Volume-targeted Mode Research Articles

The Effect of Inspiratory Effort on Circuit Compensation for Volume-Targeted Modes.

Critical-care ventilators provide patient circuit compensation (CC) to counteract the loss of volume due to patient circuit compliance. No studies show the effect of inspiratory efforts (indicating maximal value of the muscle pressure waveforms [Pmax]) on CC function. The goal of this study was to determine how Pmax affects volume delivery with or without CC for both volume control continuous mandatory ventilation with set-point targeting scheme (VC-CMVs) and pressure control continuous mandatory ventilation with adaptive targeting scheme (PC-CMVa) modes on the Servo-u ventilator. A breathing simulator was programmed to represent an adult with moderate ARDS with different Pmax. It was connected to a ventilator set to VC-CMVs or PC-CMVa. The change in tidal volume (ΔVT) was defined as the difference between VT with CC on versus off. VT error was defined as the difference between the simulator displayed VT and the set VT with CC on versus off. For both VC-CMVs and PC-CMVa modes, ΔVT decreased as Pmax increased. The VT error decreased as Pmax increas-ed for VC-CMVs. In contrast, VT error increased on PC-CMVa mode as Pmax increased and peaked 39.0% for Pmax = 15 cm H2O. For both modes, the difference in VT errors for CC on versus CC off decreased as Pmax increased. CC corrected the delivered VT for volume lost due to compression in the patient circuit as expected. This compensation volume decreases as airway pressure drops due to patient Pmax.

Volume-targeted pressure support and automatic EPAP for chronic hypoventilation syndromes: An advance in-home ventilation or just more noise?

Early in the history of non-invasive ventilation (NIV) for disorders of hypoventilation, treatment was provided by volume-limited (VL) devices. Currently, NIV is commonly provided by pressure-limited (PL) devices because of greater portability, lower cost and studies showing increased patient comfort. There are now volume-targeted (VT) devices, which aim to combine the advantages of more stable ventilation associated with VL and greater comfort of PL mode. VT devices automatically adjust pressure support, within a defined range, to target a preset level of ventilation. This review focuses on current evidence, as provided by clinical randomized controlled trial (RCT) data, for the effectiveness of VT devices. The RCT data have significant methodological limitations, including lack of study blinding, recruitment of patients who are not naïve to NIV and failure to optimize PL settings with recent polysomnography (PSG) titration. However, the data broadly show that VT has similar short-term clinical outcomes to standard PL mode with regard to measures of nocturnal and daytime ventilation and sleep quality. The literature has not clearly identified if there are subgroups that benefit from VT. Recently, automatic expiratory positive airway pressure (AutoEPAP) algorithms, which aim to automatically control the upper airway during sleep, have been added to VT devices which may obviate the need for PSG to manually titrate EPAP. VT mode has the potential to reduce reliance on PSG and so save on healthcare costs; however, to date, a clear benefit of VT over PL NIV has not been demonstrated.

Long-term volume-targeted pressure-controlled ventilation: senseornonsense?

The technology underlying the development of novel ventilatory modes for long-term noninvasive ventilation of patients with chronic hypercapnia is continuously evolving. Volume-targeted pressure-controlled ventilation is a hybrid ventilation mode designed to combine the advantages of conventional ventilation modes, while avoiding their drawbacks. However, manufacturers have created different names and have patented algorithms and set-up variables, which can result in confusion for physicians and respiratory therapists. In addition, clear evidence for the superiority of this novel mode has not yet been established. These factors have most likely hindered more widespread use of this mode in clinical practice. The current review presents the rationale, working principles, characteristics and set-up recommendations associated with volume-targeted modes. In addition, it summarises the clinical and laboratory studies that have challenged this mode.

Implementing a bedside assessment of respiratory mechanics in patients with acute respiratory distress syndrome

BackgroundDespite their potential interest for clinical management, measurements of respiratory mechanics in patients with acute respiratory distress syndrome (ARDS) are seldom performed in routine practice. We introduced a systematic assessment of respiratory mechanics in our clinical practice. After the first year of clinical use, we retrospectively assessed whether these measurements had any influence on clinical management and physiological parameters associated with clinical outcomes by comparing their value before and after performing the test.MethodsThe respiratory mechanics assessment constituted a set of bedside measurements to determine passive lung and chest wall mechanics, response to positive end-expiratory pressure, and alveolar derecruitment. It was obtained early after ARDS diagnosis. The results were provided to the clinical team to be used at their own discretion. We compared ventilator settings and physiological variables before and after the test. The physiological endpoints were oxygenation index, dead space, and plateau and driving pressures.ResultsSixty-one consecutive patients with ARDS were enrolled. Esophageal pressure was measured in 53 patients (86.9%). In 41 patients (67.2%), ventilator settings were changed after the measurements, often by reducing positive end-expiratory pressure or by switching pressure-targeted mode to volume-targeted mode. Following changes, the oxygenation index, airway plateau, and driving pressures were significantly improved, whereas the dead-space fraction remained unchanged. The oxygenation index continued to improve in the next 48 h.ConclusionsImplementing a systematic respiratory mechanics test leads to frequent individual adaptations of ventilator settings and allows improvement in oxygenation indexes and reduction of the risk of overdistention at the same time.Trial registrationThe present study involves data from our ongoing registry for respiratory mechanics (ClinicalTrials.gov identifier: NCT02623192. Registered 30 July 2015).

