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Basic Modes of Mechanical Ventilation
- 1. Mechanical Ventilation: The Basic Modes
- 2. Basic Modes of Ventilation Ventilators Control Modes Volume Control Pressure Control Support Modes Pressure Support CPAP PEEP
- 3. The Control Modes – Require a set respiratory rate Volume Control Pressure Control Gas flow adjusts to deliver a pre- determined tidal volume Gas flow adjusted to maintain constant inspiratory pressure
- 4. Volume Control • Volume control • Set volume • Set rate • Set FiO2 • Set I:E
- 5. Pressure Control • Pressure Control • Set Pinspired • Set rate • Set FiO2 • Set I:E
- 6. The Control Modes • Assist Control • Gives a full ventilator breath at the set rate - AND – for each additional breath triggered by patient effort • Synchronized Intermittent Mandatory Ventilation • Gives a full ventilator breath per the set rate - ONLY
- 7. The Support Modes – Support a Spontaneously Breathing Patient Support Modes Pressure Support CPAP PEEP
- 8. Pressure Support (PSV) • Pressure Support Ventilation (PSV) • Support pressure is set (cmH2O) • Pressure is triggered by start of inspiration • Pressure support only during inspiration
- 9. PEEP • Positive end expiratory pressure (PEEP) • Set via pressurized valve or diaphragm • Present throughout the respiratory cycle • Opens airways and alveoli • Improves oxygenation • Critical modality in “open lung” ventilation strategies for ARDS • Can be added in all modes inspir. expir. (time) 0 5 10 PEEP (press.)
- 10. PSV + PEEP = BiLevel (BPAP) Pressure Support and PEEP • Pressure support only occurs in inspiration • PEEP is present throughout respiratory cycle • They are added together during inspiration inspir. expir. (press.) (time) 0 5 10 PS PEEP this is “5 PS + 5 PEEP”:
- 11. CPAP • Continuous Positive Airway Pressure (CPAP) • A positive pressure threshold applied continuously • Requires a high-flow gas source • Prevents inspiratory pressures from falling below expiratory levels • Prevents larger airways collapse
Editor's Notes
- Indications for intubation and mechanical ventilation include four broad categories: an inability to adequately maintain oxygenation – called hypoxic respiratory failure Inadequate ventilation (or elimination of carbon dioxide) – called hypercapneic respiratory failure, or an inability to protect the airway such as during anesthesia for a procedures or after a neurologic insult such as TBI or stroke. Non-sustainable work of breathing leads can also lead to respiratory failure and need for ventilatory support.
- Basic modes of ventilation can be divided into two broad categories - Control modes and Support modes. Support modes are used in spontaneously breathing patients, meaning that the respiratory rate is set by the patient’s spontaneous effort. Support modes include pressure support, CPAP, Bi-Level and PEEP. There is no set rate on the machine. Control modes deliver breaths using a set rate the provider programs on the mechanical ventilator. Control modes deliver breaths at the rate set by the provider using either volume or pressure driven breaths.
- Control modes require the provider set a respiratory rate on the ventilator machine. The provider must also determine if the breaths will be delivered using a set tidal volume OR using a set inspiratory pressure. Look at the example on the top panel: the ventilator is set using a control mode because the respiratory rate is set. It is set at 10 bpm. The ventilator is set to deliver the breaths using volume control because the Vt is set at 500mL For each of the 10 breaths delivered in one minute, the ventilator will deliver 500mL tidal volume If you were presenting this data to others you would report – “The patient is receiving volume control ventilation at a rate of 10 bpm and a tidal volume of 500mL” Now, Look at the example on the lower panel: The ventilator is set using a control mode because the respiratory rate is set. It is set at 10 bpm. The ventilator is set to deliver the breaths using pressure control because the inspiratory pressure, or “Pinspired” is set to 20cmH20 For each of the 10 breaths delivered in one minute, the ventilator will apply 20cmH20 If you were presenting this data to others you would report – “The patient is receiving pressure control ventilation at a rate of 10 and an Inspired pressure of 20cmH20.”
- Let’s look at the volume control panel settings more closely: Tidal volume is set at 500mL and is visualized as equal to the area under the curve The wave form has a triangular shape PIP depends on compliance but is measured here as Pmax which equals 30 cmH20 The Rate = 10, which is one breath every 6 seconds The fraction of inspired oxygen being delivered is a set value and here is listed as 25%. I:E ratio describes the time spent in inhalation versus the time spent in exhalation. Here the I:E ratio is set at 1:1, which is 3 seconds spent in inhalation and 3 seconds spent in exhalation Please note that the ventilator panel reports both the set parameters programmed by the provider AND the measured parameters for each breath delivered. Although all ventilator front panels are different, the set parameters are seen here in blue boxes. The measured parameters are reported in the black boxes above.
- Now let’s look more closely at the Pressure control panel settings: Inspiratory pressure is set at 20cmH20 Tidal volume depends on compliance and is equal to the area under the curve The wave form has a square shape Notice that exhaled tidal volume is measured and is listed as Vte. It is reported to equal 475mL. The rate is 10 breaths per minute or 1 breath every 6 seconds The I:E ratio is 1:2, thus 2 seconds are spent in inspiration and 4 seconds are spent in expiration Again note the set parameters seen here in blue boxes and the measured parameters reported in the black boxes above.
- Remember that Control Modes require the provider set a respiratory rate and determine whether the breath will be delivered using a set tidal volume or a set inspiratory pressure. Even though the provider sets the respiratory rate on the ventilator, it is still possible for the patient to take more breaths than the number set. For example, if the set rate is 10 bpm, the patient may breath 12 or 14 or 22 or any other number of breaths greater than the rate that the provider sets. How the ventilator responds to additional patient generated breaths depends mode options set on the ventilator by the provider. To select a control mode, providers must choose between assist control or Synchronized Intermittent Mandatory Ventilation. In Assist control, the ventilator gives…… In SIMV, the ventilator gives a full……… SIMV is often paired with pressure support ventilation which can support any additional breaths above the set rate.
- The support modes are for a spontaneously breathing patients. There is no rate set on the ventilator. Support is most often given using pressure and can be given using Pressure support ventilation, Bi-level, CPAP, or PEEP.
- Pressure support ventilation is used with a spontaneously breathing patient who sets their own rate. With each patient-initiated breath, the ventilator will apply an inspiratory pressure that is set by the provider. This pressure is only applied during inspiration but augments the patients effort, decreases the work of breathing, and may improve gas exchange.
- PEEP is positive end-expiratory pressure. It is applied continuously through both inspiration and exhalation, but has its greatest effect at the end of exhalation by preventing alveoli from collapsing therefore decreasing atelectasis. PEEP improves oxygenation by decreasing closing capacity preventing intrapulmonary shunting. PEEP can be added to any mode of ventilation and plays a key role in the management of ARDS.
- When PEEP and PSV are added together, it is termed BiLevel. PEEP is present throughout the respiratory cycle, but the Pressure support is only applied during inspiration – therefore there are two levels of pressure applied. It is important to note that the pressure support is in addition to the value of PEEP, so the total inspiratory pressure is the PSV + the PEEP.
- CPAP is much like PEEP in that the pressure is applied throughout both inspiration and expiration. The pressures applied aim to hold airways open with positive pressure to prevent airway collapse. CPAP uses high-flow gas sources to main positive airway pressures. As gas flow increases, PEEP becomes CPAP. CPAP is often used to assist Emphysema patients with eliminating excess carbon dioxide since it prevents the larger airways from closing.