Nebulized prostacyclin (PGI2) in acute respiratory distress syndrome: impact of primary (pulmonary injury) and secondary (extrapulmonary injury) disease on gas exchange response

A Narrative Review on the Administration of Inhaled Prostaglandins in Critically Ill Adult Patients With Acute Respiratory Distress Syndrome

OBJECTIVE

To describe the effect of inhaled prostaglandins on both oxygenation and mortality in critically ill patients with acute respiratory distress syndrome (ARDS), with a focus on safety and efficacy in coronavirus disease 2019 (COVID-19)-associated ARDS and non-COVID-19 ARDS.

DATA SOURCES

A literature search of MEDLINE was performed using the following search terms: inhaled prostaglandins, inhaled epoprostenol, inhaled nitric oxide, ARDS, critically ill. All abstracts were reviewed.

STUDY SELECTION AND DATA EXTRACTION

Relevant English-language reports and studies conducted in humans between 1980 and June 2023 were considered.

DATA SYNTHESIS

Data regarding inhaled prostaglandins and their effect on oxygenation are limited but show a benefit in patients who respond to therapy, and data pertaining to their effect on mortality is scarce. Concerns exist regarding the formulation of inhaled epoprostenol (iEPO) utilized in addition to modes of medication delivery; however, the limited data surrounding their use have shown a reasonable safety profile. Other avenues and beneficial effects may exist with inhaled prostaglandins, such as use in COVID-19-associated ARDS or non-COVID-19 ARDS patients undergoing noninvasive mechanical ventilation or during patient transport.

RELEVANCE TO PATIENT CARE AND CLINICAL PRACTICE

The use of inhaled prostaglandins can be considered in critically ill patients with COVID-19-associated ARDS or non-COVID-19 ARDS who are experiencing difficulties with oxygenation refractory to nonpharmacologic strategies.

CONCLUSIONS

The use of iEPO and other inhaled prostaglandins requires further investigation to fully elucidate their effects on clinical outcomes, but it appears these medications may have a potential benefit in COVID-19-associated ARDS and non-COVID-19 ARDS patients with refractory hypoxemia but with little effect on mortality.

Inhaled Prostacyclins for Acute Respiratory Distress Syndrome: A Systematic Review and Meta-Analysis

Studies evaluating inhaled prostacyclins for the management of acute respiratory distress syndrome (ARDS) have produced inconsistent results regarding their effect on oxygenation. The purpose of this systematic review and meta-analysis was to evaluate the change in the Pao₂/Fio₂ ratio after administration of an inhaled prostacyclin in patients with ARDS.

DATA SOURCES

We searched Ovid Medline, Embase, Cumulative Index to Nursing and Allied Health Literature, Cochrane, Scopus, and Web of Science.

STUDY SELECTION

We included abstracts and trials evaluating administration of inhaled prostacyclins in patients with ARDS.

DATA EXTRACTION

Change in the Pao₂/Fio₂ ratio, Pao₂, and mean pulmonary artery pressure (mPAP) were extracted from included studies. Evidence certainty and risk of bias were evaluated using Grading of Recommendations Assessment, Development, and Evaluation and the Cochrane Risk of Bias tool.

DATA SYNTHESIS

We included 23 studies (1,658 patients) from 6,339 abstracts identified by our search strategy. The use of inhaled prostacyclins improved oxygenation by increasing the Pao₂/Fio₂ ratio from baseline (mean difference [MD], 40.35; 95% CI, 26.14-54.56; p < 0.00001; I² = 95%; very low quality evidence). Of the eight studies to evaluate change in Pao₂, inhaled prostacyclins also increased Pao₂ from baseline (MD, 12.68; 95% CI, 2.89-22.48 mm Hg; p = 0.01; I² = 96%; very low quality evidence). Only three studies evaluated change in mPAP, but inhaled prostacyclins were found to improve mPAP from baseline (MD, -3.67; 95% CI, -5.04 to -2.31 mm Hg; p < 0.00001; I² = 68%; very low quality evidence).

CONCLUSIONS

In patients with ARDS, use of inhaled prostacyclins improves oxygenation and reduces pulmonary artery pressures. Overall data are limited and there was high risk of bias and heterogeneity among included studies. Future studies evaluating inhaled prostacyclins for ARDS should evaluate their role in ARDS subphenotypes, including cardiopulmonary ARDS.

Right ventricle-specific therapies in acute respiratory distress syndrome: a scoping review

OBJECTIVE

To summarize knowledge and identify gaps in evidence regarding treatment of right ventricular dysfunction (RVD) in acute respiratory distress syndrome (ARDS).

DATA SOURCES

We conducted a comprehensive search of MEDLINE, Embase, CINAHL, Web of Science, and the Cochrane Central Register of Controlled Trials.

STUDY SELECTION

Studies were included if they reported effects of treatments on right ventricular function, whether or not the intent was to modify right ventricular function.

DATA EXTRACTION

Data extraction was performed independently and in duplicate by two authors. Data items included the study design, patient population, type of intervention, comparison group, and RV-specific outcomes.

DATA SYNTHESIS

Of 1,430 studies screened, 51 studies reporting on 1,526 patients were included. By frequency, the included studies examined the following interventions: ventilator settings (29.4%), inhaled medications (33.3%), extracorporeal life support (13.7%), intravenous or oral medications (13.7%), and prone positioning (9.8%). The majority of the studies were non-randomized experimental studies (53%), with the next most common being case reports (16%). Only 5.9% of studies were RCTs. In total, 27% of studies were conducted with the goal of modifying RV function.

CONCLUSIONS

Given the prevalence of RVD in ARDS and its association with mortality, the dearth of research on this topic is concerning. This review highlights the need for prospective trials aimed at treating RV dysfunction in ARDS.

Pulmonary Hypertension and COVID-19

Coronavirus disease 2019 (COVID-19) is a primary respiratory infectious disease, which can result in pulmonary and cardiovascular complications. From its first appearance in the city of Wuhan (China), the infection spread worldwide, leading to its declaration as a pandemic on March 11, 2020. Clinical research on SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) suggests that the virus may determine changes in the pulmonary hemodynamics through mechanisms of endothelial dysfunction, vascular leak, thrombotic microangiopathy, and venous thromboembolism that are similar to those leading to pulmonary hypertension (PH). Current available studies report echocardiographic signs of PH in approximately 12 to 13% of hospitalized patients with COVID-19. Those with chronic pulmonary obstructive disease, congestive heart failure, pulmonary embolism, and prior PH are at increased risk to develop or worsen PH. Evidence of PH seems to be associated with increased disease severity and poor outcome. Because of the importance of the pulmonary hemodynamics in the pathophysiology of COVID-19, there is growing interest in exploring the potential therapeutical benefits of inhaled vasodilators in patients with COVID-19. Treatment with inhaled nitric oxide and prostacyclin has shown encouraging results through improvement of systemic oxygenation, reduction of systolic pulmonary arterial pressure, and prevention of right ventricular failure; however, data from randomized control trials are still required.

