食管引流型与标准型喉罩通气道用于正压通气的自身对照研究

目的采用随机自身对照设计方法比较食管引流型喉罩通气道(PLMA)和标准型喉罩通气道(SLMA)用于间歇正压通气的有效性。方法选择50例经美国麻醉医师协会(ASA)身体状态分级标准分为1~2级、拟在全身麻醉下实施择期整形外科手术患者。在常规麻醉诱导后,顺序插入PLMA和SLMA,将通气罩内压充气至60cmH2O(1cm H2O=0.098kPa),评价两种喉罩通气道充气前后的肺通气满意度和气道密封压,同时进行光导纤维支气管镜(FOB)评分,确定通气罩的解剖位置。然后将潮气量设定为10ml/kg实施间歇正压通气,记录间歇正压通气后连续5次呼吸的平均呼潮气量和平均吸气峰压。结果在通气罩未充气情况下,插入PLMA后有46例(92%)患者获得了良好和尚可的肺通气效果,而插入SLMA后仅有22例(44%)患者获得了良好和尚可的肺通气效果;PLMA的气道密封压显著高于SLMA(P<0.05)。将通气罩内压充气至60cmH2O,采用PLMA的50例患者均获得良好的肺通气效果,但采用SLMA时仅有28例获得良好的肺通气效果;PLMA所需的充气量和充气后获得的气道密封压均显著高于SLMA(P均<0.05)。采用PLMA时所有患者的气道密封压均高于或等于采用SLMA时;采用PLMA时除2例患者外,其他患者所需的充气量也均高于采用SLMA时。PLMA通气罩位置的FOB评分显著低于SLMA(P<0.05)。采用PLMA维持气道的29例患者和采用SLMA维持气道的21例患者的平均呼潮气量、吸气峰压及维持气道时间差异均无显著性(P均>0.05)。结论与SLMA相比,PLMA可为正压通气提供更好的气道密封压,而且对声门和食管上端具有潜在的隔离作用,用于正压通气时PLMA比SLMA更有效、更安全。     

三种声门上通气装置在全麻患者中应用的比较

目的:比较经典喉罩(LMA)、双腔食管引流型喉罩(PLMA)和食管引流型喉管Ⅱ(LTSII)在全麻患者控制呼吸时的应用情况.方法:90例ASA Ⅰ～Ⅱ级妇科手术患者,随机分为LMA组、PLMA组和LTSII组(n=30).麻醉诱导后置入各通气装置,记录成功置入所需次数和时间.测定气道封闭压(PTOP),记录相关通气参数及需要调整装置位置以维持气道通畅的患者数.手术结束后拔除装置,记录装置外壁血迹和术后24h咽喉部不良反应.结果:LTSII有3例失败(2例置管失败,1例术中不能有效通气),喉罩则均成功(P＞0.05).与LMA和PLMA比较,LTSII所需置入次数和时间明显增多(P＜0.05).PLMA组PTOP(29.1±4.9cm)H2O明显高于LMA组(24.0±5.2 cm)H2O(P＜0.05),但与LTSII组(28.1±4.8 cm)H2O差异无统计学意义(I＞0.05).气道峰压LTSII组高于LMA和PLMA组(P＜0.05).术中需要调整装置位置患者数LTSII组高于PLMA组(P＜0.05).术后咽喉部并发症各组相似(P＞0.05).结论:三种装置均可有效用于短小手术全麻患者的气道管理.但LTSII置管相对较为困难,维持过程中需要调整位置的次数也更多.     

低牵张通气策略救治急性呼吸窘迫综合征的临床研究

目的 观察低牵张通气策略治疗急性呼吸窘迫综合征(ARDS)的临床疗效.方法 将85例ARDS患者随机分为低牵张通气组(42例)和小潮气量通气组(43例).低牵张通气组接受峰压≤35 cm H2O(1 cm H2O=0.098 kPa)的压力限制或压力支持模式以满足气道平台压≤30 cm H2O;小潮气量通气组接受潮气量≤6 ml/kg的容量辅助控制通气模式.分析比较两组患者28 d病死率、高碳酸血症发生率、镇静和肌松药物使用时间、存活患者呼吸机带机时间及住重症监护病房(ICU)时间;低牵张通气组患者根据监测呼出潮气量(Vte)分为小潮气量通气亚组(Vte≤6 ml/kg,11例)和非小潮气量通气亚组(Vte>6 ml/kg,31例),分析两个亚组间患者的28 d病死率及高碳酸血症发生率.结果 低牵张通气组患者28 d病死率与小潮气量通气组无显著差异(34.0%比37.0%,P>0.05),但低牵张通气组高碳酸血症发生率明显低于小潮气量通气组(10.6%比40.7%,P<0.05),镇静和肌松药物使用时间[(4.5±1.2)d比(8.7±2.3)d]、存活患者带机时间[(8.4±2.1)d比(10.7±1.2)d3及住ICU时间[(10.2±2.2)d比(13.7±3.1)d3均相应缩短(P均<0.05);低牵张通气组中小潮气量通气比例为26.2%,小潮气量通气亚组病死率(40.8%比13.2%)和高碳酸血症发生率(65.7%比8.6%)均显著高于非小潮气量通气亚组(P均<0.05).结论 与小潮气量通气策略比较,低牵张通气策略可降低高碳酸血症的发生率,缩短患者带机时间及住ICU时间.低牵张通气状态下,小潮气量可能与不良预后相关.     

