慢性阻塞性肺疾病的家庭无创通气治疗

家庭无创通气（HMV）通常采用无创正压通气（NPPV）,已经明确HMV治疗神经肌肉障碍性疾病,胸廓畸形和睡眠呼吸障碍性疾病导致的呼吸衰竭可以延长生命,缓解症状和改善生活质量。HMV治疗慢性阻塞性肺疾病（COPD）的结论不尽一致,HMV治疗重度COPD患者可缓解呼吸困难,多数研究表明HMV可改善生活质量,减少COPD急性加重。近期的研究表明,HMV时采用较高吸气压力支持水平治疗伴二氧化碳潴留的稳定期COPD患者,可以改善气体交换,肺功能和呼吸困难,减少COPD急性加重,而且具有较好的治疗依从性。     

Application of fiberoptic bronchscopy in patients with acute exacerbations of chronic obstructive pulmonary disease during sequential weaning of invasive-noninvasive mechanical ventilation

BACKGROUND:

Early withdrawal of invasive mechanical ventilation (IMV) followed by noninvasive MV (NIMV) is a new strategy for changing modes of treatment in patients with acute exacerbations of chronic obstructive pulmonary disease (AECOPD) with acute respiratory failure (ARF). Using pulmonary infection control window (PIC window) as the switch point for transferring from invasive to noninvasive MV, the time for early extubation can be more accurately judged, and therapy efficacy can be improved. This study aimed to prospectively investigate the clinical effectiveness of fiberoptic bronchscopy (FOB) in patients with AECOPD during sequential weaning of invasive-noninvasive MV.

METHODS:

Since July 2006 to January 2011, 106 AECOPD patients with ARF were treated with comprehensive medication and IMV after hospitalization. Patients were randomly divided into two groups according to whether fiberoptic bronchoscope is used (group A, n=54) or not (group B, n=52) during sequential weaning from invasive to noninvasive MV. In group A, for sputum suction and bronchoalveolar lavage (BAL), a fiberoptic bronchoscope was put into the airway from the outside of an endotracheal tube, which was accompanied with uninterrupted use of a ventilator. After achieving PIC window, patients of both groups changed to NIMV mode, and weaned from ventilation. The following listed indices were used to compare between the groups after treatment: 1) the occurrence time of PIC, the duration of MV, the length of ICU stay, the success rate of weaning from MV for the first time, the rate of reventilation and the occurrence rate of ventilator-associated pneumonia (VAP); 2) the convenience and safety of FOB manipulation. The results were compared using Student’s t test and the Chi-square test.

RESULTS:

The occurrence time of PIC was (5.01±1.49) d, (5.87±1.87) d in groups A and B, respectively (P<0.05); the duration of MV was (6.98±1.84) d, (8.69±2.41) d in groups A and B, respectively (P<0.01); the length of ICU stay was (9.25±1.84) d, (11.10±2.63) d in groups A and B, respectively (P<0.01); the success rate of weaning for the first time was 96.30%, 76.92% in groups A and B, respectively (P<0.01); the rate of reventilation was 5.56%, 19.23% in groups A and B, respectively (P<0.05); and the occurrence rate of VAP was 3.70%, 23.07% in groups A and B, respectively (P<0.01). Moreover, it was easy and safe to manipulate FOB, and no side effect was observed.

CONCLUSIONS:

The application of FOB in patients with AECOPD during sequential weaning of invasive-noninvasive MV is effective in ICU. It can decrease the duration of MV and the length of ICU stay, increase the success rate from weaning MV for the first time, reduce the rate of reventilation and the occurrence rate of VAP. In addition, such a method is convenient and safe in patients of this kind.KEY WORDS: Acute exacerbations of chronic obstructive pulmonary disease, Acute respiratory failure, Mechanical ventilation, Sequential weaning of invasive-noninvasive ventilation, Fiberoptic bronchscopy, Bronchoalveolar lavage, Pulmonary infection control window, Side effect, Success rate     

