‘Therapeutic hypothermia (TH) improves survival and confers neuroprotection in out of hospital cardiac arrest (OHCA).’
This is a statement that is rapidly becoming a universally accepted position in acute and emergency healthcare worldwide. Surprisingly, there continues to be a slow uptake of the technologies on offer, despite the apparent patient benefit.
Following the publication of two seminal TH articles in 2002 (Bernard et al; The Hypothermia After Cardiac Arrest Study Group, 2002), and the subsequent International Liaison Committee on Resuscitation recommendations in 2003 (Nolan et al, 2003), there has been a steady implementation of the therapy into intensive care units throughout the UK. This, however, has taken somewhat longer than what should have been reasonably expected.
A study performed by Bink et al (2010) conducted a telephone survey of all 247 intensive care departments within the NHS and found that the vast majority (85.6%) of departments are now using some form of TH in their standard care package following sudden cardiac arrest.
Analysis of their data and timescales of implementation supported the suggestion of a 5-year interim period before widespread application of new interventions recommended in the guidelines.
What about the ambulance services?
Despite recommendations for early induction of TH within the 2005 and 2010 European Resucitation Council Guidelines (Nolan et al, 2005; 2010), there has been no published, high quality research performed by any UK ambulance trust into the effectiveness of TH in the prehospital setting.
Some services have ‘dabbled’ with ice cold saline and cold packs, but not one single service in the UK has a prehospital therapeutic hypothermia standard protocol for use following return of spontaneous circulation (ROSC) after sudden cardiac arrest.
‘The results from the ‘Cool it’ trial may well be a starting point to accelerate implementation into the prehospital arena’
For those practitioners who are aware of the pathophysiology of therapeutic hypothermia and the outcome effects that cooling a patient can have, it becomes a frustration that these interventions are not becoming a common and rapidly introduced standard within the emergency setting. It can almost make one seem evangelical in their support of TH when trying to share the benefits that it can bring and persuade clinical managers to introduce the intervention into everyday guidelines.
There has yet to be the momentum created for change in the ambulance service, but the results from the ‘Cool it’ trial published in August may well be a starting point to accelerate implementation into the prehospital arena (Mooney et al, 2011).
The ‘Cool it’ protocol
In 2006, the Minneapolis Heart Institute commenced the ‘Cool it’ protocol which engaged a network of hospitals to commit to improving outcomes following OHCA by implementing therapeutic hypothermia as a standard of care across their region, and importantly, including EMS services into the network for the early application of TH devices.
The central hospital, Abbott Northwestern Hospital (ANW) is a level 1 trauma centre with full cardiothoracic facilities, along with the ability to induce and maintain TH for the recommended American Heart Association (AHA) guidelines of 32–34 °C for 24 hours post-ROSC. The system required all of the networked hospitals (n=33) within a 210 mile radius of the regional centre to transfer all patients who remained unconscious after ROSC following an OHCA to ANW.
Prehospital management added the application of ice packs to the groin, head, neck and chest to the immediate resuscitation attempts and on subsequent transfers. This was not part of the initial study protocol, but was added at a later date after the authors became aware of the added potential benefit of earlier cooling, closer to the time of ROSC.
At the ANW, the patient was then moved onto a further hypothermic device that draws chilled water through hydrogel pads placed directly on the patients skin (Arctic Sun, Medivance Inc, Louisville CO) to ensure that the induction process was continued and then maintained for the 24 hours required before careful and controlled re-warming was commenced.
If the patient was found to be having a concurrent ST elevation myocardial infarction (MI), then they were taken directly to the catheterization lab where primary percutaneous coronary intervention (PPCI) was carried out at the same time that the cooling occured.
The study team looked at two main outcome measures: survival to discharge and positive neurological outcome on survival. Results from the cool it study paint an exciting picture of what can be achieved when a coordinated and focused multi-agency team approach is applied to the continually evolving management of the out-of-hospital (and in-hospital) cardiac arrest patient.
