Inhaled aerosolized prostacyclin as a selective pulmonary vasodilator for the treatment of severe hypoxaemia

Amniotic Fluid Embolism Treated With Inhaled Milrinone: A Case Report

We present a patient with sudden cardiovascular collapse during cesarean delivery that was attributed to amniotic fluid embolism (AFE). The syndrome of AFE may be initiated by an anaphylactoid response to amniotic fluid in the maternal circulation that triggers the release of pulmonary vasoconstrictors, with transient pulmonary vasospasm, causing hemodynamic collapse and profound left ventricular failure. Milrinone, a pulmonary vasodilator used in the management of emergent right ventricular failure, was administered via a nebulizer in an effort to decrease pulmonary vascular resistance. If used immediately after AFE, inhaled milrinone may mitigate pulmonary vasoconstriction, providing a bridge to extracorporeal membrane oxygenation.

Administration of Inhaled Pulmonary Vasodilators to the Mechanically Ventilated Neonatal Patient

Pulmonary hypertension is a life-threatening condition that affects people of all ages that can occur as an idiopathic disorder at birth or as part of a variety of cardiovascular and infectious disorders. It is commonly treated with inhaled pulmonary vasodilators such as nitric oxide and less frequently using formulations and analogs of prostacyclin. To minimize systemic effects and preserve pulmonary vasodilation, vasodilators are often administered directly into the airway. Nitric oxide is the only USA Food and Drug Administration-approved inhaled pulmonary vasodilator that can be used during mechanical ventilation. Over the past two decades, interest has grown in the use of aerosolized prostacyclin and prostacyclin analogs for the treatment of pulmonary hypertension during mechanical ventilation. Clinicians who administer inhaled prostacyclin may not have a clear understanding of its risks because of the lack of data from large clinical trials examining safety and efficacy; moreover, its safe use remains poorly documented. The off-label use of drugs is legitimate, but prescribers must recognize the potential complications and liability in doing so. This manuscript aims to address potential problems related to the aerosol administration of pulmonary vasodilators in the mechanically ventilated neonatal patient.

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.

Survival after an amniotic fluid embolism following the use of sodium bicarbonate

Amniotic fluid embolism (AFE) is a rare and potentially fatal complication of pregnancy. In this case report, we highlight the successful use of sodium bicarbonate in a patient with an AFE. We present a case of a 38-year-old mother admitted for an elective caesarean section. Following the delivery of her baby, the mother suffered a cardiac arrest. Following a protracted resuscitation, transoesophageal echocardiography demonstrated evidence of acute pulmonary hypertension, with an empty left ventricle and an over-distended right ventricle. In view of these findings and no improvement noted from on-going resuscitation, sodium bicarbonate was infused as a pulmonary vasodilator. Almost instantaneous return of spontaneous circulation was noted, with normalisation of cardiac parameters. We propose that in patients suspected with AFE and who have been unresponsive to advance cardiac life support measures, and where right ventricular failure is present with acidosis and/or hypercarbia, the use of sodium bicarbonate should be considered.

Pregnancy and pulmonary hypertension

When pulmonary hypertension (PH) occurs in pregnancy, physiologic stress can overwhelm an already strained right ventricle resulting in right ventricular failure and death. Mortality remains unacceptably high (25%-30%). Patients with PH should be counseled to avoid pregnancy. This article discusses the physiologic changes of pregnancy that make it difficult for patients with PH, the pitfalls of transthoracic echocardiography in diagnosing PH in pregnancy, and the historical data regarding mortality. The causes of development of PH during pregnancy are discussed, and the limited data on management of patients with PH who choose to carry their pregnancy to term are reviewed.

Pulmonary vascular and right ventricular dysfunction in adult critical care: current and emerging options for management: a systematic literature review

INTRODUCTION

Pulmonary vascular dysfunction, pulmonary hypertension (PH), and resulting right ventricular (RV) failure occur in many critical illnesses and may be associated with a worse prognosis. PH and RV failure may be difficult to manage: principles include maintenance of appropriate RV preload, augmentation of RV function, and reduction of RV afterload by lowering pulmonary vascular resistance (PVR). We therefore provide a detailed update on the management of PH and RV failure in adult critical care.

