Mechanical ventilation is a life-saving technique for managing acute respiratory failure and other respiratory complications. The process involves using a machine known as a ventilator to supply oxygen to the lungs and assist in removing carbon dioxide. It serves as a bridge to long-term mechanical ventilation or a temporary measure until ventilatory support is discontinued. The ventilator can maintain this function for a prolonged period, providing critical support for patients until they can breathe independently.

Indications

Mechanical ventilation may be necessary for a variety of reasons. These include managing acute respiratory failure, controlling the patient's breathing during surgery or treatment, providing adequate oxygenation when the patient's own ventilatory efforts are insufficient, and allowing the respiratory muscles to rest. Several factors, including thoracic or abdominal surgery, drug overdose, neuromuscular disorders, inhalation injury, Chronic Obstructive Pulmonary Disease (COPD), multiple trauma, circulatory shock, multisystem failure, and coma, can result in respiratory failure and the need for mechanical ventilation. It allows patients on a ventilator to breathe spontaneously, alleviating the exhausting effort it would otherwise require.

Settings of Mechanical Ventilator

The settings of a mechanical ventilator are adjusted based on the patient's condition, level of consciousness, respiratory muscle strength, chest x-ray, and arterial blood gases (ABGs). These settings include:

1. Respiratory rate: It refers to the number of breaths the ventilator delivers per minute.
2. Tidal volume (VT): It is the volume of gas delivered to the patient during each ventilator breath.
3. O₂ concentration (FIO2): This fraction of inspired O₂ delivered to the patient can be set between 30% and 100%.
4. Positive-end-expiratory pressure (PEEP): Positive pressure is applied at the end of the expiration of ventilator breaths.
5. Pressure support: This is used to augment a patient's inspiratory pressure during spontaneous breathing.
6. I/E ratio: This is the duration of inspiration (I) to the duration of expiration (E).
7. Inspiratory flow rate and time: This is the speed with which the VT is delivered.
8. Sensitivity: This determines the patient's effort to initiate a breath from the ventilator.
9. Peak inspiratory pressure (PIP): This is the maximal pressure the ventilator can generate to deliver the VT.

Manipulating these settings can help correct hypoxemia and hypercarbia. As the patient's condition improves, the settings can be adjusted to allow them to take more control over their work of breathing.

Types of Mechanical Ventilation

Mechanical ventilators can be classified into two general categories: Negative pressure ventilators and positive-pressure ventilators.

Negative-pressure ventilators, also known as "iron lungs," are older modes of ventilatory support that are rarely used today.

Positive-pressure ventilators inflate the lungs by exerting positive pressure on the airway, pushing air in, similar to a bellows mechanism, and forcing the alveoli to expand during inspiration. Expiration occurs passively. These ventilators are widely used in hospital settings and include:

1. Volume-Cycled Ventilators
2. Pressure-Cycled Ventilators
3. High-Frequency Oscillatory Support Ventilators
4. Noninvasive Positive-Pressure Ventilation (NIPPV)
5. Continuous positive airway pressure (CPAP)
6. Bilevel positive airway pressure (BiPAP)

Each ventilator has distinctive features and is employed based on the patient's needs. The selection of the ventilator type is a critical decision made by healthcare professionals, made by considering the patient's current health status and the potential benefits and risks associated with each ventilator type.