Update in computer-driven weaning from mechanical ventilation

Weaning from mechanical ventilation is a complex process requiring assessment and interpretation of both objective and subjective clinical parameters. For many years, automated computerised systems for various medical processes, including respiratory management, have been proposed to optimise decision-making and reduce variation amongst clinicians. SmartCare/PS, available since 2003 as a software application for the EvitaXL ventilator (Dr?ger Medical AG & Co. KG, Lübeck, Germany), is one of the first such ventilator systems to be made commercially available. SmartCare/PS can be described as a knowledge-based weaning system, which adjusts pressure support based on measurement of the patient's respiratory status, specifically the spontaneous respiratory rate, tidal volume and end-tidal carbon dioxide with the aim of optimising the weaning process. The primary proposed advantage of this system is an ability to provide management of ventilatory weaning through continuous physiological monitoring and real-time interventions. The relatively small number of available clinical studies indicate the system is able to deliver appropriate ventilation during pressure support weaning from both short-term and prolonged ventilation. Of potential clinical note, a recent study suggested that use of SmartCare/PS might be associated with useful reductions in the duration of weaning compared to existing clinical practice using weaning protocols. One recently published randomised trial supports this conclusion. However, given the known large variation in international critical care ventilatory practices further randomised trials are desirable.     

影响肝移植术后机械通气时间延长的因素分析

目的探讨肝移植术后机械通气时间延长（PMV）患者的临床特征、预后以及影响PMV发生的相关因素。 方法回顾性分析安徽医科大学第一附属医院器官移植中心2016年4月至2021月4月收治的105例成人肝移植患者资料。根据术后机械通气时间是否超过24 h,分为PMV组（39例）和非PMV组（66例）,比较两组患者一般资料、临床特征和预后,单因素分析和Logistic多因素回归模型筛选影响肝移植术后PMV的因素;使用Kaplan-Meier曲线和Log-rank检验进行生存分析。 结果既往上腹部手术史（OR=0.284,95% CI：0.084~0.963,P=0.043）和术前Child-Pugh评分（OR=1.439,95% CI：1.026~2.017,P=0.035）是肝移植术后PMV的独立影响因素。PMV组术后180 d生存率为74.36%,非PMV组为84.85%,两组差异无统计学意义（Log-rank χ2=0.061,P=0.804）。 结论术前有无上腹部手术和Child-Pugh评分是肝移植术后PMV的独立影响因素。PMV继发耐药菌感染发生率高,但不影响肝移植患者的术后6个月生存率。充分处理患者术前合并问题,减少导致PMV的因素,可以尽可能地缩短机械通气时间,使患者获益。     

Evaluation of simple criteria to predict successful weaning from mechanical ventilation in intensive care patients

Background. There is increasing evidence that weaning protocolsimprove outcome from mechanical ventilation, but it is unclearhow best to implement such protocols in large intensive careunits. We evaluated a checklist of simple bedside criteria todetermine whether it could be used reliably to predict successfuldiscontinuation of mechanical ventilation. Methods. We carried out a prospective observational cohort studyin a 12-bedded general intensive care unit (ICU). We developeda checklist of metabolic, cardiorespiratory and neurologicalcriteria that suggested that patients should start the weaningprocess. We performed daily assessments throughout ICU stayand recorded whether the criteria were met. Ultimate ventilatorindependence was used as the reference standard. Results. We studied 325 sequential admissions to the ICU. Datawere available for 98% of patients; 97% of admissions were mechanicallyventilated on admission to ICU. Overall, 205 of the 308 ventilatedpatients (67%) achieved ventilator independence during ICU admission;the other patients died or were transferred ventilated to otherICUs. Eighty-three per cent of the patients who achieved ventilatorindependence met the set criteria. Fulfilling the criteria wasa moderately strong predictor of ultimate ventilator independence:specificity 89%, positive predictive value 94%, positive likelihoodratio (LR) 7.6. When we analysed data by the day from admissionon which patients were examined, the test was a strong predictorof subsequent ventilator independence when criteria were metby day 1 (LR 11.1) or day 2 (LR 6.9), but weaker when met bymore than/equal to 4 days (LR <3). Patients who met criteriaafter more than/equal to 4 days often had prolonged weaningand a high incidence of re-intubation. Patients who achievedventilator independence without fulfilling the criteria (n=35)had a short duration of mechanical ventilation (median 2 days,interquartile range 1–3 days). The most frequent reasonfor failing criteria before ventilator independence was a Pa_O2/FI_O2ratio less than 24 kPa (49% of cases). Conclusions. A simple checklist can assist nurse assessmentof suitability for weaning and could be used as a trigger tocommence a weaning protocol. The day on which criteria are metis a useful way of stratifying patients for likely patternsof weaning. Br J Anaesth 2004; 92: 793–9     

