Criteria for weaning from prolonged mechanical ventilation

We retrospectively studied 11 instances of patients requiring prolonged mechanical ventilation. Their spontaneous ventilatory measurements were not useful in judging their ability to wean, since these measurements did not change from the period of unsuccessful weaning to the period of progressive weaning from the ventilator. An adverse factor score and a ventilator score were created to evaluate underlying medical and respiratory problems related to ability to wean. Each score and the sum of the two scores separated patients between unsuccessful and successful weaning periods. We also found that the course and the duration of the entire weaning process could be predicted once progressive weaning had begun. We conclude that the adverse factor score and ventilator score correlate with the ability of patients receiving prolonged mechanical ventilation to wean.     

Course of weaning from prolonged mechanical ventilation after cardiac surgery

In order to determine the temporal pattern of weaning from mechanical ventilation for patients undergoing prolonged mechanical ventilation after cardiac surgery, we performed a retrospective review of 21 patients' weaning courses at our long-term acute care hospital. Using multiple regression analysis of an estimate of individual patients' percentage of mechanical ventilator support per day (%MVSD), we determined that 14 of 21 patients (67%) showed a statistically significant quadratic or cubic relationship between time and % MVSD. These patients showed little or no improvement in their ventilator dependence until a point in time when, abruptly, they began to make rapid progress (a "wean turning point"), after which they progressed to discontinuation of mechanical ventilation in a relatively short period of time. The other 7 patients appeared to have a similar weaning pattern, although the data were not statistically significant. Most patients in the study group weaned from the ventilator through a specific temporal pattern that is newly described herein. Data analysis suggested that the mechanism for the development of a wean turning point was improvement of pulmonary mechanics rather than improvement in gas exchange or respiratory load. Although these observations need to be confirmed by a prospective trial, they may have implications for weaning cardiac surgery patients from prolonged mechanical ventilation, and possibly for weaning a broader group of patients who require prolonged mechanical ventilation.     

长期机械通气患者应用指令频率通气模式撤机的临床效果

目的 探讨指令频率通气（mandatory rate ventilation，MRV）在机械通气患者撤机过程中的临床应用效果。方法 2004年1月至2006年1月ICU病房长期机械通气患者28例，随机分为两组，当患者病情平稳拟行撤机时，一组应用压力支持模式（PSV）进行撤机作为对照，另一组应用MRV模式进行撤机，记录分钟通气量、呼吸频率、撤机过程所用时间和撤机成功例数。结果 应用MRV模式撤机组和应用PSV模式撤机组比较，撤机过程中分钟通气量稳定（P＜0．05），呼吸频率明显减慢（P＜0．05），撤机过程用时明显缩短（P＜0．05），但撤机成功例数比较差异无统计学意义（P〉0．05）。结论 应用MRV模式进行撤机，患者舒适程度好，呼吸稳定，人一机协调性良好，撤机过程缩短，适合临床推广应用。     

床旁电子支气管镜在358例接受机械通气的肝衰竭患者中的应用研究

目的探讨电子支气管镜在接受机械通气的肝衰竭患者中的临床应用价值。方法对358例在ICU接受机械通气的肝衰竭患者进行了床旁电子支气管镜检查,人工气道位置判断,并进行肺泡灌洗、吸痰、气道异物吸出、病原学检查以及可能的气管导管位置调整,最后对其应用价值进行分析。结果 358例患者中,304例合并肺炎经电子支气管镜吸痰及支气管肺泡灌洗等治疗后,明确病原学证据247例(81.25%),比较24 h胸片,明显改善者106例(34.87%);54例(17.76%)通气障碍患者经电子支气管镜检查明确原因,其中27例为人工气道梗阻、痰痂或血痂形成,经电子支气管镜反复吸取,成功解除气道梗阻;21例为气管插管或套管易位、顶端贴气管壁,在电子支气管镜协助下调整或更换套管;6例肝衰竭存在肺不张患者经电子支气管镜吸痰治疗后全部复张。结论针对机械通气的肝衰竭患者,电子支气管镜在直视下吸痰、调整导管位置或留取标本,可有效减少气道出血等并发症的发生,从而安全、有效清除气道内分泌物,及早获得病原学结果,及时指导临床抗生素的应用。     

Tracheal stenosis and failure to wean from mechanical ventilation due to herpetic tracheitis

A 64-year-old man with chronic obstructive pulmonary disease presented with pneumococcal pneumonia that progressed to respiratory failure within one week, requiring mechanical ventilation. Despite a low minute ventilation and clear chest roentgenogram, multiple weaning attempts failed. Bronchoscopy revealed significant narrowing of the distal trachea with erythema, edema, and ulceration of the mucosa. Cytology of tracheal washings was consistent with herpes simplex virus, and the patient was successfully extubated following treatment with intravenous acyclovir. Bronchoscopy following acyclovir therapy demonstrated resolution of the inflammation and narrowing. Herpetic tracheitis is a rarely recognized reversible cause of tracheal stenosis, especially in a nonimmunocompromised patient. It should be suspected in patients without an obvious cause of failure to wean from mechanical ventilation, and can be successfully treated with acyclovir.     

