10/23/98 PAV 新一代无创辅助通气模式 Over the last decade the use of noninvasive pressure support ventilation has attracted much interest among clinicians in the acute and chronic environment. In the acute environment, noninvasive PSV has proven to be successful in avoiding intubation 75% of the time. Proportional Assist Ventilation or PAV may prove to be the next generation in noninvasive ventilation. PAV Workshop

成比例辅助通气 新型辅助通气模式 呼吸机产生压力与病人呼吸努力成比例 概念完全更新 随病人呼吸努力的变化而自动调节 10/23/98 PAV is a new mode of ventilation that is fundamentally different from volume and pressure ventilation as we practice today. In PAV, the ventilator generates a pressure change to cause airflow and move volume into the patients lungs. Unlike conventional ventilation the pressure is generated in proportion to the patient’s own inspiratory efforts. PAV tracks and responds to changes in patient’s breathing pattern and efforts. PAV Workshop

成比例辅助通气 辅助并扩大病人的呼吸努力 允许病人沿用原来的呼吸方式 减少病人的呼吸功耗 如何工作? 10/23/98 PAV is a mode of ventilation that assists and augments ventilation based on the patients own breathing pattern. This means the patient is able to maintain a normal breathing pattern while excess work of breathing is eliminated. PAV Workshop

成比例辅助通气 辅助并扩大病人的通气量 放大病人呼吸努力 类似助力方向盘 呼吸努力增大/辅助增大 由病人决定辅助的大小 如何工作? 10/23/98 成比例辅助通气 如何工作? 辅助并扩大病人的通气量 放大病人呼吸努力 类似助力方向盘 呼吸努力增大/辅助增大 由病人决定辅助的大小 Ventilation is not augmented based on a predetermined volume or pressure. Rather the patient’s inspiratory effort is simply amplified. The analogy of PAV to power steering is frequently made in the literature. If the patient makes a larger effort, the ventilator will adjust to supply more assistance. With a smaller effort there will be less assistance. The patient is in control. PAV Workshop

基本概念 辅助并扩大病人的通气量 1:1 2:1 ASSIST (Paw) EFFORT (Pmus) 10/23/98 This graphic illustrates the interaction between patient effort or P muscle and the assist supplied by PAV. In the first example on the right hand side of the slide, patient effort is amplified in a 1:1 proportion. In the second example, PAV amplifies the patient’s inspiratory effort in a 2:1 proportion. Airway pressure or Paw is not preset; the proportionality of support determines the extent to which the patient’s effort is amplified. Paw will vary depending on patient effort allowing the patient to be in control. PAV Workshop

成比例辅助通气 允许病人正常呼吸模式 病人努力决定 压力 潮气量 流速及波形 呼吸频率 吸呼比 如何工作? 10/23/98 The PAV mode follows the patient; the patient is responsible for establishing there own breathing pattern in every sense. The patient controls pressure, volume, inspiratory flowrate and pattern, respiratory rate and I:E ratio. There is no preset variable as in conventional ventilation. Patient effort determines airway pressure, tidal volume and inspiratory flowrate. These variables will be amplified based on the physiologic needs of the patient. PAV Workshop

成比例辅助通气 减少呼吸作功 呼吸机可分担一部分呼吸功 呼吸机的辅助比例可调 如何工作? 10/23/98 By amplifying the patient’s volume and flow, the ventilator is assuming a share of the workload. This results in an unloading of the respiratory muscles. The share or proportion of the workload assumed by the ventilator is adjustable based on the patient’s clinical needs. PAV Workshop

10/23/98 基本概念 静止 压力相等 自主呼吸 无气流 In order to provide a foundation for our discussion on PAV theory, let’s take a few minutes and review some of the basics of breathing. Normal resting ventilation is a cyclical activity consisting of the inward flow of air called inspiration and the outward flow called exhalation. During each cycle a volume of air moves in and out of the lungs. These cahnges occur as a result of pressure gradients between the airway opening or mouth and the alveoli. Prior to the beginning of inspiration, the pressures at the airway opening and in the alveoli are equivalent. Since there is no pressure gradient, there is no air movement. PAV Workshop

