Objectives:
Patient maintained sedation (PMS) is a
technique where a patient can control a target-controlled infusion of propofol
by means of a handset. The object of this study was to assess the safety of
volunteers deliberately attempting to over-sedate themselves with a new
effect-site controlled system. This unique system uses effect-site control,
i.e. the brain level of the drug calculated using a pharmacokinetic model.
Methods:
20 healthy
volunteers were instructed on use of the system. Once the handset was enabled,
the volunteer was instructed to “try to make yourself unconscious”. Vital signs
were monitored and recorded. End points were defined as loss of verbal contact
(sedation score 2 on a 4-point scale), the machine step-down (after 6 minutes
with no press), SpO2<90. At this point the subject was then asked to obey
commands (open their eyes or stick out their tongue) and whether they could
still successfully press the button was noted.
Results: (mean(SD)
unless otherwise stated)
All 20 volunteers successfully used the
system to sedate themselves. Reasons for ending the study are shown in the
table.
|
End-point of Study
|
N
|
Dose at end
(mg.ml-1)
|
Sedation Score
at conclusion
median (Range)
|
Intervention Rate (%)
|
Button Press
n (%)
|
Obeys Commands
n (%)
|
|
Machine
step-down
|
15
|
2.6(0.6)
|
3
(3-4)
|
0
|
7
(47)
|
15
(100)
|
|
Loss of Verbal Contact
|
1
|
3.3
|
2
|
0
|
0
(-)
|
0
(-)
|
|
SpO2<90%
|
4
|
2.8
(0.7)
|
2.5
(2-3)
|
50
(2
required O2)
|
1
(25)
|
3
(75)
|
Of the volunteers who desaturated: two took
a deep inspiration when instructed to, and the saturation immediately
recovered; and the remaining two required supplementary oxygen.
Conclusions:
The system is not safe in its current form
when volunteers deliberately attempt to over- sedate. Further revision of the
protocol is required before large scale trials.