Automatic Tube Compensation Research Articles

Prediction of extubation outcome: a randomised, controlled trial with automatic tube compensation vs. pressure support ventilation

IntroductionTolerance of a spontaneous breathing trial is an evidence-based strategy to predict successful weaning from mechanical ventilation. Some patients may not tolerate the trial because of the respiratory load imposed by the endotracheal tube, so varying levels of respiratory support are widely used during the trial. Automatic tube compensation (ATC), specifically developed to overcome the imposed work of breathing because of artificial airways, appears ideally suited for the weaning process. We further evaluated the use of ATC in this setting.MethodsIn a prospective study, patients who had received mechanical ventilation for more than 24 hours and met defined criteria for a weaning trial, underwent a one-hour spontaneous breathing trial with either ATC (n = 87) or pressure support ventilation (PSV; n = 93). Those tolerating the trial were immediately extubated. The primary outcome measure was the ability to maintain spontaneous, unassisted breathing for more than 48 hours after extubation. In addition, we measured the frequency/tidal volume ratio (f/VT) both with (ATC-assisted) and without ATC (unassisted-f/VT) at the start of the breathing trial as a pretrial predictor of extubation outcome.ResultsThere were no significant differences in any of the baseline characteristics between the two groups apart from a significantly higher Acute Physiology and Chronic Health Evaluation (APACHE) II score in the ATC group (p = 0.009). In the PSV group, 13 of 93 (14%) patients failed the breathing trial compared with only 6 of 87 (6%) in the ATC group; this observed 8% difference, however, did not reach statistical significance (p = 0.12). The rate of reintubation was not different between the groups (total group = 17.3%; ATC = 18.4% vs. PSV = 12.9%, p = 0.43). The percentage of patients who remained extubated for more than 48 hours was similar in both groups (ATC = 74.7% vs. PSV = 73.1%; p = 0.81). This represented a positive predictive value for PSV of 0.85 and ATC of 0.80 (p = 0.87). Finally, the ATC-assisted f/VT was found to have a significant contribution in predicting successful liberation and extubation compared with the non-significant contribution of the unassisted f/VT (unassisted f/VT, p = 0.19; ATC-assisted f/VT, p = 0.005).ConclusionsThis study confirms the usefulness of ATC during the weaning process, being at least as effective as PSV in predicting successful extubation outcome and significantly improving the predictive value of the f/VT.Trial registrationCurrent Controlled Trials ISRCTN16080446

Automatic Tube Compensation During Weaning From Mechanical Ventilation

Automatic Tube Compensation During Weaning From Mechanical Ventilation

Extubation outcome following a spontaneous breathing trial with automatic tube compensation versus continuous positive airway pressure

Extubation outcome following a spontaneous breathing trial with automatic tube compensation versus continuous positive airway pressure

Extubation outcome following a spontaneous breathing trial with automatic tube compensation versus continuous positive airway pressure

We hypothesized that the additional use of automatic tube compensation (ATC) during a spontaneous breathing trial with continuous positive airway pressure (CPAP), by minimizing respiratory work, would result in more patients undergoing successful extubation. Prospective, randomized, controlled study. A ten-bed, general intensive care department at a tertiary-care hospital. Adult patients (n=99) who had undergone mechanical ventilation for >24 hrs and met defined criteria for a weaning trial. Patients were randomized to undergo a 1-hr spontaneous breathing trial with either ATC with CPAP (ATC group, n=51) or CPAP alone (CPAP group, n=48). ATC was provided by commercially available mechanical ventilators. Patients tolerating the spontaneous breathing trial underwent immediate extubation. The primary outcome measure was successful extubation, defined as the ability to maintain spontaneous breathing for 48 hrs after discontinuation of mechanical ventilation and extubation. There were no significant differences in demographic, respiratory, or hemodynamic characteristics between the two groups at the start of the spontaneous breathing trial. There was a trend for more patients in the ATC group to tolerate the breathing trial and undergo extubation (96% vs. 85%; p=.08). The rate of reintubation was 14% in the ATC group and 24% in the CPAP group (p=.28). Significantly more patients in the ATC group thus met the criteria for successful extubation (82% vs. 65%; p=0.04). This is the largest single-center study to date assessing the use of commercially available ATC and suggests that this might be a useful mode for performing a spontaneous breathing trial preceding extubation in a general intensive care population.

