Hyperoxia may be related to delayed cerebral ischemia and poor outcome after subarachnoid haemorrhage

Postoperative care of the neurosurgical patient

PURPOSE OF REVIEW

Monitoring and therapy of patients in neurocritical care are areas of intensive research and the current evidence needs further confirmation.

RECENT FINDINGS

A consensus statement of the Neurocritical Care Society and the European Society of Intensive Care Medicine provided pragmatic guidance and recommendations for multimodal monitoring in neurocritical care patients. Only a minority of these recommendations have strong evidence. In addition, recent multicenter randomized controlled trials concerning the therapy of subarachnoidal hemorrhage and traumatic brain injury could not show decreased mortality or improved functional neurologic outcome after the interventions. The current evidence for monitoring and medical therapy in patients after traumatic brain injury and aneurysmal subarachnoid hemorrhage is highlighted in this review.

SUMMARY

Although strong evidence is lacking, multimodal monitoring is of great value in neurocritical care patients and may help to provide patients with the optimal therapy based on the individual pathophysiological changes.

Hyperoxia in intensive care, emergency, and peri-operative medicine: Dr. Jekyll or Mr. Hyde? A 2015 update

This review summarizes the (patho)-physiological effects of ventilation with high FiO₂ (0.8–1.0), with a special focus on the most recent clinical evidence on its use for the management of circulatory shock and during medical emergencies. Hyperoxia is a cornerstone of the acute management of circulatory shock, a concept which is based on compelling experimental evidence that compensating the imbalance between O₂ supply and requirements (i.e., the oxygen dept) is crucial for survival, at least after trauma. On the other hand, “oxygen toxicity” due to the increased formation of reactive oxygen species limits its use, because it may cause serious deleterious side effects, especially in conditions of ischemia/reperfusion. While these effects are particularly pronounced during long-term administration, i.e., beyond 12–24 h, several retrospective studies suggest that even hyperoxemia of shorter duration is also associated with increased mortality and morbidity. In fact, albeit the clinical evidence from prospective studies is surprisingly scarce, a recent meta-analysis suggests that hyperoxia is associated with increased mortality at least in patients after cardiac arrest, stroke, and traumatic brain injury. Most of these data, however, originate from heterogenous, observational studies with inconsistent results, and therefore, there is a need for the results from the large scale, randomized, controlled clinical trials on the use of hyperoxia, which can be anticipated within the next 2–3 years. Consequently, until then, “conservative” O₂ therapy, i.e., targeting an arterial hemoglobin O₂ saturation of 88–95 % as suggested by the guidelines of the ARDS Network and the Surviving Sepsis Campaign, represents the treatment of choice to avoid exposure to both hypoxemia and excess hyperoxemia.

Association Between Arterial Hyperoxia and Outcome in Subsets of Critical Illness: A Systematic Review, Meta-Analysis, and Meta-Regression of Cohort Studies

OBJECTIVE

Oxygen is vital during critical illness, but hyperoxia may harm patients. Our aim was to systematically evaluate the methodology and findings of cohort studies investigating the effects of hyperoxia in critically ill adults.

DATA SOURCE

A meta-analysis and meta-regression analysis of cohort studies published between 2008 and 2015 was conducted. Electronic databases of MEDLINE, EMBASE, and Web of Science were systematically searched for the keywords hyperoxia and mortality or outcome.

STUDY SELECTION

Publications assessing the effect of arterial hyperoxia on outcome in critically ill adults (≥ 18 yr) admitted to critical care units were eligible. We excluded studies in patients with chronic obstructive pulmonary disease, extracorporeal life support or hyperbaric oxygen therapy, and animal studies. Due to a lack of data, no studies dedicated to patients with acute lung injury, sepsis, shock, or multiple trauma could be included.

DATA EXTRACTION

Studies were included independent of admission diagnosis and definition of hyperoxia. The primary outcome measure was in-hospital mortality, and results were stratified for relevant subgroups (cardiac arrest, traumatic brain injury, stroke, post-cardiac surgery, and any mechanical ventilation). The effects of arterial oxygenation on functional outcome, long-term mortality, and discharge variables were studied as secondary outcomes.

DATA SYNTHESIS

Twenty-four studies were included of which five studies were only for a subset of the analyses. Nineteen studies were pooled for meta-analyses and showed that arterial hyperoxia during admission increases hospital mortality: adjusted odds ratio, 1.21 (95% CI, 1.08-1.37) (p = 0.001). Functional outcome measures were diverse and generally showed a more favorable outcome for normoxia.

CONCLUSIONS

In various subsets of critically ill patients, arterial hyperoxia was associated with poor hospital outcome. Considering the substantial heterogeneity of included studies and the lack of a clinical definition, more evidence is needed to provide optimal oxygen targets to critical care physicians.

Bench-to-bedside review: the effects of hyperoxia during critical illness

Oxygen administration is uniformly used in emergency and intensive care medicine and has life-saving potential in critical conditions. However, excessive oxygenation also has deleterious properties in various pathophysiological processes and consequently both clinical and translational studies investigating hyperoxia during critical illness have gained increasing interest. Reactive oxygen species are notorious by-products of hyperoxia and play a pivotal role in cell signaling pathways. The effects are diverse, but when the homeostatic balance is disturbed, reactive oxygen species typically conserve a vicious cycle of tissue injury, characterized by cell damage, cell death, and inflammation. The most prominent symptoms in the abundantly exposed lungs include tracheobronchitis, pulmonary edema, and respiratory failure. In addition, absorptive atelectasis results as a physiological phenomenon with increasing levels of inspiratory oxygen. Hyperoxia-induced vasoconstriction can be beneficial during vasodilatory shock, but hemodynamic changes may also impose risk when organ perfusion is impaired. In this context, oxygen may be recognized as a multifaceted agent, a modifiable risk factor, and a feasible target for intervention. Although most clinical outcomes are still under extensive investigation, careful titration of oxygen supply is warranted in order to secure adequate tissue oxygenation while preventing hyperoxic harm.