas ventilation (CV group), the second group received 10 ml/kg perflubron intratracheally in combination with mechanical gas ventilation (PLV group), the third group received 20 mg/kg Escherichia coli lipopolyssacharide (LPS) intravenously in combination with mechanical gas ventilation (LPS group), and the fourth group received PLV and LPS (PLV + LPS group). Blood levels of TNF-alpha, IL-1beta, IL-6, IL-10, INF-gamma and IL-1 receptor antagonist were significantly increased in LPS and PLV + LPS groups. mRNA expression of pro- and anti-inflammatory cytokines in the lung tissue was also significantly increased in these groups. mRNA expression of IL-6 in PLV + LPS group was significantly increased in comparison with LPS group. Other cytokine mRNA expression including IL-10 and IL-1beta was also potentiated in PLV + LPS group, however this was not significant. Our results suggest that PLV does not protect the lungs against inflammation in systemic endotoxemia in rats.

Vascular reactivity of pulmonary arteries from premature lambs subjected to liquid ventilation

This study aimed to evaluate the effect of tidal liquid ventilation (TLV) and liquid assisted high frequency oscillatory ventilation (LA-HFOV) on the contractile and relaxing properties of fetal ovine pulmonary arteries. 0.85 term lambs were subjected, after surfactant instillation, to 5 h of TLV or LA-HFOV (5 ml.kg(-1) perfluorocarbon liquid). After euthanasia of the animals, intrapulmonary arteries (fourth branch) were dissected and mounted in a myograph for isometric tension recording. Arteries from unventilated age-matched fetuses were also studied. The contractions induced by K(+), and the thromboxane A(2) mimetic U46619 were not significantly different in the TLV and the LA-HFOV groups. Acetylcholine-induced relaxation was absent after TLV and LA-HFOV but present in unventilated animals. Sodium nitroprusside-induced relaxation was also similar after TLV and LA-HFOV, but reduced when the two groups were compared with unventilated fetuses. We conclude that after TLV and LA-HFOV the pulmonary arterial responses to receptor- and non receptor-mediated contraction and to endothelium-dependent and -independent relaxation were similar.

Partial liquid ventilation with perfluorodecalin following unilateral canine lung allotransplantation in non–heart-heating donors

BACKGROUND

The purpose of this study was to evaluate canine lungs obtained from non-heart-beating donors after unilateral lung transplantation subjected to partial liquid ventilation with perfluorodecalin.

METHODS

Twelve donor dogs were killed and kept under mechanical ventilation for 3 hours. Heart-lung blocks were harvested after retrograde pulmonary hypothermic flush with Perfadex. Left lung grafts were randomly transplanted into 12 weight-matched recipient animals. Animals were divided into 2 groups: control (standard mechanical ventilation, n = 6) and PLV (partial liquid ventilation, n = 6). Forty-five minutes after transplantation, the animals in the PLV group received perfluorodecalin (15 ml/kg) via orotracheal tube. All animals received volume-controlled ventilation (FIO2) 1.0, PEEP 5 cm H(2)O) over 6 consecutive hours. Thereafter, blood-gas analysis, ventilatory mechanics and hemodynamics were registered at 30-minute intervals. After 6 hours of reperfusion the animals were killed and the transplanted lungs were extracted to obtain the wet/dry weight ratio.

RESULTS

There were significant differences in pulmonary arterial pressure, which were higher in control group animals (p < 0.009). The control animals also showed higher arterial PaO(2) than those in the PLV group (p < 0.00001), but lower PaCO(2) (p < 0.008). The peak and plateau pressures were higher in the PLV group (p < 0.00001). Neither static compliance nor wet/dry weight ratios were different in between groups.

CONCLUSIONS

PLV with perfluorodecalin yields functional results compatible with life in this model. Nonetheless, pulmonary gas exchange and mechanics were superior after reperfusion in animals given conventional mechanical ventilation up to 6 hours after left lung allotransplantation.

Perfluorochemical (PFC) combinations for acute lung injury: an in vitro and in vivo study in juvenile rabbits

