Neurogenic and humoral vasoconstriction in acute pulmonary thromboembolism

Management Strategies for Acute Pulmonary Embolism in the ICU

TOPIC IMPORTANCE

Acute pulmonary embolism (PE) is a common disease encountered by pulmonologists, cardiologists, and critical care physicians throughout the world. For patients with high-risk acute PE (defined by systemic hypotension) and intermediate high-risk acute PE (defined by the absence of systemic hypotension, but the presence of numerous other concerning clinical and imaging features), intensive care often is necessary. Initial management strategies should focus on optimization of right ventricle (RV) function while decisions about advanced interventions are being considered.

REVIEW FINDINGS

We reviewed the existing literature of various vasoactive agents, IV fluids and diuretics, and pulmonary vasodilators in both animal models and human trials of acute PE. We also reviewed the potential complications of endotracheal intubation and positive pressure ventilation in acute PE. Finally, we reviewed the data of venoarterial extracorporeal membrane oxygenation (ECMO) use in acute PE. The above interventions are discussed in the context of the underlying pathophysiologic features of acute RV failure in acute PE with corresponding illustrations.

SUMMARY

Norepinephrine is a reasonable first choice for hemodynamic support with vasopressin as an adjunct. IV loop diuretics may be useful if evidence of RV dysfunction or volume overload is present. Fluids should be given only if concern exists for hypovolemia and absence of RV dilatation. Supplemental oxygen administration should be considered even without hypoxemia. Positive pressure ventilation should be avoided if possible. venoarterial ECMO cannulation should be implemented early if ongoing deterioration occurs despite these interventions.

Heart Rate Variability Impairment Is Associated with Right Ventricular Overload and Early Mortality Risk in Patients with Acute Pulmonary Embolism

The association between heart rate variability (HRV) and mortality risk of acute pulmonary embolism (APE), as well as its association with right ventricular (RV) overload is not well established. We performed an observational study on consecutive patients with confirmed APE. In the first 48 h after admission, 24 h Holter monitoring with assessment of time-domain HRV, echocardiography and NT-proBNP (N-terminal pro-B-type natriuretic peptide) measurement were performed in all participants. We pre-examined 166 patients: 32 (20%) with low risk of early mortality, 65 (40%) with intermediate-low, 65 (40%) with intermediate-high, and 4 (0.02%) in the high risk category. The last group was excluded from further analysis due to sample size, and finally, 162 patients aged 56.3 ± 18.5 years were examined. We observed significant correlations between HRV parameters and echocardiographic signs of RV overload. SDNN (standard deviation of intervals of all normal beats) correlated with echocardiography-derived RVSP (right ventricular systolic pressure; r = -0.31, p = 0.001), TAPSE (tricuspid annulus plane systolic excursion; r = 0.21, p = 0.033), IVC (inferior vena cava diameter; r = -0.27, p = 0.002) and also with NT-proBNP concentration (r = -0.30, p = 0.004). HRV indices were also associated with APE risk stratification, especially in the low-risk category (r = 0.30, p = 0.004 for SDNN). Univariate and multivariate analyses confirmed that SDNN values were associated with signs of RV overload. In conclusion, we observed a significant association between time-domain HRV parameters and echocardiographic and biochemical signs of RV overload. Impaired HRV parameters were also associated with worse a clinical risk status of APE.

Progress in interventional radiology treatment of pulmonary embolism: A brief review

Pulmonary embolism represents a common life-threatening condition. Prompt identification and treatment of this pathological condition are mandatory. In cases of massive pulmonary embolism and hemodynamic instability or right heart failure, interventional radiology treatment for pulmonary embolism is emerging as an alternative to medical treatment (systemic thrombolysis) and surgical treatment. Interventional radiology techniques include percutaneous endovascular catheter directed therapies as selective thrombolysis and thrombus aspiration, which can prove useful in cases of failure or infeasibility of medical and surgical approaches.

The Association Between Mean Corpuscular Hemoglobin Concentration and Prognosis in Patients with Acute Pulmonary Embolism: A Retrospective Cohort Study

Introduction

Acute pulmonary embolism (APE) is a typical cardiovascular emergency worldwide. Mean hemoglobin concentration (MCHC) is a standard indicator of anemia. Studies on the association between MCHC and APE are scarce. We aimed to investigate the relationship between MCHC and APE.

Methods

Clinical data were extracted from the Medical Information Bank for Intensive Care (MIMIC)-III. Adult (≥18 years) patients with APE admitted for the first time were included in this study. An analysis was conducted to evaluate the association between MCHC and the prognosis of patients by the Cox regression analysis, generalized additives models and Kaplan–Meier survival curves. The primary outcome was 30-day mortality, and the secondary outcomes were 1-year and 3-year mortality.

Results

A total of 813 patients who met the selection criteria were enrolled, of whom 130 (16.0%) died within 30 days of admission. Univariate Cox regression indicated that MCHC was significantly associated with mortality (30-day: HR = 0.74, 95% CI = 0.66–0.82, P < 0.001; 1-year: HR = 0.80, 95% CI = 0.74–0.86, P < 0.001; 3-year: HR = 0.82, 95% CI = 0.77–0.88, P < 0.001). MCHC remains stable after adjusting multiple models. Kaplan-Meier survival curves showed that patients with lower MCHC had a poorer 30-day prognosis.

