Efficacy of inhaled nitric oxide in oleic acid-induced acute lung injury

A long-lasting porcine model of ARDS caused by pneumonia and ventilator-induced lung injury

BACKGROUND

Animal models of acute respiratory distress syndrome (ARDS) do not completely resemble human ARDS, struggling translational research. We aimed to characterize a porcine model of ARDS induced by pneumonia-the most common risk factor in humans-and analyze the additional effect of ventilator-induced lung injury (VILI).

METHODS

Bronchoscopy-guided instillation of a multidrug-resistant Pseudomonas aeruginosa strain was performed in ten healthy pigs. In six animals (pneumonia-with-VILI group), pulmonary damage was further increased by VILI applied 3 h before instillation and until ARDS was diagnosed by PaO2/FiO2 < 150 mmHg. Four animals (pneumonia-without-VILI group) were protectively ventilated 3 h before inoculum and thereafter. Gas exchange, respiratory mechanics, hemodynamics, microbiological studies and inflammatory markers were analyzed during the 96-h experiment. During necropsy, lobar samples were also analyzed.

RESULTS

All animals from pneumonia-with-VILI group reached Berlin criteria for ARDS diagnosis until the end of experiment. The mean duration under ARDS diagnosis was 46.8 ± 7.7 h; the lowest PaO2/FiO2 was 83 ± 5.45 mmHg. The group of pigs that were not subjected to VILI did not meet ARDS criteria, even when presenting with bilateral pneumonia. Animals developing ARDS presented hemodynamic instability as well as severe hypercapnia despite high-minute ventilation. Unlike the pneumonia-without-VILI group, the ARDS animals presented lower static compliance (p = 0.011) and increased pulmonary permeability (p = 0.013). The highest burden of P. aeruginosa was found at pneumonia diagnosis in all animals, as well as a high inflammatory response shown by a release of interleukin (IL)-6 and IL-8. At histological examination, only animals comprising the pneumonia-with-VILI group presented signs consistent with diffuse alveolar damage.

CONCLUSIONS

In conclusion, we established an accurate pulmonary sepsis-induced ARDS model.

Oxygenation and Lung Morphology in a Rabbit Pediatric ARDS- Model under High Peak Pressure Ventilation plus Nitric Oxide and Surfactant Compared with Veno-venous ECMO

The aim of the study is to investigate which of two treatment options of saline lavage induced ARDS in rabbits is better in terms of oxygenation and prevention of barotrauma: combined high peak pressure ventilation with surfactant administration and inhaled nitric oxide or veno-venous ECMO combined with low peak inspiratory pressure ventilation.

Materials and Methods

After saline lavage (10 cc/kg repeated as long as foamy retrieval was observed) two combined therapeutic strategies were examined: ventilation with high inspiratory pressures (35 cm H2O) with additional exogenous surfactant administration (100 mg/kg) and inhaled nitric oxide (10 PPM) (n=5, group 1) and low inspiratory pressure (20 cm H2O) ventilation under veno-venous ECMO support (n=5, group 2). The FiO2 was maintained at 1.0 in both groups. The paO2/FiO2 ratio was calculated in 30 minute intervals for 4 hours. After that the animals were sacrificed and the lungs examined macro- and microscopically. Aeration was described in a semiquantitative method using the alveolar expansion index. Oxygenation in group 1 was significantly better than in group 2, it increased significantly after surfactant but not after additional nitric oxide administration. However, the lungs in group 1 showed severe signs of baro/ergotrauma (Hyaline membranes, air leaks, infiltration of polymorphonuclear (PMN) granulocytes and macrophages, break down of alveolar capillary membranes) after 4 hrs of combined therapy, whereas the lungs in group 2 appeared normal. Adding surfactant and NO to a high tidal volume ventilation improved oxygenation, but did not prevent baro/ergotrauma. Ventilation with low inspiratory pressures combined with ECMO caused little baro/ergotrauma but adequate oxygenation could not be achieved, probably due to anatomical features of the rabbit which do not allow appropriate blood flow within the ECMO-circuit.