慢性阻塞性肺疾病患者机械通气时间的影响因素

目的 探讨影响慢性阻塞性肺疾病(COPD)患者机械通气(MV)时间的危险因素.方法 回顾性研究128例COPD合并呼吸衰竭患者插管前及通气过程中的临床指标.单凶素分析采用t检验、秩和检验及X2检验.将统计意义的变量导人多元逐步togis～e回归分析.结果 NV>7 d、14 d和21 d的患者比例分别为61%、20%和9%.MV>7 d、14 d和21 d的患者,分别与MV≤7 d、14 d和21 d的患者进行比较,在COPD病史、吸烟指数、肺功能和合并症等方面差异无统计学意义(P<0.05).多因素回归分析显示,APACHEⅡ评分是影响MV>7 d的独立危险因子(OR:2.3;95%CI:1.2～5.7,P=0.02);影响MV>21 d的危险因素是休克(OR:0.7;95%CI:1.0～1.9,P=0.04)和低白蛋白水平(OR:0.4,95%CI:0.2～0.8,P=0.003);机械通气相关性肺炎(VAP)是影响机械通气时间最重要的危险因素(P<0.05).结论 APACHEⅡ评分、血清白蛋白水平、发生休克或VAP是影响COPD患者机械通气时间的主要因素.     

纤维支气管镜在慢性阻塞性肺疾病机械通气序贯撤机中的应用

目的 观察应用纤维支气管镜(纤支镜)辅助慢性阻塞性肺疾病急性发作(AECOPD)并发呼吸衰竭患者机械通气时序贯撤机的临床疗效.方法 将106例AECOPD并发呼吸衰竭接受经口气管插管和机械通气者随机分为2组:应用纤支镜辅助有创-无创机械通气序贯撤机组(A组,54例)和有创-无创机械通气序贯撤机组(B组,52例).A组纤支镜从气管导管外进入气道,操作过程中不间断使用呼吸机.两组患者一般治疗相同,达肺部感染控制窗( PIC)后拔除气管导管改无创机械通气模式,然后依情况决定撤机.治疗后比较两组病例下列指标:(1)PIC出现时间、总机械通气时间、住ICU时间、首次撤机成功率、再上机率、呼吸机相关肺炎(VAP)发生率;(2)纤支镜操作对该类患者的安全性.结果 A组和B组PIC出现时间分别为(5.01±1.49)d、(5.87±1.87)d,p＜0.05;总机械通气时间分别为(6.98±1.84)d、(8.69±2.41)d,P＜0.01;住ICU时间分别为(9.25±1.84)d、(11.10±2.63)d,P＜0.01;首次撤机成功率分别为96.30％、76.92％,P＜0.01;再上机率分别为5.56％、19.23％,P＜0.05;VAP发生率分别为3.70％、23.07％,P＜0.01.治疗组纤支镜操作简便、安全,未发生明显不良反应.结论 AECOPD并发呼吸衰竭进行机械通气患者应用纤支镜辅助治疗可缩短机械通气时间,增加撤机成功率,减少VAP的发生,且方便安全.     

序贯机械通气治疗慢性阻塞性肺疾病急性加重期合并肺性脑病的疗效观察

目的探讨序贯机械通气治疗慢性阻塞性肺疾病急性加重期(AECOPD)合并肺性脑病的临床疗效。方法将64例AECOPD患者随机分为2组,每组32例。对照组给予有创机械通气,观察组给予有创-无创序贯机械通气,比较2组患者临床疗效。结果观察组显效率显著高于对照组;观察组有创通气时间及住呼吸重症监护室(RICU)时间均明显短于对照组,且住院费用明显少于对照组。结论有创-无创序贯机械通气治疗AECOPD合并肺性脑病患者较传统有创通气疗效确切,且能显著缩短通气时间,降低VAP发生率,减少住院费用,改善患者预后及生活质量。     