Randomized, Placebo-controlled Trial of Inhaled Treprostinil for Patients at Risk for Acute Respiratory Distress Syndrome

Rationale: Inhaled treprostinil may improve oxygenation and have additional antiinflammatory effects in early acute hypoxemic respiratory failure, potentially preventing or reducing the severity of acute respiratory distress syndrome (ARDS).Objectives: To determine whether administration of inhaled treprostinil to patients at risk for ARDS is feasible, safe, and efficacious.Methods: We performed a double-blind, placebo-controlled, single-center randomized pilot trial at a quaternary care academic medical center. Patients with acute hypoxemia due to pneumonia or signs of low-pressure pulmonary edema with a unilateral or bilateral infiltrate on chest imaging and a 4 L/min supplemental oxygen requirement not requiring positive pressure ventilation were evaluated. Randomized patients received study drug or placebo (2:1 ratio). Treatment was initiated at 6 breaths every 4 hours and titrated up to 12 breaths. Subjects were maintained on treatment for 7 days and then tapered off over a period of 4 days. Study drug was stopped if positive pressure ventilation was required (invasive or noninvasive).Results: Fourteen patients were enrolled over a period of 31 months. Baseline characteristics were not significantly different between treatment groups with respect to age, sex, race, Acute Physiologic Assessment and Chronic Health Evaluation score, lung injury prediction score, or baseline mean oxygen saturation as measured by pulse oximetry (Sp_O2):fraction of inspired oxygen (Fi_O2) ratio. Trends in daily baseline and 30-minute postdose Sp_O2:Fi_O2 ratio for all treatment points were not significantly different between placebo and treprostinil. Four patients required positive pressure ventilation in the treprostinil group versus one in the placebo group.Conclusions: Inhaled treprostinil administration is feasible in patients at risk for ARDS but was not associated with improvement in the Sp_O2:Fi_O2 ratio relative to placebo. Drug-associated adverse events were not severe nor unexpected based on the known adverse effect profile of inhaled treprostinil. The clinical benefit of this intervention is unclear at this time in the absence of larger studies.Clinical trial registered with Clinicaltrials.gov (NCT02370095).

Molecular Dynamics of Lipopolysaccharide-Induced Lung Injury in Rodents

Acute respiratory distress syndrome (ARDS) is a common disease entity in critical care medicine and is still associated with a high mortality. Because of the heterogeneous character of ARDS, animal models are an insturment to study pathology in relatively standardized conditions. Rodent models can bridge the gap from in vitro investigations to large animal and clinical trials by facilitating large sample sizes under physiological conditions at comparatively low costs. One of the most commonly used rodent models of acute lung inflammation and ARDS is administration of lipopolysaccharide (LPS), either into the airways (direct, pulmonary insult) or systemically (indirect, extra-pulmonary insult). This narrative review discusses the dynamics of important pathophysiological pathways contributing to the physiological response to LPS-induced injury. Pathophysiological pathways of LPS-induced lung injury are not only influenced by the type of the primary insult (e.g., pulmonary or extra-pulmonary) and presence of additional stimuli (e.g., mechanical ventilation), but also by time. As such, findings in animal models of LPS-induced lung injury may depend on the time point at which samples are obtained and physiological data are captured. This review summarizes the current evidence and highlights uncertainties on the molecular dynamics of LPS-induced lung injury in rodent models, encouraging researchers to take accurate timing of LPS-induced injury into account when designing experimental trials.

Effectiveness, Safety, and Economic Comparison of Inhaled Epoprostenol Brands, Flolan and Veletri, in Acute Respiratory Distress Syndrome

Background: No previous studies exist examining 2 inhaled epoprostenol formulations in an acute respiratory distress syndrome (ARDS) patient population. Objective: The study aim was to evaluate a formulary conversion from inhaled Flolan to Veletri to determine the impact on effectiveness, safety, and cost in patients with ARDS. Methods: This was a single-center, retrospective, matched cohort observational study at a tertiary care academic medical center. Patients included were mechanically ventilated, adult patients with ARDS receiving inhaled Flolan or Veletri for ≥1 hour in the intensive care unit. Results: A total of 132 patients were included in the matched cohort. There was no difference detected in change in partial pressure of arterial O₂/fraction of inspired O₂ (PaO₂/FiO₂) ratio after 1 hour of therapy between the inhaled Flolan and Veletri groups (27.2 ± 46.2 vs 30 ± 68 mm Hg, P = 0.78). Significant differences in secondary outcomes included incidence of hypotension (83% vs 95.5%, P = 0.04) and thrombocytopenia (9.1% vs 29.5%, P < 0.01) in the inhaled Flolan and Veletri groups, respectively, with no difference in cost per duration of therapy (P = 0.29). Conclusions and Relevance: There was no difference in the change in PaO₂/FiO₂ ratio after 1 hour of therapy between inhaled Flolan and Veletri in an ARDS patient population. The formulary conversion from inhaled Flolan to Veletri was likely justified.

Inhaled epoprostenol utilization pattern after implementation of an administration policy

Epoprostenol, a pulmonary vasodilator, is used to reduce pulmonary artery pressure. Its inhaled administration results in ventilation and perfusion matching with oxygenation improvement. Epoprostenol is used as treatment for various conditions, particularly acute respiratory distress syndrome (ARDS) and pulmonary arterial hypertension. In 2018, Baylor University Medical Center implemented a policy for inhaled epoprostenol utilization aimed at standardizing clinical practice. This study analyzed epoprostenol utilization patterns in patients with ARDS after implementation of this administration policy. Drug responders and nonresponders were compared for clinical outcomes and physiologic changes before and after use, and policy compliance was evaluated. Of 79 eligible patients, 30 fulfilled inclusion criteria: 14 (47%) had ARDS and 16 (53%) had non-ARDS. In all patients with ARDS, epoprostenol was a second rescue agent after neuromuscular blockade, prone positioning, corticosteroids, and extracorporeal membrane oxygenation. Epoprostenol was associated with statistically significant improvement of oxygenation before and after utilization in patients with ARDS (ratio of arterial oxygen partial pressure to fractional inspired oxygen 70 vs 140, respectively; P = 0.04). Overall, 10 (71%) ARDS patients were epoprostenol responders; 9 (56%) were deemed responders among subjects with non-ARDS. Comparison of outcomes between responders and nonresponders showed no statistically significant variations. Policy compliance was obtained in 24 (80%) patients.

Inhaled Epoprostenol Through Noninvasive Routes of Ventilator Support Systems

BACKGROUND

The administration of inhaled epoprostenol (iEPO) through noninvasive routes of ventilator support systems has never been previously evaluated.

OBJECTIVE

Describe the use of iEPO when administered through noninvasive routes of ventilator support systems.

METHODS

Critically ill patients admitted to the intensive care unit who received iEPO through noninvasive routes were analyzed. Improvements in respiratory status and hemodynamic parameters were evaluated. Safety end points assessed included hypotension, rebound hypoxemia, significant bleeding, and thrombocytopenia.

