Evaluation in animals of a system to estimate tracheal pressure from the endotracheal tube cuff

Objective. Flow through an endotracheal tube (ETT) causes a pressure loss across the tube. This loss results in a difference between pressure measured at the airway and pressure measured in the trachea. This difference can lead to errors when calculating pulmonary mechanics and when setting ventilators. We have tested a method of estimating tracheal pressure from the pressure in the ETT cuff.Methods. Pressure transducers were placed in the proximal ETT connector, in the trachea, and in the ETT cuff (through the inflation port). Instantaneous periods of zero flow, detected with a flow meter, were used to calculate the slope and offset of the line relating cuff pressure to tracheal pressure. The system was tested on the bench using a ventilator and lung simulator and in 2 dogs and 5 pigs. Tests were performed at various cuff pressures, trachea diameters, ETT sizes, respiratory rates, tidal volumes, and airway obstructions. Results. In bench tests, our estimate of tracheal pressure was within –4.0±2.6% of the actual tracheal pressure (mean = standard deviation [SD]). In animal tests, our estimation of tracheal pressure was within –0.6±5%. In all bench test measurements and in 40 of 42 animal measurements, the error was less than 1 cm H₂O.Conclusions. The cuff estimation technique gives real-time, continuous, noninvasive tracheal pressure measurements in intubated animals with cuffed ETTs.     

Optimum versus clinically established levels of continuous positive airway pressure in respiratory therapy

To evaluate the efficacy of our routine method of cardiopulmonary monitoring for accurate management of respiratory therapy, continuous positive airway pressure (CPAP) was titrated in 11 surgical intensive care patients within ±7.5 cm H₂O of the clinically selected level. Cardiopulmonary data were independently and retrospectively reviewed by three experienced critical care physicians from three outside hospitals. Each physician estimated the optimum level of CPAP for each patient. Variability between reviewers was not statistically significant. The optimum CPAP level based on all reviewers' opinions (8.6±5.7 cm H₂O, mean±SD) was significantly lower than that selected clinically (13.2±4.5 cm H₂O;P<0.05). We conclude that current methodology for monitoring respiratory therapy is inefficient for rapid adjustment of CPAP to appropriate levels. Continuous arterial and pulmonary artery oximetry may provide an improvement in the efficacy of cardiopulmonary monitoring in the future.     

Clinical Evaluation of Tracheal Pressure Estimation from the Endotracheal Tube Cuff Pressure

Objective. Air flow through an endotracheal tube causes a pressure drop across the tube. This pressure drop creates a difference between air pressure measured in the trachea and the pressure measured in the breathing circuit, which can lead to errors when calculating pulmonary mechanics and when setting ventilators. We have developed a method of estimating tracheal pressure from the pressure in the endotracheal tube cuff and tested this system in clinical trials. Methods. Pressure measurement ports were placed between the Y piece of the ventilator circuit and the ETT connector, in the trachea at the carinal end of the ETT, and in the ETT cuff inflation line. Tracheal pressures and cuff pressures were found at end-inspiration and end-expiration (no flow states) and used to define a linear relationship between cuff pressure and tracheal pressure. Using the estimated tracheal pressure (P_trach) and the measured pressure at the Y piece of the breathing circuit (P_Y), the pressure drop across the ETT was found as a function of flow through the tube. Tracheal pressure was then calculated from the flow-dependent pressure drop and P_Y. Tests of this system were performed in six patients in the operating room and six patients in the intensive care unit. Results. The flow-based tracheal pressure estimates were within 0.7 ± 0.4 cm H₂O of actual tracheal pressure (mean ± SD). At peak inspiratory pressure the difference averaged 0.5 ± 0.3 cm H₂O. The difference between our estimate of tracheal pressure and actual tracheal pressure was always less than 1 cm H₂O. Conclusion. The flow-based tracheal pressure estimates were accurate during intermittent spontaneous breathing, but not during spontaneous breathing or with a poorly inflated cuff. The estimates were more immune to noise than the cuff-based estimates of tracheal pressure. The estimates of tracheal pressure measured from the ETT cuff should be accurate enough for clinical use in the operating room.     

