The potential use of type-5 phosphodiesterase inhibitors in coronary artery bypass graft surgery

Cardiac Effects of Phosphodiesterase-5 Inhibitors: Efficacy and Safety

The coexistence of cardiovascular disease and erectile dysfunction is widespread, possibly owing to underlying endothelial dysfunction in both diseases. Millions of patients with cardiovascular disease are prescribed phosphodiesterase-5 (PDE5) inhibitors for the management of erectile dysfunction. Although the role of PDE5 inhibitors in erectile dysfunction therapy is well established, their effects on the cardiovascular system are unclear. Preclinical studies investigating the effect of PDE5 inhibitors on ischemia-reperfusion injury, pressure overload-induced hypertrophy, and chemotoxicity suggested a possible clinical role for each of these medications; however, attempts to translate these findings to the bedside have resulted in mixed outcomes. In this review, we explore the biologic preclinical effects of PDE5 inhibitors in mediating cardioprotection. We then examine clinical trials investigating PDE5 inhibition in patients with heart failure, coronary artery disease, and ventricular arrhythmias and discuss why the studies likely have yet to show positive results and efficacy with PDE5 inhibition despite no safety concerns.

Management of Right Heart Failure in the Intensive Care Unit

Right heart failure is a clinical syndrome of various causes that commonly involves failure of the right ventricle (RV). The hemodynamic hallmark of the syndrome is increasing central venous pressure and worsening cardiac output with a rising RV end-diastolic pressure. When dealing with RV failure, clinicians must assess and optimize the intravascular volume state, support RV contractility, and address any pathologic elevations of afterload so that systemic perfusion is preserved. Despite these measures, there may still be a need to offer rescue interventions to the failing RV in carefully selected patients.

Pharmacologic therapy for erectile dysfunction and its interaction with the cardiovascular system

Phosphodiesterase (PDE) enzymes are widely distributed throughout the body, having numerous effects and functions. The PDE type 5 (PDE5) inhibitors are widely used to treat erectile dysfunction (ED). Recent, intense preclinical and clinical research with PDE5 inhibitors has shed light on new mechanisms and has revealed a number of pleiotropic effects on the cardiovascular (CV) system. To date, PDE5 inhibition has been shown to be effective for the treatment of idiopathic pulmonary arterial hypertension, and both sildenafil and tadalafil are approved for this indication. However, current or future PDE5 inhibitors have the potential of becoming clinically useful in a variety of CV conditions such as heart failure, coronary artery disease, and hypertension. The present review discusses recent findings regarding pharmacologic treatment of ED and its interaction with the CV system and highlights current and future clinical applications beyond ED.

Cyclic GMP/protein kinase G type-Iα (PKG-Iα) signaling pathway promotes CREB phosphorylation and maintains higher c-IAP1, livin, survivin, and Mcl-1 expression and the inhibition of PKG-Iα kinase activity synergizes with cisplatin in non-small cell lung cancer cells

Previously, our laboratory showed that nitric oxide (NO)/cyclic GMP (cGMP)/protein kinase G type-Iα (PKG-Iα) signaling pathway plays an important role in preventing spontaneous apoptosis and promoting cell proliferation in both normal cells (bone marrow stromal cells and vascular smooth muscle cells) and certain cancer cells (ovarian cancer cells). In the present study, we investigated the novel role of the cGMP/PKG-Iα pathway in preventing spontaneous apoptosis, promoting colony formation and regulating phosphorylation of cAMP response element binding (CREB) protein and protein expression of inhibitor of apoptosis proteins (IAPs) and anti-apoptotic Bcl-2-related proteins in NCI-H460 and A549 non-small cell lung cancer (NSCLC) cells. 1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one (ODQ), which blocks endogenous NO-induced activation of cGMP/PKG-Iα, induced apoptosis and decreased colony formation. ODQ also decreased CREB ser133 phosphorylation and protein expression of c-IAP1, livin, and survivin. DT-2 (inhibitor of PKG-Iα kinase activity) increased apoptosis by twofold and decreased CREB ser133 phosphorylation and c-IAP1, livin, and survivin expression. Gene knockdown of PKG-Iα expression using small-interfering RNA increased apoptosis and decreased CREB ser133 phosphorylation, and c-IAP1, livin, survivin, and Mcl-1 expression. Inhibition of PKG-Iα kinase activity with DT-2 dramatically enhanced pro-apoptotic effects of the chemotherapeutic agent cisplatin. Combined treatment of DT-2 and cisplatin increased apoptosis compared with cisplatin or DT-2 alone, showing a synergistic effect. The data suggest that the PKG-Iα kinase activity is necessary for maintaining higher levels of CREB phosphorylation at ser133 and protein expression of c-IAP1, livin, survivin, and Mcl-1, preventing spontaneous apoptosis and promoting colony formation in NSCLC cells, which may limit the effectiveness of chemotherapeutic agents like cisplatin.