Conclusions

Lower MCHC is an independent risk factor for increased mortality in patients with APE. As an inexpensive biomarker, MCHC should receive more attention.

Efficacy of Computed Tomography Pulmonary Angiography as Non-invasive Imaging Biomarker for Risk Stratification of Acute Pulmonary Embolism

Objectives:

Massive and sub-massive pulmonary embolisms (PEs) are associated with high mortality and morbidity. The mainstay of treatment for PE is anticoagulation. However, high- and intermediate-risk patients may benefit from interventional thrombolytic therapy. Computed tomography pulmonary angiography (CTPA) is widely available, fast, and non-invasive technique, and it can identify pulmonary thrombus down to at least a segmental level. In this study, we attempt to evaluate the efficacy of CTPA as a non-invasive imaging biomarker for risk stratification of acute PE (APE) patients.

Material and Methods:

This is a prospective study conducted on 150 patients who proved to have APE by CTPA. The simplified PE severity index score was obtained. The pulmonary artery obstruction index (PAOI) using and right to left ventricular (RV/LV) diameter ratios were calculated.

Results:

The patients were divided into (1) high risk (shocked) and (2) non-high risk groups. There was a significant difference between the 1^st and 2^nd groups regarding PAOI. Hemodynamically stable patients were further subclassified according to the right ventricular dysfunction (RVD) into Group Ia (intermediate risk) and Group Ib (low risk). There was a significant difference between subgroups regarding PAOI (P < 0.0001, r = 0.385). Receiver operating characteristic curve analysis revealed PAOI >47% associated with RV/LV ratio >1.

Conclusion:

Our results support the use of CTPA as a surrogate imaging biomarker for both diagnosis and risk stratification of APE patients. CTPA allows assessment of clot burden through PAOI calculation and identification of intermediate-risk PE through the assessment of RVD.

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.

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.

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.

Endovascular treatment of pulmonary embolism: Selective review of available techniques

Acute pulmonary embolism (PE) is the third most common cause of death in hospitalized patients. The development of sophisticated diagnostic and therapeutic modalities for PE, including endovascular therapy, affords a certain level of complexity to the treatment of patients with this important clinical entity. Furthermore, the lack of level I evidence for the safety and effectiveness of catheter directed therapy brings controversy to a promising treatment approach. In this review paper, we discuss the pathophysiology and clinical presentation of PE, review the medical and surgical treatment of the condition, and describe in detail the tools that are available for the endovascular therapy of PE, including mechanical thrombectomy, suction thrombectomy, and fibrinolytic therapy. We also review the literature available to date on these methods, and describe the function of the Pulmonary Embolism Response Team.

Serum Apelin 13 Levels in Patients With Pulmonary Embolism

Introduction and Aim:

Expression and peptide immunoreactivity of apelin messenger RNA have been described in a variety of tissues, including gastrointestinal tract, adipose tissue, brain, kidney, liver, cardiovascular system, and lungs. This study aimed to investigate the possible involvement of the endogenous apelin in the pathophysiological events that occur in patients with pulmonary embolism (PE).

Materials and Methods:

In total, 53 patients with PE and 35 healthy volunteers were included the study. This cross-sectional study was conducted at a tertiary care university hospital and among patients diagnosed as having PE. The control group consisted of healthy volunteers who applied to hospital for a routine checkup examination. Serum apelin 13 levels were measured in both the groups and their results were compared.

Results:

The median ages were 57 and 53 years, and female–male ratios were 30/23 and 20/15, in the PE and control groups, respectively. The mean serum apelin 13 levels were found to be significantly higher in the PE group (76.94 ± 10.70 ng/mL) than in the control group (50.01 ± 7.13 ng/mL; P < .001).

Conclusion:

This study demonstrated that apelin 13 levels are elevated in patients with PE. These results suggest that apelin may be a novel biomarker and a potential therapeutic target in patients with acute PE in the future.

ROS Scavenger Decreases Basal Perfusion Pressure, Vasoconstriction and NO Synthase Activity in Pulmonary Circulation During Pulmonary Microembolism

Two mechanisms contribute in the development of pulmonary hypertension in pulmonary embolism (PE) – obstruction of pulmonary blood vessels and vasoconstriction. We hypothesize that hypoxia, increased shear stress and/or activation of gathered leukocytes in the PE may cause a release of reactive oxygen species (ROS). Therefore our aim was to determine the influence of the ROS scavenger Tempol on pulmonary hypertension and to describe NO synthase activity and production of NO oxidative products (NOx) after PE. In general anesthesia sephadex microspheres suspended in PSS were applied in right jugular vein as the pulmonary microembolism. Than we measured in isolated salt solution-perfused lungs the changes in perfusion pressure, activity of NO synthase and NOx plasma concentration in 7 groups of rats: C: control group (n=5), CN: C + sodium nitroprusside (SN) (n=5), EN: PE + SN (n=5), ETN: Tempol + PE + SN (n=5), CL: C + L-NAME (n=5), EL: PE + L-NAME (n=5), ETL: Tempol + PE + L-NAME (n=5). Tempol was applied intraperitoneally before PE. Animals that received Tempol (groups TN, TL) had significantly lower basal perfusion pressure than those which did not receive Tempol (EN, EL). Overall we measured a higher decrease of perfusion pressure than in the control group (C) after application of SN. Administration of L NAME after PE (EL) increased the pressure more than in the control group (NL). NOx concentration was higher after PE. We found that preventive administration of Tempol decreases the increase in perfusion pressure after PE. PE increased NO release and concentration of NOx.

