Predicting extubation failure after successful completion of a spontaneous breathing trial

OBJECTIVE: To derive a clinical prediction rule that uses bedside clinical variables to predict extubation failure (reintubation within 48 h) after a successful spontaneous breathing trial. METHODS: This prospective observational cohort study was performed at the Northwestern Memorial Hospital in Chicago, Illinois, which is a large tertiary-care university hospital. Among 673 consecutive patients who received mechanical ventilation during a 15-month period, 122 were ventilated for at least 2 days and did not undergo withdrawal of support or tracheostomy. These patients were followed after extubation to identify those who were reintubated within 48 h (extubation failure). We used logistic regression analysis to identify variables that predict reintubation, and we used bootstrap resampling to internally validate the predictors and adjust for overoptimism. RESULTS: Sixteen (13%) of the 122 patients required reintubation within 48 h. Three clinical variables predicted reintubation: moderate to copious endotracheal secretions (p = 0.001), Glasgow Coma Scale score < or =10 (p = 0.004), and hypercapnia (P(aCO(2)) > or = 44 mm Hg) during the spontaneous breathing trial (p = 0.001). Using logistic regression and bootstrap resampling to adjust for overfitting, we derived a clinical prediction rule that combined those 3 clinical variables (area under the receiver operating characteristic curve 0.87, 95% confidence interval 0.74-0.94). CONCLUSIONS: With our clinical prediction rule that incorporates an assessment of mental status, endotracheal secretions, and pre-extubation P(aCO(2)), clinicians can predict who will fail extubation despite a successful spontaneous breathing trial.     

Work of breathing during successful spontaneous breathing trial

Objective

The aim of this study was to evaluate the work of breathing (WOB) behavior during a 120-minute successful spontaneous breathing trial (SBT) with T-tube trial, and its predictive value for extubation outcome.

Design

A prospective cohort study.

Setting

2 medical-surgical intensive care units.

Patients

Fifty-one consecutive patients mechanically ventilated for more than 48 hours after a successful SBT were extubated based on the institutional protocol and followed for the occurrence of postextubation respiratory distress during 48 hours.

Measurements and Main Results

All cases were serially monitored during 120 minutes of SBT using the respiratory monitoring system Ventrak 1500 (Medical Novametrix Systems, Wallingford, CT). Successful extubation occurred in 38 (74.5%) of 51 of the sample. Respiratory and hemodynamic parameters, APACHE II score, sex, days on mechanical ventilation, and cause of respiratory failure were unable to predict extubation outcome. The WOB significantly increased during SBT in extubation failure patients (WOB at 1st minute 0.24 ± 0.06 J/L vs WOB at 120th minute = 0.39 ± 0.07 J/L; P < .01) when compared to successfully extubated patients (WOB at 1st minute 0.21 ± 0.08 J/L vs WOB at 120th minute = 0.24 ± 0.11 J/L; P = .12).The WOB variation was able to predict extubation outcome only after the 90th minute of SBT (extubation failure = 0.35 ± 0.08 J/L vs extubation success = 0.22 ± 0.11 J/L; P = .01).

Conclusion

An increase in the WOB could predict extubation failure during a T-tube trial of 120 minutes.     

Initial setting of high-flow nasal oxygen post extubation based on mean inspiratory flow during a spontaneous breathing trial

