Passive oxygenation – the jury is still out

As discussed in my blog post from April 2012, ‘Should we be passive about oxygenation?’, in the years preceding the issue of the 2010 European Resuscitation Council (ERC) and Amercian Heart Association (AHA) guidelines on resuscitation, interest in the concept of passive oxygenation, particularly as a component of CardioCerebral Resuscitation (CCR) protocols, appeared to peak. This led to considerable speculation as to how the International Liaison Committee on Resuscitation (ILCOR) would assess the published evidence regarding passive oxygenation compared to standard ventilation techniques and what the subsequent recommendations would be in the new 2010 ERC and AHA guidelines.

In the end, the ERC concluded that, ‘There is insufficient evidence to support or refute the use of passive oxygen delivery during CPR to improve outcome when compared with oxygen delivery by positive pressure ventilation’, and the AHA that, ‘This time there is insufficient evidence to support the removal of ventilations from CPR performed by ACLS providers.’

It might reasonably have been expected that such conclusions would stimulate potential investigators to intensify their efforts to provide the additional evidence needed to enable more conclusive statements in the next set of guidelines, scheduled for issue in 2015. Disappointingly, this has not been the case, so the jury is still out, with little immediate prospect of having significant new evidence to consider.

There may be any number of reasons for this. One possibility is the debate regarding airway management and ventilation in CPR has simply moved on to other areas of interest, such as the optimal airway device. However, if so, it has progressed without really resolving the question of whether passive oxygenation has a useful role to play during CPR, particularly for the first few minutes following witnessed ventricular fibrillation/ventricular tachycardia (VF/VT).

A key question regarding the concept and viability of passive oxygenation as an alternative to standard ventilation during the initial phase of CPR has always been whether chest compressions generate adequate ventilation in cardiac arrest (providing there is a patent airway).

In the 2010 AHA guidelines for CPR (Part 8), in the section on passive oxygenation delivery during CPR, it is stated that:

‘Chest compressions cause air to be expelled from the chest and oxygen to be drawn into the chest passively due to the elastic recoil of the chest. In theory, because ventilation requirements are lower than normal during cardiac arrest, oxygen supplied by passive delivery is likely to be sufficient for several minutes after onset of cardiac arrest with a patent upper airway.’

In their article, ‘Airway techniques and ventilation strategies’, Nolan and Soar, comment that:

‘A study of 17 intubated patients in an emergency department who were undergoing chest compressions using a mechanical compression device (Lund University Cardiopulmonary Assist System (LUCAS)) showed that the median tidal volume per compression was just 42ml – considerably less than the dead space. These patients had been in cardiac arrest for more than 40 min, and therefore, their lung compliance was probably poor. Nevertheless, the implication is that chest compressions alone do not generate adequate ventilation. Despite this, and based partly on further animal data, a group from the Sarver Heart Center in Tucson, Arizona, the United States, has described the use of passive oxygenation insufflation as part of their protocol for CardioCerebral Resuscitation (CCR). This group has recently reported better survival to hospital discharge after witnessed VF cardiac arrest from adults who were managed initially with passive oxygenation (insertion of an oropharyngeal airway and oxygen given at 15L/min by non-rebreather mask) compared with those given active ventilation.’

Perhaps improvements in survival rates, such as those described above, have been due to factors other than passive oxygenation? Most of the studies on passive oxygenation have included multiple treatment changes and/or a number of confounders, so this remains a possibility.

Despite the lack of significant new data, passive oxygenation has continued to be a subject of discussion in a number of recent articles.

In a review article published in ‘Current Opinion in Critical Care’ (COCC), entitled, ‘Advanced life support and mechanical ventilation’, Kill, Dersch and Wulf discuss, amongst other topics, passive oxygenation versus active ventilation. They conclude that:

‘The total number of studies dealing with mechanical ventilation during resuscitation and ALS is still limited. The still recommended standard is positive-pressure ventilation with a tidal volume of 6-7ml/kg and a respiratory rate of 10/min, purse oxygen and preferably with a ventilator. During the first few minutes of CPR, passive oxygen insufflation via a nonrebreathable mask or an airway device might be an acceptable alternative. Hyper-oxygenation should be avoided once a spontaneous circulation is restored, and waveform capnometry is an important monitoring for both ventilation and perfusion of the lungs.’

In another review published in COCC in 2013, entitled, ‘Airway Management in cardiopulmonary resuscitation’, Soar and Nolan confirm that:

‘Some EMS system protocols for adult primary cardiac arrest include airway opening and high-flow face-mask oxygen, and passive oxygenation from chest compressions for the first 6 minutes of CPR. Improved outcomes have been reported with this ‘minimally interrupted’ CPR approach although further study is needed’. A retrospective analysis of adult OHCA patients reported improved neurologically intact survival after witnessed VF/VT OHCA with passive ventilation compared with bag-valve mask ventilation. Survival was similar for unwitnessed VF/VT and nonshockable rhythms. Observational data from large registries in Japan, however, suggest that ventilation is necessary during CPR in children, after cardiac arrest with a primary respiratory cause, and during a prolonged cardiac arrest.’

As well as delivery using a non-rebreather mask and oropharyngeal airway, passive oxygenation, or passive airway managementâ„¢ (PAM), can be delivered via a supraglottic airway, such as the Intersurgical i-gel O2â„¢, which incorporates a supplementary oxygen port specifically designed for this purpose (figure 1). Such a device may offer advantages over use of a non-rebreather mask, such as providing the opportunity to switch more seamlessly from passive oxygenation to standard ventilation, thereby minimising interruption to chest compressions. However, this is speculation only and has yet to be confirmed by any published evidence.

Connecting a standard oxygen tube to the supplementary port of the i-gel O2 in preparation for the delivery of passive oxygenation

Connecting a standard oxygen tube to the supplementary port of the i-gel O2 in preparation for the delivery of passive oxygenation

In conclusion, whilst there appears to be very little new published data, passive oxygenation remains a subject of lively debate in resuscitation circles and is often mentioned in articles reviewing ventilation strategies and airway management in cardiac arrest. Before it slips from view due to a lack of new evidence, it is hoped a new wave of studies are already in progress and will soon emerge as peer reviewed published studies in the near future, enabling a more conclusive assessment to be made as to whether passive oxygenation has a useful role to play during CPR. Without doubt, at the present time, the jury remains out.

I would be most interested to hear from anyone who is currently using a protocol which incorporates passive oxygenation, is involved in a study incorporating this technique or is looking to conduct such a study in the future.

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