Declining Admission and Mortality Rates for Subarachnoid Hemorrhage in Canada Between 2004 and 2015

Atraumatic subarachnoid hemorrhage (SAH) remains a devastating disease caused mostly by rupture of intracranial aneurysms. Sudden death occurs in 12% based on postmortem studies, and reported 30-day mortality is as high as 45%.^1,2 In the past 2 decades, there have been significant changes in the management and treatment of SAH and associated complications. However, it remains unclear whether these changes have improved morbidity and mortality. Using a population-based approach, this study assessed recent trends in admission and mortality rates for SAH in Canada.

Data were derived from the Canadian Institute for Health Information Discharge Abstract Database. The data confidentiality in this study is protected under an agreement between the Canadian Institute for Health Information and the Heart and Stroke Foundation of Canada. The data cannot be released to a third party, but the source data can be accessed by the public through a request process defined by the Canadian Institute for Health Information. This database captures hospital admission for all provinces and territories in Canada, except for Quebec. Discharge records were attained for anyone discharged in 2004 to 2015 who were diagnosed with SAH as the most responsible diagnosis (International Classification of Diseases-Tenth Revision, I60). Patients were excluded if there was a previous admission in Canada for SAH in the 30 days prior. Coding consistency—a data quality measure, which refers to the consistency with which diagnoses are classified using the International Classification of Diseases-Tenth Revision—was reported to be 76% to 85% by the Canadian Institute for Health Information for years 2004 to 2015. The use of diagnostic codes for stroke based on discharge data was validated in a prior study.³ This study is an analysis of anonymized administrative data to answer specific research and quality questions, which do not require ethics board approval. Patient consent is not required as part of the data sharing agreement.

Admission rates were calculated per 100 000 person-years. The denominator for all calculated admission rates was based on Canadian census data. Statistical differences between the sexes were analyzed using an unpaired t test. Linear regression was used to calculate the unadjusted relative annual percent change (APC).

Mean and median lengths of stay were calculated. Disposition of discharged home was used as a surrogate for morbidity; this was calculated as the proportion of all discharges. In-hospital, 7-day in-hospital, and 30-day in-hospital mortality rates were calculated as the proportion of all discharges. Mortality rates were calculated based on deaths during current hospitalization. This excludes deaths after discharge. APC was calculated for proportion of patients discharged home and in-hospital, 7-day, and 30-day mortality rates. Multivariable ordered logistic regression was used to provide adjusted estimates of mortality and proportion of patients discharged home. Models were adjusted for age, sex, Charlson score, province, and year.

The total number of SAH admissions from 2004 to 2015 was 19 765, in 19 261 patients. The mean age was 58.1±15.9 years. Of the total admissions, 40.3% (n=7972) were men.

In this study, we sought to assess the admission rate and mortality rates for SAH in Canada from 2004 to 2015 and understand how the rates compare with those previously reported in Canada. Admission rates between 2004 and 2015 were lower than those reported previously for 1982 to 1991.⁴ Our admission rates are lower than those reported in England, the United States, and Australia within our study period.^5–7 Admission rates were higher in women, which has been reported in other studies.^4,6,7 We found admission rates declining more in men than in women. This is consistent with findings from Ostbye et al, which reported a decline of 15% for men and 6% for women from 1982 to 1992. Ostbye et al found admission rates peaked and plateaued at 55 to 59 for men and 69 to 74 for women. In contrast, our study found admission rates increased with age. The cause of declining admission rates for subarachnoid hemorrhage remains unclear.

It remains unclear the cause of declining admission rates for SAH. There may be an association with treatment of unruptured aneurysms and changes in previously reported modifiable risk factors. In the United States, from 1993 to 2003, the number of unruptured aneurysms repaired doubled from 11 451 to 23 224.⁸ Similar results were reported by Lin et al.⁹ It is conceivable that increased treatment of unruptured aneurysms may contribute to decreased SAH admission rates. Previously reported modifiable risk factors include hypertension and smoking.¹⁰ Declining prevalence of smoking and improvement in management of hypertension may be factors contributing to declining admission rates.

In this study, we found a lower mortality rate than previously reported in Canada with a declining trend. In Canada from 1982 to 1992, reported in-hospital and 30-day in-hospital mortality was 26.6% and 24.6%, respectively.⁴ Declining mortality has also been reported in other countries. A systematic review by Lovelock et al¹¹ reported similar results of a decreasing trend in case fatality of −0.9% per year. A study in England reported a decline in in-hospital mortality from 30% to 20% from 1979–1983 to 2004–2008.⁵ A study in Australia reported an APC of -4.4% for 30-day mortality between 2001 and 2009.⁷

We found increasing number of patients discharged home and declining mortality over time, which may be associated with increased use of endovascular techniques during the study period. After the publication of the International Subarachnoid Aneurysm Trial results in 2002, which found lower morbidity and mortality associated with endovascular repair compared with surgical repair,¹² there has been an increased use of endovascular techniques. In the United States, percentage of ruptured aneurysms repaired with endovascular technique increased from 9.3% to 42.9% from 1998–2002 to 2002–2007.¹³ Lai and Morgan¹⁴ reported a 2.1-fold increase in endovascular treatment from 2000 to 2008. Similar findings have been reported in Australia and England.^5,7 Studies on treatment of ruptured and unruptured aneurysms report decreased mortality, fewer discharged to long-term facilities, decreased number of adverse outcomes, and shorter hospitalization in patients treated with endovascular techniques.^8,9,15

This is a long-term nationwide epidemiology study using discharge data. One strength of this approach is that rates are more reliable because data are retrieved from a large registry. However, using diagnosis codes from discharge data may have inaccuracies, despite validation of this approach.³ In this study, we report admission rates, which often underestimates the overall incidence because it does not capture sudden deaths and patients who did not present to hospital. There may also be inaccuracies associated with the use of census data as the denominator for admission rate because of undercoverage and overcoverage, which impact population estimates. In this study, we report 7- and 30-day in-hospital mortality rates, which may underestimate the true 7- and 30-day mortality rates because it does not capture deaths post-discharge. Despite shortcomings with this approach, by understanding the trends of SAH, future research may focus on understanding what factors impact these trends.

This study found an admission rate lower than previously reported, with a declining trend. Admission rates remain higher in women and with increasing age. Although mortality rates remain high, rates are declining over time.

This project was reviewed and approved by the Heart and Stroke Quality Advisory Committee. Parts of this material are based on data and information provided by the Canadian Institute for Health Information. However, the analyses, conclusions, opinions, and statements expressed herein are those of the authors and not those of the Canadian Institute for Health Information.