PurposeHigh flow nasal cannula (HFNC) is commonly used post-extubation in intensive care (ICU). Patients' comfort during HFNC is affected by flow rate. The study aims to describe the relationship between pre-extubation inspiratory flow requirements and the post-extubation flow rates on HFNC that maximises patient's comfort.MethodsThis was an observational, retrospective study conducted in a university-affiliated ICU. We included patients extubated following successful spontaneous breathing trial (SBT). During the SBT we recorded variables including inspiratory flow. Patients who passed the SBT were extubated onto HFNC. HFNC was titrated from 20 L/min and increased in steps of 10 L/min, up to 60 L/min. At each step, patient's level of comfort was assessed. Fraction of inspired oxygen was titrated to maintain oxygen saturation 92–97%.ResultsNineteen participants were enrolled in the study. There was a significant positive correlation between mean inspiratory flow pre-extubation and the flow setting on HFNC which achieved the best comfort post-extubation (r² 0.88; p < 0.001). Overall, greatest comfort was observed for HFNC flows between 30 and 40 L/min but with individual variability.ConclusionMeasuring mean inspiratory flow during an SBT allows for individualised setting of HFNC flow rate immediately post-extubation and achieves the greatest comfort and interface tolerance.     

自主呼吸试验在慢性阻塞性肺病患者撤离人工气道中的作用

目的：探讨自主呼吸试验（SBT）对机械通气的慢性阻塞性肺病（COPD）患者脱离呼吸机、拔出气管插管时间的影响。方法：采用规范的SBT方法拔出气管插管的COPD患者26例（男性19例,女性7例）列入本研究,作为SBT组。回顾性分析未采用SBT方法拔出气管插管的机械通气COPD患者28 例（男性24例,女性4例）,作为No-SBT组。比较两组患者机械通气时间、拔出气管插管时间（拔管时间）,拔管后气管插管复插率（拔出气管插管48h内）心及PaO2,PaCO2血清白蛋白,血红蛋白。结果：两组患者的年龄 (P=0.683)、机械通气时间(P=0.167)差异无显著性,但是SBT组拔出气管插管的时间（60min）与No-SBT组(40—540min)比较差异有显著意义（P=0.0001）。SBT组和No-SBT组患者拔出气管插管后,需无创通气辅助的患者均为3例（P=0.717）,48h内再次气管插管患者前者为2例（2/24）,后者为3例（3/28）（P=0.900）,再次气管插管的原因均为气道分泌物排出不畅。结论：对COPD患者,在撤离呼吸机、拔出气管插管的过程中采用规范SBT方法可以明显地缩短拔管时间,而且未增加气管插管的复插率。     

Hypercapnia test as a predictor of success in spontaneous breathing trials and extubation

BACKGROUND: The ventilatory capacity of the respiratory neuromuscular system can be studied with the hypercapnia test. OBJECTIVE: To determine whether decreased response to the hypercapnia test is associated with failure to pass a spontaneous breathing trial (SBT) or extubation failure. METHODS: We studied 103 intubated patients ready for SBT. We used a hypercapnia test in which we approximately doubled the dead space and thus caused re-inhalation of expired air. We calculated 3 ratios: the ratio of P(0.1) (airway occlusion pressure 0.1 s after the onset of inspiratory effort) during hypercapnia test to baseline P(0.1); the ratio of the change in minute volume [DeltaV(E)] to the change in P(aCO(2)) (we call this ratio the hypercapnic ventilatory response); and the ratio of the change in P(0.1) [DeltaP(0.1)] to the change P(aCO(2)) (we call this ratio the hypercapnic-respiratory-drive response). RESULTS: Thirty-six patients failed the SBT, and 11 patients failed extubation. The mean values for the SBT/extubation-success group, the extubation-failure group, and the SBT-failure group, respectively, were: ratio of hypercapnia-test P(0.1) to baseline P(0.1): 4.3 +/- 2.7, 3.7 +/- 1.3, and 3.0 +/- 1.8 (P = .03); hypercapnic ventilatory response: 0.60 +/- 0.35 L/min/mm Hg, 0.50 +/- 0.26 L/min/mm Hg, and 0.31 +/- 0.21 L/min/mm Hg (P < .001); hypercapnic respiratory-drive response: 0.48 +/- 0.24 cm H(2)O/mm Hg, 0.42 +/- 0.19 cm H(2)O/mm Hg, and 0.27 +/- 0.15 cm H(2)O/mm Hg (P < .001). For predicting SBT/extubation success, the sensitivities and specificities, respectively, were: ratio of hypercapnia-test P(0.1) to baseline P(0.1) 0.80 and 0.47; hypercapnic ventilatory response 0.86 and 0.53; hypercapnic respiratory-drive response 0.82 and 0.55. CONCLUSIONS: The SBT/extubation-failure patients had less response to the hypercapnia test than did the SBT/extubation-success patients, and the hypercapnia test was not useful in predicting SBT or extubation success.     

