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The pathophysiology of acute respiratory distress syndrome involves fluid accumulation in the lungs not explained by heart failure (noncardiogenic pulmonary edema). It is typically provoked by an acute injury to the lungs that results in flooding of the lungs' microscopic air sacs responsible for the exchange of gases such as oxygen and carbon dioxide with capillaries in the lungs. [1]
The Berlin definition requires a minimum positive end expiratory pressure (PEEP) of 5 cm H 2 O for consideration of the Pa O 2 /Fi O 2 ratio. This degree of PEEP may be delivered noninvasively with CPAP to diagnose mild ARDS. The 2012 "Berlin criteria" are a modification of the prior 1994 consensus conference definitions (see history). [10]
A small amount of applied PEEP (4 to 5 cmH 2 O) is used in most mechanically ventilated patients to mitigate end-expiratory alveolar collapse. [6] A higher level of applied PEEP (>5 cmH 2 O) is sometimes used to improve hypoxemia or reduce ventilator-associated lung injury in patients with acute lung injury, acute respiratory distress syndrome ...
With a normal P a O 2 of 60–100 mmHg and an oxygen content of F I O 2 of 0.21 of room air, a normal P a O 2 /F I O 2 ratio ranges between 300 and 500 mmHg. A P a O 2 / F I O 2 ratio less than or equal to 200 mmHg is necessary for the diagnosis of acute respiratory distress syndrome by the AECC criteria . [ 7 ]
This is calculated by dividing the PaO2 by the FiO2. Example: patient who is receiving an FiO2 of .5 (i.e., 50%) with a measured PaO2 of 60 mmHg has a PaO 2 / FiO 2 ratio of 120. In healthy lungs, the Horowitz index depends on age and usually falls between 350 and 450.
Settings that can be adjusted in HFJV include 1) inspiratory time, 2) driving pressure, 3) frequency, 4) FiO2, and 5) humidity. Increases in FiO2, inspiratory time, and frequency improve oxygenation (by increasing "auto-PEEP" or pause pressure), while an increase in driving pressure and a decrease in frequency improve ventilation.
In ventilated patients, pulse oximetry is commonly used when titrating FIO2. A reliable target of Spo2 is greater than 95%. [47] The total PEEP in the patient can be determined by doing an expiratory hold on the ventilator. If this is higher than the set PEEP, this indicates air trapping. The plateau pressure can be found by doing an ...
Respiratory failure is classified as either Type 1 or Type 2, based on whether there is a high carbon dioxide level, and can be acute or chronic. In clinical trials, the definition of respiratory failure usually includes increased respiratory rate , abnormal blood gases (hypoxemia, hypercapnia, or both), and evidence of increased work of breathing.