During the study period of February 2006 to August 2009, 140 consecutive patients were included in the trial and were treated with therapeutic hypothermia. Approximately 75% of patients were transferred to the specialist centre from its feeder hospitals, with an average transport distance of 56 miles.
It is important to recognize that the inclusion criteria included all presenting rhythms (VF/Asystole and PEA) as well as those who were in cardiogenic shock. Approximately 50% of the study population were experiencing simultaneous myocardial infarction.
Results
Overall results showed that 56% (n=78) of patients survived to hospital discharge, and of those 78 patients, 92% (n=72) had a positive neurological outcome, described as a cerebral performance category score of 1 or 2 (Table 1).
|
CPC1. Good cerebral performance
|
|
CPC 2. Moderate cerebral disability
|
|
CPC 3. Severe cerebral disability
|
|
CPC 4. Coma or vegetative state
|
|
CPC 5. Brain death
|
Another interesting finding of the study was that when ‘the elapsed time between ROSC and the application of the cooling device at ANW was >2.5 hours, patients were 63% less likely to survive to discharge than when that time remained <1.5 hours’. Further data analysis by the authors after modelling the relative hazards showed that:
‘For every 1 hour in delay to initiation of cooling, the risk of death increased by 20%.’
This is the first time that such a figure has been suggested and should certainly be a stark reminder of the responsibility that ambulance services have in participating in the integrated approach that is needed to give our patients the very best chance of survival following such a life-threatening and frequently fatal event. Questions need to be asked of our practices in the care of cardiac arrest patients, and if we are truly doing everything that we can to restore them to a level of functioning so that they can continue their lives in a purposeful way.
Each and every month, more and more papers are published across the full range of clinical journals on the effectiveness and impact of cooling this group of patients. Not so long ago, almost every conclusion contained a sentence stating that further studies are required. We are now getting to the point where the evidence is becoming indisputable regarding the positive effect that this intervention has; yet we are still not embracing it in the prehospital arena.
Methods that can be used
There are different methods that can be used within the ambulance service, with various rates and mechanisms of cooling and differing financial implications. These range from simple ice packs, ice cold saline infusion, surface cooling pads and transnasal evaporation technology. The relative benefits and limitations of some of these methods will not be discussed in this article, but all readers are encouraged to research what would be the most appropriate for their service to implement cooling in the shortest possible timescale.
The cool it system used ice packs in the prehospital response, but frustratingly, the authors state that ‘many patients now arrive with core temperature reduction significantly underway’, but provide the reader with no temperature measurement on arrival at the ER or upon arrival at ASW. The use of ice packs, while easily applied, cheap and require minimal training, has previously been shown to be inefficient and slow at reducing a patients core temperature following ROSC, with a median time of 7.5 hours before reaching the target temperature of 33 °C (Busch et al, 2006). This begs the question of the actual impact in temperature reduction that the prehospital phase contributed to.
It could be argued that the greater benefit was an general increased awareness of the need for TH, and the fact that some method of cooling was actually already underway. It would have certainly helped speed along the process of cooling at ANW and would have created a greater level of knowledge into the immediate need for patient cooling in the initial post-ROSC period.
Conclusion
We can all look from a distance at what the Minneapolis Heart Institute has achieved and acknowledge the positive impact that they have had within their state area. We also need to reflect and look at the state of prehospital and in-hospital (A&E) initiated TH within our own boundaries. It is not good enough that we accept the alleged 5-year implementation lag that is becoming the accepted norm.
We should be embracing the research, the wealth of evidence available to lead our practice forward, and provide our patients with the care that will potentially save their lives.
There is obviously still a great tightening of the purse strings across the NHS, and we are all having to look at the cost savings that we can bring to our services. The cost improvement programmes continue at a great pace while we all try to be more efficient with less financial support.
In this time of competing priorities, the financing of new technologies and interventions is not the highest priority. But to what cost for our patients?