Therapy Factors
The quality and type of therapy may determine outcome. These include pharmacotherapy, defibrillator guided therapy, impedance threshold devices, CPR adjuncts, chest-compression only CPR, airway management, hypothermia, quality of hospital care. CPR and defibrillation are therapies and perhaps should be in this section but because of their intimate association with the system of care and the criticality of time these factors are in the system factors section. Therapy begins in the field and continues in the emergency department and hospital. One can argue that the evaluation clock of an EMS system should stop upon hospital admission since hospital care surely must be a determinant of the outcome. The counter argument is that hospital admission without discharge is an empty victory. The only meaningful statistic is hospital discharge and virtually all researchers in the field accept this as the only important outcome. Therefore it is important to add hospital therapy to the mix of predictive factors
| Therapy Factors | Strength of Association with Outcome |
| Pharmacotherapy | Unknown |
| Defibrillator guided therapy | + |
| Impedance threshold device | Unknown |
| CPR adjuncts | 0 |
| Chest-compression only CPR | Unknown |
| Airway management | + |
| Hypothermia | ++ |
| Quality of hospital care | Unknown |
Pharmacotherapy at the scene (unknown association with survival):
It was always assumed that pharmacological therapy delivered to a patient in cardiac arrest or shortly after the return of spontaneous circulation improved the outcome. But there are surprisingly few data to support such a belief. The main drugs administered during a resuscitation are cardiac stimulants (epinephrine or vasopressin), anti-arrhythmics (meant to stablilize the rhythm - these include lidocaine, amiodorone, beta-blockers, and rarely procainamide), pressors (meant to increase the blood pressure - most commonly used are norepinephrine or dopamine), rate increasers (atropine) and a few other miscellaneous medication such as sodium bicarbonate (meant to neutralize acidic blood). None of these medications have been rigorously evaluated or studied in randomized clinical trials and compared to a placebo though a few such as amiodarone and lidocaine have been compared to each other. Part of the reason for this lack of definitive information is that most of these drugs have been around for a long time and entered the pharmocotherapeutic armamentarium long before rigorous randomized clinical trials were mandatory. In non-randomized trials or in case series they seemed to help and consequently crept into the standard of care through the back door. And now they are difficult to study precisely because they are thought of as the standard of care.
One pharmacologic work horse, epinephrine, used in the management of intractable VF as well as asystole and PEA since resuscitation standards were first put forth, was recently evaluated in a large clinical trial in Singapore. Using a before and after study design the researchers studied one year of resuscitation without epinephrine and compared survival to one year with epinephrine added to the resuscitation protocols. There was no significant increase in survival with epinephrine.
Defibrillator guided therapy (weak association with survival):
When you and I look at the pattern of VF we see a bunch of squiggles. But a new generation of defibrillators can interpret this information and predict the likelihood that the next shock will be successful. This in turn can guide the rescuer through the timing and energy level of defibrillatory shocks or whether further CPR is required. Defibrillator guided therapy can be applied in several ways. For automated external defibrillators, the device used mostly by EMTS, the probability of a successful shock may determine whether the device advises a shock. For manual defibrillators, used mostly by paramedics, the probability may be displayed on the monitor. Since the device can calculate this probability in real time it can show the probability from 0 to 100%. If the percentage is low the rescuers should devote attention to CPR and/or administering medication and wait until the probability creeps beyond 50% before defibrillating. This technology, still in its infancy, offers great promise of seeing how CPR and therapy alter the VF waveform and may help protocols for cardiac arrest. It is even conceivable that defibrillator guided therapy can one day be combined with physiological information (such as blood lactate levels, or acid-base values) to recommend specific pharmacologic therapy and doses as well as defibrillatory therapy.
Impedance threshold devices (unknown association with survival):
ITDs are clever little devices that work well in animals and offer some promise of improving circulation during CPR and therefore improve survival. The device, about the size of a plum, works by impeding the passive return of air into the lungs with chest decompression (the upstroke of CPR). This in turn allows more blood to fill the major vessels in the chest and thereby improves blood flow with the next downward stroke of CPR. ITDs are easy to use during a cardiac arrest. The EMT simply places it between the face mask and the bag valve mask. Paramedics place it between the end of the intubation tube and the bag valve mask. It literally takes seconds to apply. In animals the ITD device raises blood pressure during CPR. It is approved by the FDA for shock conditions but not yet for cardiac arrest. Whether it helps in CPR will be the studied by the Resuscitation Outcomes Consortium (ROC).
CPR adjuncts (no association with survival):
Many CPR adjuncts have been proposed over the past several decades. These range from compressed air piston devices to perform chest compression, plunger devices to achieve active compression and active decompression of the chest, compression straps to automatically compress the chest, and so on. All are meant to save on the labor of CPR while improving cardiac output. While many of these appear promising in the animal laboratory, none seem particularly worthwhile in human use.
