Inhaled Nitric Oxide Improves Pulmonary Functions Following Massive Pulmonary Embolism: A Report of Four Patients and Review of the Literature

Anesthetic management in patients having catheter-based thrombectomy for acute pulmonary embolism: A narrative review

Pulmonary embolism is the third leading cause of cardiovascular death. Novel percutaneous catheter-based thrombectomy techniques are rapidly becoming popular in high-risk pulmonary embolism - especially in the presence of contraindications to thrombolysis. The interventional nature of these procedures and the risk of sudden cardiorespiratory compromise requires the presence of an anesthesiologist. Facilitating catheter-based thrombectomy can be challenging since qualifying patients are often critically ill. The purpose of this narrative review is to provide guidance to anesthesiologists for the assessment and management of patients having catheter-based thrombectomy for acute pulmonary embolism. First, available techniques for catheter-based thrombectomy are reviewed. Then, we discuss definitions and application of common risk stratification tools for pulmonary embolism, and how to assess patients prior to the procedure. An adjudication of risks and benefits of anesthetic strategies for catheter-based thrombectomy follows. Specifically, we give guidance and rationale for use monitored anesthesia care and general anesthesia for these procedures. For both, we review strategies for assessing and mitigating hemodynamic perturbations and right ventricular dysfunction, ranging from basic monitoring to advanced inodilator therapy. Finally, considerations for management of right ventricular failure with mechanical circulatory support are discussed.

Inhaled nitric oxide has pulmonary vasodilator efficacy both in the immediate and prolonged phase of acute pulmonary embolism

BACKGROUND

Inhaled nitric oxide (iNO) effectively reduces right ventricular afterload when administered in the immediate phase of acute pulmonary embolism (PE) in preclinical animal models. In a porcine model of intermediate-risk PE, we aimed to investigate whether iNO has pulmonary vasodilator efficacy both in the immediate and prolonged phase of acute PE.

METHODS

Anesthetized pigs (n = 18) were randomized into three subgroups. An acute PE iNO-group (n = 6) received iNO at 40 ppm at one, three, six, nine and 12 hours after onset of PE. Vehicle animals (n = 6) received PE, but no active treatment. A third group of sham animals (n = 6) received neither PE nor treatment. Animals were evaluated using intravascular pressures, respiratory parameters, biochemistry and intracardiac pressure-volume measurements.

RESULTS

The administration of PE increased mean pulmonary artery pressure (mPAP) (vehicle vs sham; 33.3 vs 17.7 mmHg, p < 0.0001), pulmonary vascular resistance (vehicle vs sham; 847.5 vs 82.0 dynes, p < 0.0001) and right ventricular arterial elastance (vehicle vs sham; 1.2 vs 0.2 mmHg/ml, p < 0.0001). Significant mPAP reduction by iNO was preserved at 12 hours after the onset of acute PE (vehicle vs iNO; 0.5 vs -3.5 mmHg, p < 0.0001). However, this response was attenuated over time (p = 0.0313). iNO did not affect the systemic circulation.

CONCLUSIONS

iNO is a safe and effective pulmonary vasodilator both in the immediate and prolonged phase of acute PE in an in-vivo porcine model of intermediate-risk PE.

Plasma catestatin level predicts sPESI score and mortality in acute pulmonary embolism

INTRODUCTION

Acute pulmonary embolism (APE) is an emergent cardiothoracic disorder. The PESI score is used to estimate 30-day mortality in patients diagnosed with non-high-risk APE. Also, there are biomarkers for predicting prognosis and mortality in APE. Catestatin (CST) is accepted as a marker ofsympathetic nervous system activity which has been shown that the sympathetic nervous system activation can contribute pathogenesis in APE. So, we attempt herein to investigate the correlation of PE diagnosis and prognostic determination with plasma CST levels in PE patients.

MATERIAL AND METHODS

Blood samples were drawn at admission for laboratory assays and CST measurements. Plasma levels of CST were measured by ELISA according to the manufacturer's instruction. Transthoracic echocardiography was performed for the assessment of RV dysfunction using a Toshiba Applio 500 echocardiographic system within 24 h of the admission.

RESULTS

Plasma CST levels were higher in patients with APE than in the control group (17.5 ±6.1 ng/ml vs. 27.3 ±5.7 ng/ml, p < 0.001). Plasma CST levels were higher in the sPESI ≥ 1 (n = 72) than in the patients with sPESI < 1 (37.3 ±6.1 vs. 24.2 ±5.3 ng/ml, p < 0.001). There was a positive correlation between CST level and sPESI score (±0.581, p < 0.001). Mortality occurred in 20 patients with sPESI ≥ 1 (27.7%) and in 9 patients with sPESI < 1 (10.2%) (p = 0.010). Receiver operating characteristic (ROC) curve analysis using a cut-off level of 31.2 ng/ml, and the CST level predicted mortality with a sensitivity of 100% and specificity of 52.6% (AUC = 0.883, 95% CI: 0.689-0.921). Furthermore, the CST level was correlated with right ventricular dysfunction.