Gaseous therapeutics in acute lung injury

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) remain major causes of morbidity and mortality in critical care medicine despite advances in therapeutic modalities. ALI can be associated with sepsis, trauma, pharmaceutical or xenobiotic exposures, high oxygen therapy (hyperoxia), and mechanical ventilation. Of the small gas molecules (NO, CO, H₂S) that arise in human beings from endogenous enzymatic activities, the physiological significance of NO is well established, whereas that of CO or H₂S remains controversial. Recent studies have explored the potential efficacy of inhalation therapies using these small gas molecules in animal models of ALI. NO has vasoregulatory and redox-active properties and can function as a selective pulmonary vasodilator. Inhaled NO (iNO) has shown promise as a therapy in animal models of ALI including endotoxin challenge, ischemia/reperfusion (I/R) injury, and lung transplantation. CO, another diatomic gas, can exert cellular tissue protection through antiapoptotic, anti-inflammatory, and antiproliferative effects. CO has shown therapeutic potential in animal models of endotoxin challenge, oxidative lung injury, I/R injury, pulmonary fibrosis, ventilator-induced lung injury, and lung transplantation. H₂S, a third potential therapeutic gas, can induce hypometabolic states in mice and can confer both pro- and anti-inflammatory effects in rodent models of ALI and sepsis. Clinical studies have shown variable results for the efficacy of iNO in lung transplantation and failure for this therapy to improve mortality in ARDS patients. No clinical studies have been conducted with H₂S. The clinical efficacy of CO remains unclear and awaits further controlled clinical studies in transplantation and sepsis.

Large-animal models of acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is characterized by an acute inflammatory response that compromises alveolar-capillary membrane integrity. Clinical symptoms include refractory hypoxemia, noncardiogenic edema, and decreased lung compliance. The purpose of this review is to summarize the different ARDS large-animal models in terms of similarity to the clinical disease and underlying pathophysiology. The repeated lavage, oleic acid, endotoxin, and smoke/burn ARDS models will be discussed in this review. While each model has significant benefits, none is without weaknesses. Thus, the choice of large-animal ARDS model must be carefully considered based upon the study focus and investigative team experience.

Nonventilatory strategies for patients with life-threatening 2009 H1N1 influenza and severe respiratory failure

Severe respiratory failure (including acute lung injury and acute respiratory distress syndrome) caused by 2009 H1N1 influenza infection has been reported worldwide. Refractory hypoxemia is a common finding in these patients and can be challenging to manage. This review focuses on nonventilatory strategies in the advanced treatment of severe respiratory failure and refractory hypoxemia such as that seen in patients with severe acute respiratory distress syndrome attributable to 2009 H1N1 influenza. Specific modalities covered include conservative fluid management, prone positioning, inhaled nitric oxide, inhaled vasodilatory prostaglandins, and extracorporeal membrane oxygenation and life support. Pharmacologic strategies (including steroids) investigated for the treatment of severe respiratory failure are also reviewed.

Multiple-center, randomized, placebo-controlled, double-blind study of the nitric oxide synthase inhibitor 546C88: effect on survival in patients with septic shock

OBJECTIVE

To assess the safety and efficacy of the nitric oxide synthase inhibitor 546C88 in patients with septic shock. The predefined primary efficacy objective was survival at day 28.

DESIGN

Multiple-center, randomized, two-stage, double-blind, placebo-controlled, safety and efficacy study.

SETTING

A total of 124 intensive care units in Europe, North America, South America, South Africa, and Australasia.

PATIENTS

A total of 797 patients with septic shock diagnosed for <24 hrs.

INTERVENTIONS

Patients with septic shock were allocated to receive 546C88 or placebo (5% dextrose) for up to 7 days (stage 1) or 14 days (stage 2) in addition to conventional therapy. Study drug was initiated at 0.05 mL.kg(-1).hr(-1) (2.5 mg.kg(-1).hr(-1) 546C88) and titrated up to a maximum rate of 0.4 mL.kg(-1).hr(-1) to maintain mean arterial pressure between 70 and 90 mm Hg while attempting to withdraw concurrent vasopressors.

MEASUREMENTS AND MAIN RESULTS

Hemodynamic variables, organ function data, microbiological data, concomitant therapy, and adverse event data were recorded at baseline, throughout treatment, and at follow-up. The primary end point was day-28 survival. The trial was stopped early after review by the independent data safety monitoring board. Day-28 mortality was 59% (259/439) in the 546C88 group and 49% (174/358) in the placebo group (p <.001). The overall incidence of adverse events was similar in both groups, although a higher proportion of the events was considered possibly attributable to study drug in the 546C88 group. Most of the events accounting for the disparity between the groups were associated with the cardiovascular system (e.g., decreased cardiac output, pulmonary hypertension, systemic arterial hypertension, heart failure). The causes of death in the study were consistent with those expected in patients with septic shock, although there was a higher proportion of cardiovascular deaths and a lower incidence of deaths caused by multiple organ failure in the 546C88 group.