RESULTS

A total of 36 patients received iEPO through noninvasive routes: high-flow oxygen therapy through nasal cannula, n = 29 (81%) and noninvasive positive-pressure ventilation, n = 7 (19%). Sixteen patients had improvement in their respiratory status: mean decrease in fraction of inspired oxygen (FiO₂), 20% ± 13%; mean increase in partial pressure of arterial oxygen to FiO₂ (PaO₂/FiO₂) ratio, 60 ± 50 mm Hg; and mean decrease in HFNC oxygen flow rate, 6 ± 3 liters per minute (LPM). Eight patients had declines in their respiratory status (mean increase in FiO₂, 30% ± 20%; mean decrease in PaO₂/FiO₂ ratio, 38 ± 20 mm Hg; and mean increase in HFNC oxygen flow rate, 15 ± 10 LPM), and 12 patients had no change in their respiratory status. Conclusion and Relevance: This represents the first evaluation of the administration of iEPO through noninvasive routes of ventilator support systems and demonstrates that in critically ill patients, iEPO could be administered through a noninvasive route. Further evaluation is needed to determine the extent of benefit with this route of administration.

Aerosolized prostacyclins for acute respiratory distress syndrome (ARDS)

BACKGROUND

Acute respiratory distress syndrome (ARDS) is a critical condition that is associated with high mortality and morbidity. Aerosolized prostacyclin has been used to improve oxygenation despite the limited evidence available so far.This review was originally published in 2010 and updated in 2017.

OBJECTIVES

To assess the benefits and harms of aerosolized prostacyclin in adults and children with ARDS.

SEARCH METHODS

In this update, we searched CENTRAL (2017, Issue 4); MEDLINE (OvidSP), Embase (OvidSP), ISI BIOSIS Previews, ISI Web of Science, LILACS, CINAHL (EBSCOhost), and three trials registers. We handsearched the reference lists of the latest reviews, randomized and non-randomized trials, and editorials, and cross-checked them with our search of MEDLINE. We contacted the main authors of included studies to request any missed, unreported or ongoing studies. The search was run from inception to 5 May 2017.

SELECTION CRITERIA

We included all randomized controlled trials (RCTs), irrespective of publication status, date of publication, blinding status, outcomes published or language. We contacted trial investigators and study authors to retrieve relevant and missing data.

DATA COLLECTION AND ANALYSIS

Three authors independently abstracted data and resolved any disagreements by discussion. Our primary outcome measure was all-cause mortality. We planned to perform subgroup and sensitivity analyses to assess the effect of aerosolized prostacyclin in adults and children, and on various clinical and physiological outcomes. We assessed the risk of bias through assessment of methodological trial components and the risk of random error through trial sequential analysis.

MAIN RESULTS

We included two RCTs with 81 participants.One RCT involved 14 critically ill children with ARDS (very low quality of evidence), and one RCT involved 67 critically ill adults (very low quality evidence).Only one RCT (paediatric trial) provided data on mortality and found no difference between intervention and control. However, this trial was eligible for meta-analysis due to a cross-over design.We assessed the benefits and harms of aerosolized prostacyclin. One RCT found no difference in improvement of partial pressure of oxygen in arterial blood/fraction of inspired oxygen (PaO₂/FiO₂) ratio (mean difference (MD) -25.35, 95% confidence interval (CI) -60.48 to 9.78; P = 0.16; 67 participants, very low quality evidence).There were no adverse events such as bleeding or organ dysfunction in any of the included trials. Due to the limited number of RCTs, we were unable to perform the prespecified subgroup and sensitivity analyses or trial sequential analysis.

AUTHORS' CONCLUSIONS

We are unable to tell from our results whether the intervention has an important effect on mortality because the results were too imprecise to rule out a small or no effect. Therefore, no current evidence supports or refutes the routine use of aerosolized prostacyclin for people with ARDS. There is an urgent need for more RCTs.

Effect of Manual Hyperinflation on Hemodynamics, Gas Exchange, and Respiratory Mechanics in Ventilated Patients

The authors investigated the effect of manual hyperinflation (MHI) with set parameters applied to patients on mechanical ventilation on hemodynamics, respiratory mechanics, and gas exchange. Sixteen critically ill patients post-septic shock, with acute lung injury, were studied. Heart rate, arterial pressure, and mean pulmonary artery pressure were recorded every minute. Pulmonary artery occlusion pressure, cardiac output, arterial blood gases, and dynamic compliance (Cdyn) were recorded pre- and post-MHI. From this, systemic vascular resistance index (SVRI), cardiac index, oxygen delivery, and partial pressure of oxygen: fraction of inspired oxygen (PaO2:FiO2) ratio were calculated. There were significant increases in SVRI ( P < 0.05) post-MHI and diastolic arterial pressure ( P < 0.01) during MHI. Cdyn increased post-MHI ( P < 0.01) and was sustained at 20 minutes post-MHI ( P < 0.01). Subjects with an intrapulmonary cause of lung disease had a significant decrease ( P = 0.02) in PaO2:FiO2, and those with extrapulmonary causes of lung disease had a significant increase ( P < 0.001) in PaO2:FiO2 post-MHI. In critically ill patients, MHI resulted in an improvement in lung mechanics and an improvement in gas exchange in patients with lung disease due to extrapulmonary events and did not result in impairment of the cardiovascular system.

The role of inhaled prostacyclin in treating acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is a syndrome of acute lung injury that is characterized by noncardiogenic pulmonary edema and severe hypoxemia second to a pathogenic impairment of gas exchange. Despite significant advances in the area, mortality remains high among ARDS patients. High mortality and a limited spectrum of therapeutic options have left clinicians searching for alternatives, spiking interest in selective pulmonary vasodilators (SPVs). Despite the lack of robust evidence, SPVs are commonly employed for their therapeutic role in improving oxygenation in patients who have developed refractory hypoxemia in ARDS. While inhaled epoprostenol (iEPO) also impacts arterial oxygenation by decreasing ventilation-perfusion (V/Q) mismatching and pulmonary shunt flow, this effect is not different from inhaled nitric oxide (iNO). The most effective and safest dose for yielding a clinically significant increase in PaO2 and reduction in pulmonary artery pressure (PAP) appears to be 20-30 ng/kg/min in adults and 30 ng/kg/min in pediatric patients. iEPO appears to have a ceiling effect above these doses in which no additional benefit may be derived. iNO and iEPO have shown similar efficacy profiles; however, they differ with respect to cost and ease of therapeutic administration. The most beneficial effects of iEPO have been seen in adult patients with secondary ARDS as compared with primary ARDS, most likely due to the difference in etiology of the two disease states, and in patients suffering from baseline right ventricular heart failure. Although iEPO has demonstrated improvements in hemodynamic parameters and oxygenation in ARDS patients, due to the limited number of randomized clinical trials and the lack of studies investigating mortality, the use of iEPO cannot be recommended as standard of care in ARDS. iEPO should be reserved for those refractory to traditional therapies.

The use of inhaled prostaglandins in patients with ARDS: a systematic review and meta-analysis

OBJECTIVE

This study aimed to determine whether inhaled prostaglandins are associated with improvement in pulmonary physiology or mortality in patients with ARDS and assess adverse effects.

