Today our topic of discussion is Positive Pressure Ventilation.
Positive Pressure Ventilation
Positive Pressure Ventilation
Unlike the earlier models of negative pressure ventilators such as druncar and Shaw tank type ventilator (iron lung) recent ventilators function on positive pressure ventilation. Positive pressure is applied at the patient’s airway through an endotracheal or tracheostomy tubes. Clinical use of positive pressure includes intermittent positive pressure ventilation.
Positive pressure brings about, complex changes in the body. It may reduce the cardiac output and hypoperfusion of the kidneys with an alternation in urine output. A reduction in venous drainage secondary to increased intrathoracic positive pressure could stimulate OSMO receptors in the hypothalamus to mediate secretion of ADH which in turn will reduce the urine output.
Types of Positive Pressure Ventilators
- Commonly the ventilators are classified by their method of cycling from the inspiratory phase to the expiratory phase in the change over from inspiratory to expiratory phase
- The term cycle is used to indicate a terminating event.
Volume cycled: This is the most common form of ventilator cycling. They terminate the inspiratory phase when a designed volume of the gas is delivered into the ventilator circuit (12-15 mL/kg body weight). They deliver the predetermined volume regardless of changing lung compliance.
Airway pressure will increase as compliance decreases and it varies from patient to patient and breath to breath. As a safety device many ventilators have a pressure limiting value, fixed or adjustable which prevents excessive
build up within the patient ventilator system on any given breath. Depending upon the type of pressure regulating device in use the breath may be terminated before the entire volume has been delivered to the patient.
This, however, can be monitored with exhaled volume measuring devices available on most volume ventilators. These devices monitor for leaks in the patient circuit. The common volume cycled ventilators used are Bennet MA 1,2. Boums, LS 104-105, Bournas Bear 1, Ohio 560, Modern ventilators which are compact and computerized are available in market now.
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