Definition of ventilators
Ventilators are the devices used for artificial ventilators.
- Respiratory failure
- Crush injuries of the chest, severe, scoliosis, major surgery
- Muscular cases like tetanus, Myasthenia gravis, Muscular dystrophy
- Pulmonary: Acute respiratory distress syndrome, Chronic obstrctive pulmonary disease, Bronchial asthma and drowing.
- CNS: Drugs, overdose of morphine, poisioning, epilepsy, Cerebrovascular accident and Poliomyelitis.
Types of Ventilators
- Negative pressure: The whole body below neck is kept in a large negative tank and a negative pressure is set in tank and this induces pressure.
- Positive pressure: Air is sent into the lungs with pressure more than atmospheric pressure, i.e Supra atmospheric pressure is set up and air is driven through trachea.
- High frequency positive: This is of two types :
a. Jet High frequency positive: 350 breathes /min
b. Oscillator High frequency positive: 1300 breathes /min.
Modes of Ventilation
This is two types. They are:
a. Full ventilatory support
b. Partial ventilatory support
The following provides both of the above
1.Controlled Mandatory ventilator: This is the fixed ventilation for definite time interevals, no provisions for spontaneous ventilatory effort,limited to intra-operative and immediate post-operative ventilation.
2.Assist control mode:This acts like controlled mandatory ventilator and when the pateint takes a spontaneous breathe, the ventilator is triggered to reach a preset level of vantilation.
3.Intermittent mandatory ventilator (IMV) and Synchronized IMV : In IMV the patient are free to breathe spontaneously between set ventilator breaths.Mandatory breathes may be synchronized with the patients spontaneous efforts.
1.Better gas distribution
2. Lower mean airway pressure
3. Less Haemodynamic disturbance
4. Less sedation is required
5. Weaning is easier
Pressure Support Ventilator
A preset inspiratory pressure is added to the ventilator circuit.
Controlled Mechanical Ventilator
Tidal volume and the respiratory rate are set in machine.
Assisted Mechanical Ventilator
Tidal volume is set and useful in weaning.
Assisted Controlled Ventilator
The tidal volume is set, the patient is allowed to respire himself.
Intermittent Mandatory Ventilator
The patient breathes by himself and in between breath rate is calculated. So machine is set.
Synchronised Mandatory Ventilator
When patient makes his effort the machine itself calculates his requirement.
Pressure Ratio Mandatory Ventilator
This sets pressure and with inspiration it is sent in by machine.
Inverse Ratio Ventilator
Normal inspiration: Expiration ratio is 1:1.5 to 1:2. So inspiration time is increased a useful in Acute respiratory distress syndrome.
Independent Lung Ventilator
Bifid endotracheal tubes are used in patient when one side of lung affected is more than other.
Setting up the Ventilator
1. Ensure the airway is secure
2. Ensure adequate sedation, opioids and muscle relaxants
3. Tidal volume: Normal (10 ml/Kg Body weight)
4. Respiratory rate: 14-16/min
5. Fraction of inspired oxygen: Usually 100% oxygen to start with there decreases slow.
Factors to be observed in case of ventilation
1. Vital signs like blood pressure, heart rate
2. Consciousness of patient
3. Secrection should be removed periodically
4. Checks alarm function of the ventilator
5. Oxygen saturation in the blood.
Classification of ventilator on Phases
Inspiratory phase: This phase has
a. Pressure generators: Exposes the lung to a pressure
b. Flow generators: Exposes the lung to the low of gas
Cycling or change over to expiration: This phase has
a. Pressure-cycled: In this phase pre-sets the pressure E.g.: Bird, Blease, Aarlow, Cyclator
b. Volume-cycled: This phase pre-sets the volume. E.g.: Bear, Bennett, Monaghan, Bromptom
c. Time-Cycled: This phase sets the length of the time E.g.: Servo, Clape, Phillips, Engstrom
Expiratory phase: PEEP and NEEP allow expiratory restriction or choice to be used so that expiration is slowed. PEEP is a positive pressure and NEEP is a negative pressure.
Cycling to inspiration: This phase sets function independently without patient so called controlled ventilation.
a. IMV: Intermittent mandatory ventilation: The gas supplied to the patient so that he can take what ever sized breathe he wishes and is able to.
b. MMV: Mandatory minute volume: This gives the patient slight assistance to her own spontaneous efforts.
c. CPAP: This phase is or mil to moderate acute respiratory insufficiency, median sternotomy and CABG. This increases functional residual capacity and improves oxygenation.
1. Due to endotracheal tube
2. Barotrauma increases pressure—Surgical emphysema, Pneumothorax
3. Fluid retention
4. Stress ulcers—Gastric or duodenal.