Adrenomedullin induces pulmonary vasodilation but does not attenuate pulmonary hypertension in a sheep model of acute pulmonary embolism

AIMS

The pulmonary vasodilation induced by adrenomedullin may be beneficial in the acute pulmonary embolism (APE) setting. This study examined effects of adrenomedullin in sheep with microsphere-induced APE.

MAIN METHODS

Twenty four anesthetized, mechanically ventilated sheep were randomly assigned into 3 groups (n=8 per group): animals not subjected to any intervention (Sham), animals with APE induced by microspheres (500 mg, intravenously) treated 30 min later by intravenous physiological saline (Emb group) or intravenous adrenomedullin (50 ng/kg/min) during 30 min (Emb+Adm group). Plasma concentrations of cyclic adenosine (cAMP) and guanosine monophosphate (cGMP) were determined by enzyme immunoassay.

KEY FINDINGS

Variables did not change over time in sham animals. In both embolized groups, microsphere injection significantly (P<0.05) increased pulmonary vascular resistance index (PVRI) and mean pulmonary artery pressure (MPAP) from baseline by 181% and 111-142%, respectively (% change in mean values). Adrenomedullin significantly decreased PVRI (18%-25%) and significantly increased cardiac index (22%-25%) from values recorded 30 min after APE (E30), without modifying MPAP. Adrenomedullin decreased mean arterial pressure (18%-24%) and systemic vascular resistance index (32%-40%). Embolization significantly increased arterial-to-end tidal CO2 gradient, alveolar-to-arterial O2 gradient, and pulmonary shunt fraction from baseline, but these variables were unaffected by adrenomedullin. While adrenomedullin significantly increased plasma cAMP, cGMP levels were unaltered.

SIGNIFICANCE

Adrenomedullin induces systemic and pulmonary vasodilation, possibly via a cAMP mediated mechanism, without modifying the gas exchange impairment associated with APE. The pulmonary anti-hypertensive effect of adrenomedullin may be offset by increases in cardiac index.

Anticoagulant treatment for acute pulmonary embolism: a pathophysiology-based clinical approach

The management of patients with acute pulmonary embolism is made challenging by its wide spectrum of clinical presentation and outcome, which is mainly related to patient haemodynamic status and right ventricular overload. Mechanical embolic obstruction and neurohumorally mediated pulmonary vasoconstriction are responsible for right ventricular overload. The pathophysiology of acute pulmonary embolism is the basis for risk stratification of patients as being at high, intermediate and low risk of adverse outcomes. This risk stratification has been advocated to tailor clinical management according to the severity of pulmonary embolism. Anticoagulation is the mainstay of the treatment of acute pulmonary embolism. New direct oral anticoagulants, which are easier to use than conventional anticoagulants, have been compared with conventional anticoagulation in five randomised clinical trials including >11 000 patients with pulmonary embolism. Patients at high risk of pulmonary embolism (those with haemodynamic compromise) were excluded from these studies. Direct oral anticoagulants have been shown to be as effective and at least as safe as conventional anticoagulation in patients with pulmonary embolism without haemodynamic compromise, who are the majority of patients with this disease. Whether these agents are appropriate for the acute-phase treatment of patients at intermediate-high risk pulmonary embolism (those with both right ventricle dysfunction and injury) regardless of any risk stratification remains undefined.

The usefulness of gated blood pool scintigraphy for right ventricular function evaluation in pulmonary embolism patients

OBJECTIVE

According to the international registry ICOPER, right ventricular (RV) dysfunction is the most significant predictor of mortality in patients with pulmonary embolism (PE).

AIM

To identify the most informative indicators of gated blood pool single photon emission computer tomography (GBP-SPECT) for evaluation of RV function in patients with PE.

METHODS

A total of 52 patients were included in the study. The main group (n = 37) comprised patients with PE, and the comparison group (n = 15) patients suffering from coronary heart disease (NYHA class I-II). All patients received GBP-SPECT, and assessment of plasma levels of endothelin-1, stable nitric oxide (NO) metabolites, and 6-keto-PG F1α.

RESULTS

In patients with PE, RV end-systolic volume, stroke volume, ejection fraction, peak ejection rate, peak filling rate, and mean filling rate were significantly lower in comparison with patients without PE. In patients with PE, the levels of endothelin-1, 6-keto-PG F1α, and stable NO metabolites were increased in comparison with patients without PE.

CONCLUSIONS

GBP-SPECT facilitates verification of RV dysfunction in patients without massive PE or severe pulmonary hypertension. Dissociation between the volume of PE and degree of RV dysfunction may be caused by an unbalance between humoral vasoactive factors.

