Evaluation of five year survival and major health care resource use following admission to Scottish intensive care units
Lone, Nazir Iftikhar
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Long-term outcomes for patients admitted to intensive care units (ICUs) are recognised to be of increasing importance. Published studies indicate that ICU survivors have significant physical impairment, impaired quality of life, and excess mortality during the post-ICU period. The period of excess mortality has been variously estimated as lasting from one to 16 years after ICU discharge. Remarkably little information about long-term mortality and healthcare resource use exists for critical care populations, and outcomes relative to a non-ICU control population are unknown. The aims of the studies presented in the thesis were (i) to describe long-term (five year) mortality and identify factors associated with mortality for patients admitted to ICUs in Scotland (ICU admission cohort) and those surviving to be discharged from hospital alive (ICU survivor cohort); (ii) to compare mortality rates with control populations after adjustment for relevant confounders; (iii) to evaluate the extent of, and factors associated with, long-term (five year) major healthcare resource use of survivors of critical illness (ICU survivor cohort); and (iv)to compare major healthcare resource use with a control hospital inpatient population. I undertook a detailed systematic review of the international literature relating to healthcare resource use in ICU survivors to inform the design of the part of the study relating to resource use. This revealed a paucity of high quality studies but led to recommendations for improving the conduct and reporting of future research in this field. Using both retrospective cohort and matched cohort study designs, I analysed data relating to all patients admitted to Scottish ICUs in 2005 from the Scottish Intensive Care Society Audit Group (SICSAG) database. Two cohorts were defined: an ICU admission cohort, representing all ICU admissions, and a subcohort of those who survived to hospital discharge (ICU survivor cohort). Matched control cohorts of non-ICU hospital inpatients were selected from national datasets. The main outcomes were five-year mortality and major healthcare resource use obtained from linkage to national datasets. Major healthcare use was measured by number of hospital readmissions, number of days spent in hospital and hospital costs during the five years after hospital discharge. Five year mortality was 53% in the ICU cohort compared with 27% for the matched control hospital cohort and 16% for an age/sex-standardised general population. Among hospital survivors, ICU patients had higher five year mortality after adjustment for confounders (HR 1.3, 95%CI 1.2 to 1.4, p<0.001). Age, comorbidity, ICU admission diagnosis and deprivation quintile were independently associated with five-year mortality. The ICU diagnosis with greatest five year mortality (relative to self-poisoning) was variceal bleeding (HR 3.9, 95%CI 2.2 to 6.7, p<0.001). The readmission rate for the 5259 ICU patients surviving to hospital discharge declined from 1.7 readmissions per person in the first year to 0.9 in the fifth year of follow-up. Overall, ICU survivors spent a mean of 29 days in hospital over the five year follow up period, at a cost of £14593 per person. Previous number of admissions was the factor most strongly associated with resource use. ICU patients had a significant increased rate of hospital admission compared with the control cohort throughout the five year follow up period (admission rate ratio 1.21 (95%CI 1.14 to 1.29, p<0.001)). In the programme of work presented in this thesis, I have systematically reviewed evidence for resource use following critical illness, and have demonstrated that ICU patients are more likely to die compared with other hospital inpatients over a five-year horizon, even when only hospital survivor cohorts are considered. Furthermore, I have demonstrated that ICU survivors utilise a significant amount of excess acute hospital resource, which is relevant to health service planning and economic evaluations.