By Kathryn Radigan, MD, MSc

Attending Physician, Division of Pulmonary and Critical Care, Stroger Hospital of Cook County, Chicago

Dr. Radigan reports no financial relationships relevant to this field of study.

SYNOPSIS: In a randomized clinical trial of 1,153 adults who were ready for weaning after at least 24 hours of mechanical ventilation, researchers found that a spontaneous breathing trial with 30 minutes of pressure support ventilation compared with two hours of T-piece ventilation led to significantly higher successful extubation rates.

SOURCE: Subirà C, Hernández G, Vásquez A, et al. 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. JAMA 2019;321:2175-2182.

Daily spontaneous breathing trials (SBTs) are the best method to assess readiness for extubation and liberation from ventilator support. Although this has been known for decades, controversy remains regarding the mode and duration of optimal SBT. Subirà and colleagues performed a multicenter, randomized clinical trial at 18 intensive care units (ICUs) in Spain. They recruited 1,153 adults who were ready for weaning after at least 24 hours of mechanical ventilation. The researchers compared rates of successful extubation for an SBT involving 30 minutes of pressure support ventilation (PSV) to an SBT involving two hours of T-piece ventilation. The first approach is considered less demanding for patients, while the second approach is considered more demanding. From January 2016 to April 2017, investigators enrolled 578 patients in the two-hour T-piece SBT and 557 patients in the 30-minute SBT with 8 cm H2O PSV. All patients were followed until July 2017. Readiness for weaning was based on resolution or improvement of the condition that led to intubation, hemodynamic stability, Glasgow Coma Scale score of 13 or greater, respiratory stability, and noncopious secretions. Patients were excluded if they had a tracheostomy or do-not-intubate orders.

Successful extubation occurred in 473 patients (82.3%) in the PSV group and 428 patients (74.0%) in the T-piece group (difference 8.2%, 95% confidence interval [CI], 3.4-13.0%; P = .001). Among the secondary outcomes, reintubation was 11.1% for the PSV group compared to 11.9% for the T-piece group (difference -0.8%; 95% CI, -4.8% to 3.1%; P = 0.63). The median ICU length of stay was nine days for the PVC group vs. 10 days for the T-piece group (mean difference -0.3 days; 95% CI, -1.7 to 1.1 days; P = 0.69); median hospital length of stay was 24 days vs. 24 days (mean difference 1.3 days; 95% CI, -2.2 to 4.9 days; P = 0.45); hospital mortality was 10.4% vs. 14.9% (difference -4.4%, 95% CI, −8.3% to -0.6%; P = 0.02); and 90-day mortality was 13.2% vs. 17.3% (difference -4.1%, 95% CI, −8.2% to 0.01%; P = 0.04; hazard ratio 0.74, 95% CI, 0.55-0.99), respectively. This clinical trial revealed that an SBT consisting of 30 minutes of PSV, compared with two hours of T-piece ventilation, led to significantly higher rates of successful extubation, supporting a shorter, less challenging ventilation strategy for spontaneous breathing trials.

COMMENTARY

The importance of timely liberation from mechanical ventilation is profoundly important. More than two decades ago, Ely and colleagues found that daily screening of the respiratory function in adults followed by trials of spontaneous breathing can shorten the duration of mechanical ventilation, lower the rate of reintubation, and lower ICU costs.1 Although it is well known that SBTs are the best way to assess whether patients are ready to discontinue mechanical ventilation, the ideal mode and duration of SBT remains controversial. To further investigate the mode and duration of SBT, Subirà and colleagues conducted a multicenter, randomized clinical trial in 18 ICUs in Spain comparing a two-hour T-piece SBT to the 30-minute PSV SBT with 8 cm H2O inspiratory pressure and 0 cm H2O positive end-expiratory pressure (PEEP). Results revealed that the use of 30 minutes of PSV, a less demanding ventilation strategy, led to higher rates of successful extubation without a higher reintubation rate in the 72 hours after extubation. Furthermore, these patients also were significantly less likely to die in the hospital or during the 90 days after randomization.

Although there has been substantial literature supporting the safety of PSV SBT, many clinicians still prefer T-piece. Many clinicians believe T-piece best reflects the physiologic conditions after extubation. This idea was further supported by a recent meta-analysis which showed that T-piece requires the same amount of work after extubation.2 Despite the evidence that T-piece may be a better weaning mode physiologically, this philosophy was challenged after a meta-analysis of four randomized trials from 2017 reported that SBT with PSV resulted in a higher rate of successful extubation at 48 hours when compared with T-piece (85% vs. 77%) along with an insignificant reduction in ICU mortality.3 The article by Subirà and colleagues further substantiates these findings.

