Flow triggering added to pressure support ventilation improves comfort and reduces work of breathing in mechanically ventilated patients

Neural control of pressure support ventilation improved patient-ventilator synchrony in patients with different respiratory system mechanical properties: a prospective, crossover trial

Background

Conventional pressure support ventilation (PS_P) is triggered and cycled off by pneumatic signals such as flow. Patient-ventilator asynchrony is common during pressure support ventilation, thereby contributing to an increased inspiratory effort. Using diaphragm electrical activity, neurally controlled pressure support (PS_N) could hypothetically eliminate the asynchrony and reduce inspiratory effort. The purpose of this study was to compare the differences between PS_N and PS_P in terms of patient-ventilator synchrony, inspiratory effort, and breathing pattern.

Methods

Eight post-operative patients without respiratory system comorbidity, eight patients with acute respiratory distress syndrome (ARDS) and obvious restrictive acute respiratory failure (ARF), and eight patients with chronic obstructive pulmonary disease (COPD) and mixed restrictive and obstructive ARF were enrolled. Patient-ventilator interactions were analyzed with macro asynchronies (ineffective, double, and auto triggering), micro asynchronies (inspiratory trigger delay, premature, and late cycling), and the total asynchrony index (AI). Inspiratory efforts for triggering and total inspiration were analyzed.

Results

Total AI of PS_N was consistently lower than that of PS_P in COPD (3% vs. 93%, P = 0.012 for 100% support level; 8% vs. 104%, P = 0.012 for 150% support level), ARDS (8% vs. 29%, P = 0.012 for 100% support level; 16% vs. 41%, P = 0.017 for 150% support level), and post-operative patients (21% vs. 35%, P = 0.012 for 100% support level; 15% vs. 50%, P = 0.017 for 150% support level). Improved support levels from 100% to 150% statistically increased total AI during PS_P but not during PS_N in patients with COPD or ARDS. Patients’ inspiratory efforts for triggering and total inspiration were significantly lower during PS_N than during PS_P in patients with COPD or ARDS under both support levels (P < 0.05). There was no difference in breathing patterns between PS_N and PS_P.

Conclusions

PS_N improves patient-ventilator synchrony and generates a respiratory pattern similar to PS_P independently of any level of support in patients with different respiratory system mechanical properties. PS_N, which reduces the trigger and total patient's inspiratory effort in patients with COPD or ARDS, might be an alternative mode for PS_P.

Trial Registration

ClinicalTrials.gov, NCT01979627; https://clinicaltrials.gov/ct2/show/record/NCT01979627.

The predictive value of serial changes in diaphragm function during the spontaneous breathing trial for weaning outcome: a study protocol

INTRODUCTION

There is a variety of tools being used in clinical practice for the prediction of weaning success from mechanical ventilation. However, their diagnostic performances are less than satisfactory. The purpose of this study is to investigate the value of serial changes in diaphragm function measured by ultrasound during the spontaneous breathing trial (SBT) as a weaning predictor.

METHODS AND ANALYSIS

This is a prospective observational study conducted in a 10-bed medical emergency intensive care unit (EICU) in a university-affiliated hospital. The study will be performed from November 2016 to December 2017. All patients in the EICU who are expected to have mechanical ventilation for more than 48 hours through endotracheal tube are potentially eligible for this study. Patients will be included if they fulfil the criteria for SBT. All enrolled patients will be ventilated with an Evita-4 by using volume assist control mode prior to SBT. Positive end-expiratory pressure (PEEP) will be set to 5 cmH₂O and fractional inspired oxygen (FiO₂) will be set to a value below 0.5 that guarantees oxygen saturation by pulse oximetry (SpO₂) greater than 90%. Enrolled patients will undergo SBT for 2 hours in semirecumbent position. During the SBT, the patients will breathe through the ventilator circuit by using flow triggering (2 L/min) with automatic tube compensation of 100% and 5 cmH₂O PEEP. The FiO₂ will be set to the same value as used before SBT. If the patients fail to tolerate the SBT, the trial will be discontinued immediately and the ventilation mode will be switched to that used before the trial. Patients who pass the 2-hour SBT will be extubated. Right diaphragm excursion and bilateral diaphragm thickening fraction will be measured by ultrasonography during spontaneous breathing. Images will be obtained immediately prior to the SBT, and at 5, 30, 60, 90 and 120 min after the initiation of SBT. Rapid shallow breathing index will be simultaneously calculated at the bedside by a respiratory nurse.

ETHICS AND DISSEMINATION

The study protocol is approved by the ethics committee of Sir Run Run Shaw Hospital, an affiliate of Zhejiang University, Medical College. The results will be published in a peer-reviewed journal and shared with the worldwide medical community.

TRIAL REGISTRATION NUMBER

ISRCTN42917473; Pre-results.

