TYPES OF VENTILATORS FOR NURSES....NURSESOUTLOOK

TYPES OF VENTILATORS

Introduction

The mechanical; ventilator is  a device that functions as a substitute for the action of thoracic cage and diaphragm

Types

1. Positive Pressure Ventilator
2. Negative Pressure Ventilator

Positive Pressure Ventilator

These ventilators use positive pressure to inflate the lungs of the patient .During inspiration a positive intra thoracic and alveolar pressure is caused by the pressure created by the ventilator. Expiration is largely passive. Different types of positive pressure ventilators are described below.

1.Pressure Cycled Ventilators .They produce an inspiratory flow of gas that inflate the lungs until a preset or predetermined pressure is reached. Volume delivered depends upon changes in the airway resistance, lung compliance and integrity  of ventilator circuit .Newer machine combine pressure cum volume cycle.

2.Time Cycled Ventilators. Time cycled ventilators terminate the inspiratory phase after the preset time They are mainly used for newborn and premature neonates because they provide precise  control over time and inspiration-to-expiration ratio.

3.Volume Cycled Ventilators. These ventilators terminate the inspiratory phase when the predetermined volume of gas  is delivered (12ml/kg body weight. Usually starting volume).These ventilators can also be used for newborn and premature neonates.

Negative Pressure Ventilators

This type of ventilators apply negative pressure around the chest wall which causes intra airway pressure to become negative,thus drawing air into the lungs .They are old generation mechanical ventilators that are not in use now.

                                                  

                                Modes of Mechanical Ventilation

1.Controlled mode Ventilation(CMV)

a.Volume Controlled Ventilation :the ventilator initiates the breaths at a preselected rate and volume. All breaths are compulsory .The patient cannot trigger a breath .Only patients who have no voluntary respiratory efforts can use this mode of ventilator.(eg.anaesthetised patient s)or those who are unable to respire spontaneously .(eg paralysed patient)

b.Pressure Controlled Ventilation (PCV):It is used when all breaths are time or patient triggered ,pressure  limited and the time cycled .The ventilator provides a constant pressure of air to the patient during respiration .which is set by the therapist .The tidal volume is based on the compliance and resistance of the patient lungs and the patient pressure.

2.Assisted Control Volume

 This is a mode of ventilation in which a fixed minimum rate and volume are delivered by the machine ,but each of patient’s spontaneous breaths trigger the ventilator to deliver a selected volume .with assisted control  mode every breath is a mandatory breath even though the patient-can trigger breath at a more rapid rate than the set machine rate.This mode allows the patient to adjust respiration to changing metabolic status.

3.Intermittent Mandatory Ventilation(IMV):IMV is a mode of ventilation in which the ventilator delivers preset tidal volume and respiratory rate . The client can take unassisted spontaneous breaths between preset breaths .

4.Synchronised Intermittent mandatory Ventilation(SIMV);This mode is similar to IMV except  that it has  a predetermined time interval. The ventilator senses the patient effort and assist the patient by synchronously delivering a mandatory breath.SIMV eliminates the problem of ‘breath stacking’ where machine breaths occur at the same time as the patient spontaneous breath. This mode is very useful as a weaning method to allow the patient to gradually assume more of the work of breathing .The SIMV/IMV mode has fewer cardiovascular side effects than most other mode of ventilatior.

Spontaneous Modes

1.Pressure Support Ventilation(PSV):Pressure Support Ventilation is a special form of assisted ventilation that is used in spontaneously breathing patients .The ventilator provides a constant pressure of gas once the patient has made an inspiratory effort .It is always assisted or patient triggered .In pure PSV there is no preset tidal volume or frequency The therapist sets the inspiratory and expiratory pressure and sensitivity. The patient determines the timing of the breaths ,tidal volume receive and rate of breathing .

2.Continous Positive Airway Pressure (CPAP): CPAP refers to positive end expiratory pressure (PEEP)applied in conjunction with spontaneous ventilation.With CPAP all patient breaths are humidified and oxygenated air from the ventilator system. During the expiratory phase ,the patient exhales to the preset positive and expiratory pressure level. While applying positive pressure through out the respiratory cycle ,it helps to keep the alveoli open and promotes oxygenation. Providing CPAP through  the ventiolator circuit during spontaneous breathing also offers the advantage of an alarm system and may reduce the patient anxiety during early trials if the patient has been taught that the machine is keeping  tack of his breathing .However  CPAP may increase resistance for spontaneous breath,  so it is often used in conjunction with pressure support ventilation.