Elsevier

Journal of Critical Care

Volume 30, Issue 6, December 2015, Pages 1232-1237
Journal of Critical Care

Mechanical Ventilation
Atelectasis and mechanical ventilation mode during conservative oxygen therapy: A before-and-after study

https://doi.org/10.1016/j.jcrc.2015.07.033Get rights and content

Abstract

Purpose

The purpose of the study is to assess the effect of a conservative oxygen therapy (COT) (target SpO2 of 90%-92%) on radiological atelectasis and mechanical ventilation modes.

Materials and methods

We conducted a secondary analysis of 105 intensive care unit patients from a pilot before-and-after study. The primary outcomes of this study were changes in atelectasis score (AS) of 555 chest radiographs assessed by radiologists blinded to treatment allocation and time to weaning from mandatory ventilation and first spontaneous ventilation trial (SVT).

Results

There was a significant difference in overall AS between groups, and COT was associated with lower time-weighted average AS. In addition, in COT patients, change from mandatory to spontaneous ventilation or time to first SVT was shortened. After adjustment for baseline characteristics and interactions between oxygen therapy, radiological atelectasis, and mechanical ventilation management, patients in the COT group had significantly lower “best” AS (adjusted odds ratio, 0.28 [95% confidence interval {CI}, 0.12-0.66]; P = .003) and greater improvement in AS in the first 7 days (adjusted odds ratio, 0.42 [95% CI, 0.17-0.99]; P = .049). Moreover, COT was associated with significantly earlier successful weaning from a mandatory ventilation mode (adjusted hazard ratio, 2.96 [95% CI, 1.73-5.04]; P < .001) and with shorter time to first SVT (adjusted hazard ratio, 1.77 [95% CI, 1.13-2.78]; P = .013).

Conclusions

In mechanically ventilated intensive care unit patients, COT might be associated with decreased radiological evidence of atelectasis, earlier weaning from mandatory ventilation modes, and earlier first trial of spontaneous ventilation.

Introduction

Supplemental oxygen is a universal therapy in mechanically ventilated patients and can be lifesaving [1]. However, supplemental oxygen therapy may also cause adverse physiological effects and deleterious clinical outcomes [1], [2], [3], [4], [5], [6]. Such reports suggest that oxygen therapy can be a 2-edged sword and that attempts should be made to optimize its use and avoid both inadequate and excessive oxygen administrations. Despite these concerns, current oxygen therapy in mechanically ventilated patients remains biased toward liberal administration. Thus, much excess oxygen is delivered without evidence of benefit and sometimes outside of published guidelines [7], [8], [9], [10].

Recently, we reported the first pilot before-and-after trial of oxygen therapy in mechanically ventilated patients targeting a SpO2 of 90% to 92% (conservative oxygen therapy [COT]). We found that such therapy could be safely implemented in the intensive care unit (ICU) [11]. Concerns, however, were raised on the impact of COT on mechanical ventilation (MV) management and the development of pulmonary atelectasis [12] because no information was provided on such outcomes in the primary analysis of the study.

To respond to such concerns, we conducted a secondary analysis of our before-and-after trial and focused on the relationship between COT, MV management, and radiological evidence of atelectasis.

Section snippets

Methods

The study design was previously described [11] and is reported in the electronic supplement. It was approved by the institutional human research ethics committee with waiver for informed consent (approval no. H2011/04252) and registered at ClinicalTrial.gov (NCT01684124). In brief, we studied patients older than 18 years and expected to require MV for more than 48 hours. Exclusion criteria were imminent death or extracorporeal membrane oxygenation. During the standard oxygen therapy period,

Treatment effect

We studied 51 patients with 1043 data points on 271 MV days in the conventional therapy group and 54 patients with 1135 data points on 297 MV days in the COT group. The baseline characteristics of the 2 treatment groups for total study population were similar (Table 1).

During the conservative treatment period, patients had a significantly lower time-weighted average SpO2 (median, 95.5% [interquartile range, 94.0-97.3] vs 98.4% [97.3-99.1]) and Pao2 (83 mm Hg [71-94] vs 107 mm Hg [94-131]) with

Key findings

We conducted a study of the impact of COT on the severity of atelectasis and the management of MV in a before-and-after trial of conservative vs liberal oxygen therapy. We found that there was a significant subsequent difference in overall AS between groups. In addition, patients in the COT group had significantly lower “best” AS and greater improvement in AS in the first 7 days. Moreover, COT was associated with significantly earlier successful weaning from a mandatory ventilation mode and

Conclusions

In a before-and-after study, a more conservative SpO2 target might be associated with less radiological evidence of atelectasis formation in the first 7 days, earlier successful weaning from mandatory ventilation mode, and earlier attempts at spontaneous ventilation. These findings justify the design and conduct of further controlled studies of COT.

Author contributions

Conception and design: SS, GME, and RB; acquisition of data: SS, GME, NG, and AGS; analysis of chest x-rays: MDG, GDN, and PES; analysis and interpretation: SS, and RB; drafting the manuscript: SS, GME, and RB. All authors made contributed to critical revision of the manuscript for important intellectual content and approved the final version submitted.

Acknowledgments

This study was supported by the Austin Hospital Intensive Care Trust Fund.

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