It is estimated that over 1000 patients each day experience cardiac arrest/sudden death. Despite ongoing research efforts to identify effective treatments to increase survival rates, to date few improvements have occurred. Outcomes of OHCA have been difficult to measure due to lack of standardization of variables such as pulse upon arrival to the ED, general return of circulation, patient survival to hospital admission, and survival to discharge with or without being neurologically intact between researchers. In 1995, adoption of uniform definitions, data collection sets, and reporting were standardized with the Utstein criteria allowing better comparison between studies.75 Despite the criteria, comparison of data is still hampered by EMS system differences, response times, and bystander CPR availability.
Several identified factors appear to be associated with an increased chance of OHCA survival. Bystander CPR, witnessed arrest, initial presenting rhythm of ventricular fibrillation, and short response times to defibrillation are all associated with increased survival rates.76,77 Eisenburger et al reported having a cardiac arrest in a public place was an independent predictor of improved outcome.78 Immediate defibrillation of patients in ventricular fibrillation results in a pulse-generating rhythm, with survival to hospital discharge, 56% of the time, but drops to 6% by the third defibrillation. Survival rates appear to be highest if defibrillation occurs within the first 6 minutes of cardiac arrest, leveling off after 11 minutes.76
Reported survival ranges for OHCA patients are quite variable and range from 6% to 46%. The largest cumulative meta-analysis study to date documented a mean survival to hospital discharge for all rhythm groups of only 7.6% and a hospital admission rate of 23.8%.13 Liu et al reported that younger age, nonwhite race, and male gender were associated with outcomes.79 Time of EMS arrival is linked to higher survival rates, with even a 1-minute decrease in mean response times showing an approximate 1% (0.7%-2.1% range) absolute increase in survival. Decreasing overall pauses in CPR is associated with better results.80 EMS-witnessed arrests have the best outcomes, followed by bystander-witnessed arrests with bystander CPR, bystander-witnessed arrests without bystander CPR, and unwitnessed arrests, respectively.81 Presenting rhythm of ventricular tachycardia or ventricular fibrillation also results in better outcomes.
One of the largest OHCA studies was the Ontario Prehospital Advanced Life Support (OPALS) study which looked at the effects of multiple variables on OHCA survival as ALS care was phased into their area for the first time. In phase one, witnessed arrest, bystander CPR, CPR by fire or police, and short EMS response times were independently associated with survival on multivariate analysis.82 In phase two, a target of 8-minute response time was set from call receipt to on scene with a defibrillator. Of the 1641 OHCA patients, 90% of calls met the response target with a 33% improvement in survival to discharge in all rhythm groups with an estimated additional 21 lives saved at a cost of $2400 per life.77 A total of 1391 patients were enrolled in the defibrillation plus BLS phase of the study, and 4247 patients enrolled in the ACLS phase. The ACLS phase had greater return of circulation rates (12.9% vs 18%; P < 0.001) and hospital admission rates (10.9% vs 14.6%, P < 0.001), but hospital discharge rates were unchanged (5.0% vs 5.1%; P = 0.83), leading to an odds ratio of 1.1 for ACLS relative to BLS. This ratio did not compare favorably with the odds ratios for witnessed arrest (4.4), early CPR (3.7), and early defibrillation (3.4), respectively.83 This is consistent with other studies of ALS care in OHCA without intravenous (IV) medications which reported no difference in return of circulation, hospital admission, or hospital discharge in shockable rhythms. However, if the initial rhythm was PEA or asystole, the IV group had better return of circulation rates (29% vs 11%; P < 0.001) and hospital admission (31% vs 16%; P < 0.001) but not hospital discharge (2% vs 3%; P = 0.65).84 The lack of change in hospital discharge was not supported in a meta-analysis of 37 articles describing 39 EMS systems and 33,124 patients. When comparing the systems with different capabilities, this study reported a survival to hospital discharge odds ratio of 1.71 for ACLS, 1.47 for a two-tiered system of BLS without defibrillation and ALS, and 2.31 for BLS with defibrillation plus ALS. This study was not sufficiently powered to demonstrate whether one- or two-tiered systems are better, but suggests that either early defibrillation or ALS is more effective than BLS alone.76
End-tidal CO2 (ETCO2) monitoring has become a valuable tool in many EMS systems. Both colormetric and waveform devices are utilized by EMS. Waveform devices are particularly useful for confirmation of airway placement with a sensitivity and specificity of 100%.85,86 The more commonly used colormetric ETCO2 is useful in conjunction with clinical judgment, but it does not appear to be as sensitive as waveform ETCO262 yielding a sensitivity of only 88%.85 Waveform ETCO2 increased with high-quality CPR and ROSC and thus has some value in OHCA prognostication. High levels appear to correlate with ROSC while levels below 10 to 14.3 mm Hg after 20 minutes of ACLS seem to be a predictor of death.87,88 This is also consistent in the pediatric population,63 but more prospective studies are needed before a definitive value as a predictor if death is determined.62,63 Waveform capnography appears to be a real-time measure of the quality of CPR and the possibility of successful resuscitation.63
OHCA outcomes are influenced by hospital destination. Hospital survival rates vary from 29% to 42% with the same prehospital treatment, and outcomes at designated “critical care medical centers” are better.79,89 Hospitals with cardiac catheterization capability that see at least 40 cardiac arrests per year have better outcomes, regardless of how many beds are in the hospital or whether it is a teaching hospital.90 OHCA caused by ST-elevation MIs generally do have better outcomes.91 Surprisingly, higher survival rates are not limited to urban areas as rural locations have documented neurologically intact hospital discharge rates as high as 22%.
Termination of resuscitation efforts in the field is generally accepted practice with only rare problems identified. When to terminate resuscitation efforts is a topic of ongoing debate, with there being a desire to not prolong efforts beyond potential benefit balanced against the desire to not declare death prematurely. Multiple validated rules exist for the termination of prehospital CPR, with the most popular one declaring that only 46% of cardiac arrests need transportation.92 This rule notes that resuscitation efforts may be terminated if there is no return of spontaneous circulation after three rounds of BLS with defibrillation every 1 to 2 minutes, no shock delivered by an AED, and the cardiac arrest was not witnessed by an EMT or firefighter. This rule has a sensitivity of 57.5% to 64.4%, a specificity of 90.2% to 100%, and a positive predictive value of 99.5% to 100%.92,93 Furthermore this rule correctly identified 100% of those discharged with good neurological outcome and 36% of those with poor neurologic outcome or without survival.94 Many EMS agencies no longer routinely transport OHCA patients without return of spontaneous circulation. However, factors that may result in transportation are airway difficulties, persistent ventricular dysrhythmias, excessively public location, family members who are unable to accept field termination, lack of intravenous cannulation, and cultural or language barriers. Additionally, many emergency physicians do not feel comfortable pronouncing a PEA code in the field. Family members generally accept termination of unsuccessful resuscitation efforts in prehospital cardiac arrest.
Prehospital OHCA can be traumatic in origin. These patients have an extremely high mortality rate, and survivors having significant morbidity. The literature suggests that a small subset of such patients can potentially benefit from timely, aggressive treatment while being transported without delay. However, prognosis is dismal in those without signs of life on ED arrival.