Nitric oxide and the CABG patient

The post surgery success of coronary artery bypass grafting (CABG) is counteracted by thrombosis and de-endothelialization, intimal hyperplasia and, over the long term, atherosclerosis. There are many reasons to assume that in CABG patients vascular bioavailability of NO generated by the endothelium plays an important role for graft function. This holds true for factors such as graft type, harvesting and storage, the type of surgery, non-pharmacologic prevention of risk factors, for example, regular physical activity (if feasible), and drug therapy. Although the precise role of graft endothelial NO bioavailability for graft patency and clinical endpoints is still uncertain, current data rather speak in favor of NO indicating that the potential of vasoprotective activities of NO in the CABG patient deserves further investigation.

Effect of DETA-NONOate and papaverine on vasodilation of human internal mammary artery

In this study, the relaxatory effect of DETA-NONOate is compared with that of papaverine on isolated human internal mammary artery. We investigated the inhibitory effects of DETA-NONOate and papaverine on phenylephrine-induced contractile response in internal mammary artery segments. The internal mammary artery segments, taken from methodologically matched patients who underwent coronary artery bypass grafting, were prepared, placed in an organ bath, and contracted with phenylephrine (10−9 to 10−4 mol/L) to investigate their relaxatory response to DETA-NONOate or papaverine. Phenylephrine dose–response contraction was obtained after 1, 2, and 3 h in segments pre-incubated with DETA-NONOate or papaverine for 30 min. The EC50 that presented for internal mammary artery segments incubated with DETA-NONOate was 3.523 ± 1.2696 × 10–7 mol/L, and for papaverine was 3.467 ± 1.2145 × 10–6 mol/L. In segments pre-incubated with DETA-NONOate, the contractile response to phenylephrine was suppressed in the first 2 h post-incubation, compared with control responsive groups (p < 0.05), but this inhibition was revoked after 3 h post-incubation. We showed that DETA-NONOate has a more significant relaxative effect by comparison with papaverine; moreover, continuous and long-lasting nitric oxide production by DETA-NONOate might be of great importance for the outcome from coronary artery bypass grafting, when internal mammary artery is used as a conduit.

Inhaled NO and sildenafil combination in cardiac surgery patients with out-of-proportion pulmonary hypertension: acute effects on postoperative gas exchange and hemodynamics

BACKGROUND

The goal of this study was to examine the effects of coadministration of sildenafil and inhaled nitric oxide (iNO) in patients with out-of-proportion pulmonary hypertension who underwent cardiac valve replacement surgery.

METHODS AND RESULTS

Twenty consecutive cardiac surgery patients with out-of-proportion pulmonary hypertension were randomly assigned postoperatively into 2 groups: group A received 10 ppm of iNO followed by sildenafil (100 mg) orally 30 minutes later, and group B initially received sildenafil (100 mg) orally followed by 10 ppm of iNO 60 minutes later. Hemodynamic and gas exchange data were obtained at baseline, after administration of either iNO or sildenafil alone, and at 90 minutes from baseline. In group A, iNO resulted in a significant reduction in mean pulmonary artery pressure (MPAP) and pulmonary vascular resistance index (PVRI) (by 9.6% and 20.8%, respectively). In group B, sildenafil administration also resulted in a significant decrease in mean arterial pressure, MPAP, pulmonary artery occlusive pressure, PVRI, and systemic vascular resistance index but also in the PaO(2)/inspired fraction of oxygen ratio (by 18.7%, 22.0%, 15.7%, 31.6%, 21.3%, and 14%, respectively). In both groups, the coadministration of the 2 drugs resulted in a significant further reduction of mean arterial pressure, MPAP, pulmonary artery occlusive pressure, systemic vascular resistance index, and PVRI, whereas cardiac index and mixed venous oxygen saturation remained unchanged. The hypoxemia after sildenafil administration in group B improved after the coadministration of iNO, and thus PaO(2)/inspired fraction of oxygen returned to values near baseline.