自主呼吸试验期间B型钠尿肽变化百分比对有创机械通气患者脱机结局预测价值的Meta分析

目的探讨自主呼吸试验（SBT）期间B型钠尿肽水平变化百分比（BNP%）对有创机械通气患者的预测价值。 方法检索PubMed、Embase、Medline、Ovid、Cochrane Central Register of Controlled Trails和the Information Sciences Institute Web of Science从建库开始到2018年3月31日发表的有关BNP%预测有创机械通气患者脱机结局文献。采用Quasas-2工具对文献进行质量评价,采用MetaDiSc软件进行异质性分析,并计算合并诊断比值比（DOR）、合并敏感度、合并特异度、合并阳性似然比（PLR）及合并阴性似然比（NLR）。同时绘制合并受试者工作特征（SROC）曲线,获得曲线下面积。 结果纳入5篇文献,共213名患者。Meta分析结果显示,合并DOR为22.33 [95%置信区间（CI）（9.25,53.91）],合并敏感度为85%[95%CI（0.78,0.91）],合并特异度为80%[95%CI（0.68,0.90）],合并PLR为3.72 [95%CI（2.11,6.55）],合并NLR为0.18 [95%CI（0.12,0.28）]。且合并DOR、合并敏感度、合并特异度、合并PLR、合并NLR分析均提示无明显异质性（P均> 0.1,I²均< 50%）,SROC曲线下面积为0.913。 结论BNP%对SBT期间有创机械通气患者脱机结局预测价值的诊断准确度高。     

Deadspace to tidal volume ratio predicts successful extubation in infants and children

OBJECTIVE: Using a modification of the Bohr equation, single-breath carbon dioxide capnography is a noninvasive technology for calculating physiologic dead space (V(D)/V(T)). The objective of this study was to identify a minimal V(D)/V(T) value for predicting successful extubation from mechanical ventilation in pediatric patients. DESIGN: Prospective, blinded, clinical study. SETTING: Medical and surgical pediatric intensive care unit of a university hospital. PATIENTS: Intubated children ranging in age from 1 wk to 18 yrs. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Forty-five patients were identified by the pediatric intensive care unit clinical team as meeting criteria for extubation. Thirty minutes before the planned extubation, each patient was begun on pressure support ventilation set to deliver an exhaled tidal volume of 6 mL/kg. After 20 mins on pressure support ventilation, an arterial blood gas was obtained, V(D)/V(T) was calculated, and the patient was extubated. Over the next 48 hrs, the clinical team managed the patient without knowledge of the preextubation V(D)/V(T) value. Of the 45 patients studied, 25 had V(D)/V(T) < or =0.50. Of these patients, 24 of 25 (96%) were successfully extubated without needing additional ventilatory support. In an intermediate group of patients with V(D)/V(T) between 0.50 and 0.65, six of ten patients (60%) successfully extubated from mechanical ventilation. However, only two of ten patients (20%) with a V(D)/V(T) > or =0.65 were successfully extubated. Logistic regression analysis revealed a significant association between lower V(D)/V(T) and successful extubation. CONCLUSIONS: A V(D)/V(T) < or =0.50 reliably predicts successful extubation, whereas a V(D)/V(T) >0.65 identifies patients at risk for respiratory failure following extubation. There appears to be an intermediate V(D)/V(T) range (0.51-0.65) that is less predictive of successful extubation. Routine V(D)/V(T) monitoring of pediatric patients may permit earlier extubation and reduce unexpected extubation failures.     