Proportional assist versus pressure support ventilation in patients with acute respiratory failure: Cardiorespiratory responses to artificially increased ventilatory demand*

To test the hypothesis that in response to increased ventilatory demand, dynamic inspiratory pressure assistance better compensates for increased workload compared with static pressure support ventilation (PSV). Randomized clinical crossover study. General intensive care u nits of a university hospital. Twelve patients with acute respiratory failure. Patients received PSV, proportional assist ventilation (PAV), and PAV+ automatic tube compensation (ATC) in random order while maintaining mean inspiratory airway pressure constant. During each setting, ventilatory demand was increased by adding deadspace without ventilator readjustment. Cardiorespiratory, ventilatory, and work of breathing variables were assessed by routine monitoring plus pneumotachography; airway, esophageal, and abdominal pressure measurements; and nitrogen washout. After deadspace addition, tidal volume and end-expiratory lung volume increased similarly in all ventilatory modalities. Ventilator work, peak inspiratory flow, and maximum airway pressure increased significantly during PAV+ATC when compared with PSV after deadspace addition. However, increase in ventilator work did not result in a smaller increase in patients' work of breathing with elevated ventilatory demand during PAV+ATC (PSV 807 +/- 204 mJ/L, PAV 802 +/- 193 mJ/L, and PAV+ATC 715 +/- 202 mJ/L, p = .11). Increase in patients' work of breathing was mainly caused by a significantly higher resistive workload during PAV and PAV+ATC. In patients with acute respiratory failure, dynamic inspiratory pressure assistance modalities are not superior to PSV with respect to cardiorespiratory function and inspiratory muscles unloading after increasing ventilatory demand. The latter might be explained by higher peak flows resulting in nonlinearly increased resistive workload that was incompletely compensated by PAV+ATC.

“Simplify your life” does not necessarily work when applying automatic tube compensation and proportional assist ventilation*

Critical Care Medicine: September 2005 - Volume 33 - Issue 9 - p 2125-2126 doi: 10.1097/01.CCM.0000178289.78396.23

Breathing pattern and workload during automatic tube compensation, pressure support and T-piece trials in weaning patients

Breathing pattern and workload during automatic tube compensation, pressure support and T-piece trials in weaning patients

Breathing pattern and workload during automatic tube compensation, pressure support and T-piece trials in weaning patients.

Automatic tube compensation has been designed as a new ventilatory mode to compensate for the non-linear resistance of the endotracheal tube. The study investigated the effects of automatic tube compensation compared with breathing through a T-piece or pressure support during a trial of spontaneous breathing used for weaning patients from mechanical ventilation of the lungs. Twelve patients were studied who were ready for weaning after prolonged mechanical ventilation (10.2 +/- 8.4 days) due to acute respiratory failure. Patients with chronic obstructive pulmonary disease were excluded. Thirty minutes of automatic tube compensation were compared with 30 min periods of 7 cmH2O pressure support and T-piece breathing. Breathing patterns and workload indices were measured at the end of each study period. During T-piece breathing, the peak inspiratory flow rate (0.65 +/- 0.20 L s(-1)) and minute ventilation (8.9 +/- 2.7L min(-1)) were lower than during either pressure support (peak inspiratory flow rate 0.81 +/- 0.25 L s(-1) minute ventilation 10.2 +/- 2.3 L min(-1), respectively) or automatic tube compensation (peak inspiratory flow rate 0.75 +/- 0.26L s(-1); minute ventilation 10.8 +/- 2.7 L min(-1)). The pressure-time product as well as patients' work of breathing were comparable during automatic tube compensation (pressure-time product 214.5 +/- 104.6 cmH2O s(-1) min(-1), patient work of breathing 1.1 +/- 0.4 J L(-1)) and T-piece breathing (pressure-time product 208.3 +/- 121.6 cmH2O s(-1) min(-1), patient work of breathing 1.1 +/- 0.4 J L(-1)), whereas pressure support resulted in a significant decrease in workload indices (pressure-time product 121.2 +/- 64.1 cmH2O s(-1) min(-1), patient work of breathing 0.7 +/- 0.4 J L(-1)). In weaning from mechanical lung ventilation, patients' work of breathing during spontaneous breathing trials is clearly reduced by the application of pressure support 7 cmH2O, whereas the workload during automatic tube compensation corresponded closely to the values during trials of breathing through a T-piece.

