What Are the Different Types of Mechanical Ventilation?

Mechanical ventilation or breathing machines are part of doctors' arsenal to treat COVID-19 coronavirus disease in patients with the worst lung symptoms.

Mechanical ventilation is a treatment to help a person breathe when they find it difficult or are unable to breathe on their own. A mechanical ventilator pushes airflow into the patient’s lungs to help them breathe. 

Mechanical ventilation may be 

• Invasive ventilation with a tube inserted into the patient’s airway, performed in the intensive care unit in the hospital.
• Noninvasive ventilation that can be used at home by people with respiratory difficulties.

Mechanical ventilation is part of the arsenal of supportive care clinicians use for COVID-19 coronavirus disease patients with the most severe lung symptoms.

A COVID-19 infection can cause fluids and mucus in the lungs that block oxygenation of lung tissue.  Mechanical ventilation can help support COVID-19 patients breathing until their immune system and treatment can clear the infection and proper lung function is restored. 

Public health experts fear there is a shortage of mechanical ventilation machines in the U.S. considering the coronavirus pandemic.

Mechanical ventilation first came into use in 1929. The two types of mechanical ventilation are 

• Positive-pressure ventilation: pushes the air into the lungs.
• Negative-pressure ventilation: sucks the air into the lungs by making the chest expand and contract.

The early ventilators were negative-pressure ventilators. Negative pressure ventilation is very little in use now.

• Iron lung: The first mechanical ventilator, a metal cylinder which enveloped the patient completely up to the neck. 
• Chest cuirass: A small shell which can be strapped to the patient’s chest to create the negative pressure. 

Positive-pressure ventilators were developed in the early 1950s to treat polio patients with respiratory paralysis. These ventilators blow the air into the patient’s lungs through a tube. They may be invasive or noninvasive.

Invasive ventilation

• Endotracheal intubation: the tube is inserted into the patient’s airway (trachea) through the mouth or nose.
• Tracheostomy: the tube is inserted through a hole made into the airway.

Noninvasive ventilation

Noninvasive mechanical ventilators come with masks and can be used at home. The three kinds are

• Continuous positive airway pressure (CPAP): delivers constant and steady air pressure.
• Autotitrating (adjustable) positive airway pressure (APAP): changes air pressure according to the breathing pattern.
• Bilevel positive airway pressure (BiPAP): delivers air with different pressures for inhalation and exhalation.

Negative-pressure ventilation

Iron Lung

The iron lung of the past forces the chest cavity to expand and contract by adjusting the air pressure inside a chamber that envelops the body up to the neck, . A vacuum pump creates a negative pressure in the iron lung’s chamber which makes the patient’s chest expand, drawing air in. When the negative pressure releases, the patient’s chest recoils, and air pushes out. 

The negative pressure created in the chamber affected the stomach and heart as well, which was a problem with the iron lung. The iron lung ventilator also curtailed the patient’s mobility and made caregiving difficult.

Cuirass

Cuirass, developed later, is a small form-fitted shell with a bladder, strapped to a patient’s chest. Cuirass applies negative pressure to stimulate the chest to expand and contract. Cuirass is used in very few situations today. It is a suitable option for patients with neuromuscular disorders, but it cannot be used for patients lying down.

Positive-pressure ventilation

Currently positive pressure ventilation is the common form of mechanical ventilation in hospitals. The positive-pressure ventilators push the air into the patient’s airway. The ventilator continually blows and stops in regular preset cycles enabling the lungs to receive oxygen and expel carbon dioxide. Positive-pressure ventilators may be

• Volume-controlled: delivers a preset volume of air into the patient’s trachea even if it entails high airway pressure. When the flow is stopped the chest recoils and expels the air out.
• Pressure-controlled: delivers air till the airway pressure limit is reached and the valve opens to expel air. The volume of air delivered may vary depending on the airway resistance and lung capacity.
• Dual control: these combine the advantages of volume control and pressure control and deliver airflow based on the requirement and response of the patient.

The mechanical ventilator does the work of a patient’s breathing so their body can rest and recover. Mechanical ventilators are used: 

• As short-term respiratory assistance in surgeries 
• For longer periods in critically ill patients
• At home by people who have difficulty breathing normally

In the last two decades several new modes of mechanical ventilation have emerged with the merging of ventilator and computer technologies. This has increasingly helped doctors meet individual requirements in mechanical ventilation.