CONCLUSIONS

In this study, the nonselective nitric oxide synthase inhibitor 546C88 increased mortality in patients with septic shock.

Cardiovascular effects of the nitric oxide synthase inhibitor NG-methyl-l-arginine hydrochloride (546C88) in patients with septic shock: Results of a randomized, double-blind, placebo-controlled multicenter study (study no. 144-002)*

OBJECTIVE

To assess the hemodynamic effects of the nitric oxide synthase inhibitor 546C88 in patients with septic shock, although this was not a stated aim of the protocol. The predefined primary efficacy objective of the protocol was resolution of shock determined at the end of a 72-hr treatment period.

DESIGN

Multicentered, randomized, placebo-controlled, safety and efficacy study.

SETTING

Forty-eight intensive care units in Europe, North America, and Australia.

PATIENTS

A total of 312 patients with septic shock diagnosed within 24 hr before randomization.

INTERVENTIONS

Patients were randomly allocated to receive either 546C88 or placebo (5% dextrose) by intravenous infusion for up to 72 hrs. Conventional vasoactive therapy was restricted to norepinephrine, dopamine, and dobutamine. Study drug was initiated at 0.1 mL/kg/hr (5 mg/kg/hr 546C88) and titrated according to response up to a maximum rate of 0.4 mL/kg/hr with the objective to maintain mean arterial pressure at 70 mm Hg while attempting to withdraw any concurrent vasopressor(s).

MEASUREMENTS AND MAIN RESULTS

Requirement for vasopressors, systemic and pulmonary hemodynamics, indices of oxygen transport, and plasma concentrations of arginine and nitrate were assessed over time. The median mean arterial pressure for both groups was maintained > or =70 mm Hg. There was an early increase in systemic and pulmonary vascular tone and oxygen extraction, whereas both cardiac index and oxygen delivery decreased for patients in the 546C88 cohort. Although these parameters subsequently returned toward baseline values, the observed differences between the treatment groups, except for pulmonary vascular resistance and oxygen extraction, persisted throughout the treatment period, despite a reduced requirement for vasopressors in the 546C88 cohort. These changes were associated with a reduction in plasma nitrate concentrations, which were elevated in both groups before the start of therapy.

CONCLUSIONS

The nitric oxide synthase inhibitor 546C88 can reduce the elevated plasma nitrate concentrations observed in patients with septic shock. In this study, treatment with 546C88 for up to 72 hrs was associated with an increase in vascular tone and a reduction in both cardiac index and oxygen delivery. The successful maintenance of a target mean arterial blood pressure > or =70 mm Hg was achieved with a reduction in the requirement for, or withdrawal of, conventional inotropic vasoconstrictor agents (i.e., dopamine and norepinephrine). There were no substantive untoward consequences accompanying these hemodynamic effects. An international, randomized, double-blind, placebo-controlled phase III study has since been conducted in patients with septic shock. Recruitment into the study was discontinued due to the emergence of increased mortality in the 546C88-treated group.

Effect of position, nitric oxide, and almitrine on lung perfusion in a porcine model of acute lung injury

In a porcine model of oleic acid-induced lung injury, the effects of inhaled nitric oxide (iNO) and intravenous almitrine bismesylate (ivALM), which enhances the hypoxic pulmonary vasoconstriction on the distribution of regional pulmonary blood flow (PBF), were assessed. After injection of 0.12 ml/kg oleic acid, 20 anesthetized and mechanically ventilated piglets [weight of 25 +/- 2.6 (SD) kg] were randomly divided into four groups: supine position, prone position, and 10 ppm iNO for 40 min followed by 4 microg x kg(-1) x min(-1) ivALM for 40 min in supine position and in prone position. PBF was measured with positron emission tomography and H(2)15O. The redistribution of PBF was studied on a pixel-by-pixel basis. Positron emission tomography scans were performed before and then 120, 160, and 200 min after injury. With prone position alone, although PBF remained prevalent in the dorsal regions it was significantly redistributed toward the ventral regions (P < 0.001). A ventral redistribution of PBF was also obtained with iNO regardless of the position (P = 0.043). Adjunction of ivALM had no further effect on PBF redistribution. PP and iNO have an additive effect on ventral redistribution of PBF.

