A mechanical ventilator is a machine that helps a patient breathe (ventilate) when he or she is recovering from surgery or critical illness, or cannot breathe on his or her own for any reason. The patient is connected to the ventilator with a hollow tube and uses it until he or she can breathe on his or her own.
A mechanical ventilator is mainly used to make it easier for very sick people to breathe. Another reason is to help raise the oxygen level for these patients. Sometimes, patients receive mechanical ventilation when they have an unpredictable or unstable health condition.
The main purpose for using a mechanical ventilator is to allow the patient time to heal. Usually, as soon as a patient can breathe effectively on his or her own, he or she is taken off the mechanical ventilator.
Who are the caregivers who take care of the patient on a mechanical ventilator?
Rate of breaths
Also referred to as respiratory rate, breathing rate, or frequency; can be a ventilator setting or respiratory status the ventilator tracks as the patient breathes
Volume of breaths
Usually expressed in milliliters (mL); frequently referred to as tidal volume or “VT”; can be a ventilator setting or respiratory status the ventilator tracks as the patient breathes
Sensitivity of breathing
Concerns how much inspiratory or “trigger” effort is required from the ventilator to recognize that the patient is trying to inhale; this can refer to a ventilator setting, but can also be used to describe the ventilator’s responsiveness to the patient’s breathing effort
Flow of breaths
Also referred to as peak flow or inspiratory flow; usually describes a ventilator setting but can be respiratory status the ventilator tracks as the patient breathes
Controls or limits on breathing volume, pressure or time
The ventilator can limit or control the inspiratory pressure, volume or time during breath delivery
Measured or mandatory breaths
Also referred to as mechanical breaths, describes breaths initiated by the ventilator delivered according to a consistent volume or pressure
Lung compliance and airway resistance
Lung compliance refers to the elasticity, stretch or ease with which the lung expands to receive volume
Airway resistance refers to the resistance encountered as oxygen enters the airway and to how easily the lung lets in air
The clinician determines appropriate ventilator settings according to the condition and needs of the patient. The settings include:
FIO2: - The measure of oxygen the ventilator is delivering during inspiration.
Rate: The number of breaths delivered by the ventilator per minute.
Tidal volume: The volume of gas/air delivered with each breath.
Sensitivity: This alerts the ventilator when to recognize the start of a patient’s spontaneous breath (or breathing effort). When the ventilator recognizes the patient’s effort, it triggers a response, either to provide a mechanical breath or to support a spontaneous one.
Peak flow: The flow of gas/air (flow rate) used to deliver each mechanical breath to the patient.
Inspiratory and expiratory times: The total time required for one complete respiratory cycle. Typically, patients are comfortable with an expiratory time two to three times longer than the inspiratory time.
Cycling: The manner in which the ventilator ends the inspiratory phase of the breath and allows the patient to exhale. Ventilator breaths can be volume cycled, time cycled or flow cycled.
Limit: This setting restricts the volume, pressure or time air is delivered to the patient during the inspiratory phase.
Ventilator manufacturers offer combinations of modes and breath types that characterize how and when a breath is delivered to the patient.
Ventilator modes most commonly found include:
All breaths delivered by the ventilator will control either volume or pressure. The ventilator delivers the same measured breath every time, whether the breath is patient initiated or ventilator initiated, based on the rate setting.
Continuous positive airway pressure ventilation (CPAP)
All breathing is initiated and sustained by the patient. The ventilator controls the delivered oxygen concentration and delivers as much flow and volume as necessary to meet the patient’s inspiratory demands. This mode also allows the patient to breathe at a continuous, elevated airway pressure that can improve oxygenation (see PEEP/CPAP).
The ventilator can also apply positive pressure during spontaneous inspirations taken during CPAP mode to reduce the patient’s work to breathe.
Synchronized intermittent mandatory ventilation (SIMV)
The ventilator synchronizes machine breath delivery with the patient’s spontaneous breath efforts. This mode is a combination of set mandatory machine breaths synchronized with the patient’s own spontaneous breaths.
Pressure control ventilation (PCV or PC)
This is a type of mandatory breath that can be used in either A/C or SIMV modes and targets a specific pressure during inspiration. Pressure support ventilation (PSV or PS)
Positive end expiratory pressure (PEEP)
Mechanical positive pressure is applied at the end of exhalation to prevent the lungs from emptying completely and returning to a “zero” reading. The benefit of positive pressure at the end of exhalation is increased lung volume for improved oxygenation.
Ventilators offer audible and visual alarms to alert the caregiver
High airway pressure alarms
These are also referred to as high inspiratory pressure (HIP) alarms. This alarm setting also provides a pressure limit function.
The alarm detects abnormally high inspiratory pressure and may activate in response to:
Low airway pressure alarms
These alarms are in response to:
Low pressure alarms can also activate if
High and low rate alarms
A low or high rate alarm will trigger an audible and/or visual alert. An agitated or fatigued patient can have an increase in respiratory rate. Sedated patients or patients with impaired neuromuscular function can have a decreased respiratory rate.
High and low volume alarms
In addition to a high respiratory rate, high volume alarms may indicate increased patient demand for gas/air because of pain, anxiety or improper ventilator settings.
Low volume alarms are typically caused by air leaks. In pressure-based ventilation, these alarms may indicate worsening airway resistance or lung compliance.
Contact healthcare provider in case of: