Myocardial ischemia and weaning failure in patients with coronary artery disease: an update

Heart-Lung Interactions

The pulmonary and cardiovascular systems have profound effects on each other. Overall cardiac function is determined by heart rate, preload, contractility, and afterload. Changes in lung volume, intrathoracic pressure (ITP), and hypoxemia can simultaneously change all of these four hemodynamic determinants for both ventricles and can even lead to cardiovascular collapse. Intubation using sedation depresses vasomotor tone. Also, the interdependence between right and left ventricles can be affected by lung volume-induced changes in pulmonary vascular resistance and the rise in ITP. An increase in venous return due to negative ITP during spontaneous inspiration can shift the septum to the left and cause a decrease in left ventricle compliance. During positive pressure ventilation, the increase in ITP causes a decrease in venous return (preload), minimizing ventricular interdependence and will decrease left ventricle afterload augmenting cardiac output. Thus, positive pressure ventilation is beneficial in acute heart failure patients and detrimental in hypovolemic patients where it can cause a significant decrease in venous return and cardiac output. Recently, this phenomenon has been used to assess patient's volume responsiveness to fluid by measuring pulse pressure variation and stroke volume variation. Heart-lung interaction is very dynamic and changes in lung volume, ITP, and oxygen level can have various effects on the cardiovascular system depending on preexisting cardiovascular function and volume status. Heart failure and either hypo or hypervolemia predispose to greater effects of ventilation of cardiovascular function and gas exchange. This review is an overview of the basics of heart-lung interaction.

Myocardial ischemia during ventilator weaning: a prospective multicenter cohort study

Background

Weaning-induced cardiac pulmonary edema (WiPO) is one of the main mechanisms of weaning failure during mechanical ventilation. We hypothesized that weaning-induced cardiac ischemia (WiCI) may contribute to weaning failure from cardiac origin.

Methods

A prospective cohort study of patients mechanically ventilated for at least 24 h who failed a first spontaneous breathing trial (SBT) was conducted in four intensive care units. Patients were explored during a second SBT using multiple tools (echocardiography, continuous 12-lead ST monitoring, biomarkers) to scrutinize the mechanisms of weaning failure. WiPO definition was based on three criteria (echocardiographic signs of increased left atrial pressure, increase in B-type natriuretic peptides, or increase in protein concentration during SBT) according to a conservative definition (at least two criteria) and a liberal definition (at least one criterion). WiCI was diagnosed according to the third universal definition of myocardial infarction proposed by the European Society of Cardiology (ESC) and the American Heart Association (AHA) statement for exercise testing.

Results

Among patients who failed a first SBT, WiPO occurred in 124/208 (59.6%) and 44/208 (21.2%) patients, according to the liberal and conservative definition, respectively. Among patients with ST monitoring, WiCI was diagnosed in 36/177 (20.3%) and 12/177 (6.8%) of them, according to the ESC and AHA definitions, respectively. WiCI was not associated with WiPO and was not associated with weaning outcomes. Only two patients of the cohort were treated for an acute coronary syndrome after the second SBT, and seven other patients required coronary angiography during the weaning period.

Conclusions

This observational study showed the common occurrence of pulmonary edema in mechanically ventilated patients who failed a first SBT, but the association with cardiac ischemia and weaning outcomes was weak.

Predictive factors of weaning from mechanical ventilation and extubation outcome: A systematic review

PURPOSE

To identify, describe and discuss the parameters used to predict weaning from mechanical ventilation and extubation outcomes.

METHODS

Systematic review of scientific articles using four electronic databases: PubMed, Embase, PEDro and Cochrane Library. Search terms included "weaning", "extubation", "withdrawal" and "discontinuation", combined with "mechanical ventilation" and "predictive factors", "predictive parameters" and "predictors for success". In this study, we included original articles that presented predictive factors for weaning or extubation outcomes in adult patients and not restricted to a single disease. Articles not written in English were excluded.

RESULTS

A total of 43 articles were included, with a total of 7929 patients and 56 different parameters related to weaning and extubation outcomes. Rapid Shallow Breathing Index (RSBI) was the most common predictor, discussed in 15 studies (2159 patients), followed by Age and Maximum Inspiratory Pressure in seven studies. The other 53 parameters were found in less than six studies.

CONCLUSION

There are several parameters used to predict weaning and extubation outcomes. RSBI was the most frequently studied and seems to be an important measurement tool in deciding whether to wean/extubate a patient. Furthermore, the results demonstrated that weaning and extubation should be guided by several parameters, and not only to respiratory ones.

An Integrative Index for Predicting Extubation Outcomes After Successful Completion of a Spontaneous Breathing Trial in an Adult Medical Intensive Care Unit

Background:

Among respiratory predictors, rapid shallow breathing index (RSBI) has been a commonly used respiratory parameter to predict extubation outcomes. However, the outcome of prediction remains inconsistent. Regarding nonrespiratory predictors, serum albumin, hemoglobin, bicarbonate, and patients’ alertness have been reported to be associated with successful weaning or extubation. We aimed to develop an integrative index combining commonly used predictors in the adult medical intensive care units (MICUs) and to compare the predictability of the index with RSBI.

