Mechanical ventilation is a life-saving treatment widely used in ICUs. Determining whether patients can be safely removed from invasive mechanical ventilation (IMV) after recovery is complex. Spontaneous breathing trials (SBT) evaluate a patient’s ability to breathe independently. Various SBT methods are employed, leading to inconsistent practices across ICUs. The most prevalent methods include low-pressure support ventilation (PSV) with or without positive end-expiratory pressure (PEEP) and T-piece trials.
A 2017 meta-analysis by Sklar et al., which reviewed 16 studies with 239 patients, indicated that unassisted SBTs like PSV at 0 cmH2O PEEP and T-piece trials better reflect the effort to breathe after extubation than those using pressure support. However, these were a small number of studies with small sample sizes and varied methodologies.
The GLOBAL WEAN study aimed to identify which SBT best represents post-extubation breathing effort across various critical illnesses, including postoperative patients, brain injuries, chest trauma, chronic obstructive pulmonary disease (COPD), and sepsis. Study authors hypothesise that unassisted SBTs, specifically PSV at 0 cmH2O and T-piece trials, will most accurately reflect post-extubation breathing effort and that physiological factors related to different clinical conditions may influence this effort.
The study included adult patients in ICUs who had been on IMV for at least 24 hours, were prepared for extubation, and participated in three 15-minute SBTs conducted randomly. The SBTs included pressure support ventilation at 7 cmH2O with 0 cmH2O positive end-expiratory pressure (PSV7PEEP0), pressure support ventilation at 0 cmH2O with 0 cmH2O PEEP (PSV0PEEP0), and a T-piece trial. The primary outcome measured was the variation in pressure-time product per minute (PTPmin) across each SBT and 20 minutes after extubation. The study focused on five categories of critical illnesses: abdominal surgery, brain injury, chest trauma, chronic obstructive pulmonary disease (COPD), and miscellaneous conditions.
One hundred patients were randomised for analysis. The cohort comprised 25 postoperative abdominal surgery patients, 22 with brain injuries, 13 with chest trauma, 16 with exacerbated COPD, and 24 miscellaneous cases (including pulmonary and non-pulmonary sepsis, massive haemorrhages, heart failure, and myasthenia gravis).
Baseline characteristics varied significantly among the critical illness subgroups, particularly regarding age (younger patients in the chest trauma subgroup), corticosteroid administration, comorbidities, and reasons for ICU admission and intubation. There were no significant differences in respiratory or haemodynamic variables at baseline, after the three SBTs, or 20 minutes post-extubation. Arterial blood gas values showed no significant changes before and after the trials.
Overall inspiratory efforts measured during the unassisted trials (PSV0PEEP0 and T-piece) did not significantly differ from the effort required post-extubation. In contrast, the assisted trial (PSV7PEEP0) resulted in a lower inspiratory effort. Results varied based on the type of critical illness; for instance, in brain injury patients, PSV0PEEP0 showed no significant difference from post-extubation efforts, while miscellaneous patients showed significant differences. In chest trauma and COPD patients, all three SBTs’ inspiratory efforts were comparable to post-extubation efforts.
For patients extubated after longer periods of IMV, the unassisted SBTs (PSV0PEEP0 and T-piece trial) best replicated post-extubation inspiratory efforts. The overall reintubation rate was 6% within 48 hours, and management after extubation included frequent chest physiotherapy and high-flow nasal oxygenation, with increased use of noninvasive ventilation in the COPD group.
The study concluded that unassisted SBTs, specifically PSV0PEEP0 and the T-piece trial, are the most effective methods for replicating post-extubation breathing effort in overall ICU patients. The study emphasises that unassisted SBTs should be prioritised in clinical practice, noting that the PSV0PEEP0 trial offers advantages such as optimal airway humidification and ease of use without requiring specialised equipment. The study also noted significant differences in inspiratory effort across various critical illnesses.
Overall, these findings demonstrate that personalised SBTs based on the type of critical illness can enhance the accuracy of predicting post-extubation breathing effort, which may improve extubation timing and overall patient outcomes. Future studies should assess inspiratory effort at different time points and consider the effects of noninvasive assistance.
Source: Intensive Care Medicine
Image Credit: iStock