Perfluorochemical (PFC) fluids of different physical properties were titrated and tested in vitro for physical properties that are appropriate for respiratory application. Two PFC liquids were studied: perfluoromethylcyclohexane (PP2), a liquid with high vapor pressure and low viscosity, and perfluoromethyldecalin (PP9), a fluid with low vapor pressure and high viscosity. Eighteen rabbits (2.05 +/- 0.07 kg; mean +/- SEM) were lung-lavaged and randomized: group I, control group; group II, partial liquid ventilation with 75% PP2 and 25% PP9; group III, partial liquid ventilation with 50% PP2 and 50% PP9; and group IV, partial liquid ventilation with 25% PP2 and 75% PP9. Ventilator volumes were kept constant during the 4-h experiment. Cardiopulmonary measurements were performed every 30 min. The lung histology was examined. The in vitro study showed PFC [viscosity/vapor pressure (in cS and mm Hg, respectively)] as follows: 100% PP2 (0.88/141); 100% PP9 (3.32/2.9); 75% PP2 and 25% PP9 (1.26/107); 50% PP2 and 50% PP9 (1.63/13.7); and 25% PP2 and 75% PP9 (2.21/4.4). The in vivo experiments found that combinations of moderate vapor pressure (groups 3 and 4) demonstrated good gas exchange, compliance, and histologic findings. Thus, combinations of PFC liquids can be formulated to modulate the physiologic outcome in acutely injured lungs, and may prove useful for alternative PFC liquid applications.

Partial liquid ventilation: Effect of initial dose and redosing strategy in acute lung injury

OBJECTIVE: Partial liquid ventilation (PLV) with perfluorochemicals has been shown to be effective in treating acute respiratory failure in animal studies and human trials. To determine the influences of perfluorochemicals on initial dose and redosing strategy, we studied their effects on gas exchange, pulmonary mechanics, and lung architecture. DESIGN: After lung injury was induced by repeated warm saline lavages, the animals were instilled endotracheally with different doses of perflubron during 5-10 mins in PLV-treated groups. The animals were randomized to five groups: PLV-12S (12 mL/kg perflubron, single dose), PLV-12M (12 mL/kg perflubron, multiple replacement doses), PLV-18S (18 mL/kg perflubron, single dose), PLV-18M (18 mL/kg perflubron, multiple replacement doses), and the control group (conventional mechanical ventilation only). Ventilator settings were kept constant during the 4-hr experiment. SETTING: An animal laboratory affiliated with Temple University School of Medicine. SUBJECTS: Twenty-eight New Zealand White juvenile rabbits (weight, 1.96 +/- 0.03 kg). INTERVENTIONS: Physiologic data were recorded every 30 mins. A constant volume (1.3 mL/kg/hr) of perflubron was replaced hourly in the PLV-12M and PLV-18M groups. The perflubron in the expired gas was measured with a thermal detector device. The hourly evaporative loss rate and the estimated residual perfluorochemical amount were calculated and analyzed. Histologic examinations of the lungs were performed. MEASUREMENTS AND MAIN RESULTS: All animals in the PLV-treated groups (PLV-12S, n = 4; PLV-12M, n = 5, PLV-18S, n = 5; PLV-18M, n = 4) demonstrated improvements in gas exchange and respiratory compliance that were significantly (p <.05) better than the control group (n = 8). However, the PLV-12S group demonstrated progressive deterioration after the initial improvement. The loss rate of perflubron did not differ among the PLV-treated groups (1.17 +/- 0.03 mL/kg/hr), but the residual perfluorochemical volume in the lungs decreased progressively and significantly in the PLV-12S and PLV-18S groups as a function of time (p <.05). Histologic examination showed good alveolar protection in the PLV-12M, PLV-18S, and PLV-18M groups. CONCLUSIONS: We conclude that the low initial dose (12 mL/kg, about two thirds the functional residual capacity volume of rabbits) of perflubron required hourly replacement to maintain the effects of PLV. With a high initial dose of 18 mL/kg perflubron (equal to a full functional residual capacity volume in rabbits), the responses are potentiated in both single and multiple dosing groups up to 4 hrs.

Aerosolized perfluorocarbon suppresses early pulmonary inflammatory response in a surfactant-depleted piglet model

The effect of new ventilation strategies on initial pulmonary inflammatory reaction was studied in a surfactant-depleted piglet model. Sixty minutes after induction of lung injury by bronchoalveolar lavage, piglets received either aerosolized FC77 (aerosol-PFC, 10 mL/kg/h, n = 5) or partial liquid ventilation (PLV) with FC77 at functional residual capacity volume (FRC-PLV, 30 mL/kg, n = 5), or at low volume (LV-PLV, 10 mL/kg per hour, n = 5), or intermittent mandatory ventilation (control, n = 5). After 2 h, perfluorocarbon application was stopped and intermittent mandatory ventilation continued for 6 h. After a total experimental period of 8 h, animals were killed and lung tissue obtained. mRNA expression of IL-1beta, IL-6, IL-8, and TGF-beta in porcine lung tissue was quantified using TaqMan real-time PCR and normalized to beta-actin (A) and hypoxanthine-guanine-phosphoribosyl-transferase (H). In the aerosol-PFC group, IL-1beta, IL-6, IL-8, and transforming growth factor (TGF)-beta mRNA expression in lung tissue was significantly lower than in the control group. Reduction was 95% for IL-1beta/H (p < 0.001), 73% for IL-6/H (p < 0.05), 87% for IL-8/H (p < 0.001), and 38% for TGF-beta/H (p < 0.01). A lower mRNA gene expression was also determined for IL-1beta and IL-8 when the aerosol-PFC group was compared with the LV-PLV group [91% for IL-1beta/H (p < 0.001), 75% for IL-8/H (p < 0.001)]. In the FRC-PLV group, mRNA expression of IL-1beta was significantly lower than in the control (p < 0.05) and LV-PLV (p < 0.01) group. In a surfactant-depleted piglet model, aerosol therapy with perfluorocarbon but not LV-PLV reduces the initial pulmonary inflammatory reaction at least as potently as PLV at FRC volume.