吸入沙丁胺醇对呼吸衰竭患者容积标限压力控制通气时通气参数的影响

目的　探讨在容积标限压力控制 (VTPC)通气时吸入支气管扩张剂沙丁胺醇后对机械通气参数的影响。方法　 10例平均年龄为 (6 8± 5 )岁的呼吸衰竭患者均接受气管插管与机械通气支持治疗 ;采用Newport e5 0 0型呼吸机 ,并实施定容型通气 (VCV) 30 min,潮气量 (VT)为 8～ 10 ml/ kg;测定气道阻力 (Raw)和静态顺应性 (Cst)以及通气参数的变化 ,包括气道峰压 (PIP)、平台压 (Pplat)、充气时间 (Tinflate)、吸气峰流速(PIF)、呼气峰流速 (PEF)和平均吸气流速 (VT/ Tinflate)。随后转为 VTPC通气 30 m in,并同样记录上述参数。通过同轴吸入装置吸入沙丁胺醇 6 0 0 μg后重复 VCV和 VTPC通气 ,并记录上述通气参数。结果　 10例患者的 Cst为 (38.4± 2 .7) ml/ cm H2 O,Raw为 (2 0 .1± 2 .0 ) cm H2 O· L- 1 · s- 1 。VTPC时 PIP和 VT/ Tinflate较 VCV时显著降低 (P均 <0 .0 5 ) ,PIF则显著增高 ,两种通气时的 Pplat无显著性差异 ,分别为 (2 2 .1± 0 .9) cm H2 O和(2 3.0± 1.2 ) cm H2 O(P>0 .0 5 )。吸入沙丁胺醇后患者的 Raw均显著降低 ,而 Cst无明显变化 ,VCV时的 PIP有所降低 ,但 Pplat无变化 ;VTPC时的 PIP和 Pplat与吸入前比较无明显改变 ,但 PIF和 PEF出现显著增高 ,Tinflate则相应缩短 (P均 <0 .0 5     

喉罩通气条件预判在腹腔镜胆囊切除术中的应用

目的探讨在腹腔镜胆囊切除手术中安全、有效使用普通喉罩的方法。方法选择腹腔镜胆囊切除手术患者100例,随机均分两组:对照组,喉罩插入后以敷料填塞双侧颈项固定。试验组,诱导期面罩去氮吸氧就开始持续正压通气,观察气道压力并对气道顺应性做评估;喉罩插入后,分别在头颈保持正中后仰位和左、右侧偏转45°时测定气道密封压,并据此选择固定位置。结果对照组,二氧化碳气腹后喉罩通气漏气9例,试验组漏气2例。组间比较有统计学差异(P<0.05)。试验组面罩通气时气道压力维持在8¹4 cmH2O,平均(12.51±1.69)cmH2O,与喉罩插入后[(14.65±2.24)cmH2O](Vt、RR未做调整)比较,有统计学差异(P<0.01)。试验组喉罩插入后气道密封压测定结果:正中后仰位占优势的13例(26%),左或右单侧占优势的12例(24%)。结论去氮吸氧时采用持续正压通气,观测气道压力,对患者肺及气道顺应性重新评估;喉罩插入后测定不同的头颈位置时气道密封压并以此选择最佳位置固定,可以减少气腹后持续正压通气时漏气率。     

机械通气治疗重症哮喘过程中发生气压伤的相关因素分析

目的：分析机械通气治疗重症哮喘过程中发生气压伤的相关因素，提高机械通气治疗重症哮喘的疗效。方法：将45例无气压伤发生和6例发生气压伤的重症哮喘患者就通气模式、潮气量、吸气峰压、平台压、呼气末正压、吸气流量、肺顺应性、呼吸频率等指标进行回顾性分析。结果：6例气压伤患者中4例机械通气的平台压大于35cm H2O，其中3例有肺大泡。结论：平台压过高是重症哮喘机械通气中致气压伤的关键因素，合理的调控平台压是防止气压伤发生的关键。     

