New data supports current management of CO2 levels in cardiac arrest patients
New data supports current management of CO2 levels in cardiac arrest patients
A promising emerging treatment for comatose adult cardiac arrest patients has been found to yield similar results to current treatment in a new study published today in the prestigious medical journal NEJM. Out-of-hospital cardiac arrests (OCHA) cause significant mortality and morbidity, and the study was one the largest trial ever conducted on cardiac arrest patients admitted to intensive care units.
The Targeted Therapeutic Mild Hypercapnia After Resuscitated Cardiac Arrest (TAME) study showed that maintaining a slightly elevated CO2 level (hypercapnia) for the first 24 hours after a cardiac arrest patient has been resuscitated did not improve neurological outcomes, functional outcomes, or quality of life at six months after the event, and did not impact six-month mortality. Conversely, it did not lead to worse outcomes, either.
Observational studies show that while many doctors follow guidelines and keep the CO2 level normal, it is common to have hypercapnia. These studies suggested hypercapnia was associated with improved outcomes, and there are many physiological reasons why this might be so, including increasing blood flow.
The TAME researchers also conducted an earlier smaller trial that suggested that hypercapnia improved outcomes, but recognised the need for a large trial to confirm this finding.
TAME leader Dr Glenn Eastwood says, “It was a really interesting hypothesis to test, as if it had shown positive results, the change in practice would have been free of cost, beyond those associated with change implementation. But our study provides the strongest evidence to date, and indicates no benefit to changing current practice.”
The TAME randomised controlled trial recruited 1,700 patients from 63 intensive care units in 17 countries, in a uniquely harmonised system that saw them partner with another clinical trial in Sweden. Hospitalised comatose adults resuscitated from out-of-hospital cardiac arrest of a presumed cardiac or unknown cause with sustained return of spontaneous circulation were eligible for enrolment. 847 patients (49.8%) were assigned to targeted mild hypercapnia and 853 (50.2%) to targeted standard care (normocapnia).
The primary outcome was a favorable neurological outcome defined by a Glasgow Outcome Scale-Extended score of 5 to 8 at six months, obtained by blinded assessors. Secondary outcomes were similarly measured at six months by other relevant, validated scales.
Dr Eastwood says, “There’s three main ways our study impacts practice and research.
“Firstly, while we found no additional harm from pursuing hypercapnia in these patients, the lack of benefit means there’s no need to change practice– it would be a waste of time and resource. So, doctors can rest assured that patients aren’t missing out if they receive standard practice.
“The second is that while we are somewhat disappointed we haven't discovered a new therapy for these patients, we demonstrated that these patients can tolerate hypercapnia without causing any harm. This can be important in ICU settings, as this allows doctors to less intensely ventilate patients on breathing machines, which can be helpful in some patient groups.
Thirdly, it points to a need for further trials and basic science research, as we seem to have a gap in our knowledge and theories about the role of arterial CO2, and how it impacts the body’s responses. Relevant work is being now conducted, to determine what blood markers can determine good outcomes and allow identification of these patients earlier. We’ve also established a global network of OHCA hospitals and investigators which are now turning to answer the next important question in this patient group.”
The results were published in the journal in a coordinated release with the Critical Care Reviews 2023 Meeting in Belfast.
You can read the NEJM article here.
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