Impact of mechanical ventilation on the pathophysiology of progressive acute lung injury

Abstract

Nieman GF, Gatto LA, Habashi NM. Impact of mechanical ventilation on the pathophysiology of progressive acute lung injury. J Appl Physiol 119: 1245-1261. First published October 15, 2015 doi:10.1152/japplphysiol.00659.2015The earliest description of what is now known as the acute respiratory distress syndrome (ARDS) was a highly lethal double pneumonia. Ashbaugh and colleagues (Ashbaugh DG, Bigelow DB, Petty TL, Levine BE Lancet 2: 319-323, 1967) correctly identified the disease as ARDS in 1967. Their initial study showing the positive effect of mechanical ventilation with positive end-expiratory pressure (PEEP) on ARDS mortality was dampened when it was discovered that improperly used mechanical ventilation can cause a secondary ventilator-induced lung injury (VILI), thereby greatly exacerbating ARDS mortality. This Synthesis Report will review the pathophysiology of ARDS and VILI from a mechanical stress-strain perspective. Although inflammation is also an important component of VILI pathology, it is secondary to the mechanical damage caused by excessive strain. The mechanical breath will be deconstructed to show that multiple parameters that comprise the breath-airway pressure, flows, volumes, and the duration during which they are applied to each breath-are critical to lung injury and protection. Specifically, the mechanisms by which a properly set mechanical breath can reduce the development of excessive fluid flux and pulmonary edema, which are a hallmark of ARDS pathology, are reviewed. Using our knowledge of how multiple parameters in the mechanical breath affect lung physiology, the optimal combination of pressures, volumes, flows, and durations that should offer maximum lung protection are postulated. acute lung injury; lung; pathophysiology ventilator; VILI THE POLIO EPIDEMIC OF 1916 inspired many treatment attempts including vitamin C therapy, hydrotherapy, and electrotherapy, but no effective therapy was found until Philip Drinker's group invented negative pressure mechanical ventilation-the iron lung. Their landmark paper, "The use of a new apparatus for the prolonged administration of artificial respiration: I. A fatal case of poliomyelitis," published in 1929, demonstrated the effective clinical use of this device (Fig. 1) (38). The concept of conversion from negative to positive pressure ventilation was based on technical advances that were made during World War II to deliver pressurized oxygen to high-altitude fighter and bomber pilots. Concomitant with these technologic advances in mechanical ventilation was the realization that what was originally thought to be a universally fatal form of double pneumonia was indeed a unique clinical entity that we now call the acute respiratory distress syndrome (ARDS). In a 1967 seminal paper published in The Lancet, Ashbaugh et al. (10) first identified and described ARDS as a collection of pathologic abnormalities that can be caused by many unrelated insults such as sepsis, hemorrhagic shock, pneumonia, and trauma to name a few. The disease and the ventil...

The role of high airway pressure and dynamic strain on ventilator-induced lung injury in a heterogeneous acute lung injury model

“…However, mechanical ventilation is a double-edged sword: although necessary for respiratory support, when set improperly, it can cause a secondary ventilator-induced lung injury (VILI) that can exacerbate ARDS mortality [3]. Thus, identifying the optimal ventilator settings necessary to minimize VILI has received a great deal of basic science [4] and clinical investigation [5]. …”

Physiology in Medicine: Understanding dynamic alveolar physiology to minimize ventilator-induced lung injury

“…PULMONARY PHYSIOLOGY AND pathophysiology in positive pressure mechanical ventilation have been studied for decades (47). Preemptive application of adequate positive end-expiratory pressure (PEEP) can reduce pulmonary edema in animal models of high vascular pressure- (14), high alveolar surface tension- (39), and high permeability-induced (53) acute respiratory distress syndrome (ARDS; 47). Knowing that adjustments in the mechanical ventilator settings (i.e., PEEP) can protect the acutely injured lung is key to managing the critically ill patient, since the mainstay of ARDS treatment is still supportive in the form of mechanical ventilation.…”

“…In the current standard of care, ventilator adjustments (Vt, PEEP, and Pplat) are made on the basis of oxygenation and airway pressure, not in response to lung mechanics (13), and VILI may or may not be averted (5,7). Although protective ventilation resulted in an initial drop in mortality, it has been disappointing that the current standard-of-care protective ventilation strategy has not further reduced mortality (47), and Villar et al (63) underscore the critical need to better understand the impact of the mechanical breath on alveolar and alveolar duct inflation and deflation, and the mechanisms of ARDS and VILI at the alveolar level, to develop protective ventilator strategies that work.…”

“Open the lung and keep it open”: a homogeneously ventilated lung is a ‘healthy lung’

“…This is an important study since it supports our current understanding of the pulmonary pathophysiology associated with ARDS and the role played by mechanical ventilation in either preventing or exacerbating this initial lung injury. A recent review on the impact of mechanical ventilation during progressive acute lung injury shows that a physiologically based ventilation strategy can block all of the pathologic tetrad that are the hallmarks of ARDS (15). Multiple combinations of mechanical breath parameters, most often Vt and PEEP, in many animal models of ARDS have been shown to reduce pulmonary vascular permeability, pulmonary edema, preserve surfactant function and stabilize alveoli, minimizing strain-induced tissue damage known as atelectrauma (15).…”

“…A recent review on the impact of mechanical ventilation during progressive acute lung injury shows that a physiologically based ventilation strategy can block all of the pathologic tetrad that are the hallmarks of ARDS (15). Multiple combinations of mechanical breath parameters, most often Vt and PEEP, in many animal models of ARDS have been shown to reduce pulmonary vascular permeability, pulmonary edema, preserve surfactant function and stabilize alveoli, minimizing strain-induced tissue damage known as atelectrauma (15). Thus, the physiologic foundation for protective mechanical ventilation is well established and all that is necessary is to identify the optimal combination of mechanical breath parameters (e.g., airway pressures, volumes, flows, rates and the duration that they are applied to the lung during both inspiration and expiration) that maximize lung tissue protection.…”