基本概念 吸气时 肌肉收缩 压力变化 空气进入肺内 自主呼吸 -2 -2 10/23/98 -2 -2 As inspiration begins, the respiratory muscels contract. The chest wall moves outward and the diaphragm descends. This creates a drop in the alveolar pressure; the pressure gradient between the airway opening and the alveoli results in an inward movement of air. The volume change that occurs is called the tidal volume. PAV Workshop

基本概念 气道阻力 弹性阻力 呼吸功 通气阻力 -2 -2 10/23/98 Normally there are forces within the respiratory system that oppose inflation of the lung and therefore ventilation. These forces can be grouped into two categories: 1) elastic opposition to expansion of the lungs and 2) the frictional opposition or resistance to air movement. The pressure change that is genereated on inspiration must be sufficient to overcome these forces. The effort required and the resulting volume change is termed “work of breathing”. Normal work of breathing is minimal. A pressure gradient of 2 - 5 cmH20 is typically needed to move a normal tidal volume when the opposing forces are normal. Let’s review the opposing forces and what they mean in terms of breathing. PAV Workshop

PAV 操作原则 PAV 控制用于: 改善生理异常 代偿呼吸肌肉衰竭 PAV 控制 10/23/98 Controls used in proportional assist ventilation function very different from those in volume and pressure ventilation. There are no controls that are used to predetermine any variable of ventilation -- volume, pressure, flow, rate etc. Instead the controls are used to target ventilation to overcome the specific physiologic abnormalities and amplifying the patient’s accordingly. PAV Workshop

基本概念 弹性阻力 肺扩张时产生的弹性回缩力 正常值 10 cmH2O/L 压力 / 容量 = 弹性阻力 10/23/98 基本概念 呼吸阻力 弹性阻力 肺扩张时产生的弹性回缩力 压力 / 容量 = 弹性阻力 正常值 10 cmH2O/L 5 cmH2O / 0.5 L = 10 cmH2O/L Because the lung tissue is made up of elastic and collagen fibers, the lungs possess a property called elastance. In physics, elastance is defined as the tendency of a structure to offer resistance to a stretching force. In terms of ventilation, elastance is the tendency of the lungs to resist inflation. A certain amount of pressure is required to stretch the lungs to a certain volume. A normal value for elastance is about 10 cmH2O/L. In disease, the lungs may become stiffer; the same pressure change may result in a smaller volume change. The elastance of the lungs is higher. What types of lung diseases would alter the elastance of the lungs? Pneumonia, pulmonary edema and ARDS are common conditions affecting elastance. Speaker note: Other responses may include fibrotic lung disease, pneumothorax, pleural effusion, kyphoscoliosis, obesity. Compliance is another term used to describe the lungs opposition to inflation. Compliance measures the distensibility of the lungs or ease with which the lungs inflate. Mathematically, compliance is the inverse (reciprocal) of elastance. For purposes of our discussions on PAV, we will always talk about elastance. PAV Workshop

基本概念 通气的摩擦阻力 空气在气道中流动时产生的阻力 正常值 2.5 cmH2O/L/sec 呼吸阻力 压力 / 流速 = 气道阻力 10/23/98 基本概念 呼吸阻力 通气的摩擦阻力 空气在气道中流动时产生的阻力 压力 / 流速 = 气道阻力 正常值 2.5 cmH2O/L/sec 5 cmH2O / 0.5 L/sec = 2.5 cmH2O/L/sec The second opposing force that is encountered in ventilation are the frictional forces. Impedance to air movement through the airways is called airways resistance. Resistance is defined as the ratio of the pressure change responsible for air movement and the rate of air flow. A normal value is 2.5 cmH2O/L/sec. Factors that affect airways resistance include the size of the airway, its shape and the caliber. Different diseases affect those properties, altering airways resistance. COPD or chronic obstructive pulmonary disease is the most frequently encountered lung disease that increases airways resistance. PAV Workshop

