Online Laboratory Investigations

Influence of Inspiration to Expiration Ratio on Cyclic Recruitment and Derecruitment of Atelectasis in a Saline Lavage Model of Acute Respiratory Distress Syndrome*

Boehme, Stefan MD^1,2; Bentley, Alexander H. MD²; Hartmann, Erik K. MD²; Chang, Shi MD, PhD^2,3; Erdoes, Gabor MD¹; Prinzing, Anatol MD^2,4; Hagmann, Michael BSc⁵; Baumgardner, James E. MD, PhD⁶; Ullrich, Roman MD, PhD¹; Markstaller, Klaus MD, PhD^1,2; David, Matthias MD, PhD²

Author Information

¹Department of Anesthesia, General Intensive Care, and Pain Management, Medical University Vienna, Vienna, Austria.

²Department of Anesthesiology, Medical Center of the Johannes-Gutenberg University Mainz, Mainz, Germany.

³Beijing Institute of Pharmacology and Toxicology, National Beijing Center for Drug Safety Evaluation and Research, Beijing, People's Republic of China.

⁴Department of Cardiovascular Surgery, German Heart Center Munich, Munich, Germany.

⁵Center for Medical Statistics, Informatics, and Intelligent Systems, Medical University Vienna, Vienna, Austria.

⁶Oscillogy LLC, Folsom, PA.

* See also p. 724.

This work was performed at Department of Anesthesia, General Intensive Care, and Pain Management, Medical University Vienna, Vienna, Austria; and Department of Anesthesiology, Medical Center of the Johannes-Gutenberg University Mainz, Mainz, Germany.

Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal’s website (http://journals.lww.com/ccmjournal).

Drs. Boehme, Bentley, Hartmann, Chang, and Prinzing and their institutions received support for article research from the German Research Council (Deutsche Forschungsgemeinschaft) (grant DFG Pak 415: Ma 2398/6). Dr. Ullrich served as a board member for MASIMO Inc. Irvine, CA, and received support for article research from the German Research Foundation. His institution received grant support from the German Research Council (PAK 415/Ma2398/6) and the German Research Foundation. Dr. David’s institution received grant support from the German Research Council (grant DFG Pak 415: Ma 2398/6). The remaining authors have disclosed that they do not have any potential conflicts of interest.

For information regarding this article, E-mail: [email protected]

Critical Care Medicine 43(3):p e65-e74, March 2015. | DOI: 10.1097/CCM.0000000000000788

Abstract

Objective:

Cyclic recruitment and derecruitment of atelectasis can occur during mechanical ventilation, especially in injured lungs. Experimentally, cyclic recruitment and derecruitment can be quantified by respiration-dependent changes in PaO₂ (ΔPaO₂), reflecting the varying intrapulmonary shunt fraction within the respiratory cycle. This study investigated the effect of inspiration to expiration ratio upon ΔPaO₂ and Horowitz index.

Design:

Prospective randomized study.

Setting:

Laboratory investigation.

Subjects:

Piglets, average weight 30 ± 2 kg.

Interventions:

At respiratory rate 6 breaths/min, end-inspiratory pressure (P_endinsp) 40 cm H₂O, positive end-expiratory pressure 5 cm H₂O, and FIO₂ 1.0, measurements were performed at randomly set inspiration to expiration ratios during baseline healthy and mild surfactant depletion injury. Lung damage was titrated by repetitive surfactant washout to induce maximal cyclic recruitment and derecruitment as measured by multifrequency phase fluorimetry. Regional ventilation distribution was evaluated by electrical impedance tomography. Step changes in airway pressure from 5 to 40 cm H₂O and vice versa were performed after lavage to calculate PO₂-based recruitment and derecruitment time constants (TAU).

Measurements and Main Results:

In baseline healthy, cyclic recruitment and derecruitment could not be provoked, whereas in model acute respiratory distress syndrome, the highest ΔPaO₂ were routinely detected at an inspiration to expiration ratio of 1:4 (range, 52–277 torr [6.9–36.9 kPa]). Shorter expiration time reduced cyclic recruitment and derecruitment significantly (158 ± 85 torr [21.1 ± 11.3 kPa] [inspiration to expiration ratio, 1:4]; 25 ± 12 torr [3.3 ± 1.6 kPa] [inspiration to expiration ratio, 4:1]; p < 0.0001), whereas the PaO₂/FIO₂ ratio increased (267 ± 50 [inspiration to expiration ratio, 1:4]; 424 ± 53 [inspiration to expiration ratio, 4:1]; p < 0.0001). Correspondingly, regional ventilation redistributed toward dependent lung regions (p < 0.0001). Recruitment was much faster (TAU: fast 1.6 s [78%]; slow 9.2 s) than derecruitment (TAU: fast 3.1 s [87%]; slow 17.7 s) (p = 0.0078).

Conclusions:

Inverse ratio ventilation minimizes cyclic recruitment and derecruitment of atelectasis in an experimental model of surfactant-depleted pigs. Time constants for recruitment and derecruitment, and regional ventilation distribution, reflect these findings and highlight the time dependency of cyclic recruitment and derecruitment.