An animal model of response and nonresponse to inhaled nitric oxide in endotoxin-induced lung injury

STUDY OBJECTIVE

Oxygenation may be improved in 40 to 60% of ARDS patients by inhalation of nitric oxide (NO). We have studied the response to inhaled NO in porcine acute lung injury 4 h and 6 h after onset of a 2-h endotoxin infusion (30 microg/kg/h), hypothesizing that a responder may change to a nonresponder over time and with progression of lung injury.

DESIGN

Animal study.

SETTING

Experimental laboratory in a university hospital.

INTERVENTIONS AND MEASUREMENTS

We studied eight pigs under general anesthesia (mean weight, 26.2 kg) receiving mechanical ventilation adjusted to normocapnia, with a fraction of inspired oxygen (FIO(2)) of 0.5 to 1.0. Blood gases, endotoxin concentration, and central hemodynamics were measured hourly, and ventilation-perfusion (/) relationships were assessed by multiple inert gas elimination technique before and after inhalation of NO. NO was delivered at 40 ppm for 10 min at 4 h and 6 h of endotoxin exposure.

RESULTS

Seven of eight pigs were responders to NO at 4 h, defined as a > or = 20% increase in oxygenation index (PaO(2)/FIO(2)) [223 +/- 43 to 330 +/- 56 mm Hg; p = 0.001]. The same pigs exhibited a > or = 20% fall in mean pulmonary artery pressure (39.4 +/- 2.2 to 30.0 +/- 2.1 mm Hg; p < 0.001). The response correlated to the perfusion to "normal /" regions (r = - 0.82) and negatively to shunt and dead space ventilation (r = 0.76 and r = 0.87, respectively). At 6 h, seven of eight pigs were nonresponders, despite unaltered hemodynamics and gas exchange. Correlations at 4 h between physiologic variables and response to NO were abolished. The logarithmic SDs of the perfusion distribution, a measure of the degree of / mismatch, increased significantly from 4 to 6 h (p = 0.04).

CONCLUSION

Response to inhaled NO is abolished over time in endotoxin-induced ARDS pig lungs. The response seems to be related to the degree of / mismatch, which may indicate an important role of hypoxic pulmonary vasoconstriction.

Inhaled nitric oxide in the management of persistent pulmonary hypertension of the newborn: a meta-analysis

OBJECTIVES

To evaluate the use of inhaled nitric oxide (NO) in the management of persistent pulmonary hypertension of the newborn.

METHODS

Computerized bibliographic search on MEDLINE, CURRENT CONTENTS and LILACS covering the period from January 1990 to March 1998; review of references of all papers found on the subject. Only randomized clinical trials evaluating nitric oxide and conventional treatment were included. OUTCOMES STUDIED: death, requirement for extracorporeal membrane oxygenation (ECMO), systemic oxygenation, complications at the central nervous system and development of chronic pulmonary disease. The methodologic quality of the studies was evaluated by a quality score system, on a scale of 13 points.

RESULTS

For infants without congenital diaphragmatic hernia, inhaled NO did not change mortality (typical odds ratio: 1.04; 95% CI: 0.6 to 1.8); the need for ECMO was reduced (relative risk: 0.73; 95% CI: 0.60 to 0.90), and the oxygenation was improved (PaO2 by a mean of 53.3 mm Hg; 95% CI: 44.8 to 61.4; oxygenation index by a mean of -12.2; 95% CI: -14.1 to -9.9). For infants with congenital diaphragmatic hernia, mortality, requirement for ECMO, and oxygenation were not changed. For all infants, central nervous system complications and incidence of chronic pulmonary disease did not change.

CONCLUSIONS

Inhaled NO improves oxygenation and reduces requirement for ECMO only in newborns with persistent pulmonary hypertension who do not have diaphragmatic hernia. The risk of complications of the central nervous system and chronic pulmonary disease were not affected by inhaled NO.

Nitric oxide and nitrogen dioxide concentrations during in vitro high-frequency oscillatory ventilation

PURPOSE

The purpose of this study was to measure nitric oxide (NO) and nitrogen dioxide (NO2) concentrations, at various ventilatory settings and sampling sites, during in vitro inhaled NO and high-frequency oscillatory ventilation therapy [iNO-HFOV].