基本概念 气道阻力 弹性阻力 呼吸功 呼吸阻力 -2 -2 10/23/98 Normally there are forces within the respiratory system that oppose inflation of the lung and therefore ventilation. These forces can be grouped into two categories: 1) elastic opposition to expansion of the lungs and 2) the frictional opposition or resistance to air movement. The pressure change that is genereated on inspiration must be sufficient to overcome these forces. The effort required and the resulting volume change is termed “work of breathing”. Normal work of breathing is minimal. A pressure gradient of 2 - 5 cmH20 is typically needed to move a normal tidal volume when the opposing forces are normal. Let’s review the opposing forces and what they mean in terms of breathing. PAV Workshop

基本概念 流速 病人努力 及/或 容量 疾患肺的呼吸情况 正常人 患者 10/23/98 This graphic represents the relation between patient effort and its impact on ventilation under normal conditions and with disease or altered elastance and resistance. In disease more effort is required to move flow or volume. PAV Workshop

基本概念 增加肺泡分钟通气量 减少呼吸功 纠正血气异常 通气支持目标 10/23/98 The goals of ventilatory support are clearly defined. They are to: improve alveolar ventilation decrease the work of breathing improve gas exchange. Mechanical ventilation, by itself, will not change the opposing forces of ventilation. The objective is to reduce the impact of those forces until the abnormalities resolve. PAV Workshop

PAV 操作原则 医生调节控制 容量辅助(VA) 流速辅助 (FA) 辅助百分比设定 PAV 控制 10/23/98 There are 3 clinician adjustable controls for the PAV mode: Volume Assist, Flow Assist, and % Set. Let’s look at each one of these to understand how they interact with the patient. PAV Workshop

PAV操作原则 目标压力克服弹性阻力 增大潮气量 容量辅助 (VA) VA 初始 容量信号 放大的 容量信号 病人 VT BiPAP 10/23/98 PAV操作原则 容量辅助 (VA) 目标压力克服弹性阻力 增大潮气量 初始 容量信号 放大的 容量信号 Volume Assist is the control that is used to counterbalance the effects of an altered elastance. Since elastance impacts inflation or volume change within the lungs, VA amplifies the patient’s effort by amplifying tidal volume. The patient’s effort generates a certain volume signal. That volume signal is then amplified based on the VA setting. VA 病人 VT BiPAP Vision 正常VT 自主努力 PAV Workshop

PAV操作原则 目标压力是克服气道阻力 增大病人的吸气流速 流速辅助 (FA) FA 正常V 初始 流速信号 放大的 流速信号 病人努力 10/23/98 PAV操作原则 流速辅助 (FA) 目标压力是克服气道阻力 增大病人的吸气流速 初始 流速信号 放大的 流速信号 Flow Assist is used to target airways resistance. Resistance is the force that opposes air flow in the airways. The FA control amplify the patient’s flow signal to achieve an appropriate flowrate. VA and FA follows the patient and amplifies his/her effort based on their specific needs. For instance, a COPD patient with a normal elastance and an increased resistance may only require assistance in overcoming resistance to airflow. FA 病人努力 病人 V BiPAP Vision 正常V PAV Workshop

PAV操作原则 决定呼吸机作功的比例 决定 VA 及 FA 辅助百分比 达到正常潮气量所需作功的百分比 达到正常吸气流速所需作功的百分比 10/23/98 PAV操作原则 辅助百分比 决定呼吸机作功的比例 决定 VA 及 FA 达到正常潮气量所需作功的百分比 达到正常吸气流速所需作功的百分比 % Set determines the proportion of work assumed by the ventilator and applies to both FA and VA. For example: if VA is set to match elastance and FA is set to match airways resistance, the ventilator would do 100% of the work. % Set would then allow you to adjust that workload. 80% Set means the patient does 20% of the work to overcome elastance and resistance and the Vision would do 80%. 病人 Vision PAV Workshop

快捷菜单 选择一项: 阻塞性疾患 Obst. 限制性疾患 Rest. 调节至病人感觉舒适 混合性 Obst. & Rest. 正常肺 10/23/98 选择一项: 阻塞性疾患 Obst. 限制性疾患 Rest. 调节至病人感觉舒适 混合性 Obst. & Rest. The method of titration described for adjusting PAV controls can be simplified by using the Quick Start Menu in the Vision. There are four options based typical elastance and compliance values for 4 different clinical situations. The patient with obstructive disease will have a relatively normal elastance and an increased resistance. The patient with restrictive disease will have an increased elastance and normal resistance. Some patients may have combined processes. For example the COPD patient that is admitted with pneumonia. This patient has an altered elastance from the pneumonia and an increased resistance from the COPD. Then there is the patient being ventilated for reasons not related to a pulmonary problem: the head injury patient, for example. When using the Quick Start options, % Set is the only control to be manipulated. 正常肺 PAV Workshop