Noninvasive positive-pressure ventilation facilitates tracheal extubation after laryngotracheal reconstruction in children.

Tracheal extubation after laryngotracheal reconstruction in children may be complicated by postoperative tracheal edema and pulmonary dysfunction. The replacement of a tracheal tube in this situation may exacerbate the existing injury to the tracheal mucosa, complicating subsequent attempts at tracheal extubation. We present two cases where noninvasive positive-pressure ventilation was employed to treat partial airway obstruction and respiratory failure in two children following laryngotracheal reconstruction. Noninvasive positive-pressure ventilation served as a bridge between mechanical ventilation via a tracheal tube and spontaneous breathing, providing airway stenting and ventilatory support while tracheal edema and pulmonary dysfunction were resolved. Under appropriate conditions, noninvasive positive-pressure ventilation may be useful in the management of these patients.     

Noninvasive ventilation after intubation and mechanical ventilation.

Patients with chronic airflow obstruction who are difficult to wean from mechanical ventilation are at increased risk of intubation-associated complications and mortality because of prolonged invasive mechanical ventilation. Noninvasive positive pressure ventilation may revert most of the pathophysiological mechanisms associated with weaning failure in these patients. Several randomized controlled trials have shown that use of noninvasive ventilation to achieve earlier extubation in difficult-to-wean patients or in patients who develop respiratory failure after apparently successful extubation can result in reduced periods of endotracheal intubation and complication rates and improved survival. However, this is not a consistent finding, and the currently available published data with outcome as the primary variable are exclusively from patients who had pre-existing lung disease. In addition, the patients were haemodynamically stable, with a normal level of consciousness, no fever and a preserved cough reflex. It remains to be seen whether noninvasive positive pressure ventilation has a role in other patient groups and situations, such as prevention of postextubation failure or unplanned extubation. The technique is, however, a useful addition to the therapeutic armamentarium for a group of patients who pose a significant clinical and economic challenge.     

The effect of a gas leak around the endotracheal tube on the mean tracheal pressure during mechanical ventilation

Infants requiring mechanical ventilation are usually intubated with uncuffed endotracheal tubes, which permit gas to leak between the tube and the trachea. This gas leak may alter the mean pressure transmitted to the trachea by changing the pattern of airway flow and modifying the resistive behavior of the endotracheal tube. To test this hypothesis, we measured mean tracheal pressure, gas flow through the endotracheal tube, and resistance of the tube in rabbits ventilated with and without a leak. We also studied the effect of the tube size and the pattern of ventilation on these measurements. We found that a leak reduced the mean tracheal pressure by 15 to 21% with respect to the mean proximal airway pressure. This reduction was caused by an increased difference between inspiratory and expiratory flow through the endotracheal tube, and by the mean expiratory resistance of the tube being lower than its mean inspiratory resistance. The rabbits with smaller tubes had lower mean tracheal pressures. A ventilatory pattern of short inspiratory times and high peak pressures was associated with a proportionally greater decrease in mean tracheal pressure caused by the leak. These findings suggest that the mean proximal airway pressure, measured at the ventilator, may overestimate the mean tracheal pressure in the presence of a gas leak around the tube. Furthermore, the decrease in mean tracheal pressure caused by the leak may decrease oxygenation despite a constant mean proximal airway pressure.     

Outcomes in post-ICU mechanical ventilation: a therapist-implemented weaning protocol