Additional work of breathing and breathing patterns in spontaneously breathing patients during pressure support ventilation, automatic tube compensation and amplified spontaneous pattern breathing

Additional work of breathing and breathing patterns in spontaneously breathing patients during pressure support ventilation, automatic tube compensation and amplified spontaneous pattern breathing

Short-term effects of positive end-expiratory pressure on breathing pattern: an interventional study in adult intensive care patients

IntroductionPositive end-expiratory pressure (PEEP) is used in mechanically ventilated patients to increase pulmonary volume and improve gas exchange. However, in clinical practice and with respect to adult, ventilator-dependent patients, little is known about the short-term effects of PEEP on breathing patterns.MethodsIn 30 tracheally intubated, spontaneously breathing patients, we sequentially applied PEEP to the trachea at 0, 5 and 10 cmH2O, and then again at 5 cmH2O for 30 s each, using the automatic tube compensation mode.ResultsIncreases in PEEP were strongly associated with drops in minute ventilation (P < 0.0001) and respiratory rate (P < 0.0001). For respiratory rate, a 1 cmH2O change in PEEP in either direction resulted in a change in rate of 0.4 breaths/min. The effects were exclusively due to changes in expiratory time. Effects began to manifest during the first breath and became fully established in the second breath for each PEEP level. Identical responses were found when PEEP levels were applied for 10 or 60 s. Post hoc analysis revealed a similar but stronger response in patients with impaired respiratory system compliance.ConclusionIn tracheally intubated, spontaneously breathing adult patients, the level of PEEP significantly influences the resting short-term breathing pattern by selectively affecting expiratory time. These findings are best explained by the Hering–Breuer inflation/deflation reflex.

Weaning from mechanical ventilation using assisted spontaneous breathing plus CPAP versus assisted spontaneous ventilation: our experience

In this retrospective study, we evaluated two different modes of weaning: assisted spontaneous breathing (ASB) plus CPAP with automatic tube compensation (Evita 4, Draeger Medical, Germany) versus assisted spontaneous ventilation (ASV) (Galileo Gold, Hamilton Medical, Switzerland) in 80 patients who had undergone abdominal surgery. Our target was to assess differences in weaning times using different modes of assistance.

Respiratory Myoclonus Produces High Airway Pressure and Tidal Volume During Automatic Tube Compensation Ventilation

INTRODUCTION: Mechanical ventilation has undergone many changes, particularly with the creation of additional modes of ventilation. Automatic tube compensation (ATC) is one of the newer, more unique modes. It is designed to precisely overcome the calculated resistance of the airway by adjusting the delivered pressure in accordance to flow rates generated by the patient. We report a case of respiratory myoclonus with unusual results while utilizing ATC.