Chest-compression only CPR (unknown association with survival):
Most communities in the US have very low rates of bystander CPR. In response, many EMS leaders argue for a radical change in public CPR training and in telephone CPR instructions – eliminate the mouth-to-mouth portion of CPR (it should properly then be called CR). Several arguments are offered in favor of compression-only CPR. First, there is the perception that the public is unwilling to perform mouth-to-mouth and would be more willing to administer compression-only CPR. Let me dispel this right away. In 25 years of monitoring telephone CPR in King County I have not noted this to be a problem, primarily since most CPR occurs in the home. Even in public situations, I am unaware of instances where a strange mouth inhibited full CPR. Nevertheless I readily acknowledge the lower rates of bystander CPR in other communities and it is certainly conceivable that performance of mouth-to-mouth may be an inhibiting factor. The second argument against the necessity of mouth-to-mouth is that, since at the moment of cardiac arrest the blood is fully oxygenated, the only need is to perform chest compression. This may be true for the first several minutes but the saturation of oxygen in the blood falls very rapidly thereafter and can only be replenished with artificial respiration (mouth-to-mouth ventilation). There are few if any systems in the world that can bring EMS personnel to the scene within three or four minutes of collapse. Peter Safar, one of the co-founders of modern CPR would be spinning in his grave if he knew that researchers were advocating the elimination of P in CPR. His elegant experiments in the 1950s convincingly demonstrated that chest compression alone was not sufficient to maintain oxygenated blood. The third argument is that chest compressions are easier for the public to perform and that mouth-to-mouth is especially difficult for dispatchers to teach over the telephone. But ease of performance is irrelevant if it remains an ineffective therapy. Furthermore, the mouth-to-mouth instructions for telephone CPR can help sort out real cardiac arrest from a false positive cardiac arrest. The mouth-to-mouth ventilation is an irritant and someone who is not in cardiac arrest is likely to push the rescuer away. Better a puff in the mouth instead of a cracked rib.
The controversy rages. The American Heart Association in their 2005 guidelines state that chest compression is an alternative if the rescuer is unwilling to do mouth-to-mouth and that dispatch centers have the option to offer chest compression only. Several EMS leaders have decided to make chest compression only part of their dispatch center instructions. Is there scientific evidence to support the benefit of chest compression only? There was one prospective randomized study of dispatcher chest compression only versus standard CPR. This 12-year study in Seattle showed no difference between the two messages. It should be pointed out, however, that the response time (dispatch time to arrival at scene) for EMTs in Seattle is 3.5 minutes, one of the fastest response times in the country. Such a quick response probably precluded the opportunity to observe benefit of mouth-to-mouth over chest compression only. In other words in a community with a very rapid response time both methods of CPR may be equally effective. In 2007 an observational study from Japan showed that chest compression only was better than standard CPR. This was not a randomized trial and did not involve telephone instructions. Furthermore, the study contained no explanation why twice as many bystanders chose to do chest compression only over standard CPR. There are currently two international randomized trials that should resolve the issue, at least as far as dispatch centers are concerned. The controversy will continue to rage for how best to train the public. There may be a middle ground to this controversy. It may turn out that chest compression only CPR is the best option for witnessed cardiac arrest, especially in communities with rapid EMS response times, but for unwitnessed cardiac arrest or arrests with long response times standard CPR may be the preferred option. The dispatcher, once he or she determines if the collapse was witnessed would give the appropriate message. Such a conditional therapy takes into account the likely duration of cardiac arrest and the amount of bystander CPR before professionals arrive to take over CPR. The message could also be determined by the response time since the dispatch center would know this information. Thus it might be possible to custom fit the CPR instructional message to the circumstances.
Airway management (weak association with survival):
It seems intuitive that good airway management will improve the odds of surviving cardiac arrest. A study of cardiac arrest patients in King County by Brad Shy demonstrated that patients who were intubated quickly had a higher survival. 46% of patients in the quick intubation group survived compared to 23% in the slow intubation group. This was a retrospective observational and hardly proof of the relationship but it suggests that the intuition may be correct. The EMS world is conflicted about the type of airway management that paramedics should be allowed to perform. The Cadillac of airway management (and the type that is perform in emergency departments and operating rooms) is endotracheal (meaning down the windpipe – trachea) intubation with paralytic medications. Yet probably less than 10% of EMS systems authorize paramedics to use paralytics. Other systems allow intubation without paralytics and still others allow airway adjunctive airways (such as laryngeal mask airways or combitube airways) which are not considered as effective as endotracheal intubation.
Hypothermia (moderate association with survival):
In 2002 two randomized trial were published in the New England Journal of Medicine demonstrating that cardiac arrest patients treated with hypothermia had better outcomes. The idea of hypothermia has been around for decades. It seems logical that cooling the body and the brain will slow metabolism and afford more time for healing. As mentioned above the postulated third phase of cardiac arrest (the metabolic phase) may respond to hypothermia. The two articles generated much excitement. Some would even say it was the best evidence of therapeutic benefit to come along in many years. Endorsements by the American Heart Association and the International Liaison Committee on Resuscitation followed in 2005 and in effect made hypothermia the new standard of hospital care. Some programs began to push the envelope even further and explore whether hypothermia could be started in the prehospital setting. For example, a pilot study in Seattle showed that two liters of cooled IV fluids can be administered by paramedics and begin cooling even before arrival at the hospital emergency department.(69) The benefits of hypothermia are still being explored. Will it benefit all rhythms or only VF? Can it be started in the prehospital setting? Are there pharmacologic adjuncts to hypothermia? Should hypothermia be induced quickly or slowly? Though the degree (pun intended) of benefit has yet to be determined, hypothermia appears to offer a new therapeutic option and thereby improve the outcome in some cardiac arrests.
Quality of hospital care (unknown association with survival):
In King County 8 hospitals receive the vast majority of resuscitated patients. If hospital care varied we’d expect to see differences in survival rates among admitted resuscitated patients among the hospitals. But such differences do not exist. The rates of discharge among the resuscitated patients are virtually identical among the hospital. Thus hospital care can be considered a constant factor which is not surprising since post-resuscitative care is fairly well standardized. A study from Sweden found contrary results. Among 3853 patients brought to 21 hospitals survival (defined as alive one month after cardiac arrest) varied from 14% to 42%. A study from neighboring Norway demonstrated that a predefined hospital post-resuscitation protocol improved survival compared to historical controls. There are too few other studies to draw definitive conclusions. Could differences be due to differing protocols or differing quality of care? Clearly this is a potentially important factor.