请看机器

转换工作模式 PAV/T 模式

设定参数 在快捷菜单中选阻塞性疾患

设定参数及后备频率 在快捷菜单中选阻塞性疾患

监护屏 在快捷菜单中选阻塞性疾患

更改参数屏 在快捷菜单中选阻塞性疾患

用户设定 起始点, 80 - 100% 确定病人合适的负荷比例 设定辅助比例 VA VA Pt Effort Pt Effort 10/23/98 用户设定 设定辅助比例 起始点, 80 - 100% 确定病人合适的负荷比例 VA VA Pt Effort Elastance Elastance In the acutely ill patient with respiratory failure, the % Set is generally set at 80 - 100%. As the patient’s muscles are rested or the underlying disease process improves the % Set can be decreased to allow the patient to reassume the work of breathing. Pt Effort Example: % Set = 75% Example: % Set = 25% PAV Workshop

容量辅助的设定 起点, 5 cmH2O/L 每次调高 2 cmH2O/L 调节至病人感觉舒适 或 “气流过大” 刚好克服其弹性阻力 10/23/98 起点, 5 cmH2O/L 每次调高 2 cmH2O/L 调节至病人感觉舒适 或 “气流过大” NO 刚好克服其弹性阻力 YES “压力过高” NO YES Volume assist can be set in one of two ways. The first method is to measure elastance and set the VA to match that measurement. Sounds simple but the difficulty arises in obtaining a measurement of elastance. There are many pitfalls in trying to obtain an accurate measurement With noninvasive ventilation, variable leaks in the system can introduce errors into measurements, So, the method typically used in noninvasive application is titration of the VA, staring with a normal value, until the point of overassist. At this point the VA is equal to or just exceeds the patient’s elastance and the setting can be decreased by 1-2 cmH2O/L. Overassist is identified through observation and patient assessment. If the patient states he is getting too much air or the pressure feels too high, this is overassist. If the patient activates his expiratory muscles to stop inspiration it is an indication of overassist. Activation of alarms may also help to identify overassist. 达到报警上限 NO YES 将VA 减小1-2个单位, 使病人感觉舒适 病人自主吸气困难 NO PAV Workshop

流量辅助的用户设定 起点, 调节至病人舒适 2 cmH2O/L/sec 每次调高 1 cmH2O/L/sec OR 等于气道阻力 10/23/98 起点, 2 cmH2O/L/sec 每次调高 1 cmH2O/L/sec 调节至病人舒适 OR 等于气道阻力 “气流过快” YES NO 达到报警上限 YES NO FA can be set to match the measurement of airways resistance. Again, accurate measurement are difficult to obtain. Titration of FA to estimate resistance is the best approach in noninvasive ventilation. The typical staring point is 2 cmH2O/L/sec which is a normal resistance. The value is then adjusted upward until the patient indicates the air is coming too fast or preset alarms are activated. 将FA减小1-2个单位, 使病人感觉舒适 吸气时漏气 YES NO PAV Workshop

PAV操作原则 克服弹性 阻力之压力 克服气道阻力之压力 10/23/98 Many times the question arises regarding the necessity to have two controls, one that generates pressure to overcome elastance and one that overcomes resistance. Why not just one control that generates pressure to overcome the opposing forces. This graph of airway pressure during a positive pressure breath illustrates the reason. The pressure generated during the first part of the breath overcomes the airway resistance. And the pressure required to overcome elastance and move volume into the lungs is more gradual. 克服气道阻力之压力 PAV Workshop