CONCLUSIONS

CST can predict sPESI score and mortality in patients with APE.

Riociguat, sildenafil and inhaled nitric oxide reduces pulmonary vascular resistance and improves right ventricular function in a porcine model of acute pulmonary embolism

BACKGROUND

Pulmonary vasodilators as add-on to current treatment strategies in acute pulmonary embolism may improve right ventricular unloading and hence improve patient outcome. We aimed to investigate whether stimulation of the nitric oxide (NO)-soluble guanylate cyclase (sGC)-cyclic guanosine monophosphate (cGMP) pathway with riociguat, sildenafil or inhaled NO causes pulmonary vasodilation and improves right ventricular function in a porcine model of acute intermediate risk pulmonary embolism.

METHODS

Two large autologous blood clots were administered to the pulmonary circulation of 28 pigs (60 kg). Animals were randomized to four increasing, clinically equivalent doses of riociguat (n=6), sildenafil (n=6), inhaled NO (n=6) or vehicle (n=6). Sham animals (n=4) did not receive pulmonary embolism or treatment. Haemodynamic responses were evaluated at baseline, after pulmonary embolism and after each dose using invasive pressure measurements, transoesophageal echocardiography, respiratory parameters and blood analysis.

RESULTS

Pulmonary embolism caused a three-fold increase in pulmonary vascular resistance compared with baseline (pulmonary embolism: 352±29 vs. baseline: 107±6 dynes, p<0.0001). All treatments lowered pulmonary vascular resistance compared with vehicle (riociguat: -158±35, sildenafil: -224±35, inhaled NO: -156±35 dynes, p<0.0001). Sildenafil, but neither inhaled NO nor riociguat, caused a decrease in systemic vascular resistance (sildenafil 678±41 vs. vehicle 1081±93 dynes, p=0.02) and increased cardiac output (sildenafil 8.8±0.8 vs. vehicle: 5.9±0.2 L/min, p<0.001). Systemic blood pressure was unaltered in all treatment groups.

CONCLUSION

Stimulation of the NO-sGC-cGMP pathway by riociguat, sildenafil and inhaled NO reduces pulmonary vascular resistance in a porcine model of acute pulmonary embolism without lowering systemic blood pressure.

Massive Pulmonary Embolism in a Recent Intracranial Hemorrhage: A Case Report of Inhaled Nitric Oxide to Improve Outcomes

Acute massive pulmonary embolism (PE) has a high mortality if left untreated. The mainstay of treatment is systemic thrombolysis which has some absolute contraindications like intracranial hemorrhage (ICH). Inhaled nitric oxide (iNO) is a selective pulmonary vasodilator that decreases pulmonary artery pressure (PAP) and allows the right ventricle of the heart to pump against less resistance. We present a case of iNO use to improve hemodynamics in a patient with a recent ICH. We believe this to be the first such case reported.

A 70-year-old female with a history of PE on Eliquis initially presented for weakness and was found to have right-sided ICH. She was discharged with instructions to hold Eliquis given ICH but was readmitted eight days later in florid cardiogenic shock requiring vasopressors and hypoxic respiratory failure refractory to intubation. CT showed bilateral PE with evidence of right heart strain and IV heparin was started. Due to her history of a recent ICH, she had an absolute contraindication prohibiting the use of systemic tissue plasminogen activator (tPA). Interventional radiology (IR) consult determined that the patient was not a candidate for catheter-directed tPA due to the recent ICH, mechanical ventilation, and hemodynamic instability based on pressor requirement. Vascular surgery and extracorporeal membrane oxygenation (ECMO) consults deemed the patient not operable. The patient was then started on iNO with immediate improvement in her blood pressure. Once vitally stable, IR consult performed pulmonary angiogram and completed a thrombectomy. The patient was eventually extubated and she restarted her Eliquis. She continues to do well 16 months after discharge.

In patients with massive PE with contraindications to systemic thrombolytics, providers are left with very few therapeutic interventions. A handful of case reports show that iNO improves systemic hemodynamics in postoperative patients with massive PE. This case highlights the potential for iNO to be a potential adjuvant in patients with absolute contraindications to systemic thrombolysis.

Management of Right Ventricular Failure in Pulmonary Embolism

Acute right ventricular failure remains the leading cause of mortality associated with acute pulmonary embolism (PE). This article reviews the pathophysiology behind acute right ventricular failure and strategies for managing right ventricular failure in acute PE. Immediate clot reduction via systemic thrombolytics, catheter based procedures, or surgery is always advocated for unstable patients. While waiting to mobilize these resources, it often becomes necessary to support the RV with vasoactive medications. Clinicians should carefully assess volume status and use caution with volume resuscitation. Right ventricular assist devices may have an expanding role in the future.

