The effect of hyperoxia following cardiac arrest - A systematic review and meta-analysis of animal trials.

AIM

There are conflicting findings from observational studies regarding the nature of the association between hyperoxia and risk of mortality in patients admitted to intensive care following cardiac arrest. This systematic review and meta-analysis evaluates animal data investigating the effect of administration of high concentrations of oxygen following cardiac arrest on neurological outcome and the clinical applicability of this data.

METHODS

A systematic search of Medline and Embase identified controlled animal studies modelling cardiac arrest with subsequent cardiopulmonary resuscitation that compared ventilation with 100% oxygen to lower concentrations following return of spontaneous circulation. Eligible studies were included in a meta-analysis in which the inverse variance weighted differences were calculated for the standardised mean difference of the primary outcome measure, the neurological deficit score.

RESULTS

Ten studies met the criteria for inclusion in the systematic review. In a meta-analysis of six studies, with 95 animals, treatment with 100% oxygen resulted in a significantly worse neurological deficit score than oxygen administered at lower concentrations, with a standardised mean difference of -0.64 (95% CI -1.06 to -0.22). In four of five studies, histological evidence of increased neuronal damage was present in animals that received 100% oxygen therapy.

CONCLUSIONS

The administration of 100% oxygen therapy is associated with worse neurological outcome than lower oxygen concentrations in animal models of cardiac arrest. However, due to limitations in study design and poor generalisability of the animal models to the situation of post cardiac arrest resuscitation in humans, the clinical applicability of this data is uncertain.