Efficacy of inhaled nitric oxide in a porcine model of adult respiratory distress syndrome

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.

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.

Effects of inhaled aerosolized iloprost and inhaled NO on pulmonary circulation and edema formation in ovine lung injury

Although inhaled NO (iNO) has been shown to lower pulmonary pressures and edema accumulation in experimental acute lung injury, its clinical use has been questioned because of a lack of improvement in outcome, rebound phenomena, and potential toxicity. We investigated the effects of aerosolized iloprost, a stable prostacyclin analogue, compared with iNO on pulmonary pressures and lung edema in 20 female sheep with oleic acid lung injury. The most effective dose of iloprost was determined in healthy animals before the experiment. Anesthetized and ventilated sheep received a central venous oleic acid infusion and were continuously infused with Ringer lactate to achieve a positive fluid balance (5 mL.kg(-1).h(-1)). In the iNO group (n = 6), iNO (20 ppm) was administered continuously for 8 h. Animals in the iloprost group (n = 6) received aerosolized iloprost (40 microg 2 h(-1)). Animals in the control group (n = 6) had no further intervention. Oleic acid infusion was associated with impaired oxygenation, pulmonary hypertension, and lung edema in all groups. Although iNO significantly decreased pulmonary vascular resistance index, effective pulmonary capillary pressure, and extravascular lung water index, these parameters were unaffected by iloprost. Oxygenation index (Pao2/Fio2) increased significantly both during NO and iloprost inhalation but also tended to improve in the control group over time. In contrast to iNO, the investigated dose of iloprost was ineffective to attenuate acute lung injury-induced changes in pulmonary hemodynamics and lung edema in this experimental model.

Increased Alveolar and Plasma Gelatinases Activity during Postpump Syndrome: Inhibition by Inhaled Nitric Oxide

Postpump syndrome is associated with systemic inflammation. Matrix metalloproteinases (MMP)-2 and -9 contribute to proinflammatory and platelet-activator reactions. Nitric oxide (NO) is involved in the regulation of MMPs. The objectives of our study were to investigate the intensity of inflammation induced by 3 different surgical procedures, the effects of inflammation on the activity of MMPs, and the regulation of inflammation by inhaled NO (20 ppm). Inhaled NO was initiated immediately after tracheal intubation and maintained for the total duration of the experiments. Thirty pigs were equally randomized into 6 groups [sham; sham + NO; cardiopulmonary bypass; bypass + NO; bypass + lipopolysaccharide (1 microg/kg for 50 min); bypass + lipopolysaccharide + NO] and animals were subjected to anesthesia and mechanical ventilation up to 24 h. The levels of MMP-2 and MMP-9 in plasma and bronchoalveolar lavage were measured using zymography. Bypass resulted in a time-dependent rise in MMP activity, an effect potentiated by lipopolysaccharide. Inhaled NO attenuated the effects of bypass + lipopolysaccharide. These results confirm that MMP-2 and MMP-9 are associated with the inflammatory process causing the postpump syndrome. Preemptive and continuous administration of inhaled NO helps to prevent increased MMP-2 and MMP-9 activity.

Pre-emptive and continuous inhaled NO counteracts the cardiopulmonary consequences of extracorporeal circulation in a pig model

Cardiopulmonary bypass (CPB) activates a systemic inflammatory response characterized clinically by alterations in cardiovascular and pulmonary function. The aim of this study was to measure the cardiopulmonary consequences in sham-operated pigs, and in animals subjected to CPB in the presence or absence of lipopolysaccharide (LPS). We also investigated, if the perioperative administration of inhaled NO exerts significant cardiopulmonary effects in an anaesthetized and mechanically ventilated pig model of extracorporeal circulation. Thirty pigs were randomized into six equal groups (sham; sham+INO; CPB; CPB+INO; CPB+LPS; CPB+LPS+INO) and subjected to anaesthesia with mechanical ventilation for up to 24h. We found that CPB+LPS group has the highest degree of lung injury. We also demonstrated that there was a significant difference on the cardiovascular parameters (heart rate, central venous pressure, stroke volume index, and mean systemic arterial blood pressure) between the CPB groups and the sham groups. The deteriorated lung mechanics was associated with a decrease in active subfraction of surfactant (LA) with time during the procedure (P=0.0003), on which inhaled NO had only an initial beneficial effect. In our model, inhaled NO had no long-term beneficial effect on lung mechanics and surfactant homeostasis despite improving lung haemodynamics, inflammation, and oxygenation. We conclude from this study that the use of pre-emptive and continuous inhaled NO therapy has protective and safe effects against lung ischemia/reperfusion associated with CPB.

The feasibility of nitric oxide delivery with high frequency jet ventilation

A 27-year-old female with acute monocytic leukaemia (M5) developed acute respiratory distress syndrome (ARDS). Because of refractory hypoxaemia and severe barotrauma during conventional mechanical ventilation, the patient was switched to high frequency jet ventilation (HFJV) as a salvage therapy. Her refractory hypoxaemia improved temporarily but worsened again. Approval of the Institutional Review Board and the Food and Drug Administration was obtained to use nitric oxide (NO) with HFJV on a compassionate basis considering the grave situation. The NO delivery system was connected to the secondary flow circuit of the HFJV immediately after the humidifier. We measured the concentration of NO at least every hour by inserting a 7-Fr catheter connected to a McNeill analyzer into the endotracheal tube. Despite improvement of oxygenation, the patient's respiratory status deteriorated further and she died. In this case we were able to achieve reliable and constant levels of NO. The purpose of this report is to discuss the technical aspects and pitfalls of this method.

The anti-inflammatory effect of inhaled nitric oxide on pulmonary inflammation in a swine model

Cardiopulmonary bypass (CPB) is associated with an inflammatory process that leads to lung injury. In this study, we hypothesized that inhaled nitric oxide (INO) possesses the ability to modulate CPB-induced inflammation. Fifteen male pigs were randomly divided into 3 groups: Sham, CPB+LPS (CPB and lipopolysaccharide), and CPB+LPS+INO. INO (20 parts per million) was administered for 24 h after anesthesia. CPB was performed for 90 min, and LPS was infused (1 µg/kg) after CPB. Bronchoalveolar lavage (BAL) fluid and blood were collected at T0(before CPB), at 4 h, and at 24 h. At 24 h, BAL interleukin-8 (IL-8) levels were not increased as expected in the CPB+LPS group compared with the Sham group, but they were reduced significantly in the CPB+LPS+INO group. Cell hypo reactivity observed in the groups receiving LPS also seemed to downregulate endothelial nitric oxide synthase NOS protein expression relative to the Sham group. Nitrite and nitrate (NOx) concentrations were decreased significantly in the groups without INO. Moreover, animals treated with INO showed higher rates of pulmonary apoptosis compared with their respective controls. These results demonstrate that NOx production is reduced after CPB and that INO acts on the inflammatory process by diminishing neutrophils and their major chemoattractant, IL-8. INO also increases cell apoptosis in the lungs under inflammatory conditions, which may explain, in part, how it resolves pulmonary inflammation.Key words: CPB, nitric oxide, apoptosis, LPS, IL-8.

