Diaphragmatic fatigue and breathing pattern during weaning from mechanical ventilation in COPD patients

The medium-term outcome of weaning from mechanical ventilation in COPD patients is not easy to anticipate because a respiratory fatigue may eventually develop. We evaluated the diaphragmatic function and the breathing pattern during 40 weaning trials on 15 patients ventilated after acute respiratory failure. We formed two groups according to the success (group B, n = 18) or failure (group A, n = 19) of the medium-term attempt (group A/less than 10 hours; group B/more than 12 hours). Provided the patients showed the classic weaning criteria (tidal volume greater than 5 ml/kg, respiratory frequency less than 30 breaths per minute, PaO2 greater than 50 mm Hg), the study of the breathing pattern did not allow differentiation between the groups. However, the transdiaphragmatic pressure (Pdi) and the Pdimax, which gave an indication of the power of diaphragm contraction, dropped early in the group that could not stand weaning, with an increase in the Pdi/Pdimax ratio. In addition, this same group showed a diaphragmatic dysfunction attested for by a frequent negative gastric pressure associated with or shortly preceded by an abdominal paradoxic motion.     

不同通气模式对慢性阻塞性肺疾病患者机械通气撤机过程的应用比较

目的观察并比较压力支持通气(Pressure support ventilation,PSV)和适应性支持通气(Adaptive support ventilation,ASV)两种通气模式对慢性阻塞性肺疾病(简称慢阻肺)患者机械通气撤机过程的影响。方法将83例慢阻肺患者随机分为两组,对照组(n=41)患者采用ASV通气模式,观察组(n=42)采用PSV通气模式;比较两组患者的临床优劣性和实用性。结果两组患者撤机前后的血气分析无显著变化(P0.05);两组患者的撤机成功率、撤机失败率、重新插管率以及撤机时间均无显著差异(P0.05);两组均未发现临床水平呼吸机相关肺损伤情况。结论 PSV和ASV在慢阻肺患者机械通气中有着较为相近的撤机成功率,临床效果无显著区别,且可以在一定程度降低呼吸负荷、保护肺组织,均能够较好地应用于临床。     

Steady-state response of conscious man to small expiratory resistive loads

To determine the predominant steady-state ventilatory responses to mild expiratory flow-resistive loads, we subjected 14 normal subjects to expiratory resistances of 0-10 cm H2O/L/sec (R0-R3). Breathing patterns and abdominal muscle activity (EMG) were recorded during quiet breathing, and when ventilation was augmented by dead space breathing (7 subjects) or treadmill walking (7 subjects). Expiratory loading increased expiratory time (TE), tidal volume and mean inspiratory flow rate, while decreasing inspiratory duty cycle and respiratory frequency. Minute ventilation (VI) remained constant. These load responses were most prominent during quiet breathing, and were attenuated or abolished as VI increased. Abdominal EMG was negligible during quiet breathing, increased when VI increased, but showed no consistent response to R1-R3. Thus, the principal defense against mild expiratory loads is prolongation of expiration, accompanied by enhanced inspiratory drive. Abdominal muscle expiratory activity is elicited by increasing ventilation, but occurs only sporadically with expiratory loading of the magnitude studied.     

The pattern of breathing during successful and unsuccessful trials of weaning from mechanical ventilation

We prospectively examined the pattern of breathing in patients being weaned from mechanical ventilation: one group (n = 10) underwent a successful weaning trial and were extubated, whereas another group (n = 7) developed respiratory failure and required the reinstitution of mechanical ventilation. During the period of ventilator support, minute ventilation (VI), tidal volume (VT), and respiratory frequency (f) were similar in the 2 groups. After discontinuation of the ventilator, VI remained similar in the 2 groups, but VT was lower and f was higher in the patients who failed the trial compared with those who were successful, 194 +/- 23 and 398 +/- 56 ml (p less than 0.001), respectively, and 32.3 +/- 2.3 and 20.9 +/- 2.8 breaths/min (p less than 0.001), respectively. The failure group displayed a significant increase in PaCO2 (p less than 0.005) during spontaneous breathing, without a concomitant increase in the alveolar-arterial PO2 difference. Eighty-one percent of the variance in PaCO2 was accounted for by the pattern of rapid, shallow breathing. During weaning, resting respiratory drive (reflected by mean inspiratory flow, VT/TI) and fractional inspiratory time (TI/Ttot) were similar in the 2 groups. The patients in the failure group showed significant increases in VT/TI, 265 +/- 27 to 328 +/- 32 ml/s (p less than 0.01), and VI, 5.82 +/- 0.53 to 7.32 +/- 0.52 L/min (p less than 0.01), from the beginning to the end of the weaning trial; VT and f showed no further change.(ABSTRACT TRUNCATED AT 250 WORDS)     