PAV操作原则 最大程度减少辅助（VA/FA）过度 2 种可调PAV 限制 最大PAV 压力 最大PAV 潮气量 PAV限制 10/23/98 PAV操作原则 PAV限制 最大程度减少辅助（VA/FA）过度 2 种可调PAV 限制 最大PAV 压力 最大PAV 潮气量 To prevent overassist, limits for pressure and volume should be set before titrating VA and FA. Dr. Magdy Younes’ work suggests that a pressure limit of 30 cmH2O should be set and a volume limit of 1.5 liters. The volume limit suggested may be low in a noninvasive application due to leaks. An appropriate setting may be 2.0 -2.5 L and should be assessed based on the interface integrity. PAV Workshop

10/23/98 通气模式的比较 Differences in the way volume, pressure and PAV ventilation respond to changes in patient effort are illustrated in this graphic. Patterns of patient effort illustrate a feeble effort, a moderate ore sustained effort, and a strong effort. Greater patient effort during volume cycled ventilation, elicit a corresponding decrease in airway pressure. In PSV, airway pressure is not affected by changes in effort. With PAV, airway pressure increases in proportion with the patient effort. The other difference illustrated in this graphic is inspiratory time. In volume ventilation, inspiratory time is related to the time it takes to deliver the set VT. By comparison, in PAV, inspiratory time is linked to the end of the patient’s inspiratory effort. PAV Workshop

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PAV 的临床研究 假设: PAV 模式可追踪病人呼吸努力并分担呼吸肌肉作功 N = 4 正常受试者 通气参数由实验中获得 10/23/98 Dr. Madgy Younes, the founding father of proportional assist ventilation, published the initial clinical trials of this mode in 1992. The first studies set out to investigate two basic assumptions. The first assumption was that PAV tracks respiratory efforts and unloads respiratory muscles under high ventilatory demand conditions. Four normal individuals were studied during exercise with and without PAV. PAV Workshop

临床研究 无辅助 PAV VT , L 2.02 2.39 f, bpm 28.0 27.5 Ti, sec 1.10 1.06 10/23/98 临床研究 正常人 无辅助 PAV VT , L 2.02 2.39 f, bpm 28.0 27.5 Ti, sec 1.10 1.06 Te, sec 1.08 1.16 VE, L/min 2.29 2.75 P pl 25 , cmH O -4.8 -2.5 75, cmH -13.7 -4.5 T Ventilatory parameters and pressure were measured when the subject was at approximately 80% of estimated maximal power output. Volume and flow measurements were higher during PAV. Effort decreased during inspiration indicating an unloading of the respiratory muscles. Waveforms analysis illustrated that PAV was able to track patient changes in ventilatory demand. 2 2 Younes, Am Rev Resp Dis 1992, 145:121-129 PAV Workshop

临床研究 假设: PAV模式上机病人气道峰压下降 N = 5 上机病人 与SIMV比较通气及血气参数 10/23/98 A second hypothesis in this study was that ventilator dependent patients can be maintained on PAV with lower airway pressures than conventional ventilation. % patients who had been ventilated for 3 - 6 days were studied on SIMV and in the PAV mode. PAV Workshop

临床研究 SIMV PAV VE, L/min 15.2 16.4 15.0 V , L 1.00 0.63 0.58 PIP, cmH O 10/23/98 临床研究 上机患者 SIMV PAV 10 min 1–3 Hrs VE, L/min 15.2 16.4 15.0 V , L 1.00 0.63 0.58 PIP, cmH 2 O 35.4 16.6 15.6 f, bpm 29.2 25.4 26.6 PaCO2, mmhg 37.8 39.0 40.4 PaO2, mmHg 102 98 107 T When the patients were switched from SIMV to PAV ventilation, tidal volume decreased but minute ventilation was maintained and gas exchange normalized. Speaker note: In SIMV, the patients tidal volume was 0.23L at a rate of 18.2. The 1.0L Vt was machine delivered at a rate of 10.4. This explains the minute ventilation of 15.2L/min As hypothesized peak airway pressures were significantly lower during PAV ventilation: Pressures in SIMV were 35.4 cmH2O and 15.6 during PAV. Conclusion drawn from this initial clinical study were that ventilation in proportion to inspiratory effort is effective. Patients can be ventilated at lower pressures and there is no deterioration in gas exchange. Younes, Am Rev Resp Dis 1992, 145:121-129 PAV Workshop