Protection of lung tissue against ischemia/reperfusion injury by preconditioning with inhaled nitric oxide in an in situ pig model of normothermic pulmonary ischemia

Topical administration of nitric oxide (NO) by inhalation is currently used as therapy in various pulmonary diseases, but preconditioning with NO to ameliorate lung ischemia/reperfusion (I/R) injury has not been fully evaluated. In this study, we investigated the effects of NO inhalation on functional pulmonary parameters using an in situ porcine model of normothermic pulmonary ischemia. After left lateral thoracotomy, left lung ischemia was maintained for 90 min, followed by a 5h reperfusion period (group I, n = 7). In group II (n = 6), I/R was preceded by inhalation of NO (10 min, 15 ppm). Animals in group III (n = 7) underwent sham surgery without NO inhalation or ischemia. In order to evaluate the effects of NO preconditioning, lung functional and hemodynamic parameters were measured, and the zymosan-stimulated release of reactive oxygen species in arterial blood was determined. Animals in group I developed significant pulmonary I/R injury, including pulmonary hypertension, a decreased pO(2) level in pulmonary venous blood of the ischemic lung, and a significant increase of the stimulated release of reactive oxygen species. All these effects were prevented, or the onset (release of reactive oxygen species) was delayed, by NO inhalation. These results indicate that preconditioning by NO inhalation before lung ischemia is protective against I/R injury in the porcine lung.

The effects of inhaled nitric oxide on cardiac pathology and energy metabolism in a canine model of smoke inhalation injury

OBJECTIVE

The effects of inhaled nitric oxide (NO) on cardiac pathology and energy metabolism were studied in a canine model of smoke inhalation injury.

MATERIAL AND METHOD

Twenty-one dogs were randomly divided into three groups: four dogs constituted the normal control group (group N), eight dogs subjected to smoke inhalation followed by O(2) inhalation (FiO(2)=0.45) constituted the injury control group (group C), and nine dogs inhaling a mixture of O(2) and 45ppm nitric oxide after smoke exposure served as the treatment group (group T). Myocardial zymograms were continuously measured, and ventricular muscles were examined for histopathology in the end of the experiment.

RESULTS

Lactate dehydrogenase (LDH), alpha-hydroxybutyrate dehydrogenase (alpha-HBD), creatine kinase (CK) and glutamic oxalacetic transaminase (GOT) in group T were less than those in group C(P<0.05, or P<0.01). ATP content and energy charge (EC) in group T were higher significantly than those in group C(P<0.01). Light microscopy and electron microscopy indicated that the ventricular pathologic changes in group T were milder than in control group.

CONCLUSION

Nitric oxide inhalation relieved myocardial damage and improved energy metabolism.

Combination of intravenously infused methylene blue and inhaled nitric oxide ameliorates endotoxin-induced lung injury in awake sheep

OBJECTIVE

To evaluate the effects of a combination of methylene blue, an inhibitor of the nitric oxide pathway, and inhaled nitric oxide on endotoxin-induced acute lung injury in awake sheep.

DESIGN

Prospective, randomized, controlled experimental study.

SETTING

University animal laboratory.

SUBJECTS

Twenty-four yearling, awake sheep.

INTERVENTIONS

The sheep were anesthetized and instrumented with vascular catheters. After 1 wk of recovery, the animals underwent tracheotomy and were subjected to intravenous infusions of endotoxin 10 ng x kg-1 x min-1 and isotonic saline 3 mL x kg-1 x hr-1 for 8 hrs. The sheep were randomly assigned to three groups of eight animals each: a) the control group received endotoxin and saline; b) the INO group received endotoxin, saline, and inhaled nitric oxide 40 ppm for 5 hrs; and c) the MB/INO group received endotoxin, saline, and methylene blue 3 mg/kg as an intravenous bolus injection followed by a continuous infusion of 3 mg x kg-1 x min-1 for 6 hrs in combination with inhaled nitric oxide 40 ppm for 5 hrs.

MEASUREMENTS AND MAIN RESULTS

Hemodynamic variables and blood gases were determined hourly. In the early phase of endotoxemia (0-2 hrs), methylene blue/inhaled nitric oxide reduced the increments in pulmonary arterial pressure, pulmonary microvascular pressure, and pulmonary vascular resistance index by 60% compared with the controls and to a greater extent than did inhaled nitric oxide alone. During the late phase, all the preceding variables returned closely to baseline following inhaled nitric oxide or methylene blue/inhaled nitric oxide but remained remarkably elevated in the control group. Inhaled nitric oxide and methylene blue/inhaled nitric oxide reduced the increase in extravascular lung water by 40% and 80%, respectively. Inhaled nitric oxide transiently attenuated the increase in venous admixture and did not prevent a decrease in arterial oxygenation. In the methylene blue/inhaled nitric oxide group, blood gases remained unchanged from baseline.

CONCLUSIONS

In sheep, methylene blue/inhaled nitric oxide protects more efficiently against acute lung injury than inhaled nitric oxide alone, as indicated by a milder pulmonary hypertension, less extravascular lung water accumulation, and maintained gas exchange.

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.

Treatment of ARDS

Improved understanding of the pathogenesis of acute lung injury (ALI)/ARDS has led to important advances in the treatment of ALI/ARDS, particularly in the area of ventilator-associated lung injury. Standard supportive care for ALI/ARDS should now include a protective ventilatory strategy with low tidal volume ventilation by the protocol developed by the National Institutes of Health ARDS Network. Further refinements of the protocol for mechanical ventilation will occur as current and future clinical trials are completed. In addition, novel modes of mechanical ventilation are being studied and may augment standard therapy in the future. Although results of anti-inflammatory strategies have been disappointing in clinical trials, further trials are underway to test the efficacy of late corticosteroids and other approaches to modulation of inflammation in ALI/ARDS.

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.

Thirty years of clinical trials in acute respiratory distress syndrome

OBJECTIVE

To systematically review clinical trials in acute respiratory distress syndrome (ARDS).

DATA SOURCES

Computerized bibliographic search of published research and citation review of relevant articles.

STUDY SELECTION

All clinical trials of therapies for ARDS were reviewed. Therapies that have been compared in prospective, randomized trials were the focus of this analysis.

DATA EXTRACTION

Data on population, interventions, and outcomes were obtained by review. Studies were graded for quality of scientific evidence.

MAIN RESULTS

Lung protective ventilator strategy is supported by improved outcome in a single large, prospective trial and a second smaller trial. Other therapies for ARDS, including noninvasive positive pressure ventilation, inverse ratio ventilation, fluid restriction, inhaled nitric oxide, almitrine, prostacyclin, liquid ventilation, surfactant, and immune-modulating therapies, cannot be recommended at this time. Results of small trials using corticosteroids in late ARDS support the need for confirmatory large clinical trials.

CONCLUSIONS

Lung protective ventilator strategy is the first therapy found to improve outcome in ARDS. Trials of prone ventilation and fluid restriction in ARDS and corticosteroids in late ARDS support the need for large, prospective, randomized trials.

Soluble nitric oxide donor and surfactant improve oxygenation and pulmonary hypertension in porcine lung injury

Acute lung injury (ALI) is associated with diminished surfactant activity and pulmonary hypertension. NONOates are soluble NO donors which release NO in solution. Intratracheal NONOates reduce pulmonary hypertension and improve oxygenation in ALI. We hypothesized that the pharmacologic properties of NO donors would be unaltered after surfactant admixture in vitro and that aerosolized NONOate activity would be enhanced by surfactant pretreatment in vivo. NO donors were added to saline or surfactant and analyzed for nitrite/nitrate production and aortic ring vasodilation. Surfactant did not alter nitrate/nitrite production or aortic ring vasodilation. A porcine model of ALI with pulmonary hypertension was produced using intravenous oleic acid. Animals were assigned to Surfactant-Saline, Surfactant-NONOate, Saline-Saline, or Saline-NONOate groups. Saline or surfactant was instilled into the trachea, followed by gas exchange, pulmonary function, and hemodynamic measurements. NONOate or saline was then aerosolized, and additional data were collected. Oxygenation was improved in the Surfactant-NONOate group, while pulmonary hypertension was selectively reduced in both NONOate groups. Aerosolized NONOate following surfactant pretreatment improves oxygenation and reduces pulmonary hypertension in ALI.