Safety and efficacy of MMV/ATC for the weaning of post-operative open-heart patients

PURPOSE: Early extubation of patients undergoing elective coronary artery bypass surgery is a trend in surgical practice. Mandatory Minute Ventilation (MMV) is a mode of ventilation that guarantees set minute ventilation but allows an automatic transition from mechanical support to spontaneous breathing. Automatic Tube Compensation (ATC) is a mode extension that provides compensation for the flow-dependent endotracheal tube resistance during both inspiration and expiration. Objective: To evaluate the safety and efficacy of a computer-driven MMV/ATC (Drager Medical, Telford, PA) as a weaning method in the post-operative open-heart patient.

Breathing pattern and work of breathing in spontaneously breathing patients during continuous positive airway pressure (CPAP) and pressure support ventilation (PSV) with and without automatic tube compensation (ATC)

Breathing pattern and work of breathing in spontaneously breathing patients during continuous positive airway pressure (CPAP) and pressure support ventilation (PSV) with and without automatic tube compensation (ATC)

Continuous monitoring of tracheal pressure including spot-check of endotracheal tube resistance

During mechanical ventilation, the resistance of the endotracheal and tracheostomy tube (ETT) highly influences analysis of respiratory system mechanics and imposes additional work of breathing for the spontaneously breathing patient which both can be circumvented by applying the automatic tube compensation (ATC) mode. In the ATC mode, tracheal pressure (ptrach) is continuously calculated on the basis of measured flow and airway pressure using predetermined tube specific coefficients. However, as during long-term ventilation the ETT might become partially obstructed by secretions or tube kinking, the predetermined coefficients are no longer valid rendering calculation of ptrach inaccurate. We propose an easy-to-handle maneuver for the bedside determination of current tube coefficients in the tracheally intubated patient. Based on check-spot measurement of ptrach, current tube coefficients are determined by a least-squares fit procedure valid for the partially obstructed ETT with the indwelling pressure-measuring catheter (PMC). To correct for the removal of the PMC, the relationship between tube coefficients with and those without indwelling PMC has been determined in a laboratory investigation. Accuracy of the procedure was determined during artificial ETT obstruction by comparing calculated with measured ptrach. Correspondence between calculated and measured ptrach has been found excellent. We conclude that by adopting this bedside procedure periodically, accurate calculation of ptrach is guaranteed and the advantages of the ATC mode are ensured even in long-term ventilatory support.

Breathing pattern and workload during automatic tube compensation, pressure support and T-piece trials in weaning patients

A reply EDITOR: We thank Dr Knight and colleagues for their interest in our paper [1]. They pointed out some aspects of the methods used and data interpretation that we would like to answer. It is true that different intrathoracic pressures will interfere with pulmonary and chest wall mechanics and, therefore, a separate effect of intrathoracic pressures might, at least in part, account for differences in the breathing workload. This effect has been shown for positive end-expiratory pressure in different patient populations. However, since mean airway pressures were similar for automatic tube compensation (ATC) and pressure support in our investigation, this would not explain differences between these modes. To clarify the role of intrathoracic pressures for the comparison with T-piece breathing, the study was repeated using high-flow continuous positive airway pressure instead of the unsupported T-piece and found essentially the same breathing pattern and workload indices as in our original study [2]. We agree with Knight and colleagues that different respiratory mechanics will probably show different responses to the modes tested and, therefore, the assumption of one chest wall compliance might be over simplistic. Since the same value for all modes tested was assumed, it was not thought that this might help to explain the differences observed in our study. It would be interesting to follow the authors' arguments and design future studies on breathing modes stratified according to respiratory mechanics. Data on PaCO2 were virtually unchanged for the three modes tested and minute ventilation was about 1 L min−1 lower for T-piece breathing compared with the supported modes in our investigation. However, no speculation was made about all the possible effects of supported versus unsupported breathing and focus was made on breathing patterns and workload indices. We do not propose here any benefit for supported modes, but question the efficacy of ATC to unload the respiratory system from the imposed workload that clearly occurs during pressure support. We agree with the speculation that dead space was probably slightly higher during the supported modes tested. We also agree with Knight and colleagues in questioning the coefficients used in the algorithm implemented in the lung ventilator (as addressed in the discussion). We discussed potential differences to former studies, which were made with prototype lung ventilators using different coefficients. For the clinical use of ATC, it will be crucial to assess the technical precision of the algorithm implemented into commercially available ventilators. Based on this, we also appreciate the comment on the potential role of humidifiers. Our study did not address this issue since no humidifier was used for the short-term measurements to circumvent this problem. Again, a technical study should assess the potential role of humidifiers for a precise setting of ATC. It might be worthwhile to find coefficients not only for given tubes, but also for the combination with given humidifiers. Again, we appreciate the comments of Knight and colleagues in giving us the opportunity to emphasize that the promisingly easy concept of ATC in bench studies might be not so easily transferred to the bedside. R. Kublen M. Max R. Dembinski S. Terbeck E. Jürgens R. Rossaint Department of Anaesthesiology; University Hospital Aachen; Aachen, Germany