The control of breathing during weaning from mechanical ventilation

Using the recruitment threshold technique, we measured the CO2 responsiveness of the unloaded respiratory pump in 14 mechanically ventilated patients prior to weaning. The CO2 recruitment threshold (CO2RT) was compared with the arterial CO2 tension during unassisted breathing (CO2SB) and with the PaCO2 during mechanical ventilation (CO2MV) at machine settings determined by the primary physician. Based on these comparisons, we tested the hypotheses that (1) patients without weaning-induced respiratory distress (group 1) maintain CO2SB near CO2RT, (2) patients with weaning-induced respiratory distress (group 2) retain CO2SB above CO2RT, thereby manifesting incomplete load compensation, and (3) CO2MV is ventilator setting dependent and provides insufficient information about the ventilatory requirement during weaning. Respiratory distress was prospectively defined as sustained tachypnea (rate greater than or equal to 30) or intense dyspnea (Borg scale rating) and limited weaning in nine of 14 patients. The average CO2RT was 40 mm Hg in both groups. All patients in group 1 maintained CO2SB near CO2RT (p greater than 0.1). Seven of nine patients in group 2 retained CO2 by greater than or equal to 3 mm Hg above CO2RT (p less than 0.01). There was no significant difference between CO2MV and CO2SB in either group. We conclude that CO2RT provides a better reference of the adequacy of ventilatory load compensation during weather than CO2MV.     

慢性阻塞性肺疾病撤机困难呼吸力学特征10例分析

目的为提高慢性阻塞性肺疾病(COPD)患者撤机成功率提供生理学依据。方法检测2006年1月至2009年12月广州医学院第一附属医院收治的10例撤机困难COPD患者的呼吸力学指标,观察患者自主呼吸(SB)及机械通气时的呼吸力学指标变化。结果 SB时的呼吸频率(RR)、潮气量(VT)和分钟通气量(Ve)分别为(27.94±8.23)次/min、(0.266±0.107)L和(6.843±1.333)L/min,机械通气时的RR降低,而VT和Ve时升高(均P<0.05)。SB和机械通气时的动态内源性呼吸末正压分别为(0.82±0.19)kPa和(0.41±1.12)kPa,SB时明显增高(P<0.01),吸气中期气道阻力(RL)(2.43±0.94)kPa/(L.S)。SB时的P0.1为(0.61±0.16)kPa。SB时的最大跨膈压、最大食管负压和最大吸气口腔压分别为(5.08±0.93)kPa、(-5.00±0.95)kPa和(-3.78±0.86)kPa。SB时跨膈压(Pdi)和吸气压力时间乘积(PTPins)分别为(0.82±0.20)kPa和(48.93±11.94)kPa.s;机械通气时较SB显著降低,分别为(0.67±0.17)kPa和(30.33±11.72)kPa.s(P均<0.05)。结论撤机困难COPD患者存在显著的呼吸力学异常,SB时呼吸浅快,动态内源性呼吸末正压、RL与呼吸中枢驱动等均增高,吸气肌肉无力;应用PSV(1.57 kPa)联合PEEP(48%动态内源性呼吸末正压)可降低约50%的动态内源性呼吸末正压、17.8%的Pdi和38%的PTPins。     

经面罩机械通气治疗慢性阻塞性肺疾病撤机失败患者的临床研究

目的探讨BiPAP呼吸机面罩机械通气(FMMV)辅助慢性阻塞性肺疾病(COPD)合并呼吸衰竭机械通气患者撤机的价值。方法将首次撤机失败的28例患者随机分为两组经BiPAP呼吸机面罩通气治疗组(A组)和人工气道机械通气组(B组),比较两组机械通气时间、住ICU时间、医疗费用及病死率等。结果机械通气时间A组(7±3)天,B组(14±3)天;住ICU时间A组(9±3)天,B组(27±6)天。医疗费用A组(13980±2000)元,B组(25000±3213)元;病死率A组14.3%,B组64.3%。两者间比较均有显著差异(P<0.01)。结论对于符合撤除有创机械通气的COPD合并呼吸衰竭而不能成功撤机的患者,应用FMMV,可以避免再插管,减少医疗费用,提高抢救成功率。     

Effects of doxapram on hypercapnic response during weaning from mechanical ventilation in COPD patients.

