Triggering of the ventilator in patient-ventilator interactions

With current ventilator triggering design, in initiating ventilator breaths patient effort is only a small fraction of the total effort expended to overcome the inspiratory load. Similarly, advances in ventilator pressure or flow delivery and inspiratory flow termination improve patient effort or inspiratory muscle work during mechanical ventilation. Yet refinements in ventilator design do not necessarily allow optimal patient-ventilator interactions, as the clinician is key in managing patient factors and selecting appropriate ventilator factors to maintain patient-ventilator synchrony. In patient-ventilator interactions, unmatched patient flow demand by ventilator flow delivery results in flow asynchrony, whereas mismatches between mechanical inspiratory time (mechanical T(I)) and neural T(I) produce timing asynchrony. Wasted efforts are an example of timing asynchrony. In the triggering phase, trigger thresholds that are set too high or the type of triggering methods induces wasted efforts. Wasted efforts can be aggravated by respiratory muscle weakness or other conditions that reduce respiratory drive. In the post-triggering phase, ventilator factors play an important role in patient-ventilator interaction; this role includes the assistance level, set inspiratory flow rate, T(I), pressurization rate, and cycling-off threshold, and to some extent, applied PEEP. This paper proposes an algorithm that clinicians can use to adjust ventilator settings with the goal to eliminate or reduce patients' wasted efforts.     

Volume monitor for mechanical ventilation in the hyperbaric chamber

Treatment of critically ill patients requiring ventilatory support and hemodynamic monitoring in the hyperbaric medicine department is a frequent occurrence. We provide mechanical ventilation principally with the Penlon Oxford ventilator; however, its simple design lacks volume, rate, and disconnect monitors. Therefore, we combined the ventilator with the Ohmeda volume monitor, a pulmonary function monitor for adult and pediatric use that gives reliable, accurate measurements of tidal volume, rate, and minute ventilation. The Ohmeda unit is easily adaptable to the Penlon ventilator, and may also be used to monitor respiratory function in the spontaneously breathing patient. To our knowledge, this is the only battery-driven monitor on the market that provides rate, volume, apnea, and minute ventilation within the same unit. It should be used as an adjunct to the Penlon Oxford ventilator in the hyperbaric chamber.     

无创正压通气治疗AECOPD伴Ⅱ型呼吸衰竭人机协调管理对策

目的探讨人机协调管理对策在无创正压通气治疗慢性阻塞性肺病急性加重期(AECOPD)伴Ⅱ型呼吸衰竭中的地位。方法分析76例无创正压通气治疗AECOPD伴Ⅱ型呼吸衰竭患者的资料,观察其症状、呼吸频率、心率、血氧饱和度、血气分析、情绪反应、不适反应等。结果血气改善者61例,呼吸频率下降者60例,氧饱和度维持在90%左右者62例,咽干5例,腹胀3例,发生人机不协调者21例(其中通过调整参数、增加舒适性、消除紧张恐惧情绪、延长监测时间而继续应用者15例,停止者3例,中转有创治疗者3例)。结论人机协调管理是保证无创正压通气治疗AECOPD伴Ⅱ型呼吸衰竭取得成功的关键。     

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.     

Advanced modes of mechanical ventilation: implications for practice

Mechanical ventilation is one of the most commonly applied interventions in intensive care units. Despite its life-saving role, mechanical ventilation is associated with additional risks to the patient and additional healthcare costs if not applied appropriately. To decrease risk, new ventilator modes continue to be developed with the goal of improving patient outcomes. Advances in ventilator modes include dual control modes that enable guaranteed tidal volume and inspiratory pressure, pressure-style modes that permit spontaneous breathing at high- and low-pressure levels, and closed-loop systems that facilitate ventilator manipulation of variables based on measured respiratory parameters. Clinicians need to develop a thorough understanding of these modes including their effects on underlying respiratory physiology to be able to deliver safe and appropriate patient care.     

