CPR: Difficult timing

“Call it.” Two simple words, but they are the culmination of one of the toughest decisions a doctor can make- when to stop CPR. Too short and someone dies when they might have survived. Too long and you're cracking ribs, protracting death and perhaps starting a heart again when the mind has died. There are no guidelines on how long CPR should be performed, partly because it's a very difficult topic to study. Imagine trying to get ethics committee approval for randomly assigning people to long or short CPR. Doubtful. Thank God.

Some evidence on CPR does exist, largely from observational studies such as the one published in The Lancet last week by Goldberger et al. One of the biggest studies of its kind, they used the world's largest registry of in-hospital cardiac arrests, including 64,339 patients who suffered a cardiac arrest at 435 hospitals in the United States from 2000-2008. Their aims were to assess whether hospitals spend different amounts of time on resuscitation attempts and whether a hospital's typical resuscitation time affected survival rates.

The study divided the hospitals in to 4 groups according to the median time they spent on resuscitation efforts in non-survivors. This was used as a measure of the hospital's tendency for longer attempts. Just 9 minutes separated those in the shortest group (16min) from those in the longest (25min). But time wasn't the only thing that separated the hospitals. The study team found that patients in hospitals which spent the longest on resuscitation events were 12% more likely to survive and go home than patients in hospitals with the shortest attempts.

Intuitively this might seem obvious- the longer you try, the more people you save, right? As one reader of the Washington University newspage commented: "*face palms and shakes her head* Jesus Mary and Joseph, people are just so stupid. Seriously, this was not obvious to doctors before the study?"

Nope. As we discussed at the outset longer isn't necessarily better- the authors expected to find that longer attempts were futile, resulting in people being 'saved' with minimal brain function. Yet this wasn't borne out in the study- hospitals with longer CPR attempts did not have higher rates of neurologically impaired survivors, just higher rates of survivors.

This brings us to every enquiring mind's favourite question: why? Well, let's start with what the study team think. They note that the patients who benefited most from longer resuscitation times were those whose type of cardiac arrest was “non-shockable”, which means they weren't suitable for defibrillation. One example is “asystole” which looks like this on an ECG.

Asystole. Image from: Ambulance Technician Study.

Note its got a bit of a wiggle to it, a perfectly “flatline” probably means your leads aren't connected, or you're in an episode of Casualty. In the UK, CPR guidelines advise against defibrillation in asystole. The study team suggest that in these non-shockable cases the extra time spent on CPR buys time for medics to figure out the underlying cause of the cardiac arrest and try to tackle it. In light of this, maybe CPR guidelines should state a minimum attempt time?

This seems reasonable, but that doesn't necessarily make it so. All this study has demonstrated is an association between the median duration of resuscitation attempts in non-survivors and post-CPR survival. This could be for other reasons- perhaps hospitals that deliver longer CPR also deliver more effective CPR or have more robust post-CPR care. Given these possible alternative explanations, this study alone isn't enough to justify a minimum CPR time for all. Goldberger himself agrees:

Dr Zachary Goldberger.
 Image:  University of Washington.

“The last thing we want is for the take-home message to be that everyone should have a long resuscitation”. A cardiologist with a-mazing glasses, a first author Lancet paper AND a recognition of the limitations of his research. No denying Zach's a catch ladies.

So, taking these limitations into account, what is the take home message? Reassurance. Reassurance that longer resuscitation times don't appear to lead to a significant increase in survivors with severe neurological damage. With this reassurance, hospitals whose resuscitation times are at the low end of the spectrum should seriously consider aiming to continue CPR for longer.

Whilst the timing of inpatient CPR timing will continue to be investigated and debated, its important to recognise this study is not applicable to people having CPR in the outside world. Just 15.4% of people in this study made it out of the hospital alive. This is because they were sick enough to be in the hospital in the first place. None of this data is transferable to when people have a cardiac arrest in the outside world. Should you ever find yourself in that situation, deciding when to stop CPR is far easier: DON'T. Unless:

1. The person starts to show signs of regaining consciousness AND starts to breathe normally
2. Professional help arrives to take over
3. You physically cannot keep doing CPR

For a CPR refresher, have a read of this and a look at this.