Methods:

This prospective observational study with retrospective data collection of planned extubations was conducted in a 14-bed adult MICU. We enrolled patients who received mechanical ventilation via an endotracheal tube in the adult MICU for >24 hours and passed a 2-hour spontaneous breathing trial and underwent extubation. Extubation failure was defined as reinstitution of invasive mechanical ventilation within 48 hours of extubation. Respiratory parameters and Glasgow Coma Scale (GCS) scores of patients were recorded prospectively. Nonrespiratory parameters were recorded retrospectively. Logistic regression was used to determine significant predictors of extubation outcomes.

Results:

Fifty-nine patients comprising 70 extubations were enrolled. Extubation failure was significantly and positively associated with lower serum albumin (albumin < 2.6 g/dL, odds ratio [OR] = 5.1; 95% confidence interval [CI], 1.04-24.66), lower hemoglobin (hemoglobin < 10.0 g/dL, OR = 10.8; 95% CI, 2.00-58.04), and lower GCS scores (GCS score ≤ 8, OR = 6.1; 95% CI = 1.15-32.34). By using an integrative index combining the 3 parameters together, the sensitivity and specificity to predict extubation outcomes were 78.6% and 75.9%, respectively. The area under the receiver operating characteristic curve of the index was significantly higher than RSBI (0.84 vs 0.61, P = .026).

Conclusion:

The integrative index combining serum albumin, hemoglobin, and GCS scores could predict extubation outcomes better than RSBI in an adult MICU.

Controversies in Weaning from Mechanical Ventilation

Invasive mechanical ventilation can successfully support the patient with acute respiratory failure, but it is associated with considerable risks. Numerous complications of invasive mechanical ventilation have been identified, and these may contribute to increased mortality. Therefore after clinical improvement has occurred, considerable emphasis is placed on expeditiously freeing the patient from the ventilator. This process of getting a patient off mechanical ventilation has been variably termed weaning, liberation, or discontinuation (terms which may be used interchangeably), and can be further divided into “readiness testing” and “progressive withdrawal.” Over the last decade, new developments in our understanding of the process of weaning have provided investigators with the tools to address a number of key questions: How should readiness for weaning (and trials of spontaneous breathing) be determined? What is the role of weaning parameters in deciding when to initiate the weaning process? What is the best mode for conducting a spontaneous breathing trial and how should the patient be monitored? What are the mechanisms for weaning (and spontaneous breathing trial) failure? What is the best technique to facilitate progressive withdrawal? What other factors can facilitate liberation from mechanical ventilation? What are the risks of extubation failure and how can extubation outcome best be predicted? What is the role for protocols in facilitating weaning from mechanical ventilation?.

Atrial Fibrillation on Intensive Care Unit Admission Independently Increases the Risk of Weaning Failure in Nonheart Failure Mechanically Ventilated Patients in a Medical Intensive Care Unit: A Retrospective Case-Control Study

Atrial fibrillation (AF) is one of the most frequent arrhythmias in clinical practice. Previous studies have reported the influence of AF on patients with heart failure (HF). The effect of AF on the non-HF critically ill patients in a medical intensive care unit (ICU) remains largely unclear. The study aimed to investigate the impact of AF presenting on ICU admission on the weaning outcome of non-HF mechanically ventilated patients in a medical ICU.A retrospective observational case-control study was conducted over a 1-year period in a medical ICU at Taipei Veterans General Hospital, a tertiary medical center in north Taiwan. Non-HF mechanically ventilated patients who were successful in their spontaneous breathing trial and underwent ventilator discontinuation were enrolled. The primary outcome measure was the ventilator status after the first episode of ventilator discontinuation.A total of 285 non-HF patients enrolled were divided into AF (n = 62) and non-AF (n = 223) groups. Compared with the non-AF patients, the AF patients were significantly associated with old age (P = 0.002), a higher rate of acute respiratory distress syndrome causing respiratory failure (P = 0.015), a higher percentage of sepsis before liberation from mechanical ventilation (MV) (P = 0.004), and a higher serum level of blood urea nitrogen on the day of liberation from MV (P = 0.003). Multivariate logistic regression analysis demonstrated that AF independently increased the risk of weaning failure [adjusted odds ratio (AOR), 3.268; 95% confidence interval (CI), 1.254-8.517; P = 0.015]. Furthermore, the AF patients were found to be independently associated with a high rate of ventilator dependence (log rank test, P = 0.026), prolonged total ventilator use (AOR, 1.979; 95% CI, 1.032-3.794; P = 0.040), increased length of ICU stay (AOR, 2.256; 95% CI, 1.049-4.849; P = 0.037), increased length of hospital stay (AOR, 2.921; 95% CI, 1.363-6.260; P = 0.006), and increased ICU mortality (AOR, 4.143; 95% CI, 1.381-12.424; P = 0.011).AF on ICU admission is an independent risk factor for weaning failure and significantly associated with poor hospital outcome in non-HF mechanically ventilated patients in a medical ICU.

Heart rate variability as a predictor of cardiac dysrhythmias during weaning from mechanical ventilation

BACKGROUND

Weaning from mechanical ventilation to spontaneous breathing is associated with changes in the hemodynamic and autonomic nervous systems that are reflected by heart rate variability. Although cardiac dysrhythmias are an important manifestation of hemodynamic alterations, the impact of heart rate variability on the occurrence of dysrhythmias during weaning has not been specifically studied.

OBJECTIVES

To describe differences in heart rate variability spectral power and occurrence of cardiac dysrhythmias at baseline and during the initial trial of weaning from mechanical ventilation and to evaluate the impact of heart rate variability during weaning on occurrence of dysrhythmias.