Interobserver agreement rate of the spontaneous breathing trial

Purpose

During the mechanical ventilation weaning process, the spontaneous breathing trial (SBT) is the confirmatory test of patients' capability to breathe unassisted. However, the SBT interobserver agreement rate (its reliability) is unknown, and our objective was to evaluate it.

Materials and Methods

This is a prospective, multicentric and observational study. Patients were included when the SBT criteria were fulfilled. Two physicians and 2 respiratory therapists (RTs) rated each SBT. The SBT interobserver agreement was measured using κ statistic and also the percentage of agreement with its 95% credible interval (CrI) calculated by a Bayesian inference.

Results

Ninety-three distinct physicians and 91 distinct RTs rated 130 SBTs. The κ coefficient was 0.46 for physicians and 0.57 for RT, indicating a moderate interobserver agreement rate. The percentage of agreement was 87.7% between physicians (95% CrI, 81.0%-92.3%) and 86.2% between RT (95% CrI, 79.2%-91.1%). The physicians' and RT' percentage of agreement were not statistically different (P = .71).

Conclusions

The SBT interobserver agreement rate is only moderate for physicians and RT. The percentage of agreement between 2 different SBT observers is 79.2% to 92.3%. Therefore, a relevant percentage of patients will have different extubation decisions depending on the SBT observer.     

Influence of different release times on spontaneous breathing pattern during airway pressure release ventilation

OBJECTIVE: Airway pressure release ventilation (APRV) is a ventilatory mode with a time cycled change between an upper (P(high)) and lower (P(low)) airway pressure level. APRV is unique because it allows unrestricted spontaneous breathing throughout the ventilatory cycle. We studied the influence of different release times (time of P(low)) on breathing pattern and gas exchange in patients during partial mechanical ventilation. SETTING: Mixed intensive care unit in a university hospital. PATIENTS: Twenty-eight patients were included in the study. Nine patients suffering from acute lung injury (ALI), 7 patients with a history of chronic obstructive pulmonary disease (COPD) and 12 patients with nearly normal lung function, ventilated for non-respiratory reasons (postoperatively), were studied prior to extubation. INTERVENTIONS: At constant pressure levels and a pre-set airway pressure release rate of 12/min, P(low) was diminished and P(high) was prolonged in four steps of 0.5 s. Each respiratory setting was studied for 20 min after a steady state period had been achieved. MEASUREMENTS AND MAIN RESULTS: We measured gas exchange and respiratory mechanics. The different time intervals of P(high) and P(low) had only minor effects on the actual spontaneous inspiration and expiration times, but the proportion of spontaneous breathing on total ventilation increased when the duration of P(low) was decreased. Gas exchange was almost unaffected by the interventions despite a significant increase in mean airway pressure. However, when P(low) was set to only 0.5 s an increase in PaCO(2) occurred in patients with COPD and ALI, probably due to a decrease in mechanical ventilatory support. CONCLUSIONS: Airway pressure release ventilation is an open system which allows patients to maintain the "time control" over the respiratory cycle independent of the chosen duration for P(high) and P(low).     

自主呼吸试验在撤机中的应用

目的 对应用自主呼吸试验(SBT)撤机方式与逐渐降低机械通气支持水平撤机方式成功拔管的患者进行比较,以寻找最佳撤机方式.方法 选择57例机械通气患者,病情稳定后通过撤机试验前评估,然后准备撤机.采用前后对照的方法将患者分为两组,2004年6月-2005年12月的21例患者作为对照组,采用逐渐降低机械通气支持水平的撤机方式拔管;2006年1月-2007年3月的36例患者作用为试验组,采用SBT的撤机方式拔管.分别观察两组患者的机械通气时间、住重症监护病房(ICU)时间、呼吸机相关性肺炎(VAP)发生率、48 h内再插管率、ICU病死率.结果 试验组与对照组的机械通气时间分别为(59.45±37.1)h和(111.4±59.8)h(P=0.001),住ICU时间分别为(8.0±5.5)d和(15.3±14.3)d(P=0.034),VAP发生率分别为16.7%和38.0%(P=0.070),48 h内再插管率分别为19.4%和5.0%(P=0.253),ICU病死率分别为25.0%和24.0%(P=0.920).结论 SBT的撤机方式比逐渐降低机械通气支持水平的撤机方式具有机械通气时间和住ICU时间短的优点,而两组VAP发生率、48 h内再插管率、ICU病死率基本相同.     

