Short communicationDelivery of titrated oxygen via a self-inflating resuscitation bag☆
Introduction
In animal models, exposure to 100% oxygen around the time of cardiac arrest leads to significantly worse neurological outcomes than oxygen administered at lower concentrations.1 In adult human cardiac arrest, the effect of hyperoxia has been examined in three large retrospective studies and while two studies reported that hyperoxia was associated with an increased mortality risk,2, 3, 4 a third study found no association after adjustment for illness severity.4 The need for a prospective randomised clinical trial to establish the efficacy and safety of controlled reoxygenation in the context of post-cardiac arrest management has been highlighted.5 However, with the exception of one small trial which was not powered to detect differences in clinical outcomes,6 no prospective study of different oxygen regimes in patients resuscitated from cardiac arrest has been performed. One impediment to the conduct of a large scale randomised trial is that standard ambulances only carry bottled oxygen and do not have the capacity to deliver specific inspired oxygen concentrations of less than 100% to ventilated patients. Typically, patients who require ventilation after resuscitation from cardiac arrest are ventilated en route to hospital with a self-inflating resuscitation bag with a reservoir connected to high flow oxygen. One potential method to achieve reduced concentrations of oxygen in these patients is through reductions in oxygen flow into the self-inflating resuscitation bag. This study evaluates the hypothesis that titration of inspired oxygen from 21% to 100% can be delivered through adjustment of oxygen flow into a self-inflating resuscitation bag with a reservoir of a type used in standard ambulance practice.
Section snippets
Study design
We performed a series of bench experiments to determine the effect of changing oxygen flow on inspired oxygen concentration using a self-inflating resuscitation bag at different tidal volumes and resuscitation bag inflation rates.
Technical information
Oxygen was delivered via an FM-1510-F4 oxygen flow metre (Amvex Corporation, Ontario, Canada) connected to a disposable 1500 ml Hsiner Manual Resuscitator with a 2500 ml reservoir bag (Hinser Ltd., Taichung City, Taiwan). This resuscitator (self-inflating resuscitation
Results
A wide range of delivered oxygen concentrations ranging between 24% and 99.5% were achieved using standard ambulance equipment (Table 2). For each combination of tidal volume and inflation rate, progressive increases in oxygen flow rate led to progressive rises in delivered oxygen concentration up until a ceiling where a percentage of delivered oxygen in the high 90 s was consistently achieved. The mean delivered oxygen concentration increased significantly with each of the increments of oxygen
Discussion
We have shown that using ambulance equipment, delivered oxygen concentration can be titrated using adjustments of oxygen flow into a self-inflating resuscitation bag with a reservoir. While particular rates of oxygen flow did not deliver fixed inspired oxygen concentrations, our data provide an estimation of likely delivered concentration that would be achieved for particular flow rates after resuscitation. For example, for a tidal volume of 600 ml and an inflation rate of 10 breaths min−1, a flow
Conclusion
Effective titration of oxygen delivery can be achieved using adjustment of oxygen flow with a standard self-inflating resuscitation bag and reservoir. Adjustment of oxygen flow may be an appropriate method of titrating oxygen to avoid exposure to hyperoxia in patients who are intubated and ventilated after cardiac arrest in the pre-hospital setting.
Conflicts of interest statement
The authors have no conflicts of interest to report.
Acknowledgements
The authors would like to acknowledge Mr Andrew Ditchburn (Anaesthetic Technician, Wellington Hospital) for providing technical support.
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A Spanish translated version of the summary of this article appears as Appendix in the final online version at http://dx.doi.org/10.1016/j.resuscitation.2012.08.330.