Nagesh Utekar Director, Rescare Medisys (India) Pvt. Ltd
To understand a process of Mechanical Ventilation let us first understand the basics of Exchange of Gases in Human Beings.
In breathing process, air is inhaled through the mouth and/or nose, pharynx, larynx, trachea and bronchial tree into tiny alveoli sacs in the lungs, where air mixes with the carbon dioxide-rich gas from the blood. Gas exchange in the lungs supplies oxygen to the blood and removes carbon dioxide collected from the cells. The air is then exhaled.
Ventilation is the “tidal” volume of gas entering or leaving the lungs in a given amount of time, and determines if the gas exchange is sufficient.
Normally this cycle repeats at a breathing rate, or frequency, for adults of about 12 breaths per minute. Infants and children breathe at a faster rate.
For mechanical ventilator to work, it must produce the right tidal volume and breathing rate for the body.
Conventional ventilators produce the normal breathing patterns of children and adults, about 12-25 breaths per minute.
Two forces expand the lungs and chest wall during breathing: the contraction of the muscles (including the diaphragm) and the contrasting pressure at the airway opening (mouth and nose) and on the outer surface of the chest wall.
Normally, the respiratory muscles expand the chest wall. This decreases the pressure on the outside of the lungs, so they expand. This enlarges the air space in the lungs and draws air into the lungs.
When respiratory muscles are unable to do the work for breathing, either one or both of these forces can be manipulated with a mechanical ventilator.
What is Mechanical Ventilator?
A positive pressure ventilator delivers gas to the patient through a set of flexible tubes, called a patient circuit. Depending on the ventilator design, this circuit can have one or two main tubes.
The circuit connects the ventilator to an endotracheal tube, tracheostomy tube for invasive ventilation or a noninvasive mask/prong.
For invasive ventilation, an endotracheal tube is inserted through the patient’s mouth or nose, or a tracheostomy tube is inserted through an opening made by incision in the neck.In noninvasive ventilation, the patient circuit connects to a mask covering the mouth and/or nose or nasal prongs. The tube used for invasive ventilation may have a balloon cuff to provide a seal. The noninvasive mask has a seal around the mouth and nose to prevent the loss of gas/air, ensuring the patient receives appropriate ventilation.
Mechanical ventilation may be used at night, during limited daytime hours, or around the clock, depending on the patient's needs. Some patients require mechanical ventilation for a short period, such as during recovery from traumatic injury. Others require ventilation long-term, and over time the needs could increase or decrease, depending on the patient’s medical status.