Variation in natriuretic peptides and mitral flow indexes during successful ventilatory weaning: a preliminary study

Cardiopulmonary interactions during ventilator weaning

Weaning a critically-ill patient from the ventilator is a crucial step in global management. This manuscript details physiological changes induced by altered heart-lung interactions during the weaning process, illustrates the main mechanisms which could lead to weaning failure of cardiac origin, and discuss a tailored management based on the monitoring of changes in central hemodynamics during weaning. The transition from positive-pressure ventilation to spontaneous breathing results in abrupt hemodynamic and metabolic changes secondary to rapidly modified heart-lung interactions, sudden changes in cardiac loading conditions, and increased oxygen demand. These modifications may elicit an excessive burden on both the respiratory and cardiovascular systems, result in a rapid and marked increase of left ventricular filling pressure, and ultimately result in a weaning-induced pulmonary oedema (WIPO). The T-piece trial induces the greatest burden on respiratory and cardiocirculatory function when compared to spontaneous breathing trial using pressure support ventilation with positive or zero end-expiratory pressure. Since LV overload is the mainstay of WIPO, positive fluid balance and SBT-induced acute hypertension are the most frequently reported mechanisms of weaning failure of cardiac origin. Although the diagnosis of WIPO historically relied on an abrupt elevation of pulmonary artery occlusion pressure measured during right heart catheterization, it is nowadays commonly documented by echocardiography Doppler. This non-invasive approach is best suited for identifying high-risk patients, depicting the origin of WIPO, and tailoring individual management. Whether this strategy increases the success rate of weaning needs to be evaluated in a population at high risk of weaning failure of cardiac origin.

Association between elevated brain natriuretic peptide levels and weaning failure: A systematic review and meta-analysis

OBJECTIVE

Cardiovascular dysfunction has been reported as an important mechanism of weaning failure, and recent data suggest that elevated brain natriuretic peptide (BNP) levels is associated with an increased risk of weaning failure. Therefore, we performed this meta-analysis to evaluate the correlation between elevated BNP levels and weaning failure in critically ill patients subject to mechanical ventilation.

METHODS

A systematic search in Cochrane Library, Embase, PubMed and Web of Science was performed up to September 25, 2019. Standard mean differences (SMD) and corresponding 95% confidence intervals (CIs) of the BNP levels were calculated for each study.

RESULTS

Nine studies with a total number of 589 were included in the final meta-analysis. The results showed that elevated BNP levels were significantly associated with the risk of weaning failure (SMD: 0.76, 95% CI: 0.47 to 1.05, P < .00001). The finding was consistent with the BNP measured before (SMD: 0.68, 95% CI: 0.26 to 1.11, P = .002) or at the end of spontaneous breathing trial (SBT) (SMD: 0.85, 95% CI: 0.52 to 1.18, P < .00001).

CONCLUSIONS

This meta-analysis showed that increased plasma BNP concentration was associated with weaning failure in ICU patients.

Left ventricular overloading identified by critical care echocardiography is key in weaning-induced pulmonary edema

Purpose

To assess the role of left ventricular overload and cumulated fluid balance in the development weaning-induced pulmonary edema (WIPO).

Methods

Ventilated patients in sinus rhythm with COPD and/or heart failure (ejection fraction ≤ 40%) were studied. Echocardiography was performed immediately before and during a 30-min spontaneous breathing trial (SBT) using a T-tube. Patients who failed were treated according to echocardiography results before undergoing a second SBT.

