Background: Liberation from mechanical ventilation in patients with Chronic Obstructive Pulmonary Disease (COPD) admitted in intensive care units (ICUs) with acute hypercapnic respiratory failure is challenging due to a number of factors. Liberation from mechanical ventilation in COPD patients is difficult due to number of fixed obstructions to expiratory airflow, increased intrinsic positive end-expiratory pressure, dynamic hyperinflation, skeletal muscle deconditioning and increased resistive work of breathing. Prolongation of ventilation is associated with several morbidities including ventilator-associated pneumonia, diaphragmatic dysfunction, delirium and ICU-acquired weakness (ICAWS) with increased risk of mortality. There are also risks of early extubation failure with complications of respiratory failure that require re-intubation, which has significant morbidity. Thus, accurate assessment of extubation readiness in these patients is very important.¹⁻⁴

Assessing readiness for extubation in patients is vital, as are the consequences of premature extubation, such as respiratory failure and subsequent reintubation, which also have poor outcomes for patients. In evaluating whether or not a patient is ready for extubation it is necessary to assess whether or not they are able to sustain spontaneous ventilation with or without support from mechanical ventilation. This is best evaluated using a spontaneous breathing trial (SBT). Typical SBTS last from 30 minutes to several hours. Several methods have been described to evaluate SBTS. The two most commonly used methods for SBTS using pressure support (PS) and those performed using a T-piece with supplemental oxygen (CPAP/S). There are several potential advantages of SBTs performed using a T-piece. The primary aim of a SBT is to assess a patient’s readiness for extubation. Therefore it would be advantageous to evaluate a patient’s work of breathing using a method that more accurately reflects their work of breathing once extubated. For patients with severe airflow limitation (such as those with COPD) using a T-piece during an SBT may be more beneficial in determining whether or not a patient will be able to manage following extubation. Furthermore the T-piece may place less physiological stress on the patient during the trial, as opposed to PS compensating for the increased resistance of the endotracheal tube and ventilation circuit.⁵⁻⁹

The best way to wean patients from mechanical ventilation is still a matter of great debate. While a number of studies have investigated the use of SBTs in a mixed medical/surgical intensive care unit population, in order to establish the optimal method of SBT for patients with COPD, more data are required, especially as these patients form a high-risk group at risk of extubation failure and subsequent need for reintubation. Therefore, while there is evidence to support the use of both pressure supported SBTs of minimal intensity and T-piece SBTs of longer duration, in clinical practice it is suggested that both methods of weaning should be used on a daily basis and that the assessment of patient’s readiness for extubation should take precedence over the choice of a single ‘best’ method.

However, even when patients successfully complete the SBT, effective cough, amount and thickness of respiratory secretions, patient's mental status, and hemodynamic stability should be considered. In addition, the use of planned post-extubation NPPV in hypercapnic patients and in other patients at risk of extubation failure should not be forgotten. The present study aimed to compare two different weaning approaches in mechanically ventilated COPD patients, i.e., SBT with pressure support delivered through the endotracheal tube and SBT with use of a T-piece, and to assess their effects on SBT tolerance, successful extubation, extubation failure and subsequent reintubation and on clinical outcome of patients in the ICU.¹⁶⁻²⁰

Study design and setting This prospective comparative study was created exclusively for training in clinical research and manuscript writing. The assumed study setting was a medical intensive care unit at a tertiary care teaching hospital. Study population Adult patients aged 40–80 years with a documented diagnosis of COPD who received invasive mechanical ventilation for acute respiratory failure for at least 24 hours were considered eligible when they fulfilled readiness criteria for an SBT. Readiness criteria Patients were considered ready for an SBT when they demonstrated: • Improvement in the cause of respiratory failure • Adequate oxygenation with fraction of inspired oxygen ≤0.40 • Positive end-expiratory pressure ≤5–8 cm H₂O • Hemodynamic stability without escalating vasopressor support • Ability to initiate spontaneous breaths • Adequate level of consciousness • Manageable respiratory secretions • Arterial pH ≥7.30 Patients with tracheostomy, uncontrolled arrhythmia, active myocardial ischemia, severe neurological impairment, neuromuscular disease, accidental extubation, do-not-reintubate orders, or incomplete clinical information were excluded. A sample of 60 patients was generated and divided equally: • Pressure support SBT group: 30 patients • T-piece SBT group: 30 patients SBT protocols Pressure support group Patients underwent a 30-minute SBT using: • Pressure support: 7 cm H₂O • Positive end-expiratory pressure: 5 cm H₂O • Fraction of inspired oxygen unchanged from pretrial settings T-piece group Patients were disconnected from the ventilator and allowed to breathe spontaneously through a T-piece for 30 minutes with humidified supplemental oxygen adjusted to maintain target oxygen saturation. Criteria for SBT failure The SBT was terminated if one or more of the following occurred: • Respiratory rate >35 breaths/min for more than five minutes • Oxygen saturation <90% • Heart rate >140 beats/min or change greater than 20% from baseline • Systolic blood pressure <90 or >180 mmHg • Marked use of accessory respiratory muscles • Diaphoresis, agitation, or reduced consciousness • Respiratory acidosis or clinically significant distress Patients successfully completing the SBT were assessed for cough effectiveness, secretion burden, consciousness, and airway protection before extubation. Outcome measures The primary outcome was successful extubation, defined as remaining alive and free from reintubation for at least 48 hours following extubation. Secondary outcomes included: • Successful completion of the SBT • Reintubation within 48 hours • Use of planned post-extubation noninvasive ventilation • Respiratory rate at the end of the SBT • Rapid shallow breathing index • Duration of invasive mechanical ventilation • Intensive care unit length of stay • Hospital mortality Statistical analysis The data were analyzed using an assumed SPSS version 26 workflow. Continuous variables were presented as mean ± standard deviation and compared using the independent-samples Student's t-test. Categorical variables were expressed as frequencies and percentages and compared using the Chi-square or Fisher's exact test. Multivariate logistic regression analysis was used to identify predictors of successful extubation. A p-value <0.05 was considered statistically significant.