METHODS

A systematic review was performed, based on a search of the literature from 1980 to 2010, by using prespecified search terms. Relevant studies were subjected to analysis based on the GRADE method.

RESULTS

Clinical studies of intensive care management of pulmonary vascular dysfunction were identified, describing volume therapy, vasopressors, sympathetic inotropes, inodilators, levosimendan, pulmonary vasodilators, and mechanical devices. The following GRADE recommendations (evidence level) are made in patients with pulmonary vascular dysfunction: 1) A weak recommendation (very-low-quality evidence) is made that close monitoring of the RV is advised as volume loading may worsen RV performance; 2) A weak recommendation (low-quality evidence) is made that low-dose norepinephrine is an effective pressor in these patients; and that 3) low-dose vasopressin may be useful to manage patients with resistant vasodilatory shock. 4) A weak recommendation (low-moderate quality evidence) is made that low-dose dobutamine improves RV function in pulmonary vascular dysfunction. 5) A strong recommendation (moderate-quality evidence) is made that phosphodiesterase type III inhibitors reduce PVR and improve RV function, although hypotension is frequent. 6) A weak recommendation (low-quality evidence) is made that levosimendan may be useful for short-term improvements in RV performance. 7) A strong recommendation (moderate-quality evidence) is made that pulmonary vasodilators reduce PVR and improve RV function, notably in pulmonary vascular dysfunction after cardiac surgery, and that the side-effect profile is reduced by using inhaled rather than systemic agents. 8) A weak recommendation (very-low-quality evidence) is made that mechanical therapies may be useful rescue therapies in some settings of pulmonary vascular dysfunction awaiting definitive therapy.

CONCLUSIONS

This systematic review highlights that although some recommendations can be made to guide the critical care management of pulmonary vascular and right ventricular dysfunction, within the limitations of this review and the GRADE methodology, the quality of the evidence base is generally low, and further high-quality research is needed.

Amniotic fluid embolism: an evidence-based review

We conducted an evidence-based review of information about [corrected] amniotic fluid embolism (AFE). The estimated incidence of AFE is 1:15,200 and 1:53,800 deliveries in North America and Europe, respectively. The case fatality rate and perinatal mortality associated with AFE are 13-30% and 9-44%, respectively. Risk factors associated with an [corrected] increased risk of AFE include advanced maternal age, placental abnormalities, operative deliveries, eclampsia, polyhydramnios, cervical lacerations, [corrected] and uterine rupture. The hemodynamic response in [corrected] AFE is biphasic, with initial pulmonary hypertension and right ventricular failure, followed by left ventricular failure. Promising therapies include selective pulmonary vasodilators and recombinant activated factor VIIa. Important topics for future research are presented.

Responding to amniotic fluid embolism

Amniotic fluid embolism (AFE), an uncommon disorder with a high fatality rate, is an obstetric emergency that requires swift recognition and intervention to save both the mother's life and that of her child.The high mortality rate and varying theories as to its cause make it difficult to diagnose AFE, which can occur at any point during labor and delivery, including during cesarean birth. These factors make it important for perioperative nurses to understand and recognize AFE when it occurs in the OR. Rapid delivery of the fetus is imperative for the survival of both mother and child. Monitoring and aggressively providing respiratory and circulatory support interventions are required if the mother is to survive AFE.

United Kingdom Amniotic Fluid Embolism Register

OBJECTIVE

The United Kingdom Amniotic Fluid Embolism Register was established to identify the incidence of the condition and examine any differences or common factors between survivors and fatalities.

DESIGN

An anonymous voluntary register.

SETTING

The United Kingdom from 1997 to 2004.

POPULATION

Any woman with a clinical diagnosis of amniotic fluid embolism. The entry criteria were as follows: acute hypotension or cardiac arrest, acute hypoxia and coagulopathy with onset during labour, caesarean section or within 30 minutes of delivery with no other clinical condition or potential explanation for the symptoms and signs.

METHODS

A data collection form was completed after reporting.

MAIN OUTCOME MEASURES

Mortality and morbidity rates in women and their babies.