METHODS

The following data sources were used: PubMed, EMBASE, CINAHL, Cochrane Central Register of Controlled Trials, Cochrane Database of Systematic Reviews, reference lists, conference proceedings, and ClinicalTrials.gov. Studies selected included randomized controlled trials and nonrandomized studies. For data extraction, two reviewers independently screened titles and abstracts for eligibility. With regard to data synthesis, 25 studies (two RCTs) published over 21 years (1993-2014) were included. The PROSPERO registration number was CRD42014013180.

RESULTS

One randomized controlled trial showed no difference in the change in mean Pao2 to Fio2 ratio when comparing inhaled alprostadil to placebo: 141.2 (95% CI, 120.8-161.5) to 161.5 (95% CI, 134.6-188.3) vs 163.4 (95% CI, 140.8-186.0) to 186.8 (95% CI, 162.9-210.7), P = .21. Meta-analysis of the remaining studies demonstrated that inhaled prostaglandins were associated with improvement in Pao2 to Fio2 ratio (16 studies; 39.0% higher; 95% CI, 26.7%-51.3%), and Pao2 (eight studies; 21.4% higher; 95% CI, 12.2%-30.6%), and a decrease in pulmonary artery pressure (-4.8 mm Hg; 95% CI, -6.8 mm Hg to -2.8 mm Hg). Risk of bias and heterogeneity were high. Meta-regression found no association with publication year (P = .862), baseline oxygenation (P = .106), and ARDS etiology (P = .816) with the treatment effect. Hypotension occurred in 17.4% of patients in observational studies.

CONCLUSIONS

In ARDS, inhaled prostaglandins improve oxygenation and decrease pulmonary artery pressures and may be associated with harm. Data are limited both in terms of methodologic quality and demonstration of clinical benefit. The use of inhaled prostaglandins in ARDS needs further study.

A review of inhaled nitric oxide and aerosolized epoprostenol in acute lung injury or acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) and acute lung injury (ALI) are conditions associated with an estimated mortality of 40–50%. The use of inhaled vasodilators can help to improve oxygenation without hemodynamic effects. This article reviews relevant studies addressing the safety and efficacy of inhaled nitric oxide (iNO) and aerosolized epoprostenol (aEPO) in the treatment of life-threatening hypoxemia associated with ARDS and ALI. In addition, the article also provides a practicable guide to the clinical application of these therapies. Nine prospective randomized controlled trials were included for iNO reporting on changes in oxygenation or clinical outcomes. Seven reports of aEPO were examined for changes in oxygenation. Based on currently available data, the use of either iNO or aEPO is safe to use in patients with ALI or ARDS to transiently improve oxygenation. No differences have been observed in survival, ventilator-free days, or attenuation in disease severity. Further studies with consistent end points using standard delivery devices and standard modes of mechanical ventilation are needed to determine the overall benefit with iNO or aEPO.

Efficacy, Safety, and Medication Errors Associated with the Use of Inhaled Epoprostenol for Adults with Acute Respiratory Distress Syndrome: A Pilot Study

BACKGROUND:

Acute respiratory distress syndrome (ARDS) is a type of hypoxic respiratory failure that results from ventilation and perfusion mismatching. Inhaled epoprostenol induces relaxation of smooth muscle in pulmonary vasculature, leading to improved oxygenation.

OBJECTIVE:

To determine if the use of inhaled epoprostenol produced a 10% or greater increase in the ratio of arterial partial pressure of oxygen (PaO2) to fraction of inspired oxygen (FiO2) in ARDS patients and to review adverse events and medication errors.

METHODS:

An observational chart review was performed based on a report generated from the electronic medical record system. Patients who received at least 1 dose of inhaled epoprostenol from January 1, 2008, to December 31, 2010, at any hospital within the Florida Hospital Health System were considered for inclusion. Demographics, dose, duration of therapy, adverse effects, medication errors, and outcomes data were collected.

RESULTS:

Sixteen patients were included in the study. Oxygenation improved by 10% or more in 62.5% (10/16) of the patients, with an initial (within the first 4 hours) median increase of 44.5% in PaO2/FiO2. The mean (SD) starting dose was 30 (10) ng/kg/min. Medication errors were observed in 25% (4/16) of patients. Hypotension was the most frequently observed adverse event, with a rate of 18.8% (3/16).

CONCLUSIONS:

Based on study findings, inhaled epoprostenol may improve oxygenation in patients with ARDS, with findings suggesting a 62.5% response to therapy. The significance of these effects on improving survival remains unknown. The frequency of medication errors observed in this study poses a significant concern regarding the administration of epoprostenol. Further controlled prospective studies are needed to determine the role of inhaled epoprostenol in improving survival in patients with ARDS.

Mechanical ventilation

The treatment of respiratory failure requiring mechanical ventilation has advanced significantly over the last 20 years. The goal of therapy in patients with acute respiratory distress syndrome should be to optimize oxygenation while minimizing the risk of ventilator-induced lung injury and providing adequate ventilation. Appropriate use of ventilation modes and strategies, positive-end expiratory pressure levels, and recruitment maneuvers can improve oxygen delivery. Salvage therapies, such as prone positioning, inhaled epoprostenol and nitric oxide, and high-frequency oscillatory ventilation, have a well-established role in supportive management and are associated with improved oxygenation but not survival.

Inhaled epoprostenol for the treatment of pulmonary arterial hypertension in critically ill adults

Pulmonary arterial hypertension (PAH) is a progressive disease without a cure. The primary treatment goal for patients with this disease is improving pulmonary blood flow through vasodilation of the pulmonary arteries. Several drugs are available that ameliorate walk distance and hemodynamics, but their maximum tolerated doses are limited in critically ill patients with PAH because of systemic vasodilation resulting in hypotension. The ideal vasodilator would be cost-effective, safe, and selective to the pulmonary vasculature; no such agent currently exists. Inhaled nitric oxide selectively reduces pulmonary pressures without systemic hypotension. However, it is expensive, potentially toxic, and requires complex technology for monitoring and administration. Inhaled epoprostenol may be an alternative therapy to minimize systemic hypotension, which often accompanies rapid intravenous titration. To evaluate the safety and efficacy of inhaled epoprostenol in critically ill patients with PAH, we conducted a literature search by using the MEDLINE, EMBASE, and Cochrane Central Register of Controlled Trials databases (1966-August 2009) for relevant studies. Case reports and in vitro studies were excluded. Overall, 11 studies met the inclusion criteria. The PAH population included patients requiring cardiac surgery, lung or heart transplantation, or nonspecific intensive care. All trials showed that inhaled epoprostenol significantly decreased pulmonary pressures without lowering systemic blood pressure. The duration of therapy in most studies was 10-15 minutes, with one study evaluating its effects up to an average of 45.6 hours. Pulmonary pressures returned to baseline soon after drug discontinuation. Minimal adverse events were reported. Thus, inhaled epoprostenol in various subgroups of critically ill patients was effective in reducing pulmonary pressures. However, the significance of these effects on improving clinical outcomes remains unknown. Further studies are needed to determine the role of inhaled epoprostenol in critically ill patients with PAH.