Pulmonary vasodilation in acute pulmonary embolism - a systematic review

Acute pulmonary embolism is the third most common cause of cardiovascular death. Pulmonary embolism increases right ventricular afterload, which causes right ventricular failure, circulatory collapse and death. Most treatments focus on removal of the mechanical obstruction caused by the embolism, but pulmonary vasoconstriction is a significant contributor to the increased right ventricular afterload and is often left untreated. Pulmonary thromboembolism causes mechanical obstruction of the pulmonary vasculature coupled with a complex interaction between humoral factors from the activated platelets, endothelial effects, reflexes and hypoxia to cause pulmonary vasoconstriction that worsens right ventricular afterload. Vasoconstrictors include serotonin, thromboxane, prostaglandins and endothelins, counterbalanced by vasodilators such as nitric oxide and prostacyclins. Exogenous administration of pulmonary vasodilators in acute pulmonary embolism seems attractive but all come with a risk of systemic vasodilation or worsening of pulmonary ventilation-perfusion mismatch. In animal models of acute pulmonary embolism, modulators of the nitric oxide-cyclic guanosine monophosphate-protein kinase G pathway, endothelin pathway and prostaglandin pathway have been investigated. But only a small number of clinical case reports and prospective clinical trials exist. The aim of this review is to give an overview of the causes of pulmonary embolism-induced pulmonary vasoconstriction and of experimental and human investigations of pulmonary vasodilation in acute pulmonary embolism.

Use of extracorporeal membrane oxygenation in patients with acute high-risk pulmonary embolism: a case series with literature review

Background

Although extracorporeal membrane oxygenation (ECMO) has been used for the treatment of acute high-risk pulmonary embolism (PE), there are limited reports which focus on this approach. Herein, we described our experience with ECMO in patients with acute high-risk PE.

Methods

We retrospectively reviewed medical records of patients diagnosed with acute high-risk PE and treated with ECMO between January 2014 and December 2018.

Results

Among 16 patients included, median age was 51 years (interquartile range [IQR], 38 to 71 years) and six (37.5%) were male. Cardiac arrest was occurred in 12 (75.0%) including two cases of out-of-hospital arrest. All patients underwent veno-arterial ECMO and median ECMO duration was 1.5 days (IQR, 0.0 to 4.5 days). Systemic thrombolysis and surgical embolectomy were performed in seven (43.8%) and nine (56.3%) patients, respectively including three patients (18.8%) received both treatments. Overall 30-day mortality rate was 43.8% (95% confidence interval, 23.1% to 66.8%) and 30-day mortality rates according to the treatment groups were ECMO alone (33.3%, n=3), ECMO with thrombolysis (50.0%, n=4) and ECMO with embolectomy (44.4%, n=9).

Conclusions

Despite the vigorous treatment efforts, patients with acute high-risk PE were related to substantial morbidity and mortality. We report our experience of ECMO as rescue therapy for refractory shock or cardiac arrest in patients with PE.

Potential role of sympathetic activity on the pathogenesis of massive pulmonary embolism with circulatory shock in rabbits

Background

We recently showed that intravenous sodium nitroprusside treatment (SNP) could relieve the pulmonary vasospasm of pulmonary embolism (PE) and non-pulmonary embolism (non-PE) regions in a rabbit massive pulmonary embolism (MPE) model associated with shock. The present study explored the potential role of cardiopulmonary sympathetic activity on the pathogenesis and the impact of vasodilators on cardiopulmonary sympathetic activity in this model.

Methods

Rabbits were randomly divided into sham operation group (S group, n = 8), model group (M, equal volume of saline intravenously, n = 11), SNP group (3.5 μg/kg/min intravenously, n = 10) and diltiazem group (DLZ, 6.0 μg/kg/min intravenously, n = 10).

Results

MPE resulted in reduced mean arterial pressure and increased mean pulmonary arterial pressure as well as reduced PaO₂ in the M, SNP and DLZ groups. Tyrosine hydroxylase (TH), neuropeptide Y (NPY) and endothelin-1 (ET-1) expression levels were significantly increased, while nitric oxide (NO) levels were reduced in both PE and non-PE regions in the M group. Both SNP and DLZ decreased mean pulmonary arterial pressure, reversed shock status, downregulated the expression of TH, NPY and ET-1, and increased NO levels in PE and non-PE regions.

Conclusion

Present results indicate that upregulation of the sympathetic medium transmitters TH and NPY in whole lung tissues serves one of the pathological features of MPE. The vasodilators SNP and DLZ could relieve pulmonary vasospasm in both embolization and non-embolization regions and reverse circulatory shock, thereby indirectly downregulating the sympathetic activation of the whole lung tissues and breaking a vicious cycle related to sympathetic activation in this model.

