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