MATERIALS AND METHODS

We used a high-frequency oscillatory ventilator (model 3100A, SensorMedics, Yorba Linda, CA), a test lung (model VT-2A Ventilator Tester, Bio-Tek Instruments, Inc., Winooski, VT), nitric oxide delivery and NO/NO2 monitoring (Pulmonox II, Pulmonox, Tofield, Canada), and scavenging systems in this study. The ventilator frequency, amplitude, and inspired oxygen concentration were systematically changed at a fixed flow of NO. The concentrations of NO and NO2, sampled at four sites, were determined by an electrochemical method (Pulmonox II). The NO and NO2 concentrations were measured at the proximal part of the inspiratory limb (site 1), near the Y-piece (site 2), the carina of the test lung (site 3), and the bellows of the test lung (site 4).

RESULTS

The concentration of NO decreased significantly (P < .001) from the proximal port (site 11 of the inspiratory circuit (86.16 +/- 0.38 ppm) through the lung bellows (site 4) (70.08 +/- 0.23 ppm). The concentration of NO2 increased significantly (P < .001) from site 1 (3.25 +/- 0.04 ppm) through site 4 (19.4 +/- 0.19 ppm). However, the total concentration of NO + NO2 (NOx) remained unchanged at both site 1 and site 4. Increasing the frequency and amplitude of the ventilator significantly altered NO and NO2 concentrations. The NO2 concentration increased significantly (P < .0001) from 5.6 ppm to 18.1 ppm at site 4 when the fraction of inspired oxygen was increased from 0.25 to 0.93. The NO2 concentration also increased significantly (P < .0001) from 0.6 ppm to 18.7 when NO concentrations were independently increased from 12 ppm to 80 ppm.

CONCLUSIONS

During HFOV, the concentrations of NO and NO2 vary between sampling sites and also are influenced by the frequency, amplitude, and inspired oxygen concentration. NO2 concentrations in the lung were significantly increased above commonly accepted toxic concentrations during ventilation with high concentrations of NO (80 ppm) and high fractional concentrations of oxygen. The excessive increase in NO2 concentration at the "alveolar" level in our test lung model warrants confirmation in an in vivo model.

Influence of inhaled nitric oxide and hyperoxia on Na,K-ATPase expression and lung edema in newborn piglets

This study was undertaken to examine the combined effect of nitric oxide (NO) and hyperoxia on lung edema and Na,K-ATPase expression. Newborn piglets were exposed to room air (FiO2 = 0.21), room air plus 50 ppm NO, hyperoxia (FiO2 >/= 0.96) or to hyperoxia plus 50 ppm NO for 4-5 days. Animals exposed to NO in room air experienced only a slight decrease in Na,K-ATPase alpha subunit protein level. Hyperoxia, in the absence of NO, induced both the mRNA and the protein level of Na,K-ATP-ase alpha subunit and significantly increased wet lung weight, extravascular lung water, and alveolar permeability. NO in hyperoxia decreased the hyperoxic-mediated induction of Na,K-ATPase alpha subunit mRNA and protein while wet lung weight, extravascular lung water, and alveolar permeability remained elevated. These results suggest that 50 ppm of inhaled NO may not improve hyperoxic-induced lung injury and may interfere with the expression of Na,K-ATPase which constitutes a part of the cellular defense mechanism against oxygen toxicity.

Response to inhaled nitric oxide in acute lung injury depends on distribution of pulmonary blood flow prior to its administration

Responses to inhaled nitric oxide (iNO) in acute lung injury (ALI), as evidenced by improvements in oxygenation, are variable. We hypothesized that the effect of iNO may be related to the pre-iNO distribution of pulmonary blood flow (PBF). In the present study we evaluated the effect of iNO on PBF in normal healthy dogs and in a canine model of ALI induced by oleic acid (OA). In Group "OA only" (n = 5), ALI was induced by central venous injection of 0.08 ml/kg OA. In Group "E+OA" (n = 5), hypoxic pulmonary vasoconstriction after ALI was blocked with low-dose endotoxin (15 microg/kg of Escherichia coli endotoxin) administered 30 min before giving the same dose of OA. Measurements of regional PBF and lung water concentration (LWC) using positron emission tomography (PET) and H215O were performed before and after OA or placebo, and then again at concentrations of 10, 40, and 0 ppm iNO. One hundred twenty minutes after OA injury, PaO2/FIO2 fell significantly in Group OA only, from 567 +/- 32 to 437 +/- 67 mm Hg. In these animals, PBF redistributed from the dorsal edematous regions of the lungs to the nondependent zones, thus partially preserving normal ventilation/ perfusion relationships. As in the normal animals, in Group OA only, iNO did not significantly change either PBF or oxygenation. In Group E+OA, the administration of low-dose endotoxin eliminated perfusion redistribution from the dorsal edematous lung regions. As a result, PaO2/FIO2 fell from 558 +/- 70 to 119 +/- 53 mm Hg, a decrease that was significantly greater than that in Group OA only. In Group E+OA, administration of iNO restored perfusion redistribution to a similar level as in Group OA only, which was associated with a significant improvement in PaO2/FIO2, from 119 +/- 53 to 251 +/- 159 (10 ppm iNO), and 259 +/- 165 mm Hg (40 ppm iNO). We conclude that the effect of iNO on oxygenation after ALI depends on the pre-iNO perfusion pattern, which may help explain the variable response to iNO often observed in patients with acute respiratory distress syndrome.