Matrix metalloproteinase inhibition attenuates right ventricular dysfunction and improves responses to dobutamine during acute pulmonary thromboembolism

Activated matrix metalloproteinases (MMPs) cause cardiomyocyte injury during acute pulmonary thromboembolism (APT). However, the functional consequences of this alteration are not known. We examined whether doxycycline (a MMP inhibitor) improves right ventricle function and the cardiac responses to dobutamine during APT. APT was induced with autologous blood clots (350 mg/kg) in anaesthetized male lambs pre-treated with doxycycline (Doxy, 10 mg/kg/day, intravenously) or saline. Non-embolized control lambs received doxycycline pre-treatment or saline. The responses to intravenous dobutamine (Dob, 1, 5, 10 μg/kg/min.) or saline infusions at 30 and 120 min. after APT induction were evaluated by echocardiography. APT increased mean pulmonary artery pressure and pulmonary vascular resistance index by ∼185%. Doxycycline partially prevented APT-induced pulmonary hypertension (P < 0.05). RV diameter increased in the APT group (from 10.7 ± 0.8 to 18.3 ± 1.6 mm, P < 0.05), but not in the Doxy+APT group (from 13.3 ± 0.9 to 14.4 ± 1.0 mm, P > 0.05). RV dysfunction on stress echocardiography was observed in embolized lambs (APT+Dob group) but not in embolized animals pre-treated with doxycycline (Doxy+APT+Dob). APT increased MMP-9 activity, oxidative stress and gelatinolytic activity in the RV. Although doxycycline had no effects on RV MMP-9 activity, it prevented the increases in RV oxidative stress and gelatinolytic activity (P < 0.05). APT increased serum cardiac troponin I concentrations (P < 0.05), doxycycline partially prevented this alteration (P < 0.05). We found evidence to support that doxycycline prevents RV dysfunction and improves the cardiac responses to dobutamine during APT.

Autonomic neural control of the airways

The airways and lungs are innervated by both sympathetic and parasympathetic nerves. Cholinergic parasympathetic innervation is well conserved in the airways while the distribution of noncholinergic parasympathetic and adrenergic sympathetic nerves varies considerably amongst species. Autonomic nerve function is regulated primarily through reflexes initiated upon bronchopulmonary vagal afferent nerves. Central regulation of autonomic tone is poorly described but some key elements have been defined.

Blood flow redistribution and ventilation-perfusion mismatch during embolic pulmonary arterial occlusion

Acute pulmonary embolism causes redistribution of blood in the lung, which impairs ventilation/perfusion matching and gas exchange and can elevate pulmonary arterial pressure (PAP) by increasing pulmonary vascular resistance (PVR). An anatomically-based multi-scale model of the human pulmonary circulation was used to simulate pre- and post-occlusion flow, to study blood flow redistribution in the presence of an embolus, and to evaluate whether reduction in perfused vascular bed is sufficient to increase PAP to hypertensive levels, or whether other vasoconstrictive mechanisms are necessary. A model of oxygen transfer from air to blood was included to assess the impact of vascular occlusion on oxygen exchange. Emboli of 5, 7, and 10 mm radius were introduced to occlude increasing proportions of the vasculature. Blood flow redistribution was calculated after arterial occlusion, giving predictions of PAP, PVR, flow redistribution, and micro-circulatory flow dynamics. Because of the large flow reserve capacity (via both capillary recruitment and distension), approximately 55% of the vasculature was occluded before PAP reached clinically significant levels indicative of hypertension. In contrast, model predictions showed that even relatively low levels of occlusion could cause localized oxygen deficit. Flow preferentially redistributed to gravitationally non-dependent regions regardless of occlusion location, due to the greater potential for capillary recruitment in this region. Red blood cell transit times decreased below the minimum time for oxygen saturation (<0.25 s) and capillary pressures became high enough to initiate cell damage (which may result in edema) only after ~80% of the lung was occluded.

Up-regulation of arginase II contributes to pulmonary vascular endothelial cell dysfunction during experimental pulmonary embolism

Pulmonary embolism (PE) causes pulmonary hypertension by mechanical obstruction and constriction of non-obstructed vasculature. We tested if experimental PE impairs pulmonary vascular endothelium-dependent dilation via activation of arginase II. Experimental PE was induced in male Sprague-Dawley rats by infusing 25 μm microspheres in the right jugular vein, producing moderate pulmonary hypertension. Shams received vehicle injection. Pulmonary arterial rings were isolated after 18 h and isometric tensions were determined. Dilations were induced with acetylcholine, calcium ionophore A23187 or nitroglycerin (NTG) in pre-contracted rings (phenylephrine). Protein expression was assessed by Western blot and immunohistochemistry. Arginase activity was inhibited by intravenous infusion of N(w)-hydroxy-nor-l-arginine (nor-NOHA). l-Arginine supplementation was also given. Endothelium-dependent dilation responses were significantly reduced in PE vs. vehicle-treated animals (ACh: 50 ± 9% vs. 93 ± 3%; A23187: 19 ± 7% vs. 85 ± 7%, p < 0.05), while endothelium-independent dilations (NTG) were unchanged. Endothelial nitric oxide synthase (eNOS) protein content was unchanged by PE. Expression of arginase II increased 4.5-fold and immunohistochemistry revealed increased arginase II staining. Nor-NOHA treatment and l-arginine supplementation significantly improved pulmonary artery ring endothelium-dependent dilation in PE (ACh: 58 ± 6% PE, 88 ± 6% PE + nor-NOHA, 84 ± 4% PE + l-arginine). Experimental PE impairs endothelium-dependent pulmonary artery dilation, while endothelium-independent dilation remains unchanged. The data support the conclusion that up-regulation of arginase II protein expression contributes to pulmonary artery endothelial dysfunction in this model of experimental PE.

