Inverse ratio ventilation
Encyclopedia
Inverse ratio ventilation (IRV) is not necessarily a mode of mechanical ventilation though it may be referred to as such. IRV is a strategy (method or style) of ventilating the lungs in such a way that some inspired air is not allowed to be exhaled, creating intrinsic positive-end expiratory pressure (autoPEEP) and allowing for a constant inflation of the lungs, ensuring they remain "recruited" (meaning they participate in gas exchange and are not allowed to deflate to get stuck together or tighten up). The primary goal for IRV is improved oxygenation by forcing inspiratory time to be greater than expiratory time (example: inhale is 3 seconds and exhalation is 1 second) increasing the mean airway pressure and potentially improving oxygenation. Normal I:E ratio is 1:2, 1:3, 1:4, so forcing the I:E to be 2:1, 3:1, 4:1, (or even as high as 20:1) is the source of the term for the strategy.
IRV has never been shown to improve important clinical outcomes, such as mortality, duration of mechanical ventilation, or duration of ICU stay. The preponderance of evidence suggests that IRV improves oxygenation, although the evidence is weak and characterized by low quality, conflicting studies.
, the type of IRV did not affect mortality.
). IRV also appears to increase the risk of pulmonary barotrauma independent of auto-PEEP. In a study of 14 patients undergoing mechanical ventilation with PC-IRV, the incidence of pneumothorax was 29 percent despite the lack of measurable auto-PEEP.
mode, also known by the brand name "BiVent". This employs an extremely high inverse ratio in a continuous pressure system similar to biphasic positive airway pressure but with several additional variables.
IRV has never been shown to improve important clinical outcomes, such as mortality, duration of mechanical ventilation, or duration of ICU stay. The preponderance of evidence suggests that IRV improves oxygenation, although the evidence is weak and characterized by low quality, conflicting studies.
Types
IRV can be performed during pressure-controlled ventilation (PC-IRV) or volume-controlled ventilation (VC-IRV). Neither is clearly superior to the other. In a multicenter, randomized trial that compared PC-IRV to VC-IRV in patients with acute respiratory distress syndromeAcute respiratory distress syndrome
Acute respiratory distress syndrome , also known as respiratory distress syndrome or adult respiratory distress syndrome is a serious reaction to various forms of injuries to the lung....
, the type of IRV did not affect mortality.
Associated risk
The shorter expiratory time during IRV increases the risk of auto-PEEP and its associated development of problems (eg, pulmonary barotrauma, hypotensionHypotension
In physiology and medicine, hypotension is abnormally low blood pressure, especially in the arteries of the systemic circulation. It is best understood as a physiologic state, rather than a disease. It is often associated with shock, though not necessarily indicative of it. Hypotension is the...
). IRV also appears to increase the risk of pulmonary barotrauma independent of auto-PEEP. In a study of 14 patients undergoing mechanical ventilation with PC-IRV, the incidence of pneumothorax was 29 percent despite the lack of measurable auto-PEEP.
Modes that utilize IRV
The most popular mode that utilizes IRV is the airway pressure release ventilationAirway pressure release ventilation
Airway pressure release ventilation — is a relatively new strategy of ventilation that became commercially available in the United States in the mid-1990s. APRV differs fundamentally from that of conventional positive-pressure ventilation...
mode, also known by the brand name "BiVent". This employs an extremely high inverse ratio in a continuous pressure system similar to biphasic positive airway pressure but with several additional variables.