正压机械通气与膈肌起搏联合通气对呼吸衰竭患者呼吸力学的影响

目的 观察正压机械通气与膈肌起搏联合通气对呼吸衰竭(呼衰)患者呼吸力学的影响.方法 采用自身前后对照研究方法,以20例中枢性呼衰患者先使用常规正压机械通气30 min作为对照组,后改用正压机械通气与膈肌起搏联合通气30 min作为试验组,观察两种通气方式下患者的呼吸力学变化.结果 与对照组比较,试验组平均气道压(Paw,cm H2O,1 cm H2O=0.098 kPa)、平台压(Pplat,cm H2O)明显降低(Paw:6.1±1.3比7.3±1.8;Pplat:10.4±2.5比12.1±2.6,均P＜0.05),峰食道压力(PPEAK ES,cm H2O)、峰食道压力与基准食道压力差(dPES,cm H2O)负值明显增加(PPEAK ES:-8.3±1.9比-3.2±1.4;dPES:-11.2±2.6比-8.2±2.2,均P＜0.05),吸气末屏气期间的跨肺压(Ptp plat,cm H2O)、呼吸系统静态顺应性(Cst,ml/cm H2O)明显增加(Ptp plat:23.6±3.8比15.6±3.1 Cst:52.7±8.2比48.3±7.2,均P＜0.05),气道阻力(Raw,cm H2O·L-1·s-1)、肺部阻力(RL,cm H2O·L-1·s-1)无明显改变(Raw:2.1±0.5比2.3±0.4; RL:2.9±0.6比3.1±0.5,均P＞0.05),患者呼吸功(WOBp,J/L)明显增加、机械呼吸功(WOBv,J/L)明显降低(WOBp:0.18±0.03比0;WOBv:0.31±0.07比0.53±0.11,均P＜0.05).结论 正压机械通气与膈肌起搏联合通气进行呼吸支持可明显降低呼衰患者气道压力,增加胸腔内压负值和跨肺压,提高肺顺应性,并能降低机械通气作功,但对气道阻力无明显影响.

Abstract：

Objective To observe the effects of combining positive pressure ventilation with diaphragm pacing on respiratory mechanics in patients with respiratory failure. Methods Twenty patients with central respiratory failure were studied with cohorts. The effects on respiratory mechanics were respectively observed in patients in control group, in whom ventilation by positive pressure only, and patients in experimental group in whom ventilation was instituted by combining positive pressure ventilation with diaphragm pacing. Results Compared with control group, mean airway pressure (Paw, cm H2O,1 cm H2O= 0. 098 kPa) and plateau pressure (Pplat, cm H2O) were significantly decreased in experimental group (Paw: 6. 1±1.3 vs. 7. 3±1.8; Pplat: 10. 4±2.5 vs. 12. 1±2. 6, both P＜0. 05), while the nagative value of peak esophageal pressure (PPEAK ES, cm H2O), the nagative value of the difference between peak and basic esophageal pressure (dPES, cm H2O), transpulmonary pressure at end of inspiration hold (Ptp plat,cm H2O), static compliance (Cst, ml/cm H2O) were significantly increased in experimental group (PPEAKES:-8.3±1.9 vs. -3.2±1.4; dPES: -11.2±2.6 vs. -8. 2±2. 2; Ptp plat: 23.6±3.8 vs. 15.6±3.1; Cst:52. 7±8. 2 vs. 48. 3 ±7. 2, all P ＜ 0. 05 ). No differences were found in airway resistance (Raw,cm H2O · L-1 · s-1) and lung resistance (RL, cm H2O · L-1 · s-1) between experimental group and control group (Raw: 2.1±0.5 vs. 2.3±0.4; RL: 2.9±0.6 vs. 3.1±0.5, both P＞0.05). Work of breath by patient (WOBp, J/L) was significantly increased and work of breath by ventilator (WOBv, J/L) was significantly decreased in experimental group compared with control group (WOBp: 0. 18± 0. 03 vs. 0;WOBv: 0.31±0.07 vs. 0.53±0.11, both P＜0.05). Conclusion Compared with positive pressure ventilation, positive pressure ventilation combined with diaphragm pacing can decrease the Paw, increase intrathoracic negative pressure, transpulmonary pressure, and Cst, and decrease WOBv, while there is no effect on Raw and RL.     

不同体位对Proseal喉罩通气功能的影响

目的:观察间歇正压(IPPV)通气下Proseal喉罩用于侧卧位手术的安全与有效性。方法:选择侧卧位经皮肾镜手术病人30例,ASAⅠ～Ⅱ级,用丙泊酚、芬太尼及维库溴铵静脉诱导,用专用引导器引导方法插入喉罩,吸入异氟醚维持麻醉。观察指标:平卧位正压通气30min(Ta),侧卧后30min(Tb)、60min(Tc),术毕(Td)的分钟通气量(MV)、潮气量(VT)、气道峰压(Pmax)、脉搏氧饱和度(SpO2)、呼吸末二氧化碳分压(PETCO2)、动脉血二氧化碳分压(PaCO2)及平卧位和侧卧位的气道密封压(PTOP)。结果:平卧位P(TOP)为(31.5±1.3)cmH2O,侧卧位PTOP为(29.6±1.5)cmH2O,比较差异无统计学意义(P>0.05);侧卧后各时间点的MV和VT与侧卧前比较都增大,差异有显著性意义(P<0.01),术毕(Td)与侧卧后30min(Tb)的MV和VT比较差异有显著性意义(P<0.05);侧卧后各时间点的Pmax与侧卧前比较增加,差异有显著性意义(P<0.01),侧卧后各时间点间的Pmax比较没有明显差异(P>0.05);侧卧后各时间点间的PETCO2及PaCO2及各时间点与侧卧前比较没有明显差异(P>0.05)。     