Results

Twelve of 59 patients failed SBT, all of them developing WIPO. Patients who succeeded SBT had lower body weight (− 2.5 kg [− 4.8; − 1] vs. + 0.75 kg [− 2.95;  + 5.57]: p = 0.02) and cumulative fluid balance (− 2326 ml [− 3715;  + 863] vs. + 143 ml [− 2654; + 4434]: p = 0.007) than those who developed WIPO. SBT-induced central hemodynamic changes were more pronounced in patients who developed WIPO, with higher E wave velocity (122 cm/s [92; 159] vs. 93 cm/s [74; 109]: p = 0.017) and E/A ratio (2.1 [1.2; 3.6] vs. 0.9 [0.8; 1.4]: p = 0.001), and shorter E wave deceleration time (85 ms [72; 125] vs. 147 ms [103; 175]: p = 0.004). After echocardiography-guided treatment, all patients who failed the first SBT were successfully extubated. Fluid balance was then negative (− 2224 ml [− 7056; + 100] vs. + 146 ml [− 2654; + 4434]: p = 0.005). Left ventricular filling pressures were lower (E/E′: 7.3 [5; 10.4] vs. 8.9 [5.9; 13.1]: p = 0.028); SBT-induced increase in E wave velocity (+ 10.6% [− 2.7/ + 18] vs. + 25.6% [+ 12.7/ + 49]: p = 0.037) and of mitral regurgitation area were significantly smaller.

Conclusion

In high-risk patients, WIPO appears related to overloaded left ventricle associated with excessive fluid balance. SBT-induced central hemodynamic changes monitored by CCE help in guiding therapy for successful weaning.

Electronic supplementary material

The online version of this article (10.1007/s00134-020-06061-y) contains supplementary material, which is available to authorized users.

Ultrasonographic evaluation of lung and heart in predicting successful weaning in mechanically ventilated neurosurgical patients

In critically ill neurosurgical patients, delayed and premature extubation increases the risk of morbidity and mortality. Assessment of critically ill patients before and during spontaneous breathing trial (SBT) is crucial in predicting weaning failure. We explored the trend of changes with integrated lung and cardiac ultrasonography in predicting success of weaning in neurosurgical patients. Lung ultrasound and cardiac ultrasound was performed before and after 30 min and 120 min of SBT. Lung ultrasound score (LUS, range 0–36) was calculated using a predefined method of assessment of six chest regions on either side. The left ventricular function was evaluated by measuring fractional area change. The maximum velocities of mitral inflow E and A waves (E/A), deceleration time of E wave (DTE) and tissue doppler based E′ wave at lateral annulus to calculate E/E′, were measured to assess left ventricular filling pressure. Twenty seven patients underwent SBT, among these 22 had success and five had failure of SBT. The SBT failure group had higher baseline LUS and progressively higher LUS during SBT compared to the success group, suggesting significant lung de-recruitment. There was significant increase in the LV filling pressure (increase E/A and E/E′, decrease in DTE) after 30 and 120 min of SBT in failure group compared to the success group. Point of care lung and cardiac ultrasonography may be useful in detecting cardiopulmonary changes induced by SBT. Higher lung aeration loss and LV filling pressure were observed with SBT failure group.

Weaning failure of cardiovascular origin: how to suspect, detect and treat-a review of the literature

Among the multiple causes of weaning failure from mechanical ventilation, cardiovascular dysfunction is increasingly recognized as a quite frequent cause that can be treated successfully. In this review, we summarize the contemporary evidence of the most important clinical and diagnostic aspects of weaning failure of cardiovascular origin with special focus on treatment. Pathophysiological mechanisms are complex and mainly include increase in right and left ventricular preload and afterload and potentially induce myocardial ischemia. Patients at risk include those with preexisting cardiopulmonary disease either known or suspected. Clinically, cardiovascular etiology as a predominant cause or a contributor to weaning failure, though critical for early diagnosis and intervention, may be difficult to be recognized and distinguished from noncardiac causes suggesting the need of high suspicion. A cardiovascular diagnostic workup including bedside echocardiography, lung ultrasound, electrocardiogram and biomarkers of cardiovascular dysfunction or other adjunct techniques and, in selected cases, right heart catheterization and/or coronary angiography, should be obtained to confirm the diagnosis. Official clinical practice guidelines that address treatment of a confirmed weaning-induced cardiovascular dysfunction do not exist. As the etiologies of weaning-induced cardiovascular dysfunction are diverse, principles of management depend on the individual pathophysiological mechanisms, including preload optimization by fluid removal, guided by B-type natriuretic peptide measurement, nitrates administration in excessive afterload and/or myocardial ischemia, contractility improvement in severe systolic dysfunction as well as other rational treatment in specific indications in order to lead to successful weaning from mechanical ventilation.

