Ventilators, types,modes,classification, indications, complications


Ventilators are the device used for artificial ventilation, (Helps you breathing) breathing machine. It is attached to a computer with knobs and buttons which is controlled by a therapist, nurse or doctor. 
Types of ventilators:-
  1. 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. 
  2. 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. 
  3. High frequency positive: This is of two types: 
  • Jet High frequency positive: 350breathes/min
  • Oscillator High frequency positive:1300breathes/min.
Modes of ventilation:-
This is of two types. They are:
  • Full ventilatory support
  • Partial ventilatory support
The following provides both of the above 
  1. Controlled Mandatory ventilators: This is the fixed ventilation for definite time intervals, no provision 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 patient takes a spontaneous breathe, the ventilator is triggered to reach a preset level of ventilation. 
  3. Intermittent mandatory ventilators (IMV), and Synchronized IMV: In IMV the patient are free to breathe spontaneously between set ventilator breathe. Mandatory breathes may be synchronized with the patient spontaneous efforts. 
  4. Pressure Support ventilators: A preset inspiratory pressure is added to the ventilator circuit during inspiration in spontaneously breathing patients. 
  5. Pressure ratio Mandatory ventilator: This sets pressure and with inspiration it is sent in by machine. 
  6. 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. 
  7. 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 (10ml/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. Secretion should be removed periodically
  4. Checks alarm function of the ventilator
  5. Oxygen saturation in the blood. 
Classification of ventilator on phases
  1. Inspiratory phase: this phase has
  • Pressure generators: Exposes the lung to a pressure
  • Flow generators: Exposes the lung to the flow of gas
      2. Cycling or change over to expiration: 
  • Pressure- cycled: This phase pre-sets the pressure eg.- Bird, Blease, Aarlow, Cyclator
  • Volume-cycled: This phase pre- sets the volume. 
  • Time- Cycled: This phase sets the length of the time
        3. 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. 
        4. Cycling to inspiration: This phase sets funtion independently without patient so called controlled ventilation. 
  • IMV: Intermittent mandatory ventilation. This gas supplied to the patient so that he can take ever sized breathe he wishes and is able to. 
  • MMV: Mandatory minute volume: This gives the patient slight assistance to her own spontaneous efforts. 
  • CPAP: This phase is or min to moderate acute respiratory insufficiency, median sternotomy and CABG. This increases functional residuals capacity and improves oxygenation. 

Indications:
  1. Respiratory failure
  2. Crush injury of the chest, severe scoliosis, major surgery
  3. Muscular cases like Tetanus, Myasthenia gravis, muscular dystrophy
  4. Pulmonary: Acute respiratory distress syndrome, Chronic obstructive pulmonary disease, Bronchial asthma and drowning. 
  5. CNS: Drugs, overdose of morphine, poisoning, epilepsy, Cerebrovascular accident and poliomyelitis. 
Complications:-
  1. Due to endotracheal tube
  2. Baro trauma increases pressure-- Surgical emphysema, Pneumothorax
  3. Fluid retention
  4. Stress ulcers-- Gastric or duodenum. 

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