Trial to Study Intubation Rates of Non-invasive Ventilation Using Pressure Support Ventilation (PSV) Versus Adaptive Support Ventilation (ASV) Mode in Patients With Acute Exacerbation of Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is a common respiratory disease, which is characterized by airflow limitation. It affects more than 3.49 per cent of adults >35 year and is associated with high morbidity and mortality. The national burden of chronic bronchitis is estimated at 14.84 million.

The clinical course of COPD is punctuated by acute exacerbations, which can lead to hypercapnic respiratory failure. The development of respiratory failure is associated with high morbidity and mortality, and significant healthcare costs. The requirement of ventilatory support also portends a reduced survival in this group of patients.

The introduction of non-invasive ventilation (NIV) has resulted in a paradigm shift in the management of patients with acute exacerbation of COPD. First, reported in 1989, by Meduri et all, the successful application of NIV via full-face mask in 10 patients, and the avoidance of intubation in 8 of them (4 of 6 with COPD, 2 of 2 with congestive heart failure, and 2 of 2 with pneumonia), demonstrated the efficacy of NIV in the management of acute exacerbation of COPD. This new modality was successful in avoiding of many of the complications associated with invasive mechanical ventilation.

Traditionally, NIV is instituted with the pressure support mode of ventilation. Wherein, the inspiratory pressure was initiated at 6-8 cm of water and expiratory pressure was set at 3-4 cm. The difference between the two pressures provided the ventilatory support. These pressures were then titrated based on patient clinical improvement by the physician.

Adaptive support ventilation (ASV) is one of the newer modes of ventilation, described by Tehrani et al in 1991 and was designed to minimise the work of breathing, mimic natural breathing and stimulate breathing and reduce weaning time. It is a closed loop system, which incorporates various feedback mechanisms into its algorithm. The operator inputs patients weight, from that the ventilator calculates required minute alveolar ventilation assuming normal dead space fraction. Then an optimal frequency is calculated based on Otis equation. The target tidal volume is calculated by MV/f. The inspiratory pressure within a breath is controlled to achieve a constant value and between the breaths the inspiratory pressure is adjusted to achieve a target tidal volume. It aims to provide a target minute ventilation by adjusting automatically the delivered pressure and respiratory rate while keeping the work of breathing to a minimum by the patient.

Due to its ability to reduce the work of breathing and meet the flow requirement of the patient by adjusting both the flow and respiratory rate depending on the respiratory mechanics, the use of ASV as a mode of ventilation during NIV may improve patient-ventilator synchrony. A study comparing ASV versus pressure support ventilation in intubated patients with acute exacerbation of COPD demonstrated that the use of ASV mode was associated with shorter weaning times with similar weaning success rates. However, a study comparing the use of ASV mode versus PSV mode during non-invasive ventilation has not been done previously. Patient-ventilator synchronization is critical for reducing the work of breathing and for successful NIV. Although PSV allows the patient to influence the breathing pattern, ventilator-cycling criteria may worsen the patient-ventilator interaction, and severe asynchronies occur in up to 43% of patients undergoing NIV for ARF. We hypothesize that the use of ASV as a mode during ventilation using NIV in patients with acute exacerbation of COPD may result in reducing the duration of ventilatory support, need for intubation, and duration of intensive care unit (ICU) and hospital length of stay, when compared with PSV mode of NIV ventilation.

Inclusion criteria

All consecutive patients with acute exacerbation of COPD will be assessed for inclusion in the current study. The diagnosis of acute exacerbation of COPD will be made based on following criteria:

• an acute sustained worsening of any of the patient's respiratory symptoms (cough, sputum quantity and/or character, dyspnea) that is beyond normal day today variation and leads to a change in medication
• arterial blood gas analysis showing a PaCO2>45 mm of Hg with either pH <7.35 ≥7.26 or respiratory rate >30/minute
• exclusion of other causes of acute breathlessness such as acute heart failure, pulmonary embolism, pneumonia, and pneumothorax.

Exclusion criteria

Patients with any one of the following criteria will be excluded from the current study:

• non-COPD acute hyper-capneic respiratory failure.
• hypotension (systolic blood pressure<90mmHg),
• severe encephalopathy (Glasgow coma scale score < 8),
• upper gastrointestinal bleeding
• inability to protect the airway and clear respiratory secretions, or abnormalities that preclude proper fit of the interface (agitated or uncooperative patient, facial trauma or burns, facial surgery, or facial anatomical abnormality).
• patients who are on home NIV.
• failure to give consent.