Cardiovascular failure and weaning

Cardiac patients are at high risk of weaning failure due to the abrupt burden to the cardiovascular system resulting from the transition from positive-pressure ventilation to spontaneous breathing. Similarly, numerous patients with borderline cardiac function, left ventricular diastolic dysfunction, chronic obstructive pulmonary disease, especially with associated fluid overload or cumulative positive fluid balance, are at high risk of weaning failure of cardiac origin. The diagnosis of weaning-induced pulmonary oedema (WiPO) relies on the measurement of elevated left ventricular filling pressure, or on the presence of a surrogate reflecting pulmonary or cardiac congestion. Plasma concentration of B-type natriuretic peptide and N-terminal proBNP, biological signs of hemoconcentration (increased circulating protein or hemoglobin levels), or measurement of extravascular pulmonary lung water using transpulmonary thermodilution have been proved valuable surrogates for the identification of weaning failure. Nevertheless, studies have not yet compared these indirect methods to precisely determine their respective diagnostic values for the identification of WiPO, especially in heart failure patients. In addition, none of these approaches directly assess left ventricular filling pressure and the mechanism of WiPO. In contrast, critical care echocardiography is ideally suited to establish the diagnosis of weaning failure of cardiac origin. It allows identifying the high-risk population, monitoring hemodynamically the patient at risk, depicting an abrupt increase of left ventricular filling pressure consistent with WiPO when the patient fails weaning, identifying the underlying mechanism of WiPO, and finally it allows tailoring the therapeutic management of the patient who failed weaning. The impact on patient-centered outcomes of such integrated management strategy based on critical care echocardiography deserves to be prospectively tested in a large population of patients at high risk of weaning failure of cardiac origin.

Critical care ultrasonography in acute respiratory failure

Acute respiratory failure (ARF) is a leading indication for performing critical care ultrasonography (CCUS) which, in these patients, combines critical care echocardiography (CCE) and chest ultrasonography. CCE is ideally suited to guide the diagnostic work-up in patients presenting with ARF since it allows the assessment of left ventricular filling pressure and pulmonary artery pressure, and the identification of a potential underlying cardiopathy. In addition, CCE precisely depicts the consequences of pulmonary vascular lesions on right ventricular function and helps in adjusting the ventilator settings in patients sustaining moderate-to-severe acute respiratory distress syndrome. Similarly, CCE helps in identifying patients at high risk of ventilator weaning failure, depicts the mechanisms of weaning pulmonary edema in those patients who fail a spontaneous breathing trial, and guides tailored therapeutic strategy. In all these clinical settings, CCE provides unparalleled information on both the efficacy and tolerance of therapeutic changes. Chest ultrasonography provides further insights into pleural and lung abnormalities associated with ARF, irrespective of its origin. It also allows the assessment of the effects of treatment on lung aeration or pleural effusions. The major limitation of lung ultrasonography is that it is currently based on a qualitative approach in the absence of standardized quantification parameters. CCE combined with chest ultrasonography rapidly provides highly relevant information in patients sustaining ARF. A pragmatic strategy based on the serial use of CCUS for the management of patients presenting with ARF of various origins is detailed in the present manuscript.

Left Ventricular Diastolic Dysfunction—An Independent Risk Factor for Weaning Failure from Mechanical Ventilation