RESULTS

Of 66 cases, 44 had sufficient information to be included. Thirteen (29.5%; 95% CI 17-45%) women died. If the five extra deaths in the Confidential Enquiry into Maternal Death were included, the mortality would be 37% (95% CI 23-52%). Of the 31 survivors, 12 women had a cardiac arrest, 7 had a hysterectomy, 2 had further laparotomies, 1 had subglottic stenosis and 2 had persisting neurological impairment. Twenty-four of the 31 survivors were admitted to intensive care units. Of the 13 women who died, 7 of their babies survived. Four were acidotic at birth, of whom two developed hypoxic ischaemic encephalopathy (HIE) and one of these is known to have developed cerebral palsy. In 18 cases, the woman survived and the baby was alive and in utero at the time of the maternal collapse. Four of these died, four had HIE with one known to have developed cerebral palsy and one other was acidotic at birth.

CONCLUSION

The mortality of amniotic fluid embolism is high but the majority of women will survive. There is significant maternal and neonatal morbidity even when the woman survives. Continuing assessment of cases of amniotic fluid embolism is important to identify ways of improving outcome.

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.

Improved Ventricular Function during Inhalation of PGI2 Aerosol Partly Relies on Enhanced Myocardial Contractility

Inhaled prostacyclin (PGI(2)) aerosol induces selective pulmonary vasodilation. Further, it improves right ventricular (RV) function, which may largely rely on pulmonary vasodilation, but also on enhanced myocardial contractility. We investigated the effects of the inhaled PGI(2) analogs epoprostenol (EPO) and iloprost (ILO) on RV function and myocardial contractility in 9 anesthetized pigs receiving aerosolized EPO (25 and 50 ng.kg(-1).min(-1)) and, consecutively, ILO (60 ng.kg(-1).min(-1)) for 20 min each. We measured pulmonary artery pressure (PAP), RV ejection fraction (RVEF) and RV end-diastolic-volume (RV-EDV), and left ventricular end-systolic pressure-volume-relation (end-systolic elastance, E(es)). EPO and ILO reduced PAP, increased RVEF and reduced RVEDV. E(es) was enhanced during all doses tested, which reached statistical significance during EPO(25 ng) and ILO, but not during EPO(50 ng). PGI(2) aerosol enhances myocardial contractility in healthy pigs, contributing to improve RV function.

Embolism during pregnancy: thrombus, air, and amniotic fluid

Pulmonary embolism is the primary cause of acute respiratory decompensation during pregnancy. Regardless of the nature of the embolism, a high index of suspicion, early diagnosis, and aggressive resuscitation need to be instituted to achieve a successful maternal and fetal outcome. Several clinical characteristics will assist practitioners to distinguish among the different forms of embolism and to institute specific measures of treatment.

Fatal amniotic fluid embolism diagnosed histologically

Although the mortality of amniotic fluid embolism remains very high, there are more and more reports of patients surviving after prompt and aggressive therapy. However its pathogenesis is controversial, and, in some cases, an anaphylactic reaction to the amniotic fluid rather than the hemodynamic changes following mechanical obstruction by an embolus has been proposed as the underlying pathophysiological mechanism. In this paper we describe a case of amniotic fluid embolism with florid clinical features and a difficult and delayed diagnosis. On autopsy, clear-cut histological changes of amniotic fluid embolism were found.

Disseminated intravascular coagulation: a review of etiology, pathophysiology, diagnosis, and management: guidelines for care

The pathophysiologic mechanisms, clinical, and laboratory manifestations of DIC are complex in part due to interrelationships within the hemostasis system. Only by clearly understanding these extraordinarily complex pathophysiologic interrelationships can the clinician and laboratory scientist appreciate the divergent and wide spectrum of often confusing clinical and laboratory findings in patients with DIC. Many therapeutic decisions to be made are controversial and lack validation. Nevertheless, newer antithrombotic agents, and agents that can block, blunt, or modify cytokine activity and the activity of vasoactive substances appear to be of value. The complexity and variable degree of clinical expression suggests that therapy should be individualized depending on the nature of DIC, age, etiology of DIC, site and severity of hemorrhage or thrombosis and hemodynamics and other appropriate clinical parameters. At present, treatment of the triggering event, low-dose heparin or antithrombin concentrate and wise choice of components when indicated appear to be the most effective modes of therapy.