METHOD

Continuous 3-lead electrocardiographic recordings were collected from 35 patients receiving mechanical ventilation for 24 hours at baseline and during the initial weaning trial. Heart rate variability was evaluated by using spectral power analysis.

RESULTS

Low-frequency power increased (P = .04) and high-frequency and very-low-frequency power did not change during weaning. The mean number of supraventricular ectopic beats per hour during weaning was higher than the mean at baseline (P < .001); the mean of ventricular ectopic beats did not change. Low-frequency power was a predictor of ventricular and supraventricular ectopic beats during weaning (P < .001). High-frequency power was predictive of ventricular and supraventricular (P = .02) ectopic beats during weaning. Very-low-frequency power was predictive of ventricular ectopic beats (P < .001) only.

CONCLUSION

Heart rate variability power spectra during weaning were predictive of dysrhythmias.

Ventilator management in the cardiac intensive care unit

Patients admitted to the Cardiac Intensive Care Unit (CICU) are of increasing complexity and often require ventilatory support. A deep understanding of respiratory physiology and the interactions between the cardiovascular and respiratory systems is essential. Ventilatory support should be tailored to the specific patient condition, ensuring effective minute ventilation, reducing work of breathing and minimizing adverse hemodynamic effects. The weaning process can stress the cardiovascular system and cardiac failure is a common cause of failure to wean. Identification of patients likely to fail and prompt pre-emptive intervention is crucial for successful weaning and avoiding complications related to prolonged mechanical ventilation.

The difficult-to-wean patient

Up to 20% of patients requiring mechanical ventilation will suffer from difficult weaning (the need of more than 7 days of weaning after the first spontaneous breathing trial), which may depend on several reversible causes: respiratory and/or cardiac load, neuromuscular and neuropsychological factors, and metabolic and endocrine disorders. Clinical consequences (and/or often causes) of prolonged mechanical ventilation comprise features such as myopathy, neuropathy, and body composition alterations and depression, which increase the costs, morbidity and mortality of this. These difficult-to-wean patients may be managed in two type of units: respiratory intermediate-care units and specialized regional weaning centers. Two weaning protocols are normally used: progressive reduction of ventilator support (which we usually use), or progressively longer periods of spontaneous breathing trials. Physiotherapy is an important component of weaning protocols. Weaning success depends strongly on patients&#x2019; complexity and comorbidities, hospital organization and personnel expertise, availability of early physiotherapy, use of weaning protocols, patients&#x2019; autonomy and families&#x2019; preparation for home discharge with mechanical ventilation.

Echocardiographic evaluation during weaning from mechanical ventilation

INTRODUCTION

Echocardiographic, electrocardiographic and other cardiorespiratory variables can change during weaning from mechanical ventilation.

OBJECTIVES

To analyze changes in cardiac function, using Doppler echocardiogram, in critical patients during weaning from mechanical ventilation, using two different weaning methods: pressure support ventilation and T-tube; and comparing patient subgroups: success vs. failure in weaning.

METHODS

Randomized crossover clinical trial including patients under mechanical ventilation for more than 48 h and considered ready for weaning. Cardiorespiratory variables, oxygenation, electrocardiogram and Doppler echocardiogram findings were analyzed at baseline and after 30 min in pressure support ventilation and T-tube. Pressure support ventilation vs. T-tube and weaning success vs. failure were compared using ANOVA and Student's t-test. The level of significance was p<0.05.

RESULTS

Twenty-four adult patients were evaluated. Seven patients failed at the first weaning attempt. No echocardiographic or electrocardiographic differences were observed between pressure support ventilation and T-tube. Weaning failure patients presented increases in left atrium, intraventricular septum thickness, posterior wall thickness and diameter of left ventricle and shorter isovolumetric relaxation time. Successfully weaned patients had higher levels of oxygenation.

CONCLUSION

No differences were observed between Doppler echocardiographic variables and electrocardiographic and other cardiorespiratory variables during pressure support ventilation and T-tube. However cardiac structures were smaller, isovolumetric relaxation time was larger, and oxygenation level was greater in successfully weaned patients.

Clinical review: liberation from mechanical ventilation

Mechanical ventilation is the defining event of intensive care unit (ICU) management. Although it is a life saving intervention in patients with acute respiratory failure and other disease entities, a major goal of critical care clinicians should be to liberate patients from mechanical ventilation as early as possible to avoid the multitude of complications and risks associated with prolonged unnecessary mechanical ventilation, including ventilator induced lung injury, ventilator associated pneumonia, increased length of ICU and hospital stay, and increased cost of care delivery. This review highlights the recent developments in assessing and testing for readiness of liberation from mechanical ventilation, the etiology of weaning failure, the value of weaning protocols, and a simple practical approach for liberation from mechanical ventilation.

