ICU Journal Club – SBT T-piece Vs PSV

by

Dr Swapnil Pawar & Dr Jose Chacko

Effect of Pressure Support vs T-Piece Ventilation Strategies During Spontaneous Breathing Trials on Successful Extubation Among Patients Receiving Mechanical Ventilation

A Randomized Clinical Trial

Background – The latest American Thoracic Society guidelines for weaning recommend PSV SBTs with moderate-quality evidence. Among patients receiving mechanical ventilation, readiness for extubation and liberation from ventilatory support is evaluated with a spontaneous breathing trial (SBT). Daily screening of respiratory function by SBT is associated with a shorter duration of mechanical ventilation. After a successful SBT and extubation, 10% to 25% of patients require reintubation, and reintubation is associated with higher mortality.3,4
What’s Known – The most common modes of SBT are T-piece ventilation and pressure support ventilation (PSV), lasting between 30minutes and 2 hours. There are no differences in the rate of successful extubation between 2-hour PSV and 2-hour T-piece ventilation, between T-piece ventilation for 30 minutes vs 2 hours, or between PSV for 30 minutes vs 2 hours. Although shorter SBTs are better tolerated, there is no evidence that they result in higher successful extubation rates.
Hypothesis – less demanding SBTs could result in a higher rate of successful extubation without increasing the reintubation rate.2weaning strategies were: an approach that is more demanding for patients (T-piece SBT for 2 hours) vs an approach that is less demanding for patients (8-cm H2O PSV for 30 minutes).
Question – What is the effect of a less demanding (30 minutes of pressure support ventilation) vs a more demanding(2 hours of T-piece ventilation) spontaneous breathing trial on rates of successful extubation?
Methods– a Multicenter non-blinded randomized clinical trial
Setting -conducted in 18 Spanish intensive care units between January 2016 and April 2017.
Inclusion Criteria – Patients aged 18 years or older undergoing mechanical ventilation for at least 24 hours who fulfilled the weaning criteria were eligible. The weaning criteria used – (1) the resolution or improvement of the condition leading to intubation; (2) hemodynamic stability, defined as systolic blood pressure between 90 and 160 mm Hg and heart rate less than 140/min without vasopressors or with low doses of vasopressors; (3) Glasgow Coma Scale score of 13 or greater; (4) respiratory stability (oxygen saturation >90% with fraction of inspired oxygen [FiO2] ≤0.4,respiratory rate <35/min, spontaneous tidal volume >5 mL/kg, ratio of respiratory rate to tidal volume <100/min per liter, and maximal inspiratory pressure >15 cm H2O); and (5) noncopious secretions (<3 aspirations in the last 8 hours).
Exclusion Criteria – Patients with tracheostomies or do-not-reintubate orders were excluded.
Randomisation – in 1:1 ratio by means of tables of computer-generated random numbers in blinded blocks of 4 patients for each centre.
Sample Size – Based on previous studies a successful extubation rate of 75% and an absolute increase in successful extubation of 7% was expected. Thus, the required sample for an α=.05 and a power of 80% was estimated to be 540 patients in each group.
Study Population  & Intervention – 2649 patients received mechanical ventilation for at least 24 hours in the participating intensive care units; 1501 of these fulfilled the inclusion criteria, and 1153 were included in the study; 578 patients were randomized to undergo a highly demanding SBT – a 2-hour T-piece SBT and 575 patients were randomized to undergo a less demanding SBT with 8-cm H2O PSV and zero positive end-expiratory pressure.
Key Characteristics in the protocol –

1. Before randomization, attending physicians had to decide on the extubation strategy (whether to reconnect the patient to the ventilator for 1 hour before extubation and whether to administer noninvasive ventilation or high-flow nasal cannula after extubation).
2. Arterial blood gas analysis was not required
3. Borg Dyspnea Scale (score range, 0-10; 0 indicates no dyspnea and 10 indicates maximal dyspnea) at the beginning and at the end of SBTs and to ask patients about their confidence in their ability to sustain breathing without a ventilator.
4. If failed, additional SBTs were not protocolized, and mode and duration were left to the discretion of attending teams.
5. Treatment of post-extubation respiratory failure was not protocolized.
6. Patients needing reintubation within 72 hours were not randomized again for weaning, but the need for tracheostomy and the date of final liberation from mechanical ventilation were registered.

Statistical Analysis – mainly Intention to treat analysis but also performed per-protocol analysis.
Results– Primary OutcomeSuccessful extubation- defined as remaining free of invasive mechanical ventilation 72 hours after the first SBT occurred in 473 patients (82.3%) in the pressure support ventilation group and 428 patients (74.0%) in the T-piece group (difference, 8.2%; 95% CI, 3.4%-13.0%; P = .001). Among secondary outcomes, for the pressure support ventilation group vs the T-piece group, respectively, reintubation rate was non-significant 11.1% vs 11.9% ( P = .63), medianintensive care unit length of stay was 9 days vs 10 days (P = .69), median hospital length of stay was 24 days vs 24 days. However, hospital mortality was 10.4% vs 14.9% P = .02), and 90-day mortality was 13.2% vs 17.3% ( P = .04] higher in t-piece SBT group.
Exploratory outcomes-

1. Reasons for reintubation were not significantly different in the 2 groups; excessive work of breathing was the most common in both groups, followed by inability to clear secretions and hypoxemia.
2. tracheostomy was performed in 41 patients (7.1%) in the PSV group and in 50 patients (8.7%) in the T-piece group (NS)
3. Postextubation respiratory failure occurred in 110 patients (20.7%) in the PSV group and in 103 patients (21.2%) in the T-piece group.

Strengths –

1. Randomised controlled trial
2. Multicentre
3. Allocation concealment
4. Good adherence to protocol
5. adds significant information on this topic – the 30-minute PSV SBT was enough to check patients’ ability to breathe without increasing the rates of post-extubation respiratory failure and reintubation.
6. Forces us to re-think our approaches to weaning

Limitations –

1. Non-blinded
2. Questionable protocol
3. Not a standard practice in every continent – ? external validity
4. ? cause for high mortality in the t-piece group
5. Non-protocolised use of NIV and high flow
6. The total duration of mechanical ventilation – 4 days only

Author’s Conclusion – Among patients receiving mechanical ventilation, a spontaneous breathing trial consisting of 30 minutes of pressure support ventilation, compared with 2 hours of T-piece ventilation, led to significantly higher rates of successful extubation. These findings support the use of a shorter, less demanding ventilation strategy for spontaneous breathing trials.

Our Conclusion –

Don’t use it as a blanket rule for all patients. Use less demanding SBT (PSV 30 min) for patients who are ventilated for short term but consider longer PSV trials for more complicated patients.