10/3/2023 0 Comments Ardsnet tidal volume chartPersistent hypoxemia was managed by increasing P-Low.This prevents patients from ever being exposed to extremely high levels of pressure. The protocol these authors used did some clever things to avoid this: Higher pressures lead to worsening lung injury, and so on as the ventilator beats up the lung: The sicker they are, the higher the pressures they require. When patients are placed on conventional ventilation, they often wind up in the vicious cycle shown below. Several components of the APRV protocol used by these authors deserve attention: #1: Limiting P-High However, this phenomenon might be generalizable to actual practice as well.Īlthough APRV is often considered as a single “intervention,” there are innumerable ways to perform APRV. The APRV protocol may require more effort, causing patients to receive more attention.More intensive titration of sedating medications may have promoted lower levels of sedation and earlier extubation. Within the APRV group, respiratory therapists were allowed to titrate analgesics and sedatives to promote spontaneous breathing.Open-label (unavoidable, given differences between APRV and conventional ventilation). Patients with APRV were more awake, receiving less sedative and pain medication: Patients treated with APRV required fewer additional therapies (proning, paralysis, and recruitment).ĪPRV was well tolerated hemodynamically, with higher blood pressure and lower heart rates. The primary endpoint was the number of ventilator-free days, which was dramatically greater in the APRV group. Patients with ARDS were randomized to receive APRV versus low tidal-volume ventilation. This is by far the largest RCT of APRV to date. A fresh RCT may help resolve this… Zhou et al 2017 APRV may be viewed as a “new” technique by medical intensivists, whereas it's been used for decades in surgical ICUs with great results ( Andrews 2013). This has led to a paradoxical situation, where APRV is often used in surgical ICUs but not medical ICUs. Weaning APRV can be a tedious process of gradually reducing the pressure.Use of large tidal volumes in the release breaths (>8-10 cc/kg) seems to violate the principles of lung-protective ventilation.Lack of evidence in the medical ICU (most experience originates from the surgical ICU).Lack of prospective RCT evidence showing a benefit of APRV versus conventional low tidal-volume ventilation.However, until recently there were several drawbacks to APRV: Since APRV involves relatively infrequent release breaths and a lower minute ventilation than conventional ventilation, this should make APRV more lung-protective (1). Ventilator-induced lung injury might be a product of the tidal volume multiplied by the frequency of ventilation (which determines the total energy absorbed by the lung figure below).Active breathing may improve venous return and cardiac output.Rapid release breaths may facilitate secretion clearance, reducing the risk of ventilator-associated pneumonia.Diaphragmatic activity promotes recruitment and ventilation of the lung bases.APRV is compatible with early-mobility initiatives (some videos from Maryland Shock Trauma feature patients walking on APRV). This may avoid complications such as myopathy and delirium. APRV is better tolerated than conventional low tidal-volume ventilation, obviating the need for paralytics and deep sedation.This allows achieving a high mean airway pressure with a relatively low plateau pressure: Great idea, little hard evidence.ĪPRV is conceptually very appealing, for example: A single pressure (P-High) is used both to recruit the lungs and also as the driving pressure for exhalation. You can't have your cake and eat it too (high PEEP and low plateau).ĪPRV solves this problem by flipping the pressure curve upside-down. Therefore, increasing the PEEP forces the plateau pressure to rise (figure below). Driving pressure can be reduced a bit, but it can't be reduced too much without causing severe hypoventilation. The obstacle to opening the lung using conventional ventilation is basic arithmetic. A recent editorial in JAMA speculated about whether the open-lung strategy is dead ( Sahetya 2017). However, subsequent efforts to advance this concept further have floundered, with several failed attempts to manipulate PEEP. ARDSnet low tidal-volume ventilation was a success for the open lung concept. Open-lung ventilation refers to the concept of recruiting the lung and then ventilating gently with small tidal volumes, to avoid either over-distension or atelectotrauma (lung damage from cyclical opening/closing of alveoli). Airway Pressure Release Ventilation (APRV): Solution to the open-lung challenge?
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