Table 1. Baseline Clinical Characteristics

The two groups were comparable with respect to age, sex, COPD severity, reason for ventilation, illness severity, and duration of ventilation before the SBT.

Table 2. Physiological Response During the Spontaneous Breathing Trial

Patients undergoing pressure support demonstrated a lower respiratory rate and rapid shallow breathing index at the end of the trial. Respiratory distress and accessory muscle use were numerically more frequent during T-piece trials.

Table 3. SBT and Extubation Outcomes

The pressure support group demonstrated higher SBT completion and successful extubation rates. Reintubation and mortality were numerically lower with pressure support, but the differences were not statistically significant in this small sample.

Table 4. Resource Outcomes and Predictors of Successful Extubation

1. Duration and resource outcomes

Pressure support was associated with a significantly shorter interval between the initial SBT and extubation. Mechanical ventilation and ICU stay were also numerically shorter in this group.

1. multivariate logistic regression for successful extubation

Successful SBT completion, effective cough, manageable secretions, and a lower rapid shallow breathing index were independent predictors of successful extubation. Pressure support favored extubation success but did not remain statistically significant after adjustment, likely reflecting the small simulated sample.

Pressure support ventilation (PSV) and T-piece spontaneous breathing trials (SBTs) are tools to assess extubation readiness in COPD patients on mechanical ventilation. In this study, patients on PSV-based SBTs had higher percentages of successful SBTs, earlier extubation, lower respiratory workload during the trial and almost but not statistically significant higher percentages of successful extubations. These results are in line with current literature regarding low levels of pressure support facilitating the removal of the endotracheal tube without compromising the assessment of a patient’s ability to breathe spontaneously.¹⁻⁵

The challenge of extubation of COPD patients in spite of advanced mechanical ventilation can be attributed to several underlying respiratory mechanics characteristics of such patients. For example, they have difficulty with expiration as a result of fixed obstruction. This difficulty is often increased during mechanical ventilation as a result of high intrathoracic pressures. As a result, such patients are at a high risk of respiratory muscle fatigue. They also have high levels of iPEEP and DH which both increase during mechanical ventilation and the work of breathing of such patients is greatly increased when compared with that required for spontaneous breathing. An important consideration during an SBT is the increased WOB as a result of removal of the ventilator and the increased resistance to gas flow and the threshold pressure of the endotracheal tube. During T-piece trials, therefore, patients breathe at a higher frequency and have higher RSBI. The use of PSV during SBTs, therefore, facilitates the assessment of the ability of such patients to breathe spontaneously by reducing WOB and thus making breathing easier for the patient. Several previous studies have reported benefits of the use of PSV during SBTs.¹⁶⁻²³

However, there are a number of clinical parameters that are more important than the type of SBT that determine whether or not extubation of a patient will be successful. These include the patient’s ability to cough effectively and clear upper airway secretions as well as their mental status, their cardiovascular stability and the condition of their respiratory muscles. In the current study, the successful extubation of patients was determined by a number of variables including the successful completion of their SBT, their ability to cough effectively, the amount of secretions that they had and their RSBI of less than 80 breaths/min/L. The findings from this study are consistent with current international practice that recommends a comprehensive clinical assessment rather than reliance on a single parameter to assess whether or not a patient on mechanical ventilation is ready for extubation.¹¹⁻¹⁵

In extubating patients with COPD, post-extubation respiratory support may be needed. Planned use of NIV in high-risk patients has been shown to decrease the rate of respiratory failure and the need for reintubation. In the current study, more than half of the patients in both groups of patients received some form of post-extubation NIV support. In terms of clinical management of patients in the ICU, the time spent in the ICU and the mortality of extubated patients are not influenced by weaning methods. Instead, these two outcomes are influenced by other factors in a comprehensive approach to extubation, including assessment of the airway and individualized post-extubation support.¹⁶⁻²¹

The data, calculations, results from this study were designed, calculated and generated to assist ICU staff in their clinical decision making with regard to patient extubation. However, there are innumerable factors that will affect the decision-making process of health care workers in relation to the extubation of individual patients. These factors may include the dose of sedation that is required for a given patient, the range of ventilation settings that have been used for that patient, the patient’s nutritional status and the degree of diaphragmatic dysfunction or other respiratory muscle dysfunction that the patient may have developed as a result of his or her critical illness. In addition, the patient’s history of co-morbid disease (e.g. cardiovascular disease) and of severe infection will also need to be taken into account. The results from this study have been presented in a very simple format. However, a large multicenter clinical trial, utilizing a number of different methods for assessing the quality of diaphragmatic contractility and the function of the patient’s respiratory muscles, and including a focus on patients with COPD, would be of great value in a number of areas including assessment of the results from trials of SBTs using PSV and T-piece, and assessment of a variety of different endpoints in a large group of patients. These results could then be measured over a prolonged period of time after the patient’s hospital discharge.²²⁻²⁵

PSV SBTs facilitated extubation in a greater proportion of patients with COPD compared with T-piece SBTs. However, the rates of reintubation or mortality were similar in the two groups of patients. Thus, the method of assessment of readiness for extubation of patients with COPD who are mechanically ventilated is not as critical as are other clinical determinants of successful extubation, such as effective cough, amount of airway secretions, respiratory muscle strength, and overall clinical condition. Thus, the SBT method that is selected for clinical use should be individualized within the framework of a structured weaning protocol and the patient post-

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