A demand valve device decreases exhaust nitric oxide and nitrogen dioxide by nitric oxide inhalation with a nasal cannula in the human

To improve patients' quality of life and decrease pollution risks to medical personnel, we tested the usefulness of a nitric oxide (NO) inhalation system consisting of a nasal cannula and a demand valve in an open circuit system. To estimate the content of NO entering the lung with the open system, concentrations of NO and nitrogen dioxide (NO2) were measured in a mechanical lung model, and then nitrocylhaemoglobin (NO-Hb), methaemoglobin (Met-Hb), and nitrite (NO2-) + nitrate (NO3-) concentrations in venous blood were measured in eight healthy subjects. Exhaust NO and NO2 in the open system were also observed in 14 healthy subjects. In the lung model, NO concentration delivered with the open system was approximately 1/11 of that in the gas tank. Increases in Met-Hb and NO2- + NO3- with the open system showed that the concentration of delivered NO was approximately 1/9 of that in the gas tank. The open system reduced exhaust NO to 1/10 in human subjects. These data suggest that this NO inhalation system delivers sufficient NO to spontaneously breathing patients. In addition, these findings indicate that there is little environmental toxicity associated with the open circuit system.

Prevention of rabbit acute lung injury by surfactant, inhaled nitric oxide, and pressure support ventilation

Improvement of pulmonary perfusion and blood oxygenation and prevention of acute lung injury (ALI) may rely on ventilation strategy. We hypothesized that application of a combined surfactant, inhaled nitric oxide (iNO), and pressure support ventilation (PSV) should more effectively protect the lungs from injury. Anesthetized and intubated adult rabbits weighing 2.8 +/- 0.3 kg were allowed to breathe room air while receiving oleic acid intravenously (60 microl/kg). Within 90 min this caused a reduction of Pa(O(2)) from 94 +/- 7 to 48 +/- 3 mm Hg and dynamic lung compliance (Cdyn) from 1.59 +/- 0.22 to 0.85 +/- 0.10 ml/cm H(2)O/kg (both p < 0.01), and increase of intrapulmonary shunting (Q S/Q T) from 9.4 +/- 1.2 to 27 +/- 5% (p < 0.05). PSV was subsequently applied with 3 cm H(2)O of continuous positive airway pressure and FI(O(2)) of 0.3, and the animals were randomly allocated to four groups, receiving: (1) PSV only (Control, n = 10); (2) iNO at 20 ppm (NO, n = 9); (3) surfactant phospholipids at 100 mg/kg (Surf, n = 8); and (4) surfactant at 100 mg/kg and iNO at 20 ppm (SNO, n = 8). PSV level was varied to maintain a tidal volume of 8 to 10 ml/kg for another 12 h or until early animal death. Five animals in the SNO, three each in the NO and Surf group, and one in the Control group survived 12 h (SNO versus Control, p < 0.05). The NO, Surf, and SNO groups had significantly improved mean Pa(O(2)) (> 70 mm Hg, p < 0.05), and reduced Q S/Q T (15, 19, and 17%, respectively, p < 0.05) at 6 and 12 h, but not in the Control group. The SNO group had the highest values of Cdyn at 12 h, alveolar aeration and disaturated phosphatidylcholine-to-total protein ratio in bronchoalveolar lavage fluid, and the lowest wet-to-dry lung weight ratio and lung injury score (p < 0.05). The results indicate that early alleviation of ALI by surfactant, iNO, and PSV is due to synergistic effects, and only PSV in this model had limited effects.

Selective vasodilation by nitric oxide inhalation during sustained pulmonary hypertension following recurrent microembolism in pigs

PURPOSE

This study establishes a new model of sustained pulmonary hypertension induced by recurrent microembolism in pigs and evaluates the effects of nitric oxide (NO) inhalation in this model.

MATERIALS AND METHODS

Fourteen pigs were embolized under general anesthesia with 300-microm microspheres intravenously three times over a period of 7 weeks. Four pigs served as untreated controls. Hemodynamic and gas exchange measurements were performed on days 1 and 7 after the last embolization.

RESULTS

Recurrent microembolism caused sustained pulmonary hypertension (mean pulmonary artery pressure [MPAP] 26 +/- 2 and 18 +/- 1 mm Hg on days 1 and 7, respectively) compared with the control group (MPAP 13 +/- 1 mm Hg each for days 1 and 7; P < .05, respectively). Right heart hypertrophy was present at autopsy as indicated by an increase in minimal myocyte diameter. Inhaled NO (5 and 40 parts per million [ppm]) was administered on days 1 and 7. On both days, inhaled NO significantly reduced MPAP and pulmonary vascular resistance without affecting systemic hemodynamics. There were no differences in responses to 5 and 40 ppm inhaled NO.

CONCLUSION

We conclude that recurrent microembolization in pigs provides a reliable model of sustained pulmonary hypertension. In this model inhaled NO is a selective pulmonary vasodilator, indicating that active vasoconstriction significantly contributes to sustained pulmonary hypertension after recurrent microembolism.

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.

Inhaled nitric oxide, oxygen, and alkalosis: dose-response interactions in a lamb model of pulmonary hypertension

Inhaled nitric oxide (NO) is currently used as an adjuvant therapy for a variety of pulmonary hypertensive disorders. In both animal and human studies, inhaled NO induces selective, dose-dependent pulmonary vasodilation. However, its potential interactions with other simultaneously used pulmonary vasodilator therapies have not been studied. Therefore, the objective of this study was to determine the potential dose-response interactions of inhaled NO, oxygen, and alkalosis therapies. Fourteen newborn lambs (age 1-6 days) were instrumented to measure vascular pressures and left pulmonary artery blood flow. After recovery, the lambs were sedated and mechanically ventilated. During steady-state pulmonary hypertension induced by U46619 (a thromboxane A2 mimic), the lambs were exposed to the following conditions: Protocol A, inhaled NO (0, 5, 40, and 80 ppm) and inspired oxygen concentrations (FiO2) of 0.21, 0.50, and 1.00; and Protocol B, inhaled NO (0, 5, 40, and 80 ppm) and arterial pH levels of 7.30, 7.40, 7.50, and 7.60. Each condition (in randomly chosen order) was maintained for 10 min, and all variables were allowed to return to baseline between conditions. Inhaled NO, oxygen, and alkalosis produced dose-dependent decreases in mean pulmonary arterial pressures (P < 0.05). Systemic arterial pressure remained unchanged. At 5 ppm of inhaled NO, alkalosis and oxygen induced further dose-dependent decreases in mean pulmonary arterial pressures (P < 0.05). At inhaled NO doses > 5 ppm, alkalosis induced further dose-independent decreases in mean pulmonary arterial pressure, while oxygen did not. We conclude that in this animal model, oxygen, alkalosis, and inhaled NO induced selective, dose-dependent pulmonary vasodilation. However, when combined, a systemic arterial pH > 7.40 augmented inhaled NO-induced pulmonary vasodilation, while an FiO2 > 0.5 did not. Therefore, weaning high FiO2 during inhaled NO therapy should be considered, since it may not diminish the pulmonary vasodilating effects. Further studies are warranted to guide the clinical weaning strategies of these pulmonary vasodilator therapies.

