Everything you should know about ventilators

Ventilators are used in emergency situations when patients have severe raspatory problems.  Ventilators forcefully push the air into our lungs forcing the patient to breathe. When you breathe air moves into the lungs when a muscle called diaphragm contracts and causes the chest cavity to expand.  Air is exhaled when muscles relax and the lung tissue  passively returns to its original size, this process is called respiration.  During this respiration process oxygen in the air passes through the nose or mouth and into pharynx or the throat, it then travels into the trachea or windpipe.

Some conditions that may lead to major respiratory problems include drowning and obstruction in the trachea, obstructive pulmonary diseases such as asthma, chronic bronchitis and emphysema. Severe respiratory distress syndrome or RDS can occur due to severe weakness of the muscles that control breathing and damage to the bones and tissues of the chest. Under these type of conditions patients usually need an additional oxygen source or breathing support through a mechanical ventilator. Mechanical ventilators are also used during surgical procedures for delivering anesthetic drugs preventing the aspiration of stomach contents into the lungs and closely controlling the levels of oxygen and carbon dioxide in the blood during surgery. 

Essentially mechanical ventilators are used when other forms of non-invasive management and support have failed to help improve the patient’s oxygenation or ventilation. Usually the decision to use ventilators is based on the patients ability to either oxygenate or ventilate themselves effectively.

There are two types of ventilators. Positive-pressure ventilators and negative-pressure ventilators. Positive pressure ventilators are getting the air from positive pressure that’s pushed into patient’s airway as opposed to negative pressure ventilation, which is how we breathe normally when air rushes when there is negative pressure in the chest cavity. 

Endotracheal intubation and mechanical ventilation

  • Indications
  • What’s the purpose of using mechanical ventilation during surgery?
  • Medical emergency when the patient cannot breath
  • Causes of hypoventilation
  • During general anesthesia


  • Deliver anesthetic drugs
  • Prevents aspiration syndrome (gastric-content aspiration)
  • Controls the PaO2 and PaCO2


Ventilator Modes

  • Continuous ventilation - Does not allow for spontaneous breathing (i.e. the machine – not the patient – is doing the work

CONS: Asynchronous breathing may occur, this is why Continuous ventilation mode is used when the patient is paralyzed or sedated


  • Intermittent ventilation - Allows the patient to make spontaneous breaths – This means that the patient can breathe between the set breaths. Used when the patient is conscious and is able to take breaths regularly


What can doctors control in ventilators?

Doctors can control the following settings of the ventilator.

  • Volume (V): tidal volume: how much air would you like to get into the patient and out
  • Pressure (P): how much pressure would you like to give?
  • Rate (R.R.): controls the pace of the patient breathing
  • Flow rate (F.R.): Flow = volume/time: how fast would you like to push the volume in
  • Oxygen (O): how much oxygen would  you like to put in
  • Who controls the work of breathing? – The machine or the patient


Combine the aforementioned factors together, and you get the MODE.

  • Assist control (AC) = Continuous mandatory ventilation (CMV)
  • Pressure control
  • Pressure support
  • Synchronized intermittent mandatory ventilation (SIMV)