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Cardiac arrest: first-line therapy
battle
Sudden heart attack? Vasopressin
works best but only on patients with asystole. The epinephrine
debate rages on
By Jadzia Jagiellowicz
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What the College of
American Emergency
Physicians had to say:
1)
The finding of a difference in response for patients
in asystole is the result of a post-hoc subgroup
analysis. As we all know, the findings of a post-hoc
subgroup analysis cannot be used to draw a conclusion
-- only to generate a hypothesis for further study
in a trial in which that hypothesis is tested
as a primary endpoint.
2)
Patients in both groups received a variety of
other interventions, for which the authors could
not control -- nor did they attempt to do so.
These certainly represent potential confounders,
the influence of which cannot be elucidated with
any degree of confidence.
3)
The number of patients in asystole was 528 (44.5%
of the total), so this subset contains a relatively
small number of patients from which to attempt
to derive a meaningful result. (It is actually
a sizable number as resuscitation studies go,
but still small.)
4) The absolute number
of patients in asystole who survived to hospital
discharge was 12 in the vasopressin group versus
4 in the epinephrine group. Many of us believe
that the only outcome that matters is neurologically
intact survival to hospital discharge. So the
question, then, is how many of those 12 patients
were neurologically intact? The answer is not
in the paper, for reasons that are unclear. The
authors used terms to describe neurologic outcome
that are not defined in the paper ("good cerebral
performance," "moderate cerebral disability,"
"severe cerebral disability" and "coma or vegetative
state"). While the reader may not know exactly
what these terms mean, we may surmise that the
latter two groups did not have the outcome we
look for in a resuscitation study, and it is entirely
uncertain how many in the first two groups returned
to playing Rachmaninoff. In any case, the paper
offers overall numbers of survivors falling into
these four categories, but no such numbers are
provided for survivors of asystole.
5) If one looks at
the statistical calculations for these numbers
(12/257 survivors to hospital discharge in the
vasopressin-treated asystole patients versus 4/262
in the epinephrine group), the P value is 0.04
and the odds ratio is 0.3. But the 95% confidence
interval for the odds ratio is 0.1-1.0. As we
know, when the 95% confidence interval touches
1.0, that includes the possibility that there
is NO statistically significant difference between
the two groups.
Source: http://www.acep.org/
1,33308,0.html
What do you think?
If you have an opinion about this issue please
email us at editors@nationalreview
ofmedicine.com
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A drug that was once thought
second-best may be just what the doctor ordered for
patients in sudden cardiac arrest. Results from a new
study of the synthetic hormone vasopressin in the January
8 issue of New England Journal of Medicine (NEJM)
showed that it was better at saving the lives of patients
in sudden cardiac arrest than the current first-line
treatment, epinephrine.
Previous evidence had pointed
to the fact that vasopressin is better than epinephrine
in resuscitating cardiac arrest victims and having them
survive over the short-term. Now European researchers
have added more evidence to that position.
Their study was conducted
in 44 medical service units in Austria, Germany and
Switzerland. Study investigators gave an injection of
either epinephrine or vasopressin to 1,186 patients
who suffered a cardiac arrest outside of a hospital
-- they presented with ventricular fibrillation, pulseless
electrical activity or asystole, the most deadly type
of cardiac arrest, followed by additional treatment
with epinephrine if needed.
The study found that vasopressin
saved more patients than did epinephrine. Almost 30%
of patients with asystole who were given vasopressin
made it to the hospital alive, compared with 20% of
those patients who had been administered epinephrine.
Unfortunately, not many patients with asystole survived
their hospital stay. The asystole patients administered
vasopressin had better survival than those given epinephrine,
but even then only 5% of them made it home. Also, vasopressin
only made a difference in patients with asystole. It
was no better than epinephrine in saving patients with
ventricular fibrillation or pulseless electrical activity.
The most recent guidelines
from the International Liaison Committee on Resuscitation
advised emergency response teams to give patients epinephrine
as a first-line treatment during CPR. They recommended
that vasopressin can be used, but only if epinephrine
does not work. However, controversy still rages in the
medical community over which drug is the most effective
and safest. Using epinephrine during CPR can cause increased
oxygen use by the myocardium (the heart's muscular wall),
ventricular arrhythmias and myocardial dysfunction after
resuscitation. But vasopressin has not exactly been
welcomed with open arms for all types of cardiac arrest.
The Canadian Association of Emergency Physicians, for
instance, concluded in an April 2001 report about the
guidelines that "clearly, more evidence is required
before vasopressin is recommended in [ventricular fibrillation]."
In North America and Europe
combined, more than 600,000 people die suddenly every
year, most of them from a heart attack or heart rhythm
disturbance.
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