A man in his 40s has a witnessed collapse and CPR is immediately started. Paramedics are on scene within 5 minutes and initiate advanced cardiac life support. He has refractory ventricular fibrillation which degenerates to asystole. He arrives in an emergency department where, with good ongoing CPR, he appears reasonably well perfused and even demonstrates some spontaneous movements and reactive pupils. He is placed on a mechanical CPR device and activation of the cardiac cath lab is requested. The patient has been in cardiac arrest now for 32 minutes. The cardiology fellow appears and asks: ‘what’s the down time?’
What’s the right answer? Would you say ‘half an hour’? ’32 minutes’?
And does it matter? Why is the cardiology fellow asking? Does she have an arbitrary cut off in mind, over which emergency coronary reperfusion will be denied?
I think there are several problems with conversations like these.
The first, is what does ‘down time’ even mean?
The second, is how relevant is a cardiac arrest time interval to prognosis in an individual patient?
The third, is what is the significance of any time interval in a patient who at the time of assessment has some signs that CPR is providing some perfusion and there is some evidence of brain function?
Let’s take the first. The definition of ‘down time’ does not appear to be standardised:
In this publication it appears to refer to the time before resuscitation is commenced, where it is demonstrated to be prognostically important.
Similarly, in this medical dictionary, it is defined as the ‘temporal duration from cardiac arrest until beginning cardiopulmonary resuscitation or advanced cardiac life support.‘
However, a post in Life in the Fast Lane defines it as ‘time to return of spontaneous circulation‘
This appears to agree with The New South Wales Government’s Intensive Care Monitoring and Coordination Unit who define it as ‘the time from when a person’s heart stops beating to the time it starts beating again‘
Yet another definition is used in King County, Washington, where it is defined as ‘the time interval from collapse to call 911‘.
So the first thing is to clarify what we’re talking about: “This patient received immediate bystander CPR. He has had resuscitation for 32 minutes”. My friend in the UK, nurse resuscitationist Fernando Candal Carballido, coined the term ‘Time of Supported Circulation‘, or TOSC. I quite like this and think it could catch on.
The next question is so what? What if it was 90 minutes? At what point do we declare futility? This is where I believe the game has changed. Multiple survivors of prolonged resuscitation are springing up in the news and in the literature. Particularly in the subgroup of patients with minimal comorbidity, early CPR, and who receive circulatory support via ECMO or mechanical CPR while they undergo coronary reperfusion.
For a great example of a prolonged CPR survivor, check out paramedic Wayne Schneider’s story,
…or listen to Steven Bernard describe amazing results from ECMO used in Melbourne in the CHEER study, which includes survivors of over two hours of CPR.
So, in summary:
- Be clear on your definitions when communicating with colleagues. ‘Down time’ does not appear to have a standard definition, so I would avoid its use.
- Some patients without comorbidities who have had early bystander CPR may survive despite long periods of CPR (or ‘TOSC’), provided the underlying cause can be treated or is reversible.
- ECMO and even more widely available mechanical CPR devices are extending the period in which these causes can be addressed.
- Bear in mind, that even if there is a period between collapse and initiation of CPR, the point that arrest occurred may not be known, and laypersons may overestimate time intervals in cardiac arrest.
Update 2016: I now use the terms ‘No Flow Time’ (time from arrest to first basic life support) and ‘Low Flow Time’ (time receiving CPR, which stops with ROSC). This is prognostically very important, with increasing numbers of reports of survivors who have had very long periods of low flow time.