3nd LECTURE

VENTILATORS Part One

Ventilators

• One of the major life support systems.• Ventilators take over the vital role of the respiratory

muscles.• Mechanical ventilation can effectively assist or

replace normal spontaneous breathing.• Some acutely ill patients are ventilator dependent.

Respiratory Failure• Respiratory failure is a life-threatening condition in which the

respiratory apparatus is unable to provide adequate oxygenation (delivery of oxygen to the blood) and/or ventilation [removal of carbon dioxide from the blood).

Causes of Respiratory Failure• Airway obstruction• Inadequacy of the ventilator muscles• Lung disease• Chest injury• Cardiac, neurological, and neuromuscular disorders• Older people are more likely to suffer from respiratory failure

Ventilators

• Ventilator: defined as: A machine designed to mechanically move breathable air into and out of the lungs, to provide the mechanism of breathing for a patient who is physically unable to breathe, or breathing insufficiently.

Work concepts of ventilators • Ventilator must generate an inspiratory flow in order to

deliver a tidal volume• a mechanical ventilator must produce a pressure gradient

(i.e., pressure difference)• The pressure gradient that must be generated between the

airway opening and the alveoli is known as the transairway pressure.

Work concepts of ventilators

• Transairway pressure is the difference between the airway opening pressure (PaO) and alveolar pressure (PA):

• Transairway pressure = Pressure airway opening (PaO) - alveolar pressure (PA )• At end- exhalation and prior to the beginning of inspiration, the

pressure at the airway opening and the alveoli are both equal to atmospheric pressure. Since these two pressures are both equal point, there is no pressure gradient and therefore no flow

Negative Pressure Ventilation• Occurs by creation of a transairway pressure gradient by

decreasing the alveolar pressures to a level below the airway opening pressure.

• Negative pressure ventilation usually below the atmospheric pressure.

• Two classical devices that provide negative pressure ventilation are:

1. The iron lung 2. The chest cuirass or chest shell.

1-The iron lung

The iron lung

spent nearly 60 years of her life in an iron lung after being diagnosed with polio as a child died on 2007 after a power failure shut down the machine that kept her breathing.

2-The chest cuirass

Positive Pressure Ventilation

• Positive pressure ventilation is achieved by applying positive pressure (a pressure greater than atmospheric pressure) at the airway opening.

• Increasing the pressure at the airway opening produces a transairway pressure gradient that generates an inspiratory flow.

• This flow in turn results in the delivery of a tidal volume

Operating Modes of Mechanical Ventilation

• A ventilator mode can be defined:As a set of operating characteristics that control how the ventilator functions.• An operating mode can be described by:1. the way ventilator is triggered into inspiration and cycled into

exhalation.2. What variables are limited during inspiration, and whether or

not the mode allows only mandatory breaths, spontaneous breaths, or both?

Operating Modes of Mechanical Ventilation

• There are 13 essential Ventilator modes available in different ventilators; two or more of these modes are often used together to achieve certain desired effects.

1. Spontaneous2. Positive End-Expiratory Pressure (PEEP)3. Continuous Positive Airway Pressure (CPAP)4. Bi-level Positive Airway Pressure (BIPAP)5. Controlled Mandatory Ventilation (CMV)6. Assist Control (AC)7. Intermittent Mandatory Ventilation (IMV)8. Synchronized Intermittent Mandatory Ventilation (SIMV)9. Mandatory Minute Ventilation (MMV)10. Pressure Support Ventilation (PSV)11. Pressure Control Ventilation (PCV)12. Airway Pressure Release Ventilation (APRV)13. Inverse Ratio Ventilation (IRV).

Operating Modes of Mechanical Ventilation

• The main modes of ventilation are:1. Positive End-Expiratory Pressure (PEEP)2. Continuous Positive Airway Pressure (CPAP)3. Controlled Mandatory Ventilation (CMV) and4. Synchronized Intermittent Mandatory Ventilation (SIMV)

Positive End-Expiratory Pressure (PEEP)• Positive end-expiratory pressure (PEEP) increases the end-

expiratory or baseline airway pressure to a value greater than atmospheric.

• It is often used to improve the patient's oxygenation status (hypoxemia).

• PEEP is not commonly regarded as a "stand alone" mode, rather it is applied in conjunction with other ventilator modes.

• PEEP is the minimum pressure which is equal to the functional residual capacity.

Continuous Positive Airway Pressure (CPAP)

• Continuous positive airway pressure (CPAP) is PEEP applied to the airway of a patient who is breathing spontaneously.

Continuous Positive Airway Pressure (CPAP)

• CPAP Mode can be used as stand alone mode .• In adults, CPAP may be given via a face mask, nasal mask, or endotracheal tube. • In neonates, nasal mask

Controlled Mandatory Ventilation (CMV)

• controlled mandatory ventilation or control mode, the ventilator delivers the preset tidal volume at a time-triggered respiratory rate.

• The control mode should only be used when the patient is properly medicated (sedated).

Controlled Mandatory Ventilation (CMV)

Controlled Mandatory Ventilation (CMV)Indication for CMV mode:1. Tetanus or other seizure activities that interrupt the delivery

of mechanical ventilation2. Complete rest for the patient typically for a period of 24

hours3. Patients with a crushed chest injury in which spontaneous

inspiratory efforts produce significant paradoxical chest wall movement

Controlled Mandatory Ventilation (CMV)Complications Associated with the Control Mode:• The potential for apnea and hypoxia if the patient should

become accidentally disconnected from the ventilator or the ventilator should fail to operate.

Synchronized Intermittent Mandatory Ventilation (SIMV)

• Synchronized intermittent mandatory ventilation (SIMV) is a mode in which the ventilator delivers either:

1. assisted breaths to the patient at the beginning of a spontaneous breath or

2. time triggered mandatory breaths• The mandatory breaths are synchronized with the patient’s

spontaneous breathing efforts so as to avoid breath stacking.

SIMV Mandatory Breath Triggering Mechanism

• The SIMV mandatory breaths may be either time triggered or patient triggered

• The triggering mechanism is determined by whether or not the patient makes a spontaneous inspiratory effort just prior to the delivery of a time triggered breath.

• Synchronization Window:The time interval just prior to time triggering in which the ventilator is responsive to the patient’s spontaneous inspiratory effort

Indications for the SIMV Mode

• The primary indication for SIMV is to provide partial ventilatory support; i.e., a desire to have the patient actively involved in providing part of the minute volume. In a practical sense, when a patient is first placed on ventilator support, full ventilatory support is appropriate to provide a period of rest, typically for the first 24 hours. After this initial period of full ventilatory support, it is typical practice to place the patient on a trial run of partial ventilatory support with SIMV.

Advantages of the SIMV Mode• 1. Maintains respiratory muscle strength/avoids muscle

atrophy,• 2. Reduces ventilation to perfusion mismatch• 3. Decreases mean airway pressure, and• 4. Facilitates weaning.