Mechanical Ventilation

Last updated: December 27, 2020

Ventilation is the process of moving air in and out of the lungs, in other words, it is the exchange of air between the lungs and the air delivered by the ventilator. The most important role of ventilation is the removal of carbon dioxide from the body while keeping the blood oxygen level constant. Ventilation is calculated as:

Ventilation = RR (Respiratory rate) x Vt (Tidal volume)

The CO2 content of the blood can be adjusted by changing either tidal volume or respiratory rate in patients that are ventilated mechanically1.

Respiratory physiology:

Respiratory physiology is broken down into two different processes — oxygenation and ventilation.

  • Oxygenation (It is the diffusion of oxygen into the blood from the alveolus. Dynamic measure of oxygenation is pulse oximetry.)
  • Ventilation (It is the movement of air in and out of the lungs. Dynamic measure of ventilation is end-tidal capnography.)

Ventilation is considered as an active process, as the lungs cannot ventilate without the activity of the respiratory muscles. While oxygenation is a passive process, as it depends merely on the diffusion gradient across the alveolar membrane. The removal of CO2 requires both ventilation and diffusion however, it is more dependent on ventilation.

Indications:

The following conditions in a patient indicate the need for ventilation:

  • Whenever the patient is no longer breathing spontaneously and has been intubated.
  • Acute respiratory failure.
  • Hypercapnia (failure of ventilation).
  • Hypoxia (failure of oxygenation).
  • Massive hemoptysis.
  • If the patient has a decreased level of unconsciousness and is unable to protect the airway.

Another indication to intubate a patient is the positive effect of ventilation. Ventilation allows medical professionals to correct the rearrangements by reducing the controlling minute ventilation, improving gas exchange by elevating alveolar recruitment, and lessening perfusion/ventilation mismatch and the work of breathing2.

Ventilation does not have any contraindications as such. All critically ill patients should be offered ventilation if needed as it is a life-saving method. The only contraindication for ventilation is if it is not stated in the patient's stated wishes for artificial life-sustaining measures.

Mechanical ventilators:

A mechanical ventilator is a machine that acts like bellow to move air in and out of the patient's lungs. The medical professionals set the ventilators in a way to control how often air enters the lungs.

Ventilation has beneficial effects in patients with chronic irreversible causes of respiratory failure like spinal cord injury or neuromuscular disease, allowing them to exist which would not have been possible before the invention of a ventilator.

Ventilation process:

The patient wears a mask or a helmet to get air from the ventilator into the lungs. The patient may require a breathing tube if his/her breathing problem is more serious. Through the nose or mouth of the patient, an endotracheal tube is inserted in the windpipe of the patient. There is rarely a need for tracheostomy (placing a tube through an opening in the patient's neck). Tracheostomy is performed either when the patient has been on a ventilator for a few days, or if the medical professionals face difficulty in placing the endotracheal tube through the mouth or nose. The patient is not able to eat or talk with the endotracheal tube however with a tracheostomy tube the patient may eat or talk but with difficulty.

Mechanical ventilators are commonly used in MEDEVAC air transport, hospitals, and ambulances, etc. If the illness is long-term and the caretakers at home have all the necessary skills and resources, the ventilators can be used at home too. A patient on a ventilator is more vulnerable to pneumonia, vocal cord damage, or any other problems. Mechanical ventilation is a life-saving procedure that has saved millions of lives of people around the world with respiratory failure.

Risks of being on ventilation:

Infections:

Pneumonia is the most common and serious risk for a patient on a ventilator. The breathing tube makes coughing hard for the patient. Coughing helps to clear germs of the airway. The breathing tube that is put into the airway can allow bacteria to enter the lungs causing pneumonia. Pneumonia is a major concern as people using ventilators are usually very sick. Pneumonia causes the cure of the disease even harder. Special antibiotics may also be needed, as the bacteria causing pneumonia develops resistance against standard antibiotics.

Sinus infection is another risk for the patients on a ventilator. These infections are also caused due to endotracheal tubes. Sinus infections are treated with antibiotics.

  • Atelectasis — This is a condition in which air sacs collapse because the lungs do not expand fully.
  • Blood clots — While using a ventilator the patient stays in bed or uses a wheelchair because of staying in one position for a longer period there is an increased risk of blood clots.
  • Pulmonary edema — fluid buildup in the inner sacs of the lungs.
  • Lung damage — Pushing too much air or air with too much pressure can cause lung damage.
  • Muscle weakness — The work of the diaphragm decreases due to a ventilator hence the respiratory muscles become weak.
  • Pneumothorax — In this condition, air leaks out of the lungs into space around the lungs that causes chest pain and shortness of breath.
  • Vocal cord damage — The breathing tube causes damage to vocal cords3.

Conclusion:

Ventilation is the process of moving air in and out of the lungs, in other words, it is the exchange of air between the lungs and the air delivered by the ventilator. The ventilator is also known as = respirator or breathing machine. It makes sure that the patient is receiving enough oxygen and getting rid of excess carbon dioxide. Ventilators have saved millions of lives worldwide however it does cause some health risks in patients too.

Resources:

  1. https://www.ncbi.nlm.nih.gov/books/NBK448186/
  2. https://www.ncbi.nlm.nih.gov/books/NBK537072/
  3. https://www.ncbi.nlm.nih.gov/books/NBK143277/
This page is last reviewed and updated by on Sep 15, 2020.