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

The aim of this study was to develop and test
a CV tool to identify and quantify women’s
preferences for alternative anaesthetic agents in
day surgery. The objectives were:
• to develop and test hypothetical scenarios,
which describe the expected outcomes of the
alternative anaesthetic agents being compared
• to identify and quantify women’s preferences
for alternative anaesthetic agents for induction
and maintenance of anaesthesia
• to assess the respondents’ ability to carry
out the valuation using the hypothetical
scenarios developed.
Methods
CVs were required to assess incremental willingness
to pay for either inhalational or intravenous induction
(scenario 1) or maintenance (scenario 2).
Hypothetical scenarios for each of these cases
were required. In-depth interviews with two female
university administrative staff who had undergone
gynaecological day surgery were used to develop
the topic guide and appropriate language for the
semi-structured interviews and the CV scenarios.
Instrument development
CV constitutes a group of methods that elicit
valuations from respondents, each with their
own strengths and weaknesses. 231,232 There is no
standard approach to the development of a CV
tool. 232 However, increasing amounts of empirical
evidence provide some guidance on design.
This study examined the willingness to pay for
one alternative over another. This equates to
the maximum amount of money that must be
taken from an individual to equalise a utility
change. 231 We aimed to elicit incremental, rather
than absolute, willingness-to-pay values for one
alternative over another. Patients would only ever
have to choose between types of anaesthetics, so
a ‘no treatment’ scenario was not included.
Elicitation of willingness-to-pay values is most
commonly carried out using direct (open ended)
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Appendix 13
Health Technology Assessment 2002; Vol. 6: No. 30
Development of the contingent
valuation tool
questions. However, such questions may produce
contradictory answers, protest answers or no
answers at all. 231 The most suitable choice of
the better close-ended methods (which constrain
the valuations given by respondents) remains
unresolved. Of the available options, we chose
payment cards. Respondents indicated a monetary
figure on a VAS that reflected how much they
valued their preferred anaesthetic. To minimise
range bias, respondents were told that they
could also give valuations beyond the VAS.
Previous experience of surgery, day surgery and
anaesthesia was therefore investigated for their
impact on willingness-to-pay values. The payment
vehicle used was private money and income was
measured as bands of household income.
Two hypothetical scenarios were developed (see
appendices 14 and 15). Scenario 1 determined
women’s preferences for induction agents.
Respondents were asked to compare propofol
(referred to as medicine A) and sevoflurane
(medicine B). Scenario 2 determined women’s
preferences for maintenance agents. Respondents
were asked to compare isoflurane (medicine C)
and propofol (medicine D). The side-effect
profiles used reflect those experienced after
gynaecological day-surgery anaesthesia. 45
Study sample and recruitment
The study took the perspective of female members
of the public who may, or may not, have had
previous experience of an operation or day surgery.
The study recruited female members of administrative
and secretarial staff, based in the engineering,
physics and accounting departments at the university.
This was to obtain a sample with a range of ages
and educational backgrounds. Non-medical and
non-clinical departments were deliberately selected
to ensure that prior medical knowledge more closely
matched that of the general population. Women
were identified from the telephone directory and
invited to participate by letter. It was not possible to
carry out a prior power analysis to determine sample
size. Forty to fifty interviews were deemed necessary
to identify variations in understanding, perception
and ability to carry out the CV.
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