**1. Introduction**

Brief History: Till mid-20th century Non-invasive Ventilation (NIV) was the mainstay of mechanical ventilatory assistance and it was delivered by negative pressure devices such as the "iron lung" that was used predominantly for poliomyelitis patients with respiratory paralysis. Ironically when its demand and supply suffered during the polio epidemic in Denmark in 1952, there was a transition to positive pressure mechanical ventilation via translaryngeal cuffed endotracheal tubes.

Curiass/shell is a shell or a cage which surrounds the chest and is then connected to a portable ventilator. Raincoat or Poncho is a tight fitting suit which is connected through the means of hoses to a portable ventilator. Rocking bed is another method for providing negative pressure ventilation which induces diaphragmatic motion by placement of the patient on a bed which rocks rapidly flat to upright while the contents of abdomen shift. A pneumobelt is a belt with a bladder which can inflate and deflate with air in a cyclic pattern. The diaphgram moves in response to changes in the intraabdominal pressure. Another form of negative pressure ventilation is a pneumowrap.

It was not until the 1980s with the development of nasal masks for continuous positive airway pressure, used for the treatment of obstructive sleep apnea, that there was a renewed interest in NIV and specifically non-invasive positive pressure ventilation.

Principles of NIV: Non-invasive ventilation (NIV) refers to the use of ventilatory methods without the use of an endotracheal tube or a tracheostomy tube which are artificial invasive methods. NIV provides ventilation through the use of a mask of similar device to the patient's upper airway (**Figure 1**). This technique is significantly different from the invasive ones which bypass the upper airway of the patient through the use of a laryngeal mask, tracheal tube or tracheostomy. Initially non-invasive ventilation through the use of masks was used in neuromuscular disorders to provide ventilatory support in the night in view of hypoventilation. This was followed by use of non-invasive ventilation used nocturnally in cases of chronic obstructive pulmonary disease leading to an improvement in the muscle strength of respiratory muscles [1]. Ultimately, NIV delivered through masks turned out to be of utmost benefit and was used as a method of standard ventilation in cases of chronic hypercapnic respiratory failure which could be due to deformities of the chest, neuromuscular disorder or impaired central respiratory drive. Few years later NIV was started to be used in respiratory failure due to lung pathologies rather than respiratory pump failures. Since then, NIV has evolved immensely with a widespread application in the Intensive Care Units.

**Figure 1.**

*Principle of NIV is application of any technique to augment alveolar ventilation without use of conduit access to airway and using interfaces at nose, mouth or both to deliver compressed air ± oxygen to lungs to improve efficiency of physiological pump.*


## **Table 1.**

*Showing the advantages and disadvantages of NIV use in intensive care unit.*

Currently NIV is also being used in about 20 to 30 percent of acute hypoxic respiratory failure. NIV has even been used in cases of acute respiratory distress syndrome with an alarming success rate of more than 50 percent with improvement being more predominant in the patients whose oxygenation had improved promptly. The advantages and disadvantages of NIV use in intensive care unit have been shown in **Table 1**.
