What is a Ventilator and How does it Works?
Ventilator: Treatment for life support is mechanical ventilation. A mechanical ventilator is a device that aids in breathing when a person is unable to breathe.
Common names for mechanical ventilators are ventilator, respirator, and breathing apparatus.
The critical care unit of a hospital is where the majority of patients who require support from a ventilator due to serious illness are hospitalized (ICU).
Long-term ventilator users may be treated at home, in a conventional hospital unit, or at a treatment center.
IMPORTANT PARAMETERS
The key factors to consider while configuring a mechanical ventilation
- Ventilator setting (volume, pressure, or dual)
- Mode (controlled, support, and assisted ventilation), and Respiratory metrics
The Major Ventilation metrics are:
Additionally, alarms for tidal and minute volume, peak pressure, respiratory frequency, FiO2, and apnea must be programmed in order to detect issues with the ventilator and changes in the patient.
DIFFERENT MODES OF VENTILATOR
A mode of ventilation refers to the patient being ventilated by the machine and the degree to which the patient will influence the ventilator pattern. the patient breathing amount will vary depending on the mode of ventilation
Below are the 3 different modes of operation:
- VOLUME MODE
- PRESSURE MODE
- CONTROL MODE
VOLUME MODES
- Assist-control (A/C) mode
- The SIMV mode or Synchronized Intermittent Mandatory Ventilation
Assist-control (A/C) mode:
The ventilator supports the patient by delivering a certain tidal volume to the patient at a predetermined rate, although the patient may choose to initiate a breath on his own.
When a patient is first intubated or when they are too weak to perform the job of breathing,
This technique of ventilation is frequently utilized to assist the patient entirely.
Advantages
- Each breath has the same tidal volume
- Every breath is supported by the ventilator
Disadvantages
- Hyperventilation
- Air trapping
- Increased work breathing may result from low flow rates or sensitivity.
Synchronized Intermittent Mandatory Ventilation (SIMV) Mode :
The ventilator gives the patient a certain number of breaths per minute at a predetermined fio2 and tidal volume.
The patient is able to breathe passively in between breaths supplied by the ventilator.
The patient maintains the respiratory rate and tidal volume; the ventilator does not help with spontaneous breathing.
The patient is weaned off the mechanical ventilator using this way of ventilation.
The obligatory breaths were gradually reduced throughout weaning in order to give the patient more breathing responsibility.
Frequently used for weaning as a first ventilation mode
Advantages
- Enabling spontaneous breathing between ventilator breaths (tidal volume controlled by the patient)
- weaning is performed by progressively lowering the set rate and allowing the patient to take on huge control.
Disadvantages
- Possibility of patient-ventilator asynchrony Pressure Modes
PRESSURE MODES
- Pressure-controlled ventilation (PCV) mode
- Pressure-support ventilation (PSV) mode
- Continuous positive airway pressure (CPAP)/PEEP mode
- Noninvasive bi-level positive airway pressure ventilation (BiPAP) mode
Pressure-controlled ventilation (PCV) mode
The PCV mode is used to control plateau pressures in conditions such as ARDS where compliance is decreased but the risk of barotraumas is high.
It is done when a patient continues to experience oxygenation issues despite having high FIO2 and high PEEP levels.
It is necessary to choose the inspiratory pressure level, respiratory rate, and inspiratory-expiratory (I: E) ratio
Tidal volume must be carefully monitored because it varies with compliance and airway resistance.
Disadvantages
- Possibility of patient-ventilator asynchrony, requiring sedation or paralysis
Pressure-support ventilation (PSV) mode
When the patient inhales, the ventilator automatically applies a predetermined amount of positive pressure to the airways. Pressure support ventilation helps each spontaneous inspiration by boosting the patient’s positive pressure during inspiration. A patient must initiate all pressure support breaths.
Assists in overcoming airway resistance and reducing the work of breathing. For a patient who is spontaneously breathing, pressure support ventilation can be used alone or in combination with other modes like SIMV.
Recommended for patients with low spontaneous tidal volumes and those who are challenging to wean. In general, if compliance declines or resistance rises, tidal volume declines and respiratory rate rises; this mode is primarily used to wean patients from mechanical ventilation.
Disadvantages
- Patients with certain conditions should use PSV mode with caution.
- Breathing problems
- Additional reactive airway issues.