Aggressive Treatment of Intermediate-Risk Patients with Acute Symptomatic Pulmonary Embolism

Contemporary studies of acute pulmonary embolism (PE) have evaluated the role of thrombolytics in intermediate-risk PE. Significant findings are that thrombolytic therapy may prevent hemodynamic deterioration and all-cause mortality but increases major bleeding. Benefits and harms are finely balanced with no convincing net benefit from thrombolytic therapy among unselected patients. Among patients with intermediate risk PE, additional prognostic factors or subtle hemodynamic changes might alter the risk-benefit assessment in favor of thrombolytic therapy before obvious hemodynamic instability.

Inhaled Nitric Oxide as an Adjunct to Thrombolytic Therapy in a Patient with Submassive Pulmonary Embolism and Severe Hypoxemia

Introduction

Inhaled nitric oxide (iNO) is a selective pulmonary vasodilator with limited indications in adults. We present a patient with hypoxemia and right ventricular dysfunction due to submassive acute pulmonary emboli where iNO was used as a bridge to thrombolysis.

Case

A 29-year-old male was admitted to the intensive care unit (ICU) for alcohol intoxication complicated with aspiration pneumonia and acute respiratory failure requiring mechanical ventilation. His medical history included morbid obesity (BMI 43) and alcohol dependence syndrome. Nine days after admission, he developed severe acute hypoxia and tachycardia with arterial oxygen tension (PaO2) of 52 mmHg requiring a positive end-expiratory pressure (PEEP) of 14 cmH2O and fraction of inspired oxygen (FiO2) of 1. Chest computed tomography (CT) revealed a large embolus in the right main pulmonary artery and transthoracic echocardiogram (TTE) reported new right ventricular dilatation with decreased right ventricular function. Due to the severe hypoxemia, he was started on iNO via the breathing circuit of the ventilator at a concentration of 20 parts per million (ppm) with steady improvement in oxygenation after 1 hour with a PaO2 of 81 mmHg on the same ventilator setting. The patient was given thrombolysis with alteplase and the iNO was slowly tapered off during the subsequent four days with concomitant successful tapering of PEEP to 8 cmH2O and FiO2 of 0.45.

Conclusion

Inhaled NO has been used to improve ventilation-perfusion matching and also to reduce pulmonary vascular resistance (PVR). Its effects on PVR may be useful in the setting of acute pulmonary emboli where vascular obstruction and vasoconstriction contribute to increased pulmonary arterial pressure and PVR which can present as acute right heart failure. We suggest that iNO, if available, could be considered in those patients with acute pulmonary emboli associated with significant hypoxemia as an adjunctive therapy or bridge to thrombolysis or thrombectomy.

Prise en charge de l'embolie pulmonaire grave en réanimation

L'embolie pulmonaire (EP) grave, définie par la présence d’un état de choc, est à l'origine d'une mortalité importante. L'objectif de cette mise au point est de synthétiser les dernières avancées et recommandations concernant la prise en charge des formes graves d'EP. La stratification du risque individuel de mortalité précoce permet d'apporter une stratégie diagnostique et thérapeutique optimisée pour chaque patient. Le traitement symptomatique consiste essentiellement en la prise en charge de l'état de choc. L'anticoagulation curative par héparine non fractionnée est réservée aux patients hémodynamiquement instables. Chez ces patients à haut risque, la thrombolyse systémique diminue la mortalité et le risque de récidive d'EP. Chez les patients à risque intermédiaire élevé, la thrombolyse systémique à dose standard diminue le risque de choc secondaire mais sans impact sur la mortalité globale. La thrombolyse est donc réservée aux patients à risque intermédiaire élevé présentant secondairement un état de choc. L'embolectomie chirurgicale reste indiquée en cas de contre-indication absolue à la thrombolyse ou en cas d'échec de celle-ci. Le positionnement dans l'algorithme thérapeutique de l'assistance extracorporelle et des techniques percutanées de revascularisation reste à définir. Leurs indications doivent donc être discutées dans des centres experts après une concertation multidisciplinaire incluant pneumologues, cardiologues, réanimateurs, radiologues interventionnels et chirurgiens cardiaques.