Aerosolized prostacyclin for acute lung injury (ALI) and acute respiratory distress syndrome (ARDS)

BACKGROUND

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are critical conditions that are associated with high mortality and morbidity. Aerosolized prostacyclin has been used to improve oxygenation despite the limited evidence available so far.

OBJECTIVES

To systematically assess the benefits and harms of aerosolized prostacyclin in critically ill patients with ALI and ARDS.

SEARCH STRATEGY

We identified randomized clinical trials (RCTs) from electronic databases: the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2010, Issue 1); MEDLINE; EMBASE; Science Citation Index Expanded; International Web of Science; CINAHL; LILACS; and the Chinese Biomedical Literature Database (to 31st January 2010). We contacted trial authors and manufacturers in the field.

SELECTION CRITERIA

We included all RCTs, irrespective of blinding or language, that compared aerosolized prostacyclin with no intervention or placebo in either children or adults with ALI or ARDS.

DATA COLLECTION AND ANALYSIS

Two authors independently abstracted data and resolved any disagreements by discussion. We presented pooled estimates of the intervention effects as relative risks (RR) with 95% confidence intervals (CI) for dichotomous outcomes. Our primary outcome measure was all cause mortality. We planned to perform subgroup and sensitivity analyses to assess the effect of aerosolized prostacyclin in adults and children, and on various clinical and physiological outcomes. We assessed the risk of bias through assessment of methodological trial components and the risk of random error through trial sequential analysis.

MAIN RESULTS

We included one paediatric RCT with low risk of bias and involving a total of 14 critically ill children with ALI or ARDS. Aersosolized prostacyclin over less than 24 hours did not reduce overall mortality at 28 days (RR 1.50, 95% CI 0.17 to 12.94) compared with aerosolized saline (a total of three deaths). The authors did not encounter any adverse events such as bleeding or organ dysfunction. We were unable to perform the prespecified subgroups and sensitivity analyses or trial sequential analysis due to the limited number of RCTs. We were also not able to assess the safety and efficacy of aerosolized prostacyclin for ALI and ARDS. We found two ongoing trials, one involving adults and the other paediatric participants. The adult trial has been finalized but the data are not yet available.

AUTHORS' CONCLUSIONS

There is no current evidence to support or refute the routine use of aerosolized prostacyclin for patients with ALI and ARDS. There is an urgent need for more randomized clinical trials.

The management of acute pulmonary arterial hypertension

Acute pulmonary arterial hypertension (PAH), which may complicate the course of many complex disorders, is always underdiagnosed and its treatment frequently begins only after serious complications have developed. Acute PAH is distinctive because they differ in their clinical presentation, diagnostic findings, and response to treatment from chronic PAH. The acute PAH may take either the form of acute onset of chronic PAH or acute PAH or surgery-related PAH. Significant pathophysiologic differences existed between acute and chronic PAH. Therapy of acute PAH should generally be aimed at acutely relieving right ventricular (RV) pressure overload and preventing RV dysfunction. There are three classes of drugs targeting the correction of abnormalities in endothelial dysfunction, which have been approved recently for the treatment of PAH: (1) prostanoids; (2) endothelin receptor antagonists; and (3) phosphodiesterase-5 inhibitors. The efficacy and safety of these compounds have been confirmed in uncontrolled studies in patients with PAH. Intravenous epoprostenol is suggested to serve as the first-line treatment for the most severe patients. In the other situations, the first-line therapy may include bosentan, sildenafil, or a prostacyclin analogue. Recent advances in the management of PAH have markedly improved prognosis.

Iloprost inhalation redistributes pulmonary perfusion and decreases arterial oxygenation in healthy volunteers

BACKGROUND

Previous studies have shown that ventilation-perfusion matching is improved in the prone as compared with that in the supine position. Regional differences in the regulation of vascular tone may explain this. We have recently demonstrated higher production of nitric oxide in dorsal compared with ventral human lung tissue. The purpose of the present study was to investigate regional differences in actions by another vasoactive mediator, namely prostacyclin. The effects on gas exchange and regional pulmonary perfusion in different body positions were investigated at increased prostacyclin levels by inhalation of a synthetic prostacyclin analogue and decreased prostacyclin levels by unselective cyclooxygenase (COX) inhibition.

METHODS

In 19 volunteers, regional pulmonary perfusion in the prone and supine position was assessed by single photon emission computed tomography using (99m)Tc macro-aggregated albumin before and after inhalation of iloprost, a stable prostacyclin analogue, or an intravenous infusion of a non-selective COX inhibitor, diclofenac. In addition, gas distribution was assessed in seven subjects using (99m)Tc-labelled ultra-fine carbon particles before and after iloprost inhalation in the supine position.

RESULTS

Iloprost inhalation decreased arterial PaO(2) in both prone (from 14.2+/-0.5 to 11.7+/-1.7 kPa, P<0.01) and supine (from 13.7+/-1.4 to 10.9+/-2.1 kPa, P<0.01) positions. Iloprost inhalation redistributed lung perfusion from non-dependent to dependent lung regions in both prone and supine positions, while ventilation in the supine position was distributed in the opposite direction. No significant effects of non-selective COX inhibition were found in this study.

CONCLUSIONS

Iloprost inhalation decreases arterial oxygenation and results in a more gravity-dependent pulmonary perfusion in both supine and prone positions in healthy humans.

Arterial pulmonary hypertension in noncardiac intensive care unit

Pulmonary artery pressure elevation complicates the course of many complex disorders treated in a noncardiac intensive care unit. Acute pulmonary hypertension, however, remains underdiagnosed and its treatment frequently begins only after serious complications have developed. Significant pathophysiologic differences between acute and chronic pulmonary hypertension make current classification and treatment recommendations for chronic pulmonary hypertension barely applicable to acute pulmonary hypertension. In order to clarify the terminology of acute pulmonary hypertension and distinguish it from chronic pulmonary hypertension, we provide a classification of acute pulmonary hypertension according to underlying pathophysiologic mechanisms, clinical features, natural history, and response to treatment. Based on available data, therapy of acute arterial pulmonary hypertension should generally be aimed at acutely relieving right ventricular (RV) pressure overload and preventing RV dysfunction. Cases of severe acute pulmonary hypertension complicated by RV failure and systemic arterial hypotension are real clinical challenges requiring tight hemodynamic monitoring and aggressive treatment including combinations of pulmonary vasodilators, inotropic agents and systemic arterial vasoconstrictors. The choice of vasopressor and inotropes in patients with acute pulmonary hypertension should take into consideration their effects on vascular resistance and cardiac output when used alone or in combinations with other agents, and must be individualized based on patient response.

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.