适当呼气末正压及不同通气模式对肝移植患者血流动力学和氧代谢动力学的影响

目的 寻找适宜的呼气末正压(PEEP),研究不同机械通气方式对肝移植术后患者血流动力学及氧代谢动力学的影响.方法 采用随机、单盲、交叉试验方法.选取11例背驮式肝移植术后呼吸机辅助通气患者为观察对象,经漂浮导管、桡动脉导管进行持续心排血量(CO)、平均肺动脉压(MPAP)、平均动脉血压(MABP)、中心静脉压(CVP)和气道压力监测.压力调节容量控制通气(PRVCV)的PEEP定为0、5、10和15 cm H2O(1 cm H2O=0.098 kPa),不同水平PEEP各用30 min;交替使用PRVCV和压力控制同步间歇指令通气加压力支持通气(PC-SIMV+PSV)各60 min;观察4种PEEP水平和两种通气模式下血流动力学和氧代谢动力学指标的变化.结果 不同水平PEEP时肝移植术后患者气道峰压、平均气道压、CVP及MPAP差异均有显著性,其中在PEEP为10 cm H2O和15 cm H2O时显著高于PEEP为0和5 cm H2O时;不同水平PEEP对pH、动脉血二氧化碳分压(PaCO2)、动脉血氧分压(PaO2)、动脉血氧饱和度(SaO2)、氧供给(DO2)、氧消耗(VO2)、氧摄取率(O2ER)均无明显影响.PRVCV模式时平均气道压明显低于PC-SIMV+PSV模式[(8.78±1.53)cm H2O比(11.64±3.30)cm H2O,P＜0.05];PRVCV模式时VO2虽低于PC-SIMV+PSV模式,但差异无显著性.两种通气模式对患者的其他血流动力学指标以及氧代谢动力学指标并无显著影响.结论 为减少对患者体循环及移植肝脏血液回流的影响,肝移植术后患者通气支持时宜选用5 cm H2O的低水平PEEP.PRVCV模式可作为肝移植术后患者呼吸支持和脱机过渡较为理想的通气模式.     

无创机械通气不同吸气压力对慢性阻塞性肺疾病急性加重期患者腹内压的影响

目的 探讨不同吸气压力(IPAP)对慢性阻塞性肺疾病急性加重期(AECOPD)无创正压机械通气患者腹内压(IAP)的影响.方法 选取60例AECOPD无创正压机械通气患者,行机械通气前测量患者IAP值,行无创正压机械通气后,按照正压机械通气不同吸气压力将患者随机分为三组:10～ 14 cm H2O(A组),15 ～19 cm H2O(B组),20～25 cm H2O(C组);每组各20例患者,分别于调整吸气压力后2h、第1～7天每天同一时间点监测患者IAP.结果 与A组、B组比较,C组患者IAP差异有统计学意义(P＜0.05);A组与B组比较差异无统计学意义(P＞0.05).同一组不同监测时间点比较,通气后2h及通气后第1天与其他时间点比较差异有统计学意义(P＜0.05).结论 对于AECOPD无创正压机械通气患者,随着吸气压力水平的升高,患者IAP有升高趋势,并且在早期较明显.因此,在无创正压机械通气早期,监测患者IAP可能有益于为患者选择适合的吸气压力支持水平.     

The size 1 LMA-ProSeal: Comparison with the LMA-Classic during pressure controlled ventilation in a neonatal intubation manikin

BACKGROUND: The classic laryngeal mask airway (cLMA) has been demonstrated to be effective for airway management during neonatal resuscitation. However, high airway pressures, when required, cannot be achieved with this device. A neonatal prototype of the LMA-ProSeal (PLMA), which might improve the oropharyngeal leak pressure, has recently been produced. The airway sealing pressures of the cLMA and the PLMA were compared in a neonatal manikin. METHODS: A neonatal PLMA and a neonatal cLMA were positioned at random in a neonatal intubation manikin (Neonate Airway Trainer; Laerdal, Norway). A Dr?eger pressure controlled ventilator (Dr?eger 8000; Dr?egerwerk AG, Germany) was connected to the airway tubes and increasing inspiratory pressures (from 10 to 40 cm H2O) of positive pressure ventilation applied. The peak and the mean airway pressures obtained with each device were recorded. RESULTS: The airway pressures obtained with PLMA were significantly higher than those obtained with cLMA (p < 0.01) at levels of positive pressure ventilation of 25, 30, 35 and 40 cm H2O. CONCLUSIONS: The neonatal PLMA allows higher airway pressure ventilation than the cLMA, in a neonatal intubation manikin. If confirmed clinically, this may have important implications during neonatal resuscitation when high airway pressures are required.     