Strategies to optimize analgesia and sedation

Achieving adequate but not excessive sedation in critically ill, mechanically ventilated patients is a complex process. Analgesics and sedatives employed in this context are extremely potent, and drug requirements and metabolism are unpredictable. Clinicians must have heightened awareness of the potential for enduring effects and are encouraged to employ strategies that maximize benefit while minimizing risk. Successful sedation protocols have three basic components: frequent assessments for pain, anxiety, and agitation using a reproducible scale; combination therapy coupling opioids and sedatives; and, most importantly, careful communication between team members, with a particular recognition that the bedside nurse must be empowered to pair assessments with drug manipulation. In recent years, two broad categories of sedation protocols have achieved clinical success in terms of decreasing duration of mechanical ventilation and intensive care unit length of stay by minimizing drug accumulation. Patient-targeted sedation protocols (the first category) rely on structured assessments to guide a careful schema of titrated drug escalation and withdrawal. Variation exists in the assessment tool utilized, but the optimal goal in all strategies is a patient who is awake and can be readily examined. Alternatively, daily interruption of continuous sedative infusions (the second category) may be employed to focus care providers on the goal of achieving a period of awakening in the earliest phases of critical illness possible. Newer literature has focused on the safety of this strategy and its comparison with intermittent drug administration. Ongoing investigations are evaluating the broad applicability of these types of protocols, and currently one may only speculate on whether one strategy is superior to another.

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.

Liberation from mechanical ventilation: what monitoring matters?

Over the past 2 decades, the art of "weaning" from mechanical ventilation has been informed by increasing published basic science and outcomes studies. Although monitoring technologies can provide vast amounts of information before, during, and after liberation from mechanical ventilation, little data exists on how to maximally harness even routinely monitored, basic physiologic parameters. Overdependence on technology and derived variables, without data to demonstrate benefit, may even inhibit the patient's progress if it is used inappropriately. We review the scientific evidence for best using routinely available physiologic data and a few more sophisticated and invasive monitoring technologies during weaning. We also suggest future study designs that would better inform the process of liberation from the ventilator and endotracheal extubation.

Prevalence of myocardial ischemia during mechanical ventilation and weaning and its effects on weaning success

BACKGROUND

Myocardial ischemia may be considered both a consequence of weaning from ventilation and a potential cause of weaning failure. A limited number of investigations have evaluated myocardial ischemia during mechanical ventilation and weaning and its effect on weaning success. The purpose of this pilot investigation was to determine the prevalence of myocardial ischemia in a diverse group of medical intensive care unit (MICU) patients during baseline mechanical ventilation, during weaning using continuous positive airway pressure, and up to 24 hours after extubation and to evaluate the relationship between ischemia and weaning failure.

METHODS

This study was a prospective, repeated-measure, descriptive investigation that studied 43 ventilated MICU patients. Slightly more than half of participants were male (53%), and participants had a mean age of 51.1 +/- 14.6 years and were ventilated an average of 11.7 +/- 11.3 days. Myocardial ischemia was evaluated by examination of plasma cardiac troponin I, creatine phosphokinase-myocardial band (CK-MB), and ST-segment changes on electrocardiogram. Continuous electrocardiographic data were obtained by a calibrated, frequency-modulated, continuous 3-channel electrocardiographic recorder using leads I, II, and V2.

RESULTS

Seventy percent of these participants (n = 30) exhibited ST-segment deviation at some point during data collection (baseline mechanical ventilation, during weaning, after extubation). Twenty-four participants exhibited ST-segment deviation at baseline, 7 during weaning, and 8 after extubation. Nine participants exhibited ST-segment deviation at >1 data collection time point. None had ST-segment deviation at all 3 time points. Cardiac enzyme concentrations were highly variable; five participants demonstrated clinically important increases in either CK-MB and/or troponin I. Thirty-five percent of participants required >1 weaning trial. Participants who exhibited ST-segment deviation during baseline ventilation were 60% more likely to fail their initial weaning trial. There were no significant differences in CK-MB or troponin I levels between those participants who were successfully weaned with 1 trial and those who failed to wean during that first trial.

CONCLUSIONS

Silent myocardial ischemia was a common occurrence in this diverse group of MICU patients, although only 21% had previously diagnosed coronary disease. Clinicians must be aware of the potential for silent ischemia, monitor and evaluate their patients for such, and intervene to promote optimal cardiovascular function, particularly during the stress of ventilator weaning.

Cardiopulmonary interactions in patients with heart failure

PURPOSE OF REVIEW

The purpose of this review was to summarize recent findings concerning the consequences of cardiopulmonary interactions in acute cardiogenic pulmonary edema, weaning from mechanical ventilation and fluid-responsiveness assessment by respiratory variations of stroke volume.

RECENT FINDINGS

The efficacy of continuous or bilevel positive airway pressure in patients with acute cardiogenic pulmonary edema was strongly suggested by two recent meta-analyses. There is growing evidence to suggest that weaning-induced cardiac dysfunction and acute cardiogenic pulmonary edema could explain a large amount of liberation failure from mechanical ventilation. Despite a potential role for echocardiography and plasma measurements of B-type natriuretic peptide in demonstrating a cardiac origin to weaning failure, the demonstration of a significant increase in pulmonary-artery occlusion pressure during the weaning trial remains the gold standard for this purpose. In patients with heart failure there is no evidence for revisiting the reliability of the respiratory variation of stroke-volume surrogates to predict fluid responsiveness.

SUMMARY

For clinical practice, the knowledge of cardiopulmonary interactions is of paramount importance in understanding the crucial role of mechanical ventilation for treating patients with heart failure and, by contrast, the deleterious cardiovascular effects of weaning in patients with overt or hidden cardiac failure.

Daily sedative interruption in mechanically ventilated patients at risk for coronary artery disease*

OBJECTIVES

To determine the prevalence of myocardial ischemia in mechanically ventilated patients with coronary risk factors and compare periods of sedative interruption vs. sedative infusion.

DESIGN

Prospective, blinded observational study.

SETTING

Medical intensive care unit of tertiary care medical center.