膈肌增厚分数指导慢性阻塞性肺疾病机械通气患者撤机的临床研究

目的：通过床旁超声评估慢性阻塞性肺疾病机械通气患者的膈肌功能,明确膈肌超声指标对撤机的指导价值。方法研究对象为2015年2月至2015年8月浙江大学附属邵逸夫医院危重医学科诊治的需行有创机械通气的慢性阻塞性肺疾病患者。在患者符合临床撤机筛查条件后进行自主呼吸试验1h。自主呼吸试验结束时采用床旁 B 型超声评估患者膈肌指标,包括吸气末膈肌厚度（ diaphragmatic thickness at the end of inspiration, DTei）、呼气末膈肌厚度（ diaphragmatic thickness at the end of expiration, DTee）、膈肌增厚分数（ diaphragmatic thickening fraction, DTF）,同时记录浅快呼吸指数及其他生理参数。对符合临床撤机标准者进行撤机。统计分析膈肌超声指标与撤机结果之间的关系,采用接受者操作特征曲线（ ROC）分别评价DTF和浅快呼吸指数对撤机成功的预测价值。结果共43例患者纳入本研究,其中撤机成功25例,撤机失败18例。撤机成功组和失败组的撤机前参数如年龄、体质量指数、急性生理学和慢性健康状况评分Ⅱ、机械通气时间、心率、平均动脉压、分钟通气量、氧合指数等差异均无统计学意义（ P＞0.05）。膈肌静态指标DTei、 DTee在撤机成功组和失败组之间差异无统计学意义（ P＞0.05）。撤机成功组撤机前的DTF （39.66±13.22）％vs.（23.84±8.85）％显著高于撤机失败组（P＜0.05）。以DTF≥30％为标准预测撤机成功,敏感度84％,特异度83.33％, ROC曲线下面积0.872（95％ CI：0.759～0.985）。撤机成功组撤机前的浅快呼吸指数（62.74±26.05） vs.（98.89±35.44）显著低于撤机失败组（ P＜0.05）。以浅快呼吸指数≤105为标准预测撤机成功,敏感度92％,特异度38.89％, ROC 曲线下面积0.804（95％ CI：0.669～0.940）。结论膈肌超声指标DTF对慢性阻塞性肺疾病机械通气患者撤机时机选择和撤机结果预测具有指导作用。     

Noninvasive ventilation for chronic obstructive pulmonary disease

Noninvasive positive-pressure ventilation (NPPV) should be considered a standard of care to treat COPD exacerbations in selected patients, because NPPV markedly reduces the need for intubation and improves outcomes, including lowering complication and mortality rates and shortening hospital stay. Weaker evidence indicates that NPPV is beneficial for COPD patients suffering respiratory failure precipitated by superimposed pneumonia or postoperative complications, to allow earlier extubation, to avoid re-intubation in patients who fail extubation, or to assist do-not-intubate patients. NPPV patient-selection guidelines help to identify patients who need ventilatory assistance and exclude patients who are too ill to safely use NPPV. Predictors of success with NPPV for COPD exacerbations have been identified and include patient cooperativeness, ability to protect the airway, acuteness of illness not too severe, and a good initial response (within first 1-2 h of NPPV). In applying NPPV, the clinician must pay attention to patient comfort, mask fit and air leak, patient-ventilator synchrony, sternocleidomastoid muscle activity, vital signs, hours of NPPV use, problems with patient adaptation to NPPV (eg, nasal congestion, dryness, gastric insufflation, conjunctival irritation, inability to sleep), symptoms (eg, dyspnea, fatigue, morning headache, hypersomnolence), and gas exchange while awake and asleep. For severe stable COPD, preliminary evidence suggests that NPPV might improve daytime and nocturnal gas exchange, increase sleep duration, improve quality of life, and possibly reduce the need for hospitalization, but further study is needed. There is consensus, but without strong supportive evidence, that COPD patients who have substantial daytime hypercapnia and superimposed nocturnal hypoventilation are the most likely to benefit from NPPV. Adherence to NPPV is problematic among patients with severe stable COPD.     