While it is interesting that Subirà’s data further supports SBT with PSV, it also triggers the question of whether all patients will benefit from the same strategy. For instance, are advanced heart failure patients or chronic obstructive pulmonary disease (COPD) patients the same as a patient with a heroin overdose or a patient with resolving septic shock? Interestingly, Subirà’s findings were consistent for COPD patients but, of course, the severity of COPD was unknown. One would consider that a patient with severe emphysema, a very compliant state, may gain additional support with a pressure support trial of 8 cm H2O. A recent study from Pelligrini and colleagues further investigated this concern. This group compared 30 minutes of T-piece and PSV at 10 cm H2O with all COPD patients undergoing noninvasive ventilation after extubation and found the SBT technique did not influence mechanical ventilation duration for patients with COPD unless the patient was within the difficult/prolonged weaning COPD subgroup.4 There also is concern for patients with heart failure. Although a PEEP of 5 cm H2O and pressure support ≤ 8 cm H2O may be considered a trivial amount of support, even small amounts of pressure support and PEEP in patients with decompensated heart failure can have significant hemodynamic effects and may reduce work of breathing.5 There is concern that removal of this support may result in rapid deterioration of left ventricular function leading to pulmonary edema. T-piece trials may be considered in patients with impaired cardiac function as this mode may reveal the need for further optimization to prevent re-intubation.

It also is important to question whether the techniques that were used postextubation provided a benefit for these patients and made an impact on outcomes. Prior to randomization, attending physicians had to determine the extubation strategy (i.e., whether to reconnect the patient to the ventilator for one hour before extubation and whether to administer noninvasive ventilation [NIV] or high flow nasal cannula [HFNC] after extubation). Interestingly, physicians were not blinded, and more patients were subjected to prophylactic HFNC or NIV in the PSV group (24.7% vs. 18.7%). Of course, concern was raised that this may have impacted the results, especially if these strategies were used for postextubation respiratory failure rather than prophylaxis. The authors addressed these concerns and explained that respiratory failure postextubation occurred in 103 patients in the T-piece group (21.2%) and 110 patients in the PSV group (20.7%) (P = 0.84). NIV was provided to 43 patients in the T-piece group (41.7%) and to 48 patients in the PSV group (43.6%) (P = 0.78). HFNC was provided to 28 patients in the T-piece group (27.2%) and to 19 patients (17.3%) in the PSV group (P = 0.08). Four patients in each group received both treatments. The decision to use NIV or HFNC as prophylaxis was prior to randomization, which reinforces the idea that the higher successful extubation rate in PSV was not due to more aggressive use of HFNC or NIV in patients with postextubation respiratory failure. The higher use of prophylactic HFNC or NIV in the PSV group may have been due to chance or been chosen by the clinician to provide more confidence for a successful outcome after a less demanding SBT.

Subirà and colleagues support the use of 30 minutes of PSV during an initial SBT for most patients. Unfortunately, their data also may raise questions in regard to higher risk patient populations and should inspire clinicians to further investigate the most successful approach to liberation from mechanical ventilation for these specific patient populations.

REFERENCES

  1. Ely EW, et al. Effect on the duration of mechanical ventilation of identifying patients capable of breathing spontaneously. N Engl J Med 1996;335:1864-1869.
  2. Sklar MC, et al. Effort to breathe with various spontaneous breathing trial techniques. A physiologic meta-analysis. Am J Respir Crit Care Med 2017;195:1477-1485.
  3. Girard TD, et al. An Official American Thoracic Society/American College of Chest Physicians Clinical Practice Guideline: Liberation from mechanical ventilation in critically ill adults. Rehabilitation protocols, ventilator liberation protocols, and cuff leak tests. Am J Respir Crit Care Med 2017;195:120-133.
  4. Santos Pellegrini JA, et al. Pressure-support ventilation or T-piece spontaneous breathing trials for patients with chronic obstructive pulmonary disease - A randomized controlled trial. PLoS One 2018;13:e0202404.
  5. Kuhn BT, et al. Management of mechanical ventilation in decompensated heart failure. J Cardiovasc Dev Dis 2016;3.