Effects of mechanical unloading/loading on respiratory loop gain and periodic breathing in man

Comparative Efficacy and Safety of Four Different Spontaneous Breathing Trials for Weaning From Mechanical Ventilation: A Systematic Review and Network Meta-Analysis

Background: Spontaneous breathing trial (SBT) has been used to predict the optimal time of weaning from ventilator. However, it remains controversial which trial should be preferentially selected. We aimed to compare and rank four common SBT modes including automatic tube compensation (ATC), pressure support ventilation (PSV), continuous positive airway pressure (CPAP), and T-piece among critically ill patients receiving mechanical ventilation (MV).

Methods: We searched PubMed, EMBASE, and the Cochrane Central Register of Controlled Trials (CENTRAL) to identify studies that investigated the comparative efficacy and safety of at least two SBT strategies among critically ill patients up to May 17, 2020. We estimated the surface under the cumulative ranking curve (SUCRA) to rank SBT techniques, and determined the certainty of evidence using the Grading of Recommendations Assessment, Development and Evaluation method. Primary outcome was weaning success. Secondary outcomes were reintubation, SBT success, duration of acute care, and intensive care unit (ICU) mortality. Statistical analysis was conducted by using RevMan 5.4, Stata, and R software.

Results: We enrolled 24 trials finally. Extubation success rate was significantly higher in ATC than that in T-piece (OR, 0.28; 95% CI, 0.13–0.64) or PSV (OR, 0.53; 95% CI, 0.32–0.88). For SBT success, ATC was better than other SBT techniques, with a pooled OR ranging from 0.17 to 0.42. For reintubation rate, CPAP was worse than T-piece (OR, 2.76; 95% CI, 1.08 to 7.06). No significant difference was detected between SBT modes for the length of stay in ICU or long-term weaning unit (LWU). Similar result was also found for ICU mortality between PSV and T-piece. Majority direct results were confirmed by network meta-analysis. Besides, ATC ranks at the first, first, and fourth place with a SUCRA of 91.7, 99.7, and 39.9%, respectively in increasing weaning success and SBT success and in prolonging ICU or LWU length of stay among four SBT strategies. The confidences in evidences were rated as low for most comparisons.

Conclusion: ATC seems to be the optimal choice of predicting successful weaning from ventilator among critically ill patients. However, randomized controlled trials (RCTs) with high quality are needed to further establish these findings.

How Mechanical Ventilation Measurement, Cutoff and Duration Affect Rapid Shallow Breathing Index Accuracy: A Randomized Trial

BACKGROUND

Decreased accuracy of the rapid shallow breathing index (RSBI) can stem from 1) the method used to obtain this index, 2) duration of mechanical ventilation (MV), and 3) the established cutoff point. The objective was to evaluate the values of RSBI determined by three different methods, using distinct MV times and cutoff points.

METHODS

This prospective study included 40 subjects. Before extubation, three different methods were employed to measure RSBI: pressure support ventilator (PSV) (PSV = 5 - 8 cm H₂O; positive end-expiratory pressure (PEEP) = 5 cm H₂O) (RSBI_MIN), automatic tube compensation (ATC) (PSV = 0, PEEP = 5 cm H₂O, and 100% tube compensation) (RSBI_ATC), and disconnected MV (RSBI_SP). The results were analyzed according to the MV period (less than or over 72 h) and to the outcome of extubation (< 72 h, successful and failed; > 72 h successful and failed). The accuracy of each method was determined at different cutoff points (105, 78, and 50 cycles/min/L).

RESULTS

The RSBI_MIN, RSBI_ATC, and RSBI_SP values in the group < 72 h were 38 ± 18, 45 ± 26 and 55 ± 22; in the group > 72 h, RSBI_SP value was higher than those of RSBI_ATC and RSBI_MIN (78 ± 29, 51 ± 19 and 39 ± 14) (P < 0.001). For patients with MV > 72 h who failed in removing MV, the RSBI_SP was higher (93 ± 28, 58 ± 18 and 41 ± 10) (P < 0.000), with greater accuracy at cutoff of 78.

CONCLUSION

RSBI_SP associated with cutoff point < 78 cycles/min/L seems to be the best strategy to identify failed extubation in subjects with MV for over 72 h.

Airway pressure release ventilation

Airway pressure release ventilation was introduced to clinical practice about two decades ago as an alternative mode for mechanical ventilation; however, it had not gained popularity until recently as an effective safe alternative for difficult-to-oxygenate patients with acute lung injury/ acute respiratory distress syndrome This review will cover the definition and mechanism of airway pressure release ventilation, its advantages, indications, and guidance.

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

OBJECTIVE

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.

DESIGN

Prospective, randomized, controlled study.

SETTING

A ten-bed, general intensive care department at a tertiary-care hospital.

PATIENTS

Adult patients (n=99) who had undergone mechanical ventilation for >24 hrs and met defined criteria for a weaning trial.

INTERVENTIONS

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.

MEASUREMENTS AND MAIN RESULTS

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).

CONCLUSION

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.

Other approaches to open-lung ventilation: Airway pressure release ventilation

OBJECTIVE

To review the use of airway pressure release ventilation (APRV) in the treatment of acute lung injury/acute respiratory distress syndrome.

DATA SOURCE

Published animal studies, human studies, and review articles of APRV.

DATA SUMMARY

APRV has been successfully used in neonatal, pediatric, and adult forms of respiratory failure. Experimental and clinical use of APRV has been shown to facilitate spontaneous breathing and is associated with decreased peak airway pressures and improved oxygenation/ventilation when compared with conventional ventilation. Additionally, improvements in hemodynamic parameters, splanchnic perfusion, and reduced sedation/neuromuscular blocker requirements have been reported.