Optimization of high-frequency oscillatory ventilation for the treatment of experimental pneumothorax

OBJECTIVE: To determine the effect of frequency, amplitude, inspiratory time, and mean airway pressure on gas flow through a chest tube in an animal model of pneumothorax treated with high-frequency oscillatory ventilation (HFOV). DESIGN: Observational study. SETTING: Animal laboratory. SUBJECTS: Neonatal piglets (n = 12). INTERVENTIONS: After saline lavage, a model of experimental pneumothorax was created by selective right mainstem intubation and manual ventilation at high-peak inspiratory pressure. A chest tube was placed, and gas flow through the chest tube was measured with a pneumotachometer during HFOV with the SensorMedics 3100A. The effects of frequency, inspiratory time, amplitude, and mean airway pressure on chest tube gas flow were determined. MEASUREMENTS AND MAIN RESULTS: Gas flow through the chest tube was significantly higher (p <.001) at 5 Hz (601 +/- 23 mL/min) than at 10 Hz (464 +/- 64 mL/min) or 15 Hz (400 +/- 11 mL/min), while mean airway pressure, inspiratory time, and PaCO2 were kept constant. Gas flow was higher at an inspiratory time of 50% compared with one of 30% (645 +/- 49 vs. 436 +/- 36 mL/min, respectively). Gas flow was directly related to amplitude (284 mL/min at an amplitude of 10 cm H2O, increasing to 877 mL/min at an amplitude of 80 cm H2O) when a 3.5-mm endotracheal tube was used; however, gas flow was attenuated at amplitudes of >40 cm H2O when smaller endotracheal tubes were used. Gas flow increased significantly with the increase of mean airway pressure from 92 mL/min at 15 cm H2O to 1433 mL/min at 30 cm H2O. CONCLUSIONS: In a neonatal piglet model of pneumothorax treated with HFOV, with amplitude adjusted to maintain constant alveolar ventilation, gas flow through the chest tube was significantly lower at 15 Hz compared with either 10 Hz or 5 Hz. Chest tube gas flow increased with increasing inspiratory time, amplitude, and mean airway pressure. These findings support the use of higher frequencies, short inspiratory times, low amplitudes, and low mean airway pressures for healing air leak with HFOV.     

Physiologic effects of transtracheal open ventilation in postextubation patients with high upper airway resistance

OBJECTIVE: To investigate whether transtracheal open ventilation (TOV), pressure control ventilation (PCV) through a minitracheotomy tube (internal diameter 4 mm), is an effective method of inspiratory assistance under high upper airway resistance in postextubation patients; to compare, in a lung model study, TOV with other methods. DESIGN: Clinical study: A prospective, controlled, crossover study. Lung model study: A prospective laboratory trial. SETTING: Clinical study: A six-bed general intensive care unit in a teaching hospital. Lung model study: Animal research laboratory. PATIENTS: Clinical study: Eleven postextubation patients, who had undergone minitracheotomy for sputum retention between January 1997 and December 1997. SUBJECT: Lung model study: Two-bellows-in-a-box lung model, which included ordinary and high levels of upper airway resistance. INTERVENTIONS: Clinical study: Ventilatory settings were: assist/control (A/C) mode, 2 breaths/min of A/C back-up rate, 35-40 cm H2O of PCV, 0.6-0.8 secs of inspiratory time, and 0 cm H2O of positive end-expiratory pressure. The ventilatory parameters of TOV were compared with those of spontaneous breathing (SB). Lung model study: Effect of TOV on inspiratory assistance was compared with those of SB, open minitracheotomy, 5 L/min of transtracheal gas insufflation, and 5 and 10 cm H2O of pressure support ventilation (PSV), which simulated noninvasive positive ventilation. TOV ventilatory settings were: A/C mode; 30, 40, and 50 cm H2O of PCV, 0.9 secs of inspiratory time, and 0 cm H2O of positive end-expiratory pressure. At each ventilatory setting, we adjusted the inspiratory effort of the model to give a tidal volume of 0.5 L. MEASUREMENTS AND MAIN RESULTS: Clinical study: TOV was performed for 76.6 +/- 38.6 hrs (mean +/- sd) over 5.6 +/- 2.6 days without major complication. Peak tracheal pressure, which was measured distal to the minitracheotomy tube in six patients by a catheter pressure transducer, was 4.33 +/- 0.59 cm H2O. Inspiratory tidal volume delivered by the ventilator was 0.51 +/- 0.06 L. Respiratory rate during TOV was lower than during SB. According to esophageal pressure and respiratory inductive plethysmography, TOV reduced the patient's inspiratory work and improved the breathing pattern. Lung model study: Mean tracheal pressure during TOV and 10 cm H2O of PSV were positive values and they had larger inspiratory assistance according to the pressure-time product of pleural pressure. Although high upper airway resistance reduced the inspiratory assistance of PSV, it did not change the effects of TOV. CONCLUSIONS: TOV effectively reduced patient's inspiratory work and was more useful than open minitracheotomy and transtracheal gas insufflation. TOV also improved the breathing pattern. TOV may be useful for resolving some postextubation respiratory problems and avoiding the need for reintubation.     