文献复习 急性呼吸窘迫 11 例急性呼吸衰竭患者 入选指征 : 呼吸衰竭的原因: 需要立即插管 清醒 临床情况可逆转 肺水肿 10/23/98 文献复习 急性呼吸窘迫 11 例急性呼吸衰竭患者 入选指征 : 需要立即插管 清醒 临床情况可逆转 呼吸衰竭的原因: 肺水肿 败血症/ARDS 哮喘持续状态 肺炎 In 1996, Dr. Patrick and colleagues evaluated the efficacy of noninvasive ventilation in patients with acute respiratory failure as a result of an acute reversible medical condition. The mode of ventilation used was proportional assist. The eleven patients admitted to the studied were considered to be candidates for immediate intubation. Additionally these patients were conscious with spontaneous breathing efforts and the precipitating condition was considered to be reversible. The cause of respiratory failure varied. Five patients had pulmonary edema secondary to CHF, two had ARDS, two were in status asthmaticus and two had pneumonia. FA and VA were adjusted to patient comfort or overassist. Three patients failed early; two because of interface intolerance and one patient had a depressed respiratory drive. PAV Workshop

文献复习 Pre-Assist PAV Assist 7.27 7.31 52.8 45.5 8.4 2.9 4.0 1.2 37.3 23 10/23/98 文献复习 急性呼吸窘迫 Pre-Assist PAV Assist pH 7.27 7.31 PaCO2 52.8 45.5 Borg Scale 8.4 2.9 Accessory Muscle 4.0 1.2 Respiratory Rate 37.3 23 In the 8 patients gas exchange improved upon initiation of PAV. pH increased and PCO2 values decreased into the normal range. Objective measures of respiratory distress and accessory muscle use showed a significant decrease. In assessing respiratory distress a 10 point Borg scale was utilized. In assessment prior to initiation of PAV, patient categorized distress as severe; after PAV distress improved into the mild to moderate range. Initially accessory muscle use was vigorous with accessory muscle retractions noted. During support with PAV, accessory muscles use decreased to taut neck muscles. Respiratory Rate, a common indicator of fatigue, decreased dramatically from 37 to 23. Patrick, Am J Respir Crit Care Med 1996; 153:1005-1011 PAV Workshop

文献复习 结论: 成功率达73% 避免插管 缓解呼吸窘迫 减少辅助呼吸肌肉使用 减慢呼吸频率 急性呼吸窘迫 10/23/98 Eight out of eleven or 73% of the patients were successfully ventilated noninvasively with PAV. Intubation was avoided, symptoms of distress were decreased and respiratory rate decreased. The success rate in this study, while a small sample size follows the success rate seen in noninvasive pressure support. PAV Workshop

无创通气下 PSV 与 PAV的比较 多中心试验 N = 44 急性呼衰 结果基本评价: 安全性 插管率 病人舒适度 死亡率 住院时间 10/23/98 无创通气下 PSV 与 PAV的比较 通气模式的比较 多中心试验 N = 44 急性呼衰 结果基本评价: 安全性 插管率 病人舒适度 死亡率 住院时间 In an attempt to demonstrate safety and efficacy relative to conventional methods of noninvasive support, a multi-center trial is currently underway. At this time approximately 44 adult patients diagnosed with acute respiratory failure have been enrolled in a randomized controlled study and treated using either PSV or PAV. Primary outcomes include: safety rate of intubation mortality patient comfort length of hospital stay At this time the data looks promising in the early phases of this investigation. PAV Workshop

Richard, Wysocki, Am J Respir Crit Care Med , Abst. Suppl, 1997 10/23/98 NPPV 评价 通气模式比较 PAV 与 PSV 静止 呼吸运动 呼吸功分析 N = 7 % WOB Dr. Wysocki completed an evaluation of 7 healthy subjects with compromised chest wall compliance at rest and during 10 minutes of exercise. All subjects were evaluated using both PSV and PAV. PAV was set to 80% of overassist, while PSV was set to provide a mean airway pressure equivalent to mean airway pressure obtained during PAV. The ratio of ventilator work of breathing to the total work of breathing were computed over ten breaths. At rest PAV and PSV demonstrated similar results in unloading muscle effort as expected. However, during exercise PAV was much more effective in unloading the excess work. During PAV, the ventilator assumed 60% of the workload while on PSV the patient work was nearly 80% of the total work. 结论: PAV 效率提高3倍. Richard, Wysocki, Am J Respir Crit Care Med , Abst. Suppl, 1997 PAV Workshop