BACKGROUND: Therapist-implemented protocols have been used to extubate or wean patients in the ICU setting. Barlow Respiratory Hospital (BRH) functions as a center for weaning patients from prolonged mechanical ventilation (PMV) in the post-ICU setting of a long-term acute-care (LTAC) facility. A therapist-implemented patient-specific (TIPS) weaning protocol was developed at BRH to standardize weaning from PMV. STUDY DESIGN: Prospective cohort study with historical control. METHODS: A weaning protocol incorporating the procedures and pace of LTAC weaning was developed using available scientific evidence and expert consensus. After training of staff, collection and analysis of pilot data, and revisions and refinement of the protocol, the TIPS protocol was implemented hospital-wide. It was monitored for outcome, variance, and respiratory care practitioner (RCP) and physician compliance. RESULTS: Forty-six RCPs worked with eight pulmonologists treating 271 consecutive patients admitted for weaning from PMV during an 18-month period. Nineteen patients were excluded from weaning attempts by any method after initial physician evaluation. The remaining 252 patients (9,135 total ventilator days) were compared with a group of 238 patients treated by the same physicians in the 2 years before instituting protocol weaning. Median time to wean declined significantly from 29 days in historical control subjects to 17 days for TIPS protocol patients (p < 0.001). Outcomes (scored at discharge) were comparable for the two groups (TIPS group vs control group): weaned, 54.7% vs 58.4%; ventilator-dependent, 17.9% vs 10.9%; died, 27.4% vs 30.7% (p = 0.10). Variances incurred by physicians and RCPs were 324 and 136, respectively, for the 9,135 ventilator days. CONCLUSIONS: Patients weaned from PMV using a new therapist-implemented protocol at BRH, an LTAC facility specializing in weaning, had significantly shorter time to weaning than historical control subjects, with comparable outcomes. The weaning outcome data collected after the implementation of the TIPS protocol are in fact attributable to its use, as we found a high degree of compliance with the protocol.     

A prospective comparison of IMV and T-piece weaning from mechanical ventilation

Two hundred (200) consecutive medical and surgical patients requiring mechanical ventilation were entered into a prospective randomized trial of weaning by either intermittent mandatory ventilation (IMV) or T-piece. Patients in these groups were of similar age and sex and had the same total ventilation time (TVT). The study design provided equal time for each weaning mode after specific criteria for oxygenation and ventilation were satisfied (PaO2 greater than 55 mm Hg on FIO2 less than 0.5; VE less than 12 L/min and two of the following four parameters: MVV greater than 2 VE, VT greater than 5 ml/kg, FVC greater than 10 ml/kg, NIF less than or equal to -20 cm H2O). Of the original 200 patients 165 were entered into the weaning phase; 35 patients were withdrawn prior to weaning due to the discretion of the attending physician or protocol error. Weaning time was not different between the IMV (5.3 +/- 1.2 h, mean +/- SEM) and T-piece groups (5.9 +/- 1.4 h, p = NS). Of the 165 patients, 155 (93 percent) were weaned successfully by protocol, 79 in the IMV and 76 in the T-piece group. Of 155 patients, 136 (88 percent) were weaned on the first attempt by protocol. Of the 19 who were not weaned, 11 were weaned successfully on the second and five on the third trial; three patients required three-day weans. We conclude that clinically stable patients who require short-term mechanical ventilation and meet standard bedside weaning criteria can be weaned efficiently by protocol using either IMV or T-piece techniques.     

Early mobilization of LVAD recipients who require prolonged mechanical ventilation

Early mobilization and aggressive physical therapy are essential in patients who receive left ventricular assist devices (LVADs) due to long-term, end-stage heart failure. Some of these patients remain ventilator dependent for quite some time after device implantation. We report our regimen of mobilization with the aid of a portable ventilator, in patients with cardiac cachexia and LVAD implantation. Further, we describe the specific physical therapy interventions used in an LVAD patient who required prolonged mechanical ventilation after device implantation. The patient was critically ill for 5 weeks before the surgery and was ventilator dependent for 48 days postoperatively. There were significant functional gains during the period of prolonged mechanical ventilation. The patient was able to walk up to 600 feet by the time he was weaned from the ventilator and transferred out of the intensive care unit. He underwent successful heart transplantation 6 weeks after being weaned from the ventilator We believe that improving the mobility of LVAD patients who require mechanical ventilation has the potential both to facilitate ventilator weaning and to improve the outcomes of transplantation.     

Predicting 3-day and 7-day outcomes of weaning from mechanical ventilation.

