The "ZEEP-PEEP test" to evaluate the response to positive end-expiratory pressure delivered by helmet: A prospective physiologic study

Marco Giani; Benedetta Fumagalli; Francesco Cipulli; Emanuele Rezoagli; Matteo Pozzi; Denise Fumagalli; Letizia Fumagalli; Katia Ferrari; Roberto Rona; Giacomo Bellani; Alberto Lucchini; Giuseppe Foti

doi:10.1016/j.heliyon.2024.e28339

The "ZEEP-PEEP test" to evaluate the response to positive end-expiratory pressure delivered by helmet: A prospective physiologic study

Heliyon. 2024 Mar 16;10(6):e28339. doi: 10.1016/j.heliyon.2024.e28339. eCollection 2024 Mar 30.

Authors

Marco Giani^{1

2}, Benedetta Fumagalli¹, Francesco Cipulli², Emanuele Rezoagli^{1

2}, Matteo Pozzi², Denise Fumagalli¹, Letizia Fumagalli², Katia Ferrari², Roberto Rona², Giacomo Bellani^{3

4}, Alberto Lucchini^{1

2}, Giuseppe Foti^{1

2}

Affiliations

¹ School of Medicine and Surgery, University of Milano-Bicocca, Monza, Italy.
² Department of Emergency and Intensive Care, Fondazione IRCCS San Gerardo dei Tintori, Monza, Italy.
³ Department of Medical Sciences, University of Trento, Trento, Italy.
⁴ Department of Anesthesia and Intensive Care, Santa Chiara Regional Hospital, APSS Trento, Trento, Italy.

Abstract

Introduction: The improvement in oxygenation after helmet application in hypoxemic patients may be explained by the alveolar recruitment obtained with positive end expiratory pressure (PEEP) or by the administration of a more accurate inspiratory fraction of oxygen (F_iO₂). We have designed the "ZEEP-PEEP test", capable to distinguish between the F_iO₂-related or PEEP-related oxygenation improvement. Our primary aim was to describe the use of this test during helmet CPAP to assess the oxygenation improvement attributable to PEEP application.

Material and methods: We performed a prospective physiological study including adult critically ill patients. Respiratory and hemodynamic parameters were recorded before helmet application (PRE step), after helmet application without PEEP (ZEEP step) and after the application of the PEEP valve (PEEP step), while maintaining a constant FiO₂. We defined as "PEEP responders" patients showing a PaO₂/FiO₂ ratio improvement ≥10% after PEEP application.

Results: 93 patients were enrolled. Compared to the PRE step, PaO2/FiO2 ratio was significantly improved during helmet CPAP both at ZEEP and PEEP step (189 ± 55, 219 ± 74 and 241 ± 82 mmHg, respectively, p < 0.01). Both PEEP responders (41%) and non-responders showed a significant improvement of PaO2/FiO2 ratio after the application of helmet at ZEEP, PEEP responders also showed a significant improvement of oxygenation after PEEP application (208 ± 70 vs 267 ± 85, p < 0.01).

Conclusions: Helmet CPAP improved oxygenation. This improvement was not only due to the PEEP effect, but also to the increase of the effective inspired FiO₂. Performing the ZEEP-PEEP test may help to identify patients who benefit from PEEP.

Keywords: Acute respiratory failure; CPAP; Continuous positive end-expiratory pressure; Helmet; Non-invasive ventilation; PEEP.