#ResusciTuesdays is back! (Sorry for the delay - it turns out starting working life is quite tiring and time consuming!) But this week we are back and today we will be talking about Ultrasound in Cardiac Arrest.

I thought an interesting way to cover this topic would be to live tweet along with the @TheResusRoom podcast on this topic whilst I listen to it - so we can all learn together! I do encourage you to go out and listen for yourself and also read the evidence for yourself too!

So what are some of the obvious benefits of ultrasound in arrest? Well it provides us with direct imaging of what is actually happening inside the patient! It also doesn't care any direct harm to the patient as is seen in some other forms of imaging!

And how does ultrasound work? Well apparently it is like if you were to hold the face of a bat against your patient - and as the sonic waves bounce back, they provide you with a blurry grey image!

If the area on the image is bright, then this means lots of the wave has bounced back, so there was a dense object in the way. If the area is dark, then it means that the wave has passed through and not bounced back, suggesting a less dense area such as fluid!

In cardiac ultrasound we typically use a phased array ultrasound probe which is a low frequency probe. This will therefore give a low quality image, but will penetrate effectively and show a detailed enough image for us to recognise the gross pathology that we are looking for!

So when in cardiac arrest should we be using cardiac arrest? Well in a patient with a shockable rhythm we know that the most effective treatment is CPR and defibrillation. Therefore there is no benefit to gaining extra information in these patients, so no use for POCUS.

So if we have our patient in a non-shockable rhythm, what uses may we have? Well how about prognostication? A 2012 systematic review found that there was a significant association between cardiac activity on POCUS and achieving a ROSC.

As is so often the case with a systematic review, there was significant heterogeneity between the studies. In particular with regards to the differences of definition of cardiac motion (e.g. Any Motion, Movement of Valves, Ventricular Activity) so can we draw strong conclusions?

Well given there are still positive outcomes in both groups - we can't make too many decisions based on this anyway, but it does provide more information. A smaller study of 48 patients looking at regular ultrasound through a cardiac arrest also found some interesting results:

They found that in patients with cardiac standstill for more than 10 minutes there was 100% mortality. Whilst this is only a small study the result is interesting and may suggest that regular ultrasound in arrest provides the extra information needed to allow for prognostication.

This use of serial ultrasound will also allow greater agreement between the team on whether there is cardiac activity present and whether or not there has been a step change over time.

So how about identification of reversible causes of cardiac arrest? Well ultrasound can effectively identify at least two of these: 1) Cardiac Tamponade (As fluid in the pericardium) and 2) PE (As right heart dilatation).

But while we know that RV dilation is useful in live patients for suggesting PE, but are our patients in arrest definitely the same? We know that our patients have low flow and there is evidence that multiple things (including misinterpration) can lead to RV dilation!

So there is disagreement on whether RV dilation on USS in cardiac arrest provides useful information, and whether it is therefore reasonable to act on this information (alongside your other information) to give thrombolysis in cardiac arrest!

How about scanning the lungs to look for pneumothorax? There is little evidence that this is effective. Our arrest patients will be being ventilated and therefore the person ventilating will have information about resistance to ventilation. USS may therefore not be necessary.

So what do we already know? We know that CPR and effective ALS improve outcomes. We therefore should not allow our use of ultrasound to interrupt this. We know that pauses to CPR cause worse outcomes. We therefore should ensure that the use of POCUS does not prolong pulse checks.

There is evidence that POCUS in arrest does prolong pulse checks - but many of these studies were run a few years ago and therefore we may have improved our ability to use ultrasound and this may no longer be the case.

It is also the role of the team leader to ensure that this prolongation does not occur even if the desired images have not yet been achieved.

So to get these images quickly; We we need to have a skilled sonographer, the USS must be turned on and in position prior to the pulse check. We then must focus on getting a good image which we can then save and review after, rather than diagnosing during the pulse check!

In summary - there is good evidence for POCUS for prognostication, we just don't have enough detail to make many decisions based on the results yet. There is mixed evidence on RV dilation and PE and there is a chance that the use of POCUS can prolong gaps in CPR.

This means that POCUS may have a useful role in cardiac arrest, but like many things it needs more evidence! If you are to use it, it is important that it is within a system ready for its use, and that team leaders are aware of the harm it may cause if pulse checks are prolonged.