Development and application of a method for estimating daily case-mix adjusted costs of adult critical care units.

Patients referred for treatment in an adult critical care unit are in, or at
imminent risk of developing single or multiple organ failure. Despite
the high treatment costs, knowledge of the costs of care is limited. The
aims of this thesis were to synthesise current knowledge about the
different methods used to estimate costs and to develop and apply a
method for estimating daily case-mix adjusted costs for developing a
set of Healthcare Resource Groups (HRGs) and for use in a trial-based
economic evaluation. HRGs were required to support the Department
of Health's new policy on reimbursing adult critical care called
'Reforming NHS Financial Flows: Introducing Payment By Results'.
A systematic review of 20 published studies provided the background
to, and justification for the methods employed in two empirical studies.
The first empirical study was performed in a single critical care unit
and using very detailed data on individual patients evaluated factors
that had the potential to correlate with daily costs of critical care.
Univariate and multivariate statistical analyses were undertaken using
two different data sets. Patients' daily organ supports were identified as
the key 'cost generating events'. A prospective, observational,
longitudinal multi-centre study involving a volunteer sample of 70
critical care units followed, where organ support data on 7,243
consecutive admissions and monthly data on critical care unit
expenditure were collected. Different ways of modelling the organ
support and expenditure data were explored. The overall R2 for the
chosen model- the daily number of organs supported was 0.52. Daily
organ support weights for the average daily costs of critical care were
0.577 for 0 or 1 organ supported, 1.137 for 2 organs supported and
1.156 for 3 or more organs supported. These weights were then applied
to average daily costs estimated for patients recruited to a clinical trial
of Extracorporeal Membrane Oxygenation (ECMO) vs. conventional
therapy for severe, but potentially reversible, respiratory failure.