临床应用 适应征 禁忌征 急性呼衰 有自主呼吸 呼吸驱动正常 中枢性呼吸暂停 中枢神经系统抑制 病人选择 10/23/98 PAV is a mode of ventilation that is indicated whenever noninvasive ventilation is considered. Patients with acute respiratory failure as indicated by acute distress with accessory muscle use, moderate to severe dyspnea and abdominal paradox should be considered. Further criteria would include a pH < 7.35 and a PCO2 > 45 mmHg and a respiratory rate > 25 bpm. Additional the patient must have an intact respiratory drive. PAV is an assist mode of ventilation . The patient must have spontaneous efforts. A patient with a central apnea or central nervous system depression due to sedation or neurological disorders is not a candidate for this mode. PAV Workshop

临床应用 消除呼吸困难 改善: 血气正常化 呼吸节律 潮气量 呼吸频率 吸气流速 气道峰压 预期结果 10/23/98 PAV is an assist mode of ventilation. When patients are managed in this mode of ventilation, inspiratory efforts will be evident but without respiratory distress. Variability is a key word with PAV. There is variability in the breathing pattern among patients and and breath-to-breath variability. The patient’s respiratory control system establishes there own breathing pattern; some may breath slowly and deeply while others breath in a rapid, shallow pattern. There is typically a certain amount of variability in VT, respiratory rate, and flow rate. VTs may be smaller than what we are used to during mechanical ventilation, typically 7ml/kg. Airway pressures will show this variability as well. As seen in the Initial Clinical Trials, airway pressures tend to be lower. If the patient is being switched from one mode to PAV, PaO2 will be maintained with the same FiO2. PCO2 may increase initially, depending on whether they were previously overventilated. On PAV, the patient will select his/her own PCO2, whereas on other modes the ventilator settings determine ventilation. An increase may be perfectly acceptable if the patient is comfortable, pH is normal and there is not a progressive increase. If PAV is initiated prior to any other form of ventilation, PCO2 usually declines with some hypercapnia and acedemia subsiding over a few hours. Without distress, this slow normalization is acceptable. PAV Workshop

临床应用 问题: 在较高支持水平下,仍有呼吸困难 可能原因: 持续充气过度 表现: 吸气触发困难 10/23/98 临床应用 问题解决 问题: 在较高支持水平下,仍有呼吸困难 可能原因: 持续充气过度 表现: 吸气触发困难 流速曲线表现为trapping Pattern 解决方法: 提高EPAP Infrequently a patient may experience respiratory distress on PAV in spite of adequate or even high levels of support. One possible cause is the presence of dynamic hyperinflation or Auto-PEEP. Indications that Auto-PEEP may be causing the respiratory distress are: 1) the patient appears to be having difficulty triggering a breath or there seems to be a delay in the trigger. 2) The flow waveform pattern will also help to identify the presence of airtrapping and Auto-PEEP. In this situation, EPAP may be titrated to counteract the triggering difficulty because of Auto-PEEP. Other medical interventions, bronchodilator administration may be appropriate to decrease airways resistance. PAV Workshop

伴有Auto-PEEP时的吸气情况 在吸气相时，患者所做的努力必须超过Auto-PEEP 如 Auto-PEEP = +8 则患者的吸气努 10/23/98 伴有Auto-PEEP时的吸气情况 在吸气相时，患者所做的努力必须超过Auto-PEEP 如 Auto-PEEP = +8 则患者的吸气努 必须 > -8才能触发呼吸机给气 With Auto-PEEP, in order to initiate gas flow the patient must generate an effort greater than the Auto-PEEP. What happens if the effort is less than the Auto-PEEP? Nothing, a pressure differential is not created, therefore gas flow is not generated By adding EPAP to the airway, the pressures would be equal and triggering would be easier. This would reduce excess work done by the patient + 8 + 8 - 9 - 9 PAV Workshop

