Liberation from mechanical ventilation: a decade of progress

Ideology and Palliative Care: Moral Hazards at the Bedside

Palliative care has had a long-standing commitment to teaching medical students and other medical professionals about pain management, communication, supporting patients in their decisions, and providing compassionate end-of-life care. Palliative care programs also have a critical role in helping patients understand medical conditions, and in supporting them in dealing with pain, fear of dying, and the experiences of the terminal phase of their lives. We applaud their efforts to provide that critical training and fully support their continued important work in meeting the needs of patients and families. Although we appreciate the contributions of palliative care services, we have noted a problem involving some palliative care professionals' attitudes, methods of decisionmaking, and use of language. In this article we explain these problems by discussing two cases that we encountered.

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?.

Levine’s Framework in Long-Term Ventilated Patients During the Weaning Course

Within the context of Levine’s conceptual framework, this study evaluated fatigue and protein calorie malnutrition affecting adult, long-term ventilated patients during the weaning process. Levine’s principles of energy and structural integrity provided the basis for an evaluation of the fatigue and prealbumin levels for 11 patients. During the weaning process (1 to 4 weeks), fatigue data were collected at multiple points while prealbumin levels were collected weekly. Statistically significant findings revealed that long-term ventilated patients had distinctive fatigue trends in addition to trends associated with low prealbumin levels, which can affect the patient’s weaning ability.

Nonvocal Ventilated Patients Perceptions of Being Understood

This metasynthesis presents an enlarged interpretation and understanding of nonvocal mechanically ventilated patients’experiences with communication. Peplau’s interpersonal relations theory provided the theoretical framework for the metasynthesis. The final sample included 12 qualitative studies, for a total of 111 participants. The data, methods, and theoretical frameworks were critically interpreted. Commonthreads detected across study participants’individual experiences were synthesized to form a greater understanding of nonvocal ventilated patients’ perceptions of being understood. Five overarching themes were divided into two groups. The first group of themes was categorized as the characteristics of nonvocal ventilated patients’communication experiences. Nonvocal individuals were often not understood, which resulted in loss of control and negative emotional responses. The second group of themes was categorized as the kind of nursing care desired by nonvocal patients in order to be understood. Nonvocal patients wanted nursing care that was delivered in an individualized, caring manner. This facilitated positive interpersonal relations between the patient and the nurse. Findings are discussed in relation to the current state of knowledge on this topic.

Protocol-Driven Ventilator Management in Children: Comparison to Nonprotocol Care

The purpose of this study was to compare ventilator weaning time, time to spontaneous breathing, and overall ventilator hours duration with use of a ventilator management protocol (VMP) versus standard nonprotocol-based care in a pediatric intensive care unit. A multidisciplinary task force developed a comprehensive protocol for ventilator management with four specific phases: initial ventilator set up and adjustment, weaning, minimal settings, and spontaneous mode prior to extubation. Medical records of ventilated patients both before and after protocol implementation were reviewed. A total of 187 patients were studied (89 nonprotocol and 98 VMP patients). No differences were seen between groups in PRISM scores, Murray scores, or oxygenation indices, but VMP patients were significantly younger (P= .03). Ventilator weaning times (P= .005) and time to spontaneous breathing modes (P= .006) were significantly decreased in VMP patients compared to nonprotocol patients, but overall ventilator duration was not significantly different. No significant differences were seen in extubation failure, use of corticosteroids, or use of racemic epinephrine between groups. Use of an institution-specific VMP developed by a multidisciplinary team was associated with significantly reduced ventilator weaning time and time to spontaneous breathing. Further studies are needed.

Weaning of mechanically ventilated chronic obstructive pulmonary disease patients by using non-invasive positive pressure ventilation: A prospective study

BACKGROUND

Chronic obstructive pulmonary disease (COPD) patients frequently pose difficulty in weaning from invasive mechanical ventilation (MV). Prolonged invasive ventilation brings along various complications. Non-invasive positive pressure ventilation (NIPPV) is proposed to be a useful weaning modality in such cases.

OBJECTIVE

To evaluate the usefulness of NIPPV in weaning COPD patients from invasive MV, and compare it with weaning by conventional pressure support ventilation (PSV).

MATERIALS AND METHODS

For this prospective randomized controlled study, we included 50 COPD patients with type II respiratory failure requiring initial invasive MV. Upon satisfying weaning criteria and failing a t-piece weaning trial, they were randomized into two groups: Group I (25 patients) weaned by NIPPV, and group II (25 patients) weaned by conventional PSV. The groups were similar in terms of disease severity, demographic, clinical and biochemical parameters. They were compared in terms of duration of MV, weaning duration, length of intensive care unit (ICU) stay, occurrence of nosocomial pneumonia and outcome.