Automatic tube compensation in patients after cardiac surgery: effects on oxygen consumption and breathing pattern

OBJECTIVE: To evaluate patients without prior pulmonary disease after cardiac surgery and to determine whether resistive unloading by automatic tube compensation, pressure support ventilation, and continuous positive airway pressure has different effects on oxygen consumption, breathing pattern, gas exchange, and hemodynamics. DESIGN: Prospective, randomized, controlled study. SETTING: Tertiary care, postoperative intensive care unit. PATIENTS: Twenty-one patients scheduled for open heart coronary artery bypass graft surgery. INTERVENTIONS: Each patient was ventilated with all three modes in random order. MEASUREMENTS AND MAIN RESULTS: Patients were ventilated in three modes, each applied for 30 mins according to computer-generated randomization: pressure support ventilation with 5 cm H2O, continuous positive airway pressure, and automatic tube compensation. Oxygen consumption was calculated by means of indirect calorimetry. The hypnotic state of the patients was monitored by Bispectral Index. For hemodynamic measurements, a fiberoptic pulmonary artery catheter was inserted. The main finding of our study was that oxygen consumption and breathing pattern (tidal volume and respiratory rate) did not differ significantly during automatic tube compensation and pressure support ventilation compared with continuous positive airway pressure (oxygen consumption, 170 +/- 29 vs. 170 +/- 26 vs. 174 +/- 29 mL.min.m, respectively; tidal volume, 466 +/- 132 vs. 484 +/- 125 vs. 470 +/- 119 mL, respectively; respiratory rate, 16 +/- 4 vs. 15 +/- 4 vs. 16 +/- 4 breaths/min, respectively). Automatic tube compensation and pressure support ventilation had no clinical effects on gas exchange and hemodynamic variables compared with continuous positive airway pressure. None of the variables differed significantly during the three ventilatory settings. CONCLUSION: In postoperative tracheally intubated patients with normal ventilatory demand, automatic tube compensation and pressure support ventilation with 5 cm H2O lead to identical oxygen consumption, breathing patterns, gas exchange, and hemodynamics. We, therefore, suggest that this group of patients does not need any additional positive pressure support from the ventilator to overcome the additional work of breathing imposed by the endotracheal tube during the weaning phase from mechanical ventilation.     

Tracheal pressure control provides automatic and variable inspiratory pressure assist to decrease the imposed resistive work of breathing

OBJECTIVE: To evaluate the operation of a continuous positive airway pressure system by using tracheal airway pressure (PT) as the control signal for system operation (i.e., tracheal pressure control). DESIGN: Repeated measures. SETTING: University research laboratory. SUBJECTS: Twelve anesthetized, spontaneously breathing swine. INTERVENTIONS: Subjects were intubated and connected to a tracheal pressure control system (5 cm H2O continuous positive airway pressure). Varying inspiratory flow demands and degrees of partial endotracheal tube occlusion (25%, 50%, and 75%) were studied. Tracheal pressure control was compared with a conventionally controlled system (pressure from breathing circuit Y-piece [PY] used as control signal) during endotracheal tube occlusion. MEASUREMENTS AND RESULTS: Imposed resistive work of breathing (work to spontaneously inhale through endotracheal tube and ventilator circuit), work by ventilation system assisting inhalation, PT, PY, tidal volume, and inspiratory flow demands were measured. As inspiratory flow demands increased (range, 0.2-2.3 L/sec), pressure assist increased automatically (range, 5-40 cm H2O) as well as work of breathing by ventilation system assisting inhalation (range, 0.2-2.5 J/L). Imposed resistive work of breathing was nullified at the lower and was negligible at the higher flow demands. During endotracheal tube occlusion with a conventionally controlled system, PY was unchanged, whereas PT decreased (up to -15 cm H2O) and imposed resistive work of breathing increased (up to 1.05 J/L). With tracheal pressure control, PY increased automatically (range, 8-52 cm H2O), whereas PT varied slightly (range, 2 to -4.6 cm H2O). Imposed resistive work of breathing was negligible (range, 0-0.2 J/L). Breathing circuit pressure (PY), not pulmonary airway pressure (PT), increased significantly during tracheal pressure control. CONCLUSIONS: Tracheal pressure control results in automatic and variable levels of pressure assist to decrease imposed resistive work of breathing under conditions of varying spontaneous inspiratory flow demands and endotracheal tube occlusion. Conventional systems are potentially flawed when PY is used as the control signal because they do not function in this manner and do not accurately assess pulmonary airway pressure.     