PATIENTS

Intubated, mechanically ventilated patients with established coronary artery disease risk factors.

INTERVENTIONS

Continuous three-lead Holter monitors with ST-segment analysis by a blinded cardiologist were used to detect myocardial ischemia. Ischemia was defined as ST-segment elevation or depression of >0.1 mV from baseline.

MEASUREMENTS AND MAIN RESULTS

Comparisons between periods of awakening from sedation vs. sedative infusion were made. Vital signs, catecholamine levels, and time with ischemia detected by Holter monitor during the two periods were compared. Heart rate, mean arterial pressure, rate-pressure product, respiratory rate, and catecholamine levels were all significantly higher during sedative interruption. Eighteen of 74 patients (24%) demonstrated ischemic changes. Patients with myocardial ischemia had a longer intensive care unit length of stay (17.4+/-17.5 vs. 9.6+/-6.7 days, p=.04). Despite changes in vital signs and catecholamine levels during sedative interruption, fraction of ischemic time did not differ between the time awake vs. time sedated [median [interquartile range] of 0% [0, 0] compared with 0% [0, 0] while they were sedated [p=.17]). The finding of similar fractions of ischemic time between awake and sedated states persisted with analysis of the subgroup of 18 patients with ischemia.

CONCLUSIONS

Myocardial ischemia is common in critically ill mechanically ventilated patients with coronary artery disease risk factors. Daily sedative interruption is not associated with an increased occurrence of myocardial ischemia in these patients.

Hemodynamic Changes During Discontinuation of Mechanical Ventilation in Medical Intensive Care Unit Patients

• Background Cardiac dysfunction can prevent successful discontinuation of mechanical ventilation. Critically ill patients may have undetected cardiac disease, and cardiac dysfunction can be produced or exacerbated by underlying pathophysiology.

• Objective To describe and compare hemodynamic function and cardiac rhythm during baseline mechanical ventilation with function and rhythm during a trial of continuous positive airway pressure in medical intensive care patients.

• Methods A convenience sample of 43 patients (53% men; mean age 51.1 years) who required mechanical ventilation were recruited for this pilot study. Cardiac output, stroke volume, arterial blood pressure, heart rate, cardiac rhythm, and plasma catecholamine levels were measured during mechanical ventilation and during a trial of continuous positive airway pressure.

• Results One third of the patients had difficulty discontinuing mechanical ventilation. Successful patients had significantly increased cardiac output and stroke volume without changes in heart rate or arterial pressure during the trial of continuous positive airway pressure. Unsuccessful patients had no significant changes in cardiac output, stroke volume, or heart rate but had a significant increase in mean arterial pressure. The 2 groups of patients also had different patterns in ectopy. Concurrently, catecholamine concentrations decreased in the successful patients and significantly increased in the unsuccessful patients during the trial.

• Conclusions Patterns of cardiac function and plasma catecholamine levels differed between patients who did or did not achieve spontaneous ventilation with a trial of continuous positive airway pressure. Cardiac function must be systematically considered before and during the return to spontaneous ventilation to optimize the likelihood of success.

Sedation in the mechanically ventilated patient

OBJECTIVE

To discuss the approach to sedation of the mechanically ventilated patient.

DATA SYNTHESIS

Mechanically ventilated patients in the intensive care unit frequently require sedation and analgesia for anxiety and pain experienced during the time they are intubated. Multiple drugs are available for this purpose. Strategies that optimize comfort while minimizing the predilection for sedative and analgesic drug accumulation with prolongation of effect have been shown to improve outcomes. In particular, such strategies may decrease mechanical ventilation duration, intensive care unit length of stay, and complications associated with critical illness.

CONCLUSIONS

Sedation and analgesia are important in the management of patients who require mechanical ventilation. An evidence-based approach to administering sedatives and analgesics is necessary to optimize short- and long-term outcomes in mechanically ventilated patients.

B-type natriuretic peptide and weaning from mechanical ventilation

OBJECTIVE

Cardiac function and volume status could play a critical role in the setting of weaning failure. B-type natriuretic peptide (BNP) is a powerful marker of cardiac dysfunction. We assessed the value of BNP during the weaning process.

DESIGN, SETTING AND PATIENTS

One hundred and two consecutive patients considered ready to undergo a 1-h weaning trial (T-piece or low-pressure support level) were prospectively included in a medical intensive care unit of a university hospital. Weaning was considered successful if the patient passed the trial and sustained spontaneous breathing for more than 48 h after extubation.

INTERVENTIONS

Plasma BNP was measured just before the trial in all patients, and at the end of the trial in the first 60 patients.

RESULTS

Overall, 42 patients (41.2%) failed the weaning process (37 patients failed the trial and 5 failed extubation). Logistic regression analysis identified high BNP level before the trial and the product of airway pressure and breathing frequency during ventilation as independent risk factors for weaning failure. BNP values were not different at the end of the trial. In nine of the patients in whom the weaning process failed, it succeeded on a later occasion after diuretic therapy. Their BNP level before weaning decreased between the two attempts (517 vs 226 pg/ml, p=0.01). In survivors, BNP level was significantly correlated to weaning duration (rho=0.52, p<0.01).

CONCLUSIONS

Baseline plasma BNP level before the first weaning attempt is higher in patients with subsequent weaning failure and correlates to weaning duration.