- Used as a weaning technique and occasionally for dyssynchrony
Continuous Positive Airway Pressure CPAP
It is a PEEP variant.
Positive pressure is applied at the end of the expiration when a patient breathes spontaneously.
No mandatory breaths are taken (ventilator-initiated delivery is used in this mode), and the patient initiates all ventilation on their own.
Patients with hypoxemia who are resistant to oxygen therapy are treated with PEEP and CPAP. They increase oxygenation by expanding collapsing alveoli and preventing them from collapsing at the end of expiration.
While the patient is still using the ventilator, CPAP enables the nurse to observe whether the patient can breathe on their own.
When spontaneous breathing occurs, CPAP is provided. Positive end-expiratory pressure with positive-pressure (machine) breaths is referred to as PEEP.
CPAP helps spontaneously breathing patients improve their oxygenation by increasing the end-expiratory pressure in the lungs throughout the respiratory cycle. Both intubated and non-intubated patients can use CPAP.
Advantages
- Applied to both intubated and non-intubated patients
Disadvantages
- On some systems, if the respiratory rate drops there is no alarm.
- Keep an eye out for breathing difficulty.
Noninvasive bi-level positive airway pressure ventilation (BiPAP) mode
BiPAP is a noninvasive method of mechanical ventilation that uses a full-face mask, nasal prongs, or both. It is used as a bridge to weaning patients off mechanical ventilation, as an alternative to conventional mechanical ventilation in patients who are ventilated in their homes, and in the treatment of patients with chronic respiratory insufficiency to manage acute or chronic respiratory failure without intubations and conventional mechanical ventilation.
Advantages
- Lower costs when patients can receive care at home
- Avoidance of artificial airway
Disadvantages
- Patient discomfort or claustrophobia
- Gastric distension
- Air leaks from the mouth
SUMMARY OF VENTILATION MODALITY PARAMETERS
1. VOLUME MODALITIES
1.1 Tidal Volume
- It is the amount of air delivered to a patient during a ventilator breath, i.e. how much air is inspired and expelled with each breath.
- Pressure-support ventilation (PSV) mode
- Continuous positive airway pressure (CPAP)/PEEP mode
- Noninvasive bi-level positive airway pressure ventilation (BiPAP) mode
1.2. Minute Volume
- It’s the volume of air that has expired in a minute.
- Minute ventilation is equal to respiratory rate time’s tidal volume. – VE = (VT x F) (VT x F)
- Alveolar ventilation is determined by minute volume.
- Decreased PaCO2 with increasing minute volume. On the other hand, raising the minute volume lowers the PaCO2.
2. PRESSURE MODALITIES
Peak Pressure
- When the peak airway pressure in adults is consistently higher than 45 cmH2O, there is a higher risk of barotrauma, so measures should be taken to try and lower the peak airway pressure.
- It is unknown what level of peak pressure may cause harm in infants and children. Peak pressures should ideally be kept below 30 in general.
- The percentage of oxygen inspiration (FIO2)
- The percentage of oxygen concentration that the patient receives from the ventilator.
- The normal rate is between 21% & 100%
3. Respiratory Frequency
- Respiratory rate (breaths per minute).
- The number of breaths taken per minute is the respiratory frequency of a person.
- Adults should take 12 to 20 breaths per minute on average while at rest.
- An abnormal respiration rate is one that is less than 12 or greater than 25 breaths per minute.
4. Positive End-Expiratory Pressure
- When using a ventilator, positive pressure is used at the end of expiration.
- The PEEP control modifies the pressure that is kept in the lungs at the conclusion of expiration.
- PEEP can be seen on the respiratory pressure gauge or display.
- The pressure value decreases to the PEEP level at the end of expiration rather than returning to zero (atmospheric pressure).
5. Inspiratory Time
The inspiratory time is the time it takes to inhale. The amount of time it takes to deliver the tidal volume of air to the lung is referred to as the inspiratory time.
6. Inspiratory-To-Expiratory Ratio
In most cases, inspiration is an active process. Expiration is passive and usually takes longer than exhalation, resulting in a no-flow period.
When breathing spontaneously, the work of breathing is reduced by keeping inspiratory times short and tidal volumes low enough to eliminate the CO2 produced. Under anesthesia, the optimal I: E ratio is most likely 1:1, not 1:2. With an I: E ratio of 1:1, a respiratory rate of about 12 is a good place to start. Normal I: E ratios are 1:2 or less during rest and sleep.
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