Effects of pressure support ventilation and continuous positive airway pressure on diaphragm performance

Many patients who are on mechanical ventilation are on ventilator modes called pressure support ventilation (PSV) and continuous positive airway pressure (CPAP) particularly when they are being weaned. As the diaphragm is responsible for approximately 75% of breathing, it is important to promote diaphragm shortening to optimize weaning from mechanical ventilation. The purpose of our 1998 quasi-experimental study was to explore the effects of PSV and CPVP on diaphragm shortening. An animal model was utilized using four Sprague-Dawley rats from the same litter purchased from Sasco (Kansas City, USA). Also measured in this study were intrathoracic pressure (DeltaITP), positive inspiratory pressure, respiratory rate, tidal volume, end-tidal carbon dioxide, central venous pressure (CVP) and mean arterial pressure (MAP). Pressure support was increased in increments of 5 cm H2O at CPAP levels of 0, 2 and 4 cm H2O. A direct assessment of diaphragm shortening was achieved through the adherence of a miniaturized ultrasonic sensor to the inferior surface of the middle costal surface of the right hemidiaphragm of four Sprague-Dawley rats. Limitations of this study included a small sample size, anaesthetized rats and abdominal dissection for insertion of the ultrasonic sensor. As PSV was increased, there was a decrease in MAP, CVP, respiratory rate and end-tidal CO2. When increasing levels of CPAP were added to PSV, a decrease in diaphragm shortening was observed. These results support that higher levels CPAP may hinder diaphragmatic function thus prolong mechanical ventilation. The purpose of this pilot study was to explore the effects of PSV and CPAP on diaphragm shortening. Also measured were DeltaITP, positive inspiratory pressure, respiratory rate, tidal volume, end-tidal carbon dioxide, CVP and MAP. Pressure support was increased in increments of 5 cm H2O at CPAP levels of 0, 2 and 4 cm H2O. A direct assessment of diaphragm shortening was achieved through the adherence of a miniaturized ultrasonic sensor to the inferior surface of the middle costal surface of the right hemidiaphragm of four Sprague-Dawley rats. Limitations of this study included a small sample size, anaesthetized rats and abdominal dissection for insertion of the ultrasonic sensor. As PSV was increased, there was a decrease in MAP, CVP, respiratory rate and end-tidal CO2. When increasing levels of CPAP were added to PSV, a decrease in diaphragm shortening was observed.     

Optimizing bag-valve-mask ventilation with a new mouth-to-bag resuscitator

When ventilating an unintubated patient with a self-inflating bag, high peak inspiratory flow rates may result in high peak airway pressure with subsequent stomach inflation; this may occur frequently when rescuers without daily experience in bag-valve-mask ventilation need to perform advanced airway management. The purpose of this study was to assess the effects of a newly developed self-inflating bag (mouth-to-bag resuscitator; Ambu, Glostrup, Denmark) that limits peak inspiratory flow. A bench model simulating a patient with an unintubated airway was used, consisting of a face mask, manikin head, training lung (lung compliance, 100 ml/0.098 kPa (100 ml/cm H(2)O)); airway resistance, 0.39 kPa/l per second (4 cm H(2)O/l/s), oesophagus (LESP, 1.96 kPa (20 cm H(2)O)) and simulated stomach. Twenty nurses were randomised to ventilate the manikin for 1 min (respiratory rate: 12 per minute) with either a standard self-inflating bag or the mouth-to-bag resuscitator, which requires the rescuer to blow up a single-use balloon inside the self-inflating bag, which in turns displaces air towards the patient. When supplemental oxygen is added, ventilation with up to 100% oxygen may be obtained, since expired air is only used as the driving gas. The mouth-to-bag resuscitator therefore allows two instead of one hand sealing the mask on the patient's face. The volunteers were blinded to the experimental design of the model until completion of the experimental protocol. The mouth-to-bag resuscitator versus standard self-inflating bag resulted in significantly (P<0.05) higher mean+/-S.D. mask tidal volumes (1048+/-161 vs. 785+/-174 ml) and lung tidal volumes (911+/-148 vs. 678+/-157 ml), longer inspiratory times (1.7+/-0.4 vs. 1.4+/-0.4 s), but significantly lower peak inspiratory flow rates (50+/-9 vs. 62+/-13 l/min) and mask leakage (10+/-4 vs. 15+/-9%); peak inspiratory pressure (17+/-2 vs. 17+/-2 cm H(2)O) and stomach tidal volumes (16+/-30 vs. 18+/-35 ml) were comparable. In conclusion, employing the mouth-to-bag resuscitator during simulated ventilation of an unintubated patient in respiratory arrest significantly decreased inspiratory flow rate and improved lung tidal volumes, while decreasing mask leakage.     