Inhaled nitric oxide prevents left ventricular impairment during endotoxemia

We evaluated the effect of long-term inhalation of nitric oxide (NO) on cardiac contractility after endotoxemia by using the end-systolic elastance of the left ventricle (LV) as a load-independent contractility index. Chronic instrumentation in 12 pigs included implantation of two pairs of endocardial dimension transducers to measure LV volume and a micromanometer to measure LV pressure. One week later, the animals were divided into a control group (n = 6) or a NO group (n = 6). All animals received intravenous Escherichia coli endotoxin (10 micrograms. kg-1. h-1) and equivalent lactated Ringer solution. NO inhalation (20 parts/million) was begun 30 min after the initiation of endotoxemia and was continued for 24 h. In both groups, tachycardia, pulmonary hypertension, and systemic hyperdynamic changes were noted. The end-systolic elastance in the control group was significantly decreased beyond 7 h. NO inhalation maintained the end-systolic elastance at baseline levels and prevented its impairment. These findings indicate that NO exerts a protective effect on LV contractility in this model of endotoxemia.

Aerosolized soluble nitric oxide donor improves oxygenation and pulmonary hypertension in acute lung injury

Acute respiratory distress syndrome (ARDS) is a major cause of morbidity and mortality in critically ill patients. The associated ventilation/perfusion mismatch and pulmonary hypertension are amenable to treatment with inhaled nitric oxide (NO) gas. Compounds formed by reacting NO with various nucleophiles (NONOates) release NO spontaneously and induce vasodilation. Intratracheally administered NONOates result in selective reduction in pulmonary hypertension. We hypothesized that a nebulized NONOate would improve oxygenation and reduce pulmonary vascular resistance in oleic acid-induced acute lung injury and pulmonary hypertension. Pigs underwent catheterization of the pulmonary artery, left atrium, and right atrium, and a flow probe was positioned around the pulmonary artery. Acute lung injury and pulmonary hypertension were induced with intravenous oleic acid. Animals were randomly assigned to receive either nebulized saline or the NONOate 2-(dimethylamino)ethylputreanine/NO (DMAEP/NO). Hemodynamic, gas exchange, pulmonary function, methemoglobin, and nitrite/nitrate measurements were obtained for 60 min. Animals in the DMAEP/NO group had improvement in PaO2 as compared with control animals (from 139 +/- 19 mm Hg to 180 +/- 19 mm Hg in the DMAEP/NO group [n = 6]; and from 144 +/- 6 mm Hg to 150 +/- 9 mm Hg in the saline group [n = 6], p < 0.05). After aerosol treatment, animals in the DMAEP/NO group had a greater reduction in pulmonary vascular resistance index (PVRI) than did control animals (from 81 +/- 17 dyne. s/cm5/kg to 34 +/- 8 dyne. s/cm5/kg; and from 104 +/- 16 dyne. s/cm5/kg to 64 +/- 11 dyne. sec/cm5/ kg in the saline group at 60 min, p < 0.05). There were no differences between the groups in systemic vascular resistance index (SVRI), cardiac index (CI), methemoglobin, nitrite/nitrate, or lung pathology scores. We conclude that DMAEP/NO improves oxygenation and has selective pulmonary vasodilating properties without causing significant systemic toxicity in this porcine model of acute lung injury.

Inhaled nitric oxide reduces lung fluid filtration after endotoxin in awake sheep

We studied the effect on lung fluid filtration of 37.6 ppm inhaled nitric oxide (NO) imposed for 1 h 2.5 h after endotoxin in seven awake sheep, with seven control subjects. The effects of NO on the longitudinal distribution of pulmonary vascular resistance (PVR) before and after endotoxin were specifically addressed in six sheep. Following endotoxin, sheep developed respiratory distress; PaO2, the alveolar-arterial oxygen tension difference (AaPO2) and venous admixture (Q S/Q T) changed significantly, as did the pulmonary artery pressure (Ppa), PVR, and lung lymph flow (Q L). Inhaled NO reduced Ppa and PVR by 50%; Q L decreased from 7.8 +/- 0.34 ml/15 min to 4.7 +/- 0.80 ml/15 min (mean +/- SEM), and lymph protein clearance from 4.9 +/- 0.18 ml/15 min to 3.6 +/- 0.75 ml/15 min. Lymph/plasma protein concentration ratio (L/P) increased from 0.63 +/- 0.016 to 0.72 +/- 0.006, concomitant with the decrease in Q L. The L/P - Q L relationships shifted from left, at baseline, to the right during endotoxemia, as did the permeability surface product (PS) isolines. The rightward shift was significantly less in the NO group. Inhaled NO significantly improved PaO2, AaPO2, and Q S/Q T, reduced the increase in pulmonary microwedge pressure back to baseline and decreased upstream and downstream PVR at 3.0 through 4. 0 h. We conclude that, in sheep, inhaled NO reduces lung fluid filtration by decreasing microvascular pressure and apparently also by declining the enhanced microvascular permeability during the late phase of endotoxemia.

The therapeutic potential of nitric oxide in lung transplantation

Endogenously produced oxides of nitrogen appear to play important roles in tissue and organ homeostasis. Endogenous production of nitric oxide, which can be altered in response to various stimuli, can modulate vascular tone, oxyradical cascades, cell adhesion, and other aspects of inflammation. Because exogenously administered (inhaled) nitric oxide can mediate pulmonary vasodilatation and improve pulmonary function in some patients with lung injury, treatment of lung allograft recipients with inhaled nitric oxide may ameliorate ischemia-reperfusion injury, thereby improving perioperative pulmonary function and diminishing ventilatory support requirements. This review examines the biology of nitric oxide and present data that support its potential therapeutic effects for lung transplant recipients.

Chronic hypoxia decreases nitric oxide production and endothelial nitric oxide synthase in newborn pig lungs

To examine the effect of chronic hypoxia on nitric oxide (NO) production and the amount of the endothelial isoform of nitric oxide synthase (eNOS) in lungs of newborn piglets, studies were performed using 1- to 3-day-old piglets raised in room air (control) or 10% O2 (chronic hypoxia) for 10-12 days. Exhaled NO output and plasma nitrites and nitrates (collectively termed NOx-) were measured in anesthetized animals. NOx- concentrations were measured in the perfusate of isolated lungs. eNOS amounts were assessed in whole lung homogenates. In the intact piglets, exhaled NO outputs and plasma NOx- were lower in the chronically hypoxic (exhaled NO output = 0.2 +/- 0.1 nmol/min; plasma NOx- = 10.3 +/- 3.7 nmol/ml) than in control animals (exhaled NO output = 0.8 +/- 0.2 nmol/min; plasma NOx- = 22.3 +/- 4.3 nmol/ml). In perfused lungs, the perfusate accumulation of NOx- was lower in chronic hypoxia (1.0 +/- 0.3 nmol/min) than in control (2.6 +/- 0.6 nmol/min) piglets. The amount of whole lung homogenate eNOS from the chronic hypoxia piglets was 40 +/- 8% less than that from the control piglets. The reduced NO production observed in anesthetized animals or perfused lungs of chronically hypoxic newborn piglets is consistent with the finding of reduced lung eNOS protein amounts. Decreased NO production might contribute to the development of chronic hypoxia-induced pulmonary hypertension in newborns.