A comparison of two methods to perform a breathing trial before extubation in pediatric intensive care patients

OBJECTIVE: To compare the percentage of infants and children successfully extubated after a trial of breathing performed with either pressure support or T-piece. DESIGN: Prospective and randomized study. SETTING: Three medical-surgical pediatric intensive care units (PICUs). PATIENTS: Two hundred fifty-seven consecutive infants and children who received mechanical ventilation for at least 48 h and were deemed ready to undergo a breathing trial by their primary physician. INTERVENTIONS: Patients were randomly assigned to undergo a trial of breathing in one of two ways: pressure support of 10 cmH2O or T-piece. Bedside measurements of respiratory function were obtained immediately before discontinuation of mechanical ventilation and within the first 5 min of breathing through a T-piece. The primary physicians were unaware of those measurements, and the decision to extubate a patient at the end of the breathing trial was made by them. MEASUREMENTS AND MAIN RESULTS: Of the 125 patients in the pressure support group, 99 (79.2%) completed the breathing trial and were extubated, but 15 of them (15.1%) required reintubation within 48 h. Of the 132 patients in the T-piece group, 102 (77.5%) completed the breathing trial and were extubated, but 13 of them (12.7%) required reintubation within 48 h. The percentage of patients who remained extubated for 48 h after the breathing trial did not differ in the pressure support and T-piece groups (67.2% versus 67.4%, p=0.97). CONCLUSIONS: In infants and children mechanically ventilated, successful extubation was achieved equally effectively after a first breathing trial performed with pressure support of 10 cmH2O or a T-piece.     

Suppression of spontaneous breathing during high-frequency jet ventilation

The effect of ventilatory frequency of high-frequency jet ventilation (HFJV) from 1 to 5 Hz, apart from changes in thoracic volume, on spontaneous breathing activity was studied in Yorkshire piglets under pentobarbital anesthesia. The highest P_aCO₂ at which the animals did not breathe against the ventilator (apnea point) was established either by changing minute volume of ventilation or by adding CO₂ to the respiratory gas. The higher the apnea point, the higher the suppression of spontaneous breathing activity was assumed to be. If the apnea point was searched for by changing minute volume a progressive increase of suppression of spontaneous respiratory activity was found at ventilatory rates of 3 Hz or more, concomitantly with a rise in end-expiratory pressure (P_EE). In case the tidal volume was kept constant, increase of ventilatory rate resulted in a tremendous increase of lung volume, together with considerably higher levels of P_EE. When under these conditions the apnea point was searched for by adding CO₂ to the respiratory gas a much higher CO₂-drive was needed for spontaneous breathing and therefore a much stronger inhibition of spontaneous breathing was concluded. By placing the animals in a body box in which pressure could be varied, thoracic volume could be kept constant during HFJV. When thoracic volume was kept constant in this way a constant tidal volume at increasing jet frequencies resulted in only a slight increase in suppression of spontaneous breathing.We conclude that the increase in lung volume is a major factor in suppressing central respiratory activity during HFJV. Jet frequency by itself might be an additional suppressive factor. Airway CO₂ did not seem to have an important effect.     