Successful weaning from mechanical ventilation after coronary angioplasty

Weaning failure can be caused by myocardial ischaemia duringthe switch from mechanical to spontaneous ventilation. We reportischaemic left ventricular failure and ischaemic mitral insufficiencyduring weaning. Angiography showed that the coronary vesselswere stenosed. Transluminal angioplasty made weaning possible.We conclude that acute ischaemic mitral insufficiency may contributeto cardiac failure during weaning and that angioplasty, by reversingit, can allow successful weaning.     

Contribution of rib cage and abdominal movement to ventilation for successful weaning from mechanical ventilation

In order to test the hypothesis whether the breathing pattern is helpful in predicting weaning outcome in patients being weaned from mechanical ventilation, 38 patients who underwent operation for esophageal cancer were evaluated at weaning from mechanical ventilation (19 unsuccessful weanings, group U, and 19 successful weanings in age-matched patients, group S). Since all patients initially fullfilled our weaning criteria, ventilatory parameters such as tidal volume, respiratory frequency, minute ventilation, and arterial blood gas analysis showed no significant differences between the groups. The breathing pattern was registered quantitatively by means of respiratory inductive plethysmography at 3 cmH²O (0.3 kPa) of CPAP prior to weaning. The contribution of rib cage movement to tidal volume (%RC) was significantly greater in group U than in group S (P<0.05). Indeed, 84% of the patients in group S showed %RC less than 50%, compared to only 16% of the patients in group U ((P<0.05). The results suggest that the breathing pattern is one important factor in predicting the outcome of weaning in patients after thoraco-abdominal surgery. Diaphragmatic fatigue is suspected to be the mechanism for the increase in the RC component in patients with unsuccessful weaning outcome.     

Inspiratory muscle training to enhance weaning from mechanical ventilation

This report describes the use of specific inspiratory muscle training to enhance weaning from mechanical ventilation in a patient who had failed conventional weaning strategies. A 79-year-old man remained ventilator-dependent 17 days following laparotomy. A program of daily inspiratory muscle training was initiated. The mean training threshold increased progressively during the program and simultaneously the periods of unassisted breathing achieved gradually increased. By day 27, mechanical ventilation was no longer required. Inspiratory muscle training can be implemented effectively in the difficult to wean patient and should be considered for patients who have failed conventional weaning strategies.     

Lung transplantation in patients in mechanical ventilation before transplantation

Mechanical ventilation before lung transplantation has been identified as a risk factor for early death after surgery. However, several studies have reported patient series in which ventilation assistance was given preoperatively without increasing the rates of postoperative complications and death, apart from increasing time of postoperative intubation. The present retrospective analysis of the postoperative course of patients who had been mechanically ventilated before transplantation encompasses a period of 5 years in our hospital. Eight transplants (7 double- and 1 single-lung procedures) were performed. Six patients (75%) required extracorporeal oxygenation during surgery. Three patients (37.5%) died within 30 days of receiving the transplanted lung. The mean time of intubation after the operation was 10.3 days and the mean stay in the postoperative recovery and intensive care unit was 27.5 days. The most common postoperative complications were respiratory colonization (100%), with infection in 3 patients, and reimplantation injury (50%). Pretransplant mechanical ventilation was associated with high risk in the patient series we report; however, the survival rate observed suggest that such patients should be considered acceptable candidates to receive grafts if indicated.     