Hemodynamic effect of apelin in a canine model of acute pulmonary thromboembolism

The peptide apelin is expressed in the pulmonary vasculature and is involved in the pathogenesis of many cardiovascular diseases. It has a biphasic role in the regulation of vasomotor tone related to the vascular endothelium. In this study, we induced acute pulmonary embolism (APE) in dogs with autologous blood clots to assess the effect of apelin on pulmonary and systemic circulation in the acute phase of APE. The expression of apelin mRNA was found to be upregulated in the lung tissue in the early several hours after APE induction and decreased at 24 h. The expression of apelin protein in the pulmonary arteries did not change within 24 h after APE, but significantly increased in the bronchial epithelial cells as early as 1h and decreased at 24 h. In normal anesthetized dogs, intravenous bolus administration of apelin significantly reduced the mean arterial pressure (MAP), but did not significantly affect the mean pulmonary arterial pressure (MPAP). In the dogs with APE, apelin decreased MPAP, whereas its impact on MAP was not significantly different from that in the control group. Taken together, the level of endogenous apelin did not change significantly in the pulmonary arterial wall, whereas its expression in the bronchial epithelium was upregulated in the early stage of APE. The effect of exogenous apelin on vasomotor tone was complicated: it resulted in differential changes in the pulmonary and systemic arterial pressures under different physiological and pathological conditions.

Sildenafil in Acute Pulmonary Embolism: Case Report and Review of Literature

We discuss the use of sildenafil in a patient who sustained a massive pulmonary embolism (PE). She remained haemodynamically unstable after thrombolysis, and needed large doses of inotropic support. She was treated with oral sildenafil at a dose of 75 mg three times a day which enabled weaning from inotropic support and clinical improvement.

Use of initial distribution volume of glucose to determine fluid volume loading in pulmonary thromboembolism and right ventricular myocardial infarction

We report a case of acute right ventricular myocardial infarction (right AMI) following pulmonary thromboembolism (PTE). Following percutaneous coronary intervention, the patient was treated in our intensive care unit (ICU) with intraortic balloon pumping, anticoagulants, and plasma expansion. Fluid overload may cause a further leftward shift of the interventricular septum in patients with PTE, resulting in decreased cardiac output (CO). The initial distribution volume of glucose (IDVG) has been reported to indicate central extracellular fluid volume. As both PTE and right AMI affect cardiac filling pressures, such as central venous pressure (CVP) and pulmonary artery wedge pressure (PAWP), we measured IDVG in order to evaluate the patient's cardiac preload, comparing it with the cardiac filling pressures. Fluid volume loading over 12 h yielded an obvious increase in IDVG. However, low arterial blood pressure and CO, associated with high CVP, remained unchanged and were accompanied by deteriorating pulmonary oxygenation. Accordingly, volume loading was discontinued and the rates of infusion of catecholamines were increased instead. At 12 h thereafter, IDVG became normal, and both CO and blood pressure became improved. However, the cardiac filling pressures remained increased. Although the patient died on the subsequent day, this case report could support the usefulness of IDVG as a fluid volume marker in critically ill patients, especially those with right AMI.

Dose-dependent beneficial hemodynamic effects of BAY 41-2272 in a canine model of acute pulmonary thromboembolism

The current therapy of acute pulmonary embolism is focused on removing the mechanical obstruction of the pulmonary vessels. However, accumulating evidence suggests that pulmonary vasoconstriction drives many of the hemodynamic changes found in this condition. We examined the effects of stimulation of soluble guanylate cyclase with BAY 41-2272 (5-Cyclopropyl-2-[1-(2-fluoro-benzyl)-1H-pyrazolo[3,4-b]pyridin-3-yl]-pyrim idin-4-ylamine) in an anesthetized dog model of acute pulmonary embolism. Hemodynamic and arterial blood gas evaluations were performed in non-embolized dogs treated with vehicle (N=5), and in embolized dogs (intravenous injections of microspheres) that received BAY 41-2272 intravenously in doses of 0.03, 0.1, 0.3, and 1 mg/kg/h or vehicle (1 ml/kg/h of 1.13% ethanol in saline, volume/volume). Plasma cGMP and thiobarbituric acid reactive substances concentrations were determined using a commercial enzyme immunoassay and a fluorometric method, respectively. The infusion of BAY 41-2272 resulted in a decrease in pulmonary artery pressure by approximately 29%, and in pulmonary vascular resistance by approximately 46% of the respective increases induced by lung embolization (both P<0.05). While the higher doses of BAY 41-2272 produced no additional effects on the pulmonary circulation, they caused significant arterial hypotension and reduction in systemic vascular resistance (both P<0.05). Although BAY 41-2272 increased cGMP concentrations (P<0.05), it did not affect the hypoxemia and the increased oxidative stress caused by lung embolization. These results suggest that stimulation of soluble guanylate cyclase with low (but not high) doses of BAY 41-2272 produces selective pulmonary vasodilation during acute pulmonary embolism. The dose-dependent systemic effects produced by BAY 41-2272, however, may limit its usefulness in larger doses.