Noninvasive ventilation with complex critical care ventilator in the treatment of acute exacerbation of chronic obstructive pulmonary disease

OBJECTIVE

To compare the clinical effect of noninvasive positive-pressure ventilation (NIPPV), delivered via critical care ventilator or miniventilator, in patients with acute exacerbation of chronic obstructive pulmonary disease (AECOPD).

METHODS

Prospective comparison study. Patients with AECOPD underwent NIPPV via: miniventilator with BiLevel positive airway pressure (BiPAP; Group A); critical care ventilator with pressure support ventilation and positive end expiratory pressure (PSV + PEEP; Group B); critical care ventilator with pressure-synchronized intermittent mandatory ventilation (P-SIMV)+PSV + PEEP (Group C). Physiological parameters were recorded before, during and after ventilation.

RESULTS

Patients in Group C (n = 21) showed significantly better improvements in physiological parameters (compared with pretreatment values) than those in Group B (n = 20) or Group A (n = 22).

CONCLUSION

NIPPV delivered via critical care ventilator has a better treatment effect than miniventilator NIPPV in patients with AECOPD. The use of P-SIMV + PSV + PEEP mode provides a significantly better treatment effect than PSV + PEEP alone.

A study of noninvasive positive-pressure mechanical ventilation in the treatment of acute lung injury with a complex critical care ventilator

OBJECTIVE

To test the hypothesis that there would be better clinical outcomes following the treatment of patients with acute lung injury (ALI) using noninvasive positive-pressure mechanical ventilation (NIPPV) delivered via a complex critical care ventilator compared with a conventional mini-ventilator.

METHODS

Patients with ALI who required NIPPV were prospectively enrolled and randomly divided between three intervention groups: group A was ventilated using a mini-ventilator; groups B and C were ventilated using a complex critical care ventilator using different settings. Clinical parameters were recorded before and after 8 h of mechanical ventilation.

RESULTS

A total of 51 patients with ALI were enrolled in the study. Clinical parameters in groups B and C underwent greater improvements than those in group A. Group C demonstrated the lowest treatment failure rate (23.5%). Failure rates were highest in group A (58.8%).

CONCLUSION

The findings of this present study suggest that there were more satisfactory clinical outcomes following the treatment of patients with ALI when NIPPV was delivered using a complex critical care ventilator compared with a conventional mini-ventilator.

Predictive value of rapid shallow breathing index measured at initiation and termination of a 2-hour spontaneous breathing trial for weaning outcome in ICU patients

BACKGROUND/PURPOSE

The rapid shallow breathing index (RSBI) is a weaning parameter usually measured at the start of a spontaneous breathing trial (SBT). This study investigated the value of RSBI measured at the beginning and termination of SBT as a predictor of weaning outcome.

METHODS

RSBI was measured during the initial 1 minute (RSBI1) and at termination (RSBI2) of an SBT in 172 patients recovering from acute respiratory failure.

RESULTS

Weaning was successful in 106 patients and failed in 66 patients. Among the 66 patients with weaning failure, 12 required reintubation within 48 hours (extubation failure), and the remaining 54 patients could not be extubated after SBT (trial failure). There were no differences between RSBI1 in the three groups (69.4 +/- 27.5, 81.7 +/- 24.4 and 75.5 +/- 26.5, respectively), but RSBI2 was significantly higher in patients with extubation failure (95.9 +/- 20.6) and trial failure (98.0 +/- 50.0) than in patients with weaning success (64.6 +/- 26.3) (both p < 0.001). Logistic regression revealed that RSBI2 was superior to RSBI1 and various physiologic indices in predicting weaning outcome. For the 118 extubated patients, the mean area under the receiver operating characteristic curve for RSBI2 and RSBI1 was 0.83 and 0.63, respectively. Using a threshold value of 105, the sensitivity, specificity, accuracy and likelihood ratio for weaning outcome were 0.91, 0.25, 0.85 and 1.38 for RSBI2 and 0.89, 0.16, 0.60 and 1.06 for RSBI1, respectively.

CONCLUSION

This study found that RSBI measured at the completion of SBT was superior to that measured at the start in predicting weaning outcome in critically ill patients.

Patient-ventilator asynchrony

The basic mechanism of patient-ventilator asynchrony is the mismatching between neural inspiratory and mechanical inspiratory time. Alterations in respiratory drive, timing, respiratory muscle pressure, and respiratory system mechanics influence the interaction between the patient and the ventilator. None of the currently available partial ventilatory support modes are exempt from problems with patient-ventilator asynchrony. Ventilator triggering design in the trigger phase and the set variables in the post-trigger phase contribute to patient-ventilator interaction. The set inspiratory flow rate in the post-trigger phase for assist-control volume cycled ventilation affects patient-ventilator asynchrony. Likewise, the initial pressure rise time, the pressure support level, and the flow-threshold for cycling off inspiration for pressure support ventilation are important factors affecting patient-ventilator asynchrony. Current investigations have advanced our understanding in this area; however, its prevalence and the extent to which patient-ventilator asynchrony affect the duration of mechanical ventilation remain unclear.