RESULTS

Statistically significant difference was found between the two groups in terms of duration of MV, weaning duration, length of ICU stay, occurrence of nosocomial pneumonia and outcome.

CONCLUSION

NIPPV appears to be a promising weaning modality for mechanically ventilated COPD patients and should be tried in resource-limited settings especially in developing countries.

A clinical description of extubation failure in patients with primary brain injury

BACKGROUND

Patients with acute brain injury but normal lung function are often intubated for airway protection, but extubation often fails. Currently, no clinical data exist that describe the events leading to extubation failure in this population. We examined the extubation failure rate, reintubation rate, and clinical characteristics of patients whose reason for intubation was a primary neurological injury. We then identified the clinical characteristics of those patients with primary brain injury who were reintubated.

METHODS

We conducted a retrospective review of patients admitted to the neurocritical care unit of a tertiary care hospital from January 2002 to March 2007.

RESULTS

Of 1,265 patients who were intubated because of primary neurological injury of brain, spinal cord, or peripheral nerve, 25 (2%) died before extubation and 767 (61%) were successfully extubated. Tracheostomies were placed in 181 (14%) patients, of which, 77 (6.1%) were completed before a trial of extubation and 104 (8.2%) after extubation failure. A total of 129 (10%) patients were reintubated; 77 (6.1%) were reintubated within 72 h, meeting the definition of extubation failure. The other 52 (4.1%) were intubated after 72 h usually in the setting of pneumonia or decreased mental status. Ninety-nine of the patients reintubated had primary brain injury and resulting encephalopathy. All were successfully reintubated. Most patients intubated as a result of a primary brain injury (981) were successfully extubated. The most common clinical scenario leading to reintubation in these encephalopathic patients was respiratory distress associated with altered mental status [59 patients (59%)]. These patients usually had atelectasis and decreased minute ventilation, independent of fever, pneumonia, aspiration, and increased work of breathing [39 patients (39%)].

CONCLUSION

The extubation failure rate in our neurocritical care unit is low. In patients with encephalopathy and primary brain injury who were reintubated, respiratory distress caused by altered mental status was the most common cause of reintubation. These patients demonstrated signs disrupted ventilation usually with periods of prolonged hypoventilation. Increased work of breathing from lung injury due to pneumonia or aspiration was not the most common cause of reintubation in this population.

Risk factors associated with early reintubation in trauma patients: a prospective observational study

BACKGROUND

After mechanical ventilation, extubation failure is associated with poor outcomes and prolonged hospital and intensive care unit (ICU) stays. We hypothesize that specific and unique risk factors exist for failed extubation in trauma patients. The purpose of this study was to identify the risk factors in trauma patients.

METHODS

We performed an 18-month (January 2008-June 2009) prospective, cohort study of all adult (8 years or older) trauma patients admitted to the ICU who required mechanical ventilation. Failure of extubation was defined as reintubation within 24 hours of extubation. Patients who failed extubation (failed group) were compared with those who were successfully extubated (successful group) to identify independent risk factors for failed extubation.

RESULTS

A total of 276 patients were 38 years old, 76% male, 84% sustained blunt trauma, with an mean Injury Severity Score = 21, Glasgow Coma Scale (GCS) score = 7, and systolic blood pressure = 125 mm Hg. Indications for initial intubation included airway (4%), breathing (13%), circulation (2%), and neurologic disability (81%). A total of 17 patients (6%) failed extubation and failures occurred a mean of 15 hours after extubation. Independent risk factors to fail extubation included spine fracture, airway intubation, GCS at extubation, and delirium tremens. Patients who failed extubation spent more days in the ICU (11 vs. 6, p = 0.006) and hospital (19 vs. 11, p = 0.002). Mortality was 6% (n = 1) in the failed group and 0.4% (n = 1) in the successful extubation group.

CONCLUSIONS

Independent risk factors for trauma patients to fail extubation include spine fracture, initial intubation for airway, GCS at extubation, and delirium tremens. Trauma patients with these four risk factors should be observed for 24 hours after extubation, because the mean time to failure was 15 hours. In addition, increased complications, extended need for mechanical ventilation, and prolonged ICU and hospital stays should be expected for trauma patients who fail extubation.