Management of patients with high-risk pulmonary embolism: a narrative review

High-risk pulmonary embolism (PE) is a life-threatening disorder associated with high mortality and morbidity. Most deaths in patients with shock occur within the first few hours after presentation, and rapid diagnosis and treatment is therefore essential to save patients’ lives. The main manifestations of major PE are acute right ventricular (RV) failure and hypoxia. RV pressure overload is predominantly related to the interaction between the mechanical pulmonary vascular obstruction and the underlying cardiopulmonary status. Computed tomography angiography allows not only adequate visualization of the pulmonary thromboemboli down to at least the segmental level but also RV enlargement as an indicator of RV dysfunction. Bedside echocardiography is an acceptable alternative under such circumstances. Although it does not usually provide a definitive diagnosis or exclude pulmonary embolism, echocardiography can confirm or exclude severe RV pressure overload and dysfunction. Extracorporeal membrane oxygenation support can be an effective procedure in patients with PE-induced circulatory collapse. Thrombolysis is generally accepted in unstable patients with high-risk PE; however, thrombolytic agents cannot be fully administered to patients with a high risk of bleeding. Conversely, catheter-directed treatment is an optimal treatment strategy for patients with high-risk PE who have contraindications for thrombolysis and is a minimally invasive alternative to surgical embolectomy. It can be performed with a minimum dose of thrombolytic agents or without, and it can be combined with various procedures including catheter fragmentation or embolectomy in accordance with the extent of the thrombus on a pulmonary angiogram. Hybrid catheter-directed treatment can reduce a rapid heart rate and high pulmonary artery pressure and can improve the gas exchange indices and outcomes. Surgical embolectomy is also performed in patients with contraindications for or an inadequate response to thrombolysis. Large hospitals having an intensive care unit should preemptively establish diagnostic and therapeutic protocols and rehearse multidisciplinary management for patients with high-risk PE. Coordination with a skilled team comprising intensivists, cardiologists, cardiac surgeons, radiologists, and other specialists is crucial to maximize success.

Hospital and intensive care unit management of decompensated pulmonary hypertension and right ventricular failure

Pulmonary hypertension and concomitant right ventricular failure present a diagnostic and therapeutic challenge in the intensive care unit and have been associated with a high mortality. Significant co-morbidities and hemodynamic instability are often present, and routine critical care unit resuscitation may worsen hemodynamics and limit the chances of survival in patients with an already underlying poor prognosis. Right ventricular failure results from structural or functional processes that limit the right ventricle’s ability to maintain adequate cardiac output. It is commonly seen as the result of left heart failure, acute pulmonary embolism, progression or decompensation of pulmonary hypertension, sepsis, acute lung injury, or in the perioperative setting. Prompt recognition of the underlying cause and institution of treatment with a thorough understanding of the elements necessary to optimize preload, cardiac contractility, enhance systemic arterial perfusion, and reduce right ventricular afterload are of paramount importance. Moreover, the emergence of previously uncommon entities in patients with pulmonary hypertension (pregnancy, sepsis, liver disease, etc.) and the availability of modern devices to provide support pose additional challenges that must be addressed with an in-depth knowledge of this disease.

Inflammatory response and pneumocyte apoptosis during lung ischemia-reperfusion injury in an experimental pulmonary thromboembolism model

Lung ischemia-reperfusion injury (LIRI) may occur in the region of the affected lung after reperfusion therapy. The inflammatory response mechanisms related to LIRI in pulmonary thromboembolism (PTE), especially in chronic PTE, need to be studied further. In a PTE model, inflammatory response and apoptosis may occur during LIRI and nitric oxide (NO) inhalation may alleviate the inflammatory response and apoptosis of pneumocytes during LIRI. A PTE canine model was established through blood clot embolism to the right lower lobar pulmonary artery. Two weeks later, we performed embolectomy with reperfusion to examine the LIRI changes among different groups. In particular, the ratio of arterial oxygen partial pressure to fractional inspired oxygen (PaO2/FiO2), serum concentrations of tumor necrosis factor-α (TNF-α), myeloperoxidase concentrations in lung homogenates, alveolar polymorphonuclear neutrophils (PMNs), lobar lung wet to dry ratio (W/D ratio), apoptotic pneumocytes, and lung sample ultrastructure were assessed. The PaO2/FiO2 in the NO inhalation group increased significantly when compared with the reperfusion group 4 and 6 h after reperfusion (368.83 ± 55.29 vs. 287.90 ± 54.84 mmHg, P < 0.05 and 380.63 ± 56.83 vs. 292.83 ± 6 0.34 mmHg, P < 0.05, respectively). In the NO inhalation group, TNF-α concentrations and alveolar PMN infiltration were significantly decreased as compared with those of the reperfusion group, 6 h after reperfusion (7.28 ± 1.49 vs. 8.90 ± 1.43 pg/mL, P < 0.05 and [(19 ± 6)/10 high power field (HPF) vs. (31 ± 11)/10 HPF, P < 0.05, respectively]. The amount of apoptotic pneumocytes in the lower lobar lung was negatively correlated with the arterial blood PaO2/FiO2, presented a positive correlation trend with the W/D ratio of the lower lobar lung, and a positive correlation with alveolar PMN in the reperfusion group and NO inhalation group. NO provided at 20 ppm for 6 h significantly alleviated LIRI in the PTE model. Our data indicate that, during LIRI, an obvious inflammatory response and apoptosis occur in our PTE model and NO inhalation may be useful in treating LIRI by alleviating the inflammatory response and pneumocyte apoptosis. This potential application warrants further investigation.

