Age, risk, and life expectancy in Norwegian intensive care: a registry-based population modelling study

Abstract

Background: Knowledge about the expected life years gained from intensive care unit (ICU) admission could inform priority-setting decisions across groups of ICU patients and across medical specialties. The aim of this study was to estimate expected remaining lifetime for patients admitted to ICUs during 2008-2010 and to estimate the gain in life years from ICU admission.

Methods: This is a descriptive, population modelling study of 30,712 adult mixed ICU admissions from the Norwegian Intensive Care Registry. The expected remaining lifetime for each patient was estimated using a decision-analytical model. Transition probabilities were based on registered Simplified Acute Physiology Score (SAPS) II, and standard and adjusted Norwegian life-tables.

Results: The hospital mortality was 19.4% (n = 5,958 deaths). 24% of the patients were estimated to die within the first year after ICU admission in our model. Under an intermediate (base case), optimistic (O), and pessimistic (P) scenario with respect to long-term mortality, the average expected remaining lifetime was 19.4, 19.9, and 12.7 years. The majority of patients had a life expectancy of more than five years (84.8% in the base case, 89.4% in scenario O, and 55.6% in scenario P), and few had a life expectancy of less than one year (0.7%, 0.1%, and 12.7%). The incremental gain from ICU admission compared to counterfactual general ward care was estimated to be 0.04 (scenario P, age 85+) to 1.14 (scenario O, age < 45) extra life years per patient.

Conclusions: Our research demonstrated a novel way of using routinely collected registry data to estimate and evaluate the expected lifetime outcomes for ICU patients upon admission. The majority had high life expectancies. The youngest age groups seemed to benefit the most from ICU admission. The study raises the question whether availability and rationing of ICU services are too strict in Norway.

Fig 1. State transition diagram.

H (alive hospital), D (dead), and S_x (alive at age x, post hospital discharge) represent the health states. PRD is the predicted risk of death during hospitalisation, and p_x is the probability of death at age x derived from the Norwegian life table 2011.

Fig 2. Outcome chart.

The expected outcome by the short term predicted risk of death and age. The remaining life expectancy is indicated at the right end of the contours. Colours signify long to short life expectancy: green, > 5 years; light green 4–5 years; yellow, 3–4 years; orange, 2–3 years; red, 1–2 years; dark red, < 1 year).

Fig 3. Patient selection.

Order of exclusion of patients for the purpose of our study. The source population constitutes all patient records in the National Intensive Care Registry in the years 2008, 2009 and 2010. The numbers refer to patients who were excluded from our analysis.

Fig 4. Expected remaining lifetime.

A. Number of patients (95% confidence intervals) in categories defined by the size of the expected outcome in terms of expected remaining life years. Three different scenarios in each category regarding the calculation of post hospital mortality: according to a life table with moderately high long-term mortality (base case), a standard life table (Scenario O), and life table with very high long-term mortality (Scenario P). B. Proportion of patients by type of admission: planned surgical, acute surgical, and medical (base case).

Fig 5. Projected survival.

A. Survival of the modelled ICU population at ICU admission (admission), hospital discharge (hospital) and subsequent years. Three different scenarios of post hospital mortality are illustrated in each time cycle: according to a life table with moderately high long-term mortality (base case), a standard life table (Scenario O), and life table with very high long-term mortality (Scenario P). B. Survival of the modelled ICU population by type of admission (base case).