Objectives: High oxygen concentration in blood may be harmful in the reperfusion phase after cardiopulmonary resuscitation. We compared the effect of 30 and 100% inspired oxygen concentrations on blood oxygenation and the level of serum markers (NSE, S-100) of neuronal injury during the early post-resuscitation period in humans.
Methods: Patients resuscitated from witnessed out-of-hospital ventricular fibrillation were randomised after the return of spontaneous circulation (ROSC) to be ventilated either with 30% (group A) or 100% (group B) oxygen for 60 min. Main outcome measures were NSE and S-100 levels at 24 and 48 h after ROSC, the adequacy of oxygenation at 10 and 60 min after ROSC and, in group A, the need to raise FiO(2) to avoid hypoxaemia. Blood oxygen saturation <95% was the threshold for this intervention.
Results: Thirty-two patients were randomised and 28 (14 in group A and 14 in group B) remained eligible for the final analysis. The mean PaO(2) at 10 min was 21.1 kPa in group A and 49.7 kPa in group B. The corresponding values at 60 min were 14.6 and 46.5 kPa. PaO(2) values did not fall to the hypoxaemic level in group A. In another group FiO(2) had to be raised in five cases (36%) but in two cases it was returned to 0.30 rapidly. The mean NSE at 24 and 48 h was 10.9 and 14.2 microg/l in group A and 13.0 and 18.6 microg/l in group B (ns). S-100 at corresponding time points was 0.21 and 0.23 microg/l in group A and 0.73 and 0.49 microg/l in group B (ns). In the subgroup not treated with therapeutic hypothermia in hospital NSE at 24h was higher in group B (mean 7.6 versus 13.5 microg/l, p=0.0487).
Conclusions: Most patients had acceptable arterial oxygenation when ventilated with 30% oxygen during the immediate post-resuscitation period. There was no indication that 30% oxygen with SpO(2) monitoring and oxygen backup to avoid SpO(2)<95% did worse that the group receiving 100% oxygen. The use of 100% oxygen was associated with increased level of NSE at 24h in patients not treated with therapeutic hypothermia. The clinical significance of this finding is unknown and an outcome-powered study is feasible.