Every Breath They Take: Part 2

PART 2 of 2

In this episode, Dr. Michael Lauria is joined by several EM/Critical Care and Transport/Retrieval physicians as we discuss the management of acute respiratory distress syndrome (ARDS) in the critical care transport setting. We cover the pathophysiology of ARDS, the criteria for diagnosis, and the basics of lung protective ventilation. We also explore the concept of driving pressure and its role in determining optimal ventilation settings. The conversation highlights the importance of individualizing treatment based on patient characteristics and monitoring parameters such as plateau pressure, driving pressure, and compliance. 

Our team provides practical tips for adjusting ventilation settings and emphasizes the need for ongoing assessment and optimization. In the previous episode, we started out with some fundamental concepts of mechanical ventilation: the approach to low tidal volumes in ARDS patients and the use of point-of-care blood gases. We also explored the use of steroids in ARDS, the target oxygen saturation levels, and the use of paralysis in unstable patients. In addition, we touched on controversial topics such as inhaled pulmonary vasodilators in ARDS as well as the application of evidenced-based therapies such as proning in the transport environment (in this episode, part 2). Also, in this part of the conversation, we review the use of alternative ventilator modes, such as APRV, and the indications for ECMO in refractory ARDS. We emphasize the importance of optimizing conventional, evidence-based therapies before considering ECMO and highlight the need for clear guidelines and training when using these advanced interventions. We also discuss the challenges and potential complications associated with ECMO. 

Takeaways

• ARDS is a syndrome characterized by acute onset, bilateral infiltrates on imaging, and hypoxemia.
• The diagnosis of ARDS is based on criteria such as acute onset, infectious or inflammatory etiology, bilateral opacities on imaging, and impaired oxygenation.
• Lung protective ventilation aims to minimize lung injury by using low tidal volumes (6-8 ml/kg), maintaining plateau pressures below 30 cmH2O, and keeping FiO2 below 60%.
• Driving pressure, the difference between plateau pressure and PEEP, is a marker of lung compliance and can be used to guide ventilation adjustments.
• Individualized management is crucial, considering factors such as patient characteristics, response to therapy, and monitoring parameters.
• Regular assessment and optimization of ventilation settings are necessary to ensure effective and safe management of ARDS. 
• Low tidal volumes should be based on the patient's pH and PCO2, with a focus on maintaining a safe pH level.  If crews are unable to measure these parameters not decreasing tidal volumes lower than 4 cc/kg is reasonable.
• Point-of-care blood gases are essential for monitoring patients on low tidal volumes and making adjustments as needed.
• Oxygen saturation targets should be individualized based on the patient's condition and physiology, with a range above 88-92% often considered reasonable. However, this issue is controversial, and occasionally, lower saturations are considered acceptable.
• Steroids may be beneficial in ARDS patients, especially those with severe pneumonia, but the timing and dosing should be determined based on the patient's specific situation.
• Paralysis can be considered in unstable ARDS patients who cannot tolerate low tidal volumes, but it should be used selectively and in conjunction with deep sedation.
• The use of inhaled pulmonary vasodilators in ARDS is controversial, and no significant mortality benefit has been demonstrated. However, they may be considered a salvage therapy in patients on their way to an ECMO center or when other interventions have been exhausted. Inhaled pulmonary vasodilators, such as epoprostenol, can improve oxygenation and pulmonary arterial pressure in patients with ARDS and RV failure.
• The use of inhaled pulmonary vasodilators should be based on individual patient characteristics and the availability of resources.
• Proning in transport has been shown to be safe and effective.  It should be considered for select cases, such as patients with high pulmonary arterial pressure or basilar atelectasis.
• Transport teams should be prepared to continue inhaled pulmonary vasodilator therapy if the patient is already receiving it.
• ECMO should be considered when conventional therapies have failed, and the patient's condition is reversible and not contraindicated.
• ECMO transport requires specialized training, clear guidelines, and ongoing communication with the receiving center.
• Alternative ventilator modes, such as APRV, have not shown significant benefit in large trials.  Their use is controversial but not unreasonable in certain circumstances.  Implementing these settings requires training, education, and clear protocols.  Generally speaking, they should be used judiciously and in consultation with the receiving physician.
• Optimizing conventional therapies and providing high-quality care can often obviate the need for ECMO.
• Transport teams should be proactive in discussing potential ECMO candidates with the receiving physician and considering the appropriateness of ECMO for each patient.

References:

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