The objective of this study was to investigate the contribution of left ventricular (LV) diastolic dysfunction to weaning failure, along with the levels of the currently used cardiac biomarkers. Forty-two mechanically ventilated patients, who fulfilled criteria for weaning from mechanical ventilation (MV), underwent a two-hour spontaneous breathing trial (SBT). Transthoracic echocardiography (TTE) was performed before the start of the SBT. The grade of LV diastolic dysfunction was assessed by pulsed-wave Doppler and tissue Doppler imaging at the level of the mitral valve. Haemodynamic and respiratory parameters were recorded. Blood levels of B-type natriuretic peptide (BNP), troponin I, creatine kinase–MB, and myoglobin were measured on MV and at the end of the SBT. Weaning success was defined as the patient's ability to tolerate spontaneous breathing for more than 48 hours. Fifteen patients failed to wean. LV diastolic dysfunction was significantly associated with weaning failure ( P <0.001). The grade of diastolic dysfunction was significantly correlated with BNP levels both on MV and at the end of the SBT ( P <0.001, r = 0.703 and P <0.001, r = 0.709, respectively). BNP levels on MV were lower in patients who successfully weaned compared to those who did not (361 ± 523 ng/l versus 643 ± 382 ng/l respectively, P=0.008). The presence of diastolic dysfunction was independently associated with weaning failure (odds ratio [OR] 11.23, confidence interval [CI] 1.16–109.1, P=0.037) followed by respiratory frequency/tidal volume (OR 1.05, CI 1.00–1.10, P=0.048). Therefore, assessment of LV diastolic function before the start of weaning could be useful to identify patients at risk of weaning failure.

Ultrasonography evaluation during the weaning process: the heart, the diaphragm, the pleura and the lung

PURPOSE

On a regular basis, the intensivist encounters the patient who is difficult to wean from mechanical ventilatory support. The causes for failure to wean from mechanical ventilatory support are often multifactorial and involve a complex interplay between cardiac and pulmonary dysfunction. A potential application of point of care ultrasonography relates to its utility in the process of weaning the patient from mechanical ventilatory support.

METHODS

This article reviews some applications of ultrasonography that may be relevant to the process of weaning from mechanical ventilatory support.

RESULTS

The authors have divided these applications of ultrasonography into four separate categories: the assessment of cardiac, diaphragmatic, and lung function; and the identification of pleural effusion; which can all be evaluated with ultrasonography during a dynamic process in which the intensivist is uniquely positioned to use ultrasonography at the point of care.

CONCLUSIONS

Ultrasonography may have useful application during the weaning process from mechanical ventilatory support.

Assessment of acute lung injury/acute respiratory distress syndrome using B-type brain natriuretic peptide

OBJECTIVES

To investigate the clinical value of B-type natriuretic peptide (BNP) in the assessment of severity and prognosis in acute lung injury/acute respiratory distress syndrome (ALI/ARDS).

METHODS

Plasma BNP level, arterial blood gases, serum C-reactive protein level, alveolar-arterial oxygen tension difference and oxygenation index were measured in patients with and without ALI/ARDS within 24 h of admission to an intensive care unit. Patients with ALI/ARDS were divided into mild, moderate or severe groups according to the degree of hypoxaemia. Survival >28 days was recorded.

RESULTS

A total of 59 patients with ALI/ARDS and 14 patients without ALI/ARDS were included in the study. Of the patients with ALI/ARDS, 18 had mild hypoxaemia, 20 had moderate hypoxaemia and 21 had severe hypoxaemia. The mean ± SD BNP level was significantly higher in all three ALI/ARDS groups (92.41 ± 28.19 pg/ml, 170.64 ± 57.34 pg/ml and 239.06 ± 59.62 pg/ml, respectively, in the mild, moderate and severe groups) than in the non-ALI/ARDS group (47.27 ± 19.63 pg/ml); the increase in BNP level with increasing severity was also statistically significant. When divided according to outcome, the BNP level in the death group (267.07 ± 45.06 pg/ml) was significantly higher than in the survival group (128.99 ± 45.42 pg/ml).

CONCLUSIONS

The BNP level may be of value in evaluating severity and prognosis in patients with ALI/ARDS.

Weaning-induced cardiac dysfunction: where are we today?

INTRODUCTION

The concept of weaning-induced cardiac dysfunction emerged 26 years ago with the publication of a clinical study conducted by François Lemaire and collaborators.

OBJECTIVES

One objective of this article is to remember the results and the historical context under which our pivotal study was conducted. Another objective is to review some of the subsequent studies that aimed to analyze the underlying mechanisms, to noninvasively detect the cardiac origin of weaning failure, and to propose specific therapies enabling weaning success.