Noninvasive proportional assist ventilation compared with noninvasive pressure support ventilation in hypercapnic acute respiratory failure

OBJECTIVES: To compare short-term administration of noninvasive proportional assist ventilation (NIV-PAV) and pressure support ventilation (NIV-PSV). DESIGN: Prospective, crossover, randomized study. SETTING: Medicosurgical intensive care unit in a nonteaching hospital. PATIENTS: Twelve chronic obstructive pulmonary disease patients admitted for hypercapnic acute respiratory failure. INTERVENTION: NIV-PSV and NIV-PAV given in a randomized order after baseline evaluation in continuous positive airway pressure. Using a flow-triggering ventilator, NIV-PAV was adjusted using the runaway method and compared with NIV-PSV at similar peak inspiratory airway pressure. MEASUREMENTS AND MAIN RESULTS: Flow, airway pressure, and changes in esophageal pressure were measured and the tidal volume, the patient's inspiratory work of breathing, and the esophageal pressure--time product were calculated. Arterial pH and PaCO(2) were measured and breathing comfort was assessed using a visual analogic scale. Peak inspiratory airway pressure (17 +/- 3 cm H(2)O) and tidal volume were similarly increased with the two modalities with no change in respiratory rate. The change in esophageal pressure was similarly decreased (from 20 +/- 8 cm H(2)O in continuous positive airway pressure to 12 +/- 7 in NIV-PSV and 10 +/- 5 cm H(2)O in NIV-PAV) as well as inspiratory muscle effort indexes. Arterial pH and PaCO(2) were similarly improved. Breathing comfort was significantly improved in NIV-PAV (+38 +/- 38%) but not in NIV-PSV (+11 +/- 23%). The tidal volume was more variable in NIV-PAV (89 +/- 18%) than in NIV-PSV (15 +/- 8%) and changes in tidal volume variability were significantly correlated (p =.02) with changes in breathing comfort. CONCLUSIONS: In chronic obstructive pulmonary disease patients with hypercapnic acute respiratory failure, NIV-PAV was able to unload inspiratory muscles similarly to NIV-PSV but may be more comfortable than NIV-PSV.     

Decreasing peak flow rate with a new bag-valve-mask device: effects on respiratory mechanics,and gas distribution in a bench model of an unprotected airway

Reducing inspiratory flow rate and peak airway pressure may be important in order to minimise the risk of stomach inflation when ventilating an unprotected airway with positive pressure ventilation. The purpose of this study was to assess the effects of a newly developed bag-valve-mask device (SMART BAG), O-Two Systems International, Ont., Canada) that limits peak inspiratory flow. A bench model simulating a patient with an unintubated airway was used consisting of a face mask, manikin head, training lung (lung compliance, 100 ml/cm H(2)O, airway resistance 4 cm H(2)O/l/s, lower oesophageal sphincter pressure 20 cm H(2)O and simulated stomach). Twenty nurses were randomised to each ventilate the manikin using a standard single person technique for 1 min (respiratory rate, 12/min) with either a standard adult self-inflating bag, or the SMART BAG. The volunteers were blinded to the experimental design of the model until completion of the experimental protocol. The SMART BAG vs. standard self-inflating bag resulted in significantly (P<0.05) lower mean+/-S.D. peak inspiratory flow rates (32+/-2 vs. 61+/-13 l/min), peak inspiratory pressure (12+/-2 vs. 17+/-2 cm H(2)O), lung tidal volumes (525+/-111 vs. 680+/-154 ml) and stomach tidal volumes (0+/-0 vs. 17+/-36 ml), longer inspiratory times (1.9+/-0.3 vs. 1.5+/-0.3 s), but significantly higher mask leakage (26+/-13 vs. 14+/-8%); mask tidal volumes (700+/-104 vs. 785+/-172 ml) were comparable. The mask leakage observed is not an uncommon factor in bag-valve-mask ventilation with leakage fractions of 25-40% having been previously reported. The differences observed between the standard BVM and the SMART BAG are due more to the anatomical design of the mask and the non-anatomical shape of the manikin face than the function of the device. Future studies should remove the mask to manikin interface and should introduce a standardized mask leakage fraction. The use of a two-person technique may have removed the problem of mask leakage. In conclusion, using the SMART BAG during simulated ventilation of an unintubated patient in respiratory arrest significantly decreased inspiratory flow rate, peak inspiratory pressure, stomach tidal volume, and resulted in a significantly longer inspiratory time when compared to a standard self-inflating bag.