Nonventilatory interventions in the acute respiratory distress syndrome

Acute respiratory distress syndrome was first described in 1967. Acute respiratory distress syndrome and acute lung injury are diseases the busy intensivist treats almost daily. The etiologies of acute respiratory distress syndrome are many. A significant distinction is based on whether the insult to the lung was direct, such as in pneumonia, or indirect, such as trauma or sepsis. Strategies for managing patients with acute respiratory distress syndrome/acute lung injury can be subdivided into 2 large groups, those based in manipulation of mechanical ventilation and those based in nonventilatory modalities. This review focuses on the nonventlilatory strategies and includes fluid restriction, exogenous surfactant, inhaled nitric oxide, manipulation of production, or administration of eicosanoids, neuromuscular blocking agents, prone position ventilation, glucocorticoids, extracorporeal membrane oxygenation, and administration of beta-agonists. Most of these therapies either have not been studied in large trials or have failed to show a benefit in terms of long-term patient mortality. Many of these therapies have shown promise in terms of improved oxygenation and may therefore be beneficial as rescue therapy for severely hypoxic patients. Recommendations regarding the use of each of these strategies are made, and an algorithm for implementing these strategies is suggested.

Is the mortality higher in the pulmonary vs the extrapulmonary ARDS? A meta analysis

BACKGROUND AND AIM

ARDS can occur from the following two pathogenetic pathways: a direct pulmonary injury (ARDSp); and an indirect injury (ARDSexp). The predisposing clinical factor can influence the pathogenesis and clinical outcome of ARDS. This metaanalysis was aimed at evaluating whether there is any difference in mortality between the two groups.

METHODS

We searched the MEDLINE, EMBASE, and CINAHL databases for relevant studies published from 1987 to 2007, and included studies that have reported mortality in the two groups of ARDS. We calculated the odds ratio (OR) and 95% confidence interval (CI) to assess mortality in patients with ARDSp vs patients with ARDSexp and pooled the results using three different statistical models.

RESULTS

Our search yielded 34 studies. In all, the studies involved 4,311 patients with 2,330 patients in the ARDSp group and 1,981 patients in the ARDSexp group. The OR of mortality in ARDSp group compared to the ARDSexp group was 1.11 (95% CI, 0.88 to 1.39), as determined by the random-effects model; 1.04 (95% CI, 0.92 to 1.18), as determined by the fixed-effects model; and 1.04 (95% CI, 0.92 to 1.18), as determined by the exact method, indicating that mortality is similar in the two groups. The mortality was no different whether the studies were classified as prospective (OR, 1.15; 95% CI, 0.87 to 1.51) or retrospective (OR, 1.01; 95% CI, 0.61 to 1.69); small (OR, 1.11; 95% CI, 0.77 to 1.60) or large (OR, 1.1; 95% CI, 0.82 to 1.49); or observational (OR, 1.10; 95% CI, 0.82 to 1.49) or interventional (OR, 0.97; 95% CI, 0.79 to 1.19). There was methodological and statistical heterogeneity (I(2), 50.9%; 95% CI, 21.3 to 66.2%; chi(2) statistic, 67.22; p = 0.0004).

CONCLUSIONS

The results of this study suggest that there is no difference in mortality between these two groups. Further studies should focus on specific etiologies within the subgroups rather than focusing on the broader division of ARDSp and ARDSexp.

Treatment with aerosols in mechanically ventilated patients: is it worthwhile?

Aerosol medications are commonly used in mechanically ventilated patients. Several classes of drugs with different properties and indications may be given by inhalation. In all cases, compared with the systemic route, the inhaled therapy has the main advantage that for a given therapeutic response, the drug dose is several-fold lower, while the systemic absorption is negligible, thus the side effects are greatly minimized. In addition, for some medications the systemic route either causes non-acceptable side effects or results in considerably inferior therapeutic response, rendering the inhaled route the method of choice of drug administration. Bronchodilators, corticosteroids, vasoactive drugs, surfactants, antibiotics, helium and perfluorocarbons are the medications that can be given by inhalation during mechanical ventilation. Some of those represent part of the standard treatment for various groups of mechanically ventilated patients, while the role of others has not been well established yet.

Inhaled prostacyclin following surgical repair of congenital heart disease--a pilot study

BACKGROUND

The development of additional therapies for the treatment of pulmonary hypertension would be a significant advancement in the treatment of congenital heart disease. Recently, studies have found inhaled prostacyclin (PGI2) is an effective pulmonary vasodilator, comparable with nitric oxide. In this prospective interventional pilot study, we examined the physiologic effects of inhaled PGI2 in children with congenital heart disease and pulmonary hypertension.

METHODS

Six children (median age 6 months, range 5 to 21 months) with congenital heart disease and preoperative pulmonary hypertension (mean pulmonary artery pressure [MPAP] greater than 50% systemic) received a 15-minute course of inhaled PGI2 intraoperatively postrepair. The inhaled PGI2 was delivered by aerosolizing the IV formulation (Flolan, Glaxo-Wellcome) to achieve a dose of 50 ng/kg/min. Physiologic parameters measured during the medication period were compared with measurements taken during two 15-minute baseline periods before and after the medication period.

RESULTS

Inhaled PGI2 significantly reduced the mean pulmonary artery pressure from 25 +/- 3 to 21 +/- 3 (p < 0.01) and improved the PaO2/FiO2 ratio from 275 +/- 181 to 433 +/- 285 (p = 0.01). There were no significant changes in systemic blood pressure, heart rate, or cardiac index.

CONCLUSIONS

Children with congenital heart disease and pulmonary hypertension may benefit from inhaled PGI2. Inhaled PGI2 reduced pulmonary blood pressures and improved oxygenation in this small study. PGI2 acts through cyclic adenosine monophosphate mediated pulmonary vasodilation, a mechanism different from nitric oxide. In children with inadequate response to nitric oxide, inhaled PGI2 may be a useful alternative pulmonary vasodilator.

Evolution of treatments for patients with acute lung injury

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are acute life-threatening forms of hypoxemic respiratory failure. ALI/ARDS patients require intensive care with prolonged mechanical ventilation. Despite advances in our understanding of the pathophysiology of ALI/ARDS, mortality rates remain > 30% and survivors suffer significant decrements in their quality of life. The evolving understanding of ALI/ARDS and the complex interactions involved in ALI/ARDS open the door for many potential targets for treatment. The condition is characterised by an acute inflammatory state that leads to increased capillary permeability and accumulation of proteinaceous pulmonary oedema. The changes that occur as a result of this inflammation clinically manifest themselves as hypoxemia, infiltrates on chest radiograph and reduced lung compliance. Many years have been dedicated to analysing the complexities involved in ALI/ARDS in order to improve current and future possibilities for treatment, with the aim of improving patient outcomes. Although some therapies have demonstrated benefits of improved oxygenation, such as surfactant and nitric oxide, these benefits have not translated into reductions in the duration of mechanical ventilation or mortality. Inflammatory mediator-targeted therapies were promising early on; however, larger trials have found therapies such as cytokine modulation, platelet-activating factor inhibition and neutrophil elastase inhibitors to be ineffective in the treatment of ALI/ARDS. Preclinical studies with beta2-agonists and granulocyte macrophage colony-stimulating factor have shown promise for restoring alveolar capillary barrier integrity or reducing pulmonary oedema, and further studies are being conducted to test for true clinical benefit. Despite previous therapeutic failures, newer surfactant formulations have shown promise, particularly in patients with direct forms of lung injury, and are currently in Phase III trials. Anticoagulant therapy with activated protein C has been shown to improve survival in sepsis, the most common risk factor for the development of ALI/ARDS, and is now being studied in ALI/ARDS. Until new data emerge, the focus must remain on supportive care, including optimised mechanical ventilation, nutritional support, manipulation of fluid balance and prevention of intervening medical complications.