Failure of weaning from mechanical ventilation in COPD patients is often related to diaphragmatic fatigue. Whether there is a central respiratory drive fatigue and a reserve of excitability is still debated. The purpose of this study was to analyze the following in 13 COPD patients weaned from mechanical ventilation: (1) ventilatory (VE/PETCO2) and neuromuscular (P0.1/PETCO2) response to hypercapnia; (2) the maximum reserve capacity measured through changes in the VE/PETCO2 and P0.1/PETCO2 slopes after doxapram (DXP) infusion, which, given during the test, allows measurement of the maximum response capacity to overstimulation; and (3) analyze the influence of these changes on the outcome of weaning. The results show a variable P0.1/PETCO2 response and a low VE/PETCO2. DXP infusion does not change the slopes of these relations but increases the end-expiratory volume (delta FRCd); (p less than 0.02). Since there was no change in the VE/PETCO2, P0.1/PETCO2, and delta FRC values with or without DXP, there was no excitability reserve in patients who were successfully weaned. When weaning failed, DXP did not change VE/PETCO2 and P0.1/PETCO2 slope, but delta FRCd was greater the delta FRC (p less than 0.001). The excitability reserve in these patients leads to an increase in end-expiratory volume, probably worsening the diaphragm dysfunction.     

Reduced inspiratory muscle endurance following successful weaning from prolonged mechanical ventilation

STUDY OBJECTIVES: Respiratory muscle weakness and decreased endurance have been demonstrated following mechanical ventilation. However, its relationship to the duration of mechanical ventilation is not known. The aim of this study was to assess respiratory muscle endurance and its relationship to the duration of mechanical ventilation. DESIGN: Prospective study. SETTING: Tertiary teaching hospital ICU. PATIENTS: Twenty subjects were recruited for the study who had received mechanical ventilation for > or = 48 h and had been discharged from the ICU. MEASUREMENTS: FEV1, FVC, and maximal inspiratory pressure (P(I(max)) at functional residual capacity were recorded. The P(I(max)) attained following resisted inspiration at 30% of the initial P(I(max)) for 2 min was recorded, and the fatigue resistance index (FRI) [P(I(max)) final/P(I(max))initial] was calculated. The duration of ICU length of stay (ICULOS), duration of mechanical ventilation (MVD), duration of weaning (WD), and Charlson comorbidities score (CCS) were also recorded. Relationships between fatigue and other parameters were analyzed using the Spearman correlations (rho). RESULTS: Subjects were admitted to the ICU for a mean duration of 7.7 days (SD, 3.7 days) and required mechanical ventilation for a mean duration of 4.6 days (SD, 2.5 days). The mean FRI was 0.88 (SD, 0.13), indicating a 12% fall in P(I(max)), and was negatively correlated with MVD (r = -0.65; p = 0.007). No correlations were found between the FRI and FEV1, FVC, ICULOS, WD, or CCS. CONCLUSIONS: Patients who had received mechanical ventilation for > 48 h have reduced inspiratory muscle endurance that worsens with the duration of mechanical ventilation and is present following successful weaning. These data suggest that patients needing prolonged mechanical ventilation are at risk of respiratory muscle fatigue and may benefit from respiratory muscle training.     

慢性阻塞性肺疾病呼吸衰竭机械通气脱机策略

目的 探讨COPD呼吸衰竭有创机械通气脱机策略.方法 机械通气治疗COPD呼吸衰竭108例,分析治疗结果.结果 106例患者成功脱机、拔管,抢救成功率达98％.结论 采取恰当有创机械通气脱机策略,有较高抢救成功率.     