Nitric oxide potentiates acute lung injury in an isolated rabbit lung model

BACKGROUND

The effect of inhaled nitric oxide (NO) treatment on pulmonary function in the setting of adult respiratory distress syndrome is controversial. We examined the effect of inhaled NO on pulmonary function in an isolated rabbit lung model of oleic acid (OA)-induced acute lung injury. We hypothesized that NO would decrease pulmonary artery pressure and improve oxygenation.

METHODS

Rabbit heart-lung blocks were isolated, flushed in vivo, harvested, and immediately perfused with whole blood and ventilated with 50% oxygen (O2). Pulmonary artery pressure was determined every 15 seconds for 60 minutes of perfusion. Oxygenation was determined by blood gas analysis of pulmonary venous effluent at 0, 20, 40, and 60 minutes after initiation of OA infusion. Rabbits were randomized into four study groups: saline control; OA control, which received a 20-minute infusion of 50% OA/ethanol solution; NO treatment (20 ppm NO inhaled before OA infusion); and NO control, which underwent NO (20 ppm) pretreatment, followed by saline infusion. Pulmonary artery pressure, oxygenation (arteriovenous O2 difference), compliance, and wet/dry lung weight were determined.

RESULTS

Pretreatment with NO caused significant increases in pulmonary artery pressure (NO treatment versus NO control and saline control; no significant difference between NO treatment group and OA control group), and did not improve oxygenation in our model.

CONCLUSIONS

Contrary to our hypothesis, pretreatment with NO potentiates acute lung injury in our isolated lung model. There was significant exacerbation of pulmonary hypertension and no improvement in oxygenation. Further investigation of the possible deleterious effects of NO in acute lung injury are needed, especially in the early acute phases of this process.

The Utility of Nitric Oxide in the Postoperative Period

Inhaled nitric oxide (iNO) is a pulmonary-selective vaso dilator with minimal bronchodilator activity in humans. NO also inhibits platelet and neutrophil activation and adhesion and inhibits ischemia-reperfusion injury. The pulmonary vasodilatory property of iNO causes a reduc tion in pulmonary vascular resistance and improvement in arterial oxygenation in a wide spectrum of diseases characterized by pulmonary hypertension and hypox emia. Promising examples of diseases for which NO may provide beneficial physiologic effects are primary and secondary pulmonary hypertension, right ventricu lar failure, cardiac transplantation, pulmonary embo lism, protamine reactions, acute respiratory distress syndrome, lung transplantation and, perhaps, chronic obstructive airways disease. The usefulness of iNO may be improved by concomitant therapy with pulmonary- selective intravenous vasoconstrictors (eg, Almitrine; Vectarian, Neuilly, France) and cGMP phosphodiester ase V inhibitors (eg, Zaprinast; Research Biochemicals International, Natick, MA). Almitrine improves oxygen ation, synergistically with iNO, and may be useful in disease states characterized primarily by hypoxemia. Zaprinast may be useful for weaning iNO and avoidance of rebound pulmonary hypertension.

Cardiopulmonary effects of inhaled nitric oxide in normal dogs and during E. coli pneumonia and sepsis

We investigated the effect of inhaled nitric oxide (NO) at increasing fractional inspired O2 concentrations (FIO2) on hemodynamic and pulmonary function during Escherichia coli pneumonia. Thirty-eight conscious, spontaneously breathing, tracheotomized 2-yr-old beagles had intrabronchial inoculation with either 0.75 or 1.5 x 10(10) colony-forming units/kg of E. coli 0111:B4 (infected) or 0.9% saline (noninfected) in one or four pulmonary lobes. We found that neither the severity nor distribution (lobar vs. diffuse) of bacterial pneumonia altered the effects of NO. However, in infected animals, with increasing FIO2 (0.08, 0.21, 0.50, and 0.85), NO (80 parts/million) progressively increased arterial PO2 [-0.3 +/- 0.6, 3 +/- 1, 13 +/- 4, 10 +/- 9 (mean +/- SE) Torr, respectively] and decreased the mean arterial-alveolar O2 gradient (0.5 +/- 0.3, 4 +/- 2, -8 +/- 7, -10 +/- 9 Torr, respectively). In contrast, in noninfected animals, the effect of NO was significantly different and opposite; NO progressively decreased mean PO2 with increasing FIO2 (2 +/- 1, -5 +/- 3, -2 +/- 3, and -12 +/- 5 Torr, respectively; P < 0.05 compared with infected animals) and increased mean arterial-alveolar O2 gradient (0.3 +/- 0.04, 2 +/- 2, 1 +/- 3, 11 +/- 5 Torr; P < 0.05 compared with infected animals). In normal and infected animals alike, only at FIO2 < or = 0.21 did NO significantly lower mean pulmonary artery pressure, pulmonary artery occlusion pressure, and pulmonary vascular resistance index (all P < 0.01). However, inhaled NO had no significant effect on increases in mean pulmonary artery pressure associated with bacterial pneumonia. Thus, during bacterial pneumonia, inhaled NO had only modest effects on oxygenation dependent on high FIO2 and did not affect sepsis-induced pulmonary hypertension. These data do not support a role for inhaled NO in bacterial pneumonia. Further studies are necessary to determine whether, in combination with ventilatory support, NO may have more pronounced effects.

Effect of inhaled nitroglycerine and sodium nitroprusside aerosol on hemodynamics and oxygenation in dogs with pulmonary hypertension

PURPOSE

To test the hypothesis that inhalation of aerosol of glyceryl trinitrate or sodium nitroprusside might produce selective pulmonary vasodilation, causing an improvement of oxygenation with minimal systemic hypotension as inhaled nitric oxide gas, we investigated the effect of inhaled nitroglycerine and sodium nitroprusside aerosol on hemodynamics and oxygenation in dogs with pulmonary hypertension.

METHODS

Pulmonary hypertension was induced by a continuous infusion of 1.0 to 4.0μg·kg^-1·min^-1 U-46619 in anesthetized and mechanically ventilated dogs. Aerosol preparations consisted of normal saline, 250, 500, 1000, and 2000 ppm solutions of either glyceryl trinitrate or sodium nitroprusside were administered sequentially via the breathing circuit.

RESULTS

Inhaled nitroglycerine and sodium nitroprusside aerosol caused neither selective pulmonary vasodilation nor improved oxygenation in this pulmonary hypertension model, unlike inhaled nitric oxide gas.

CONCLUSION

These findings suggest that inhaled nitroglycerine and sodium nitroprusside aerosol is not effective in improving hemodynamic derangement or oxygenation in pulmonary hypertension. However, the effect of the substances in higher dose ranges remains to be defined.

Circulating methemoglobin and nitrite/nitrate concentrations as indicators of nitric oxide overproduction in critically ill children with septic shock

OBJECTIVES

To examine the relationship between circulating methemoglobin and nitrite/nitrate concentrations and to compare these markers of nitric oxide overproduction with clinical variables in children diagnosed with septic shock.

DESIGN

Prospective, controlled, clinical study.

SETTING

Pediatric intensive care unit and outpatient clinic in a children's hospital.

PATIENTS

Twenty-two children diagnosed with septic shock and ten age-matched healthy control patients.

INTERVENTIONS

Patients diagnosed with septic shock had blood specimens taken on study entry and every 6 hrs for 72 hrs for methemoglobin and nitrite/nitrate determinations. Single blood specimens were obtained from controls.