Time course of platelet aggregation during thrombolytic treatment of massive pulmonary embolism

We studied changes in platelet aggregation and fibrinogen levels during thrombolysis with massive or submassive pulmonary embolism. Fifteen patients were randomized into ultrahigh-dose streptokinase (UH-SK n = 8) or alteplase (tPA n = 7) groups. Arterial blood samples were taken before and after thrombolysis every 4 h between 4 and 36 h, and once daily between 2 and 30 days. In-vitro platelet aggregation was examined as spontaneous (0.9% NaCl) and induced aggregation with adrenaline 10 micromol/l, collagen 2 microg/ml and ADP 10 micromol/l. D-dimer and fibrinogen were measured every 8 h on first day, and later as above. In the UH-SK group, adrenaline-induced platelet aggregation decreased at 4 and 8 h compared with baseline (P < 0.03). Adrenaline-induced platelet aggregation was significantly lower in the UH-SK group than in the tPA group at 36 h and on day 3 (P < 0.03). Platelet aggregation induced by ADP was lower at 4 h than at baseline in the UH-SK group (P < 0.05). Collagen-induced platelet aggregation was lower at 4 and 8 h than at baseline (P < 0.05) in the UH-SK group. Compared with baseline, fibrinogen levels decreased in both groups after thrombolysis. D-dimer levels were elevated in both groups at 8 h (tPA group, P < 0.0004; UH-SK group, P < 0.05). Spontaneous platelet aggregation, major bleeding or re-embolism was not documented. Platelet aggregation decreased after thrombolysis with UH-SK for 12 h, in comparison tPA caused an insignificant decrease. Fibrinogen level decreased with UH-SK treatment for 5 days but in case of tPA we could not measure significant changes. According to our findings, tPA is a more suitable drug but streptokinase is also effective because of its cost-benefit ratio.

Natural History of Right Ventricular Dysfunction After Acute Pulmonary Embolism

BACKGROUND

Acute pulmonary embolism (PE) associated with right ventricular (RV) dysfunction has an adverse prognosis. We investigated individual parameters of RV dysfunction after acute PE, assessing their correlation with the PE extent and recovery during 6 months.

METHODS

In all, 35 patients (age 63 +/- 18 years) with acute PE were prospectively investigated for 6 months with serial echocardiography, incorporating longitudinal myocardial-velocity and strain imaging. The extent of PE was quantified on day 1 by ventilation/perfusion pulmonary scintigraphy with PE defined as large when there was greater than 30% lung involvement.

RESULTS

PE extent correlated strongly with a number of parameters of RV function, and the strongest univariate correlates were tricuspid annular motion (TAM) (r = -0.65, P < .0001) and the ratio of RV apical to RV basal systolic velocity (r = 0.66, P < .0001). Multivariate analysis identified TAM (P < .0001) and RV basal late-diastolic velocity (P = .01) as independently predicting PE extent, with a combined correlation (R2 = 0.52, P < .0001). A TAM of less than 2.0 cm had sensitivity, specificity, and positive- and negative-predictive values of 75%, 84%, 75%, and 79%, respectively, in predicting large PE. Prospective follow-up identified that RV:left ventricular end-diastolic area ratio returned to normal within 6 weeks, whereas TAM and ratio of RV apical to RV basal systolic velocity normalized after 3 to 6 months.

CONCLUSION

TAM and ratio of RV apical to RV basal systolic velocity are useful indicators of the extent of PE, and provide unique insights into the recovery of RV function after acute PE.

Pulmonary embolism after brain hemorrhage in a hypertensive patient: the therapeutic dilemma

Massive pulmonary embolism is a life-threatening condition to be treated with anticoagulants or even thrombolytic agents in selected cases. However, these drugs are controindicated after a recent hemorrhagic episode. We report the case of a 46-year-old patient with uncontrolled systemic hypertension who was affected by severe spontaneous cerebral hemorrhage and left hemiparesis. After some days of rehabilitation care he developed sudden dyspnea, tachycardia and hypotension secondary to bilateral pulmonary embolism. Owing to controindication to the use of thrombolytic agents, anticoagulant therapy with high-dose intravenous unfractionated heparin followed by oral warfarin was begun, with a successful and uncomplicated outcome. The therapeutic approach to similar not uncommon cases is debated and some hypotheses are made about the aetiology of pulmonary embolism in these patients.

Increase in exhaled nitric oxide and protective role of the nitric oxide system in experimental pulmonary embolism

BACKGROUND AND PURPOSE

Pulmonary embolism (PE) represents a real diagnostic challenge. PE is associated with pulmonary hypertension due to pulmonary vascular obstruction and vasoconstriction. We recently reported that pulmonary gas embolism transiently increases exhaled nitric oxide (FENO), but it is not known whether solid emboli may alter FENO, and whether an intact endogenous NO synthesis has a beneficial effect in experimental solid pulmonary embolism.

EXPERIMENTAL APPROACH

We used anaesthetised and ventilated rabbits in these experiments. To mimic PE, a single intravenous infusion of homogenized autologous skeletal muscle tissue (MPE) was given to rabbits with intact NO production (MPE of 60, 15, or 7.5 mg kg(-1); group 1) and to another group (group 2) with inhibited NO synthesis (L-NAME 30 mg kg(-1); MPE of 7.5, 15 or 30 mg kg(-1)).