CONCLUSION

Weaning-induced cardiac dysfunction has become an established cause of weaning failure. Underlying mechanisms may differ from one patient to another. Important progress has already been made in its diagnosis thanks to relevant clinical research studies. Ongoing and future technological advances in ultrasonography and in biomarker research should certainly help in diagnosing weaning induced-pulmonary edema and in identifying the main mechanisms responsible for its development. Progress on appropriate therapeutic options on an individual basis is still expected.

Ventricular diastolic abnormalities in the critically ill

PURPOSE OF REVIEW

Left-ventricular diastolic dysfunction is associated with various conditions frequently encountered in ICU patients. Due to prolonged relaxation and increased left-ventricular stiffness, patients with diastolic dysfunction are at high risk of developing abrupt pulmonary venous congestion. The present review describes the clinical spectrum of left-ventricular diastolic abnormalities in ICU patients.

RECENT FINDINGS

Left-ventricular diastolic dysfunction is associated with a preserved ejection fraction in half of the patients presenting with acute pulmonary edema. These patients may have dramatic presentation, such as flash pulmonary edema during a hypertensive crisis. Left-ventricular diastolic dysfunction is frequently involved in patients who fail extubation and may trigger weaning pulmonary edema. Sepsis and myocardial ischemia may also be associated with left-ventricular diastolic dysfunction. The diagnosis of left-ventricular diastolic dysfunction practically relies on two-dimensional and Doppler echocardiography. Further large-scale clinical studies are needed to better characterize the prevalence, the clinical relevance and time-course of left-ventricular diastolic dysfunction in ICU patients.

SUMMARY

Left-ventricular diastolic dysfunction accounts for a growing proportion of cardiogenic pulmonary edema and weaning failure in ICU patients. It may be reversible when induced by sepsis or myocardial ischemia. Its prognostic value in the ICU settings remains to be further investigated.

Ultrasound assessment of lung aeration loss during a successful weaning trial predicts postextubation distress*

OBJECTIVE

Postextubation distress after a successful spontaneous breathing trial is associated with increased morbidity and mortality. Predicting postextubation distress is therefore a major issue in critically ill patients. To assess whether lung derecruitment during spontaneous breathing trial assessed by lung ultrasound is predictive of postextubation distress.

DESIGN AND SETTING

Prospective study in two multidisciplinary intensive care units within University Hospital.

PATIENTS AND METHODS

One hundred patients were included in the study. Lung ultrasound, echocardiography, and plasma B-type natriuretic peptide levels were determined before and at the end of a 60-min spontaneous breathing trial and 4 hrs after extubation. To quantify lung aeration, a lung ultrasound score was calculated. Patients were followed up to hospital discharge.

MEASUREMENTS AND MAIN RESULTS

Fourteen patients failed the spontaneous breathing trial, 86 were extubated, 57 were definitively weaned (group 1), and 29 suffered from postextubation distress (group 2). Loss of lung aeration during the successful spontaneous breathing trial was observed only in group 2 patients: lung ultrasound scores increased from 15 [13;17] to 19 [16; 21] (p < .01). End-spontaneous breathing trial lung ultrasound scores were significantly higher in group 2 than in group 1 patients: 19 [16;21] vs. 10 [7;13], respectively (p < .001) and predicted postextubation distress with an area under the receiver operating characteristic curve of 0.86. Although significantly higher in group 2, B-type natriuretic peptide and echocardiography cardiac filling pressures were not clinically helpful in predicting postextubation distress.

CONCLUSION

Lung ultrasound determination of aeration changes during a successful spontaneous breathing trial may accurately predict postextubation distress.

Left ventricular diastolic dysfunction in the intensive care unit: trends and perspectives

Heart failure with a normal or nearly normal left ventricular (LV) ejection fraction (HFNEF) may represent more than 50% of heart failure cases. Although HFNEF is being increasingly recognized, there is a relative lack of information regarding its incidence and prognostic implications in intensive care unit (ICU) patients. In the ICU, many factors related to patient's history, or applied therapies, may induce or aggravate LV diastolic dysfunction. This may impact on patients' morbidity and mortality. This paper discusses methods for assessing LV diastolic function and the feasibility of their implementation for diagnosing HFNEF in the ICU.