OBJECTIVE: To determine the correlation of acute physiology and chronic health evaluation (APACHE) II score and various weaning indexes (WIs) with 3- and 7-day weaning outcomes. DESIGN: Prospective, observational. SETTING: The medical ICU of a teaching, urban hospital. METHODS: The study included 118 adults referred for weaning from mechanical ventilation (MV). Critical care physicians, critical care nurses, and respiratory care practitioners were asked to predict whether it would take < or =3 days, 4 to 7 days, or > or =8 days to wean each patient from MV. The WIs and APACHE II scores were measured or calculated. The causes of respiratory failure, the duration of MV before initiating weaning assessment, and the 3- and 7-day weaning outcomes were obtained. Significance was set at p<0.05. RESULTS: The most common causes of respiratory failure were pneumonia (38 cases) and acute exacerbation of COPD (29 cases). Fifty-seven patients (48%) were successfully weaned from MV within 3 days of weaning assessment, and 67 (57%) were weaned within 7 days. The percentages of correct prediction of 3-day weaning outcome by critical care physicians, critical care nurses, and respiratory care practitioners were 64%, 62%, and 59%, respectively; for 7-day weaning outcome, 60%, 64%, and 58%, respectively. The successfully weaned groups had significantly lower APACHE II scores and higher maximal inspiratory pressures than the unsuccessfully weaned (failure) groups. There were no significant differences between the two groups for the remaining indexes, including rapid shallow breathing, dynamic compliance, static compliance, spontaneous respiratory rate, and the ratio of PaO2 to the fraction of inspired oxygen. CONCLUSIONS: The overall severity of illness as assessed by APACHE II score correlates better with 3- and 7-day weaning outcome than the published WIs.     

Post-ICU mechanical ventilation at 23 long-term care hospitals: a multicenter outcomes study

STUDY OBJECTIVES: This multicenter study was undertaken to characterize the population of ventilator-dependent patients admitted to long-term care hospitals (LTCHs) with weaning programs, and to report treatments, complications, weaning outcome, discharge disposition, and survival in these patients. DESIGN: Observational study with concurrent data collection. SETTING: Twenty-three LTCHs in the United States. PATIENTS: Consecutive ventilator-dependent patients admitted over a 1-year period: March 1, 2002, to February 28, 2003. RESULTS: A total of 1,419 patients were enrolled in the Ventilation Outcomes Study. Median age of patients was 71.8 years (range, 18 to 97.7 years). Patients averaged 6.9 procedures and treatments during the LTCH hospitalization; median length of stay was 40 days (range, 1 to 365 days). Seven of the 10 most frequent complications treated at the LTCH were infections; congestive heart failure and diabetes mellitus were the most common comorbidities requiring treatment. Outcomes of weaning attempts, scored at LTCH discharge, were 54.1% weaned, 20.9% ventilator dependent, and 25.0% deceased. Median time to wean (n = 766) was 15 days (range, 7 to 30 days). Discharge disposition included 28.8% to home, 49.2% to rehabilitation and extended-care facilities, and 19.5% to short-stay acute hospitals. Nearly one third of patients were known to be alive 12 months after admission to the LTCH. CONCLUSIONS: Patients admitted to LTCHs for weaning attempts were elderly, with acute-on-chronic diseases, and continued to require considerable medical interventions and treatments. The frequency and type of complications were not surprising following prolonged and aggressive ICU interventions. In the continuum of critical care medicine, more than half of ventilator-dependent survivors of catastrophic illness transferred from the ICU were successfully weaned from prolonged mechanical ventilation in the setting of an LTCH.     

Factors associated with failure of weaning from long-term mechanical ventilation after cardiac surgery

The purpose of this prospective, quantitative, comparative study, conducted at the 55 bed cardiothoracic intensive care unit of the Heart Institute (InCor), University of Sao Paulo Medical School, was to identify factors involved in the weaning of patients who require long-term (> 10 days) mechanical ventilation after cardiac surgery. The subjects included all patients who underwent open-heart surgery with cardiopulmonary bypass during a 10 month period from April 2000 to January 2001 (n = 946). From this group, 52 (5.7%) patients who required a tracheotomy for the management of long-term mechanical ventilation after cardiac surgery with cardiopulmonary bypass were selected. Pre-, intra- and postoperative data from patients who were not successfully weaned after reintubation and who underwent an elective tracheotomy were compared. Parameters of respiratory mechanics such as respiratory complications, oxygenation, and cardiac, renal, and neurological function were evaluated. Weaning success was defined as the ability of a patient to tolerate 48 hours without pressure or flow support from a mechanical ventilator. A patient was considered to have failed weaning if they died or remained under ventilation for more than 8 weeks. Of the 52 patients studied, 25 were successfully weaned, 21 died, and 6 remained ventilated for more than 8 weeks. We found significant statistical differences (P < 0.05) between the groups with respect to success or failure in LVEF (P = 0.0035), the need for vasoactive agents (P = 0.0018), and renal failure (P = 0.002). Parameters of respiratory mechanics and oxygenation (eg, static airway compliance, airway resistance) did not influence the success or failure of weaning. There was a significant difference in relation to the presence of pneumonia (P = 0.0086) between the two groups. Although neurological complications were more frequent in patients in the weaning success group, the failure group had lower GCS scores, which is indicative of worse prognoses. It is concluded that cardiac dysfunction, the need for dialysis, and pneumonia are determinants for weaning failure in patients undergoing long-term mechanical ventilation after cardiac surgery.     