MEASUREMENTS AND MAIN RESULTS

Circulating methemoglobin and nitrite/nitrate concentrations were significantly higher in children diagnosed with septic shock in comparison with healthy control children (p = .01 and .05, respectively). Peak nitrite/nitrate concentrations correlated with serum creatinine (r2 = .19; p = .04) and were inversely correlated with arterial pH (r2 = .28; p = .01) and urine output (r2 = .21; p = .03) when analyzed by log-linear regression. There were no significant relationships between methemoglobin and nitrite/nitrate or between methemoglobin and any other clinical variable.

CONCLUSIONS

Circulating methemoglobin and nitrite/nitrate concentrations are increased in children diagnosed with septic shock. Plasma nitrite/nitrate values correlate with selected clinical variables in these children. Circulating methemoglobin measurements are not superior to plasma nitrite/nitrate concentrations as an indicator of endogenous overproduction of nitric oxide in children diagnosed with septic shock. A need remains to develop markers of endogenous nitric oxide activity that have greater accuracy and reliability.

Inhaled nitric oxide: clinical applications, indications, and toxicology

PURPOSE

Although the analogy of nitric oxide (NO) to Endothelium-derived Relaxing Factor remains controversial, medical use of exogenous NO gas by inhalation has grown exponentially. This review presents the mechanisms of action of inhaled NO in pulmonary hypertension, hypoxaemia, inflammation and oedema, as well as its therapeutic and diagnostic indications with emphasis on acute respiratory distress syndrome (ARDS) and toxicology.

SOURCE

Two medical databases (Current Contents, Medline) were searched for citations containing the above-mentioned key words to December 1996. Moreover, many presentations in congresses such as 4th International Meeting of Biology of Nitric Oxide, 52nd and 53rd Annual Meeting of Canadian Anaesthetists' Society or 10th Annual Meeting of European Association of Cardiothoracic Anaesthesiologists were used.

PRINCIPAL FINDINGS

Inhaled NO is now recognized as an invaluable tool in neonatal and paediatric critical care, and for heart/lung surgery. Other clinical applications in adults, such as chronic obstructive pulmonary disease and ARDS, require a cautious approach. The inhaled NO therapy is fairly inexpensive, but it would seem that it is not indicated for everybody with regards to the paradigm of its efficiency and potential toxicity. The recent discovery of its anti-inflammatory and extrapulmonary effects open new horizons for future applications.

CONCLUSION

Clinical use of inhaled NO was mostly reported in case series, properly designed clinical trials must now be performed to establish its real therapeutic role. These trials would permit adequate selection of the cardiopulmonary disorders, and subsequently the patients that would maximally benefit from inhaled NO therapy.

Effects of inhaled nitric oxide on gas exchange in lungs with shunt or poorly ventilated areas

Inhaled nitric oxide (NO) is a selective pulmonary vasodilator with beneficial effects on some lung diseases, yet conflicting results, particularly in chronic obstructive pulmonary disease, have been reported. We hypothesized that although inhaled NO would improve gas exchange in the presence of shunt (by increasing blood flow to normal areas), it could worsen gas exchange when areas of low ventilation-perfusion (VA/Q) ratio were present since these areas could be preferentially vasodilated by NO. We examined how approximately 80 ppm inhaled NO altered pulmonary gas exchange in anesthetized ventilated dogs with the following: (1) normal lungs (n = 8), (2) shunt (n = 9, 24.7% shunt) produced by complete obstruction of one lobar bronchus, and (3) VA/Q inequality (n = 8) created by partial obstruction of one lobar bronchus resulting in a bimodal VA/Q distribution with 13% perfusion of low VA/Q areas (0.005 < VA/Q < 0.1) without shunt. Inhaled No significantly reduced pulmonary arterial (p < 0.001) and wedge pressures (p < 0.01) and pulmonary vascular resistance (p < 0.01) without changing cardiac output in each group. In normal lungs, NO did not alter PaO2 or VA/Q inequality. However, with complete obstruction, shunt fell slightly (p < 0.001) with NO. In lungs with VA/Q inequality, NO variably affected VA/Q matching, which was improved in some dogs and worsened in others. In these lungs, changes in pulmonary vascular resistance of the abnormal area of the lung were negatively correlated with changes in VA/Q dispersion (logSDQ) (R = -0.85, p < 0.01) and positively correlated with PaO2 (R = 0.79, p < 0.05). We conclude that NO has net effects on pulmonary gas exchange, depending on the underlying lung pathology consistent with competing vasodilatory effects on the normal and abnormal areas that receive the gas.

Pretreatment with inhaled nitric oxide inhibits neutrophil migration and oxidative activity resulting in attenuated sepsis-induced acute lung injury

OBJECTIVE

To determine if, and by what mechanisms, inhaled nitric oxide attenuates acute lung injury in a porcine model of adult respiratory distress syndrome induced by Gram-negative sepsis.

DESIGN

Nonrandomized, controlled study.

SETTING

Laboratory at a university medical center.

SUBJECTS

Thirty pathogen-free Yorkshire swine (15 to 20 kg).

INTERVENTIONS

Four groups of swine were anesthetized, mechanically ventilated, and studied for 5 hrs. Both control-nitric oxide and septic-nitric oxide animals received inhaled nitric oxide at 20 parts per million throughout the study. Control (n = 10) and control-nitric oxide (n = 5) animals received a 1-hr infusion of sterile saline. Sepsis was induced in septic (n = 10) and septic-nitric oxide (n = 5) animals with a 1-hr intravenous infusion of live Pseudomonas aeruginosa.

MEASUREMENTS AND MAIN RESULTS

Untreated septic animals developed a progressive decrease in Pao2 that was prevented in septic-nitric oxide animals (73 +/- 4 vs. 214 +/- 23 torr [9.7 +/- 0.5 vs. 28.5 +/- 3.1 kPa], respectively, at 5 hrs, p < .05). Untreated septic animals showed a significant increase in bronchoalveolar lavage protein and neutrophil count at 5 hrs, compared with the baseline value, indicating acute lung injury. Septic-nitric oxide animals showed no significant increase in these parameters. Peripheral blood neutrophils from untreated septic animals and septic-nitric oxide animals exhibited significant (p < .05) up-regulation of CD18 receptor expression and oxidant activity (10.5 +/- 0.9 and 5.0 +/- 0.9 nmol of superoxide anion/10(6) neutrophils/10 mins, respectively) compared with both control and control-nitric oxide animals (3.0 +/- 0.6 and 2.6 +/- 0.2 nmol of superoxide anion/10(6) neutrophils/10 mins, respectively). Also, priming for the oxidant burst at 5 hrs was decreased by 50% in septic-nitric oxide animals compared with untreated septic animals. Both untreated septic and septic-nitric oxide animals showed a significant increase in pulmonary arterial pressure at 30 mins (47.5 +/- 2.4 and 51.0 +/- 3.0 mm Hg, respectively), followed by a progressive decrease (32.8 +/- 2.6 and 31.3 +/- 5.4 mm Hg, respectively, at 5 hrs). Both of these changes were significant (p < .05) compared with baseline values and compared with the control groups. There was no significant difference in pulmonary arterial pressure or systemic arterial pressure at any time between untreated septic and septic-nitric oxide animals.

CONCLUSIONS

These results demonstrate that inhaled nitric oxide attenuates alveolar-capillary membrane injury in this porcine model of Gram-negative sepsis but does not adversely affect systemic hemodynamics. The data suggest that inhaled nitric oxide preserves alveolar-capillary membrane integrity by the following means: a) inhibiting transendothelial migration of activated, tightly adherent neutrophils; and b) possibly by attenuating the neutrophil oxidant burst.

