Flow Triggering Research Articles

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.

Confounding factors in brain death: Cardiogenic ventilator autotriggering and implications for organ transplantation

Brain death is characterised by a flaccid, areflexic neurological examination; fixed, dilated and midpoint pupils and total absence of intrinsic respiratory drive. A non-reversible clinical state or brain lesion must also be identified. Integral to brain death diagnosis is loss of respiratory drive. Following terminal brainstem herniation, a cardiovascular hyperdynamic state often occurs. This hyperdynamic state causes cyclical volume displacement within the chest in phase with the cardiac cycle, causing oscillations in gas flow patterns and may be reflected in ventilator airway pressure and flow waveforms. When these flow/pressure waveform oscillations meet or exceed ventilator flow or pressure trigger sensitivity, ventilator breaths may be triggered in the total absence of intrinsic respiratory drive. In a patient with no apparent neurological function who is still triggering ventilator breaths, detailed analysis of ventilator pressure/flow waveforms in context with neurological assessment findings can identify cardiac autotriggering in a brain-dead patient. Undetected, cardiogenic ventilator autotriggering results in prolonged ICU stay and potential loss of transplantable organs. Collaborative practice and aggressive surveillance to determine loss of all neurologic function and evaluate possible autotriggering in this population is paramount and can minimise ICU stay, reduce costs of care, decrease family stress and facilitate recovery of transplantable organs.

Comparison of pressure‐, flow‐, and NAVA‐Triggering in pediatric and neonatal ventilatory care

To compare conventional trigger modes (pressure and flow trigger) to neurally adjusted ventilatory assist (NAVA), a novel sensing technique, and to observe the patient-ventilator interactions during these modes. In this prospective, crossover comparison study in tertiary care pediatric and neonatal intensive care unit, 18 patients (age from 30 weeks of postconceptional age to 16 years) needing mechanical ventilation were randomized. Three patients were excluded from the analysis because of problems in data collection. Patients were ventilated with three different trigger modes (pressure, flow, NAVA), for 10 min each. Patients were randomly allocated to six groups according to the order of trigger modes used. The primary end point was the time in asynchrony between the patient and the ventilator. Secondary end points were peak and mean airway pressures (MAP), breathing frequency, tidal volume (TV), and vital parameters during each trigger mode. The proportion of time in asynchrony was significantly shorter in the NAVA group (8.8%) than in the pressure (33.4%) and flow (30.8%) groups (P < 0.001 for both). In the NAVA group, the peak inspiratory pressure was 2 to 1.9 cmH(2) O lower than in the pressure and flow groups, respectively (P < 0.05 for both) and the breathing frequency was 10 breaths/min higher than in the pressure group (P = 0.001). There was a tendency toward a lower MAP (P = 0.047) but the mean TV was about the same (6.4-6.8 ml/kg) in all three groups (P = 0.55). There were no differences in oxygen saturation or vital parameters between the groups. NAVA offers a novel way of sensing patients' spontaneous breathing and significantly improves short-term patient-ventilator synchrony in a pediatric population.

Monitoring muscle strength by using ventilatory flow triggering during recovery of neuromuscular blockade

Monitoring muscle strength by using ventilatory flow triggering during recovery of neuromuscular blockade

Debris-flow impact, vulnerability, and response

This paper calls attention to vulnerable groups that are disproportionately affected by smaller, less-publicized debris flow events and do not always receive the advantages of recent technical advances. The most vulnerable groups tend to be economically restricted to live in relatively inexpensive and more dangerous locations, are often forced to live in topographically cramped areas due to expansion and development, and have limited influence and power needed to bring about mitigative efforts. Technical issues have long been the focus for debris-flow hazard reduction, but the collective judgment of many of those working toward natural hazards reduction, especially in developing countries, is that socio-cultural issues are at least as important as technical choices on the effectiveness of hazard and risk-reduction efforts. This awareness may result in (1) selecting simple designs that use local materials, local construction techniques and skills, and that recognize limited financial means; (2) selecting mitigative methods that require minimal maintenance, can withstand exposure to vandalism and scavenging, and will minimize misappropriation of resources; and (3) capitalizing on local techniques of dealing with other hazards, such as flooding, earthquakes, and landslides. Because of the difficulty in predicting and controlling debris flows, it is useful if mitigative systems can employ multiple elements to enhance the chance of success. These can include: education of the local populace, avoidance and warning to the degree possible, and some combination of channelization and interception of debris. For watersheds disturbed by fire, logging, mining, or construction, hillside treatment can be added to the mitigative methods to reduce water flow and sediment transport. Examples provided in this paper show that these mitigative systems can be tailored to fit widely varying socio-cultural settings, with different geological characteristics and different debris flow–triggering events.

