Until further data are available, the best strategy may be to, at least, offer HACA to those PEA/asystole patients who are judged to have some chance of a recovery (eg, short time to ROSC, readily reversible cause of CA, younger or healthier patients).
PEA and asystole are the initial rhythms in 60% of all OHCA64,65 although the proportion has been as high as 93% in some series.66 The two major trials of HACA included only VF and/or VT patients, essentially excluding the majority of OHCA patients.37,38 The large trials focused on VF/VT because it has a better outcome than PEA/asystole, and therefore smaller sample sizes would suffice to show a treatment effect.
A word of caution before moving forward: One must be careful in interpreting outcome rates for OHCA, as this is heavily dependent on the choice of denominator.67 Did the study in question include all patients encountered by EMS, most of whom did not obtain ROSC? This would create the largest possible denominator, and yield the poorest outcome rates. Other studies look only at those who attained ROSC and remained alive by ED arrival. Still others focus only on those who survived to ICU admission. Any data on neuroprotective strategies in PEA/asystole patients should be compared against the outcomes of this last subset of PEA/asystole patients, as other patients would not be amenable to neuroprotective treatment. In the pre-HACA era, 17% to 26% of these patients survived to discharge68-71 (Table 10-3). In addition, one must be cognizant of the types of patients included in these series. Some studies include only patients whose arrest was cardiac in origin (ie, no drug overdoses, choking victims) or whose time to ROSC was within a certain limit.
Table 10-3.Summary of PEA/Asystole Outcome Data in Pre-HACA Era ||Download (.pdf) Table 10-3. Summary of PEA/Asystole Outcome Data in Pre-HACA Era
|Investigators ||Design ||Patients ||N Admitted to ICU ||Survival to discharge, n (%) ||Survival at 1 y (%) |
|Niemann et al71 ||Retrospective ||Cardiac-only, < 10 min downtime before paramedics arrive ||39 ||10 (26) || |
|Böttiger et al68 ||Prospective ||Cardiac-only ||62 ||12 (19) ||9 (15) |
|Engdahl et al70 ||Prospective ||All causes ||324 ||54 (17) || |
|Don et al69 ||Retrospective ||All causes ||191a ||37 (19) || |
Oddo et al prospectively collected data after the institution of a HACA program.72 Of 74 consecutive patients (excluded age ≥80 years or known terminal disease), 36 had PEA/asystole, and all patients underwent HACA. Seventeen percent of PEA/asystole patients survived to discharge, which is in line with survival estimates in the pre-HACA era discussed above. Using stepwise logistic regression, only time to ROSC and lactate levels were found to be associated with poor outcome, whereas initial rhythm, shock, age, and gender were not. The investigators concluded that PEA/asystole carries a poorer chance of recovery compared with VF/VT because PEA/asystole generally has a longer time to ROSC, not because of anything inherent to the rhythms of PEA/asystole.
Nielsen et al published data from an international HACA registry.73 PEA/asystole was the initial rhythm in 283 of 986 patients, and 30% of these survived to discharge (73% of these survivors with good function). The exclusion criteria were left up to individual centers, and these criteria were not disclosed, so these results may reflect a selection bias.
Don et al published their single-center experience before and after institution of a HACA protocol.69 They found no difference in outcomes for PEA/asystole after they began cooling patients. However, there are several issues with the analysis. Patient ascertainment and data collection were done retrospectively, and all patients who presented to the ED were included even if they did not survive to ICU admission or receive HACA. The latter would certainly dilute any effect of hypothermia for PEA/asystole patients. It is stated that an analysis restricted to patients admitted to the ICU failed to show any difference for PEA/asystole patients, but further details were not provided.
Cronberg et al cooled consecutive CA patients74 unless there was a comorbidity which assured a poor outcome or time to ROSC was long/unknown (T. Cronberg, MD, personal communication via email, January 17, 2011). PEA/asystole was the initial rhythm in 29 of 94 patients. Although outcome at discharge is not provided, 31% of PEA/asystole patients had good functional outcome at approximately 6 months. This is substantially better than even survival to discharge in the pre-HACA era.68-71
As it stands, there is no clear data to advocate one way or the other for HACA in PEA/asystole. Based on the above studies and others,75-79 there is no hint that HACA is less safe in PEA/asystole patients compared with VF/VT. The 2010 ILCOR guidelines endorse HACA as an option for PEA/asystole.40