New generation neonatal high frequency ventilators: effect of oscillatory frequency and working principles on performance.

Several new generation neonatal ventilators that incorporate conventional as well as high frequency ventilation (HFOV) have appeared on the market. Most of them offer the possibility to use HFOV in a volume-targeted mode, despite absence of any preclinical data. With a bench test, we evaluated the performances of 4 new neonatal HFOV devices and compared them to the SensorMedics HFOV device. Expiratory tidal volumes (V(T)) were measured for various ventilator settings and lung characteristics (ie, modifications of compliance and resistance of the system), to mimic several clinical conditions of pre-term and term infants. Increasing the frequency proportionally decreased the V(T) for all the ventilators, although the magnitude of the decrease was highly variable between ventilators. At 15 Hz and a pressure amplitude of 60 cm H2O, the delivered V(T) ranged from 3.5 to 5.9 mL between devices while simulating pre-term infant conditions and from 2.6 to 6.3 mL while simulating term infant conditions. Activating the volume-targeted mode in the 3 machines that offer this mode allowed the V(T) to remain constant over the range of frequencies and with changes of lung mechanical properties, for pre-term infant settings only while targeting a V(T) of 1 mL. These new generation neonatal ventilators were able to deliver adequate V(T) under pre-term infant, but not term infant respiratory system conditions. The clinical relevance of these findings will need to be determined by further studies.

Lung protective ventilation in extremely preterm infants

The lungs of an extremely preterm infant ≤28 weeks gestation are structurally and biochemically immature and vulnerable to injury from positive pressure ventilation. A lung protective approach to respiratory support is vital, aiming to ventilate an open lung, using the lowest pressure settings that maintain recruitment and oxygenation and avoiding hyperinflation with each tidal breath. For infants with severe respiratory distress syndrome and persistent atelectasis, lung protective ventilation requires recruitment using stepwise pressure increments, followed by reduction in ventilator pressures in search of an optimal point at which to maintain ventilation. Several studies, including a single randomised controlled trial, have found this lung protective strategy to be more effectively administered using high-frequency oscillatory ventilation rather than conventional ventilation. Many extremely preterm infants have minimal atelectasis and low oxygen requirements in the first days of life, and the ventilatory approach in this case should be one of avoidance of factors including overdistension that are known to contribute to later pulmonary deterioration. From a practical perspective, this means setting positive end-expiratory pressure at the lowest value that maintains oxygenation and restricting tidal volume using a volume-targeted mode of ventilation.

Mechanical Ventilation of the Premature Neonate

Although the trend in the neonatal intensive care unit is to use noninvasive ventilation whenever possible, invasive ventilation is still often necessary for supporting pre-term neonates with lung disease. Many different ventilation modes and ventilation strategies are available to assist with the optimization of mechanical ventilation and prevention of ventilator-induced lung injury. Patient-triggered ventilation is favored over machine-triggered forms of invasive ventilation for improving gas exchange and patient-ventilator interaction. However, no studies have shown that patient-triggered ventilation improves mortality or morbidity in premature neonates. A promising new form of patient-triggered ventilation, neurally adjusted ventilatory assist (NAVA), was recently FDA approved for invasive and noninvasive ventilation. Clinical trials are underway to evaluate outcomes in neonates who receive NAVA. New evidence suggests that volume-targeted ventilation modes (ie, volume control or pressure control with adaptive targeting) may provide better lung protection than traditional pressure control modes. Several volume-targeted modes that provide accurate tidal volume delivery in the face of a large endotracheal tube leak were recently introduced to the clinical setting. There is ongoing debate about whether neonates should be managed invasively with high-frequency ventilation or conventional ventilation at birth. The majority of clinical trials performed to date have compared high-frequency ventilation to pressure control modes. Future trials with premature neonates should compare high-frequency ventilation to conventional ventilation with volume-targeted modes. Over the last decade many new promising approaches to lung-protective ventilation have evolved. The key to protecting the neonatal lung during mechanical ventilation is optimizing lung volume and limiting excessive lung expansion, by applying appropriate PEEP and using shorter inspiratory time, smaller tidal volume (4-6 mL/kg), and permissive hypercapnia. This paper reviews new and established neonatal ventilation modes and strategies and evaluates their impact on neonatal outcomes.