Field intensive care--weaning and extubation

Injury following ballistic trauma is the most prevalent indication for providing organ system support within an ICU in the field. Following damage control surgery, postoperative ventilatory support may be required, but multiple factors may influence the indications for and duration of invasive mechanical ventilation. Ballistic trauma and surgery may trigger the systemic inflammatory response syndrome (SIRS) and are important causative factors in the development of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). However, their pathophysiological effect on the respiratory system is unpredictable and variable. Invasive mechanical ventilation is associated with numerous complications and the return to spontaneous ventilation has many physiological benefits. Following trauma, shorter periods of ICU sedation-amnesia and a protocol for early weaning and extubation, may minimize complications and have a beneficial effect on their psychological recovery. In the presence of stable respiratory function, appropriate analgesia and favourable operational and transfer criteria, we believe that the prompt restoration of spontaneous ventilation and early tracheal extubation should be a clinical objective for casualties within the field ICU.

Monitoring the mechanically ventilated patient

In the intensive care setting, monitored data relevant to the output, efficiency, and reserve of the respiratory system alert the clinician to sudden untoward events, aid in diagnosis, help guide management decisions, aid in determining prognosis, and enable the assessment of therapeutic response. This review addresses those aspects of monitoring we find of most value in the care of patients receiving ventilatory support. We concentrate on those modalities and variables that are routinely available or easily calculated from data readily collected at the bedside.

Implementing a Ventilator Bundle in a Community Hospital

BACKGROUND

Mercy & Unity Hospitals of Minnesota implemented the ventilator bundle concept as part of an Institute for Healthcare Improvement (IHI) collaborative on improving care in the intensive care unit (ICU).

METHODS

The two hospitals, which function as a single hospital, have a total of 450 beds, and each has a 20-bed ICU. The IHI bundle was composed of (1) head-of-bed elevation, (2) a daily "sedation vacation" along with a readiness-to-wean assessment, (3) peptic ulcer disease prophylaxis, and (4) deep vein thrombosis prophylaxis. Additional interventions likely complementary to the ventilator bundle were a hand hygiene campaign and an oral care protocol.

RESULTS

Overall compliance with the four bundle elements reached 100% by January 2004. At the end of the collaborative, Mercy's VAP rate decreased from 6.1 to 2.70 per 1000 ventilator days, and Unity's VAP rate decreased from 2.66 to 0 per 1000 ventilator days.

DISCUSSION

The all-or-none nature of the bundle may have helped multidisciplinary staff members perceive the project as a systemic change versus a one-time intervention. Staff members needed to implement both structural changes, such as preprinted order sets for ventilator management and sedation, and cultural changes, such as increased collaboration with respiratory therapy.

CONCLUSION

The decrease in VAP provides a promising example of the potential of intervention techniques and bundle implementation in a community hospital.

Weaning from Mechanical Ventilation

Approximately 20% of all mechanically ventilated patients fail their first attempt to wean. Prolonged mechanical ventilation increases morbidity, mortality, and costs. No single weaning parameter predicts patient ability to wean. Weaning studies suggest that daily trials of spontaneous breathing for appropriate patients assured by standing protocol and driven by respiratory care practitioners and/or nurses improve the weaning process and patient outcome.

Lung Function Accurately Predicts Hypercapnia in Patients With Duchenne Muscular Dystrophy

BACKGROUND

In patients with Duchenne muscular dystrophy (DMD), implementation of mechanical ventilation depends on sleep investigation and measurement of CO2 tension. The objective of this cross-sectional study was to determine which noninvasive lung function parameter best predicts nocturnal hypercapnia and diurnal hypercapnia in these patients.

METHODS

According to transcutaneous CO2 (TcCO2) measurement, 114 DMD patients were classified into three groups: nocturnal hypercapnia (n = 38) [group N], diurnal hypercapnia (n = 39), despite nocturnal ventilation (group D), and 24-h normocapnia and spontaneous breathing (n = 37) [group S] as control. TcCO2 tension and lung function variables included vital capacity (VC) and maximal inspiratory pressure (MIP), and breathing pattern variables included tidal volume (Vt) and respiratory rate (RR), measured at the time of group inclusion. The rapid and shallow breathing index (RSBI [RR/Vt]) and Vt/VC ratio were calculated. Areas under the curve from the receiver operating characteristic (ROC) were calculated for those parameters.

RESULTS

Compared to group S, lung function was significantly worse in group N and group D. VC, RR, and RSBI distinguished group S from group N by ROC comparison. Cut-off values of VC < or = 680 mL (ROC, 0.968), MIP < or = 22 cm H2O (ROC, 0.928), and Vt/VC > 0.33 (ROC, 0.923) accurately discriminated group D from group N, but RSBI, RR, and Vt did not.

CONCLUSIONS

Lung function is useful to predict nocturnal hypercapnia in patients with DMD. Moreover, VC < 680 mL is very sensitive to predict daytime hypercapnia.