Clinical review: Biphasic positive airway pressure and airway pressure release ventilation

This review focuses on mechanical ventilation strategies that allow unsupported spontaneous breathing activity in any phase of the ventilatory cycle. By allowing patients with the acute respiratory distress syndrome to breathe spontaneously, one can expect improvements in gas exchange and systemic blood flow, based on findings from both experimental and clinical trials. In addition, by increasing end-expiratory lung volume, as occurs when using biphasic positive airway pressure or airway pressure release ventilation, recruitment of collapsed or consolidated lung is likely to occur, especially in juxtadiaphragmatic lung legions. Traditional approaches to mechanical ventilatory support of patients with acute respiratory distress syndrome require adaptation of the patient to the mechanical ventilator using heavy sedation and even muscle relaxation. Recent investigations have questioned the utility of sedation, muscle paralysis and mechanical control of ventilation. Furthermore, evidence exists that lowering sedation levels will decrease the duration of mechanical ventilatory support, length of stay in the intensive care unit, and overall costs of hospitalization. Based on currently available data, we suggest considering the use of techniques of mechanical ventilatory support that maintain, rather than suppress, spontaneous ventilatory effort, especially in patients with severe pulmonary dysfunction.     

Monitoring for disconnection: Ventilators with bellows rising on expiration can deliver tidal volumes after disconnection

Anesthesia ventilators with bellows that rise on expiration (standing bellows) are favored over ventilators with bellows that descend during expiration (hanging bellows). Standing bellows will not rise if there is a disconnection, and thus they facilitate detection of disconnections. Yet, during a disconnection of ventilators with standing bellows, mechanical inspiration compresses the empty bellows beyond its resting position; with expiration the elastic bellows recoils and aspirates up to 140 ml, depending upon the fresh gas flow. Tidal volumes recorded after disconnection ranged from 50 to 140 ml (mean, 112.2 ± 9.22 [SD]) at adult settings and from 55 to 90 ml (mean, 69.8 ± 4.28 [SD]) at pediatric settings. Thus, spirometers that measure tidal volume (Vt) in the expiratory limb of the breathing system may falsely indicate an expiratory Vt after a disconnection of the breathing system at the Y-piece or the endotracheal tube. Existing low-pressure alarms and capnography alarms provide redundant warning of disconnection, however, should the ventilator continue to deliver small Vts after a disconnection.     

Blood pressure monitoring: Automated oscillometric devices

An understanding of the principles of blood pressure measurement with automated oscillometric devices (e.g., Dinamap) allows a user to realize the purpose and level of accuracy for which the equipment is designed. Good technique calls for various actions: (1) using a cuff of proper size (too large a cuff will generally work acceptably, but too small a cuff will yield erroneously high readings); (2) squeezing all of the residual air out of the cuff before applying it to the arm or leg; (3) wrapping the cuff snugly around the arm or leg; (4) instructing the patient to refrain from talking or moving and letting nothing press against the cuff during measurement; (5) keeping the cuff and heart at the same horizontal level. (6) When instrument malfunction is suspected, first checking the status of the patient (not the status of the instrument) to be sure that a clinical emergency is not causing the suspected malfunction; (7) repeating a reading several times when it is suspicious and, if necessary, modifying the measurement conditions by using, for example, different limbs or different cuffs until the question is resolved; and (8) remembering that a leak in the cuff, hoses, or connection can cause an unexpected malfunction.     

气道压力释放通气和持续气道正压开放肺的比较

目的探讨气道压力释放通气（APRV）与持续气道正压（CPAP）通气两种通气模式实施肺复张策略治疗急性呼吸窘迫综合征（ARDS）对血流动力学、肺力学和氧代谢指标的影响。方法选择ARDS行机械通气及脉搏轮廓法持续血流动力学监测的患者15例，随机实施APRV模式肺复张或CPAP模式肺复张，每隔4h复张1次。其中APRV组设定高水平压力（Phigh）为35cm H2O（1cm H2O=0．098kPa），低水平压力（Plow）为压力-容积（P—V）曲线的下拐点（LIP）；CPAP组设定CPAP为35cm H2O；两组持续时间均为40s。记录复张前后的肺力学、氧代谢指标以及复张时的血流动力学变化。结果在APRV模式下行肺复张时心脏指数（CI）轻度下降，且持续时间较短。两种复张模式均可使肺顺应性等力学参数及氧合明显改善，以APRV模式尤为明显。结论采用APRV模式进行ARDS肺复张治疗可避免镇静剂的使用，对血流动力学干扰较小，对肺力学及氧合的改善优于CPAP模式。     