序贯机械通气治疗慢性阻塞性肺疾病并发呼吸衰竭病人的护理

[目的]评价序贯机械通气治疗慢性阻塞性肺疾病（COPD）呼吸衰竭的效果。[方法]选择19例行气管插管机械通气COPD病人作为序贯治疗组,以同步间歇指令通气＋压力支持＋呼气末正压通气（SIMV＋PSV＋PEEP）方式行机械通气,待＂肺部感染控制窗＂出现后拔除气管插管,改为经面罩双水平正压无创通气,渐至脱机。另选病情相同的19例为对照组,行常规有创通气,最后以PSV方式至撤机。动态观察两组病例有创通气时间、呼吸机相关肺炎（VAP）发生例数、总机械通气时间、住院时间、住院费用。[结果]序贯治疗组可有效减少有创通气时间,从而减少VAP发生率,大大降低住院费用,缩短住院时间,减轻病人经济负担。[结论]无创正压通气（NIPPV）作为COPD病人从有创机械通气脱机过渡具有较好的效果,细心护理和严密监测是保证COPD病人实施有创—无创序贯机械通气的前提。     

序贯机械通气治疗慢性阻塞性肺疾病并发呼吸衰竭病人的护理

[目的]评价序贯机械通气治疗慢性阻塞性肺疾病(COPD)呼吸衰竭的效果.[方法]选择19例行气管插管机械通气COPD病人作为序贯治疗组,以同步间歇指令通气 压力支持 呼气末正压通气(SIMV PSV PEEP)方式行机械通气,待"肺部感染控制窗"出现后拔除气管插管,改为经面罩双水平正压无创通气,渐至脱机.另选病情相同的19例为对照组,行常规有创通气,最后以PSV方式至撤机.动态观察两组病例有创通气时间、呼吸机相关肺炎(VAP)发生例数、总机械通气时间、住院时间、住院费用.[结果]序贯治疗组可有效减少有创通气时间.从而减少VAP发生率,大大降低住院费用,缩短住院时间,减轻病人经济负担.[结论]无创正压通气(NIPPV)作为COPD病人从有创机械通气脱机过渡具有较好的效果,细心护理和严密监测是保证COPD病人实施有创一无创序贯机械通气的前提.     

Intrapulmonary haematoma complicating mechanical ventilation in patients with chronic obstructive pulmonary disease

Intrapulmonary haematomas occurred during mechanical ventilation of two patients with advanced chronic obstructive pulmonary disease and bullous dystrophy. In both cases, the haematomas were revealed by blood-stained aspirates, a fall in haemoglobin level, and the appearance of radiological opacities. Haematoma occurrence in the area of a bulla which recently has rapidly increased in size, suggests that the haematoma is due to the rupture of stretched vessels embedded in the wall of the bulla.     

浅快呼吸指数对COPD机械通气病人撤机的意义

目的研究浅快呼吸指数(RSBI,f/Vt)对慢性阻塞性肺病(COPD)机械通气病人撤机的指导意义.方法对符合临床撤机条件的132例COPD机械通气病人,在无任何呼吸支持条件下测定RSBI值,然后进行撤机试验,并对符合撤机条件者进行撤机,观察RSBI值与撤机结果之间的关系.结果撤机成功组80例,RSBI值为64.97±26.84bpm/L;撤机失败组52例,RSBI值为85.67±28.52 bpm/L;撤机失败组的RSBI明显高于成功组(P＜0.05).撤机成功组中,68例RSBI≤105bpm/L,12例＞105bpm/L;失败组中,34例RSBI≤105bpm/L,18例＞105bpm/L;以RSBI≤105bpm/L为标准,其预测撤机成功的灵敏度为85.0%,特异度为34.6%.结论RSBI对COPD机械通气病人的撤机有一定指导意义.     

