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

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Economic evaluation methods
The lists of random allocations were held at the
study office and batches of sealed envelopes
labelled numerically and by surgical group were
dispatched to the study sites for the adult and
paediatric studies. An envelope was opened, in
numerical order, by the research nurses after the
patient consented to enter the study.
Measures
Primary clinical outcome measure
The literature review (see chapter 2) identified
PONV as the most relevant primary clinical
outcome measure to quantify the effectiveness
of anaesthetic agents for day surgery. PONV
was recorded using the following scale: 0, no
nausea or vomiting; 1, nausea; 2, one episode of
vomiting; 3, multiple episodes of vomiting. PONV
was monitored postoperatively in recovery and
on the ward. PONV was used to estimate the
sample size requirement and as the primary
effectiveness measure for the estimation of
cost-effectiveness ratios.
Secondary clinical outcome measures
Further clinical outcome measures were also
considered. The secondary clinical outcome
measures recorded were orientation in the
recovery room, time to recovery room discharge,
time to readiness for hospital discharge, and
overnight stay on the ward. Orientation of the
patient when in the recovery area was graded
by the recovery staff using predefined categories:
alert and awake, agitated and distressed, and
drowsy. The time to recovery room discharge and
readiness for hospital discharge were collected
from the nursing or medical records. If the patient
was admitted overnight, the reason for admission
and the subsequent duration of admission was
recorded. This information was obtained from
the relevant ward nursing staff.
The incidence of adverse events in the anaesthetic
room, theatre, recovery and on the ward
was monitored and collected. The primary
adverse events noted in the anaesthetic room
were breath-holding, cough, excessive salivation,
excitatory movement during induction, hiccough,
laryngospasm and pain on injection. Other
adverse events were noted and recorded as they
occurred throughout the day-patient episode.
Patient preferences
CV was used to determine patient preferences for
alternative anaesthetic agents. The CV method is
used to elicit values for items not typically traded
in private markets, such as health. Valuation is
based on the contingency of the hypothetical
market for health. The development of any CV
tool requires an explicit handling of the development
process. The challenge is to construct hypothetical
scenarios that are meaningful to the
respondent but free from bias. Valuations of
willingness to pay can be carried out using openended
or closed-ended methods. Open-ended
methods may produce contradictory answers,
protest answers or no answers at all. 231 The CV
instrument used in this study was developed in
a pilot study (see appendix 13). 34,45,231–240
The CV pilot study developed and tested the
hypothetical descriptive scenarios of the process
and outcome of anaesthesia from interviews with
40 female members of the public. The pilot study
examined the direction and value of preferences
for one alternative anaesthetic agent over another
by asking respondents what they would be willing
to pay for the preferred option(s). Respondents’
understanding of the CV process was checked
by asking them to explain the reasons for their
preference for one medicine rather than the other.
The pilot study confirmed that the majority of
respondents (85%) understood the hypothetical
scenarios and that the instrument was suitable
for use in the empirical study. The values used
on the subsequent VAS were developed during
the pilot study.
In the empirical study the adult and paediatric
patient groups were provided with two scenarios:
• Scenario 1: valuation of inhalational versus
intravenous induction (see appendix 14).
• Scenario 2: valuation of inhalational versus
intravenous maintenance (see appendix 15).
Scenario 1 described the likely events that the
patient would experience if they received propofol
(intravenous) or sevoflurane (inhalational) for
induction of anaesthesia. The principal differences
here were mode of administration and the pain
on injection experienced with propofol.
Scenario 2 described the likely events that the
patient would experience if they received inhalational
(sevoflurane or isoflurane) or intravenous
(propofol) maintenance anaesthesia. The principal
difference between the agents and techniques
described was the difference in the risk of PONV. 176
The differences in risk of PONV were based on
quantified reductions in the risk of PONV in order