Continuous positive airway pressure (CPAP) vs. intermittent mandatory pressure release ventilation (IMPRV) in patients with acute respiratory failure

Intermittent Mandatory Pressure Release Ventilation (IMPRV) is a positive pressure spontaneous breathing ventilatory mode in which airway pressure is released intermittently and synchronously with patient's spontaneous expiration in order to provide ventilatory assistance. Eight critically ill patients free of any factor known to alter chest wall mechanics (group 1) and 8 critically ill patients whose spontaneous respiratory activity was markedly altered by a flail chest, or by a C₅ quadraplegia and/or by the administration of opioids (group 2) were studied prospectively. CPAP and IMPRV were administered to each patient in a random order during a 1 h period using a CESAR ventilator. Gas flow, tidal volume, tracheal pressure, esophageal pressure, end-expiratory lung volume and hemodynamic parameters were measured. In group 1 patients, the ventilatory assistance provided by IMPRV was associated with a significant decrease in spontaneous tidal volume whereas all other respiratory parameters remained unchanged. In group 2 patients, IMPRV increased minute ventilation from 8.0±2.61/min to 12.2±1.81/min (p<0.05), decreased PaCO₂ from 46±7.3 mmHg to 38±6.8 mmHg (p<0.05) and reduced respiratory frequency from 21±10 bpm to 14±5.7 bpm (p<0.07). These results show that IMPRV provides significant ventilatory assistance to patients with mild acute respiratory failure either by decreasing patient's contribution to minute ventilation or by increasing alveolar ventilation in presence of respiratory depression of central or peripheral origin.Presented in part at the 32th Congrès National d'Anesthésie-Réanimation, Paris, September, 24, 1990 and at the Annual Meeting of the American Society of Anesthesiologists, Las Vegas, Nevada, October 22, 1990     

Prototype ventilator and alarm algorithm for the NASA space station

An alarm algorithm was developed to monitor the ventilator on the National Aeronautics and Space Administration space station. The algorithm automatically identifies and interprets critical events so that an untrained user can manage the mechanical ventilation of a critically injured crew member. The algorithm was tested in two healthy volunteers by simulating 260 critical events in each volunteer while the volunteer breathed via the ventilator. Thirteen critical events were induced eight times in random order, for the five different modes of ventilation. These events included various ventilator tubing disconnects, leaks, and occlusions, as well as power and gas supply failures. The algorithm identified the critical events and generated alarms in response to 99.2% (516 of 520, total) of the events. The alarm textual messages were correct 98% (505 of 516 messages) of the time. The alarm algorithm is an improvement over current alarms found on most ventilators because its alarm messages specifically identify failures in the patient breathing circuit or ventilator. The system may improve patient care by helping critical care personnel respond more rapidly and correctly to critical events.     

双水平正压通气在急性心源性肺水肿中的应用

目的:探讨双水平正压通气治疗急性心源性肺水肿的疗效。方法:收集内科2003年1月至2007年8月收治的92例急性心源性肺水肿患者的临床资料并进行分析。治疗组46例在应用常规抗心源性肺水肿药物的同时联用BiPAPS/T30或BiPAP-Synchrony呼吸机进行无创通气治疗,对照组46例只应用常规药物治疗。结果:治疗组患者临床症状、体征明显改善,心率、呼吸频率、血压与治疗前比较显著降低,SaO2与治疗前比较显著增高(P<0.05),总有效率93.5%。对照组总有效率仅为82.6%。结论:双水平正压通气治疗急性心源性肺水肿疗效确切。     