Hypophosphatemia induced by mechanical ventilation in patients with chronic obstructive pulmonary disease

The aim of this study was to assess prospectively the variations of serum phosphorus concentration (P) after onset of mechanical ventilation (MV) in patients with chronic obstructive pulmonary disease (COPD) and acute respiratory acidosis. In 14 COPD patients, we measured P, PaCO2, and pH, immediately before MV (H0), then one hour (H1), 4 (H4), 7 (H7), 12 (H12), and 24 h (H24) after starting MV. P at H0 was in or above the normal range in ten patients and below normal range in four patients. P decreased significantly (p less than .001) after MV at H1, H4, H7, H12, and H24. Hypophosphatemia was present in all patients after MV, but was severe (p less than .3 mmol/L) in only two patients. There was a significant correlation (r = .56 p less than .01) between the decrease of P and the increase of pH after MV. Hypophosphatemia was a constant and early finding after institution of MV in COPD patients and was presumably related to an intracellular shift of P secondary to the correction of respiratory acidosis.     

慢性阻塞性肺疾病机械通气患者两种不同通气模式的比较

目的探讨适应性支持通气（ASV）在慢性阻塞性肺疾病（COPD）机械通气患者中的应用。方法24例存在自主呼吸行机械通气的COPD患者随机分成两组,一组先使用辅助／控制通气（A／C）模式后改为ASV模式,另一组先使用A／C模式后改为同步间歇指令通气联合压力支持通气（SIMV＋PSV）模式,采用对照性研究方法,比较前后两种通气模式对患者的呼吸力学、血流动力学和血气分析的影响,以及两组间的有创通气时间、机械通气总时间、撤机成功率及调机次数。结果从A／C模式改为ASV后患者的呼吸频率（RR）、气道峰压（Pp）、平均气道压（Pro）、气道闭合压（P0．1）和浅快呼吸指数（RSB）下降,潮气量（VT）和肺顺应性（C）上升（P〈0．01）;从A／C模式改为SIMV＋PSV后RR、Pp、Pm、P0.1和RSB下降（P〈0．01）。两组其余呼吸力学、血流动力学及血气分析指标变更模式前后差异均无统计学意义,两组之间的有创通气时间、机械通气总时间、撤机成功率差异无统计学意义,但是ASV组的调机次数明显少于SIMV＋PSV组（8．5±2．2vs13．1±3．1,P〈0．01）。结论ASV和SIMV＋PSV与A／C比较能在一定程度上降低呼吸负荷,保护肺组织。运用于撤机时两种模式效果无明显差别,但ASV操作相对简单,适合于临床医师使用。     

应用无创和有创机械通气治疗肺性脑病的临床疗效分析

目的 分析无创机械通气和有创机械通气治疗慢性阻塞性肺疾病（COPD）并发肺性脑病的疗效.方法 回顾性分析西安医学院第一附属医院呼吸内科2010年1月至2011年6月收治的COPD合并肺性脑病患者的临床资料,选取采用机械通气治疗的患者,根据机械通气的方式不同分为无创组和有创组,分析两组的治疗效果.结果 两组治疗后在血气分析上均明显改善,但有效率和病死率比较差异无统计学意义,同时无创组的并发症明显低于有创组.结论 对COPD合并肺性脑病的患者治疗上首选机械通气治疗,并且无创机械通气并不是绝对禁忌证,值得推广.     

