Abstract
IntroductionThe safety of arterial hyperoxia is under increasing scrutiny. We performed a systematic review of the literature to determine whether any association exists between arterial hyperoxia and mortality in critically ill patient subsets.MethodsMedline, Thomson Reuters Web of Science and Scopus databases were searched from inception to June 2014. Observational or interventional studies evaluating the relationship between hyperoxia (defined as a supranormal arterial O2 tension) and mortality in adult intensive care unit (ICU) patients were included. Studies primarily involving patients with exacerbations of chronic pulmonary disease, acute lung injury and perioperative administration were excluded. Adjusted odds ratio (OR) of patients exposed versus those not exposed to hyperoxia were extracted, if available. Alternatively, unadjusted outcome data were recorded. Data on patients, study characteristics and the criteria used for defining hyperoxia exposure were also extracted. Random-effects models were used for quantitative synthesis of the data, with a primary outcome of hospital mortality.ResultsIn total 17 studies (16 observational, 1 prospective before-after) were identified in different patient categories: mechanically ventilated ICU (number of studies (k) = 4, number of participants (n) = 189,143), post-cardiac arrest (k = 6, n = 19,144), stroke (k = 2, n = 5,537), and traumatic brain injury (k = 5, n = 7,488). Different criteria were used to define hyperoxia in terms of PaO2 value (first, highest, worst, mean), time of assessment and predetermined cutoffs. Data from studies on ICU patients were not pooled because of extreme heterogeneity (inconsistency (I2) 96.73%). Hyperoxia was associated with increased mortality in post-cardiac arrest patients (OR = 1.42 (1.04 to 1.92) I2 67.73%) stroke (OR = 1.23 (1.06 to 1.43) I2 0%) and traumatic brain injury (OR = 1.41 (1.03 to 1.94) I2 64.54%). However, these results are limited by significant heterogeneity between studies.ConclusionsHyperoxia may be associated with increased mortality in patients with stroke, traumatic brain injury and those resuscitated from cardiac arrest. However, these results are limited by the high heterogeneity of the included studies.Electronic supplementary materialThe online version of this article (doi:10.1186/s13054-014-0711-x) contains supplementary material, which is available to authorized users.
Highlights
The safety of arterial hyperoxia is under increasing scrutiny
From the 2,389 articles that were initially identified (Figure 1), 70 potentially relevant original articles were examined in full text (κ = 0.87)
Two studies were identified in which hyperoxia exposure was defined on the basis of a peripheral O2 saturation (SpO2) >98% [2,32]; it is questionable whether these patients were really hyperoxic to a significant degree, we decided to include these studies in the analysis as the reported time-weighted arterial partial oxygen pressure (PaO2) values were above the upper normal limit of 100 mmHg in both cases [2,32]
Summary
The safety of arterial hyperoxia is under increasing scrutiny. Normobaric hyperoxia is touted as a potential therapeutic strategy for patients with traumatic brain injury or stroke [7], with an underlying rationale of increased brain O2 delivery [8] and protection of the ischemic penumbra through inducing redistribution of blood from normal to ischemic areas [9]. These potential benefits must be weighed against the injurious effects of high-dose supplemental O2. In both animal and human studies there are reports of pulmonary
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