动态监测气道闭合压在预测脱机成功率中的应用

目的：探讨动态监测气道闭合压（Ｐ０．１）在预测成功脱机中的应用意义。方法：各种呼吸衰竭需要机械通气患者在应用压力支持通气（ＰＳＶ）脱机时，每８小时测定１次Ｐ０．１，同时记录患者的潮气量（ＶＴ）、通气量（ＶＥ）、呼吸频率（ＲＲ）、潮气末二氧化碳分压（ＥＴＣＯ２）、经皮血氧饱和度（ＳｐＯ２），以及压力支持（ＰＳ）水平，将患者分为脱机成功组（２４例）和脱机失败组（１６例）进行对照分析。结果：在ＰＳＶ期间，脱机成功组Ｐ０．１、ＶＥ均无明显变化（Ｐ＞０．０５）；脱机失败组Ｐ０．１结束前值（０．７５±０．３６ｋＰａ，１ｋＰａ＝１０．２０ｃｍＨ２Ｏ）与基础值（０．４１±０．２８ｋＰａ）以及与脱机成功组同期值（０．２７±０．０９ｋＰａ，０．２８±０．１５ｋＰａ）比较均明显升高（Ｐ均＜０．０１），ＶＥ较脱机成功组明显升高（Ｐ＜０．０５）。Ｐ０．１与ＶＥ明显相关（ｒ＝０．６２，Ｐ＜０．０５）。结论：动态观察Ｐ０．１，对于常规参数处于边缘值欲脱机患者将可明显提高脱机成功率。     

重症监护病房人工气道气囊压力连续监测的方法探究

目的连续监测重症监护病房有创呼吸机治疗的气管插管建立人工气道的危重病人气囊压力的变化。方法采用专用的PORTEX气囊压力监测表,通过首次气囊压力校正后,分别于校正后2 h、4 h、6 h、8 h连续监测患者气囊压力。结果首次气囊压力校正后2 h、4 h、6 h8、h,患者气囊压力分别为(2.85±0.23)kPa,(2.00±0.35)kPa,(1.81±1.98)kPa以及(1.77±0.00)kPa。校正后6 h参与气囊压力测量人数降为初始测量人数的50%,校正后8 h参与气囊压力测量人数则降为初始测量人数的12.5%。结论对于收入重症监护病房治疗的气管插管建立人工气道的危重病人,应该至少每隔4 h注气校正一次,才能防止套囊漏气及相应并发症的发生。     

Evaluation of a microcomputer-based clinical laboratory data acquisition system linked with a minicomputer-based patient data management system

We describe a microcomputer-based clinical laboratory data acquisition system linked with a minicomputer-based patient data management system and report on its performance. The system consists of a microcomputer and six laboratory analyzers: a blood gas analyzer, a flame photometer, a plasma osmotic pressure meter, a chloride ion titrator, a blood sugar analyzer, and a hemoglobin concentration and saturation meter. With the addition of a previously developed microinterface unit to each laboratory analyzer, data from each analyzer can be automatically transmitted to the micro-computer through a communication network. These data are then automatically transmitted to the patient data management system and thereby become part of that data base. Performance of this system was evaluated in two ways: (1) by comparing the turnaround time from an anesthetist's order for a laboratory analysis to receipt of the analysis with the time required in a control situation and (2) by comparing the number of steps a laboratory technician is required to walk to obtain and deliver the laboratory result with the number of steps required in a control situation in which no system was used. The turnaround time and the number of steps walked using this system were 552±41 seconds (n=19,P<0.001) and 197±31 steps, respectively (n=19,P<0.001), contrasted with 622±52 seconds and 374±87 steps without the system.     

Optimal endexpiratory airway pressure for ventilated patients

In patients ventilated for acute respiratory failure PEEP was changed either by gradual increase and decrease (5 cm H₂O/min) or in steps of 5 cm H₂O. The effects on gas exchange, pulmonary mechanics and pulmonary and systemic circulation were studied. Total compliance did not change uniformly and cardiac index decreased so much due to PEEP that the increase in P_aO₂ could not prevent the decrease of arterial oxygen transport. No variable was found helpful to predict the best PEEP in a clinical situation.With the support of the Swiss National Fund for the advancement of Scientific Research, Berne. Application No. 3.831-0.79     

A proposal for scientific validation of instruments for indirect blood pressure measurement at rest,during exercise,and in critical care

Objective. The purpose of this study was to provide a critical review and comprehensive outline of published guidelines for the validation of monitors for indirect blood pressure (BP) measurement in light of recent research and practical clinical experienceMethods. Studies testing the reliability and validity of BP monitors and available guidelines for validation have been reviewed and comparedResults. The validation studies of instruments for indirect BP measurement have used a wide variety of sample pools, BP ranges, protocols, reference instruments, and statistical procedures, thereby making it impossible to reach a consensus Few existing recommendations for validation have been found to be incomplete with respect to BP in various physiological states, sequence of procedures, sample, and statistical analysisConclusions. A new sequence of procedures for validation, including assessment of instruments during exercise and in critical care, is introduced Previously suggested sample sizes for study subjects, age, and BP groups, as well as margins of error, are statistically challenged Insufficiency of linear relationship and aggregate agreement alone in determining the interchangeability between a reference and test instrument is demonstrated by quantification of agreement     