神经调节辅助通气在AECOPD患者呼吸机撤离中的应用

目的 比较神经调节辅助通气(NAVA)与压力支持通气(PSV)模式对AECOPD呼吸衰竭患者呼吸机撤离期间人机同步性、呼吸肌做功及脱机成功率等方面的影响.方法 30例进行机械通气治疗的AECOPDⅢ级患者采用自身对照方法每例随机先后应用PSV和NAVA,比较两种通气模式气道峰值压(Ppeak)、气道平台压(Pplat)、EAdi峰值信号、患者呼吸功占总呼吸功的百分比(WOBp/WOBt)等呼吸力学指标及触发延迟时间、无效触发、吸/呼气切换延迟时间等人机同步性指标.再将30例患者随机分为PSV组和NAVA组,每组15例,比较两组脱机成功率、48 h再插管率及ICU住院时间.结果 NAVA模式时患者吸气触发延迟时间及吸/呼气切换延迟时间较PSV模式明显缩短(P<0.001),EAdi幅度低于PSV模式(P<0.05),Pplat和Ppeak低于PSV模式(P<0.05和P<0.01),WOBp/WOBt显著低于PSV模式(P<0.01),PSV模式时呼吸机通气频率显著低于中枢呼吸频率(t=2.509,P=0.017).NAVA组最终脱机成功率与PSV组比较差异无统计学意义,但直接脱机成功率高于PSV组(P<0.05),48 h内再插管率低于PSV组(P<0.05),ICU住院时间低于PSV组(P=0.038).直接脱机失败患者首次试脱机前EAdi峰值显著高于其他患者(P=0.002).结论 与传统机械通气模式PSV比较,NAVA能改善AECOPD机械通气患者人机协调性,减少患者呼吸做功;EAdi监测有助于临床脱机时机的选择及对呼吸肌状态的评估;NAVA是否能提高患者最终脱机成功率需深入研究.     

无创正压通气在慢性阻塞性肺疾病所致严重呼吸衰竭机械通气脱机过程中的应用

目的 探讨无创正压通气在慢性阻塞性肺疾病(COPD)并发呼吸衰竭患者有创机械通气撤机后的应用时机及治疗效果.方法 选择36例COPD患者,随机选取18例行气管插管机械通气并作为实验组,以同步间歇指令通气(SIMV) 压力支持通气(PSV) 呼气末正压(PEEP)方式行机械通气,待肺部感染控制窗出现,拔除气管插管,改为经面罩BIPAP无创通气,逐渐脱机.余18例做为对照组,行常规有创通气,最后以PSV方式至撤机.现察两组病例的呼吸机相关性肺炎(VAP)的发生例数、病死率、机械通气天数、总住院天数、动脉血气分析.结果 实验组住院时间少于对照组,(21.1±1.8)天vs(27.1±1.4)天(P<0.05);机械通气时间为(11.4±0.8)天vs(14.8±2.4)天(P<0.05);呼吸机相关性肺炎发生率为0 vs 5例(P<0.01);死亡例数为1例vs 4倒.实验组撤机前后血气分析比较差异无统计学意义(P>0.05);对照组撤机后pH降低、PaCO2升高(P<0.05).结论 对COPD并发呼吸衰竭患者采用早期有创机械通气,序贯应用无创正压通气可以显著降低VAP发生率,提高撤机成功率,缩短住院时间.     

Early prediction of successful weaning during pressure support ventilation in chronic obstructive pulmonary disease patients.

