There is one question that is always asked when a patient who has experienced a cardiac arrest is brought to the ED.
What’s the downtime?
(Nearly) Every team leader in history
In the past I have seen this term used (together with pupil responses – and don’t get me started on that) as a a primary prognostic factor in determining the enthusiasm for continuing resuscitation efforts. I’ve probably been guilty of this myself, but I’m not sure it’s as useful as we think.
Let’s consider what we might mean by ‘downtime’
- Does it start
- When cardiac arrest starts
- At the start of each loss of output
- At the start of each loss of rhythm associated with cardiac arrest (VF/asystole)
- Is it defined by
- A non perfusing rhythm
- The loss of a pulse
- A loss of other signs of life
- A loss of cardiac motion on USS
- Many patients have intermittent periods of ROSC/Rhythm. Should we consider downtime to be
- From the first loss of output to where we are now
- An estimate of the overall time in a no-flow state
- Should time we differentiate between
- TIme when our patient is likely in cardiac arrest with no CPR
- TIme when our patient is likely in cardiac arrest with high quality CPR
- TIme when our patient may be in a low-flow (but not a no-flow) state.
- What determines cardiac arrest?
- A lack of a pulse?
- A lack of an arterial trace (if available)?
- A lack of cardiac motion on USS (if available)?
All these factors legitimately could be considered components of what constitutes downtime, but it’s clearly so complex as to be unhelpful.
Let me suggest an example to put this into context.
You arrive at your local ED with a patient who had a witnessed cardiac arrest by a paramedic crew 1-hour earlier.
At scene, BLS was immediately established. ALS, including airway management with an iGel followed soon after together with vascular access and a LUCAS device. Your patient was initially in VF. They had three cycles of ALS and then went into PEA in a disorganised rhythm, but one which would likely lead to an output.
Over the next 30 mins the patient is highly unstable with intermittent episodes of VF (approx 5), PEA with no output, and then occasionally a palpable pulse. They receive regular adrenaline doses and Amiodarone as per ALS guidelines.
At approximately 20 mins post arrest an enhanced care team arrive. They intubate the patient and perform an ECHO which shows that the heart is moving despite no palpable pulse. The patient then develops an adrenaline dependent cardiac output, but it is largely sustained. The patient is transferred to hospital. They maintain a palpable pulse during transport, but lose their pulse on arrival. You take the patient into resus with the LUCAS on, but on transfer to the ED trolley and a pulse check they again have a ROSC.
The EM team leader turns to you after your handover and asks ‘what’s the downtime?’
You answer ‘I honestly don’t know, she arrested 1-hour ago, but it’s been a combination of no flow with great CPR, low flow with CPR and ROSC.’
The EM team leader turns to the team and states. ‘She’s been down for an hour’. You can feel the enthusiasm in the room drop down a notch…….
Having been on both sides of this conversation I can absolutely see it from both perspectives, but I’m hoping that we can be a little more sophisticated than simply stating a single time for a complex and nuanced question. For many patients who are persistently in a single, non-perfusing rhythm it is arguably an easy answer, but for those with ROSC (intermittent or sustained), high quality CPR with reversible rhythms and potential low flow states in PEA I think we can be more granular in describing what is actually happening to our patient.
Unsurprisingly, this problem has been considered by others wiser than myself. Cliff Reid, back in 2014, identified a range of definitions for downtime on the resus.me blog. At the time Cliff referred to his friend nurse resuscitationist colleague, Fernando Candal Carballido, who coined the term ‘Time of Supported Circulation‘, or TOSC. I agree with Cliff that this is helpful So for our patient above it might mean that we would describe them as being 1-hour from their first cardiac arrest. During the last hour the patient has had approximately 35 minutes of supported circulation, and for a maximum period of 15 minutes at the time of their initial arrest. I think Scott Wenigart has similarly drawn attention to this in the past too (though I can’t find the link today).
We can further clarify cardiac output with an estimation of how much of the time was low-flow and how much was no-flow. This is something that cardiac ultrasound, or an indwelling arterial line can help differentiate. Understanding low vs. no flow states is useful and I think that combining this with the concept of TOSC, is a useful adjunct to the resuscitationist vocabulary. For those of an EBM persuasion then you might ask whether differentiating between low and no-flow states is something that has been proven in the literature to make a difference? Intuitively, a low flow state must be better than a no-flow state, but by how much and for how long I don’t know for sure, but I believe it to be important. What literature there is on the topic also points in this direction with better outcomes for a reduced no-flow time, but the paradox is that without clear definitions comparing research is tricky. Most studies define no-flow as time without CPR in cardiac arrest, and low flow as time with CPR. Using those definitions there is evidence in a range of observational studies that a decreased no-flow time is better (no surprise). What is increasingly an issue, and what does not fall into the definitions given above is when we have alternative information from invasive monitoring and/or USS where a pulse may not be easily palpable, but cardiac activity, pressure, and/or flow are demonstrable. It seems that the more information we have, the more blurred the definitions and assumptions become. The matter becomes even more complex when ECPR is considered.
Final thoughts.
Language really matters in resuscitation. We are often required to make time critical, information light decisions for our patients in environments that present a number of non-technical challenges and where clear communication and understanding is vital. All the great resuscitation clinicians I have met stress the importance of a shared mental model, but in this area, and with the examples given earlier it is clear to me that we can do better.
Some may be argue that this blogpost is about semantics, but I would disagree. The case above (anonymised and altered) is based on a patient I saw who subsequently walked out of hospital neurologically intact after the team was encouraged to take a different view of what was meant by ‘downtime’, and I have a colleague who is still troubled by a case much earlier in their career where a decision to stop was perhaps made earlier than it should be as a result of a misunderstanding of what ‘downtime’ meant.
Whatever I think it’s clear that the concept of downtime is a factor in sharing the likely success or failure of resuscitation, but it is poorly understood and/or agreed. There are better ways of communicating what has happened to our patients and with a bit more thought in how we do this we might get better understanding and perhaps better patient outcomes.
I like the idea of TOSC, and I like the idea of describing low and no-flow states (if that information is available) when giving a hand over. If I’m receiving a handover and the term downtime is used then I will endeavour to clarify exactly what is meant by the term.
As always we would be interested in your thoughts and (within the rules of confidentiality), your experiences in practice.
vb
S
Further reading.
Adnet F. Cardiopulmonary resuscitation duration and survival in out-of-hospital cardiac arrest patients. Resuscitation 2016. https://pubmed.ncbi.nlm.nih.gov/27987396/
Sawyer K, Kurz M. Caution when defining prolonged downtime in out of hospital cardiac arrest as extracorporeal cardiopulmonary resuscitation becomes accessible and feasible. Resuscitation 85 (2014) 979–980
Deshpande P et al: Prolonged cardiopulmonary resuscitation and low flow state are not contraindications for extracorporeal support. Resuscitation 2019. https://doi.org/10.1177/0391398819876940
Matsuyama T et al. Impact of Low-Flow Duration on Favorable Neurological Outcomes of Extracorporeal Cardiopulmonary Resuscitation After Out-of-Hospital Cardiac Arrest. Circulation 2020 https://www.ahajournals.org/doi/10.1161/CIRCULATIONAHA.119.044285
Down with "down" time!
