Aanesthetic Agents for Day Surgery - NIHR Health Technology ...

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Economic evaluation methods
Table 17 provides a summary of the types of
resource-use data collected at all stages of the
empirical study. Resource use was divided into
perioperative (anaesthetic room and theatre data)
postoperative (recovery room and ward data)
and postdischarge data.
Variable costs
Variable costs include items where the quantity
of resources used is determined only by the need
for them as inputs to individual patient care
(see appendix 17). 243,244,245 Variable costs were
primarily drugs and disposable equipment.
Drug doses and routine events (e.g. use of a
laryngeal mask) were recorded as they occurred,
and the disposables and fluids associated with
their administration were incorporated in the
overall cost per dose. All disposables used
during adverse events, including PONV,
were recorded prospectively.
Inhalational agent resource use was recorded
by the measurement of gas flow rates and by
recording vaporiser settings at predefined
intervals during the anaesthetic period. The
Dion algebraic approximation was used to
calculate the amount of volatile agent used. 24
A substudy was designed to assess the validity
of the algebraic approximation used to estimate
the quantity of volatile anaesthetic used by
comparison with a weighing method
(see appendix 18). 22,24,28,220,246,247
Posthospital resource use was collected by a telephone
interview with the patient or the patient’s
parent or guardian 7 days after discharge. If the
patients were not contacted by telephone they
were lost to follow-up.
Semi-fixed costs
Semi-fixed costs are those where the quantity of
resources used is determined by organisational
requirements as well as the need for them to
provide care for individual patients (e.g. staff
time). A substudy was designed to provide
information on staff deployment and skill mix
during the day-surgery episode. A semi-fixed
resource use component was included for each
arm of the study (see appendices 19 248,249 and
20 245,250,251 ). Standard semi-fixed costs associated
with staff resource use for admitting and
discharging patients from the ward, transferring
patients to and from theatre and monitoring
patients postoperatively in recovery and on the
ward were used in the baseline economic evaluation.
Anaesthetic room and operating theatre
semi-fixed costs were calculated using a different
method. Average semi-fixed costs per minute
were multiplied by the respective length of time
patients spent in these areas for the adult and
paediatric study, respectively.
Fixed costs
Fixed resource use associated with maintaining
an anaesthetic room, operating theatre and ward
for day-surgery procedures was included for each
arm of the study (see appendix 21). The fixed
cost per day-patient was estimated for three
sections (ward, theatre, anaesthetic room)
of the day-surgery episode.
Unit costs
Unit costs were obtained from the two NHS trusts
in the study.
Data
A summary of the parameters investigated and the
data collected prospectively in the CESA RCT is
given in Table 17. A predefined quality control
procedure was used to ensure consistency in data
collection (see appendix 22). 252
Data analysis
Clinical outcomes
PONV
The incidence of nausea, vomiting, and nausea
and vomiting was analysed for each arm of
the two studies. The incidence for the whole
postoperative period was analysed. To assess
whether any differences in PONV were due to
the anaesthetic regimens or due to confounding
factors such as age or gender, cross-tabulation
and logistic regression were undertaken. Logistic
regression was also used to adjust estimates of
PONV risk, to allow for any residual effects of
confounding variables arising from their not
being exactly evenly distributed across the
randomisation groups.
Adverse events
The incidence of individual adverse events, and the
total incidence, was calculated for each arm of the
study during the day-surgery episode. The total
number and type of adverse events was recorded.
Patient preferences
The CVs collected were continuous variables.
CVs that were categorised as invalid were excluded
from the analysis. Descriptive summary statistics
of the distribution of CVs were calculated.