Combined surfactant therapy and inhaled nitric oxide in rabbits with oleic acid-induced acute respiratory distress syndrome

Intratracheal administration of surfactant and inhaled nitric oxide (INO) have had variable effects in clinical trials on patients with acute respiratory distress syndrome (ARDS). We hypothesized that combined treatment with exogenous surfactant and INO may have effects in experimental ARDS. After intravenous infusion of oleic acid in adult rabbits and 4-6 h of ventilation, there was more than a 40% reduction in both dynamic compliance (Cdyn) of the respiratory system and functional residual capacity (FRC), a 50% increment of respiratory resistance (Rrs), a 70% reduction in PaO2 /FIO2, and an increase in intrapulmonary shunting (Q S/Q T) from 4.4 to 33.5%. The animals were then allocated to groups receiving (1) neither surfactant nor INO (control), (2) 100 mg/kg of surfactant (S) administered intratracheally, (3) 20 ppm INO (NO), or (4) 100 mg/kg of surfactant and 20 ppm INO (SNO), and subsequently ventilated for 6 h. After the period of ventilation, the animal lungs were used for analysis of disaturated phosphatidylcholine (DSPC) and total proteins (TP) in bronchoalveolar lavage fluid (BALF), and for determination of alveolar volume density (VV). The animals in the control group had the lowest survival rate, and no improvement in lung mechanics and blood oxygenation, whereas those in the S group had a modest but statistically significant improvement in Cdyn, Rrs, PaO2 and FRC, reduced Q S/Q T, lowered minimum surface tension (gammamin) of BALF, and increased DSPC/ TP and alveolar VV. The NO group had increased PaO2 and reduced Q S/Q T. The SNO group showed improved Cdyn, Rrs, FRC, DSPC/TP, alveolar VV, and gammamin of BALF comparable to the S group, but there was a further increase in survival rate and PaO2, and additional reduction in Q S/Q T and TP in BALF. These results indicate that, in this animal model of ARDS, a combination of surfactant therapy and INO is more effective than either treatment alone.

The combination of partial liquid ventilation and inhaled nitric oxide in the severe oleic acid lung injury model

STUDY OBJECTIVES

To elucidate the efficacy of the combination of inhaled nitric oxide (NO) and partial liquid ventilation (PLV) in ARDS.

DESIGN

Prospective, randomized, controlled study.

SETTING

A research laboratory at a university medical center.

SUBJECTS

Thirty-two rabbits.

INTERVENTIONS

Animals were anesthetized and ventilated via tracheostomy (tidal volume=40 mL; respiratory rate=25 breaths/min; fraction of inspired oxygen=0.99). After 0.08 mL/kg (0.071 g/kg) oleic acid was administered via the central venous route, animals were randomly divided into the following four groups depending on the ventilatory mode: (1) Gas ventilation (GV)-control group: GV was continued throughout the study; (2) GV-NO group: NO inhalation (10 ppm) was performed under GV; (3) PLV-control group: PLV using perflubron (15 mL/kg) was continued until the end of the study; and (4) PLV-NO group: NO inhalation (10 ppm) was performed under PLV.

MEASUREMENTS AND RESULTS

NO inhalation improved PaO2 in the PLV-NO group (from 133+/-20 to 167+/-23 mm Hg; p=0.0008), but not in the GV-NO group (from 67+/-6 to 63+/-9 mm Hg), although pulmonary vascular resistance decreased both in the GV-NO (from 4,604+/-328 to 4,337+/-322 dyne x s x cm(-5); p=0.0116) and the PLV-NO group (from 4,727+/-665 to 4,112+/-560 dyne x s x cm(-5); p=0.0036). (Data were expressed as mean+/-SEM.)

CONCLUSION

PLV augmented the effect of inhaled NO on pulmonary gas exchange. The combination of PLV and NO inhalation could be effective in severe ARDS.