Predictors of extubation failure in patients with chronic obstructive pulmonary disease

Few studies have focused on extubation outcome in patients with chronic obstructive pulmonary disease (COPD) requiring mechanical ventilation (MV). We conducted a study using prospectively collected data in a cohort of patients with COPD requiring invasive MV to identify variables associated with extubation failure. Use of noninvasive or invasive MV within 48 hours after extubation was defined as extubation failure. A total of 148 patients with COPD were studied. Extubation failure occurred in 35% of studied patients. Using multiple regression analysis, independent predictors of extubation failure were physiologic abnormalities measured by Simplified Acute Physiology Score II above 35 on intensive care unit (ICU) admission (odds ratio [OR], 3.88; 95% confidence interval [CI], 1.65-9.12), home noninvasive MV (OR, 12.99; 95% CI, 2.86-58.89), and sterile endotracheal aspirations on the day of extubation were predictors of success (OR, 0.23; 95% CI, 0.10-0.52). Despite high rate of extubation failure, survival to ICU discharge was 91% of the studied population. Extubation failure in patients with COPD remains high despite a successful spontaneous breathing on T piece. Simplified Acute Physiology Score II at ICU admission, home noninvasive MV, and isolated pathogens on quantitative cultures of tracheobronchial secretions within 72 hours preceding extubation were predictors of extubation failure in the study population.

Association between Adrenal Insufficiency and Ventilator Weaning

RATIONALE

Adrenal insufficiency is a common disorder in critically ill patients with mechanical ventilation and is usually associated with higher mortality and poor clinical outcome.

OBJECTIVES

To determine whether stress dose corticosteroid supplementation can improve ventilator weaning and clinical outcome in patients with adrenal insufficiency.

METHODS

A prospective, randomized, placebo controlled, double-blinded study was conducted in the intensive care unit of a tertiary teaching hospital. A total of 93 mechanically ventilated patients were enrolled in the ventilator weaning trial. Adrenal function was assessed in all patients. Patients with adrenal insufficiency were randomized to the treatment group (50 mg intravenous hydrocortisone every 6 h) and the placebo group.

MEASUREMENTS AND MAIN RESULTS

The successful ventilator weaning percentage was significantly higher in the adequate adrenal reserve group (88.4%) and in the stress dose hydrocortisone treatment group (91.4%) than in the placebo group (68.6%). The weaning period was shorter in the hydrocortisone treatment group than in the placebo group. No significant adverse effects were observed in the corticosteroid treatment group.

CONCLUSIONS

For patients with respiratory failure, early identification of adrenal insufficiency and appropriate supplementation with stress dose hydrocortisone increase the success of ventilator weaning and shortens the weaning period.

Does taking endurance into account improve the prediction of weaning outcome in mechanically ventilated children?

INTRODUCTION

We conducted the present study to determine whether a combination of the mechanical ventilation weaning predictors proposed by the collective Task Force of the American College of Chest Physicians (TF) and weaning endurance indices enhance prediction of weaning success.

METHOD

Conducted in a tertiary paediatric intensive care unit at a university hospital, this prospective study included 54 children receiving mechanical ventilation (> or = 6 hours) who underwent 57 episodes of weaning. We calculated the indices proposed by the TF (spontaneous respiratory rate, paediatric rapid shallow breathing, rapid shallow breathing occlusion pressure [ROP] and maximal inspiratory pressure during an occlusion test [Pimax]) and weaning endurance indices (pressure-time index, tension-time index obtained from P(0.1) [TTI1] and from airway pressure [TTI2]) during spontaneous breathing. Performances of each TF index and combinations of them were calculated, and the best single index and combination were identified. Weaning endurance parameters (TTI1 and TTI2) were calculated and the best index was determined using a logistic regression model. Regression coefficients were estimated using the maximum likelihood ratio (LR) method. Hosmer-Lemeshow test was used to estimate goodness-of-fit of the model. An equation was constructed to predict weaning success. Finally, we calculated the performances of combinations of best TF indices and best endurance index.

RESULTS

The best single TF index was ROP, the best TF combination was represented by the expression (0.66 x ROP) + (0.34 x Pimax), and the best endurance index was the TTI2, although their performance was poor. The best model resulting from the combination of these indices was defined by the following expression: (0.6 x ROP) - (0.1 x Pimax) + (0.5 x TTI2). This integrated index was a good weaning predictor (P < 0.01), with a LR+ of 6.4 and LR+/LR- ratio of 12.5. However, at a threshold value < 1.3 it was only predictive of weaning success (LR- = 0.5).

CONCLUSION

The proposed combined index, incorporating endurance, was of modest value in predicting weaning outcome. This is the first report of the value of endurance parameters in predicting weaning success in children. Currently, clinical judgement associated with spontaneous breathing trials apparently remain superior.