Transthoracic Echocardiography with Doppler Tissue Imaging predicts weaning failure from mechanical ventilation: evolution of the left ventricle relaxation rate during a spontaneous breathing trial is the key factor in weaning outcome

Introduction

There is growing evidence to suggest that transthoracic echocardiography (TTE) should be used to identify the cardiac origin of respiratory weaning failure. The aims of our study were: first, to evaluate the ability of transthoracic echocardiography, with mitral Doppler inflow E velocity to annular tissue Doppler Ea wave velocity (E/Ea) ratio measurement, to predict weaning failure from mechanical ventilation in patients, including those with atrial fibrillation; and second, to determine whether the depressed left ejection fraction and/or diastolic dysfunction participate in weaning outcome.

Methods

The sample included patients on mechanical ventilation for over 48 hours. A complete echocardiography was performed just before the spontaneous breathing trial (SBT) and 10 minutes after starting the SBT. Systolic dysfunction was defined by a left ventricle ejection fraction under 50% and relaxation impairment by a protodiastolic annulus mitral velocity Ea under or equal to 8 cm/second.

Results

A total of 68 patients were included. Twenty failed the weaning process and the other 48 patients succeeded. Before the SBT, the E/Ea ratio was higher in the failed group than in the successful group. The E/Ea measured during the SBT was also higher in the failed group. The cut-off value, obtained from receiver operating characteristics (ROC) curve analysis, to predict weaning failure gave an E/Ea ratio during the SBT of 14.5 with a sensitivity of 75% and a specificity of 95.8%. The left ventricular ejection fraction did not differ between the two groups whereas Ea was lower in the failed group. Ea increased during SBT in the successful group while no change occurred in the failed group.

Conclusions

Measurement of the E/Ea ratio with TTE could predict weaning failure. Diastolic dysfunction with relaxation impairment is strongly associated with weaning failure. Moreover, the impossibility of enhancing the left ventricle relaxation rate during the SBT seems to be the key factor of weaning failure. In contrast, the systolic dysfunction was not associated with weaning outcome.

B-type natriuretic peptides for prediction and diagnosis of weaning failure from cardiac origin

AIM

To evaluate and compare BNP and NT-proBNP concentrations to predict weaning failure from mechanical ventilation (MV) due to heart failure (HF) before a spontaneous breathing trial (SBT) and to identify HF as the cause of failure.

METHODS

Prospective, observational study in a university hospital. The sample included 100 patients on MV for over 48 h who underwent an SBT. Echocardiography and sampling for natriuretic peptides were performed immediately before and at the end of SBT. HF was diagnosed by pulmonary artery occlusion pressure >18 mm Hg or signs of elevated filling pressures in echocardiography.

RESULTS

Thirty-two patients failed the SBT, 12 due to HF and 20 due to respiratory failure (RF). Before SBT, BNP and NT-proBNP were higher in patients failing due to HF than RF or in successfully weaned patients. Cut-off values using ROC curve analyses to predict HF were 263 ng/L for BNP (p < 0.001) and 1,343 ng/L for NT-proBNP (p = 0.08). BNP and NT-proBNP increased significantly during SBT in patients failing due to HF. Increases in BNP and NT-proBNP of 48 and 21 ng/L, respectively, showed a diagnostic accuracy for HF of 88.9 and 83.3% (p < 0.001). BNP performed better than NT-proBNP for HF prediction (p = 0.01) and diagnosis (p = 0.009).

CONCLUSION

B-type natriuretic peptides, particularly BNP, can predict weaning failure due to HF before an SBT; increases in natriuretic peptides during SBT are diagnostic of HF as the cause of weaning failure. BNP performs better than NT-proBNP in prediction and diagnosis of HF.

Echocardiography: a help in the weaning process

Introduction

To evaluate the ability of transthoracic echocardiography (TTE) to detect the effects of spontaneous breathing trial (SBT) on central hemodynamics and to identify indices predictive of cardiac-related weaning failure.