KEY RESULTS

In group 1, after MPE, FENO increased rapidly and dose-dependently and FENO was still significantly elevated after 60 min with the two highest emboli doses. All these animals survived more than 60 min after embolization. In group 2, MPE of 7.5, 15 and 30 mg kg(-1), in combination with NO synthesis inhibition, resulted in 67%, 50% and 25% survival at 60 min respectively, representing a statistically significant decrease in survival. Cardiovascular and blood-gas changes after MPE were intensified by pre-treatment with NO synthesis inhibitor.

CONCLUSIONS AND IMPLICATIONS

We conclude that solid PE causes a sustained, dose-dependent increase in FENO, giving FENO a diagnostic potential in PE. Furthermore, intact NO production appears critical for tolerance to acute PE.

Prognostic Value of Arterial/Alveolar Oxygen Tension Ratio (a/APO2) in Acute Pulmonary Embolism

BACKGROUND

Because the arterial/alveolar oxygen tension ratio (a/APO2) is relatively constant throughout the entire range of fractional inspired oxygen concentration (FiO2), its use in determining the prognosis of acute pulmonary embolism (APE) was investigated.

METHODS AND RESULTS

This study retrospectively assessed 202 consecutive patients with APE confirmed by computed tomography or high probability lung scintigraphy. All patients underwent initial arterial blood gas analysis during the first 24 h of admission. Receiver-operating characteristic analyses were performed to determine the a/APO2 cut-off value for predicting 30-day death or 30-day composite events. Cut-off values for a/APO2 were used to determine stability in all patients and 2 subgroups (0.49 for all patients; 0.49 for FiO2 =0.21; 0.46 for FiO2 >0.21). Using the cut-off value of a/APO2 <0.49 for predicting 30-day death, the negative predictive value (NPV) was 90%, and the positive predictive value (PPV) was 30.3%. For the 30-day composite end point, the NPV was 81.3%, and the PPV was 40.9%. Excluding massive APE, the a/APO2 also had high NPV and moderate PPV in predicting short-term prognosis. This study additionally demonstrated a linear relationship between platelet count and a/APO2.

CONCLUSIONS

The cut-off value of a/APO2 <0.49 exhibits stability at variable FiO2 values and is a useful prognostic predictor in APE.

Reperfusion pulmonary edema after the removal of hepatocellular carcinoma embolus

To report a non-fatal case of reperfusion pulmonary edema (RPE) after the removal of a hepatocellular carcinoma embolus, which had caused an acute obstruction of the tricuspid valve and pulmonary vasculature during a hepatic lobectomy. Pulmonary embolism caused by hepatocellular carcinoma embolus is extremely rare, and, in the present case, it was associated with unusual clinical features. A 69-year-old ASA II woman with hepatocellular carcinoma was presented for an elective left hepatic lobectomy. During the surgery, the tumor embolus was dislodged from the interior of the lumen of the inferior vena cava (IVC), which then drifted into the tricuspid valve area and pulmonary vasculature. The patient showed the specific signs of acute pulmonary embolism, such as a reduction in end-tidal carbon dioxide, an increase in central venous pressure, and a decrease in arterial pressure. The patient exhibited the symptoms for about 10 minutes. After this period, however, cardiovascular variables became relatively stable, even during a mechanical obstruction due to cross-clamping the pulmonary artery for embolectomy. After several hours of pulmonary embolectomy, the patient experienced an episode of RPE. The ventilatory supports for the treatment of RPE were successful, and the patient recovered without any complications. The patient's case in the present study demonstrates that pulmonary embolism may occur as a result of a hepatocellular carcinoma extending into the IVC during operative management. The anesthesiologist should be careful of the possibilities of RPE after removal of the tumor embolus.

Hemodynamic effects of sildenafil interaction with a nitric oxide donor compound in a dog model of acute pulmonary embolism

Sildenafil attenuates acute pulmonary embolism (APE)-induced pulmonary hypertension. However, the hemodynamic effects of sildenafil in combination with other vasodilators during APE have not been examined yet. In the present study, we examined the hemodynamic effects of combined diethylenetriamine/nonoate (DETA-NO, 1microMol kg(-1), i.v.) and sildenafil (0.25mg/kg, i.v.) in an anesthetized dog model of APE. Plasma nitrite/nitrate (NO(x)) and cyclic GMP concentrations were determined using an ozone-based chemiluminescence assay and a commercial enzyme immunoassay, respectively. We found that this dose of DETA-NO did not attenuate APE-induced pulmonary hypertension. However, significant decreases in mean pulmonary artery pressure were observed 15, 30 and 45min after the administration of sildenafil alone or after the combined administration of DETA-NO and sildenafil (all P<0.05). No significant differences among groups were observed in the respiratory parameters. While DETA-NO significantly increased NO(x) concentrations by approximately 4microM, cyclic GMP concentrations increased only when sildenafil was administered (all P<0.05). These results show that the combined administration of 1microMol kg(-1) of DETA-NO and sildenafil is not advantageous compared with sildenafil alone, thus suggesting that sildenafil alone produced maximum attenuation of APE-induced pulmonary hypertension, as far as the NO-cGMP pathway is concerned.