High body mass index and long duration of intubation increase post-extubation stridor in patients with mechanical ventilation

Approximately 20% of mechanically ventilated patients experience post-extubation stridor (PES) and reintubation, which subsequently may lead to an increased risk of morbidity and mortality. The risk of PES development is significantly higher in obese patients. Low air leakage between the endotracheal tube and the trachea, following cuff deflation, may indicate a higher risk for the development of PES. The aim of this study is to identify the relationship between body mass index (BMI) and PES using the cuff-leak test in patients intubated in the respiratory intensive care unit. A total of 67 consecutive intubations on 56 different ventilated patients were included in this study. The mean age was 63.6 +/- 12.1 years and 84% of the patients were male. PES developed in seven patients (10.4%). The mean cuff-leak volume was 395 +/- 187 ml in non-PES patients and 240 +/- 93 ml in PES patients (p = 0.023). The mean BMI was 36 +/- 13 kg/m2 in PES patients and 24 +/- 7 kg/m2 in non-PES patients (p = 0.046). BMI > 26.5 kg/m2 (OR: 1.2), low cuff-leak volume (< 283 ml) and mechanical ventilation required for more than 5 days (OR: 0.9) were independent variables for PES occurrence. We therefore suggest that non-obese patients, short-term intubated patients and those having a high air leakage around the endotracheal tube could be extubated without much difficulty.

Weaning prediction: esophageal pressure monitoring complements readiness testing

Several variables are recommended for identifying if a patient is ready for a trial of weaning from mechanical ventilation, but there is no agreement as to whether monitoring any variable during the trial enhances patient management. To determine whether repeated measurements of esophageal pressure throughout a trial are more reliable than measurements of esophageal pressure or frequency-to-VT ratio during the first minute of the trial, we studied 60 patients. A trend index that quantified esophageal pressure swings over time was more reliable than the first-minute measurements: sensitivity, 0.91, and specificity, 0.89. Area under receiver operating characteristic curve for trend index (0.94) was greater than for first-minute measurement of esophageal pressure (0.44, p < 0.05) and tended to be greater than that for frequency-to-VT ratio (0.78, p = 0.13). The likelihood ratio was highest for the trend index (8.2, p < 0.05). The advantage of the trend index may be related to the progressive increase in esophageal pressure throughout a failed weaning trial, whereas breathing pattern changed little after 2 minutes of spontaneous breathing. In conclusion, continuous monitoring of esophageal pressure swings during a spontaneous breathing trial provides additional guidance in patient management over tests used for deciding when to initiate weaning.

Pressões respiratórias máximas e capacidade vital: comparação entre avaliações através de bocal e de máscara facial

INTRODUÇÃO: A medida das pressões respiratórias máximas e a capacidade vital são importantes na avaliação da função pulmonar, no entanto, variações metodológicas podem interferir na interpretação dos resultados obtidos. OBJETIVO: Comparar os valores das pressões respiratórias máximas e da capacidade vital, obtidos através de bocal e de máscara facial. MÉTODO: Foram estudados 30 pacientes (16 homens), com idade de 55,9 ± 15,7 anos, em período pré-operatório de cirurgia abdominal. As variáveis pressão inspiratória máxima, pressão expiratória máxima e capacidade vital foram avaliadas através de um bocal rígido achatado e de uma máscara facial, em ordem randomizada. RESULTADOS: A avaliação com máscara facial não alterou de forma significativa os valores de capacidade vital e pressão inspiratória máxima, porém a pressão expiratória máxima foi significantemente menor do que quando avaliado com bocal rigido. A presença de escape aéreo ao redor da máscara durante a medida da pressão expiratória máxima foi observada em 60% das avaliações. Quando consideradas apenas as medidas de pressão expiratória máxima avaliadas sem a presença de escape de ar, os valores com o uso da máscara foram maiores do que os com o bocal. CONCLUSÃO: A avaliação da pressão inspiratória máxima e capacidade vital pode ser realizada com uso de máscara facial, sem interferência nos resultados obtidos. A avaliação da pressão expiratória máxima através de máscara facial mostrou-se adequado quando foi possível evitar o escape de ar ao redor da máscara, porém a grande prevalência de vazamentos e a conseqüente redução dos valores obtidos na avaliação tornam seu uso limitado.

Mechanical Ventilation

Mechanical ventilation is the second most frequently performed therapeutic intervention after treatment for cardiac arrhythmias in intensive care units today. Countless lives have been saved with its use despite being associated with a greater than 30% in-hospital mortality rate. As life expectancies increase and people with chronic illnesses survive longer, artificial support with mechanical ventilation is also expected to rise. In one survey, over half of senior internal medicine residents reported their training on mechanical ventilation as inadequate, whereas the majority of critical care nurses reported having received no formal education on its use. Technological advances resulting in the availability of sleeker ventilators with graphic waveform displays and new modes of ventilation have challenged the bedside clinicians to incorporate this new data along with evidenced-based research into their daily practice. A review of current thoughts on mechanical ventilation and weaning is presented.