Early criteria predictive of prolonged mechanical ventilation.

This study was performed to determine if prolonged mechanical ventilation (MV) could be predicted by objective clinical variables present at 48 hours after MV was instituted. During a 3-month period, 49 (54%) of 91 mechanically ventilated surgical intensive care unit patients required MV for 2 or more days. Twelve (24%) of these patients died. Patients requiring 2-13 days of MV had significantly lower alveolar-arterial oxygen gradients (PAO2 - PAO2), PEEP, and FIO2 on MV day 2 compared with patients with MV greater than or equal to 14 days. PAO2 - PAO2 greater than or equal to 175 mm Hg on day 2 in patients without chronic obstructive pulmonary disease (COPD) was 60% sensitive and 91% specific for MV greater than or equal to 14 days. In survivors, a day-2 PAO2 - PAO2 greater than or equal to 175 mm Hg (without COPD) or a GCS score less than or equal to 9 had a 91% positive predictive value and a 96% negative predictive value for MV greater than or equal to 14 days. We conclude that mechanical ventilation for 14 or more days can be accurately predicted at 48 hours after the institution of ventilatory support by these objective criteria.     

Noninvasive ventilation in adult liver transplantation

Noninvasive ventilation (NIV) has proven to be a safe and effective technique in the treatment of respiratory failure complicating various medical and surgical diseases. In recent years, a growing interest has emerged in its adoption for ventilatory assistance in immunocompromised patients, such as those undergoing bone marrow, liver, lung, cardiac, and kidney transplantation. Weaning from the ventilator after liver transplantation can take longer because of unsatisfactory gas exchange during various attempts of T-piece trials. Rapid extubation followed by an immediate NIV application should be considered in this setting to shorten and accelerate the weaning process in those recipients who do not completely fulfill the criteria for safe extubation. By adding the pressure support (PS) mode with a continuous positive end expiratory pressure (PEEP), NIV could prevent the loss of vital capacity and impede severe lung derecruitment following extubation. Clinical experience has shown that properly delivered NIV mostly benefits moderately dyspneic recipients in acute respiratory failure, while it appears less promising and efficient in patients ventilated for extended periods of time. It has proven safe and efficient mainly as (1) a tool to promote an early ventilatory discontinuation and extubation; (2) a prophylactic strategy for preventing postoperative pulmonary complications; and (3) a simple method to start with in cases of acute hypoxic and/or hypercapnic respiratory failure. The improvements in arterial hypoxemia, the decreased ventilatory demand provided with an inspiratory support, as well as the scarcity of hemodynamic repercussions are among the major benefits of this method.     

Acute left ventricular dysfunction during unsuccessful weaning from mechanical ventilation

The authors studied the hemodynamic effects of rapidly weaning from mechanical ventilation (MV) 15 patients with severe chronic obstructive pulmonary disease (COPD) and cardiovascular disease who were recovering from acute cardiopulmonary decompensation. In each patient, 10 min of spontaneous ventilation (SV) with supplemental oxygen resulted in reducing the mean esophageal pressure (X +/- SD, + 5 +/- 3 to -2 +/- 2.5 mmHg, P less than .01) and increasing cardiac index (CI) 3.2 +/- 0.9 to 4.3 +/- 1.3 1/min/M2, P less than .001), systemic blood pressure (BP 77 +/- 12 to 90 +/- 11 mmHg, P less than .001), heart rate (HR 97 +/- 12 to 112 +/- 16 beats/min, P less than .001), and, most importantly, transmural pulmonary artery occlusion pressure markedly increased (PAOPtm 8 +/- 5 to 25 +/- 13 mmHg, P less than .001), mandating a reinstitution of MV. In four patients with left ventricular (LV) catheters, the PAOP correlated with the LV end-diastolic pressure during both MV and SV. Gated blood pool imaging showed SV increased the LV end-diastolic volume index (65 +/- 24 to 83 +/- 32/M2, P less than .002) with LV ejection fraction unchanged. Patients were treated for a mean of 10 days with diuretics, resulting in a reduction of blood volume (4.55 +/- 0.9 1 to 3.56 +/- 0.55 1) and body weight (-5 kg, P less than .001). Subsequently, nine of the 15 patients were weaned successfully from mechanical ventilation with unchanged PAOP.     