Amniotic fluid embolus: a review of the literature

PURPOSE

To review the literature since 1979 to determine the natural history, etiology, diagnosis and potential treatment of amniotic fluid embolus (AFE).

SOURCE

English language articles and books published between June 1976 and June 1998 were identified by a computerized medline search using the title or text word amniotic fluid embolus. This same search strategy was repeated and updated to October 1999 by an independent individual using both Medline and Embase. The search was also expanded to include Science Citation Index listing Morgan's 1979 review article. All relevant publications were retrieved and their bibliographies were scanned for additional sources.

PRINCIPAL FINDINGS

Randomized controlled trials are not possible with amniotic fluid emboli. The majority of the literature consists of clinical reports combined with occasional limited reviews. Knowledge obtained from these reports suggests that amniotic fluid emboli present as a spectrum of disease that ranges from a subclinical entity to one that is rapidly fatal. Because cases are sporadic and the diagnosis is often unconfirmed, little progress has been made towards understanding its etiology or defining the risk factors. Present management is empirical and directed towards the maintenance of oxygenation, circulatory support and the correction of coagulopathy.

CONCLUSION

Amniotic fluid embolus continues to be a life-threatening but potentially reversible complication unique to pregnancy. It cannot be predicted nor prevented. Review of the literature reveals that there are no standardized investigational methods or protocols to confirm the diagnosis in suspected cases.

Syndromes of disseminated intravascular coagulation in obstetrics, pregnancy, and gynecology. Objective criteria for diagnosis and management

This article presents current understanding of the causes, pathophysiology, clinical, and laboratory diagnosis, and management of fulminant and low-grade DIC, as they apply to obstetric, pregnant, and gynecologic patients. General medical complications leading to DIC, which may often be seen in these patients, are also discussed. Considerable attention has been given to interrelationships within the hemostasis system. Only by clearly understanding these pathophysiologic interrelationships can the obstetrician/gynecologist appreciate the divergent and wide spectrum of often confusing clinical and laboratory findings in patients with DIC. Objective clinical and laboratory criteria for diagnosis of DIC have been outlined to eliminate unnecessary confusion and the need to make empiric decisions regarding the diagnosis. Particularly in the obstetric patient, if a condition is observed that is associated with DIC, or if any suspicion of DIC arises from either clinical or laboratory findings, it is imperative to monitor the patient carefully with clinical and laboratory tools to assess any progression to a catastrophic event. In most instances of DIC in obstetric patients, the disease can be ameliorated easily at early stages. Many therapeutic decisions are straightforward, particularly in obstetric and gynecologic patients. For more serious and complicated cases of DIC in these patients, however, efficacy and choices of therapy will remain unclear until more information is published regarding response rates and survival patterns. Also, therapy must be highly individualized according to the nature of DIC, patient's age, origin of DIC, site and severity of hemorrhage or thrombosis, and hemodynamic and other clinical parameters. Finally, many syndromes that are often categorized as organ-specific disorders and are sometimes identified as independent disease entities, such as AFE syndrome, HELLP syndrome, adult shock lung syndrome, eclampsia, and many others, either share common pathophysiology with DIC or are simply a form of DIC. These entities represent the varied modes of clinical expression of DIC and illustrate the diverse clinical and anatomic manifestations of this syndrome.

Pulmonary toxicity of inhaled aerosolized prostacyclin therapy--an observational study

Large white/landrace piglets (mass 11 to 21 kg) were exposed to aerosolized alkaline glycine diluent (n = 2) or inhaled aerosolized prostacyclin (n = 2) for five to eight hours. Pigs receiving these aerosols developed mild acute sterile tracheitis, involving the superficial layers of the trachea, shown histologically and ultrastructurally. Pigs receiving the diluent aerosol also showed mild inflammatory changes in the bronchioles. These findings suggest caution with the use of high volumes of aerosolized alkaline glycine diluent during inhaled aerosolized prostacyclin therapy.

Dose-response to inhaled aerosolized prostacyclin for hypoxemia due to ARDS

STUDY OBJECTIVES

This study was carried out to determine the efficacy of and dose-response relationships to inhaled aerosolized prostacyclin (IAP), when used as a selective pulmonary vasodilator (SPV) in patients with severe hypoxemia due to ARDS.