CONCLUSION

APRV may offer potential clinical advantages for ventilator management of acute lung injury/acute respiratory distress syndrome and may be considered as an alternative "open lung approach" to mechanical ventilation. Whether APRV reduces mortality or increases ventilator-free days compared with a conventional volume-cycled "lung protective" strategy will require future randomized, controlled trials.

Accuracy of automatic tube compensation in new-generation mechanical ventilators*

OBJECTIVE

To compare performance of flow-adapted compensation of endotracheal tube resistance (automatic tube compensation, ATC) between the original ATC system and ATC systems incorporated in commercially available ventilators.

DESIGN

Bench study.

SETTING

University research laboratory.

SUBJECTS

The original ATC system, Dräger Evita 2 prototype, Dräger Evita 4, Puritan-Bennett 840.

INTERVENTIONS

The four ventilators under investigation were alternatively connected via different sized endotracheal tubes and an artificial trachea to an active lung model. Test conditions consisted of two ventilatory modes (ATC vs. continuous positive airway pressure), three different sized endotracheal tubes (inner diameter 7.0, 8.0, and 9.0 mm), two ventilatory rates (15/min and 30/min), and four levels of positive end-expiratory pressure (0, 5, 10, and 15 cm H2O).

MEASUREMENTS AND MAIN RESULTS

Performance of tube compensation was assessed by the amount of tube-related (additional) work of breathing (WOBadd), which was calculated on the basis of pressure gradient across the endotracheal tube. Compared with continuous positive airway pressure, ATC reduced inspiratory WOBadd by 58%, 68%, 50%, and 97% when using the Evita 4, the Evita 2 prototype, the Puritan-Bennett 840, and the original ATC system, respectively. Depending on endotracheal tube diameter and ventilatory pattern, inspiratory WOBadd was 0.12-5.2 J/L with the original ATC system, 1.5-28.9 J/L with the Puritan-Bennett 840, 10.4-21.0 J/L with the Evita 2 prototype, and 10.1-36.1 J/L with the Evita 4 (difference between each ventilator at identical test situations, p <.025). Expiratory WOBadd was reduced by 5%, 26%, 1%, and 70% with the Evita 4, the Evita 2 prototype, the Puritan-Bennett 840, and the original ATC system, respectively. The expiratory WOBadd caused by an endotracheal tube of 7.0 mm inner diameter was 5.5-42.2 J/L at a low ventilatory rate and 19.6-82.3 J/L at a high ventilatory rate. It was lowest with the original ATC system and highest with the Evita 4 ventilator (p <.025).

CONCLUSIONS

Flow-adapted tube compensation by the original ATC system significantly reduced tube-related inspiratory and expiratory work of breathing. The commercially available ATC modes investigated here may be adequate for inspiratory but probably not for expiratory tube compensation.

Reduction of correlation dimension in human respiration by inhaling a mixture gas of 5% carbon dioxide and 95% oxygen

In order to investigate the effect of the respiratory control system on deterministic behavior in respiration, we used nonlinear analysis in subjects breathing a mixture gas of 5% carbon dioxide (CO2) and 95% oxygen (O2) (CO2-mixed gas). The respiratory movements during breathing air or CO2-mixed gas in eight healthy volunteers were measured. We estimated the values of the correlation dimension (D2) in respiratory movement using Grassberger-Procaccia algorithm. The respiratory movements during inhaling either air or CO2-mixed gas showed a nonlinear behavior using surrogate data method. The values of D2 in respiratory movement during inhaling CO2-mixed gas (1.77 +/- 0.17) were significantly smaller than those during inhaling air (2.52 +/- 0.60) (P < 0.05). This might be related to a prompt change in the nonlinear signal from the central respiratory chemical system.

Extubation after breathing trials with automatic tube compensation, T-tube, or pressure support ventilation

BACKGROUND

Automatic tube compensation (ATC) is a new option to compensate for the pressure drop across the endotracheal or tracheostomy tube (ETT), especially during ventilator-assisted spontaneous breathing. While several benefits of this mode have so far been documented, ATC has not yet been used to predict whether the ETT could be safely removed at the end of weaning, from mechanical ventilation.

METHODS

We undertook a systematic trial using a randomized block design. During a 2-year period, all eligible patients of a medical intensive care unit were treated with ATC, conventional pressure support ventilation (PSV, 5 cmH2O), or T-tube for 2-h. Tolerance of the breathing trial served as a basis for the decision to remove the endotracheal tube. Extubation failure was considered if reintubation was necessary or if the patient required non-invasive ventilatory assistance (both within 48 h).

RESULTS AND CONCLUSIONS

After the inclusion of 90 patients (30 per group) we did not observe significant differences between the modes. Twelve patients failed the initial weaning trial. However, half of the patients who appeared to fail the spontaneous breathing trial on the T-tube, PSV, or both, were successfully extubated after a succeeding trial with ATC. Extubation was thus withheld from four and three of these patients while breathing with PSV or the T-tube, respectively, but to any patient breathing with ATC. It seems that ATC can be used as an alternative mode during the final phase of weaning from mechanical ventilation. Furthermore, this study may promote a larger multicenter trial on weaning with ATC compared with standard modes.

Proportional assist ventilation in infants

Proportional assist ventilation and respiratory mechanical unloading is a new mode of respiratory assistance that produces similar gas exchange with lower airway pressures than conventional ventilation in infants. This is achieved by tailoring the ventilator pressure contour to the specific derangements in lung mechanics and by a near perfect synchronization with the infant's own inspiratory effort. In contrast to conventional ventilation, PAV only amplifies the effect on ventilation of the spontaneous respiratory effort and relies on the subject's respiratory control. Whether PAV will reduce the incidence of acute complications and chronic pulmonary sequelae in infants needs to be evaluated in randomized controlled trials.