Design Concepts and Principle of Operation of the HeartWare Ventricular Assist System

Implantable left ventricular assist devices provide circulatory support for patients at risk of death from refractory, end-stage heart failure. Rotary blood pumps have been designed for increased reliability and smaller size for use in a broader population of patients than the first-generation pulsatile devices. The design concepts and principle of operation of the HeartWare System are discussed. The HeartWare Ventricular Assist System (HVAD) is a small centrifugal flow pump with a displacement volume of 50 ml and an output capacity of 10 L/min. A unique wide-blade impeller is suspended by hybrid passive magnets and hydrodynamic forces. An integrated inflow cannula is inserted into the left ventricle and is held in position by an adjustable sewing ring; the pump is positioned in the pericardial space. The 10-mm outflow graft is anastomosed to the ascending aorta. External system components include the microprocessor-based controller, a monitor, lithium-ion battery packs, alternating current and direct current power adapters, and a battery charger. Physiologic control algorithms are incorporated for safe operation. Preclinical life cycle tests have shown the HVAD to be highly reliable. This system design offers reliability, portability, and ease of use for ambulatory patients.

Mechanical ventilation and the total artificial heart: optimal ventilator trigger to avoid post-operative autocycling - a case series and literature review

Many patients with end-stage cardiomyopathy are now being implanted with Total Artificial Hearts (TAHs). We have observed individual cases of post-operative mechanical ventilator autocycling with a flow trigger, and subsequent loss of autocycling after switching to a pressure trigger. These observations prompted us to do a retrospective review of all TAH devices placed at our institution between August 2007 and May 2009. We found that in the immediate post-operative period following TAH placement, autocycling was present in 50% (5/10) of cases. There was immediate cessation of autocycling in all patients after being changed from a flow trigger of 2 L/minute to a pressure trigger of 2 cm H2O. The autocycling group was found to have significantly higher CVP values than the non-autocycling group (P = 0.012). Our data suggest that mechanical ventilator autocycling may be resolved or prevented by the use of a pressure trigger rather than a flow trigger setting in patients with TAHs who require mechanical ventilation.

Recent changes in rainfall characteristics and their influence on thresholds for debris flow triggering in the Dolomitic area of Cortina d'Ampezzo, north-eastern Italian Alps

Abstract. In this paper, we examine variations in climate characteristics near the area of Cortina d'Ampezzo (Dolomites, Eastern Italian Alps), with particular reference to the possible implications for debris-flow occurrence. The study area is prone to debris-flow release in response to summer high-intensity short-duration rainfalls and, therefore, it is of the utmost importance to investigate the potential increase in debris-flow triggering rainfall events. The critical rainfall threshold is agreed to be a crucial triggering factor for debris-flows. Data from a monitoring system, placed in a catchment near Cortina (Acquabona), show that debris-flows were triggered by rainfalls with peak rainfall intensities ranging from 4.9 to 17.4 mm/10 min. The analyses of meteorological data, collected from 1921 to 1994 at several stations in the study area, show a negative trend of annual rainfall, a considerable variation in the monthly rainfall distribution, and an increase in the temperature range, possibly related to global climate changes. Moreover, high-intensity and short-duration rainfall events, derived from data collected from 1990 and 2008, show an increase in exceptional rainfall events. The results obtained in a peak-over-threshold framework, applied to the rainfall data measured at the Faloria rain gauge station from 1990 to 2008, clearly show that the interarrival time of over-threshold events computed for different threshold values decreased in the last decade. This suggests that local climatic changes might produce an increase in the frequency of rainfall events, potentially triggering debris flows in the study area.

On the Effects of Uncertainty on Investment Timing and Option Value

This article demonstrates that when the relationship between systematic risk and project value is taken into account, the sensitivity of investments with respect to volatility changes dramatically. By taking cash flows as a fundamental variable, the article shows that the value of an option to invest can be decreasing in volatility, contradicting the conventional wisdom. Second, the recent proposition, according to which the expected time to invest is U-shaped, does not generally hold; the expected time and the cash flow trigger are likely to be always increasing in volatility.