Retrospective evaluation of inhaled prostaglandins in patients with acute respiratory distress syndrome

STUDY OBJECTIVES

To determine whether use of inhaled alprostadil (PGE 1 ) or epoprostenol (PGI 2 ) significantly improved oxygenation in patients with acute respiratory distress syndrome (ARDS), and to determine whether differences between the two drugs exist with regard to oxygenation, duration of mechanical ventilation and hospitalization, adverse effects, and survival.

DESIGN

Retrospective chart review.

SETTING

A 360-bed tertiary care teaching facility with medical and surgical intensive care units.

PATIENTS

Twenty-seven patients admitted to the hospital who received either PGI 2 or PGE 1 for a primary or secondary diagnosis of ARDS.

MEASUREMENTS AND MAIN RESULTS

Seventeen patients received inhaled PGE 1 and 10 received inhaled PGI 2 . There were no significant changes in the ratio of arterial partial pressure of oxygen (PaO 2 ):fraction of inspired oxygen (FiO 2 ) and in the PaO 2 , from baseline to any time point that was analyzed during treatment, for patients receiving either PGE 1 (p=0.2120 and 0.3399, respectively) or PGI 2 (p=0.1655 and 0.0784, respectively).

CONCLUSION

No statistically significant improvement in oxygenation was observed in patients receiving either PGE 1 or PGI 2 . In addition, no significant differences were found between the two prostaglandins for the variables studied. Until positive results from large, prospective studies are available, we recommend that these inhaled prostaglandins not be used to treat ARDS.

Inhaled alternatives to nitric oxide

OBJECTIVE

Inhaled nitric oxide has gained an established place in the management of pulmonary hypertension. However, cost, potential toxicity, and the lack of positive outcome data with inhaled nitric oxide therapy has generated interest in alternative inhaled, selective pulmonary vasodilators. This article describes those alternatives that have been studied to date.

DESIGN

Literature review of inhaled, selective pulmonary vasodilators other than nitric oxide.

METHODS

A review of the molecular mechanisms, potential side effects, and the studies to date in both animal models and clinical studies describing the physiologic effects of alternative agents to inhaled nitric oxide.

CONCLUSION

There are a number of available agents that have comparable physiologic effects as inhaled nitric oxide. The best studied of these are the inhaled prostanoids (prostacyclin and iloprost), and there is growing interest in novel therapies such as phosphodiesterase inhibitors and neuropeptides.

Pulmonary and extrapulmonary acute respiratory distress syndrome: are they different?

PURPOSE OF REVIEW

Acute respiratory distress syndrome has been considered a morphologic and functional expression of lung injury caused by a variety of insults. Two distinct forms of acute respiratory distress syndrome/acute lung injury are described, because there are differences between pulmonary acute respiratory distress syndrome (direct effects on lung cells) and extrapulmonary acute respiratory distress syndrome (reflecting lung involvement in a more distant systemic inflammatory response). This article will focus on the differences in lung histology and morphology, respiratory mechanics, and response to ventilatory strategies and pharmacologic therapies in pulmonary and extrapulmonary acute respiratory distress syndrome.

RECENT FINDINGS

Many researchers recognize that experimental pulmonary and extrapulmonary acute respiratory distress syndrome are not identical. In addition, clinical studies have described the detection of differences radiographically, functionally, and by analysis of the responses to therapeutic interventions (ventilatory strategies, positive end-expiratory pressure, prone position, drugs). However, there are contradictions among the different studies addressing these issues, which could be attributed to the fact that the distinction between pulmonary and extrapulmonary acute respiratory distress syndrome is not always clear and simple. Furthermore, there may be frequent overlapping in pathogenetic mechanisms and morphologic alterations.

SUMMARY

The understanding of acute respiratory distress syndrome needs to take into account its origin. If each pathogenetic mechanism were to be considered, clinical management would be more precise, and probably the outcome could include real amelioration.

Randomized controlled trial of aerosolized prostacyclin therapy in children with acute lung injury

OBJECTIVES

To investigate whether aerosolized prostacyclin improves oxygenation in children with acute lung injury.

DESIGN

Double-blind, randomized, and placebo-controlled trial.

SETTING

Pediatric intensive care unit at a university hospital.

PATIENTS

Fourteen children with acute lung injury defined by the criteria of an American-European Consensus Conference.

INTERVENTIONS

Aerosolized prostacyclin (epoprostenol sodium) by stepwise increments of different doses (10, 20, 30, 40, and 50 ng x kg x min) vs. aerosolized normal saline (placebo).

MEASUREMENTS AND MAIN RESULTS

Before the start of the study, and before and after each dose of prostacyclin/placebo, the following variables were measured: arterial blood gases, heart rate, mean arterial blood pressure, and ventilator settings required. Changes in oxygenation were measured by calculation of the oxygenation index (mean airway pressure x 100 x Pao2/Fio2). After treatment with aerosolized prostacyclin, there was a significant 26% (interquartile range, 3%, 35%) improvement in oxygenation index at 30 ng x kg x min compared with placebo (p =.001). The response to prostacyclin was not the same in all children. We saw an improvement of > or = 20% in eight of 14 children (i.e., responders), and the number needed to treat was 1.8 (95% confidence interval, 1.2-3.2). No adverse effects were observed.

CONCLUSIONS

Aerosolized prostacyclin improves oxygenation in children with acute lung injury. Future trials should investigate whether this treatment will positively affect outcome.

Vascular pharmacology of acute lung injury and acute respiratory distress syndrome

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) following sepsis, major trauma and surgery are leading causes of respiratory insufficiency, warranting artificial ventilation in the intensive care unit. It is caused by an inflammatory reaction in the lung upon exogenous or endogenous etiologies eliciting proinflammatory factors, and results in increased alveolocapillary permeability and protein-rich alveolar edema. The interstitial and alveolar inflammation and edema alter ventilation perfusion matching, gas exchange and mechanical properties of the lung. The current therapy of the condition is supportive, paying careful attention to fluid balance, relieving the increased work of breathing and improving gas exchange by mechanical ventilation, but in vitro, animal and some clinical research is done to evaluate the value of anti-inflammatory therapies on morbidity and outcome, including inflammatory cell-stabilizing corticosteroids, xanthine derivates, prostanoids and inhibitors, O(2) radical scavenging factors such as N-acetylcysteine, surfactant replacement, vasodilators including inhaled nitric oxide, vasoconstrictors such as almitrine, and others. None of these compounds has been proven to benefit survival in patients, however, even though carrying a physiologic benefit, except perhaps for steroids that may improve outcome in the later stage of ARDS. This partly relates to the difficulty to assess the lung injury at the bedside, to the multifactorial pathogenesis and the severity of comorbidity, adversely affecting survival.