CONCLUSION

In this study, the postoperative coadministration of iNO and oral sildenafil in patients with out-of-proportion pulmonary hypertension undergoing cardiac surgery is safe and results in an additive favorable effect on pulmonary arterial pressure and pulmonary vascular resistance, without systemic hypotension and ventilation/perfusion mismatch.

Essential roles of the nitric oxide (no)/cGMP/protein kinase G type-Iα (PKG-Iα) signaling pathway and the atrial natriuretic peptide (ANP)/cGMP/PKG-Iα autocrine loop in promoting proliferation and cell survival of OP9 bone marrow stromal cells

Inappropriate signaling conditions within bone marrow stromal cells (BMSCs) can lead to loss of BMSC survival, contributing to the loss of a proper micro-environmental niche for hematopoietic stem cells (HSCs), ultimately causing bone marrow failure. In the present study, we investigated the novel role of endogenous atrial natriuretic peptide (ANP) and the nitric oxide (NO)/cGMP/protein kinase G type-Iα (PKG-Iα) signaling pathway in regulating BMSC survival and proliferation, using the OP9 BMSC cell line commonly used for facilitating the differentiation of HSCs. Using an ANP-receptor blocker, endogenously produced ANP was found to promote cell proliferation and prevent apoptosis. NO donor SNAP (S-nitroso-N-acetylpenicillamine) at low concentrations (10 and 50 µM), which would moderately stimulate PKG activity, protected these BMSCs against spontaneous apoptosis. YC-1, a soluble guanylyl cyclase (sGC) activator, decreased the levels of apoptosis, similar to the cytoprotective effects of low-level NO. ODQ (1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one), which blocks endogenous NO-induced activation of sGC and thus lowers endogenous cGMP/PKG activity, significantly elevated apoptotic levels by 2.5- and three-fold. Pre-incubation with 8-Bromo-cGMP or ANP, which bypass the ODQ block, almost completely prevented the ODQ-induced apoptosis. A highly-specific PKG inhibitor, DT-3, at 20, and 30 µM, caused 1.5- and two-fold increases in apoptosis, respectively. ODQ and DT-3 also decreased BMSCs proliferation and colony formation. Small Interfering RNA gene knockdown of PKG-Iα increased apoptosis and decreased proliferation in BMSCs. The data suggest that basal NO/cGMP/PKG-Iα activity and autocrine ANP/cGMP/PKG-Iα are necessary for preserving OP9 cell survival and promoting cell proliferation and migration.

Medical and surgical treatment of acute right ventricular failure

Acute right ventricular (RV) failure is a frequent and serious clinical challenge in the intensive care unit. It is usually seen as a consequence of left ventricular failure, pulmonary embolism, pulmonary hypertension, sepsis, acute lung injury or after cardiothoracic surgery. The presence of acute RV failure not only carries substantial morbidity and mortality, but also complicates the use of commonly used treatment strategies in critically ill patients. In contrast to the left ventricle, the RV remains relatively understudied, and investigations of the treatment of isolated RV failure are rare and usually limited to nonrandomized observations. We searched PubMed for papers in the English language by using the search words right ventricle, right ventricular failure, pulmonary hypertension, sepsis, shock, acute lung injury, cardiothoracic surgery, mechanical ventilation, vasopressors, inotropes, and pulmonary vasodilators. These were used in various combinations. We read the abstracts of the relevant titles to confirm their relevance, and the full papers were then extracted. References from extracted papers were checked for any additional relevant papers. This review summarizes the general measures, ventilation strategies, vasoactive substances, and surgical as well as mechanical approaches that are currently used or actively investigated in the treatment of the acutely failing RV.

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.

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.

Variation in perioperative vasoactive therapy in cardiovascular surgical care: data from the Society of Thoracic Surgeons

BACKGROUND

The appropriate use of vasoactive cardiovascular drugs in high-risk coronary artery bypass grafting (CABG) patients has not been well characterized.