Effects of N omega-nitro-L-arginine methyl ester on the endotoxin-induced disseminated intravascular coagulation in porcine septic shock

OBJECTIVES

Nitric oxide is known to prevent platelet aggregation and clot formation. Inhibitors of nitric oxide synthase might promote or enhance endotoxin disseminated intravascular coagulation. The present study was designed to evaluate the effects of the arginine analog, N omega-nitro-L-arginine methyl ester (L-NAME), on the endotoxin-induced disseminated intravascular coagulation in a porcine model of septic shock.

DESIGN

Prospective, comparative, experimental study.

SETTING

Laboratory at a large university hospital.

SUBJECTS

Sixteen female piglets, weighing 20 to 28 kg.

INTERVENTIONS

Three groups of animals were studied: a control group (n = 6); a lipopolysaccharide (LPS)-treated group (n = 5) receiving Escherichia coli endotoxin (5 micrograms/kg/min over 30 mins); and an LPS + L-NAME group (n = 5) receiving endotoxin and, 1 hr after, a bolus of L-NAME (25 mg/kg).

MEASUREMENTS AND MAIN RESULTS

Hemodynamic changes, usual coagulation parameters, and plasma concentrations of thrombin-antithrombin complexes, antithrombin III activity (At III), tissue plasminogen activator, plasminogen activator inhibitor type 1, and von Willebrand factor were measured at baseline, and at 30, 60, 90, 120, 180, 240, and 300 mins. After euthanasia or death, lungs and kidneys were withdrawn for histologic study. The extent of microvascular thrombosis was assessed by a semiquantitative disseminated intravascular coagulation score. In both septic endotoxin group, administration of LPS resulted in hemodynamic changes typical of severe septic shock, with disseminated intravascular coagulation and histologic changes characterized by adult respiratory distress syndrome and kidney microthrombosis. L-NAME administration normalized mean arterial pressure with a dramatic increase in systemic vascular resistances and a marked decrease in cardiac index. The changes in usual coagulation parameters, AT III, tissue plasminogen activator, and plasminogen-activator inhibitor type 1 concentrations were not different between both septic groups. However, in the LPS + L-NAME group, thrombin-antithrombin complexes and von Willebrand factor were higher and associated with a higher histologic disseminated intravascular coagulation score.

CONCLUSION

In this model of endotoxin septic shock, L-NAME administration resulted in histologic and coagulation changes consistent with an increased activation of intravascular coagulation.

Nitric oxide dose response during moderate and severe hypoxia in swine

BACKGROUND

Elucidation of factors that influence the dose response to inhaled nitric oxide is crucial to optimizing its therapeutic benefit. We investigated whether severity of hypoxia is one such factor.

METHODS

Seven Yorkshire swine underwent 14 triphasic experiments: (1) control period of mechanical ventilation (fractional concentration of oxygen = 0.3); (2) induction of hypoxic pulmonary hypertension (fractional concentration of oxygen = 0.1 to 0.15); and (3) inhaled nitric oxide at 5, 10, 20, 40, and 80 parts per million (ppm). Hemodynamics and arterial blood gases were measured by pulmonary and systemic arterial catheters.

RESULTS

Experiments were divided into two groups of seven based on hypoxia severity: severe (arterial oxygen tension, 25 to 40 mm Hg) and moderate (arterial oxygen tension, 41 to 60 mm Hg). The percent changes in mean pulmonary artery pressure after each dose were compared within each group by repeated measure analysis of variance and each dose was compared between the two groups by Student's t test. A statistically significant dose response existed in both groups (p < 0.02). Low doses resulted in significantly less vasodilation in the severe versus the moderate hypoxia group (5 ppm, 59% +/- 6% versus 94% +/- 7%, p = 0.003; 10 ppm, 69% +/- 8% versus 99% +/- 8%, p = 0.017).

CONCLUSIONS

Lower doses are significantly less effective in achieving maximal pulmonary vasodilation during severe hypoxia. Therefore, the degree of hypoxia is a determinant of the inhaled nitric oxide dose response.

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

OBJECTIVE

To assess the efficacy of inhaled nitric oxide in improving pulmonary hypertension and gas exchange following oleic acid-induced acute lung injury.

DESIGN

Prospective, pharmacologic study.

SETTING

Surgical research laboratory at the University of Pittsburgh, Pittsburgh, PA.

SUBJECTS

Instrumented, intubated pigs weighing 16 to 27 kg.

INTERVENTIONS

Intravenous oleic acid and inhaled nitric oxide.

MEASUREMENTS AND MAIN RESULTS

All pigs treated with intravenous oleic acid (0.11 mL/kg) developed a severe lung injury with pulmonary hypertension, accompanied by impaired oxygenation, intrapulmonary shunting, and increased extravascular lung water (p < .05 compared with baseline). Following nitric oxide inhalation, although pulmonary hypertension decreased in a dose-dependent fashion, no amelioration in pulmonary gas exchange was observed, as reflected by PaO2 and intrapulmonary shunt. Plasma nitrite and nitrate concentrations, the stable end products of nitric oxide metabolism, did not increase following nitric oxide exposure in this model of severe lung injury.

CONCLUSIONS

The effect of inhaled nitric oxide, restricted to relieving pulmonary vasoconstriction in this model of lung injury, may have limited benefit in improving pulmonary gas exchange when diffusion is impaired by severe lung injury and inflammatory thickening of the alveolar-capillary barrier. Nitric oxide inhalation may have better results when used at an earlier, less severe stage of acute lung injury.

Nitric oxide decreases lung injury after intestinal ischemia

After injury to a primary organ, mediators are released into the circulation and may initiate inflammation of remote organs. We hypothesized that the local production of nitric oxide (NO) may act to limit the spread of inflammation to secondarily targeted organs. In anesthetized rats, 30 min of intestinal ischemia followed by 2 h of reperfusion (I/R) did not increase lung albumin leak. However, after treatment with NG-nitro-L-arginine methyl ester (L-NAME), intestinal I/R led to increased lung leak, suggesting a protective effect of endogenous NO. The site of action of NO appeared to be the lung and not the gut because 1) after treatment with L-NAME, local delivery of NO to the lung by inhalation abolished the increase in intestinal I/R-induced lung leak; 2) L-NAME had no effect on epithelial permeability (51Cr-labeled EDTA clearance) of reperfused small bowel; and 3) after treatment with L-NAME, local delivery of NO to the gut by luminal perfusion did not improve epithelial permeability of reperfused intestines. Furthermore, L-NAME increased, and inhaled NO decreased, the density of lung neutrophils in rats subjected to intestinal I/R, and treatment with the selectin antagonist fucoidan abolished L-NAME-induced lung leak in rats subjected to intestinal I/R. We conclude that endogenous lung NO limits secondary lung injury after intestinal I/R by decreasing pulmonary neutrophil retention.

Inhaled nitric oxide improved the outcome of severe right ventricular failure caused by lipopolysaccharide administration

OBJECTIVE

To evaluate the efficacy of nitric oxide (NO) inhalation against endotoxin-induced lung injury.

DESIGN

Randomized prospective short-term study.

SETTING

University school of Medicine Laboratory.

INTERVENTIONS

Animal experiment (using 16 Japanese white rabbits). The animals inhaled NO at a concentration of 10 ppm.