Effects of partial liquid ventilation with FC-77 on acute lung injury in newborn piglets

Partial liquid ventilation (PLV) with various types of perfluorochemicals (PFC) has been shown to be beneficial in treating acute lung injury. FC-77 is a type of PFC with relatively high vapor pressure and evaporative losses during PLV. This study tested the hypothesis that using FC-77 for PLV with hourly replacement is effective in treating acute lung injury. Fifteen neonatal piglets were randomly and evenly divided into 3 study groups: 1) lavage-induced lung injury followed by conventional mechanical ventilation (Lavage-CMV); 2) lavage-induced lung injury followed by PLV using FC-77 with hourly replacement (11.2 +/- 1.5 mL/kg/hr) (Lavage-PLV); and 3) sham lavage injury followed by conventional mechanical ventilation (Control). Immediately after induction, repeated saline lavages induced acute lung injury characterized by decreases in dynamic lung compliance, arterial oxygen tension, and arterial pH, and increases in arterial CO(2) tension and oxygenation index, whereas the sham lavage procedure failed to do so. During the 3-hr period of CMV, these pulmonary and cardiovascular parameters remained stable in the Control group, but deteriorated in the Lavage-CMV group. In contrast, after acute lung injury, low lung compliance, abnormal gas exchange, acidosis, and inadequate oxygenation significantly improved in the Lavage-PLV group. Histological analysis of these 3 study groups revealed that the Lavage-CMV group had the highest lung injury score and the Control group had the lowest. These results suggest that, in comparison to CMV, PLV with FC-77 and hourly replacement of FC-77 promotes more favorable pulmonary mechanics, gas exchange, oxygenation, and lung histology in a piglet model of acute lung injury.

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.

Surfactant and partial liquid ventilation via conventional and high-frequency techniques in an animal model of respiratory distress syndrome

OBJECTIVE: To compare the physiologic and pathologic effects of conventional ventilation (CV) and high-frequency ventilation (HFV) during partial liquid ventilation (PLV) with perflubron after surfactant treatment with the results of HFV plus surfactant in an animal lung-injury model created by saline lavage. We also studied the dose effects of perflubron during HFV. DESIGN: Randomized experimental study. SETTING: Research animal laboratory. SUBJECTS: A total of 32 newborn piglets. INTERVENTIONS: After lung injury was induced, the animals were randomized to one of four groups: a) CV + surfactant + perflubron to functional residual capacity (FRC); b) HFV + surfactant + perflubron to FRC; c) HFV + surfactant + 10 mL/kg perflubron; and d) HFV + surfactant. All then received intratracheal surfactant. After 30 mins, perflubron was administered to the PLV groups. The animals underwent ventilation for 20 hrs. MEASUREMENTS AND MAIN RESULTS: Arterial blood gases and hemodynamic variables were continuously monitored. Pulmonary histologic and morphometric analyses were performed after death or euthanasia at 20 hrs. All animals had sustained improvements in arterial/alveolar oxygen ratios, and no differences were observed among groups. All HFV groups required higher mean airway pressures to maintain oxygenation (p <.05). Hemodynamics did not differ among groups. Pathologic analysis demonstrated decreased lung injury in both cranial-dorsal (nondependent) and caudal-ventral (dependent) lobes of all animals treated with PLV when compared with those treated with HFV + surfactant (p <.05). CONCLUSIONS: After surfactant treatment, physiologic support over 20 hrs was similar during HFV with or without perflubron and CV with perflubron. All PLV modalities improved lung pathologic factors uniformly to a greater degree than did HFV + surfactant. A lower treatment volume of perflubron during HFV produced physiologic and pathologic results similar to those produced by perflubron with respect to FRC during either CV or HFV.