Recent advances in the management of pulmonary embolism: focus on the critically ill patients

The aim of this narrative review is to summarize for intensivists or any physicians managing “severe” pulmonary embolism (PE) the main recent advances or recommendations in the care of patients including risk stratification, diagnostic algorithm, hemodynamic management in the intensive care unit (ICU), recent data regarding the use of thrombolytic treatment and retrievable vena cava filters and finally results of direct oral anticoagulants. Thanks to the improvements achieved in the risk stratification of patients with PE, a better therapeutic approach is now recommended from diagnosis algorithm and indication to admission in ICU to indication of thrombolysis and general hemodynamic support in patients with shock. Given at current dosage, thrombolytic therapy is associated with a reduction in the combined end-point of mortality and hemodynamic decompensation in patients with intermediate-risk PE, but this is obtained without a decrease in overall mortality and with a significant increase in major extracranial and intracranial bleeding. In patients with high-intermediate-risk PE, thrombolytic therapy should be given in case of hemodynamic worsening. Vena cava filters are of little help when anticoagulant treatment is not contraindicated, even in patients with PE and features of clinical severity. Finally, direct oral anticoagulants have been shown to be as effective as and safer than the combination of low molecular weight heparin and vitamin K antagonist(s) in patients with venous thromboembolism and low- to intermediate-risk PE.

Beneficial effects of inhaled NO on apoptotic pneumocytes in pulmonary thromboembolism model

BACKGROUND

Lung ischemia-reperfusion injury (LIRI) may occur in the region of the affected lung after reperfusion therapy. Inhaled NO may be useful in treating acute and chronic pulmonary thromboembolism (PTE) due to the biological effect property of NO.

METHODS

A PTE canine model was established through selectively embolizing blood clots to an intended right lower lobar pulmonary artery. PaO2/FiO2, the mPAP and PVR were investigated at the time points of 2, 4, 6 hours after inhaled NO. Masson's trichrome stain, apoptotic pneumocytes and lung sample ultrastructure were also investigated among different groups.

RESULTS

The PaO2/FiO2 in the Inhaled NO group increased significantly when compared with the Reperfusion group at time points of 4 and 6 hours after reperfusion, mPAP decreased significantly at point of 2 hours and the PVR decreased significantly at point of 6 hours after reperfusion. The amounts of apoptotic type II pneumocytes in the lower lobar lung have negative correlation trend with the arterial blood PaO2/FiO2 in Reperfusion group and Inhaled NO group. Inhaled nitric oxide given at 20 ppm for 6 hours can significantly alleviate the LIRI in the model.

CONCLUSIONS

Dramatic physiological improvements are seen during the therapeutic use of inhaled NO in pulmonary thromboembolism canine model. Inhaled NO may be useful in treating LIRI in acute or chronic PTE by alleviating apoptotic type II pneumocytes. This potential application warrants further investigation.

Management dilemmas in acute pulmonary embolism

Background

Physicians treating acute pulmonary embolism (PE) are faced with difficult management decisions while specific guidance from recent guidelines may be absent.

Methods

Fourteen clinical dilemmas were identified by physicians and haematologists with specific interests in acute and chronic PE. Current evidence was reviewed and a practical approach suggested.

Results

Management dilemmas discussed include: sub-massive PE, PE following recent stroke or surgery, thrombolysis dosing and use in cardiac arrest, surgical or catheter-based therapy, failure to respond to initial thrombolysis, PE in pregnancy, right atrial thrombus, role of caval filter insertion, incidental and sub-segmental PE, differentiating acute from chronic PE, early discharge and novel oral anticoagulants.

Conclusion

The suggested approaches are based on a review of the available evidence and guidelines and on our clinical experience. Management in an individual patient requires clinical assessment of risks and benefits and also depends on local availability of therapeutic interventions.

Massive pulmonary embolism

Massive pulmonary embolism (PE) is a potentially lethal condition, with death usually caused by right ventricular (RV) failure and cardiogenic shock. Systemic thrombolysis (unless contraindicated) is recommended as the first-line treatment of massive PE to decrease the thromboembolic burden on the RV and increase pulmonary perfusion. Surgical pulmonary embolectomy or catheter-directed thrombectomy should be considered in patients with contraindications to fibrinolysis, or those with persistent hemodynamic compromise or RV dysfunction despite fibrinolytic therapy. Critical care management predominantly involves supporting the RV, by optimizing preload, RV contractility, and coronary perfusion pressure and minimizing afterload. Despite these interventions, mortality remains high.

