Outcome of Non-Invasive Ventilation in Patients of Acute Respiratory failure

Acute Respiratory failure (ARF) is a condition in which the respiratory system fails in one or both of its gas exchange functions, i.e. oxygenation and/or elimination of carbon dioxide from mixed venous blood. Hypoxemic respiratory failure (type I) is characterized by an arterial oxygen tension (PaO2) <8kpa (60 mmHg) with a normal or low arterial Introduction: Non-invasive ventilation (NIV) is a method of ventilator support or delivery of positive pressure into the lungs usually through a face mask, mostly initiated before severe acidosis occurs. NIV failure requiring invasive mechanical ventilation in decompensated chronic obstructive pulmonary disease (COPD) patients is low, but, in critical patients, it is as high as 60%. Acute respiratory failure (ARF) is the common reason for admission to the intensive care unit. This study assesses the outcome of NIV among patients with acute respiratory failure, the duration of use, stay in ICU, and failure rate of NIV. Such type of study result is scarce in our country.


INTRODUCTION
Outcome of Non-Invasive Ventilation in Patients of Acute Respiratory Failure. carbon dioxide tension (PaCO2). 1 Hypercapnic respiratory failure (type II) is characterized by a PaCO2 >6.0kPa (45 mmHg). Common etiologies include drug overdose, neuromuscular disease, chest wall abnormalities, and severe airway disorders like COPD. 2 Noninvasive ventilation (NIV) refers to the delivery of ventilator support or positive pressure into the lungs without an invasive endotracheal airway usually through a mask. To ensure better outcomes in terms of preventing intubation and mortality, NIV should be initiated early, before severe acidosis occurs.The rate of NIV failure requiring invasive mechanical ventilation (IMV) in decompensated COPD patients is low, but in critical patients it may be as high as 60% (5% to 60%). 3 NIV appears to be of benefit in the immediate treatment of patients with acute cardiogenic pulmonary edema and may reduce mortality. NIV produces greater improvements in oxygenation and carbon dioxide clearance and a greater reduction in the work of breathing in patients with pulmonary edema. 4 Pandey R et al study revealed that out of 28 patients, 27 received bi-level and most common cause was chronic obstructive pulmonary disease with type 2 respiratory failures in 67.8%. 5 Rationale of this study was to see the effectiveness of NIV in ARF patients despite any cause, stay of ICU duration and its outcomes and failure rate of NIV.

METHODS
A single-center, cross-sectional, observational study at medical ICU of a tertiary level hospital in Nepal was conducted. All patients above age 18 years presented to the hospital diagnosed to have acute respiratory failure by arterial blood gas analysis with pH < 7.3 were admitted in MICU. Patient's identification and details regarding admission requirement to be kept in Non-invasive ventilation were filled in the proforma. All the details of clinical parameters during the admission and ABG findings during admission were recorded before putting the patient in NIPPV.
During NIV via Mechanical Ventilator parameters like PEEP, Pressure Support (PS) or Inspiratory positive airway pressure (IPAP) with required fraction of inspired oxygen (FiO2) were set and recorded. Any changes in the parameters during the NIV application were also be recorded as per the proforma.
NIV was delivered through a face mask by a ventilator with oxygen of maximum FiO2 60% in order to maintain peripheral oxygen saturation above 88%. NIV was started at an inspiratory positive airway pressure of 8 cm of water and an expiratory positive airway pressure of 4 cm of water and increased to a maximum inspiratory pressure of 20 cm of water and a maximum expiratory pressure of 10 cm of water. Depending on the severity of the illness, informed written or witnessed oral consent from the patient or witnessed consent from a relative were obtained at entry into the study. Data will be tabulated and interim analysis be performed in Microsoft Excel. Results will be presented in tables, graphs and diagrams. Appropriate statistical tests will be performed and the statistical significance of the results will be assessed.

Exclusion criteria for NIV:
Need of Intubation (Lifesaving or emergency intervention).

Need of high dose vassopressor Support
Facial Injury.

RESULTS
Total 35 patients were enrolled in this study, had the median age being 73 years (Range: 39 -89 years) out of which 40.0 % were males and 74.3 % were current smokers. Majority of the patients (91.4 %) presented with shortness of breath and cough (40.0 %), fever (14.3 %). Table  1 describes the patients according to diagnosis who received NIV.           Limitations of our study are the relatively small sample size and this was an observational study. Failure of NIV could potentially represent a risk factor for complications.

CONCLUSIONS
Usage of NIV among ARF patients was associated with lower intubation and ICU mortality rate. COPD patients showed most benefit with NIV. Whereas patients suffering from Interstitial Lung disease, Lung Cancer had less benefit, with NIV failure of 57.8%. The median duration of NIV use among success group was 17 h and failure group 10h.