Noninvasive positive pressure ventilation in infants with upper airway obstruction: comparison of continuous and bilevel positive pressure

Objective This study evaluated the efficacy of noninvasive continuous positive pressure (CPAP) ventilation in infants with severe upper airway obstruction and compared CPAP to bilevel positive airway pressure (BIPAP) ventilation.Design and setting Prospective, randomized, controlled study in the pulmonary pediatric department of a university hospital.Patients Ten infants (median age 9.5 months, range 3—18) with laryngomalacia (n=5), tracheomalacia (n=3), tracheal hypoplasia (n=1), and Pierre Robin syndrome (n=1)Interventions Breathing pattern and respiratory effort were measured by esophageal and transdiaphragmatic pressure monitoring during spontaneous breathing, with or without CPAP and BIPAP ventilation.Measurements and results Median respiratory rate decreased from 45 breaths/min (range 24–84) during spontaneous breathing to 29 (range 18–60) during CPAP ventilation. All indices of respiratory effort decreased significantly during CPAP ventilation compared to unassisted spontaneous breathing (median, range): esophageal pressure swing from 28 to 10 cmH₂O (13–76 to 7–28), esophageal pressure time product from 695 to 143 cmH₂O/s per minute (264–1417 to 98–469), diaphragmatic pressure time product from 845 to 195 cmH₂O/s per minute (264–1417 to 159–1183) During BIPAP ventilation a similar decrease in respiratory effort was observed but with patient-ventilator asynchrony in all patients.Conclusions This short-term study shows that noninvasive CPAP and BIPAP ventilation are associated with a significant and comparable decrease in respiratory effort in infants with upper airway obstruction. However, BIPAP ventilation was associated with patient-ventilator asynchrony.     

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。     

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.     

The evaluation of a new intravascular blood gas monitoring system in the pig

Objective. Our objective was to investigate the accuracy of a new intravascular blood gas sensor, the Paratrend 7 (P7) (Biomedical Sensors Ltd, Pfizer Hospital Products Group, High Wycombe, England) in a porcine model.Methods. A total of 12 sensors were inserted into 10 animals under total intravenous anesthesia. Changes in blood gas chemistry were produced over a wide range by manipulating the inspired oxygen and carbon dioxide concentrations and by adjustments in minute ventilation. Blood gas samples (BGA) were taken and analyzed during periods of stability; the results obtained were compared with the readings from the intravascular sensor.Results. A total of 292 blood gas samples were taken and analyzed for pHa, Paco ₂, andPo ₂; the results were compared with the readings from the intravascular sensor. Correlation coefficients ofr=0.98 forPco ₂ andr=0.99 for Po ₂ were obtained. Analysis of bias and precision as mean±SD of the difference (P7 — BGA) gave the following results: pH bias=–0.03, precision=±0.04;Pco ₂ bias = 0.65 mm Hg, precision=±3.1 mm Hg; andPo ₂ bias=–6.50 mm Hg, precision=±0.6 mm Hg. No problems with clot formation on the sensor were seen, and the sensors did not appear to show the wall effect seen with other systems.Conclusions. The results obtained were well within the requirements for a clinically useful blood gas monitoring system.     

持续气道正压-比例压力支持-自动管道补偿与双水平气道正压-压力支持通气两种模式撤机方法的比较

目的 :比较持续气道正压比例压力支持自动管道补偿 (CPAP PPS ATC)与双水平气道正压压力支持通气 (BIPAP PSV)两种模式撤机方法的结果。方法 :CPAP PPS ATC组 42例 ,BIPAP PSV组 40例 ,采用对照研究方法 ,比较两种通气模式、起始参数的调节、解决通气机依赖特点及撤机成功率。结果 :两种模式的撤机成功率无明显差异 (P>0 .0 5 ) ,两种模式均无人机对抗 ,CPAP PPS ATC模式较 BIPAP PSV模式对通气机依赖患者有更大的自主性 ,更容易实现撤机。结论 :BIPAP PSV为压力控制与自主呼吸相结合模式 ,CPAP PPS ATC为自主模式 ,CPAP PPS ATC是一种更好的机械通气撤机模式