Pros and Cons of Medical Ventilators

Medical Ventilators

Mechanical Ventilators 101

Welcome to this video tutorial – mechanical ventilation 101.

Ventilators can be quite overwhelming, so let’s go over some of the basics.

Mechanical ventilation is a means to mechanically assist or replace spontaneous respiration.

It is indicated for patients who aren’t breathing (apneic) or breathing ineffectively (causing ventilation problems).

Mechanical ventilation is used to help the patient ventilate & oxygenate with the end goal being to wean before complications arise.

Mechanical ventilation can be provided noninvasively by face or nasal mask,or by an invasive airway (intubation).

Noninvasive mechanical ventilation (NIV) requires an alert, cooperative, hemodynamically stable patient.
Ventilation is delivered by a CPAP or BiPAP device by way of a face or nasal mask.

CPAP is Continuous Positive Airway Pressure – It provides a constant end-expiratory pressure that keeps the airway open, providing supplemental oxygen if needed
Whether breathing in or out, the continuous pressure keeps the alveoli open & the tongue forward, preventing sleep apnea.

BiPAP is Bi-level Positive Airway Pressure – Similar to CPAP, but it delivers different levels of pressure during inspiration & expiration.
If the patient is not a candidate for NIV or if NIV is not maintaining adequate ventilation, intubation is required for invasive mechanical ventilation.
Intubation is achieved with an endotracheal tube (ETT) or tracheostomy (trach).

ET tubes are inserted into the trachea through the mouth or nose. Oral intubation is preferred and more common (due to increased risk of pneumonia & sinus infections with nasal intubation).
ET tubes can be left in place for several weeks – but after 10-14 days, tracheostomy is considered.

A tracheostomy is an artificial opening in the trachea, into which a tracheostomy tube is inserted.

Two basic types of ventilators are available:

     Volume-cycled ventilators
Pressure-cycled ventilators

Volume-cycled vents are used most frequently – they deliver a constant volume of air with each breath.
Pressure-cycled vents deliver a volume of gas to the airway using positive pressure during inspiration – once the set pressure has been reached, the machine cycles off & exhalation occurs passively.

Our focus will be on volume-cycled ventilators, since they are used more frequently.

Ventilator Modes

     Assist Control (AC) – full support
Synchronized Intermittent Mandatory Ventilation (SIMV) – intermediate mode
Pressure Support Ventilation (PSV) – stepping stone before extubation

Assist Control (A/C) Mode
– Most common ventilation mode used in ICU
– “Full support” mode – Every breath is a positive pressure ventilator breath, but it can be initiated by the machine or the patient
– Patient receives a mandatory RATE (RR) & a mandatory VOLUME (TV)

Benefit of AC mode:
– Decreases the work of breathing.
It can be used for patients who have some spontaneous breathing & those who don’t – it provides the set number of breaths every minute, but also allows the patient to initiate breaths on their own, decreasing anxiety.

Disadvantage of AC mode:
Due to the low work of breathing, respiratory muscles weaken (can cause breath-stacking, where air never fully exits the alveoli before another breath is taken).
Every breath is the same size & if patient wants larger breaths than the set TV, it can cause anxiety, leading to tachypnea & hyperventilation.

SIMV – Synchronized Intermittent Mandatory Ventilation
– Another common mode used in ICU & often in surgical patients requiring ventilator support for a short time post-op.
– A set number of breaths are delivered each minute, but patient can breathe as often as he feels the need to – vent breaths are synchronized with patient’s spontaneous breaths.
– The ventilator breaths deliver the full TV, but patient-initiated breaths require the patient to inhale the TV independently.
– This helps work the respiratory muscles by providing periods of decreased support – rate can be turned down & pt can start to be weaned.
– Ventilator breaths are synchronized with patient’s spontaneous breaths.
– The ventilator breaths deliver the full TV, but patient-initiated breaths require the patient to inhale the TV independently.

PS – Pressure Support
– Used alone or with SIMV, this provides a small amount of pressure during inspiration to help the patient take in a spontaneous breath.
– The patient regulates his own respiratory rate & tidal volume.
– PS provides a constant end-expiratory pressure that keeps the alveoli open, providing supplemental oxygen if needed.
– This mode is used as a stepping stone between a dependent ventilator mode & extubation, because it reduces the work of breathing for the patient.

Ventilator Settings
4 basic settings we will cover:

    Respiratory Rate (RR)
Tidal Volume (TV)
Fractional inspiration of oxygen (FiO2)
Positive end-expiratory pressure (PEEP)

Respiratory rate – minimum amount of breaths the patient will take (between 12-18).

TV (Tidal volume) – amount of air going into patient’s lungs with each breath (set between 400mL – 800mL, based on body weight).

FiO2 (Fractional inspiration of oxygen) – the percentage of O2 concentration going into the lungs required to maintain adequate blood oxygen levels.

PEEP (Positive end-expiratory pressure) – amount of pressure left in the circuit at the end of exhalation – helps keep alveoli open, allowing for better oxygenation (set between 5-10 cm H2O).

Ventilator alarms
Anytime an alarm goes off – always look at your patient first! Do not immediately silence the alarm – we need to figure out why the vent is alarming. Alarm systems vary between machines, but there are 2 basic alarms:

      -High-pressure alarm: Increased resistance somewhere in the
system – equipment obstruction, patient obstruction
(coughing or secretions), or water/condensation in the tubing.
-Low-pressure alarm: A leak in the system – a disconnection somewhere –
check all your connections

Troubleshoot the alarm, starting with the patient & moving toward the machine.

Weaning off the ventilator
Prolonged mechanical ventilation is dangerous & expensive, with the occurrence of pneumonia increasing each day the patient is on the vent.

Certain criteria must be met for weaning to be initiated:

     Acceptable ABG’s & normal hematocrit
Patient breathing on their own, TV > 10ml/kg
FiO2 less than 0.5 (room air is 0.21 or 21% oxygen)
Intact gag reflex, ability to cough & take in a deep breath

Review:
2 Basic Noninvasive Ventilator Modes:

    CPAP - Continuous Positive Airway Pressure
BiPAP - Bi-level Positive Airway Pressure

3 Basic Invasive Ventilator Modes:

    AC - Assist Control – full support
SIMV - Synchronized Intermittent Mandatory Ventilation – intermediate mode
Pressure Support Ventilation (PSV) - last step before extubating

4 basic settings:

    Respiratory Rate (RR)
Tidal Volume (TV)
Fractional inspiration of oxygen (FiO2)
Positive end-expiratory pressure (PEEP)
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