To the best of our knowledge, the present study is the first to describe a new subtype of CA in the ED: CA that occurs in patients who are initially assessed as not requiring immediate therapy or strict monitoring. Generally, data on CA in the ED are scarce; moreover, we have not come across reports of studies that analysed similarly specified sub-populations: patients who underwent CA were classified as stable. We believe that this population is important and requires further attention. It may be hypothesised that proper classification of these subjects could lead to the prevention of CA in some cases. Therefore, at least some deaths resulting from unex-CAED could be classified as potentially avoidable deaths.
Avoidable deaths and avoidable CA represent a significant part of in-hospital CA and in-hospital deaths. Hodgetts found that 62% of primary in-hospital CA (including ED) were potentially avoidable. Moreover, the risk of primary CA was increased in patients staying in a non-critical area, and 17% of CA occurred in patients hospitalised in an area not appropriate to their conditions. In total, 95% of the latter CA cases were classified as potentially avoidable, which corresponds well with our definition of unex-CAED.7 Rogne et al., in a recent study, found a lower frequency of avoidable in-hospital deaths (6.7%) but still suggested the importance of this issue.8 Therefore, clinical characterisation of patients with unex-CAED may lead to improvements in patient safety.
Our definition of unexpected CAED is not based on clinical criteria, but only on logistic criteria. We wanted our definition to be universal and repetitive in other departments. That is why we decided that the event would be classified as unexpected if it occurred in the area of the ED not designed as an area for patients requiring strict monitoring or therapy; therefore, ED staff were not prepared for extremely urgent intervention.
The frequency of CA described in our study was comparable to that in other studies focusing on CA in ED.9,10 We did not find data on unex-CAED from other centres for comparison. Our analysis showed that patients with unex-CAED did not differ from patients with expected CA (according to our definition) in terms of age, sex, and known comorbidities. In both groups, unshockable rhythms were found more frequently, which is in agreement with data from other studies. The only difference was the higher frequency of PEA in unex-CA and a higher frequency of asystole in expected CA. Successful ROSC and survival until the end of hospitalisation were more frequent in unex-CA patients, although the difference did not reach statistical significance. This trend can be explained by the fact that those subjects were initially in a better clinical condition (none of them received the highest triage priority). It remains consistent with the observation that CA in ED have better prognoses.3 As shown by Bircher et al., the shorter the time to cardiopulmonary resuscitation (CPR), defibrillation, or adrenaline (epinephrine) usage (whenever indicated), the higher the probability of survival. At the ED, staff are trained to start appropriate CPR immediately and the equipment needed is on-site (e.g., defibrillator or ampules with adrenaline).11
Our data show certain options for avoiding ex-CAED. We found three cases of unexpected CAED that occurred directly after the arrival of patients in the ED (all three patients arrived in the ED by ambulance). The initial assessment of patients in the pre-hospital phase could suggest a risk for CA. Therefore, pre-notification in such cases would allow ED to be prepared for patients in need of urgent intensive therapy. Pre-notification improves functions of ED.12,13 Our data suggest that dyspnoea, disorders of consciousness, generalised unspecified weakness, and chest pain are the commonest symptoms in patients experiencing unexpected CA. Therefore, patients with these symptoms should be monitored immediately after arrival at the ED. A noticeable fraction of unexpected CA occurred in patients diagnosed and waiting for boarding to other wards. Their presence in the ED is a consequence of ED overcrowding, which has been described as a factor that increases the risk of CA in ED patients.10,14 ED, which plays a crucial role in any healthcare system, requires many measurements of the quality of care. The measures proposed thus far include length of stay, boarding time, and number of patients who leave without being seen by a doctor.15,16 The frequency of unex-CAED may successfully serve as a measurement index of the efficiency of the triage system and the medical examination for determining which patients are at risk of sudden CA.
By definition, the unex-CAED created unexpected outcomes in patients admitted to the ED. Our data showed that there was no difference in the efficacy of resuscitation between patients experiencing unex-CAED and those experiencing ex-CAED. Nevertheless, the specificity of unexpected CA is a good index of staff readiness to undertake resuscitation. Therefore, we postulate that the effectiveness of resuscitation in unexpected CAED may serve as a routine measure of how well team members are prepared for starting resuscitation.
Limitations
Our study has some limitations. The sample size analysed in the present study was small. Observations from longer timespan or multicentre studies focusing on unex-CAED should facilitate the collection of more information. Another limitation of this project is that the small number of patients described does not allow generalisation of the findings to different populations. Studies with such a protocol are at risk of selection bias; however, we formulated the inclusion/exclusion criteria using a general and obvious allocation method to ensure that the sample selection was not biased. As our study was observational, we could not prove the causality of unex-CAED. Our preliminary results should be verified in prospective, multicentre studies with larger samples of patients.