Protocol-driven ventilator weaning reduces use of mechanical ventilation, rate of early reintubation, and ventilator-associated pneumonia

BACKGROUND

Mechanical ventilation is the defining event of intensive care unit management. To reduce use, a literature-based protocol was introduced to facilitate weaning. The effect of protocol-driven ventilator weaning on ventilator use, ventilator-associated pneumonia (VAP), and intensive care unit (ICU) length of stay (LOS) is described in a survey of 2 years' activity in a multidisciplinary surgical ICU.

METHODS

Data were gathered from April to September 2000 and from April to September 2002 before and after introduction of nurse/therapist-driven weaning. VAP was identified by chest radiography, clinical presentation, Gram's stains, and cultures from tracheal aspirates or bronchoalveolar lavage. Infection control practitioners diagnosed VAP. Failed extubation was defined as reintubation within 72 hours.

RESULTS

Overall, there was a 2:1 ratio of male patients to female patients. The total number of patients and days of mechanical ventilation increased, but the use ratio (ventilator days/ICU days) fell from 0.47 to 0.33. Patients failing extubation fell from 43 (in 2000) to 25 (in 2002). From these patients, 17 cases of VAP occurred in 2000 and 5 in 2002. Mean age (40 years), Injury Severity Score (24), and ICU LOS (5.7-7.4 days; p = not significant) were unchanged in injured patients. ICU discharge was frequently delayed because of the need for subsequent respiratory care.

CONCLUSION

Protocol-driven weaning reduces use of mechanical ventilation and VAP. Injured and general surgical patients show reduction in complications, but shorter ICU LOS depends on resources elsewhere in the health care system.

Anesthesia and sleep

Although both general anesthesia and naturally occurring sleep depress consciousness, distinct physiological differences exist between the two states. Recent lines of evidence have suggested that sleep and anesthesia may be more similar than previously realized. Localization studies of brain nuclei involved in sleep have indicated that such nuclei are important in anesthetic action. Additional observations that regional brain activity during anesthesia resembles that in the sleeping brain have raised the possibility that anesthesia may exert its effects by activating neuronal networks normally involved in sleep. In animals, behavioral interactions between sleep and anesthesia appear to support these mechanistic similarities. Rat studies demonstrate that sleep debt accrued during prolonged wakefulness dissipate during anesthesia. Moreover, anesthetic potency is subject both to circadian effects and to the degree of prior sleep deprivation. Such interactions may partly explain anesthetic variability among patients. Finally, sleep and anesthesia interact physiologically. Endogenous neuromodulators known to regulate sleep also alter anesthetic action, and anesthetics cause sleep with direct administration into brain nuclei known to regulate sleep. Together, these observations provide new research directions for understanding sleep regulation and generation, and suggest the possibility of new clinical therapies both for patients with sleep disturbances and for sleep deprived patients receiving anesthesia.

The neurologic assessment and treatment of the “difficult to extubate” patient

Neurologic issues are involved in the patient who is difficult to wean. Assessing the patient and performing a complete neurologic examination are important when developing a successful weaning strategy. The neurologist contributes to this process by providing expertise in the various neurologic conditions and skill in performing a thorough neurologic examination.

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.

Automatic tube compensation-assisted respiratory rate to tidal volume ratio improves the prediction of weaning outcome

OBJECTIVE

To assess whether the respiratory rate to tidal volume ratio (RVR) measured while receiving automatic tube compensation (ATC) [RVRATC] would have a better predictive value as a weaning measure than unassisted RVR.

DESIGN

Prospective cohort study.

SETTING

General ICU of a tertiary-care university hospital.

PATIENTS

Forty-three patients who received mechanical ventilation for > 24 h and were considered ready for weaning.

INTERVENTIONS

All patients underwent a 60-min spontaneous breathing trial (SBT) [positive end-expiratory pressure of 5 cm H(2)O; ATC, 100%]. Patients tolerating the trial (n = 35) were extubated immediately. The following parameters were measured at the onset and end of the SBT: RVR, RVRATC, peak airway pressure (Paw), airway occlusion pressure, and minute ventilation. The outcome measure was successful extubation (ability to maintain spontaneous breathing for > 48 h).

