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Mechanical Ventilation

Mechanical Ventilation


Mechanical ventilation is a device that breathes for someone who is unable to breathe for themselves.

Mechanical ventilation is also called positive pressure ventilation. Following an inspiratory trigger , a predetermined mixture of oxygen is forced into the central airways and then flows into the alveoli. 

Mechanical ventilators are set to deliver a constant volume , a constant pressure or a combination of both with each breath. Modes of ventilation that maintain a minimum respiratory rates regardless of whether or not the patient initiates a spontaneous breath are referred to as assist control. Because pressures and volumes are directly linked by the pressure volume curve, any given volume will correspond to a specific pressure, and vice versa, regardless of whether the ventilator is pressure or volume cycled.

Why is it needed ? 

Brain and spinal cord injury or disease : 
An injury or disease to the brain can interfere with the signs that control breathing. Damage to the spinal cord can block the brain's signals from reaching the breathing muscles.

Disorders of the Muscles : 
Can weaken the breathing muscles or change the way in which they receive signals from the brain. This can happens with polio and muscular dystrophy.

Lung Disorders : 
Affect the tissues of the lungs making it difficult for a person to breathe on their own. These disorders include COPD, asthma, chronic bronchitis, emphysema, interstitial , or fibrotic lung disease.

Sleep Disorders : 
Sleep apnea is a condition in which people stop breathing during sleep . These patients may use a form of ventilation only while sleeping called CPAP or BiPAP .

How Does it Work ? 

Mechanical Ventilation is different from how we naturally breathe. During natural inhalation , the diaphragm muscle contracts and the chest expands. This creates a vacuum that pulls air into the lungs. During a natural exhalation, the diaphragm muscle relaxes and air leaves the lungs.

A ventilator works by pushing air into the lungs. The air is pushed in until it reaches a pre set volume or pre set pressure. Once the lungs are full, the vent stops pushing the air into the lungs. This is similar to letting air out of a full balloon.  

Modes of ventilator :

  • Controlled : The ventilator provides the breath when a patient is unable to breath on their own.
  • Supported : The patient is able to breath on their own but needs a little help.The ventilator will provide a small amount of pressure to increase the size of their natural breath.
  • Combination : A combination of controlled and supported breathing that fine tunes the breath.
The ventilator will deliver the breath in 2 different ways :
  1. Volume : The ventilator delivers a pre set volume of air with every breath.
  2. Pressure : The ventilator will deliver a breath until a pre set pressure is reached.
Ventilator and Patient Monitoring :

Patient monitoring and ventilator checks re generally performed every 4 hours in the hospital. This is important to guarantee proper ventilator function and to know if there is a patient issue , such as :
  • The patient needs suctioning
  • The patient needs a breathing treatment
  • The equipment is functioning properly.
Alarms : 
The ventilator is equipped with the safety alarms. An alarm will sound if the ventilator exceeds or drops below certain limits. Always look at and attend to the patient first. Address the alarm situation first.
  • Low pressure alarm : indicates that the pressure in the ventilator circuit has dropped. Low pressure alarm are usually caused by a leak or disconnect.
  • Low Minute Ventilation :  This alarm will sound when the amount of air taken in per minute drops below a set value.  
  • High pressure volume : This will sound when the pressure in the circuit has increased.
Moisture and Humidity : 
It is important to heat and humidify the air delivered from a ventilator. Dry, cold air can damage the delicate tissues of the airways and cause mucus plugs.
Heat and humidity can be delivered in 2 different ways :
  1. HME (Heat Moisture Exchanger) 
  2. Heated Humidifier 

In order to reduce the chance of infection :
  • Wear gloves when touching the ventilator circuit or trach tube.
  • Wash your hands before and after contact with the patient.
  • Wear a mask if the patient has a contagious respiratory diseases or if you are sick and could infect the patient. 
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