Breathing pattern and workload during automatic tube compensation, pressure support and T-piece trials in weaning patients

EDITOR: We congratulate Dr Kuhlen and colleagues on an interesting and well-designed study comparing work of breathing during automated tube compensation, pressure support and T-piece trials [1]. However, we would question some aspects of the methodology and data interpretation. The authors state that the patient work of breathing was the same in the automated tube compensation and T-piece trials. However, the increased mean airway pressure in automated tube compensation and pressure support modes has an independent beneficial effect on pulmonary and chest wall compliance (as does positive end-expiratory pressure) and results in improved compliance. Furthermore, the chest wall compliance quoted seems unduly high for the population examined and the assumption that this figure is constant in critically ill patients seems unlikely [2]. Would varying chest wall compliance in supported and unsupported modes alter the reported results? It is also interesting to note that despite the lower-minute ventilation, the PaCO2 was lower in the T-piece group. This probably reflects the increased alveolar dead space in the pressure support and automated tube compensation groups [3]. Thus, any proposed benefits of automated tube compensation or pressure support should be viewed in terms of the whole cardiopulmonary unit, not just respiratory mechanics. A number of explanations for the lack of benefit of automated tube compensation vs. T-piece weaning, exist. We note that only nonlinear coefficients for calculation of resistance are used in automated tube compensation when, in reality, pressure drop across the tube is sum of both linear and nonlinear flow components as the authors state. It would be helpful to know how the authors' automated tube compensation algorithms compared to previously published work that includes linear and nonlinear components. We assume that all inspiratory gases were humidified; yet the methods incorporated are not mentioned. If a heat and moisture exchanger were used, then alterations in resistance and dead space [4] would have adversely affected the conditions for optimal automated tube compensation function. If a heated humidification system were used, then the flow characteristics of the resultant inspiratory gas would also be different to the coefficients used in calculating automated tube compensation. We believe that these questions can be answered either by re-analysis of existing data or by modifications of the original study. D. J. W. Knight I. K. Moppett J. G. Hardman University Department of Anaesthesia; University Hospital; Nottingham, UK

Measurement of functional residual capacity by nitrogen washout during partial ventilatory support.