A novel inline PEEP valve design for differential multi-ventilation

BackgroundVentilator sharing is one option to emergently increase ventilator capacity during a crisis but has been criticized for its inability to adjust for individual patient needs. Newer ventilator sharing designs use valves and restrictors to control pressures for each patient. A key component of these designs is an inline Positive End Expiratory Pressure (PEEP) Valve but these are not readily available. Creating an inline PEEP valve by converting a standard bag-valve-mask PEEP valve is possible with the addition of a 3D printed collar.MethodsThis was a feasibility study assessing the performance and safety of a method for converting a standard PEEP valve into an inline PEEP valve. A collar was designed and printed that covers the exhaust ports of the valve and returns exhaled gases to the ventilator.ResultsThe collar piece was simple to print and easily assembled with the standard PEEP valve. In bench testing it successfully created differential pressures in 2 simulated expiratory limbs without leaking to the atmosphere at pressures greater than 60 cm of H2O.ConclusionOur novel inline PEEP valve design shows promise as an option for building a safer ventilator sharing system.     

BiPAP呼吸机治疗呼吸衰竭的疗效观察及护理

[目的]观察BiPAP呼吸机治疗呼吸衰竭的疗效并总结护理经验。[方法]总结和分析采用BiPAP呼吸机治疗57例急慢性呼吸衰竭病人的护理经验。[结果]经BiPAP呼吸机治疗后顺利出院54例,2例中途放弃治疗,1例病情恶化,改用气管内插管接多功能呼吸机机械通气。[结论]合理治疗和系统化护理对提高呼吸衰竭病人的治疗效果、增加病人舒适度和降低并发症具有积极意义。     

Effect of PEEP-valve placement on function of a home-care ventilator

BACKGROUND: The addition of a PEEP valve to the circuit of a home-care ventilator like the Aequitron LP-6 can be viewed as a consumer modification of the system. We sought to determine the effect that such a modification would have on ventilator function. METHODS & MATERIALS: Part 1. We tested the effect of PEEP level and PEEP-valve position on volume delivered at the ventilator Y-adapter, over a range of tidal volumes. Part 2. We held tidal volume, frequency, and inspiratory time constant, and varied PEEP level and PEEP-valve position to test the effect of PEEP-valve position on pressures measured at the ventilator outlet, patient-Y, and within the exhalation-valve pressurization line. RESULTS: Conventional placement of the PEEP value (distal to, or 'after,' the exhalation valve) in the LP-6 ventilator circuit resulted in statistically significant and potentially clinically important decreases in the volumes delivered to the patient at some ventilator settings. Proximal placement of the PEEP valve (proximal to, or 'before,' the exhalation valve) resulted in consistent volumes delivered to the patient at all levels tested, without changing the ventilatory performance characteristics of the ventilator as reflected by pressure waveforms. CONCLUSION: We recommend that appropriate observations and measurements be made to verify system function before a home-care ventilator modified to provide PEEP is applied to the patient.     

Inadvertent triggering of the ventilator caused by surgically placed pacer wires

Inadvertent ventilator triggering can occur for various reasons. Leaks in the ventilator circuit, endotracheal tube leaks, tracheal cuff leaks, cardiac oscillations, water condensate causing oscillations in the circuit tubing, ventilator expiratory valve integrity, and overly sensitive triggering mechanism settings may precipitate this phenomena. We present a case of inadvertent ventilator triggering caused by electrical stimulation of the diaphragm from surgically placed pacing wires post cardiothoracic surgery. A 47-year-old woman underwent surgical placement of a left (LVAD) and right (RVAD) ventricular assist device for severe end stage cardiomyopathy, as a bridge to cardiac transplantation. The patient was observed to have inadvertent ventilator triggering while deeply sedated postoperatively. The ventilator set respiratory rate was 16 breaths/min, with patient respiratory rate of 30 breaths/min while deeply sedated. Upon assessment of ventilator waveforms and arterial blood gas revealing a profound respiratory alkalosis, the pressure/time waveform demonstrated a -2 cm H(2)O decrease in pressure prior to each cycled breath. The ventilator was subsequently changed from flow trigger sensitivity of 3 L/min to pressure trigger sensitivity of -3 cm H(2)O to eliminate the autotriggering. Later in the patient's ICU stay, inadvertent ventilator triggering was again observed. Further adjustment of the pressure trigger sensitivity to -3 cm H(2)O eliminated the autotriggering. Clinical assessment found the pacing wires were responsible for stimulating the patient's diaphragm, therefore causing airway pressure decreases and premature breath delivery. Once the electrical amplitude of the pacemaker was decreased, the inadvertent ventilator triggering resolved and normal trigger sensitivity and pH was restored.     