Hemodynamic effects of combined sildenafil and L-arginine during acute pulmonary embolism-induced pulmonary hypertension

Sildenafil attenuates acute pulmonary embolism-induced pulmonary hypertension. However, the hemodynamic effects of sildenafil in combination with other vasodilators during acute pulmonary embolism have not been examined yet. In the present study, we examined the hemodynamic effects of combined sildenafil (0.25 mg/kg, i.v.) and L-arginine (100, 200, 500, and 1000 mg/kg/h, i.v.) in an anesthetized dog model of acute pulmonary embolism. Plasma nitrite/nitrate (NO(x)) and cGMP concentrations were determined using an ozone-based chemiluminescence assay and a commercial enzyme immunoassay, respectively. We found that L-arginine alone did not attenuate acute pulmonary embolism-induced pulmonary hypertension. However, significant decreases in mean pulmonary artery pressure were observed 30, 45, 60, and 75 min after the administration of sildenafil alone or after the combined administration of sildenafil and L-arginine (all P < 0.05). No significant differences among groups were observed in the respiratory parameters. While L-arginine significantly increased NO(x) concentrations, cGMP concentrations increased only when sildenafil was administered (all P < 0.05). These results suggest that while sildenafil attenuates acute pulmonary embolism-induced pulmonary hypertension, L-arginine does not enhance the beneficial hemodynamic effects of sildenafil. In addition, these findings suggest that stimulation of NO synthesis with L-arginine during acute pulmonary embolism does not produce beneficial effects.

The Effect of Sildenafil on Pulmonary Embolism-Induced Oxidative Stress and Pulmonary Hypertension

Acute pulmonary embolism (APE) is a major cause of pulmonary hypertension and death. We examined the effects of sildenafil on the hemodynamic changes caused by APE in anesthetized dogs. Sham-operated dogs (n = 3) received only saline. APE was induced by stepwise IV injections of 300 mum microspheres in amounts adjusted to increase mean pulmonary artery pressures by 20 mm Hg. Hemodynamic evaluation was performed at baseline, after APE was induced, and then after sildenafil 0.25 mg/kg (n = 8), or sildenafil 1 mg/kg + 0.3 mg . kg(-1) . h(-1) (n = 8) or saline (n = 9) infusions were started. Similar experiments were conducted to examine the effects of sildenafil in rat isolated perfused lung preparation. Plasma thiobarbituric acid reactive species were also determined in both studies to measure oxidative stress. Both doses of sildenafil reduced mean pulmonary artery pressures in dogs by approximately 8 to 16 mm Hg (both P < 0.05) and attenuated the increase in oxidative stress after APE. Mean arterial blood pressure remained unaltered after both doses of sildenafil. Sildenafil produced similar effects after APE in rat isolated perfused lung preparation. These findings indicate that IV sildenafil can selectively attenuate the increases in mean pulmonary artery pressures after APE, possibly through antioxidant mechanisms.

Sildenafil selectively inhibits acute pulmonary embolism-induced pulmonary hypertension

Selective pulmonary vasodilators attenuate acute pulmonary embolism (APE)-induced pulmonary hypertension. We examined the effects of intravenous sildenafil on the hemodynamic and respiratory changes caused by APE in anesthetized dogs. Sham operated animals (n=3) received only saline infusions. APE was induced by intravenous injections of microspheres in amounts adjusted to increase mean pulmonary artery pressures (MPAP) by 20 mmHg. Hemodynamic evaluation was performed and arterial blood samples were drawn for blood gas analysis at baseline, 15 and 30 min after APE was induced, and then 15, 30, and 45 min after the sildenafil infusion (1 mg kg(-1) infused intravenously in 15 min followed by 0.3 mg kg(-1) h(-1) for 30 min) started in the Sildenafil group (n=7), or saline infusion started in the control group (n=8). APE induced sustained pulmonary hypertension and 325% increase in pulmonary vascular resistance index (PVRI) without significant changes in the other hemodynamic parameters. While the animals in the control group showed no further changes in MPAP and PVRI, a significant decrease in MPAP and PVRI (-25 and -45%, respectively; P<0.05 both) was observed with sildenafil. No significant changes in the other hemodynamic parameters were observed in both groups. APE decreased PaO2, whereas sildenafil attenuated the decrease in PaO2 (P<0.05). We conclude that intravenous sildenafil can selectively attenuate the increases in MPAP and PVRI after APE.

What’s new and novel in obstetric anesthesia? Contributions from the 2003 scientific literature

THE PREGNANT PATIENT: Age; maternal disease; prophylactic antibiotics; gastroesophageal reflux; obesity; starvation; genotyping; coagulopathy; infection; substance abuse; altered drug responses in pregnancy; physiological changes of pregnancy. THE FETUS: Fetal monitoring; intrauterine surgery. THE NEWBORN: Breastfeeding; maternal infection, fever, and neonatal sepsis evaluation. OBSTETRIC COMPLICATIONS: Embolic phenomena; hemorrhage; preeclampsia; preterm delivery. OBSTETRIC MANAGEMENT: External cephalic version and cervical cerclage; elective cesarean delivery; fetal malpresentation; vaginal birth after cesarean delivery; termination of pregnancy. OBSTETRIC ANESTHESIA: Analgesia for labor and delivery; anesthesia for cesarean delivery; anesthesia for short obstetric operations; complications of anesthesia. MISCELLANEOUS: Consent; ethics; history; labor support; websites/books/leaflets/journal announcements.