Mechanical ventilation

Posted by e-Medical PPT
Mechanical ventilation is a method to mechanically assist or replace spontaneous breathing.
Mechanical ventilation is indicated when the patient's spontaneous ventilation is inadequate to maintain life. It is also indicated as prophylaxis for imminent collapse of other physiologic functions, or ineffective gas exchange in the lungs.
Common medical indications for use include:

    * Acute lung injury (including ARDS, trauma)
    * Apnea with respiratory arrest, including cases from intoxication
    * Chronic obstructive pulmonary disease (COPD)
    * Acute respiratory acidosis with partial pressure of carbon dioxide (pCO2) > 50 mmHg and pH < 7.25, which may be due to paralysis of the diaphragm due to Guillain-BarrĂ© syndrome, Myasthenia Gravis, spinal cord injury, or the effect of anaesthetic and muscle relaxant drugs
    * Increased work of breathing as evidenced by significant tachypnea, retractions, and other physical signs of respiratory distress
    * Hypoxemia with arterial partial pressure of oxygen (PaO2) with supplemental fraction of inspired oxygen (FiO2) < 55 mm Hg
    * Hypotension including sepsis, shock, congestive heart failure
    * Neurological diseases such as Muscular Dystrophy and Amyotrophic Lateral Sclerosis

Modes of ventilation
Assist Control (AC). In this mode the ventilator provides a mechanical breath with either a pre-set tidal volume or peak pressure every time the patient initiates a breath.When a preset peak pressure is used this is also sometimes termed Intermittent Positive Pressure Ventilation or IPPV.
Synchronized Intermittent Mandatory Ventilation (SIMV). In this mode the ventilator provides a pre-set mechanical breath (pressure or volume limited) every specified number of seconds
Controlled Mechanical Ventilation (CMV). In this mode the ventilator provides a mechanical breath on a preset timing.
Pressure Support Ventilation (PSV). When a patient attempts to breathe spontaneously through an endotracheal tube, the narrowed diameter of the airway results in higher resistance to airflow, and thus a higher work of breathing.
Continuous Positive Airway Pressure (CPAP). A continuous level of elevated pressure is provided through the patient circuit to maintain adequate oxygenation, decrease the work of breathing, and decrease the work of the heart
Positive end-expiratory pressure (PEEP) is functionally the same as CPAP, but refers to the use of an elevated pressure during the expiratory phase of the ventilatory cycle.

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