Pharmacotherapy of acute respiratory distress syndrome

To date, the only therapeutic option that has convincingly been shown to decrease mortality in acute respiratory distress syndrome (ARDS) has been to use a lung-protective strategy that minimises the iatrogenic consequences of providing adequate life support through the use of mechanical ventilation. In terms of the pharmacological options for ARDS, no single drug or treatment has been shown to be the magic bullet in this disease. The search for novel therapies and pharmacological agents is active and relentless. Important pathophysiological areas of focus are preventative therapy, supportive care and treatment of the underlying inflammatory process. In this paper we will review current and experimental approaches to the management of ARDS. In addition, the pathophysiological basis for their putative modes of action, the current state of the literature and the potential for future clinical development will be discussed.

Pulmonary versus extrapulmonary acute respiratory distress syndrome: different diseases or just a useful concept?

The acute respiratory distress syndrome may complicate both pulmonary and extrapulmonary conditions. There is a growing belief that the predisposition to, and clinical course of, the syndrome may be influenced by the extent to which the lung is directly involved in the precipitating pathologic changes. Several studies have highlighted differences in morphology and respiratory physiology between the two subgroups in the early stages of acute respiratory distress syndrome. Further, preliminary reports have suggested that the effects of therapeutic interventions such as alterations in positive end-expiratory pressure, prone ventilation, and the use of inhaled vasoactive agents may differ between pulmonary and extrapulmonary acute respiratory distress syndrome. There are, however, inconsistencies between various studies addressing these issues, which may relate in part to differences in etiologic case mix. There are also practical difficulties in assigning certain cases to one of these two groups. Finally, there are as yet no outcome data to support any modification of clinical management on the basis of this distinction.

Searching the ideal inhaled vasodilator: from nitric oxide to prostacyclin

Today, the technique to directly administer vasodilators via the airway to treat pulmonary hypertension and to improve pulmonary gas exchange is widely accepted among clinicians. The flood of scientific work focussing on this new therapeutic concept had been initiated by a fundamental new observation by Pepke-Zaba [1]and Frostell in 1991 [2]: Both scientists reported, that inhalation of exogenous nitric oxide (NO) gas selectively dilates pulmonary vessels without a concomittant systemic vasodilation. No more than another decade ago NO was identified as an important endogenous vasodilator [3]while having merely been regarded an environmental pollutant before that time. Although inhaled NO proved to be efficacious, alternatives were sought-after due to NO's potential side-effects. In search for the ideal inhaled vasodilator another group of endogenous mediators -- the prostanoids -- came into the focus of interest. The evidence for safety and efficacy of inhaled prostanoids is -- among a lot of other valuable work -- based on a series of experimental and clinical investigations that have been performed or designed at the Institute for Surgical Research under the guidance and mentorship of Prof. Dr. med. Dr. h.c. mult. K. Messmer [4-19]. In the following, the current and newly emerging clinical applications of inhaled prostanoids and the experimental data which they are based on, will be reviewed.

ARDS and the multiple organ dysfunction syndrome. Common mechanisms of a common systemic process

The multiple organ dysfunction syndrome is a common but poorly understood complication of critical illness. Its evolution reflects the interactions of an acute, life-threatening insult, the response of the host to that insult, and the therapeutic measures instituted to restore normal homeostasis. Although the cellular mechanisms remain elusive, processes such as inflammation, microvascular thrombosis, apoptosis, and fibrosis and tissue repair contribute to its clinical expression. In the lung, these forces create the characteristic changes of ARDS; that common disorder, however, is better seen as one manifestation of a systemic process than as an isolated problem of the lung. Therapy, in the absence of a more sophisticated understanding of pathologic mechanism, is supportive. The growing recognition that iatrogenic factors contribute to the expression of MODS has highlighted the need for the clinician to be aware of the potential for harm inherent with every intervention.

Clinical developments for treating ARDS

Acute respiratory distress syndrome (ARDS), is characterised by capillary permeability and pulmonary oedema formation and may complicate a variety of medical and surgical illnesses. As a self-perpetuating state of inflammatory derangement, acute lung injury (ALI)/ARDS is manifest clinically as rapid development of radiographic infiltrates, severe hypoxaemia and reduced lung compliance. Over the years, researchers have made significant progress in elucidating the pathophysiology of this complex syndrome. Therapies targeting specific pathophysiologic steps in the development or persistence of this syndrome are in various stages of laboratory and clinical testing. Results to date have shown nitric oxide (NO) to improve oxygenation in the majority of patients but fail to improve mortality. Surfactant replacement has had limited success in adults, but new formulations and delivery methods may prove beneficial. Several inflammatory mediator-targeted therapies have progressed successfully through early clinical evaluation. Among these, neutrophil elastase inhibitors have shown the most promise and are currently undergoing Phase III trials. Other mediator-targeted therapies, such as prostaglandin E1, IL-10 and platelet activating factor antagonists, have not been found efficacious in large clinical trials of ARDS. However, these therapies, along with coagulation modulators, may have a favourable impact on ARDS by improving outcomes in sepsis, the greatest risk factor for developing this condition. In the interim, supportive care through improvements in mechanical ventilation are beneficial, while specific fluid balance and nutrition strategies may prove advantageous.

Inhaled prostacyclin (PGI2) is an effective addition to the treatment of pulmonary hypertension and hypoxia in the operating room and intensive care unit

PURPOSE

There is a growing interest in the intraoperative and intensive care use of inhaled epoprostenol (PGI2) for the treatment of pulmonary hypertension (PHT) and hypoxia of cardiac or non-cardiac origin. We report our experience with this form of therapy.

METHODS

A retrospective chart review of all patients who received inhaled PGI2 over a one-year period was undertaken. Demographic, hemodynamic, oxygenation status, mode of administration, side effects, duration of hospital stay, and mortality were noted.

RESULTS

Thirty-five patients, of which 33 (92%) were in the intensive care unit, received inhaled PGI2. Of the 27 patients whose pulmonary artery pressure (PAP) was monitored, a significant decrease in mean PAP from 34.8 +/- 11.8 mmHg to 32.1 +/- 11.8 mmHg was observed within one hour after the start of therapy (P=0.0017). Selective pulmonary vasodilatation occurred in 77.8% of the patients. Thirty-three patients had arterial blood gases before and after therapy. There was an improvement in the PaO2/FIO2 ratio in 88% of these with a 175% improvement on average. The ratio of PaO2/FIO2 improved from 108 +/- 8 to 138 +/- 105 (P=0.001). Six patients (17%) presented hypotension, two had subsequent pneumothorax, one had bronchospasm and in one patient PGI2 inhalation was stopped because of increasing peak pulmonary pressures from the secondary flow coming from the nebulizer. Mortality of the cohort was 54%.

CONCLUSION

Inhaled PGI2 can be useful in the treatment of patients with PHT and severe hypoxia. It can however be associated with systemic side effects.