MEASUREMENTS AND RESULTS

Median age was 55 years (range, 25 to 88 years), median APACHE (acute physiology and chronic health evaluation) II score was 15.5 (range, 3 to 29), and median duration of mechanical ventilation prior to the SBT was 7 days (range, 1 to 40 days). Extubation was successful in 25 patients (72%). There were no significant differences in baseline characteristics between patients successfully extubated (group 1) and those requiring reintubation. On multivariate analysis, RVRATC measured at 60 min (RVR(60)ATC) was most predictive of successful extubation (p = 0.03). The area under the receiver operator characteristic curve was also highest for RVR(60)ATC (0.81 +/- 0.03) as compared to RVR (0.77 +/- 0.03), RVRATC (0.75 +/- 0.04), and RVR measured at 60 min (0.69 +/- 0.05). The ratio of RVR(60)ATC to Paw was the best predictor (0.84 +/- 0.02).

CONCLUSIONS

RVRATC measured at the end of the SBT was the best predictor of successful extubation. A new ratio (ratio of RVRATC to Paw) was most predictive and deserves further study.

Expanding a performance improvement initiative in critical care from hospital to system

BACKGROUND

Concern about the expense and effects of intensive care prompted the development and implementation of a hospital-based performance improvement initiative in critical care at North Shore University Hospital, Manhasset, New York, a 730-bed acute care teaching hospital. THE HOSPITAL-BASED PERFORMANCE IMPROVEMENT INITIATIVE IN CRITICAL CARE: The initiative was intended to use a uniform set of measurements and guidelines to improve patient care and resource utilization in the intensive care units (ICUs), to establish and implement best practices (regarding admission and discharge criteria, nursing competency, unplanned extubations, and end-of-life care), and to improve performance in the other hospitals in the North Shore-Long Island Jewish Health System. In the medical ICU, the percentage of low-risk (low-acuity) patients was reduced from 42% to 22%. ICU length of stay was reduced from 4.6 days to 4.1 days.

IMPLEMENTING THE CRITICAL CARE PROJECT SYSTEMWIDE

A system-level critical care committee was convened in 1996 and charged with replicating the initiative. By and large, system efforts to integrate and implement policies have been successful. The critical care initiative has provided important comparative data and information from which to gauge individual hospital performance.

DISCUSSION

Changing the critical care delivered on multiple units at multiple hospitals required sensitivity to existing organizational cultures and leadership styles. Merging organizational cultures is most successful when senior leadership set clear expectations that support the need for change. The process of collecting, trending, and communicating quality data has been instrumental in improving care practices and fostering a culture of safety throughout the health care system.

Variations in the measurement of weaning parameters: a survey of respiratory therapists

OBJECTIVES

Respiratory therapists differ in the methods used to obtain weaning parameters. A questionnaire survey was conducted to better characterize those differences.

DESIGN

A questionnaire survey was conducted among respiratory therapists from nine hospitals in the Los Angeles area. The four-page, 32-question instrument was self-administered and anonymous. Responses were tabulated for analysis.

SETTING

Respondents from nine hospitals, three hospitals with residency training programs and six community hospitals without training programs in the Los Angeles area.

PARTICIPANTS

One hundred two respiratory therapists.

RESULTS

There was no universally acknowledged group of weaning parameters, although four parameters were named by > 90%. There was wide variation in methods used to obtaining weaning parameters. Almost all (91%) obtained measurements with the patients breathing their current fraction of inspired oxygen, but there was great variability in the ventilator mode used to collect these parameters (T-tube, continuous positive airway pressure, pressure support), with an equally wide range of pressures added to each mode (0 to 10 cm H(2)O). There was great variation in the time (< 1 to > 15 min) before recording weaning parameters. Measurement of parameters was done either with bedside instruments or read from the ventilator display. The maximal inspiratory pressure had great variation in the duration of airway occlusion (< 1 to 20 s), with the most frequent time frame being 2 to 4 s. Differences were noted between therapists from the same hospital as well as between hospitals.

CONCLUSIONS

There is great variation among respiratory therapists when obtaining weaning parameters. This calls for further standardization of the measurement of weaning parameters.

A pilot study to investigate any relationship between sustained maximal inspiratory pressure and extubation outcome

OBJECTIVE

To establish whether any relationship exists between extubation outcome and sustained maximal inspiratory pressures (SMIP).

DESIGN AND SETTING

Prospective clinical study in the 7-bed general intensive care unit of a university hospital.

SUBJECTS

Twenty-seven intubated adults who were deemed ready for extubation were enrolled.

MEASUREMENTS

Standard respiratory parameters and inspiratory muscle function data (ie, SMIP and peak maximal inspiratory pressures [MIP]) were recorded before extubation.

