We found that 18.3% of patients in this cohort of Medicare beneficiaries receiving in-hospital CPR survived to hospital discharge. With our analysis limited to older adults, it is surprising that survival was slightly higher than that seen in the NRCPR study of nearly 15,000 cardiac arrests in patients of all ages (17%).9
The over-representation of large, urban, academic hospitals in NRCPR may result in over-representation of patients with higher acuity of illness.
There are numerous possible explanations for our finding no increase in survival following in-hospital CPR from 1992 to 2005. One possibility is that attempts at enhancing CPR delivery have not improved outcomes after inpatient cardiopulmonary arrest. Systems changes in the out-of-hospital setting contributing to improved survival including widespread bystander CPR, emergency response crew-witnessed cardiac arrest, telephone dispatcher-assisted CPR, and automated external defibrillator use, do not have analogues in the in-hospital setting.20, 21
Another possibility is that cardiac arrest patients’ acuity of illness, underlying cause of cardiac arrest, or initial arrest rhythm have changed over time. Although all patients requiring CPR have severe acute illness by virtue of needing CPR, there may be differences in the type or severity of the acute illness leading to CPR that may influence outcomes. Perhaps declining cardiovascular mortality and morbidity, coupled with the increasing incidence of critical illnesses such as severe sepsis, has led to a decrease in the proportion of patients whose initial cardiac arrest rhythm is either ventricular fibrillation or ventricular tachycardia, both of which are associated with higher survival.9, 22-24
Therefore a static survival rate could occur if CPR delivery has actually improved but been offset by an increasing proportion of patients with non-survivable primary illnesses receiving CPR.
Overall cumulative incidence of CPR was 2.73 per 1000 hospital admissions and fell within the range of 1 to 5 per 1000 reported previously.25-28
An important finding of this study is that although the incidence of CPR did not change substantially during the study period, the proportion in-patient deaths preceded by CPR increased. Since we observed the same trend when the denominator was all beneficiary deaths, the movement towards more death in the home or hospice cannot explain this increase. While do-not-resuscitate (DNR) orders became more common throughout the 1980s, our findings suggest either a reversal in that trend or that DNR orders are not effectively limiting CPR in individuals unlikely to benefit from resuscitation.29
Perhaps this increase represents a trend towards poorer candidates for CPR being more likely to receive resuscitation, and if so, provides another potential explanation for the observed static survival following CPR. The significant increase in the proportion of survivors having discharge destinations other than home may indicate a trend towards poorer neurologic and functional outcomes among CPR survivors. However, this trend may be confounded by a shortening of inpatient hospitalizations during the study.30
The associations of greater age, male sex, and a higher chronic illness burden with poorer survival are not surprising. Our finding that residence in a skilled nursing facility prior to admission was associated with poorer survival provides further evidence that chronic illness impacts outcomes following CPR. Our finding that CPR in a smaller or non-metropolitan hospital was associated with greater survival is unexpected, although residual confounding by severity of acute illness is likely, given our inability to assess this factor.
We found a strong association between race and survival, with black and other non-white patients having significantly higher likelihood of receiving CPR and lower odds of survival. This association did not change when adjusted for patient factors but was slightly attenuated by adjusting for individual hospital, suggesting that the difference in survival between white and non-white patients may be partially explained by the fact that non-white patients were more likely to receive care in hospitals where patients had lower odds of survival following CPR, regardless of their race. Prior studies have found reduced survival in black individuals following both in- and out-of-hospital arrest, and recent work has reported that black race is associated with delayed defibrillation in the hospital.12-14
Initial cardiac arrest rhythm may differ by race, suggesting that differences in the biology of cardiac arrest, perhaps due to genetic and environmental factors, could partially explain racial differences in survival.13
It is also possible that the quality of care before, during, and after cardiac arrest is lower for black patients.31
Finally, recent findings suggest that systems factors may affect survival following CPR. For example, variations in survival by time of day appeared lower in hospitals with more extensive monitoring, suggesting that system-level variations in quality of care may help explain hospital differences in survival and between-hospital differences in systems facilitating rapid resuscitation may partially explain racial differences in survival.32, 33
We found the incidence of in-hospital CPR is higher and increasing faster for black patients than for other patients, a result mirroring the higher incidence of out-of-hospital cardiac arrest seen in black patients.13
This racial difference in incidence may result from higher chronic illness burden, as reflected by higher Deyo-Charlson scores, in black patients. The higher incidence and severity of diseases such as cardiovascular disease among black patients may also play a role in this difference.34
Thus, the increasing incidence of in-hospital CPR could partially result from increasing severity of acute and chronic illness among hospitalized black patients.
We also found that a higher proportion of black patients dying in the hospital received CPR compared to members of other racial groups, which coincides with evidence that black patients are more likely to receive higher intensity of care, including ICU care, at the end of life.35
This may result from black patients less frequently choosing DNR status, a mechanism that could also partially explain the difference in incidence of in-hospital CPR by race.36-38
If more commonly choosing to be resuscitated results in more CPR being performed among patients with lower likelihood of survival, this could account for much of the racial difference in survival.
There are several important limitations of this study. First, our definition of CPR is dependent on ICD-9 codes. This definition has not been validated within Medicare data, and the specificity and sensitivity may vary between hospitals. However, our estimates of CPR survival and incidence are similar to prior studies, supporting the accuracy of this definition. Furthermore, it is unlikely that the sensitivity and specificity have changed over time, making it likely that these trends in survival and incidence are accurate. Finally, short of conducting a detailed prospective observational study, validating our definition of in-hospital CPR within Medicare data is virtually impossible because there is no “gold standard” with which to compare it. A second limitation is the absence of some potential predictors of survival following CPR within MedPAR. These include severity and type of underlying acute illness, initial rhythm during arrest, location within the hospital, and time to defibrillation. Such features may be particularly important in understanding differences in survival by race and hospital. Finally, survival to discharge may not be the most clinically relevant outcome following CPR. The ability to evaluate longer term outcomes, including the degree of neurological impairment after CPR, would be valuable.
In summary, we found that survival to discharge following in-hospital CPR has not changed among Medicare beneficiaries 65 and older between 1992 and 2005. The incidence of in-hospital CPR has also not substantially changed during this time period. Of significant concern is our finding that the proportion of patients receiving CPR prior to death has increased during a time of more education and awareness about the limits of CPR in patients with advanced chronic illness and life-threatening acute disease.39
Our findings that survivors of in-hospital CPR are less frequently being discharged to home is also concerning, but may be confounded by trends toward shorter hospital stays. Factors associated with lower odds of survival included older age, male sex, chronic disease burden, and non-white race. Some, but not all, of the racial difference in survival appears to be attributable to the hospitals where patients receive care, with black patients more often receiving care at hospitals where patients of all races have lower odds of survival after CPR. We have also found that black patients are more likely to receive in-hospital CPR prior to death. A greater preference for CPR, despite prognosis, may provide another explanation for differences in survival by race. This study provides information useful to older patients and their clinicians when considering preferences for CPR since the proportion of elderly patients choosing CPR is directly related to the probability of survival presented to these patients.40
Our findings also provide stimulus for further research to better understand the association between race and survival, not only with the goal of eliminating racial disparities in the quality of medical care, but also to help understand factors associated with the occurrence of and survival following CPR for patients of all races.