Ventilator-associated lung injury (VALI), an acute lung injury that can develop during mechanical ventilation, increases complications and mortality risk in the intensive care unit.
By Phyllis Hanlon
Since 1994 when the National Heart, Lung, and Blood Institute (NHLBI), National Institutes of Health (NIH), established the ARDS Network “to efficiently test promising agents, devices, or management strategies to improve the care of patients with ARDS (acute respiratory distress syndrome),” many, but not all, hospitals have complied with the recommendations.1 In fact, during the last 22 years, a number of other strategies have been attempted to achieve appropriate ventilation without the risk of ventilator-associated/induced lung injury (VALI/VILI).
Even though 6cc/kg patient body weight of tidal volume has become the “ideal,” Robert Duncan Hite, MD, chairman, Critical Care Medicine at Cleveland Clinic, questions its validity. “There is evidence it may be too big. Admittedly, 6 cc is much safer than 12,” he said. “Over 24 hours the patient occasionally asks the machine to take a bigger breath. During the course of a day if it’s 7.2, is that unsafe? We don’t know.”
Hite pointed out that current techniques and tools employ a “straightforward approach,” ie, they reduce the amount of volume to reduce the risk of injury. “But synchrony between the patient and the ventilator is the biggest single challenge. On a breath-by-breath basis the patient is interacting with the device. There is a need to constantly balance,” he said. “You can’t control every breath. The technology on the vent allows you to do that, but it might not be consistent with the patient’s needs.”
Furthermore, current practices focus on the moment the respiratory therapist and physician are standing at the bedside looking at the ventilator, according to Hite. “That’s important, but I think the next level is to develop the capability of capturing what’s happening when they are not there. The more we can utilize the ability to summarize information from the patient during the day or during a specific time, the better the outcome will be,” he said. “We can use the trending data to see the range of volume, the frequency of distribution over six to 24 hours, an element of utilization of the device that could give us a better advantage.”
Experience and training is key to understanding the nuances of the ventilator as it performs its functions, according to Hite. “There is patient-to-patient variation. In fact, within one patient there might be variation during the day or over the course of hours. To understand all the nuances of what the software is supposed to do takes a lot of experience. We know that giving too big a volume is a reasonably predictable way to cause injury,” he said, adding that understanding other variables, such as the size of the breath and the amount of change in pressure, will help predict a good outcome.
Edwin Coombs, MA, RRT-NPS, ACCS, FAARC, Dräger, noted that positive end expiratory pressure (PEEP) is currently the ventilator parameter that is most often personalized to the individual patient’s lung pathology and used to keep the lung open and stable. “Personalized PEEP can be set using a variety of techniques most of which require a lung recruitment maneuver,” he said. “However, when using APRV (airway pressure release ventilation), the lung is kept open and stable by setting a very short expiratory duration to maintain both a level of PEEP but, more important, to be shorter than the collapse time constant of the alveolus.”
Two studies,2-3 one from 2005 and a more recent one from 2016, cite the importance of “measuring the change in the slope of the expiratory flow curve, which becomes steeper with increasing lung injury. Coombs explained that Dräger’s unique feature, known as “Auto-Release,” tracks the patient’s lung dynamics and adjusts the Tlow setting to maintain the desired peak expiratory flow rate (PEFR).
Creating appropriate ventilator protocols requires collaboration, said Coombs. “When developing a mechanical ventilation protocol to reduce or prevent VALI/VILI, an inter-disciplinary group of physicians, respiratory therapists and critical care nurses should be created to examine the current standards of care, controversies or questions surrounding studies, promising new approaches, and the like. The goal of avoiding alveolar distention and alveolar shear-stress should be kept in mind,” he said.
“Regardless of the specific protective approach selected, the protocol should be applied consistently with well-trained clinicians operating the ventilator. One consideration of executing a protocol using Dräger ventilator technology is to base initial parameter settings based on ideal body weight, which can support standardization when initiating mechanical ventilation support.”
Today’s ventilators are more sophisticated and can carefully titrate gases based on the patient’s desire. Newer models blend three variables: flow, pressure and volume. Hite explained that these devices can adapt to patient need and are better able to provide flow and control volume and pressure concurrently on a continuous basis. “If all patients were on a device with sophisticated ability to titrate the three variables, it would make a difference in a patient’s comfort and the outcome,” he said.
Even with enhanced features, ventilator settings still need to be adjusted at times. When making adjustments, clinicians should consider how these changes will impact the microenvironment (ie alveoli and alveolar ducts), Coombs pointed out. “Thus, a major challenge is better understanding of how mechanical ventilator settings impact alveolar microstrain, where strain is the change in alveolar size in response to a given stress; in the case of mechanical ventilation the stress is the size of the tidal volume,” Coombs said.
A 2014 study4 examined which components of the mechanical breath caused the most and the least alveolar microstrain and found that APRV, with a prolonged inspiratory phase and a brief expiratory release phase, was optimal at reducing strain at the alveolar level.
Another study5 has shown that reducing whole lung dynamic strain by reducing tidal volume and increasing PEEP could prevent ARDS in a large animal model. “Combined, these studies suggest that if the mechanical breath can be delivered to induce minimal dynamic strain that the lung will be protected,” said Coombs.