RESULTS

SMIP was found to be significantly greater in those who were successfully extubated than in those who underwent a failed extubation (P <.01). Receiver operating characteristic curves for SMIP data indicated that a cutoff point of 57.5 pressure time units would give a sensitivity and specificity of 1.0 for extubation outcome prediction. Peak MIP was also significantly greater in those successfully extubated (P =.04); a cutoff point of 17.5 cm H(2)O gave a sensitivity of 1.0 and a specificity of 0.5.

CONCLUSIONS

In this study, peak MIP was not specific enough to be clinically useful as a predictor of extubation outcome. SMIP was associated with extubation outcome with equally high sensitivity and specificity and may therefore have a role in outcome prediction.

Sleep inducing effects of propofol microinjection into the medial preoptic area are blocked by flumazenil

The intravenous anesthetic, propofol, has been shown to increase sleep when microinjected into the medial preoptic area (MPA) of the rat. Similar increases in sleep have also been observed with triazolam, pentobarbital and ethanol microinjection. Together, these findings implicate the MPA as an important anatomic site mediating the effects of sedatives on naturally occurring sleep. Although the molecular mechanism by which propofol in the MPA acts to induce sleep is unclear, potentiating effects on the GABA(A) receptor complex may play a role. To assess this possibility, we microinjected propofol alone, and in combination with the benzodiazepine receptor antagonist flumazenil, into the MPA. At a dose of 0.76 microg, flumazenil had no effect on sleep when given alone, and completely blocked the increase in sleep caused by a 40-ng dose of propofol although it did not affect the increase in sleep caused by an 80-ng dose of propofol. These data suggest that the sleep inducing property of propofol is in part mediated by direct or indirect actions on the GABA(A)-benzodiazepine receptor complex.

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.

A comparison of human and machine-based predictions of successful weaning from mechanical ventilation

PURPOSE

To evaluate the ability of an appropriately trained neural network to correctly interpret a set of weaning parameters to predict the liberation of a patient from mechanical ventilation, and to contrast these predictions with those of human experts restricted to the same limited set of physiologic data.

METHODS

For each set of weaning parameters, a prediction was made by multiple realizations of a neural network and six expert volunteers.

RESULTS

The percentage of correct predictions made by the neural network when the decision threshold was set to 0.5 (range 0-1) was 83.3 +/- 4.2 (mean +/- SD) and that for the experts was 83.3 +/- 4.7. Predictions by the network when the threshold was 0.5 had a sensitivity of 0.83 and a specificity of 0.84, compared with 0.90 and 0.77, respectively, for the experts. However, sensitivity and specificity comparable to those of the human experts could be obtained by adjusting the decision threshold of the network predictor so that only the most clearly ventilator-dependent patients would not be given a trial of extubation.

CONCLUSION

When both are restricted to the same limited set of patient data, appropriately trained neural networks can be as effective as human experts in predicting whether weaning from mechanical ventilation will be successful.

Capnometric recirculation gas tonometry and weaning from mechanical ventilation

The aim of this study was to describe changes in regional intramucosal PCO(2) (Pr(CO(2)) measured with capnometric recirculation gas tonometry [CRGT]) in patients with acute respiratory failure, who proceed from mechanical ventilation to weaning. In addition, we compared the predictive power for the weaning outcome of CRGT measurements obtained during mechanical ventilation to the frequency/ tidal volume (f/VT) ratio. A total of 24 patients (31 weaning trials) were included in the study, but four of the 24 patients (17%) were excluded because of extubation failure. Of the remaining 27 weaning trials in 20 patients, 12 (44%) were unsuccessful. Changes observed in patients with weaning failure (increase in Pr(CO(2)) from 60.4 +/- 15.0 mm Hg in mechanical ventilation to 67.4 +/- 21.0 mm Hg, in weaning) were significantly different (p = 0.046) from those observed in patients with weaning success (fall in Pr(CO(2)) from 61.5 +/- 15.0 mm Hg in mechanical ventilation to 56.3 +/- 16.7 mm Hg in weaning). However, absolute values of Pr(CO(2)) were not significantly different between patients with weaning success and failure, neither during mechanical ventilation (success, 61.5 +/- 15.0 versus failure, 60.4 +/- 15.0 mm Hg, p = 0.848) nor during weaning (success, 56.3 +/- 16.7 versus failure, 67.4 +/- 21.0 mm Hg, p = 0.135). The best single predictor for weaning outcome was the f/VT ratio measured early during weaning (area under the curve: 0.844 +/- 0.081; adjusted odds ratio for threshold value </= 105: 42.0, 95% CI 3.8 to 469.1, p = 0.002). CRGT could confirm a significant increase in Pr(CO(2)) during weaning in patients who finally failed the weaning trial. However, differences between patients with weaning success and failure were small and CRGT did not replace or improve the predictive power of the f/VT ratio for weaning outcome.