Continuous ST-segment monitoring: raising the bar

ST-segment monitoring is recommended by clinical experts to assist in the early detection of transient myocardial ischemia; however, a gap exists between the recommendations and clinical practice. This article provides a review of research to support the use of ST-segment monitoring in a variety of clinical situations. Patient selection for monitoring, techniques, and strategies to facilitate successful implementation of ST monitoring are included. Nurses are encouraged to advocate for patients by raising the bar of electrocardiogram monitoring practice to aid in optimizing patient outcomes.

Cardiovascular issues in respiratory care

The hemodynamic effects of ventilation are complex but can be grouped under four clinically relevant concepts. First, spontaneous ventilation is exercise, and critically ill patients may not withstand the increased work of breathing. Initiation of mechanical ventilatory support will improve oxygen delivery to the remainder of the body by decreasing oxygen consumption. To the extent that mixed venous oxygen also increases, Pao(2) will increase without any improvement in gas exchange. Similarly, weaning from mechanical ventilatory support is a cardiovascular stress test. Patients who fail to wean also manifest cardiovascular insufficiency during the failed weaning attempts. Improving cardiovascular reserve or supplementing support with inotropic therapy may allow patients to wean from mechanical ventilation. Second, changes in lung volume alter autonomic tone and pulmonary vascular resistance (PVR), and at high lung volumes compress the heart in the cardiac fossa. Hyperinflation increases PVR and pulmonary artery pressure, impeding right ventricular ejection. Decreases in lung volume induce alveolar collapse and hypoxia, stimulating an increased pulmonary vasomotor tone by the process of hypoxic pulmonary vasoconstriction. Recruitment maneuvers, positive end-expiratory pressure, and continuous positive airway pressure may reverse hypoxic pulmonary vasoconstriction and reduce pulmonary artery pressure. Third, spontaneous inspiration and spontaneous inspiratory efforts decrease intrathoracic pressure (ITP). Since diaphragmatic descent increases intra-abdominal pressure, these combined effects cause right atrial pressure inside the thorax to decrease but venous pressure in the abdomen to increase, markedly increasing the pressure gradient for systemic venous return. Furthermore, the greater the decrease in ITP, the greater the increase in left ventricular (LV) afterload for a constant arterial pressure. Mechanical ventilation, by abolishing the negative swings in ITP, will selectively decrease LV afterload, as long as the increases in lung volume and ITP are small. Finally, positive-pressure ventilation increases ITP. Since diaphragmatic descent increases intra-abdominal pressure, the decrease in the pressure gradient for venous return is less than would otherwise occur if the only change were an increase in right atrial pressure. However, in hypovolemic states, positive-pressure ventilation can induce profound decreases in venous return. Increases in ITP decrease LV afterload and will augment LV ejection. In patients with hypervolemic heart failure, this afterload reducing effect can result in improved LV ejection, increased cardiac output, and reduced myocardial oxygen demand.

AHA scientific statement: practice standards for electrocardiographic monitoring in hospital settings: an American Heart Association Scientific Statement from the Councils on Cardiovascular Nursing, Clinical Cardiology, and Cardiovascular Disease in the Young: endorsed by the International Society of Computerized electrocardiology and the American Association of Critical-Care Nurses

The goals of electrocardiographic (ECG) monitoring in hospital settings have expanded from simple heart rate and basic rhythm determination to the diagnosis of complex arrhythmias, myocardial ischemia, and prolonged QT interval. Whereas Computerized arrhythmia analysis is automatic in cardiac monitoring systems, computerized ST-segment ischemia analysis is available only in newer-generation monitors, and computerized QT-interval monitoring is currently unavailable. Even in hospitals with ST-monitoring capability, ischemia monitoring is vastly underutilized by healthcare professionals. Moreover, because no computerized analysis is available for QT monitoring, healthcare professionals must determine when it is appropriate to manually measure QT intervals (eg, when a patient is started on a potentially proarrhythmic drug). The purpose of the present review is to provide "best practices" for hospital ECG monitoring. Randomized clinical trials in this area are almost nonexistent; therefore, expert opinions are based upon clinical experience and related research in the field of electrocardiography. This consensus document encompasses all areas of hospital cardiac monitoring in both children and adults. The emphasis is on information clinicians need to know to monitor patients safely and effectively. Recommendations are made with regard to indications, time frames, and strategies to improve the diagnostic accuracy of cardiac arrhythmia, ischemia, and QT-interval monitoring. Currently available ECG lead systems are described, and recommendations related to staffing, training, and methods to improve quality are provided.

Practice Standards for Electrocardiographic Monitoring in Hospital Settings

The goals of electrocardiographic (ECG) monitoring in hospital settings have expanded from simple heart rate and basic rhythm determination to the diagnosis of complex arrhythmias, myocardial ischemia, and prolonged QT interval. Whereas computerized arrhythmia analysis is automatic in cardiac monitoring systems, computerized ST-segment ischemia analysis is available only in newer-generation monitors, and computerized QT-interval monitoring is currently unavailable. Even in hospitals with ST-monitoring capability, ischemia monitoring is vastly underutilized by healthcare professionals. Moreover, because no computerized analysis is available for QT monitoring, healthcare professionals must determine when it is appropriate to manually measure QT intervals (eg, when a patient is started on a potentially proarrhythmic drug). The purpose of the present review is to provide ‘best practices’ for hospital ECG monitoring. Randomized clinical trials in this area are almost nonexistent; therefore, expert opinions are based upon clinical experience and related research in the field of electrocardiography. This consensus document encompasses all areas of hospital cardiac monitoring in both children and adults. The emphasis is on information clinicians need to know to monitor patients safely and effectively. Recommendations are made with regard to indications, timeframes, and strategies to improve the diagnostic accuracy of cardiac arrhythmia, ischemia, and QT-interval monitoring. Currently available ECG lead systems are described, and recommendations related to staffing, training, and methods to improve quality are provided.