Interacción paciente-ventilador en ventilación mecánica no invasiva

Noninvasive mechanical ventilation is one more step in the treatment of patients with acute respiratory failure. In addition to gas exchange disorders, its primary indication to initiate it is the presence of signs of respiratory muscles fatigue. To assure successful mechanical ventilation, the ventilator and patient must be synchronized, that is, the effort the patient makes to start inspiration is recognized by the ventilator and it quickly delivers gas flow, that the flow provided by the ventilator adapts to the flow need of the patient during delivery of gas phase and that the ventilator recognizes the cessation of inspiratory activity by the patient, ends the delivery of gas and opens the expiratory valve to allow the patient expiration. This sequence of events, which seem so logical, is almost never achieved in the clinical practice, commonly observing some asynchrony in ventilated patients. The presence of patient-ventilator asynchrony leads to increased breathing work, which would lead to the failure of the main objective of ventilatory support, that is none other than decline in the patient's respiratory work.     

咪唑安定在机械通气中人机拮抗时的应用

目的:观察咪唑安定在机械通气中改善人机拮抗的临床疗效。方法:2000年11月至2001年12月对机械通气时出现人机拮抗的126例应用咪唑安定治疗,观察咪唑安定应用前、后患者动脉血气分析指标中pH、PaO_2、PaCO_2、SatO_2及通气状态的变化,采用自身对照t检验进行分析,P<0.05有显著统计学意义。结果:应用咪唑安定后,患者pH、PaO_2、SatO_2均有明显改善(P<0.001),通气状态好转,而PaCO_2无显著性差异。结论:咪唑安定对机械通气中的人机拮抗有较好疗效,可改善病人的通气状况。     

Interactions patient–ventilateur

During assisted ventilation like inspiratory pressure support or assist-control ventilation, patient–ventilator asynchrony may occur when the patient's inspiration fails to coincide exactly with the ventilator's insufflation. The new generation of ventilators with large screens facilitate the detection of gross asynchronies by careful examination of flow and airway-pressure tracings. The main asynchrony is ineffective triggering, defined as failure of a patient's inspiratory effort to trigger a ventilator breath. Ineffective triggering is caused by dynamic hyperinflation at the time of a triggering attempt. Other major asynchronies include double triggering, in which two consecutive ventilator cycles are triggered by a single patient effort; and autotriggering, in which the ventilator is triggered by signals that do not come from the patient. More discreet asynchronies such as prolonged insufflation during pressure-support ventilation or inadequate flow rate during assist-control ventilation can also be suspected from the flow and airway-pressure traces. Simple delays in triggering or cycling are extremely common but difficult to detect. At least one study suggests that nearly one-fourth of intubated patients exhibit frequent asynchronies (> 10%) during assisted ventilation. A frequent occurrence of asynchrony is associated with a longer duration of mechanical ventilation. This may reflect not only greater disease severity, but also inappropriate ventilator settings. Optimizing the ventilator settings, most notably by reducing ventilatory support or insufflation time, can minimize ineffective triggering. Whether optimizing ventilation shortens the duration of mechanical ventilation by reducing the occurrence of asynchrony is still an open question.     

Monitoring of patient-ventilator interaction at the bedside

Monitoring of patient-ventilator interactions at the bedside involves evaluation of patient breathing pattern on ventilator settings. One goal of mechanical ventilation is to have ventilator-assisted breathing coincide with patient breathing. The objectives of this goal are to have patient breath initiation result in ventilator triggering without undue patient effort, to match assisted-breath delivery with patient inspiratory effort, and to have assisted breathing cease when the patient terminates inspiration, thus avoiding ventilator-assisted inspiration during patient exhalation. Asynchrony can occur throughout the respiratory cycle, and this paper describes common asynchronies. The types of asynchronies discussed are trigger asynchrony (ie, breath initiation that may manifest as ineffective triggering, double-triggering, or auto-triggering); flow asynchrony (ie, breath-delivery asynchrony, which may manifest as assisted-breath delivery being faster or slower than what patient desires); and cycling asynchronies (ie, termination of assisted inspiration does not coincide with patient breath termination, which may manifest as delayed cycling or premature cycling). Various waveforms are displayed and graphically demonstrate asynchronies; basic principles of waveform interpretation are discussed.     

Impact on ventilator-check time of an in-circuit computerized respiratory monitoring system.