METHODS

We performed a detailed chart analysis on 2,390 randomly selected patients undergoing CABG between January 2004 and June 2005 at 55 hospitals participating in the Society of Thoracic Surgeons' National Adult Cardiac Surgery Database. Patients were eligible if they had elective/urgent CABG with an ejection fraction (EF) <40%, or if they had an elective or urgent CABG at > or =65 years with diabetes, or a glomerular filtration rate <60 mL/min per 1.73 m(2). Logistic regression modeling was used to determine predictors of and provide risk-adjusted frequencies of postoperative vasoactive therapies.

RESULTS

Vasoactive therapy was used in 90% of patients. Inotropes/vasopressors were used in 28% (668), vasodilators in 18% (430), and the combination in 43% (1,037). Predictors of any inotrope use were preoperative atrial fibrillation (odds ratio [OR] 1.48), other arrhythmia (OR 2.09), EF (OR 1.09 per 5-unit decrease), severe mitral regurgitation (OR 2.56), 3-vessel coronary artery disease (OR 1.35), New York Heart Association class IV (1.38), on-pump (OR 1.86), other procedure (OR 2.51), and peripheral vascular disease (OR 1.28) (all OR P < .05). Hospital-level risk-adjusted rates of any inotrope use varied significantly from 100% to 35% (P < .01) and vasodilator rates varied from 100% to 10% (P < .01).

CONCLUSIONS

There is marked hospital variation in the use of vasoactive therapies in high-risk CABG patients in clinical practice, indicating an important area for further research to better clarify best practice.

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.

Pivotal effects of phosphodiesterase inhibitors on myocyte contractility and viability in normal and ischemic hearts

Phosphodiesterases (PDEs) are enzymes that degrade cellular cAMP and cGMP and are thus essential for regulating the cyclic nucleotides. At least 11 families of PDEs have been identified, each with a distinctive structure, activity, expression, and tissue distribution. The PDE type-3, -4, and -5 (PDE3, PDE4, PDE5) are localized to specific regions of the cardiomyocyte, such as the sarcoplasmic reticulum and Z-disc, where they are likely to influence cAMP/cGMP signaling to the end effectors of contractility. Several PDE inhibitors exhibit remarkable hemodynamic and inotropic properties that may be valuable to clinical practice. In particular, PDE3 inhibitors have potent cardiotonic effects that can be used for short-term inotropic support, especially in situations where adrenergic stimulation is insufficient. Most relevant to this review, PDE inhibitors have also been found to have cytoprotective effects in the heart. For example, PDE3 inhibitors have been shown to be cardioprotective when given before ischemic attack, whereas PDE5 inhibitors, which include three widely used erectile dysfunction drugs (sildenafil, vardenafil and tadalafil), can induce remarkable cardioprotection when administered either prior to ischemia or upon reperfusion. This article provides an overview of the current laboratory and clinical evidence, as well as the cellular mechanisms by which the inhibitors of PDE3, PDE4 and PDE5 exert their beneficial effects on normal and ischemic hearts. It seems that PDE inhibitors hold great promise as clinically applicable agents that can improve cardiac performance and cell survival under critical situations, such as ischemic heart attack, cardiopulmonary bypass surgery, and heart failure.

Oral phosphodiesterase type 5 inhibitors: nonerectogenic beneficial uses

INTRODUCTION

Phosphodiesterase type 5 (PDE5) hydrolyses cyclic guanylate monophosphate (cGMP) specifically to 5' GMP. PDE5 inhibitors were a breakthrough medication that addressed a previously unfulfilled medical need. They promoted vascular relaxation in the corpora cavernosa and penile erection during sexual stimulation. Sildenafil, vardenafil, and tadalafil were approved then introduced as effective treatments for male erectile dysfunction. This impact has stimulated academic, clinical, and industrial research.

AIM

To highlight the nonerectogenic beneficial uses of oral PDE5 inhibitors.

METHOD

A systematic review of published studies in this affair based on a Pubmed and medical subject heading databases search of all concerned articles.

MAIN OUTCOME MEASURES

Demonstrated beneficial as well as applicable uses of oral PDE5 inhibitors.