Successful weaning from mechanical ventilation after coronary angioplasty

Weaning failure can be caused by myocardial ischaemia during the switch from mechanical to spontaneous ventilation. We report ischaemic left ventricular failure and ischaemic mitral insufficiency during weaning. Angiography showed that the coronary vessels were stenosed. Transluminal angioplasty made weaning possible. We conclude that acute ischaemic mitral insufficiency may contribute to cardiac failure during weaning and that angioplasty, by reversing it, can allow successful weaning.

Narcotic and benzodiazepine use after withdrawal of life support: association with time to death?

OBJECTIVE

To determine whether the dose of narcotics and benzodiazepines is associated with length of time from mechanical ventilation withdrawal to death in the setting of withdrawal of life-sustaining treatment in the ICU.

DESIGN

Retrospective chart review.

SETTING

University-affiliated, level I trauma center.

PATIENTS

Consecutive critically ill patients who had mechanical ventilation withdrawn and subsequently died in the ICU during two study time periods.

RESULTS

There were 75 eligible patients with a mean age of 59 years. The primary ICU admission diagnoses included intracranial hemorrhage (37%), trauma (27%), acute respiratory failure (27%), and acute renal failure (20%). Patients died during a median of 35 min (range, 1 to 890 min) after ventilator withdrawal. On average, 16.2 mg/h opiates in morphine equivalents and 7.5 mg/h benzodiazepine in lorazepam equivalents were administered during the time period starting 1 h before ventilator withdrawal and ending at death. There was no statistically significant relationship between the average hourly narcotic and benzodiazepine use during the 1-h period prior to ventilator withdrawal until death, and the time from ventilator withdrawal to death. The restriction of medication assessment in the last 2 h of life showed an inverse association between the use of benzodiazepines and time to death. For every 1 mg/h increase in benzodiazepine use, time to death was increased by 13 min (p = 0.015). There was no relationship between narcotic dose and time to death during the last 2 h of life (p = 0.11).

CONCLUSIONS

We found no evidence that the use of narcotics or benzodiazepines to treat discomfort after the withdrawal of life support hastens death in critically ill patients at our center. Clinicians should strive to control patient symptoms in this setting and should document the rationale for escalating drug doses.

Continuous ST-Segment Monitoring

Continuous ST-segment monitoring has been shown to be beneficial for patients with acute coronary syndromes as well as for other patients in the intensive care unit (ICU). This article reviews the significance and value of continuous ST-segment monitoring with emphasis on the value of 12-lead ST-segment monitoring across the continuum of care from the emergency department, to the cardiac catheterization laboratory, the ICU, and the telemetry unit.

Extubation failure: magnitude of the problem, impact on outcomes, and prevention

Extubation failure, defined as the need for reinstitution of ventilatory support within 24 to 72 hours of planned endotracheal tube removal, occurs in 2 to 25% of extubated patients. The pathophysiologic causes of extubation failure include an imbalance between respiratory muscle capacity and work of breathing, upper airway obstruction, excess respiratory secretions, inadequate cough, encephalopathy, and cardiac dysfunction. Compared with patients who tolerate extubation, those who require reintubation have a higher incidence of hospital mortality, increased length of ICU and hospital stay, prolonged duration of mechanical ventilation, higher hospital costs, and an increased need for tracheostomy. Given the lack of proven treatments for extubation failure, clinicians must be aware of the factors that predict extubation outcome to improve clinical decision making. Risk factors for extubation failure include being a medical, multidisciplinary, or pediatric patient; age greater than 70 years; a longer duration of mechanical ventilation; continuous intravenous sedation; and anemia. Tests designed to assess for upper airway obstruction, secretion volume, and the effectiveness of cough can help to improve prediction of extubation failure. Rapid reinstitution of ventilatory support in patients who fail extubation may improve outcome.

The pulmonary physician in critical care. 10: difficult weaning

The study of patients being weaned from mechanical ventilation has offered new insights into the physiology of respiratory failure. Assessment of the balance between respiratory muscle strength, work and central drive is essential if difficulty in weaning occurs, and optimisation of these elements may improve the success of weaning. Psychological support of patients and the creation of units specialising in weaning have also resulted in a higher success rate.

Palliative care of the chronically critically ill patient

Evidence is accumulating that distressing physical and emotional symptoms are prevalent among patients with critical illness, including those requiring prolonged mechanical ventilation, and that suffering is underestimated and undertreated by caregivers. Although patients and their families rank communication as a preeminent concern, it remains deficient in process and content, even when the illness requires weeks of critical care. Strategies are available to improve symptom management and communication about appropriate goals of care. For the CCI, whose risks of death, disability, and suffering are so high, it is essential that excellent palliative care be provided along with restorative treatment in an integrated way.

Predictors of extubation outcome in patients who have successfully completed a spontaneous breathing trial

BACKGROUND

After patients recovering from respiratory failure have successfully completed a spontaneous breathing trial (SBT), clinicians must determine whether an artificial airway is still required. We hypothesized that cough strength and the magnitude of endotracheal secretions affect extubation outcomes.

