We read with interest “Randomized Feasibility Trial of a Low Tidal Volume-Airway Pressure Release Ventilation Protocol Compared With Traditional Airway Pressure Release Ventilation and Volume Control Ventilation Protocols” by Hirshberg, et al.(1) In our opinion, the authors’ conclusion is not supported by their data; namely large-scale trials using airway pressure release ventilation (APRV) targeting Low Tidal Volumes (LVt) is not feasible absent a reproducible protocol to consistently deliver LVt using APRV. We have concerns recently published data was ignored. The authors imply Vt >6cc/kg in isolation is harmful regardless of the resting lung volume. However, LVt is not universally protective nor high Vt universally injurious. For example, exercise physiology studies confirm normal lungs withstand Vt >3 liters without damage, suggesting the state of the lung is an important consideration. Further, Vt normalized to compliance (ΔP=Vt/Comp) (i.e. driving pressure) predicts outcome and barotrauma rather than Vt alone. The authors do not discuss that despite larger Vt displayed on the ventilator, APRV has shown greater alveolar homogeneity and stability with lower alveolar Vt and strain as compared to LVt.(2) Additionally, Silva et al., showed LVt upregulated amphiregulin expression whereas TCAV did not, suggesting the TCAV protocol does not produce overdistension.(3)
New data indicates regional and heterogenous lung strain, and not over-distension of the “baby lung”, is necessary for VILI progression. Cereda, et al, using paired CT images, identified unstable inflation as areas of injury progression and worsening compliance.(4) Xin, et al similarly showed minimizing unstable inflation with early prone position contains injury progression where LVt did not.(5) Our data and other suggest limiting unstable inflation as paramount in halting lung injury propagation.
Lastly, aspects of the Habashi method (HM) were not discussed suggesting they were overlooked. The HM utilizes the Time Controlled Adaptive Ventilation (TCAV) protocol within the APRV mode where the slope of the expiratory flow-time curve is vital when setting T-Low. Slope analysis guides: 1) expiratory flow termination / expiratory peak flow(EFT/EPF) at75%, (validated clinically and experimentally to optimize alveolar stability); and 2) the slope reflects elastance of the respiratory system, providing real-time assessment of lung mechanics.(6) During TCAV, the slope becomes more acute with increasing elastance resulting in a <75% (EFT/EPF) as recoil forces intensify necessitating a reduced release time (T-Low). The T-Low adjustment yields a corresponding Vt decrease as elastance increases and conversely Vt increases with decreasing elastance. TCAV correlates Vt to changes in elastance rather than based on ideal body weight (IBW). This parallels residual lung aeration (“baby lung” size) which correlates with compliance rather than IBW.(7) Our 26-year experience with TCAV used as “rescue” on patients with increased elastance, results in Vt <6 mL/kg, frequently 3–5 mL/kg. Our review of the 30-year evolution of APRV found most publications use the acronym APRV but apply different methodologies, leaving the acronym useless for scientific study.(8)
In the 70s and 80s, clinicians targeted blood gas; currently we target ventilator settings. Is it time to target the patient’s unique mechanics and personalize the settings to precisely meet their evolving needs?
Copyright form disclosure:
Dr. Habashi, Ms. Andrews, and Mr. Nieman have presented and received honoraria and/or travel reimbursement at event(s) sponsored by Dräger Medical Systems, Inc., outside of the published work. Dr. Habashi is the founder of ICON (of which Ms. Andrews is an employee), and Dr. Habashi holds patents on a method of initiating, managing and/or weaning airway pressure release ventilation, as well as controlling a ventilator in accordance with the same; these patents are not commercialized, licensed nor royalty-producing. The authors maintain that industry had no role in the design and conduct of the study; the collection, management, analysis, or interpretation of the data; nor the preparation, review, or approval of the manuscript. Mr. Satalin and Mr. Nieman received support for article research from the National Institutes of Health (NIH). Dr. Gatto received funding from the NIH (summer consultant). All authors have lectured for Intensive Care Online Network, Inc. (ICON).
Footnotes
Disclosures: PLA, GFN, and NMH have presented and received honoraria and/or travel reimbursement at event(s) sponsored by Dräger Medical Systems, Inc., outside of the published work. PLA, GFN, JS, LAG and NMH have lectured for Intensive Care Online Network, Inc. (ICON). NMH is the founder of ICON, of which PLA is an employee. NMH holds patents on a method of initiating, managing and/or weaning airway pressure release ventilation, as well as controlling a ventilator in accordance with the same, but these patents are not commercialized, licensed nor royalty-producing. The authors maintain that industry had no role in the design and conduct of the study; the collection, management, analysis, or interpretation of the data; nor the preparation, review, or approval of the manuscript.
References
- 1.Hirshberg EL, Lanspa MJ, Peterson J, et al. Randomized Feasibility Trial of a Low Tidal Volume-Airway Pressure Release Ventilation Protocol Compared With Traditional Airway Pressure Release Ventilation and Volume Control Ventilation Protocols. Critical care medicine 2018;46(12):1943–1952. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 2.Kollisch-Singule M, Emr B, Smith B, et al. Mechanical Breath Profile of Airway Pressure Release Ventilation: The Effect on Alveolar Recruitment and Microstrain in Acute Lung Injury. JAMA Surg 2014;149(11):1138–1145. [DOI] [PubMed] [Google Scholar]
- 3.Silva PL, Cruz FF, Samary CDS, et al. Biological Response to Time-Controlled Adaptive Ventilation Depends on Acute Respiratory Distress Syndrome Etiology. Critical care medicine 2018. [DOI] [PubMed] [Google Scholar]
- 4.Cereda M, Xin Y, Hamedani H, et al. Tidal changes on CT and progression of ARDS. Thorax 2017;72(11):981–989. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 5.Xin Y, Cereda M, Hamedani H, et al. Unstable Inflation Causing Injury: Insight from Prone Position and Paired CT Scans. American journal of respiratory and critical care medicine 2018. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 6.Brody AW. Mechanical compliance and resistance of the lung-thorax calculated from the flow recorded during passive expiration. The American journal of physiology 1954;178(2):189–196. [DOI] [PubMed] [Google Scholar]
- 7.Gattinoni L, Pesenti A. The concept of “baby lung”. Intensive care medicine 2005;31(6):776–784. [DOI] [PubMed] [Google Scholar]
- 8.Jain SV, Kollisch-Singule M, Sadowitz B, et al. The 30-year evolution of airway pressure release ventilation (APRV). Intensive Care Med Exp 2016;4(1):11. [DOI] [PMC free article] [PubMed] [Google Scholar]