507 Volume-Targeted Ventilation Reduces the Risk of Death or Bpd: A Cochrane Meta-Analysis

Background and aims: Volutrauma is associated with neonatal lung injury. Modern ventilators offer volume-targeted modes aiming to reduce volutrauma and improve PaCO2 stability. The objectives were to determine whether volume-targeted ventilation (VTV), compared with pressure-limited ventilation (PLV), reduces mortality, bronchopulmonary dysplasia (BPD) and other outcomes. Methods: Cochrane systematic review of randomised clinical trials comparing VTV with PLV. Risk ratios (RR) or weighted mean difference with 95% confidence intervals (CI) were obtained from meta-analysis using a fixed effect model. Numbers needed to treat (NNT) were derived from risk differences. Results: Nine parallel trials (629 infants) and three crossover trials (64 infants) met inclusion criteria. There was no difference in hospital mortality {RR 0.80 (95% CI 0.53, 1.20)}. The use of VTV-modes resulted in a reduction in the combined outcome death or BPD {RR 0.73 (95% CI 0.57 to 0.93), NNT 8 (95% CI 5 to 33)}. VTV-modes also resulted in reductions in pneumothorax {RR 0.46 (95% CI 0.25 to 0.84), NNT 17 (95% CI 10 to 100)}, days of ventilation {MD -2.36 (95% CI -3.9 to -0.8)}, risk of hypocarbia {RR 0.56 (95% CI 0.33 to 0.96), NNT 4 (95% CI 2 to 25)} and the combined outcome PVL or grade 3-4 IVH {RR 0.48 (95% CI 0.28 to 0.84), NNT 11 (95% CI 7 to 50)}. Conclusions: Infants ventilated using VTV-modes had reduced death or BPD compared with infants ventilated using PLV-modes. Further research is needed to identify whether VTV-modes improve neurodevelopmental outcomes, and to determine best VTV practice.

Volume-targeted modes of modern neonatal ventilators: how stable is the delivered tidal volume?

Volume-targeted modes are designed to deliver a constant tidal volume (V(t)) at lowest possible pressure independently of changes in compliance, resistance, and leak of the respiratory system. We examined whether these volume-targeted modes respond rapidly enough to sudden changes in respiratory mechanics (e.g., selective intubation, surfactant administration, endotracheal tube kinking, de-kinking, obstruction), resulting in insufficient or excessive V(t) delivery. Bench study of six neonatal ventilators in the volume-targeted mode simulating preterm and full-term infant settings on a test lung. Breath-to-breath expiratory V(t) were measured after rapid compliance, resistance, and leak changes. Under our test settings all ventilators showed important volume overshooting following rapid increase in compliance or decrease in resistance. Between one and 16 inflations were required to return to the set V(t). Some ventilators delivered inaccurate V(t) under steady state condition while others showed considerable breath-to-breath V(t) variability. We observed inaccurate V(t) delivery under specific conditions as well as immediate and sometimes prolonged volume overshooting after a rapid respiratory system compliance increase or resistance decrease in volume-targeted modes of modern neonatal ventilators. Similar discrepancies between the set V(t) and the delivered inflations can be harmful in clinical situations, especially in newborns. Their clinical relevance needs to be clarified with safety studies in the neonatal population and we encourage manufacturers to further improve the ventilators algorithms.

Newer modes of mechanical ventilation for the neonate.

For decades, the overwhelming majority of infants requiring mechanical ventilation for respiratory failure were treated with standard time-cycled, pressure-limited intermittent mandatory ventilation. Technologic advances in the 1990s brought forth sophisticated transducers and microprocessor-based mechanical ventilators that enabled implementation of many newer modes of mechanical ventilation. Some of these are volume-targeted rather than pressure-targeted, and many allow an element of patient control of the ventilator, including initiation and termination of inspiration and control of flow. Some modes are even hybrids, combining the best features of both pressure-targeted and volume-targeted modes. This article reviews the principles and salient clinical features of the newer ventilatory modes for newborns with respiratory failure.

Leak compensation in positive pressure ventilators: a lung model study

Leak compensating abilities of six different positive pressure ventilators commonly used to deliver noninvasive positive pressure ventilation, including the bilevel positive airway pressure (BiPAP) S/T-D and Quantum (Respironics Inc, Murrysville, PA, USA), 335 and O'NYX (Mallinckrodt Inc, St Louis, MO, USA), PLV 102 (Respironics), and Siemens Servo 900C (Siemens Inc, Danvers, MA, USA). Using a test lung model, compensatory capabilities of the ventilators were tested for smaller and larger leaks using the assist/control or timed modes. Back-up rate was 20 min(-1), inspiratory pressure was 18 cmH2O, and expiratory pressure was 5 cmH2O. It was found that even in the absence of air leaking, delivered tidal volume differed substantially between the ventilators during use of pressure-targeted modes, depending on inspiratory flows, inaccuracies in set versus delivered pressures, and inspiratory duration. Also during pressure-targeted ventilation, increasing the tI/ttot up to, but not beyond, 0.5 improved compensation by lengthening inspiratory duration, whereas use of a sensitive flow trigger setting tended to cause autocycling during leaking, interfering with compensation. Leaking interfered with cycling of the BiPAP S/T, inverting the I:E ratio, shortening expiratory time, and reducing delivered tidal volume. Volume-targeted modes achieved limited compensation for small air leaks, but compensated poorly for large leaks. To conclude, leak-compensating capabilities differ markedly between ventilators but pressure-targeted ventilators are preferred for noninvasive positive pressure ventilation in patients with substantial air leaking. Adequate inspiratory flows and durations should be used, triggering sensitivity should be adjusted to prevent autocycling, and a mechanism should be available to limit inspiratory time and avoid I:E ratio inversion.