METHODS

We conducted a prospective study of 91 adult patients treated in medical-cardiac ICUs who were recovering from respiratory failure, had successfully completed an SBT, and were about to be extubated. A number of demographic and physiologic parameters were recorded with the patient receiving full ventilatory support and during the SBT, just prior to extubation. Cough strength on command was measured with a semiobjective scale of 0 to 5, and the magnitude of endotracheal secretions was measured as none, mild, moderate, or abundant by a single observer. In addition, patients were asked to cough onto a white card held 1 to 2 cm from the endotracheal tube; if secretions were propelled onto the card, it was termed a positive white card test (WCT) result. All patients were then extubated from T-piece or continuous positive airway pressure breathing trials. If 72 h elapsed and patients did not require reintubation, they were defined as successfully extubated.

RESULTS

Ninety-one patients with a mean (+/- SE) age of 65.2 +/- 1.6 years, ICU admission APACHE (acute physiology and chronic health evaluation) II score of 17.7 +/- 0.7, and duration of mechanical ventilation of 5.0 +/- 0.5 days were studied over 100 extubations. Sixteen patients could not be extubated, and 2 patients underwent two unsuccessful extubation attempts, for a total of 18 unsuccessful extubations. Age, severity of illness, duration of mechanical ventilation, oxygenation, rapid shallow breathing index, and vital signs during SBTs did not differ between patients with successful extubations vs patients with unsuccessful extubations. The WCT result was highly correlated with cough strength. Patients with weak (grade 0 to 2) coughs were four times as likely to have unsuccessful extubations, compared to those with moderate-to-strong (grade 3 to 5) coughs (risk ratio [RR], 4.0; 95% confidence interval [CI],1.8 to 8.9). Patients with moderate-to-abundant secretions were more than eight times as times as likely to have unsuccessful extubations as those with no or mild secretions (RR, 8.7; 95% CI, 2.1 to 35.7). Patients with negative WCT results were three times as likely to have unsuccessful extubations as those with positive WCT results (RR, 3.0; 95% CI, 1.3 to 6.7). Poor cough strength and endotracheal secretions were synergistic in predicting extubation failure (Rothman synergy index, 3.7; RR, 31.9; 95% CI, 4.5 to 225.3). Patients with PaO(2)/fraction of inspired oxygen (P:F) ratios of 120 to 200 (receiving mechanical ventilation) were not less likely to be successfully extubated than those with P:F ratios of > 200, but those with hemoglobin levels < or = 10 g/dL were more than five times as likely to have unsuccessful extubations as those with hemoglobin levels > 10 g/dL.

CONCLUSIONS

After patients recovering from respiratory failure have successfully completed an SBT, factors affecting airway competence, such as cough strength and amount of endotracheal secretions, may be important predictors of extubation outcomes. Also, a majority (89%) of medically ill patients with P:F ratios of 120 to 200 (four of five patients with P:F ratios from 120 to 150), values sometimes used to preclude weaning, were extubated successfully.

Do blood transfusions improve outcomes related to mechanical ventilation?

BACKGROUND

Correcting the decrease in oxygen delivery from anemia using allogeneic RBC transfusions has been hypothesized to help with increased oxygen demands during weaning from mechanical ventilation. However, it is also possible that transfusions hinder the process because RBCs may not be able to adequately increase oxygen delivery. In this study, we determined whether a liberal RBC transfusion strategy improved outcomes related to mechanical ventilation.

METHODS

Seven hundred thirteen patients receiving mechanical ventilation, representing a subgroup of patients from a larger trial, were randomized to either a restrictive transfusion strategy, receiving allogeneic RBC transfusions at a hemoglobin concentration of 7.0 g/dL (and maintained between 7.0 g/dL and to 9.0 g/dL), or to a liberal transfusion strategy, receiving RBCs at 10.0 g/dL (and maintained between 10.0 g/dL and 12.0 g/dL). The larger trial was designed to evaluate transfusion practice rather than weaning per se.

RESULTS

Baseline characteristics in the restrictive-strategy group (n = 357) and the liberal-strategy group (n = 356) were comparable. The average durations of mechanical ventilation were 8.3 +/- 8.1 days and 8.3 +/- 8.1 days (95% confidence interval [CI] around difference, - 0.79 to 1.68; p = 0.48), while ventilator-free days were 17.5 +/- 10.9 days and 16.1 +/- 11.4 days (95% CI around difference, - 3.07 to 0.21; p = 0.09) in the restrictive-strategy group vs the liberal-strategy group, respectively. Eighty-two percent of the patients in the restrictive-strategy group were considered successfully weaned and extubated for at least 24 h, compared to 78% for the liberal-strategy group (p = 0.19). The relative risk (RR) of extubation success in the restrictive-strategy group compared to the liberal-strategy group, adjusted for the confounding effects of age, APACHE (acute physiology and chronic health evaluation) II score, and comorbid illness, was 1.07 (95% CI, 0.96 to 1.26; p = 0.43). The adjusted RR of extubation success associated with restrictive transfusion in the 219 patients who received mechanical ventilation for > 7 days was 1.1 (95% CI, 0.84 to 1.45; p = 0.47).

CONCLUSION

In this study, there was no evidence that a liberal RBC transfusion strategy decreased the duration of mechanical ventilation in a heterogeneous population of critically ill patients.