The role of spontaneous breathing during mechanical ventilation

The tremendous progress in microprocessor-driven ventilator technology over the last years has facilitated the introduction of a broad variety of different ventilatory modes into the clinical practice of mechanical ventilation. Many of these newer modalities are designed for partial ventilatory support, which might reflect the complexity of the issue of patient ventilator interactions when spontaneous breathing activity is present compared to controlled mechanical ventilation. There are reasons to believe that allowing some degree of spontaneous breathing activity during mechanical ventilation is useful not only to gradually withdraw ventilatory assistance in the process of weaning but also to avoid some of the adverse effects of mechanical ventilation in the early phase of acute respiratory failure when classically controlled modes of ventilation are used. It is the aim of this article to review the effects of preserved spontaneous breathing activity during mechanical ventilation with different ventilatory modalities in acute respiratory failure patients.     

The impact of spontaneous breathing during mechanical ventilation

PURPOSE OF REVIEW: In patients with acute respiratory distress syndrome, controlled mechanical ventilation is generally used in the initial phase to ensure adequate alveolar ventilation, arterial oxygenation, and to reduce work of breathing without causing further damage to the lungs. Although introduced as weaning techniques, partial ventilator support modes have become standard techniques for primary mechanical ventilator support. This review evaluates the physiological and clinical effects of persisting spontaneous breathing during ventilator support in patients with acute respiratory distress syndrome. RECENT FINDINGS: The improvements in pulmonary gas exchange, systemic blood flow and oxygen supply to the tissue which have been observed when spontaneous breathing has been maintained during mechanical ventilation are reflected in the clinical improvement in the patient's condition. Computer tomography observations demonstrated that spontaneous breathing improves gas exchange by redistribution of ventilation and end-expiratory gas to dependent, juxtadiaphragmatic lung regions and thereby promotes alveolar recruitment. Thus, spontaneous breathing during ventilator support counters the undesirable cyclic alveolar collapse in dependent lung regions. In addition, spontaneous breathing during ventilator support may prevent increase in sedation beyond a level of comfort to adapt the patient to mechanical ventilation which decreases duration of mechanical ventilator support, length of stay in the intensive care unit, and overall costs of care giving. SUMMARY: In view of the recently available data, it can be concluded that maintained spontaneous breathing during mechanical ventilation should not be suppressed even in patients with severe pulmonary functional disorders.     

Suppression of spontaneous breathing during high-frequency jet ventilation

Conditions which suppress spontaneous breathing activity during high-frequency jet ventilation (HFJV) were analysed in Yorkshire piglets under pentobarbital anesthesia. The highest P_aCO₂ at which the animals did not breathe against the ventilator (apnea point) was established during different patterns of ventilation, either by changing the minute volume or by adding CO₂ to the inspiratory gas. Arterial oxygen tension was maintained throughout the study above 80 mm Hg. An elevation of ventilatory rate increased the apnea point, suggesting a progressive suppression of spontaneous breathing. This suppression did not depend on the amount of lung stretch during insufflation, because at higher rates lower tidal volumes were used. Suppression also appeared to be independent of insufflatory flow, i.e. the velocity of lung stretch. At higher frequencies end-expiratory airway pressure (P_EE) increased and there appeared to be a positive relationship between the apnea point and P_EE. In a separate series this positive relationship between the apnea point and P_EE was confirmed. A hysteresis effect in this relationship, however, suggests that other than jet frequency, lung volume rather than positive end-expiratory pressure (PEEP) is a major determinant of suppression of spontaneous breathing activity during HFJV.     

Intrapulmonary percussive ventilation superimposed on spontaneous breathing: a physiological study in patients at risk for extubation failure

Purpose  

Intrapulmonary percussive ventilation (IPV) is a high-frequency ventilation modality that can be superimposed on spontaneous breathing. IPV may diminish respiratory muscle loading and help to mobilize secretions. The aim of this prospective study was to assess the short-term effects of IPV in patients at high risk for extubation failure who were receiving preventive non-invasive ventilation (NIV) after extubation.