Impact of Positive End-Expiratory Pressure and FiO2 on Lung Mechanics and Intrapulmonary Shunt in Mechanically Ventilated Patients with ARDS Due to COVID-19 Pneumonia

Gaetano Florio; Alberto Zanella; Douglas Slobod; Amedeo Guzzardella; Ilaria Protti; Eleonora Carlesso; Arif Canakoglu; Jacopo Fumagalli; Vittorio Scaravilli; Sebastiano M Colombo; Alessio Caccioppola; Matteo Brioni; Antonio M Pesenti; Giacomo Grasselli

doi:10.1177/08850666231210485

Impact of Positive End-Expiratory Pressure and FiO₂ on Lung Mechanics and Intrapulmonary Shunt in Mechanically Ventilated Patients with ARDS Due to COVID-19 Pneumonia

J Intensive Care Med. 2024 May;39(5):420-428. doi: 10.1177/08850666231210485. Epub 2023 Nov 5.

Authors

Gaetano Florio^{1

2}, Alberto Zanella^{1

2}, Douglas Slobod³, Amedeo Guzzardella¹, Ilaria Protti¹, Eleonora Carlesso¹, Arif Canakoglu², Jacopo Fumagalli², Vittorio Scaravilli², Sebastiano M Colombo², Alessio Caccioppola², Matteo Brioni², Antonio M Pesenti^{1

2}, Giacomo Grasselli^{1

2}

Affiliations

¹ Department of Pathophysiology and Transplantation, University of Milan, Milan, Italy.
² Department of Anesthesia, Critical Care and Emergency, Fondazione Istituto di Ricovero e cura a Carattere Scientifico Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy.
³ Department of Critical Care Medicine, McGill University, Montreal, Quebec, Canada.

PMID: 37926984
DOI: 10.1177/08850666231210485

Abstract

Purpose: This study aimed to investigate the effects of inspired oxygen fraction (FiO₂) and positive end-expiratory pressure (PEEP) on gas exchange in mechanically ventilated patients with COVID-19. Methods: Two FiO₂ (100%, 40%) were tested at 3 decreasing levels of PEEP (15, 10, and 5 cmH₂O). At each FiO₂ and PEEP, gas exchange, respiratory mechanics, hemodynamics, and the distribution of ventilation and perfusion were assessed with electrical impedance tomography. The impact of FiO₂ on the intrapulmonary shunt (delta shunt) was analyzed as the difference between the calculated shunt at FiO₂ 100% (shunt) and venous admixture at FiO₂ 40% (venous admixture). Results: Fourteen patients were studied. Decreasing PEEP from 15 to 10 cmH₂O did not change shunt (24 [21-28] vs 27 [24-29]%) or venous admixture (18 [15-26] vs 23 [18-34]%) while partial pressure of arterial oxygen (FiO₂ 100%) was higher at PEEP 15 (262 [198-338] vs 256 [147-315] mmHg; P < .05). Instead when PEEP was decreased from 10 to 5 cmH₂O, shunt increased to 36 [30-39]% (P < .05) and venous admixture increased to 33 [30-43]% (P < .05) and partial pressure of arterial oxygen (100%) decreased to 109 [76-177] mmHg (P < .05). At PEEP 15, administration of 100% FiO₂ resulted in a shunt greater than venous admixture at 40% FiO_2, ((24 [21-28] vs 18 [15-26]%, P = .005), delta shunt 5.5% (2.3-8.8)). Compared to PEEP 10, PEEP of 5 and 15 cmH₂O resulted in decreased global and pixel-level compliance. Cardiac output at FiO₂ 100% resulted higher at PEEP 5 (5.4 [4.4-6.5]) compared to PEEP 10 (4.8 [4.1-5.5], P < .05) and PEEP 15 cmH₂O (4.7 [4.5-5.4], P < .05). Conclusion: In this study, PEEP of 15 cmH₂O, despite resulting in the highest oxygenation, was associated with overdistension. PEEP of 5 cmH₂O was associated with increased shunt and alveolar collapse. Administration of 100% FiO₂ was associated with an increase in intrapulmonary shunt in the setting of high PEEP. Trial registration: NCT05132933.

Keywords: ARDS; COVID-19; compliance; hypoxemia; intrapulmonary shunt; oxygen; positive end-expiratory pressure; venous admixture.

MeSH terms

COVID-19* / complications
COVID-19* / therapy
Humans
Lung / diagnostic imaging
Lung Diseases*
Oxygen
Positive-Pressure Respiration / methods
Respiration, Artificial
Respiratory Distress Syndrome* / therapy
Respiratory Mechanics

Substances

Oxygen

Associated data

ClinicalTrials.gov/NCT05132933