Pilot study of a protocol to administer inhaled nitric oxide to treat severe acute submassive pulmonary embolism

OBJECTIVE

Inhaled nitric oxide has been reported to benefit patients with acute pulmonary embolism (PE). To date, all published literature has derived from case reports or case series conducted without a structured protocol. Here we report the results of a phase I trial with a predefined clinical protocol to treat patients with CT-demonstrated, submassive PE and moderate to severe dyspnoea.

METHODS

Patients were recruited from the emergency department of an academic teaching hospital. Informed consent and the entire treatment protocol was administered by a study physician. Nitric oxide was administered using a commercial device (Inovent) and a custom-made non-rebreathing face mask. The NO concentration was increased at 1 ppm/min (parts per million) until a maximum of 25 ppm and continued for 120 min and then weaned at 1 ppm/min. Dyspnoea was assessed with the Borg score, oxygenation by pulse oximetry, and haemodynamic status by shock index (HR/SBP).

RESULTS

Eight patients were enrolled. All patients tolerated the entire protocol without adverse events, and all had decreased numerical Borg score by >50%. The changes from baseline to 155 min were as follows: Borg score 7.5±2.5 to 2.3±1.9 (p=0.06, Signed rank test), SaO2% 93±5 to 97±3 and shock index 1.0±0.11 to 0.86±0.09. No patient experienced worsening during weaning.

CONCLUSIONS

Inhaled NO reduced dyspnoea without adverse events in eight patients with severe submassive PE. This protocol can serve as the basis for a phase II trial or for a compassionate use protocol.

Pulmonary Embolism in the Mechanically-Ventilated Critically Ill Patient: Is it Different?

Pulmonary embolism (PE) confers significant in-hospital morbidity and mortality, and critically ill patients remain at risk for venous thromboembolism despite thromboprophylaxis. Recognition of the clinical manifestations and immediate management of PE are of paramount importance. Despite diagnostic advances, PE is often undiagnosed and untreated in patients receiving mechanical ventilation, as these patients do not exhibit the common clinical features of the condition, making the diagnosis very challenging. Computed tomographic pulmonary angiography is probably the reference standard for the diagnosis of acute PE in the haemodynamically stable, ventilated patient. In the setting of circulatory collapse, bedside echocardiography may be used to risk stratify these patients, based on the presence or absence of right ventricular dysfunction, and guide further management. Treatment options include anticoagulation alone, anticoagulation plus thrombolysis, surgical or catheter embolectomy. Inotropes, vasopressors and pulmonary artery vasodilators may be considered after initial resuscitation of the right ventricle. Few studies have focused on estimating the prevalence of PE among mechanically-ventilated intensive care unit (ICU) patients and there is notable lack of data assessing predictive factors, prevention, diagnostic strategy and management of PE in the ICU setting.

A soluble guanylate cyclase stimulator, BAY 41-8543, preserves right ventricular function in experimental pulmonary embolism

Pulmonary embolism (PE) increases pulmonary vascular resistance, causing right ventricular (RV) dysfunction, and poor clinical outcome. Present studies test if the soluble guanylate cyclase stimulator BAY 41-8543 reduces pulmonary vascular resistance and protects RV function. Experimental PE was induced in anesthetized, male Sprague-Dawley rats by infusing 25 μm polystyrene microspheres (1.95 million/100 g body wt, right jugular vein) producing moderate PE. Pulmonary artery vascular resistance, estimated as RVPSP/CO, increased 3-fold after 5 h of PE. Treatment with BAY 41-8543 (50 μg/kg, I.V.; given at the time of PE induction) normalized this index by reducing RVPSP and markedly increasing CO, via preservation of heart rate and stroke volume. Ex vivo RV heart function showed minimal changes at 5 h of PE, but decreased significantly after 18 h of PE, including peak systolic pressure (PSP, Control 39 ± 1 mmHg vs. 19 ± 3 PE), +dP/dt (1192 ± 93 mmHg/s vs. 444 ± 64) and -dP/dt (-576 ± 60 mmHg/s vs. -278 ± 40). BAY 41-8543 significantly improved all three indices of RV heart function (PSP 35 ± 3.5, +dP/dt 1129 ± 100, -dP/dt -568 ± 87). Experimental PE produced increased PVR and RV dysfunction, which were ameliorated by treatment with BAY 41-8543. Thus, there is vasodilator reserve in this model of experimental PE that can be exploited to reduce the stress upon the heart and preserve RV contractile function.

Acute lung failure

Lung failure is the most common organ failure seen in the intensive care unit. The pathogenesis of acute respiratory failure (ARF) can be classified as (1) neuromuscular in origin, (2) secondary to acute and chronic obstructive airway diseases, (3) alveolar processes such as cardiogenic and noncardiogenic pulmonary edema and pneumonia, and (4) vascular diseases such as acute or chronic pulmonary embolism. This article reviews the more common causes of ARF from each group, including the pathological mechanisms and the principles of critical care management, focusing on the supportive, specific, and adjunctive therapies for each condition.