Reference: Duration of resuscitation efforts and survival after in-hospital cardiac arrest: an observational study. Goldberger et al. The Lancet, Early Online Publication, 5 September 2012 doi:10.1016/S0140-6736(12)60862-9. Accessed: 16/09/12

Bleeding science

Cambridge was a strange place. Take our physiology practicals- over the course of a year they made us collect our pee in the lab, stab ourselves and deliver electric shocks to our arms. And then document it all. For one experiment we had to drink one of three liquids (water, cranberry juice or a mystery alkaline cocktail of the departments making, eeeps) then titrate our pee. I kid you not. Can't for the life of me remember the point, or the results, but I'll never forget the boys competing to see who filled the biggest measuring cylinder, or the girl who spilled her pee across the desk . I never knew her name and forever after she was just the girl who pee'd on her practical book...But I digress. This week I've been reminded of a physiology blood glucose practical by an article in the New England Journal of Medicine. We skipped breakfast and took our own blood glucose, before and after a Mars bar. The chocolate was good, the repeated stabbing less so. Like us, the NEJM study was interested in fasting blood glucose- the blood glucose level after 8 hours of refraining from consuming anything other than water. Unlike us, they executed a pretty decent study on the topic which is worth discussing here.

The premise of the study is simple- elevated fasting plasma glucose is associated with an increase risk of cardiovascular disease. It's thought this is due to low background levels of insulin and therefore it has been hypothesised that correcting this deficiency would reduce cardiovascular disease. However, much of the evidence to date has been equivocal, with no clear reduction in cardiovascular disease and suggestions that treatment with insulin might carry an increased cancer risk. Recently, the balance shifted in favour of tight blood glucose with the publication of the UK Prospective Diabetes Study (UKPDS) which found that tighter blood glucose control in new diabetics was associated a 15% reduced risk of heart attack and a 13% lower mortality rate. So, perhaps tight blood glucose control is worthwhile?

Cue ORIGIN, the subject of our musings today. This study involved 12,537 people from 40 countries, who had elevated fasting glucose, impaired glucose tolerance (blood glucose is higher than normal 2hr after consuming glucose) or early Type 2 diabetes in addition to other cardiovascular risk factors. Participants were randomly allocated to receive either a) standard care or b) to inject insulin in addition to their normal glucose control regime aiming for a fasting blood glucose of 5.3 mmol/litre or less. They were then followed for 6 years.

So what did they find? Well, there was no difference between the two groups with regards cardiovascular outcomes (including stroke and heart attacks), cancer or overall mortality. However, they did find that the insulin group were less likely than the standard group to develop Type 2 diabetes (30% vs 35% at 100days after the end of the trial, p=0.05). So, aggressive blood glucose control in non-diabetics with raised fasting glucose or impaired glucose tolerance doesn't make a jot of difference to mortality at 6 years, but it might make you less likely to develop diabetes. Yay? Well, the downside was the insulin group were more likely to experience symptoms from low blood glucose (hypoglycaemia), which include shakiness, anxiety, headache and nausea. 57% of the insulin group experienced at least one episode of symptomatic hypolycaemia, compared to 25% of the standard group. The insulin group also experienced weight gain (median gain 1.6kg) which the standard group did not (median loss of 0.5kg).

Now, the study has its limitations- it's male dominated (65% of participants) and only includes the over 50s, making it hard to know how applicable it is to younger people and women. They only followed up for 6 years which isn't a very long time to catch relatively rare events. Plus only 44% of the eligible insulin group and 47% of the eligible standard group returned to be tested for diabetes at the 100 day point, which leaves a hefty chunk of unknown outcomes. 11% of the non-insulin group ended up taking insulin which further confuses the results. Also there's a depressingly epic list of investigators paid by pharmaceutical companies and the study itself was industry funded by the make of the insulin used. Nuff said.

But the overriding, screaming question for me is would you stab yourself every day, probably put on weight and suffer hypoglycaemia for the possibility that you might be one of the people who doesn't develop diabetes by doing all that? You have to be really motivated. The individuals selected for this trial were motivated and supported- they all said they were up for injecting insulin and they subsequently received regular contact from the trial organisers which can support people to stick with medications. Even in this environment 1 in 5 of those allocated to insulin had ditched it by the end of 5 years.

Diabetes comes with a host of awful complications- leg ulcers, kidney damage, eye damage. I know all this, but I'm still not sure I'd be up for daily insulin to moderately dial down my risk of getting diabetes. But then I paid tuition fees to collect my own pee and stab and electrocute myself, so perhaps sensible life choices are not my forte... What would you do?

Ref: Basal Insulin and Cardiovascular and Other Outcomes in Dysglycemia.The ORIGIN Trial Investigators. N Engl J Med 2012; 367:319-328 http://www.nejm.org/doi/full/10.1056/NEJMoa1203858