There are two main types of mechanical ventilator which are negative pressure ventilator and positive pressure ventilator.

Negative Pressure Ventilator

Negative pressure ventilators were used extensively in the past to treat patients with polio. The idea of the device is to put the patient inside a rectangle or a tightly closed capsule to prevent leakage. At the end of the capsule is a piston that, when moved, creates a vacuum around the patient’s chest, which causes the chest to expand and the lungs to fill with air. When the vacuum is released, the patient’s chest contracts, forcing air out of the lungs. The piston is linked to a motor. If the electricity is cut off, the piston can be controlled manually. The device is connected to the patient naturally, without connections, because the patient is inside it and the only visible part of him is his head.

Negative pressure ventilators are less commonly used today because positive pressure ventilators are generally more effective and easier to use. However, negative pressure ventilators may still be used in some cases, such as when a patient is unable to tolerate positive pressure ventilation. Iron lung is an example to negative pressure.

Advantages

  1. Lower risk of barotrauma: Negative pressure ventilators do not subject the lungs to the same high pressures as positive pressure ventilators.
  2. Reduced risk of infections such as ventilator-associated pneumonia.
  3. More comfortable for patients as it does not require a tube to be inserted into the airway.

Disadvantages

  1. Limited tidal volume: Negative pressure ventilators are not as effective at delivering high tidal volumes as positive pressure ventilators, which may limit their use in patients with severe respiratory distress.
  2. Limited applications: Negative pressure ventilators are typically only used for patients with specific respiratory conditions, such as neuromuscular diseases or chest wall deformities.
  3. Slower response time: Negative pressure ventilators may have a slower response time than positive pressure ventilators, making it more difficult to respond to changes in the patient’s breathing patterns.

Positive Pressure Ventilator

Positive pressure ventilators are the most common type of ventilator used in hospitals today. These devices work by delivering air or oxygen under pressure to the patient’s lungs. This pressure helps to open up the patient’s airways, allowing oxygen to flow in and carbon dioxide to flow out.

Advantages

  1. More effective at delivering higher tidal volumes: Positive pressure ventilators can deliver higher tidal volumes than negative pressure ventilators.
  2. More versatile: Positive pressure ventilators can be used for a wide range of respiratory conditions, including acute respiratory distress syndrome, chronic obstructive pulmonary disease, and pneumonia.
  3. Faster response time: Positive pressure ventilators can respond more quickly to changes in the patient’s breathing patterns, allowing for more precise control of the ventilation.

Disadvantages

  1. Risk of barotrauma which is a condition in which the lungs are damaged by the pressure of the air being delivered.
  2. Increased risk of infections  particularly ventilator-associated pneumonia.
  3. Higher cost: Positive pressure ventilators are generally more expensive than negative pressure ventilators.

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