DESIGN

Unblinded, interventional, prospective clinical study.

SETTING

A general ICU in a university-affiliated, tertiary referral center.

PATIENTS

Nine adult patients with severe ARDS (lung injury score, > or = 2.5).

INTERVENTIONS

All patients received IAP over the dose range 0 to 50 ng/kg/min. The IAP was delivered via a jet nebulizer placed in the ventilator circuit. Dose increments were 10 ng/kg/min every 30 min.

MEASUREMENTS AND RESULTS

Cardiovascular parameters (cardiac index and mean pulmonary and systemic pressures), indexes of oxygenation (PaO(2)/fraction of inspired oxygen [FIO(2)] ratio and alveolar-arterial oxygen partial pressure difference [P(A-a)O(2)]) and shunt fraction were measured or calculated at each dose interval, as were platelet aggregation and systemic levels of prostacyclin metabolite (6-keto prostaglandin F1(alpha)). A generalized linear regression model was used to determine a dose effect of IAP on these parameters. The Wilcoxon rank sum test for related measures was used to compare the effects of various doses of IAP. IAP acted as an SPV, with a statistically significant dose-related improvement in PaO(2)/FIO(2) ratio (p = 0.003) and P(A-a)O(2) (p = 0.01). Systemic prostacyclin metabolite levels increased significantly in response to delivered IAP (p = 0.001). There was no significant dose effect on systemic or pulmonary arterial pressures, or on platelet function, as determined by platelet aggregation in response to challenge with adenosine diphosphate.

CONCLUSIONS

IAP is an efficacious SPV, with marked dose-related improvement in oxygenation and with no demonstrable effect on systemic arterial pressures over the dose range 0 to 50 ng/kg/min. Despite significant systemic levels of prostacyclin metabolite, there was no demonstrable platelet function defect.

Successful weaning from cardiopulmonary bypass with central venous prostaglandin E1 and left atrial norepinephrine infusion in patients with acute pulmonary hypertension

OBJECTIVE

Postoperative pulmonary hypertension increases the mortality risk in cardiac surgery. We have used central venous prostaglandin E1 (PGE1) and left atrial norepinephrine (NE) infusion to wean from cardiopulmonary bypass (CPB) patients with refractory postoperative pulmonary hypertension.

DESIGN

Observational, nonrandomized study.

SETTING

Department of Cardiac Surgery in a university hospital.

PATIENTS

We studied 10 nonconsecutive American Society of Anesthesiologists III and New York Heart Association class III-IV patients with postoperative pulmonary hypertension and low cardiac output syndrome preventing separation from CPB.

INTERVENTIONS

Patients received right atrial PGE1 (31.5 +/- 6.26 ng/kg/min) and left atrial NE (0.11 +/- 0.02 microg/kg/min) infusion. Hemodynamic data were obtained before CPB (T0), after CPB under maximal inotropes and vasodilator infusion (T1), 10 mins (T2) and 12 hrs (T3) after PGE1 and NE infusion, and 48 hrs after withdrawal of PGE1 and NE (T4).

MEASUREMENTS AND MAIN RESULTS

All patients were successfully weaned from CPB and survived. The biatrial infusion of PGE1 and NE caused a dramatic reduction in mean pulmonary artery pressure (from 42.8 +/- 5.1 mm Hg at T1 to 28.5 +/- 2.6 mm Hg at T2 and 20.5 +/- 2.0 mm Hg at T4), pulmonary vascular resistance index (from 1158 +/- 269 dyne x sec/cm5 x m2 at T1 to 501 +/- 99 dyne x sec/cm5 x m2 at T2 and 246 +/- 50 dyne x sec/cm5 x m2 at T4), and pulmonary-to-systemic vascular resistance index ratio (from 0.61 +/- 0.17 at T1 to 0.20 +/- 0.04 at T2 and 0.11 +/- 0.03 at T4). Cardiac index increased from 1.7 +/- 0.2 L/min/m2 at T1 to 2.3 +/- 0.2 L/min/m2 at T2 and 2.9 +/- 0.1 L/min/m2 at T4.