Evaluation of an open circuit multiple breath nitrogen washout (MBNW) technique for measurement of functional residual capacity (FRC) during partial ventilatory support using corrections for gas viscosity, sampling delay time, and re-inspired nitrogen. Measurements in a lung model with known reference volume simulating spontaneous breathing and duplicate measurements in patients breathing spontaneously with partial ventilatory support. SETTING. Experimental laboratory and intensive care units of a university hospital. Eighteen patients with acute respiratory failure. Change of FiO(2) from baseline to 1.0. FRC was measured by MBNW during spontaneous breathing with continuous positive airway pressure, pressure support ventilation, proportional assist ventilation, automatic tube compensation, and airway pressure release ventilation. In the lung model, repeated measurements at three volumes were done with all partial ventilatory support modalities, and baseline FiO(2 )was varied with one mode and FRC. The mean of differences between MBNW (FRC(MBNW)) and reference was 28 ml (1.6%), and the 2.SD-interval was 84 ml (4.9%) for all modes. Measurements up to a baseline FiO(2) of 0.8 showed differences of 5 ml (-0.3%) and the 2.SD-interval of 38 ml (2.2%) between reference and FRC(MBNW). In 18 patients, 66 duplicate measurements revealed a mean difference of 30 ml (0.9%) with a coefficient of repeatability of 358 ml (13%) independent of ventilatory mode and chronological order. This study suggests that, using corrections for gas viscosity, sampling delay time, and re-inspired nitrogen, FRC can be determined with good repeatability in patients and good accuracy in a lung model during partial ventilatory support.

Proportional assist ventilation combined with automatic tube compensation. A promising concept of augmented spontaneous breathing?

The combination of proportional assist ventilation (PAV) and automatic tube compensation (ATC) is a promising concept for partial ventilatory support. In contrast to conventional pressure support ventilation (PSV), PAV+ATC provides dynamic pressure support depending on the patient's initial inspiratory effort. PAV+ATC should selectively unload the respiratory muscles from the additional workload imposed by increased respiratory system resistance and elastance as well as by endotracheal tube resistance. Patients have the ability to modify the tidal volume in response to changes in ventilatory demand, thereby improving patient-ventilator interaction and breathing comfort when compared with PSV. However, since routine measurements of respiratory mechanics during augmented spontaneous breathing are currently unavailable but would be necessary for setting the support level as a function of respiratory system mechanics during PAV, this mode cannot yet be generally recommended for routine clinical use.

Breathing pattern and workload during automatic tube compensation, pressure support and T-piece trials in weaning patients

Background and objective: Automatic tube compensation has been designed as a new ventilatory mode to compensate for the non-linear resistance of the endotracheal tube. The study investigated the effects of automatic tube compensation compared with breathing through a T-piece or pressure support during a trial of spontaneous breathing used for weaning patients from mechanical ventilation of the lungs. Methods: Twelve patients were studied who were ready for weaning after prolonged mechanical ventilation (10.2 ± 8.4 days) due to acute respiratory failure. Patients with chronic obstructive pulmonary disease were excluded. Thirty minutes of automatic tube compensation were compared with 30 min periods of 7 cmH2O pressure support and T-piece breathing. Breathing patterns and workload indices were measured at the end of each study period. Results: During T-piece breathing, the peak inspiratory flow rate (0.65 ± 0.20 L s−1) and minute ventilation (8.9 ± 2.7 L min−1) were lower than during either pressure support (peak inspiratory flow rate 0.81 ± 0.25 L s−1; minute ventilation 10.2 ± 2.3 L min−1, respectively) or automatic tube compensation (peak inspiratory flow rate 0.75 ± 0.26 L s−1; minute ventilation 10.8 ± 2.7 L min−1). The pressure-time product as well as patients' work of breathing were comparable during automatic tube compensation (pressure-time product 214.5 ± 104.6 cmH2O s−1 min−1, patient work of breathing 1.1 ± 0.4 J L−1) and T-piece breathing (pressure-time product 208.3 ± 121.6 cmH2O s−1 min−1, patient work of breathing 1.1 ± 0.4 J L−1), whereas pressure support resulted in a significant decrease in workload indices (pressure-time product 121.2 ± 64.1 cmH2O s−1 min−1, patient work of breathing 0.7 ± 0.4 J L−1). Conclusions: In weaning from mechanical lung ventilation, patients' work of breathing during spontaneous breathing trials is clearly reduced by the application of pressure support 7 cmH2O, whereas the workload during automatic tube compensation corresponded closely to the values during trials of breathing through a T-piece.