A mechanical ventilator or positive pressure ventilator is an instrument used to help a patient to breathe when they are unable to breathe on their own. Over the past few decades, the technology surrounding ventilators has undergone massive development.
Some common aspects of mechanical ventilation, however, have not changed and these include:
- Parameters such as air pressure, flow and volume and the timing of each individual breath can be set by the operator.
- There is a mechanism by which the ventilator breathing is begun and ended
- There are mechanisms that can help synchronize the patient's own breathing mechanism with the ventilator's rhythm
- Mechanical ventilation requires supervision by medical experts to increase the safety and efficacy of the ventilation provided
Parameters of the ventilator
There are four key parameters that need to be carefully selected and monitored during the delivery of ventilator breaths. These include:
- The pressure of the ventilated air that flows in and out of the lungs
- The volume of the breath taken into and breathed out of the lungs
- The flow rate of the air into the lungs
- The inspiratory and expiratory time
Mechanical ventilation definitions
Some of the terminology most commonly used in mechanical ventilation include:
- Peak inspiratory pressure - This is the highest pressure that can be obtained using gas delivery
- Mean airway pressure - This is the average pressure across the ventilation period
- Plateau pressure - This is the pressure that remains at the end of inspiration or one deep breath when there is no gas flow
- End expiratory pressure - This is the pressure at the end of expiration or after breathing out
- Positive end expiratory pressure (PEEP) - In this type of ventilation, a fixed amount of positive pressure is applied during the mechanical ventilation cycle
- Continuous positive airway pressure (CPAP) - This is a form of ventilation where a fixed amount of positive airway pressure is added to breaths taken spontaneously by the patient in the presence or absence of an endotracheal tube.
Both PEEP and CPAP are used together with other modes of ventilation or along with spontaneous breathing.
Risks associated with the use of mechanical ventilation include:
- Lung injury
- Ventilator induced pneumonias
- Risk of pressure injuries to the lungs
- Lowering of blood pressure
- Fall in cardiac output
- More laboured breathing and dependence on the ventilator for breathing
- Fluid retention in the body