Meaning: Mechanical ventilator is a device that inflates the lungs by positive pressure which is able to carryout alveolar ventilation and maintain lung mechanics.
1) Mechanical failure of ventilation.
a) Neuromuscular disease
b) CNS depression (drug intoxication,respiratory depressants and cardiac arrest )
c) Inefficiency in thoracic cage for generating pressure gradients necessary for ventilation( chest injury, thoracic malformation)
d) When ventilatory support is needed post operatively
2) Disorders of pulmonary gas exchange.
a) Acute respiratory failure
b) Chronic respiratory failure
c) Left sided heart failure
d) Pulmonary disease resulting in diffusion abnormality.
e) Pulmonary disease resulting V/Q (Ventilation/perfusion ratio) mismatch.
f) acute lung injury
Methods of ventilation
1.Non invasive ventilation
- Non invasive Negative pressure ventilation
- Non invasive Positive pressure ventilation
2.Invasive methods of ventilation (positive pressure ventilation)
- Volume targeted (volume cycled) ventilation
- Pressure targeted (pressure cycled) ventilation
- Time cycled ventilation
Non invasive ventilation
No artificial airway is necessary, patient must be able to control and protect own airway.
Indicated for patient' s with respiratory neuromuscular problems, or as adjunct to weaning from positive pressure ventilators.
Non invasive negative pressure ventilation
- Patients with central sleep apnea or neuromuscular problems who require ventilator support during sleep.
- Device typically encloses the thorax of the patient and allow the head and airway access to the ambient atmosphere.
- Applies negative pressure around the chest wall → Increased intra-thorasic pressure changes prompt inspiration to occur
- Example: iron lung tank ventilators
Non invasive positive pressure ventilation (NPPV)
- Is a therapy to manage chronic respiratory failure or acute respiratory insufficiency which is expected to resolve quickly.
- Breaths are delivered through tight-fit face masks.
- NPPV provides low levels of continuous positive airway pressure (CPAP) to facilitate gas exchange.
- Some devices apply positive pressure during both inspiration and expiration and are referred as bilevel positive airway pressure (BiPAP) device.
Invasive methods of ventilation
- Requires a stable artificial airway.
- Most common method of ventilating patient in acute care setting.
- This method uses positive pressure to force air into the lungs via artificial airway.
Volume targeted ventilation
- A specific volume for delivery of inspiration is set.
- The ventilator is set to allow airflow into the lungs until a preset volume has been reached.
- Terminates the inspiratory phase when preset volume of gas is delivered.
Pressure targeted ventilation
- A specific positive inspiratory pressure (PIP) is set for delivery of inspiration.
- The ventilator is set to allow air to flow into the lungs until preset pressure has been reached.
- Once the pressure is reached, a valve closes and expiration begins.
- Time-cycled ventilators deliver oxygenation over a preset time period.