Patient-Ventilator Dyssynchrony: Clinical Significance and Implications for Practice

The cost of providing care to critically ill patients in the United States consumes roughly 15% of all health care dollars, or 1% of the gross national product.1 Contributing to this economic burden are patients admitted to the intensive care unit (ICU) who require mechanical ventilation and patients with complications from their dependence on this technology.2,3 In fact, 50% of ICU patients receive mechanical ventilation.4 Often, sedation is required to increase patients’ tolerance of the endotracheal tube, reduce anxiety, and facilitate sleep. In particular, sedation is used frequently to reduce patient-ventilator dyssynchrony (PVD).5–9 Sassoon and Foster10 define PVD as a mismatching between the patient’s breaths (neural) and ventilator-assisted breaths (phase asynchrony), as well as the inability of the ventilator’s flow delivery to match the patient’s flow demand (flow asynchrony). This definition suggests a faulty interaction between the patient and ventilator that is commonly managed by sedation and advanced ventilator modes and adjustments. The correction of PVD is complex and multifaceted given the current capabilities of traditional ventilators. An imperfect solution exists because the sensitivity and responsiveness of both the patient and the ventilator during the interaction is confounded by factors related to the patient and the ventilator. However, in light of the most serious complications (hypoxemia, barotrauma, prolonged mechanical ventilation, and discomfort) of PVD, and an imperfect solution for the resolution of PVD at the current time, nurses continue to face the challenge of preventing the consequences of PVD as well as complications due to oversedation or undersedation. In this article, we discuss the factors contributing to PVD; the manifestations, measurement, types, and causes of PVD; nursing implications; and future directions for improvement, with nursing research questions proposed for consideration.

Autotriggering During Pressure Support Ventilation Due to Cardiogenic Oscillations

Newer generation anesthesia machines are equipped with a pressure support mode of ventilation, which can be used to support spontaneous ventilation in anesthetized patients. The Drager Apollo anesthesia machine uses an inspiratory limb hot-wire flow sensor to measure inspiratory flow rates. Detected flow rates that exceed the pressure support flow trigger will trigger pressure support breaths (Internal communication document. Drager Medical, 2007). In the case we are presenting, cardiac oscillations produced inspiratory flow rates that exceeded the flow trigger and autotriggered pressure support breaths. Autotriggering could be suppressed by increasing the trigger threshold or the positive end-expiratory pressure setting.

Variability in rainfall threshold for debris flow after the Chi-Chi earthquake in central Taiwan, China

The purpose of this study is to analyze variability in rainfall threshold for debris flow (critical rainfall for debris flow triggering) after the M L 7.3 Chi-Chi earthquake in central Taiwan in 1999. Two study sites with different geological conditions were surveyed in the earthquake area. Streambed surveys were conducted to continuously monitor debris flows between 1999 and 2006. During the 7-year study period, every debris flow event was identified, and the streambed characterized. Results show that the rainfall threshold for debris flow was remarkably lower just after the Chi-Chi Earthquake, but gradually recovered. To date, this rainfall threshold is still lower than the original level prior to the earthquake. This variability in rainfall threshold is closely related to the amount of sediment material in the initiation area of debris flow, which increased rapidly due to landslides resulting from the earthquake. With the increase in sediment material, the rainfall threshold was lowered severely during the first year following the Chi-Chi earthquake. However, heavy rainfalls mobilized the sediment material, causing debris flows and transporting sediment downstream. With the decrease in sediment material, the rainfall threshold recovered gradually over time. Furthermore, debris flows occurred only in the subbasins that had sufficient sediment material to cause significant movement. Hence, these results confirm that the sediment material in the initiation area of debris flow is a crucial component of the rainfall threshold for debris flow.

Field observations of the June 30, 2001 debris flow at Acquabona (Dolomites, Italy)

On June 30, 2001, a debris flow occurred in the Acquabona Creek, a small catchment of the Eastern Dolomites, Italy. This debris flow originated shortly after an intense rainstorm, characterised by a peak intensity of 8.6 mm per 10 min; it transported a total volume of 30,000 m3, consisting of poorly sorted gravely sand with boulders up to 3 m in diameter. The sediment erosion yield rate reached as high as 20 m3/m. In order to verify the accuracy of the field measurements, the total volume of debris deposits have was calculated using three different topographic measurement techniques: 3D laser scanning, terrestrial stereo-photogrammetry survey and total topographic station survey. Data collected so far show that no debris flow has occurred at Acquabona with a rainfall intensity lower than 4.6 mm per 10 min. Channel cross section measurements indicate that debris flow velocity ranges from 2.0 to 7.2 m/s along the lower flow channel and peak discharge ranges between 22 and 300 m3/s. Field estimates of the rheological properties indicate a yield strength ranging from 2,088 to 5,313 Pa and Bingham viscosity between 70 and 337 Pa · s. It is not still possible to identify a rainfall intensity and amount threshold for debris flow triggering, but the data so far collected emphasise that debris flows do not occur with a rainfall intensity lower than 4.6 mm per 10 min.