Effect of aging on respiratory responses to CO2 and inspiratory resistive loads

We studied 10 elderly individuals over 60 years of age and 18 individuals less than 30 years to determine whether aging affects the response of the respiratory control system to chemical stimuli or to altered mechanical conditions. Both groups consisted of males and females who were nonsmokers. Ventilation and the isometric force developed by the inspiratory muscles (occlusion pressure) was assessed during hypercapnia while the subjects breathed under control conditions or through a load at the mouth that increased inspiratory resistance. Ventilation responses to progressively increasing CO2 were lower but not significantly so in the older group. There were significant differences in ventilatory pattern in the two groups. However, occlusion pressure responses to hypercapnia and to resistive loads were the same. The results suggest that aging has little or no adverse effect on respiratory control.     

慢性阻塞性肺疾病患者长期人工通气撤机指标的临床研究

目的评价床边综合肺功能作为长期人工通气的慢性阻塞性肺疾病（COPD）患者脱机指标的指导意义。方法监测58例（成功组：43例,失败组：15例）通气时间＞72h的COPD呼衰患者达到临床脱机标准后的血气分析、肺功能及呼吸力学的改变情况。结果两组患者的血气分析、急性生理、慢性健康评分（APACHEⅡ）、氧合指数、动态顺应性及气道阻力均无显著差异（P均＞0．05）;成功组患者的肺活量／潮气量（VC／V_T）、最大吸气负压（Pi_(max)）和浅快呼吸指数（f／V_T）分别为：2．10±0．20、（－21±4）cmH_2O及（74±30）次·min~(-1)·L~(-1);失败组患者则依次为1．30±0．20、（－13±3）cmH_2O及（115±20）次·min~(-1)·L~(-1),两组结果比较差异有显著性,P均＜0．05。以VC／V_T＞1．8、Pi_(max)＜－18cmH_2O和f／V_T＜105次·min~(-1)·L~(-1)作为临界值预测此类患者脱机成功与否,具有较高的敏感性（84％）和特异性（90％）。结论　综合肺功能指标（VC／V_T、Pi_(max)及f／V_T）可用于指导长期通气的COPD患者选择脱机时机,适宜在我国目前条件下推广普及。     

Effect of home mechanical ventilation on inspiratory muscle strength in COPD

BACKGROUND: The mechanism responsible for chronic hypercapnic respiratory failure (HRF) in patients with COPD remains unclear. In this study, we tested the hypothesis that chronic HRF in patients with COPD is associated with low-frequency fatigue (LFF) of the diaphragm. METHODS: To test this hypothesis, we measured the twitch transdiaphragmatic pressure (Tw Pdi) elicited by stimulation of the phrenic nerves in 25 patients with chronic HRF (mean [+/- SD] Paco(2), 55.2 +/- 5.2 mm Hg) due to COPD before and 2 months after the initiation of noninvasive mechanical ventilation (NIV) [pressure-cycled ventilation with inspiratory positive airway pressure of 19.0 +/- 2.5 cm H(2)O]. We reasoned that had LFF been present, Tw Pdi should rise after effective NIV. RESULTS: The treatment compliance with NIV was good (median of machine usage was 7.1 h per night). Paco(2) decreased from 55.2 +/- 5.2 to 48.8 +/- 5.9 mm Hg (p < 0.001), and Pao(2) increased from 53.1 +/- 5.9 to 57.7 +/- 7.0 mm Hg (p = 0.007). Mean Tw Pdi at baseline was 11.1 +/- 6.6 cm H(2)O and after treatment was 11.7 +/- 7.2 cm H(2)O (not significant). Also, maximal static inspiratory mouth pressure did not change significantly (44.3 +/- 15.9 cm H(2)O vs 46.5 +/- 19.7 cm H(2)O). CONCLUSION: LFF of the diaphragm does not accompany chronic HRF in patients with COPD.     