RESULTS

As chemical molecules, these drugs were shown to exert potential nonerectogenic beneficial effects. They showed efficacy as a useful adjunct in the management of pulmonary hypertension. Additional uses were extended to different utilities: essential hypertension, benign prostatic hyperplasia, gastrointestinal disorders, endothelial dysfunction, female sexual dysfunction, genital blood flow, exercise capacity, Raynaud's phenomenon, sperm motility, etc.

CONCLUSION

Exploring PDE5 inhibitors for their possible medical applications in diverse specialties seems to be beneficial in making use of these molecules for the welfare of humanity.

Crosstalk between G-protein and Ca2+ pathways switches intracellular cAMP levels

Cyclic adenosine monophosphate and cyclic guanosine monophosphate are universal intracellular messengers whose concentrations are regulated by molecular networks comprised of different isoforms of the synthases adenylate cyclase or guanylate cyclase and the phosphodiesterases which degrade these compounds. In this paper, we employ a systems biology approach to develop mathematical models of these networks that, for the first time, take into account the different biochemical properties of the isoforms involved. To investigate the mechanisms underlying the joint regulation of cAMP and cGMP, we apply our models to analyse the regulation of cilia beat frequency in Paramecium by Ca(2+). Based on our analysis of these models, we propose that the diversity of isoform combinations that occurs in living cells provides an explanation for the huge variety of intracellular processes that are dependent on these networks. The inclusion of both G-protein receptor and Ca(2+)-dependent regulation of AC in our models allows us to propose a new explanation for the switching properties of G-protein subunits involved in nucleotide regulation. Analysis of the models suggests that, depending on whether the G-protein subunit is bound to AC, Ca(2+) can either activate or inhibit AC in a concentration-dependent manner. The resulting analysis provides an explanation for previous experimental results that showed that alterations in Ca(2+) concentrations can either increase or decrease cilia beat frequency over particular Ca(2+) concentration ranges.

Superoxide from NADPH oxidase upregulates type 5 phosphodiesterase in human vascular smooth muscle cells: inhibition with iloprost and NONOate

BACKGROUND AND PURPOSE

To determine whether there is an association between vascular NADPH oxidase (NOX), superoxide, the small GTPase Rac(1) and PDE type 5 (PDE5) in human vascular smooth muscle cell (hVSMCs).

EXPERIMENTAL APPROACH

hVSMCs were incubated with xanthine-xanthine oxidase (X-XO; a superoxide generating system) or the thromboxane A(2) analogue, U46619 (+/-superoxide dismutase (SOD) or apocynin) for 16 h. The expression of PDE5 and NOX-1 was assessed using Western blotting and superoxide measured. The role of Rac(1) in superoxide generation was assessed by overexpressing either the dominant-negative or constitutively active Rac isoforms. The effects of iloprost, DETA-NONOate and the Rho-kinase inhibitor, Y27632, on PDE5 and NOX-1 expression were also studied.

KEY RESULTS

Following 16 h incubation, U46619 and X-XO promoted the expression of PDE5 and NOX-1, an effect blocked by SOD or apocynin when co-incubated over the same time course. X-XO and U46619 both promoted the formation of superoxide. Overexpression of dominant-negative Rac(1) or addition of iloprost, DETA-NONOate or Y27632 completely blocked both superoxide release and PDE5 protein expression and activity.

CONCLUSIONS AND IMPLICATIONS

These data demonstrate that superoxide derived from NOX upregulates the expression of PDE5 in human VSMCs. As PDE5 hydrolyses cyclic GMP, this effect may blunt the vasculoprotective actions of NO.

Management strategies for patients with pulmonary hypertension in the intensive care unit

OBJECTIVE

Pulmonary hypertension may be encountered in the intensive care unit in patients with critical illnesses such as acute respiratory distress syndrome, left ventricular dysfunction, and pulmonary embolism, as well as after cardiothoracic surgery. Pulmonary hypertension also may be encountered in patients with preexisting pulmonary vascular, lung, liver, or cardiac diseases. The intensive care unit management of patients can prove extremely challenging, particularly when they become hemodynamically unstable. The objective of this review is to discuss the pathogenesis and physiology of pulmonary hypertension and the utility of various diagnostic tools, and to provide recommendations regarding the use of vasopressors and pulmonary vasodilators in intensive care.