Effect of bacterial filter on measurement of interrupter resistance in preschool and school‐aged children

The interrupter technique is increasingly used in preschool children to assess airway resistance (Rint). Use of a bacterial filter is essential for prevention of cross-infection in a clinical setting. It is not known how large an effect this extra resistance and compliance exert upon interrupter measurements, especially on obstructive airways and in smaller children. We aim to determine the contribution of the filter to Rint, in a sample of children attending lung function testing at an asthma clinic. Interrupter measurements were performed according to ATS/ERS guidelines during quiet normal breathing at an expiratory flow trigger of 200 ml s(-1), with the child seated upright with cheeks supported and wearing a nose clip. A minimum of 10 interrupter measurements was made with and without a bacterial filter. Spirometric and plethysmographic tests were also performed. A small but significant difference (0.12 (95% CI 0.06-0.17) kPa s L(-1), P = 0.0002) with 2x SD of 0.34 kPa s L(-1) was observed between Rint with and without filter in 39 children, with a large spread. This difference was not dependent on Rint magnitude, age or height, nor on lung function parameters (effective resistance, forced expiratory volume in 1 sec, and maximal expiratory flow at 50% of expired vital capacity). A bacterial filter causes a small difference but is not clinically significant, with a wide spread comparable to the variability of the technique and recommended cut-offs for assessing repeatability and bronchodilation. Age, height or severity of obstruction need not be corrected for in general.

Sedation in the intensive care unit

Sedation allows the depression of patients’ awareness of the environment and reduction of their response to external stimulation. It plays a pivotal role in the care of the critically ill patient, and encompasses a wide spectrum of symptom control that will vary between patients, and among individuals throughout the course of their illnesses. Heavy sedation in critical care to facilitate endotracheal tube tolerance and ventilator synchronization, often with neuromuscular blocking agents, was routine until relatively recently. The modern ICU ventilator is equipped with a wide range of ventilatory modes and, with the addition of electronic flow triggering, synchronization problems have largely disappeared. The replacement of an endotracheal tube by a tracheostomy reduces the discomfort associated with an artificial airway and may often remove the need for sedation entirely. Thus, modern day sedation involves more than tube tolerance and is now focused on the multifactorial individual needs of the patient. Critical illness can be a frightening experience for a variety of reasons, and adequate sedation may reduce this. Pain is a common problem and may be worsened by invasive and unpleasant procedures. Agitation is thought to occur at least once in 71% of patients in a medical-surgical ICU.

Rain-induced debris and mudflow triggering factors assessment in the Santiago cordilleran foothills, Central Chile

Debris and mudflows are some of the main geological hazards in the mountain foothills of the Chilean capital city of Santiago. There, the risk of flows triggered in the basins of ravines that drain the range into the city increases with time due to the city growth. A multivariate statistical study based on the logistic regression method is presented. The model provides equations that allow the computation of combined meteorological triggering factors associated with a probability of rain-induced flow occurrence. Daily rainfall, accumulated rainfall and the snowfall level, traditionally considered as the relevant factors, are analysed for a 25-year period. The results show a strong relevance of the rainfall on the day of the flow event over the other factors. However, the relatively low probabilities returned for some real flow events suggest that the model does not capture all the significant variables and the problem is more complex than as it has been traditionally assumed, and further investigations are needed to develop predictive models of flow triggering.

Clarifying Equipment Specifications and Performance Characteristics

Clarifying Equipment Specifications and Performance Characteristics

The ATLAS Data Acquisition and Trigger: concept, design and status

This article presents the base-line design and implementation of the ATLAS Trigger and Data Acquisition system, in particular the Data Flow and High Level Trigger components. The status of the installation and commissioning of the system is also presented.

Application of physical modelling of debris flow triggering to field conditions: Limitations posed by boundary conditions

Debris flows are often triggered by Hortonian overland flow during high-intensity rainstorms. Data derived from debris flow trigger zones in the southern French Alps were fed into a physical model of debris flow triggering based on Takahashi. Using a Monte Carlo approach with 1000 runs, the results show a wide distribution of safety factor values, indicating that physical modelling based on actual field measurements may not always be practical. As all safety factor values obtained are well below 1 even though debris flows only occur during very high-intensity rainstorms, the model used must be inappropriate. Apparently, the composition of the overland flow plays an important role: during high-intensity rainstorms it usually has a very high sediment content and contains stones. This prevents it from flowing through the pores of coarse debris accumulations in the central gully of a trigger zone; it will rather run over the debris. This situation is more stable than with the fluid flowing through the pores. The behaviour switch of the fluid above a certain sediment and stone content thus drastically changes the triggering conditions for debris flows and it is concluded that debris flow triggering in the area requires the occurrence of both overland flow and landsliding.

Flow or pressure triggering during pressure support ventilation?

Pressure and flow triggering have improved greatly in the new generation of ventilators. The routine use of one or the other in adult patients in the ICU setting is not yet well established.