CONCLUSIONS

In patients with refractory postoperative pulmonary hypertension, the combined administration of low-dose PGE1 in the right atrium and NE in the left atrium is an effective means to wean patients from cardiopulmonary bypass.

Low-dose prostacyclin is superior to terbutaline and aminophylline in reducing capillary permeability in cat skeletal muscle in vivo

OBJECTIVE

To analyze and compare the capillary permeability-reducing effects of prostacyclin, terbutaline, and aminophylline.

DESIGN

A prospective, experimental study.

SETTING

A university laboratory.

SUBJECTS

Fourteen adult, anesthetized cats.

INTERVENTIONS

The study was performed on an autoperfused calf muscle preparation enclosed in a plethysmograph, with continuous recordings of tissue volume, arterial and venous blood pressures, and blood flow. The capillary filtration coefficient was used as a measure of capillary hydraulic permeability, and measured at different doses of intravenous infusions of prostacyclin, terbutaline, and aminophylline. These analyses were made from normal and from raised permeability levels, the latter by prior and simultaneous infusion of tumor necrosis factor-a (TNF-a) or histamine. All three of the drugs analyzed were given at low doses, without vasodilator effect, and at doses with a clear vasodilator effect.

MAIN RESULTS

Prostacyclin infusion reduced capillary permeability to a value of about 25% below the initial control value, and this level was reached both from normal and increased permeability levels. The maximal reduction level was obtained at a low nonvasodilator dose of 2 ng/kg/min. Terbutaline and aminophylline had no significant effect on capillary filtration coefficient when tested from the initial control permeability level. From a TNF-alpha-raised permeability level (about 50% above control) and from a histamine-raised permeability level (about 60% above control), both drugs induced small reductions in the capillary filtration coefficient.

CONCLUSION

Low-dose prostacyclin effectively reduces hydraulic capillary permeability in cat skeletal muscle and is superior to terbutaline and aminophylline.

Vasodilators in mechanical ventilation

Vasodilators that affect the pulmonary vasculature are appealing adjuncts in many cardiopulmonary conditions that require mechanical ventilation such as ARDS, COPD, PPHN, and cardiothoracic surgery. The adverse systemic effects of parenteral PGE1 and parenteral prostacyclin limit their usefulness in critically ill patients. Liposomal PGE1 has few systemic effects, but thus far has not resulted in a significant clinical benefit in patients with ARDS. Inhaled NO and aerosolized prostacyclin offer the advantage of selective pulmonary vasodilation with minimal systemic effects. Both agents decrease PAP and in many clinical situations improve oxygenation; however, the physiologic effects of inhaled NO and aerosolized prostacyclin have not convincingly led to improved clinical outcomes. Currently, use of vasodilators in mechanically ventilated patients remains investigational.

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.

Pulmonary hypertension and selective pulmonary vasodilators in acute lung injury

The pulmonary circulation and the mechanisms which generate pulmonary hypertension are reviewed. The role of these mechanisms in the common pulmonary hypertensive states are analysed, particularly those in acute lung injury. Management options are discussed, with particular emphasis on the use of selective pulmonary vasodilators.

Systemic levels of 6-keto-prostaglandin F1 alpha following administration of inhaled aerosolized prostacyclin

A case is described where systemic levels of prostacyclin metabolite were measured during inhaled aerosolized prostacyclin (IAP) therapy for severe hypoxaemia in a patient with the acute respiratory distress syndrome. Comparable levels of prostacyclin metabolite have been associated with a marked platelet aggregation defect in vitro. A platelet aggregation defect was also demonstrated in vivo in this patient. Haemodynamic and gas exchange data during the IAP therapy are described.

Inhaled aerosolized prostacyclin and nitric oxide as selective pulmonary vasodilators in ARDS--a pilot study

Nitric oxide 10 ppm and inhaled aerosolized prostacyclin 50 ng/kg/min were compared as selective pulmonary vasodilators in five patients with hypoxaemia secondary to acute respiratory distress syndrome. Neither agent resulted in systemic haemodynamic changes, indicating true pulmonary selectivity. Inhaled aerolized prostacyclin improved oxygenation to a degree comparable to nitric oxide, as measured by the arterial alveolar oxygen partial pressure gradient and shunt fraction.