Survival of in-hospital cardiac arrest in men and women in a large Swedish cohort

The impact of sex on survival after cardiac arrest remains in the current situation somewhat unclear with conflicting results. Previous studies show that men are overrepresented in the cardiac arrest population, constituting approximately 60% of all cases but have about a 10% lower chance of 30-day survival than women [1‐3]. This decreased survival for men has been shown despite unfavourable prehospital factors among out-of-hospital cardiac arrests (OHCA) such as higher age, fewer witnessed arrests and less likely to receive bystander-CPR for women [3]. Also, women with in-hospital cardiac arrest (IHCA) have both higher age and prevalence of non-shockable first rhythm [2]. The phenomenon that these studies demonstrate has been described as the ‘gender paradox’, where women survive cardiac arrests to a greater extent despite disadvantageous prerequisites [4]. One explanatory factor proposed for this ‘gender paradox’, have been that women are older when getting coronary artery disease, the reason for this is still unsolved, a so-called cardiovascular protective ‘oestrogen effect’ has been proposed [3, 5]. Another explanatory factor was presented in an American study from 2014, where female gender was associated with longer CPR-duration in patients with an IHCA not achieving ROSC [6].

Still, there are conflicting results and sex has not been shown as a prognostic factor for survival after an IHCA [7]. In summary, women appear to have better outcome than men regarding cardiac arrests and the causal factor of this phenomenon is yet unknown. Therefore, we conducted a cohort study with the aim of assessing differences in patient characteristics, intra arrest factors as well as post-ROSC treatments between men and women as well as the association with gender and 30-day survival after an IHCA.

This cohort study over 10 years illuminates an almost equal distribution of patient characteristics and cardiac arrest factors and possibly therefore an equal 30-day survival after an IHCA for men and women.

Still this study confirms previous findings of disadvantageous prerequisites such as higher age in women and more often shockable rhythm in men, but also indicates that men might have more severely deranged vital signs or not having their vital signs checked equally often as women which deserves future attention and might indicate residual confounding.

The results on age and shockable rhythm are in line with previous studies [2, 15], but no previously published study has investigated sex differences in CCI, NEWS and decision to withhold/withdraw treatment post-ROSC among a cardiac arrest population, and therefore comparisons to other studies are not possible. A factor affecting both the incidence to have an IHCA and the outcome of such is the admission to intensive care. Previous studies have shown that women are less likely to receive early invasive strategies such as PCI [16‐18] as well as being admitted to ICU as well as received less advanced treatment while at the ICU, discussed to be a consequence of more assessments by Rapid Response Teams in men and more decisions to withhold/withdraw treatment in women [19]. However this could not be shown within our study. Interestingly, the same research group has shown that there is no difference in willingness to admit men or women to ICU but female physicians tended to be more willing to admit patients, regardless of the patient being a man or a woman, than their male counterparts [20]. Also, women tend to be placed in ordinary internal medicine unites instead of CCU’s [21, 22].

Regarding the previously shown increased early survival, i.e. ROSC or admitted alive to hospital for women [3, 4], we found no difference in either portion having ROSC or CPR durations between men and women.

The disadvantageous prerequisites for women compared to men in studies regarding OHCA were identified as higher age, more likely to present with an OHCA in a non-public space, less likely to have a witnessed OHCA and a lower frequency of initial shockable rhythm, [2]. Solely age and initial rhythm are directly translatable in a hospital setting, which causes issues when comparing with this study.

Limitations of the study include residual confounding in variables not captured within this study such as PCI and etiology of the cardiac arrest which is important since cardiac etiologies are more common in shockable rhythms than non-shockable one. Further, factors involved in and affecting daily care not even known to clinicians and researchers are a major limitation. Further, we lack information about intake of estrogen among women, however Swedish guidelines do not recommend estrogen in women of the ages having IHCA [21].

Strengths include the inclusion of two separate different hospital-sites over ten years. Further, collection of data was based on a strict a priori determined protocol and another strength is the complete information about the outcome, i.e. 30-day survival or not due to Swedish Personal Identification Numbers and registries [14].

In conclusion, this is the first study following patients with IHCA comparing men and women over 10 years. We found equal distribution of patient characteristics and cardiac arrest factors and possibly therefore an equal 30-day survival after an IHCA for men and women.

However, our study confirms previous findings of disadvantageous prerequisites such as higher age in women and more often shockable rhythm in men, but also indicates that men might have more severely deranged vital signs or not having their vital signs checked equally often as women which deserves future attention and might indicate residual confounding.