DATA SOURCES AND EXTRACTION

We undertook a comprehensive review of the literature regarding the management of pulmonary hypertension in the setting of critical illness. We performed a MEDLINE search of articles published from January 1970 to March 2007. Medical subject headings and keywords searched and cross-referenced with each other were: pulmonary hypertension, vasopressor agents, therapeutics, critical illness, intensive care, right ventricular failure, mitral stenosis, prostacyclin, nitric oxide, sildenafil, dopamine, dobutamine, phenylephrine, isoproterenol, and vasopressin. Both human and animal studies related to pulmonary hypertension were reviewed.

CONCLUSIONS

Pulmonary hypertension presents a particular challenge in critically ill patients, because typical therapies such as volume resuscitation and mechanical ventilation may worsen hemodynamics in patients with pulmonary hypertension and right ventricular failure. Patients with decompensated pulmonary hypertension, including those with pulmonary hypertension associated with cardiothoracic surgery, require therapy for right ventricular failure. Very few human studies have addressed the use of vasopressors and pulmonary vasodilators in these patients, but the use of dobutamine, milrinone, inhaled nitric oxide, and intravenous prostacyclin have the greatest support in the literature. Treatment of pulmonary hypertension resulting from critical illness or chronic lung diseases should address the primary cause of hemodynamic deterioration, and pulmonary vasodilators usually are not necessary.

Sildenafil in the treatment of pulmonary hypertension

The therapy of pulmonary hypertension has evolved rapidly in the last 10 years from the use of non-selective vasodilators to drugs that specifically target pulmonary vasodilation, endothelial function, and vascular remodeling. Sildenafil is a phosphodiesterase type 5 inhibitor that has an expanding role in the treatment of pulmonary hypertension. Case series and small studies, as well as the first large randomized controlled trial, have demonstrated the safety and efficacy of sildenafil in improving mean pulmonary artery pressure, pulmonary vascular resistance, cardiac index, and exercise tolerance in pulmonary arterial hypertension. It may be useful in adults, children, and neonates after cardiac surgery, with left heart failure, in fibrotic pulmonary disease, high altitude exposure, and thromboembolic disease, and in combination with other therapies for pulmonary hypertension, such as inhaled iloprost. The oral formulation and favorable adverse effect profile make sildenafil an attractive alternative in the treatment of selected patients with pulmonary hypertension.

Effect of oral sildenafil citrate on intraoperative hemodynamics in patients with pulmonary hypertension undergoing valvular heart surgery

OBJECTIVE

Pulmonary hypertension remains a major problem during the perioperative period for surgical correction of long-standing valvular heart disease. Sildenafil citrate (INN sildenafil) is a selective phosphodiesterase type 5 inhibitor that is being increasingly recognized as a treatment modality for pulmonary hypertension. There is lack of evidence, however, regarding its pulmonary vasodilatory effect in anesthetized cardiac surgical patients. We therefore evaluated the effects of sildenafil on hemodynamics in patients with concomitant pulmonary hypertension undergoing valvular heart surgery in a controlled, prospective, randomized, double-blind trial.

METHODS

Fifty-three patients scheduled for valvular heart surgery with mean pulmonary arterial pressure greater than 30 mm Hg were randomly treated with either 50 mg oral sildenafil (n = 26) or placebo (n = 27) 10 minutes before induction of anesthesia. Hemodynamic variables were measured 5 minutes after induction of anesthesia (baseline) and at 30 and 60 minutes after medication.

RESULTS

Patient characteristics and baseline hemodynamics were similar between groups. Systolic and mean pulmonary arterial pressures and pulmonary vascular resistance were significantly lower in the sildenafil group at 30 minutes after medication, without any changes in mean systemic arterial pressure and systemic vascular resistance.

CONCLUSION

Sildenafil produced significant pulmonary vasodilatory effect relative to placebo in anesthetized cardiac surgical patients with pulmonary hypertension. With respect to the predominant selectivity of sildenafil to pulmonary vasculature shown in this study and other potentially beneficial effects such as myocardial protection, use of sildenafil in the intraoperative period in cardiac surgical patients with pulmonary hypertension should be considered.