MEASUREMENTS AND RESULTS

The rabbits were randomly divided into the NO inhaling group (n = 7) and the control group (n = 9). Both groups received continuous infusion of 1200 mcg lipopolysaccharide (LPS) and the NO group inhaled 10 ppm NO during the LPS administration. In the control group, severe right ventricular (RV) failure was observed at 30-90 min of LPS infusion, and 4 of 9 animals died within 90 min of LPS infusion. In the NO group, none of the animals died and the early phase hemodynamic deterioration was milder than in the control group. But pulmonary gas exchange was not significantly different between the two groups throughout the study. At the end of the study there were no significant differences in any parameters of the surviving animals between the two groups.

CONCLUSION

Although an improvement of pulmonary gas exchange was not demonstrated, NO inhalation (10 ppm) improved the outcome of severe RV failure caused by LPS infusion.

Nitric oxide improves transpulmonary vascular mechanics but does not change intrinsic right ventricular contractility in an acute respiratory distress syndrome model with permissive hypercapnia

OBJECTIVE

To test the hypothesis that in a swine model of acute respiratory distress syndrome (ARDS) with permissive hypercapnia, inhaled nitric oxide would improve transpulmonary vascular mechanics and right ventricular workload while not changing intrinsic right ventricular contractility.

DESIGN

Prospective, randomized, controlled laboratory trial.

SETTING

University research laboratory.

SUBJECTS

Eleven swine (30 to 46 kg).

INTERVENTIONS

The swine were anesthetized, intubated, and paralyzed. After median sternotomy, pressure transducers were placed in the right ventricle, pulmonary artery, and left atrium. An ultrasonic flow probe was placed around the pulmonary artery. Ultrasonic dimension transducers were sutured onto the heart at the base, apex, left ventricle (anterior, posterior, free wall), and right ventricle (free wall). An additional transducer was placed in the interventricular septum. A surfactant depletion model of ARDS was created by saline lung lavage. Nitric oxide was administered at 2, 4, and 6 parts per million (ppm), in a random order, under the condition of permissive hypercapnia (Paco2 55 to 75 torr [7.3 to 10.0 kPa]).

MEASUREMENTS AND MAIN RESULTS

We evaluated the pulmonary vascular and right ventricular effects of permissive hypercapnia, with and without inhaled nitric oxide, by measuring variables of transpulmonary vascular mechanics and right ventricular function. These variables included mean pulmonary arterial pressure, right ventricular total power, right ventricular stroke work, transpulmonary vascular efficiency, and right ventricular intrinsic contractility. Data were obtained after lung injury under the following conditions: a) normocapnia (Paco2 35 to 45 torr [4.7 to 6.0 kPa]) and nitric oxide at 0 ppm; b) hypercapnia and nitric oxide at 0 ppm; c) hypercapnia and nitric oxide at 2, 4, and 6 ppm; and d) repeat measurements with hypercapnia and nitric oxide at 0 ppm. In ARDS with permissive hypercapnia, inhaled nitric oxide therapy (2 to 6 ppm) improved transpulmonary vascular mechanics and right ventricular workload by lowering pulmonary arterial pressure (29.6 +/- 1.3 vs. 24.6 +/- 1.0 mm Hg, p = .0001), increasing transpulmonary vascular efficiency (13.9 +/- 0.5 vs. 16.1 +/- 0.7 L/W-min, p = .0001), decreasing right ventricular total power (142 +/- 9 vs. 115 +/- 9 mW, p = .001), and decreasing right ventricular stroke work (653 +/- 37 vs. 525 +/- 32 ergs x 10(3), p = .001). Inhaled nitric oxide did not change right ventricular contractility, as measured by preload-recruitable stroke work.

CONCLUSIONS

Inhaled nitric oxide ameliorated any negative effects of hypoxic and hypercapnic pulmonary vasoconstriction. The beneficial effects of inhaled nitric oxide are related to alterations in right ventricular afterload and not intrinsic right ventricular contractility. The improved cardiopulmonary effects of inhaled nitric oxide with permissive hypercapnia potentially expand the use of nitric oxide in ARDS and other conditions in which this strategy is employed.

Intestinal reperfusion up-regulates inducible nitric oxide synthase activity within the lung

BACKGROUND

This study examines the hypothesis that pulmonary inducible nitric oxide synthase (iNOS) activity is up-regulated during intestinal reperfusion and that inhibition of NO generation exacerbates pulmonary microvascular dysfunction.

METHODS

Sprague-Dawley rats underwent intestinal ischemia and reperfusion (IIR) or sham operation (SHAM). Pulmonary iNOS activity was measured by quantitating the conversion of L-arginine (L-Arg) to L-citrulline. Another set of animals undergoing IIR or SHAM received an inhibitor of NOS (NG-nitro-L-arginine methylester; L-NAME; 20 mg/kg intravenously), substrate for NO generation (L-Arg; 300 mg/kg intravenously), or vehicle (normal saline solution; 3 ml). Pulmonary microvascular dysfunction was then quantitated by measuring the extravasation of Evans blue dye (EBD) into the lung.

RESULTS

Inducible NOS activity was six times greater in the lungs of animals sustaining IIR when compared with SHAM (p = 0.0005). The concentration of EBD within the lungs of animals sustaining IIR was 30% greater than SHAM (p < 0.05). Inhibiting NOS with L-NAME significantly increased pulmonary EBD concentration of both IIR and SHAM groups when compared with normal saline solution-treated animals (p < 0.0001). Treatment with L-Arg prevented this IIR-induced increase in pulmonary dye extravasation.

CONCLUSIONS

These data suggest that pulmonary iNOS activity is up-regulated in animals sustaining IIR and that this may serve as a compensatory protective response to remote organ injury.

Severity of hypoxia predicts response to nitric oxide in a porcine pulmonary hypertension model

Although inhaled nitric oxide (NO) has been variably successful in resolving pulmonary hypertension in neonates, children, and adults, no parameters predictive of response to this therapy have been elucidated. We conducted an animal study to determine if severity of hypoxia can predict magnitude and sustenance of response to inhaled NO therapy. Seven Yorkshire swine weighing 11 to 20 kg underwent 16 experiments, each consisting of four phases: Phase 1: Control period of ventilation on FIO2 .3; phase 2: Hypoxic period on FIO2 .10 to .15, establishing pulmonary hypertension; phase 3: Treatment period with NO starting at five parts per million (ppm), doubling dose every 10 min to 80 ppm; phase 4: Posttreatment observation period after discontinuation of NO while maintaining hypoxia for 1 hour or until circulatory failure or pulmonary hypertension of pre-NO magnitude developed. Each animal underwent a maximum of three experiments in random order of hypoxia severity before sacrifice with pentobarbital overdose. Continuous hemodynamic parameters, intermittent cardiac output and pulmonary capillary wedge pressure, and intermittent arterial blood gas analyses were obtained through pulmonary and systemic artery catheters placed by femoral cutdown. Pulmonary and systemic vascular resistances (PVR and SVR) were calculated by standard formulas. Experiments were divided into two groups (n = 8 in each): group 1 with severe hypoxia (PaO2, 25 to 35) and group 2 with moderate hypoxia (PaO2, 36 to 65). Data for all hemodynamic parameters were expressed as mean percentage change from baseline (phase 1) +/- SEM under each set of conditions, and the two groups were compared by two-way analysis of variance and covariance adjusted for order of experimentation.(ABSTRACT TRUNCATED AT 250 WORDS)