Cardiac arrest occurring outside hospital will be treated using emergency medical
services that might have a range of resources available, including advanced life
support systems with cardiopulmonary resuscitation, defibrillation, intubation,
artificial ventilation and intravenous administration of medication. A new
meta-analysis [1] has explored the literature to see whether any particular technique
or combination is better.
Search
The review searched MEDLINE up to mid 1977 for articles in English, and examined
bibliographies of papers. It included only published studies that looked at a several
different systems (Table 1), and which had data on survival to hospital discharge.
This information was extracted, plus response time interval, the proportion of
patients to whom bystanders had applied cardiopulmonary resuscitation and the type of
system used to treat patients.
Table 1: Definitions of different systems of life support after cardiac arrest
examined in the study
|
System of support
|
Definition
|
| Basic life support (BLS) |
Administration of oxygen and cardio-pulmonary resuscitation |
| BLS with defibrillation (BLS-D) |
Additional use of automatic or manual defibrillators |
| Advanced life support (ALS) |
Providers trained to perform endotracheal intubation and
administer intravenous medications |
| BLS + ALS |
Where basic life support is followed by advanced life
support |
| BLS-D + ALS |
Where basic life support with defibrillator is followed by
advanced life support |
Results
Thirty-seven articles had information on over 33,000 people suffering cardiac
arrest out of hospital. None of the studies was randomised. The analysis
investigated the effect of independent variables - the proportion of bystander
cardiopulmonary resuscitation, defibrillator response interval and type of system
used - on the survival to hospital discharge.
Table 2 shows both the crude survival figures and the odds ratios after making
allowance for other variables. Greater survival to hospital discharge was
associated with the type of system used, and also with increases in bystander
cardiopulmonary resuscitation and reduced defibrillator response time interval.
Table 2: Outcomes with different systems of life support after cardiac arrest
examined in the study, using both crude survival percentage and odds ratios after
allowance for differing rates of bystander cardiopulmonary resuscitation and
other confounders
|
|
System of support
|
Survivors / Total
|
Percent (95% CI)
|
Odds ratio (95% CI)
|
| BLS-D |
815/12433 |
6.6 (6.1 to 7.0) |
1 |
| ALS |
560/10072 |
5.6 (5.1 to 6.0) |
1.71 (1.09 to 2.70) |
| BLS + ALS |
842/7502 |
11.2 (10.5 to 11.9) |
1.47 (0.89 to 2.42) |
| BLS-D + ALS |
221/2359 |
9.4 (8.2 to 10.5) |
2.31 (1.47 to 3.62) |
For bystander cardiopulmonary resuscitation, every 5% increase was associated in
an absolute increase in survival of between 0.3% and 1%. A 1 minute decrease in
the defibrillator response time was associated with an absolute increase in
survival of 0.7% to 2.1%.
Comment
The review perhaps emphasises what we might have guessed. Getting in early with
cardiopulmonary resuscitation, defibrillation and pre-hospital advanced life
support all contribute to improved chances of survival for someone suffering from
cardiac arrest outside hospital. There may be no randomised trials, but this is
the best information we have. It is a carefully and cleverly done review that
would help anyone responsible for designing or delivering emergency services
(though readers in Wales may be distressed to find that it claims south Glamorgan
for England!). There is nothing here about quality of survival. What proportion
of the survivors had hypoxic brain damage?
Reference:
- G Nichol et al. A cumulative meta-analysis of the effectiveness of
defibrillator-capable emergency medical services for victims of out-of-hospital
cardiac arrest. Annals of Emergency Medicine 1999 34: 517-525.
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