Methods

TTE was performed just before and at the end of a 30-min SBT in 117 patients fulfilling weaning criteria. Maximal velocities of mitral E and A waves, deceleration time of E wave (DTE), maximal velocity of E' wave (tissue Doppler at the lateral mitral annulus), and left ventricular (LV) stroke volume were measured. Values of TTE parameters were compared between baseline (pressure support ventilation) and SBT in all patients and according to LV ejection fraction (EF): >50% (n = 58), 35% to 50% (n = 30), and <35% (n = 29). Baseline TTE indices were also compared between patients who were weaned (n = 94) and those who failed (n = 23).

Results

Weaning failure was of cardiac origin in 20/23 patients (87%). SBT resulted in a significant increase in cardiac output and E/A, and a shortened DTE. At baseline, DTE was significantly shorter in patients with LVEF <35% when compared to other subgroups (median [25^th-75^th percentiles]: 119 ms [90-153]; vs. 187 ms [144-224] vs. 174 ms [152-193]; P < 0.01) and E/E' was greater (7.9 [5.4-9.1] vs. 6.0 [5.3-9.0] vs. 5.2 [4.7-6.0]; P < 0.01). When compared to patients who were successfully weaned, those patients who failed exhibited at baseline a significantly lower LVEF (36% [27-55] vs. 51% [43-55]: P = 0.04) and higher E/E' (7.0 [5.0-9.2] vs. 5.6 [5.2-6.3]: P = 0.04).

Conclusions

TTE detects SBT-induced changes in central hemodynamics. When performed by an experienced operator prior to SBT, TTE helps in identifying patients at high risk of cardiac-related weaning failure when documenting a depressed LVEF, shortened DTE and increased E/E'. Further studies are needed to evaluate the impact of this screening strategy on the weaning process and patient outcome.

Use of B-type natriuretic peptide in critically ill patients

B-type natriuretic peptide (BNP) is increasingly used in emergency departments to assess the cause of acute dyspnea and in cardiology to follow treatments and predict outcome. It is increasingly used in the intensive care unit in situations such as respiratory failure (acute pulmonary edema, exacerbation of chronic obstructive pulmonary disease and difficult weaning from ventilator) or when pulmonary embolism is suspected. BNP has also been used to assess alteration of myocardial function in sepsis. Plasma BNP is very high in septic-shock patients (>1000 pg/ml), which is suggested to relate to both myocardial stretch and to an alteration in one of the BNP clearance pathways. Whether BNP at admission or at discharge may predict outcome requires further investigation.

The use of natriuretic peptides in the intensive care unit

PURPOSE OF REVIEW

B-type natriuretic peptides are quantitative markers of heart failure (and/or cardiac stress) that summarize the extent of systolic and diastolic left ventricular dysfunction, valvular dysfunction, and right ventricular dysfunction. Based on the observation that heart failure is common albeit difficult to diagnose in the ICU, several studies have begun to evaluate the potential use of B-type natriuretic peptides in various ICU settings.

RECENT FINDINGS

Previous pilot studies have examined the use of B-type natriuretic peptide in the differential diagnosis of hypoxemic respiratory failure, to differentiate cardiogenic from noncardiogenic shocks or to predict fluid responsiveness, to assess myocardial dysfunction and prognosis in patients with severe sepsis, and to predict ventilatory weaning failure.

SUMMARY

Although previous studies were small, they highlight the potential of using B-type natriuretic peptides as a noninvasive easily available tool to quantify cardiac stress.

Cardiovascular effects of mechanical ventilation and weaning

Because of their anatomic position in the closed thoracic cavity, the heart and lungs interact during each ventilation cycle. The application of mechanical ventilation and subsequent removal changes normal ventilatory mechanics and produces alterations in cardiac preload and afterload that influence global hemodynamic state and delivery of oxygen and nutrients. Adverse cardiovascular responses to mechanical ventilation and weaning from ventilation include hemodynamic alterations and instability, myocardial ischemia, autonomic dysfunction, and cardiac dysrhythmias. Clinicians must have a clear understanding of the cardiovascular effects of mechanical ventilation and weaning so they may anticipate, recognize, and effectively manage negative effects and improve patient outcomes.