The role of dead space ventilation in predicting outcome of successful weaning from mechanical ventilation.

BACKGROUND: The exact mechanism by which tracheostomy results in clinical improvement in respiratory function and liberation from mechanical ventilation remains unknown. Physiologic dead space, which includes both normal and abnormal components of non-gas exchange tidal volume, is a clinical measure of the efficiency of ventilation. Theoretically, tracheostomy should reduce dead space ventilation and improve pulmonary mechanics, thereby facilitating weaning from mechanical ventilation. METHODS: This study compares arterial blood gases (ABG), pulmonary mechanics, including minute ventilation (VE) and dead space ventilation (Vd/Vt) within 24 hours before and after tracheostomy in 45 patients admitted to a surgical intensive care unit. RESULTS: There was no difference noted in patients' ABG or VE. Pre- and posttracheostomy change in Vd/Vt was negligible (50.7 and 10 vs. 51.9 and 11; p = NS). On subgroup analysis, those patients that were weaned from mechanical ventilation with 72 hours of tracheostomy (T3) were compared with those patients weaned from mechanical ventilation 5 days or more after tracheostomy (T+5). Again, no difference was found in pulmonary mechanics or Vd/Vt pre- and posttracheostomy. CONCLUSION: There is minimal improvement in pulmonary mechanics after tracheostomy. The change in physiologic dead space posttracheostomy does not predict the outcome of weaning from mechanical ventilation. Tracheostomy does allow better pulmonary toilet, and easier initiation and removal of mechanical ventilation and control of the upper airway.     

An evaluation of protocolised weaning on the duration of mechanical ventilation

Using a before and after study design, we compared protocolised weaning from mechanical ventilation with usual non-protocolised practice in intensive care. Outcomes (duration of mechanical ventilation, duration of intubation, intensive care stay) and complications (re-intubations, tracheostomy, mortality) were compared between baseline (Phase I) and following implementation of protocolised weaning (Phase II). Over the same period, we collected data in a second (reference) unit to monitor practice changes over time. In the intervention unit, outcomes were longer in Phase II compared with Phase I (all p < 0.005). When adjusted for admission APACHE II score and diagnostic category, only intensive care stay remained significantly longer (p = 0.002). There were significantly more tracheostomies in Phase II (p = 0.004). The reference unit demonstrated no statistically significant differences in study outcomes or complications between Phases. Protocolised weaning did not reduce the duration of mechanical ventilation and was not associated with an increased rate of re-intubation or intensive care unit mortality.     

A successful weaning from mechanical ventilation by diaphragmatic plication for unilateral diaphragmatic paralysis

A patient with unilateral diaphragmatic paralysis (UDP) after cardiac surgery, commonly extubated without any troubles, encounters a serious fetal respiratory complication in a rare case. We had a case of a 68-year-old man under long term mechanical ventilation (MV) because of UDP and phrenic nerve injuries after the replacement of the ascending aorta. After this operation he suffered from mediastinal infection and needed MV for a few days. Thereafter, he was extubated successfully and returned to the ward, but his chest X-p showed right diaphragmatic elevation. Two days after returning to the ward, he developed dyspnea and tachypnea and received MV for two months. We decided to perform diaphragmatic plication (DP) because of long term MV and difficulty in respiratory weaning. The patient was successfully weaned from MV on the 4th postoperative day of the right DP. Pulmonary function test was improved dramatically. In a case of long term MV due to UDP, DP can be one of effective treatments.