OBJECTIVE: The aim of this study was to examine variables for early prediction of successful weaning in chronic obstructive pulmonary disease (COPD) patients during pressure support ventilation weaning. DESIGN: Thirteen COPD patients were prospectively studied to compare the respiratory pattern (inspiratory time, expiratory time, total breath cycle duration, tidal volume, respiratory rate, minute ventilation), the respiratory drive (airway occlusion pressure at 0.1 sec, tidal volume/inspiratory time), and blood gases after 30 mins of pressure support weaning. SETTING: The study was performed in the 20-bed General Critical Care Unit of the Rome "La Sapienza" University Hospital. PATIENTS: We evaluated 13 consecutive COPD patients fulfilling the standard weaning criteria (including clinical status, blood gases, forced vital capacity, maximum inspiratory pressure, and spontaneous respiratory rate after a 30-min T-piece trial) in which we compared respiratory pattern, respiratory drive, and blood gases after 30 mins of pressure support weaning. MEASUREMENTS AND MAIN RESULTS: After 30 mins of pressure support ventilation weaning (pressure support level 20 cm H2O), we measured respiratory pattern (airway pressure and airflow tracing), airway occlusion pressure at 0.1 sec (occluding the inspiratory line during expiration with a rubber balloon), tidal volume/inspiratory time, maximal inspiratory pressure, and blood gases. According to the result of the weaning trial, the patients were divided into two groups (not weaned and weaned), and the statistical difference between the evaluated variables was analyzed in weaned and not weaned groups. We did not observe a significant difference in breathing pattern data and arterial blood gases between weaned and not weaned patients. By contrast, airway occlusion pressure at 0.1 sec and maximum inspiratory pressure measured after 30 mins of weaning trial appeared significantly (p less than .001) different in patients in whom the weaning trial succeeded or failed. Considering maximum inspiratory pressure, we could not separate weaned from not weaned patients, while all patients showing values of airway occlusion pressure at 0.1 sec less than 4.5 cm H2O were easily weaned. CONCLUSIONS: This study confirms that conventional weaning criteria are often inadequate in predicting successful weaning of COPD patients, while airway occlusion pressure at 0.1 sec during the first phase of pressure support ventilation weaning can represent a good weaning predictor.     

慢性阻塞性肺疾病机械通气病人的营养支持与护理

慢性阻塞性肺疾病(COPD)是一种以气流受限为特征的疾病,COPD病人营养不良的发生率为25%～65%,随着病情的发展,营养不良逐步加重[1]。营养不良、免疫低下和严重感染是COPD病人重要的致病因素,三者互为因果,形成恶性循环。有研究表明,营养不良也是影响COPD病人预后的一个重要因     

Pulmonary gas exchange response to weaning with pressure-support ventilation in exacerbated chronic obstructive pulmonary disease patients

OBJECTIVE: To assess if pressure-support ventilation (PSV) can improve ventilation-perfusion (V(A)/Q) imbalance observed during the transition from positive-pressure ventilation to spontaneous breathing in intubated chronic obstructive pulmonary disease (COPD) patients during weaning. DESIGN: Prospective study. SETTING: Respiratory intensive care unit of a tertiary university hospital. PATIENTS: Seven mechanically ventilated COPD male patients (age 68+/-6 (SD) years; FEV(1) 26+/-6% predicted) during weaning. INTERVENTIONS: Patients were studied during three ventilatory modalities: (1) assist-control ventilation (ACV), tidal volume (V(T)), 8-10 ml. kg(-1); (2) PSV aimed to match V(T)in ACV, 15+/-1 cmH(2)O and (3) spontaneous breathing. MEASUREMENTS AND RESULTS: Arterial and mixed venous respiratory blood gases, V(A)/Q distributions, hemodynamics and breathing pattern were measured. Compared with both ACV and PSV, during spontaneous breathing patients exhibited decreases in V(T) (of 43%, p<0.001) and increases in respiratory rate (of 79%, p<0.001), PaCO(2) (of 8.5 mmHg, p=0.001), cardiac output (of 27%, p<0.001) and mixed venous oxygen tension (of 3.4 mmHg, p=0.003), while PaO(2) remained unchanged throughout the study. Except for a shift of the pulmonary blood flow distribution to areas with lower V(A)/Q ratios (p=0.044) and an increase of dead space (of 25%, p=0.004) during spontaneous breathing, no other changes in V(A)/Q distributions occurred. No differences were shown between ACV and PSV modalities. CONCLUSION: In COPD patients during weaning, PSV avoided V(A)/Q worsening during the transition from positive-pressure ventilation to spontaneous breathing. Hemodynamics, blood gases or V(A)/Q mismatch were no different between ACV and PSV when both modalities provided similar levels of ventilatory assistance.