To ensure appropriate quality control of mechanical ventilatory support in our institution, checks of patient status and ventilator performance are made every 2 hours. Our standard method of surveillance requires disconnecting the patient from the ventilator and connecting him to extraneous monitoring devices. We assessed the use of an in-circuit computerized respiratory monitoring system for ventilator surveillance and found that with this system significantly less therapist time was required to perform a check (5.8 +/- 1.18 minutes vs 9.9 +/- 1.53 minutes for the standard procedure) and that use of this system avoids the potential hazards associated with disconnecting a patient from the ventilator and introducing additional monitoring devices to the airway.     

The effects of pressure control versus volume control assisted ventilation on patient work of breathing in acute lung injury and acute respiratory distress syndrome

BACKGROUND: Patient work of breathing (WOB) during assisted ventilation is reduced when inspiratory flow (V(I)) from the ventilator exceeds patient flow demand. Patients in acute respiratory failure often have unstable breathing patterns and their requirements for V(I) may change from breath to breath. Volume control ventilation (VCV) traditionally incorporates a pre-set ventilator V(I) that remains constant even under conditions of changing patient flow demand. In contrast, pressure control ventilation (PCV) incorporates a variable decelerating flow wave form with a high ventilator V(I) as inspiration commences. We compared the effects of flow patterns on assisted WOB during VCV and PCV. METHODS: WOB was measured with a BICORE CP-100 monitor (incorporating a Campbell Diagram) in a prospective, randomized cross-over study of 18 mechanically ventilated adult patients with acute lung injury (ALI) or acute respiratory distress syndrome (ARDS). Tidal volume, inspiratory time, and mean ventilator V(I) were constant in each mode. RESULTS: At comparable levels of respiratory drive and minute ventilation, patient WOB was significantly lower with PCV than with VCV (0.59 +/- 0.42 J/L vs 0.70 +/- 0.58 J/L, respectively, p < 0.05). Ventilator peak V(I) was significantly higher with PCV than with VCV (103.2 +/- 22.8 L/min vs 43.8 L/min, respectively, p < 0.01). CONCLUSIONS: In the setting of ALI and ARDS, PCV significantly reduced patient WOB relative to VCV. The decrease in patient WOB was attributed to the higher ventilator peak V(I) of PCV.     

Multifaceted interventions are likely to be more effective to increase adherence to the ventilator care bundle: A systematic review of strategies to improve care bundle compliance

BackgroundThe implementation of ventilator care bundles has remained suboptimal. However, it is unclear whether improving adherence has a positive relationship with patient outcomes.ObjectivesTo identify the most effective implementation strategies to improve adherence to ventilator bundles and to investigate the relationship between adherence to ventilator bundles and patient outcomes.MethodsA systematic review followed the PRISMA guidelines. A systematic literature search from the inception of ventilator care bundles 2001 to January 2021 of relevant databases, screening and data extraction according to Cochrane methodology.ResultsIn total, 6035 records were screened, and 24 studies met the eligibility criteria. The implementation strategies were provider-level interventions (n = 15), included educational activities, checklist, and audit/feedback. Organizational-level interventions include (n = 8) included change of medical record system and multidisciplinary team. System-level intervention (n = 1) had motivation and reward. The most common strategies were education, checklists, audit feedback, which are probably effective in improving adherence. We could not perform a meta-analysis due to heterogeneity of the strategies and types of adherence measurement. Most studies (n = 7) had a high risk of bias. There were some conflicting results in determining the associations between adherence and patient outcomes because of the poor quality of the studies.ConclusionMultifaceted interventions are likely to be effective for consistent improvement in adherence. It remains uncertain whether improvements in adherence have positive outcomes on patients due to limited evidence of low to moderate uncertainty. We recommend the need for robust research methodology to assess the effectiveness of implementation strategies on improving adherence and patient outcomes.     

Patient–ventilator synchrony and sleep quality with proportional assist and pressure support ventilation

Objective

To examine patient–ventilator asynchrony and sleep quality in non-sedated critically ill patients ventilated with proportional assist ventilation with load adjustable gain factors (PAV+) and pressure support (PSV).

Methods

This was a randomized crossover physiological study conducted in an adult ICU at a tertiary hospital. Patients who exhibited patient–ventilator asynchrony on PSV were selected. Polysomnography was performed in these patients over 24 h, during which respiratory variables were continuously recorded. During the study period, each patient was randomized to receive alternating 4-h periods of PSV and PAV+ equally distributed during the day and night. Sleep architecture was analyzed manually using predetermined criteria. Patient–ventilator asynchrony was evaluated breath by breath using the flow–time and airway pressure–time waveforms.