[Pulmonary thromboembolism]

Pulmonary thromboembolism is a frequent disease in emergency departments and often poses a diagnostic challenge that requires appropriate strategies. Clinical information, laboratory tests such as a D-dimer and imaging techniques such as computed tomography (CT) angiography, ventilation-perfusion scintigraphy or echocardiography help to establish clinical probability and the severity of the disease. With all this information, risk scores can be constructed, such as the Pulmonary Embolism Severity Index (PESI) score, which has high sensitivity in predicting mortality. Treatment should be started immediately with heparin, usually low molecular weight heparin. If the patient is at high risk, thrombolytic therapy is indicated, although possible contraindications should be thoroughly assessed. Supportive treatment may be considered in a few patients.

Bench-to-bedside review: Inhaled nitric oxide therapy in adults

Nitric oxide (NO) is an endogenous mediator of vascular tone and host defence. Inhaled nitric oxide (iNO) results in preferential pulmonary vasodilatation and lowers pulmonary vascular resistance. The route of administration delivers NO selectively to ventilated lung units so that its effect augments that of hypoxic pulmonary vasoconstriction and improves oxygenation. This 'Bench-to-bedside' review focuses on the mechanisms of action of iNO and its clinical applications, with emphasis on acute lung injury and the acute respiratory distress syndrome. Developments in our understanding of the cellular and molecular actions of NO may help to explain the hitherto disappointing results of randomised controlled trials of iNO.

Guidelines on the diagnosis and management of acute pulmonary embolism: the Task Force for the Diagnosis and Management of Acute Pulmonary Embolism of the European Society of Cardiology (ESC)

Non-thrombotic PE does not represent a distinct clinical syndrome. It may be due to a variety of embolic materials and result in a wide spectrum of clinical presentations, making the diagnosis difficult. With the exception of severe air and fat embolism, the haemodynamic consequences of non-thrombotic emboli are usually mild. Treatment is mostly supportive but may differ according to the type of embolic material and clinical severity.

Pulmonary vasodilators--treating the right ventricle

Pulmonary hypertension remains a significant complication of several systemic and cardiothoracic diseases. It is important to emphasize that the hemodynamic relevance relates to the effect of pulmonary hypertension on right ventricular function and right-left ventricular interaction. The goal of pulmonary vasodilation should focus on optimizing right ventricular function and improving systemic perfusion. The properties of an optimum vasodilator include selective pulmonary vasodilation (avoiding systemic vasodilation), rapid onset of action, short half-life, and ease of administration. Inhaled nitric oxide or nebulization of traditional systemically administered agents offers the greatest clinical promise. An additional merit of selective pulmonary vasodilation consists of augmenting oxygenation by improving ventilation perfusion matching.

[Pulmonary hypertension and right ventricular failure in critical care medicine]

The management of pulmonary hypertension and right ventricular failure in hemodynamically unstable patients is one of the most challenging situations in critical care medicine. Inadequate therapy, e.g. aggressive fluid resuscitation or invasive ventilation, may even harm patients with pulmonary hypertension. Identifying the underlying etiology therefore remains the primary focus for initiating successful management of patients with decompensated pulmonary hypertension and right ventricular failure. Pulmonary embolism requires immediate restoration of pulmonary vascular patency. The body of evidence from studies is scarce and favors dobutamine, NO inhalation, and intravenous prostacyclin. However, the use of other vasoactive substances, inotropes, and supportive measures has been successful in individual patients; it should be guided by the expected effects on the pulmonary vasculature or right ventricle, and should be adapted to the patient's concomitant diseases.

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.

Pulmonary Embolism in the Critically Ill

Pulmonary embolism in the critically ill requires considerations beyond anticoagulant therapy. Measurements of chamber size by echocardiography and CT and of circulating biomarkers identify higher-risk patients with moderate accuracy and may aid determination of patient acuity. Preserving right ventricular function requires judicious use of volume administration, vasopressor, and perhaps vasodilator therapies. Obstructing thrombus can be treated with fibrinolytic drugs, percutaneous instrumentation, or surgically, but these treatments may not be equally effective or safe. Anticoagulant therapy in critically ill patients is likely best administered IV. Bleeding complications should be assiduously sought but do not necessitate anticoagulant discontinuation in every case. The antidotes protamine, desmopressin acetate, factor VIII inhibitory bypass activity, and recombinant factor VIIa may each have a place in controlling anticoagulant-related bleeding. The grave prognosis of heparin-induced thrombocytopenia warrants close surveillance, with rapid switching to lepirudin, argatroban, or fondaparinux necessary if it is suspected. Retrievable vena cava filters can be lifesaving, and at least one type may be safely removed after residence of nearly 1 year.