Elsevier

Journal of Critical Care

Volume 39, June 2017, Pages 199-204
Journal of Critical Care

Neuroscience
Hyperoxia: At what level of SpO2 is a patient safe? A study in mechanically ventilated ICU patients

https://doi.org/10.1016/j.jcrc.2017.02.031Get rights and content

Highlights

  • Concerns have been expressed regarding a possible association between arterial hyperoxia and adverse outcomes in ICU patients

  • The risk of hyperoxia, defined as PaO2 > 100mmHg or > 125mmHg, was negligible when SpO2 was  95% or  96%, respectively

  • The majority (89% and 54%, respectively for PaO2 > 100mmHg and 125mmHg) of ICU patients with SpO2 of 100% had hyperoxia

Abstract

Background

Concerns have been expressed regarding a possible association between arterial hyperoxia and adverse outcomes in critically ill patients. Oxygen status is commonly monitored noninvasively by peripheral saturation monitoring (SpO2). However, the risk of hyperoxia above specific SpO2 levels in critically ill patients is unknown. The purpose of this study was to determine a threshold value of SpO2 above which the prevalence of arterial hyperoxia distinctly increases.

Methods

This is a cross-sectional study in adult mechanically ventilated intensive care patients in a tertiary referral center. In 100 patients, we collected 200 arterial blood gases (ABG) and simultaneously registered SpO2 levels, as well as hemodynamic and ventilation parameters and vasoactive medication. Patients under therapeutic hypothermia were excluded.

Results

The risk of arterial hyperoxia, defined as PaO2 > 100 mm Hg or > 125 mm Hg, was negligible when SpO2 was ≤ 95% or ≤ 96%, respectively. The majority (89% and 54%, respectively for PaO2 > 100 mm Hg and 125 mm Hg) of ICU patients with SpO2 of 100% had arterial hyperoxia. The relation between SpO2 and PaO2 was not clearly affected by hemodynamic or other clinical variables (pH, pCO2, body temperature, recent blood transfusion).

Conclusion

In critically ill patients, the prevalence of arterial hyperoxia increases when SpO2 is > 95%. Above this saturation level, supplemental oxygen should be administered with caution in patients potentially susceptible to adverse effects of hyperoxia.

Introduction

Supplemental oxygen administration is one of the most common therapies in the intensive care unit (ICU). Recently, however, concerns have been expressed about potential negative effects of supra-physiological arterial PaO2 (partial arterial oxygen pressure), or ‘hyperoxia’, including disturbed organ perfusion and increased mortality in several clinical conditions [1], [2], [3], [4], [5], [6]. Despite a relative paucity of randomized controlled trials, the British Thoracic Society guideline recommends a target peripheral oxygen saturation (SpO2) of 94–98% for most acutely ill patients [7]. The Acute Respiratory Distress Syndrome (ARDS) Network guideline [8] suggests keeping PaO2 values between 55 and 80 mm Hg.

Monitoring PaO2 in arterial blood gas analysis (ABGA) is the reference test for detecting arterial hyperoxia. In clinical practice, measurement of SpO2 by pulse oximetry is used as a convenient derivative of PaO2 for non-invasive continuous monitoring. Pulse oximetry is primarily designed to detect hypoxia and cannot detect hyperoxia if hemoglobin is 100% saturated [9]. A relevant question is, however, at what level hyperoxia in arterial blood can occur when SpO2 is < 100%.

In view of the potential effects of arterial hyperoxia in severely ill patients, the nature of the relation between SpO2 and PaO2, in particular the prevalence of arterial hyperoxia above specific SpO2 cutoff levels is relevant. To our knowledge, no previous study has evaluated this relation in the normal to hyperoxic range in critically ill patients.

The aim of this study was to determine the relation between SpO2 and PaO2 in mechanically ventilated critically ill patients. In particular, we aimed to identify a possible SpO2 limit above which the prevalence of arterial hyperoxia distinctly increases.

Section snippets

Study design

Between November 2014 and January 2015 we performed a single-centre, prospective, cross-sectional study in the ICU of the VU University medical center. SpO2 and PaO2 data were obtained from adult mechanically ventilated patients. Arterial blood samples were drawn as part of routine care. For each patient, data were collected on 1 to 4 time points, at least 2 h apart, within the first 3 days of admission. Each time arterial blood was collected from the arterial line, SpO2 was simultaneously

Results

A total of 200 simultaneous SpO2 and PaO2 measurements were collected, 14 of which (7%) were excluded due to MetHb > 1.5%, leaving 186 for statistical analyses. No data points were excluded due to hyperbilirubinemia, unreliable pulsatile curve or high COHb. These data were collected from 100 mechanically ventilated patients. The demographic data of included patients are shown in Table 1, and characteristics of collected data are shown in Table 2.

Discussion

There is a substantial amount of literature on the relation between PaO2 and SpO2. However, the first large-scale validation of the mathematical model of the relation was published only recently [9]. To our knowledge no previous study has evaluated the relation between SpO2 and PaO2 in the normal to hyperoxic range, nor assessed a specific SpO2 cutoff level as a proxy for arterial hyperoxemia.

Our data suggest that aiming for a target SpO2 range of 94–98%, as recommended by the British Thoracic

Conclusions

In this cross-sectional study of a heterogeneous group of mechanically ventilated patients admitted to the ICU the prevalence of hyperoxia (defined as PaO2 > 100 mm Hg resp. 125 mm Hg) appeared to be negligible as long as SpO2 did not exceed 95% resp. 96%. The majority of ventilated ICU patients with SpO2 of 100% have arterial hyperoxia.

Abbreviations

    ICU

    Intensive Care Unit

    VUmc

    Vrije Universiteit Medisch Centrum

    SpO2

    peripheral oxygen saturation

    SaO2

    arterial oxygen saturation

    FiO2

    fraction of inspired oxygen

    PaO2

    arterial partial oxygen pressure

    PaCO2

    arterial partial carbon dioxide

    ARDS

    Acute Respiratory Distress Syndrome

    Hb

    hemoglobin

    MetHb

    methemoglobin

    COHb

    carboxyhemoglobin

    MAP

    mean arterial pressure

    M/F

    male/female

    SD

    standard deviation

    CPAP

    continuous positive airway pressure

    PEEP

    positive end-expiratory pressure

    APACHE

    acute physiology age chronic health

Ethical approval and consent to participate

The Medical Ethics Review Committee confirmed that the Medical Research Involving Human Subjevts Act (WMO) does not apply to this study and waived the need for an official approval of this study by this committee is not required. The Medical Ethics Review Committee of VU University Medical Center is registered with the US Office for Human Research Protections (OHRP) as IRB00002991. The FWA number assigned to VU University Medical Center is FWA00017598.

Consent for publication

Not applicable.

Availability of supporting data

The datasets during and/or analyzed during the current study available from the corresponding author on reasonable request.

Competing interests

The authors declare that they have no competing interests.

Funding

Not applicable.

Disclosures

We have no financial or non-financial competing interests to disclose.

Authors' contributions

All authors were involved in creating the article. EMJD, AMES and YMS were involved in the conception and design of the work. EMJD, AMES, HMO and YMS were involved in data analysis and interpretation. EMJD and HJG performed the statistical analysis. EMJD prepared the presented figures and tables. EMJD was the major contributor in data collection. EMJD, AMES and YMS were the main contributors in writing the manuscript. All authors were involved in critical revision of the article. All authors

Acknowledgements

Not applicable.

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