Respiratory failure and mechanical ventilation: Pathophysiology and methods of promoting weaning

Respiratory failure may be manifested either by impaired gas exchange or by impaired ventilatory function. The latter results in more severe problems in weaning patients from mechanical ventilation. Ventilatory failure may result from inadequate respiratory drive, excessive respiratory workload, inadequate respiratory muscle endurance, or a combination of these factors. Simple bedside tests of ventilatory function are useful for evaluating the severity of respiratory failure and the potential for successful weaning. However, even when the results are discouraging, properly monitored weaning attempts may be successful. Although there are no convincing data to prove the superiority of either the T-piece weaning method or intermittent mandatory ventilation, we prefer to use the T-piece, and describe here a comprehensive approach to weaning the difficult patient. New approaches that have been developed to help wean difficult patients include continuous positive airway pressure breathing (CPAP), pharmacologic interventions (aminophylline and others), nutritional supplementation, inspiratory muscle resistive training, psychiatric interventions, and chronic mechanical ventilation.     

Care of the patient requiring invasive mechanical ventilation

Patients who require prolonged invasive mechanical ventilation pose a unique set of circumstances to the pulmonary and critical care practitioner. This requires a delineation of the primary cause for respiratory failure, and, in most cases, a comprehensive multidisciplinary approach to the treatment of not only the primary disturbance causing respiratory failure, but the consequences that immobility, illness, and prolonged ventilation have on swallowing and ambulatory function, psychosocial interaction, and the ability to wean from mechanical ventilation. The development of multidisciplinary rehabilitative units for patients requiring prolonged mechanical ventilation have showed not only a reduction in hospital costs and lengths of stay, but also an improvement in patient survival, functional status, reduction in ventilator days or need for mechanical ventilation at discharge, and, overall, the achievement of a satisfactory quality of life.     

撤机和撤机技术

机械通气作为一种极为重要的生命支持治疗手段,为原发疾病的治疗创造了条件和争取了时间。但当病因消除或得到控制时,自主呼吸恢复到一定水平后,应及时撤离机械通气,避免造成呼吸机依赖和减少机械通气相关并发症的发生。由于目前对呼吸机的撤离尚缺乏系统的认识以及对撤机过程的最佳方法缺少一个指导性方案,机械通气的撤离已成为临床上面临的重大挑战之一。现就呼吸机的撤离及其相关技术做一综述。     

Positive airway pressure in patients receiving intermittent mandatory ventilation at zero rate. The role in weaning in chronic obstructive pulmonary disease

Over a 20-month period, we treated 180 mechanically ventilated patients in our respiratory intensive care unit. Among these patients, we observed an interesting previously unreported phenomenon in 20 patients with severe chronic obstructive disease. During the weaning from mechanical ventilators of these 20 patients, there was a marked clinical deterioration when the mode of ventilation was changed from intermittent mandatory ventilation (IMV) at zero rate to that of a T-tube setup. To explain this previously unreported observation, we studied and compared nine different intubated patients for possible differences in airway pressure between IMV set up at zero rate and a T tube. We observed that peak airway pressures were greater on IMV at zero rate compared to the peak airway pressures on the T piece in all nine patients. At the end of expiration, seven out of the nine patients had higher airway pressures on IMV at zero rate compared to the T tube. These differences in the peak airway pressures and end-expiratory pressures were statistically significant in both groups. In spite of the obvious limitation of extrapolating the experimental results obtained in one group of patients to explain the clinical observations made in another group of patients, we believe that the higher airway pressures on the IMV system (even without any mechanical ventilation) prevent early collapse of the airways, and this may be of significant importance in successfully weaning patients with COPD.     

Two cases of acute respiratory failure associated with pneumonia requiring mechanical ventilation before diagnosis of amyotrophic lateral sclerosis]

We present two cases of acute respiratory failure requiring mechanical ventilation before diagnosis of amyotrophic lateral sclerosis (ALS). The patients were men of 60 (patient 1) and 74-years old (patient 2), both of whom exhibited acute respiratory failure requiring mechanical ventilation. Diagnoses of ALS were made because of continuous aspiration caused by bulbar palsy in patient 1, and, in patient 2, because of the progressive muscle atrophy that occurred during unsuccessful attempts to wean the patient from ventilatory support. Physicians should be aware of the possibility of ALS in cases of acute respiratory failure, CO2 narcosis, continuous aspiration, and difficulty of weaning from mechanical ventilation.