血浆BNP对慢性阻塞性肺疾病有创机械通气撤机的指导价值

目的探讨撤机前后血浆BNP水平及其变化对慢性阻塞性肺疾病(简称慢阻肺)患者有创机械通气撤机的指导价值。方法回顾性调查满足条件的70例患者,测定患者开始有创机械通气时,自主呼吸试验(SBT)前、后的血浆BNP水平,分别标为(BNP 0、BNP 1、BNP 2),SBT前、后的血浆BNP水平差值(ΔBNP),并根据患者撤机结局分为撤机成功组与撤机失败组。绘制ROC曲线,分析血浆BNP水平对慢阻肺患者撤机结局的预测价值。结果 70例患者中,成功撤机52例,撤机失败18例。BNP 0、BNP 1、BNP 2预测慢阻肺患者撤机失败的AUC分别为0.6079、0.8568、0.9081,ΔBNP预测撤机失败的AUC为0.9466。结论血浆BNP水平对预测慢阻肺患者撤机结局有指导价值,其中ΔBNP预测慢阻肺患者撤机结局的价值最大。     

肠道营养支持在COPD机械通气患者中的应用

营养不良是COPD机械通气患者常见的并发症。而营养不良更易累及呼吸肌，使其收缩力和耐力降低，损害通气驱动功能，导致机械通气患者的脱机困难。因此，肠道营养支持对COPD机械通气患者的作用尤为重要。我科自2001年2月至2003年12月对COPD机械通气患者26例进行了部分肠内和部分肠外营养支持，取得了满意的效果，现报告如下。     

浅快呼吸指数对机械通气脑梗死患者撤机成功率的预测价值

目的研究浅快呼吸指数(RSBI)对机械通气脑梗死患者撤机成功率的预测价值。方法采用程序化撤机策略对机械通气>24h且符合筛查试验标准的急性脑梗死患者34例,根据撤机成功与否分为成功组23例,失败组11例。应用低水平压力支持通气法进行自主呼吸试验(SBT)。SBT前和开始3min时测定呼吸频率、潮气量、心率和血氧饱和度等指标。对通过3min SBT的患者继续完成120min SBT,持续监测上述指标,每15min记录1次,血气分析分别于30、60、120min采取。结果失败组合并冠心病比例、SBT后15、30、60、90、120min的RSBI较成功组明显升高(P<0.05)。SBT前和SBT后3、15、30、60、90、120min的RSBI与撤机结果的ROC曲线下面积分别为0.581、0.745、0.658、0.838、0.925、0.889、0.881,提示SBT 60min时的RSBI预测撤机的准确性最高。SBT 60min时,以RSBI≤60次/(min·L)为标准,RSBI预测撤机成功的敏感性为100%,特异性为81.81%,准确性为84.12%。结论动态观察RSBI对机械通气脑梗死患者撤机成功率有一定的预测价值。     

不同呼吸过滤器在机械通气中对气道峰压的影响

目的 综合性评价不同类型呼吸过滤器(breathing filter,BF)在机械通气中对气道峰压(peak inspiratory pressure,PIP)的影响.方法 选择择期全麻下行腹部手术患者60例,年龄18～65 岁,手术时间约3 h,既往无呼吸系统疾患及心力衰竭病史,随机分为4组(每组15例):PALL BB 25S(P)组、DAR 352/5805(D)组、Vital signs 5702 TMP(V1)组和Vital signs 5708 HEPA(V2)组,记录应用BF前5 min (t1)、应用BF后5 min(t2)及术毕即刻(t3)时的PIP值.结果 4组在同一时点比较中PIP值差异无统计学意义(P＞0.05);4组组内t2与t1时刻比较以及t3与t2时刻比较PIP值升高差异均有统计学意义(P＜0.05).结论 在机械通气中使用呼吸过滤器会增加一定程度的PIP,但PIP的实际测量值均在临床允许范围之内.     

机械通气治疗COPD撤机失败原因的回顾性研究

目的研究机械通气治疗COPD患者撤机失败的原因。方法收集我院2004年1月至2008年12月住院的38例共45次COPD患者撤机失败、进行回顾性研究,总结撤机失败的原因。结果38例45次撤机失败的原因：感染未控制18例次（40．0％）;呼吸肌疲劳10例次（22．2％）;呼吸机依赖7例次（15．6％）;并发症致再次接机6例次（13．3％）;误吸致再次接机3例次（6．7％）,其他1例次（2．2％）。结论有效的抗感染治疗,加强营养支持,防治并发症和注意心理疏导是防止撤机失败的主要措施。