10/23/98 Auto-PEEP的流速曲线特征 正常 ---------------------------------------------------------------- 流速不能回零 -- Auto-PEEP The expiratory limb of flow is used to identify Auto-PEEP. If the expiratory limb of the flow pattern does not return to zero before the next breath, Auto-PEEP is present. PAV Workshop

临床应用 问题：在较高支持水平下,仍有呼吸困难 可能原因: 呼吸驱动过强 解决办法: 少量镇静药物, 医学干预或用其他通气模式 激动或焦虑 10/23/98 临床应用 问题与解决方法 问题：在较高支持水平下,仍有呼吸困难 可能原因: 呼吸驱动过强 激动或焦虑 代谢性酸中毒 休克 解决办法: 少量镇静药物, 医学干预或用其他通气模式 Continued respiratory distress may be related to a high respiratory drive due to agitation, metabolic acidosis or shock. Mild sedation may ease anxiety; the emphasis here though is on Mild. It may be necessary to switch to an alternate mode of ventilation which would permit heavy sedation. With metabolic acidosis and shock states heavy sedation may also be necessary until the underlying condition can be corrected with medical intervention. PAV Workshop

临床应用 解决方法: 问题:屏幕提示多次达到PAV上限 可能原因: 肺功能恢复 大量漏气 减小辅助比例，使病人感到舒适 适当调整，减少漏气 10/23/98 临床应用 问题与解决方法 问题:屏幕提示多次达到PAV上限 可能原因: 肺功能恢复 大量漏气 解决方法: 减小辅助比例，使病人感到舒适 适当调整，减少漏气 In the event that the Max PAV limits -- pressure or volume -- are frequently activated, it may be necessary to evaluate the level of support. Most frequently this indicates an improvement in the patient’s pulmonary mechanics. Adjusting the % Set and assessing patient response will correct the situation. The introduction of a new large leak into the system may cause the volume limit to be activated. If the leak is stable and tolerated by the patient, the Max PAV Volume limit should be adjusted upward. If the leak is uncomfortable to the patient, assess the interface. PAV Workshop

临床应用 解决方法： 问题: 可能原因: 问题与解决方法 过多镇静药物 中枢神经病变 慢性CO2 换用其他通气方式 10/23/98 临床应用 问题与解决方法 问题: 呼吸性酸中毒或PaCO2升高 可能原因: 过多镇静药物 中枢神经病变 慢性CO2 解决方法： 换用其他通气方式 适当调整参数继续使用PAV Hypoventilation and respiratory acidosis without distress may occur with the development of central depression. Many times the cause is excess sedation. Conventional modes of ventilation may be needed until the sedation wears off. This may also be the appropriate action where the cause of the central depression is undiagnosed. In a patient with chronic CO2 retention a clinical decision should be made as to whether this is acceptable. If the pH is acceptable, maintenance on PAV may facilitate weaning. PAV Workshop

PAV 局限性 需要有自主呼吸 不能给定潮气量和压力 新概念 10/23/98 Limitations of this new mode of ventilation are few. First, the mode is an assist mode of ventilation and should not be utilized on patients without spontaneous efforts. Second, difficulty in obtaining accurate measurements of elastance and resistance make it necessary to titrate VA & FA. This becomes of subjective assessment and will require a skilled practitioner. Third, PAV is a new concept and is a completely different way of ventilating. Terminology will be new to many and will require education of clinicians. PAV Workshop

PAV的益处 舒适 同步性能提高 气道峰压下降 镇静药物用量减少 减少过度通气 不发生肌肉萎缩 无创通气的理想选择 病人方面 10/23/98 PAV的益处 病人方面 舒适 同步性能提高 气道峰压下降 镇静药物用量减少 减少过度通气 不发生肌肉萎缩 无创通气的理想选择 On the other hand, PAV represents an exciting change in the way we ventilate patients. It is the first real change since pressure support was introduced in the 1980’s. Many attempts have been made to improve synchrony by adjusting the trigger mechanism with some success. PAV takes synchrony to a new level. By following the patient rather than leading, the mode is very comfortable. PAV offers the benefits of lower airway pressures, less need for sedation, reduced overventilation, and no muscle atrophy. PAV Workshop

Modify Parameters Screen 10/23/98 Custom Option PAV Workshop

10/23/98 Monitoring Screen PAV Workshop