Additionally, the clinician should consider the potential impact of the mechanical breath at causing both “volutrauma” and “atelectrauma.” Coombs said, “Understanding these two VILI mechanisms, and using a ventilator strategy that creates a homogeneously ventilated lung will minimize the risk of VALI/VILI, which would exacerbate ARDS incidence, morbidity and mortality.” The 2013 study5 found that the normal homogeneous lung can tolerate higher plateau pressures (ie: 40 cm H2O) when not exposed to cyclic collapse during exhalation.
Device Manufacturers’ Role
Once a hospital purchases a mechanical ventilator, or any other medical device, the manufacturer generally provides in-service education for their devices, which might include hands-on training as well as didactic training to raise the level of understanding in how their respective devices operate, according to Coombs. “To reduce variability in a lung protective approach, the importance of establishing a protocol cannot be understated, and requires the facility to have a multi-disciplinary team working together,” he said. “Understanding not only training opportunities but how an integrated approach to providing overarching solutions in the ICU, NICU, and OR to improve workflow, safety, efficiency and cost-effectiveness are key when having discussions with vendors/manufacturers.”
In addition to routine device in-services, Dräger provides a number of value added education services for its customers and respiratory therapists.
“Our ‘Breath Ahead’ education and networking portal provides the RT marketplace the opportunity to discuss topics with key leaders in the field as well as receive complimentary education credits. Dräger customers have access to our partner, Intensive Care Online (ICON) where monthly webinars, online training, 24×7 live phone support and other supportive/educational opportunities are provided. The interdisciplinary staff at ICON includes physicians, nurses, respiratory therapists and pharmacists who can help transfer the advancements in treatment enabled by modern ventilators into improved outcomes for customers,” Coombs said.
“Throughout the year, Dräger offers regional conferences and often supports high-fidelity lab training. Additionally, as a corporate partner of the AARC, Dräger sponsors various education programs and key initiatives for its members.”
ARDSNet Follow Up
The greater Colorado academic system, which includes the University of Colorado, Denver Health and Jewish National Health, participated in ARDSNet, according to Kenneth E. Lyn-Kew, MD, section head, Critical Care Medicine, assistant professor in the Department of Medicine, Division of Pulmonary, Critical Care and Sleep Medicine at National Jewish Health in Denver.
Lyn-Kew reported that National Jewish is now participating in a follow up project. PETAL (Prevention and Early Treatment of Acute Lung Injury) builds on the goals, strengths and accomplishments of ARDSNet and is also exploring new therapies. “Twelve clinical centers and one clinical coordinating center, funded by the NHLBI, will test new treatments or approaches to improve clinical outcomes,” said Lyn-Kew. “PETAL forces the ICU to continue to ensure it’s delivering state-of-the-art care for the patient. The hallmark is low tidal volume ventilation. The PETAL Network will continue to look at ways to minimize and prevent ARDS.”
Moving forward, Lyn-Kew foresees additional studies regarding lung protection strategies. “We learned from the ARDSNet after 20 years of research that other than turning down the pressure and volume in the ventilator there has been an arm’s length of other things to protect the lung that haven’t worked, such as steroids, high levels of PEEP, multiple drug studies,” he said. “There will be continued collaborative multi-center trials looking for additional technology and therapies.”
Until a consensus can be developed, which requires further study, a clinician should utilize evidence-based medicine to guide decision-making, according to Coombs. “The bedside clinician should have a full understanding of the ventilator being used, its advantages and its limitations. The approach to mechanical ventilation should be interdisciplinary and protective in nature to avoid VILI/ARDS, which should include early goal-directed therapy for patients identified as ‘at risk’ or susceptible to VILI,” he said. “This should address low tidal volume, moderate to high PEEP levels, and opportunity to evaluate dynamic pulmonary mechanics to consider APRV with a personalized mechanical breath profile.”
Phyllis Hanlon is a contributing writer to RT. For further information, contact [email protected]
Editor’s note: this article was originally published in the September 2016 issue of RT magazine.
- Villar, J. Sulemanji, D. Kacmarek, RM. “The acute respiratory distress syndrome: incidence and mortality, has it changed?” Current Opinion Critical Care, 2014; 20(1)3-9.
- Habashi, N. “Other approaches to open-lung ventilation: Airway pressure release ventilation.” Critical Care Medicine, March 2005, 33 (3), S228-S240.
- Sumeet V. Jain, Michaela Kollisch-Singule, et al. “The 30-year evolution of airway pressure release ventilation (APRV),” Intensive Care Medicine, 2016, 4:11, 1-18.
- Michaela Kollisch-Singule, MD, Bryanna Emr, et al. “Airway Pressure Release Ventilation Reduces Conducting Airway Micro-Strain in Lung Injury.” Journal of American College of Surgery, 2014, 09.011, 968-974.
- Alessandro Protti, MD1; Davide T. et al. “Lung Stress and Strain during Mechanical Ventilation: Any Difference between Statics and Dynamics?” Critical Care Medicine, April 2013, 41:4, 1046-1055.