23-05-2012, 12:02 PM
Mechanical Ventilation
MECHAN~1.PPT (Size: 811 KB / Downloads: 65)
Origins of mechanical ventilation
Negative-pressure ventilators (“iron lungs”)
Non-invasive ventilation first used in Boston Children’s Hospital in 1928
Used extensively during polio outbreaks in 1940s – 1950s
Positive-pressure ventilators
Invasive ventilation first used at Massachusetts General Hospital in 1955
Now the modern standard of mechanical ventilation
Principles (2): Oxygenation
Alveolar-arterial O2 gradient (PAO2 – PaO2)
Equilibrium between oxygen in blood and oxygen in alveoli
A-a gradient measures efficiency of oxygenation
PaO2 partially depends on ventilation but more on V/Q matching
Oxygenation in context of ICU
V/Q mismatching
Patient position (supine)
Airway pressure, pulmonary parenchymal disease, small-airway disease
Adjustments: FiO2 and PEEP
Pressure-cycled modes
Pressure Support Ventilation (PSV)
Pressure Control Ventilation (PCV)
CPAP
BiPAP
Volume-cycled modes
Control
Assist
Assist/Control
Intermittent Mandatory Ventilation (IMV)
Synchronous Intermittent Mandatory Ventilation (SIMV)
CPAP and BiPAP
Parameters
CPAP – PEEP set at 5-10 cm H2O
BiPAP – CPAP with Pressure Support (5-20 cm H2O)
Shown to reduce need for intubation and mortality in COPD pts
Indications
When medical therapy fails (tachypnea, hypoxemia, respiratory acidosis)
Use in conjunction with bronchodilators, steroids, oral/parenteral steroids, antibiotics to prevent/delay intubation
Weaning protocols
Obstructive Sleep Apnea