Results

Fourteen patients were studied. The majority (85.7 %) had either acute exacerbation of COPD as admission diagnosis or COPD as comorbidity. During sleep, compared to PSV, PAV+ significantly reduced the patient–ventilator asynchrony events per hour of sleep [5 (1–17) vs. 40 (4–443), p = 0.02, median (25–75th interquartile range)]. Compared to PSV, PAV+ was associated with slightly but significantly greater sleep fragmentation [18.8 (13.1–33.1) versus 18.1 (7.0–22.8) events/h, p = 0.01] and less REM sleep [0.0 % (0.0–8.4) vs. 5.8 % (0.0–21.9), p = 0.02).

Conclusions

PAV+ failed to improve sleep in mechanically ventilated patients despite the fact that this mode was associated with better synchrony between the patient and ventilator. These results do not support the hypothesis that patient–ventilator synchrony plays a central role in determining sleep quality in this group of patients.     

How often does patient-ventilator asynchrony occur and what are the consequences?

Mechanical ventilation can be life-saving for patients with acute respiratory failure. In between the 2 extremes of complete and no ventilatory support, both patient and machine contribute to ventilatory work. Ideally, ventilator gas delivery would perfectly match patient demand. This patient-ventilator interaction depends on how the ventilator responds to patient respiratory effort and, in turn, how the patient responds to the breath delivered by the ventilator. It is now evident that the interaction between patient and ventilator is frequently suboptimal and that patient-ventilator asynchrony is common. Its prevalence depends on numerous factors, including timing and duration of observation, technique used for detection, patient population, type of asynchrony, ventilation mode and settings (eg, trigger, flow, and cycle criteria), and confounding factors (eg, state of wakefulness, sedation). Patient-ventilator asynchrony is associated with adverse effects, including higher/wasted work of breathing, patient discomfort, increased need for sedation, confusion during the weaning process, prolonged mechanical ventilation, longer stay, and possibly higher mortality. Whether asynchrony is a marker of poor prognosis or causes these adverse outcomes remains to be determined.     

Characteristics and health service utilization patterns of ventilator-dependent patients cared for within a vertically integrated health system.

OBJECTIVE: To describe the characteristics and service utilization patterns of long-term ventilator-dependent patients. DESIGN: Using medical records, a cohort of ventilator-dependent patients was identified and followed. SETTING: A vertically integrated healthcare system in southwestern Pennsylvania. PATIENTS: Forty-nine adults requiring prolonged ventilatory assistance. MEASURES: Demographics, admission date, admission diagnosis, discharge diagnosis, reason for ventilator dependency, level of care to which the patient was admitted, dates of all transfer orders, dates of all transfers between levels of care, discharge destination and subsequent readmissions. RESULTS: The major reason for long-term ventilator dependency was progressive debilitating disease of either a pulmonary or nonpulmonary nature. The mean length of stay within the system was 72.6 days +/- 42.55 (median = 59 days, range = 24 to 267 days). Patients had an average of 3.3 transfers +/- 2.53 within the system (median = 3, range = 0 to 10). No delays in transfer to lower levels of care were found. Health utilization variables were largely unrelated to reason for ventilator dependency. Almost half of the patients (n = 24 or 49.0%) died in the system. Patients who died in the system were significantly older than patients for whom discharge home was possible. CONCLUSIONS: Additional studies are necessary to describe the prevalence, etiology, health status and functional status of ventilator patients at all levels of care; the impact of different system approaches on patient well-being and cost of care; and the process of medical decision making. Economic analyses of costs and outcomes for ventilator-dependent patients using a cost-utility approach are also needed.     

A new system for understanding modes of mechanical ventilation

Numerous ventilation modes and ventilation options have become available as new mechanical ventilators have reached the market. Ventilator manufacturers have no standardized terminology for ventilator modes and ventilation options, and ventilator operator's manuals do not help the clinician compare the modes of ventilators from different manufacturers. This article proposes a standardized system for classifying ventilation modes, based on general engineering principles and a small set of explicit definitions. Though there may be resistance by ventilator manufacturers to a standardized system of ventilation terminology, clinicians and health care equipment purchasers should adopt such a system in the interest of clear communication--the lack of which prevents clinicians from fully understanding the therapies they administer and could compromise the quality of patient care.