Psychiatric Bulletin (2002) 26: 455-457. doi: 10.1192/pb.26.12.455
© 2002 The Royal College of Psychiatrists
Psychiatric Bulletin (2002) 26: 455-457
© 2002 The Royal College of Psychiatrists
Induction agents in electroconvulsive therapy: a comparison of methohexitone and propofol
Allan Scott, Consultant Psychiatrist and Honorary Senior Lecturer, c/o
Research/Administration Assistant
Special Committee on ECT, The Royal College of Psychiatrists, Scottish
Division, 9 Queen St, Edinburgh EH2 1JQ, UK
Harold Boddy, Senior House Officer in Psychiatry
Andrew Duncan Clinic, Royal Edinburgh Hospital, Morningside Terrace,
Edinburgh EH10 5HF
Declaration of interest
None.
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Abstract
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AIMS AND METHOD
To compare methohexitone and propofol in electroconvulsive therapy (ECT). A
retrospective within-subject comparison was made of the use of these drugs in
separate courses of bilateral ECT in one clinic over 10 years. Patients taking
mood stabilising or anti-epileptic drugs were excluded. The initial seizure
threshold and seizure duration were of particular interest.
RESULTS
The median initial seizure thresholds were identical (75 mC). The median
initial seizure duration with threshold stimulation was 25% shorter with
propofol (21 v. 28 s). The median total numbers of treatments in the
courses were identical (eight treatments).
CLINICAL IMPLICATIONS
The shorter seizure duration observed with propofol was not associated with
a commensurate rise in the initial seizure threshold. The shorter seizure
duration may therefore have no effect on the therapeutic efficacy of
treatment.
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Introduction
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Methohexitone ceased to be available commercially in the UK in 1999. At
that time it was the drug of choice for the induction of anaesthesia in
electroconvulsive therapy (ECT) (Special
Committee on ECT, 1995). Many anaesthetists chose propofol as its
replacement because it is a non-barbiturate drug that is metabolised rapidly
and causes less haemodynamic change than methohexitone. Some psychiatrists
were concerned about the use of propofol because they observed that its use
was associated with shorter seizures. This raised the concern that induction
with propofol might compromise the therapeutic efficacy of ECT. Randomised,
controlled comparisons of induction with propofol and methohexitone have not
supported this concern: see Martin et al
(1998) for a review of the
literature. Nevertheless, some practitioners remain concerned about the use of
propofol and there continue to be anecdotal reports of difficulties in the
induction of seizures that are attributed to the use of propofol. Seizure
duration itself has never been shown to be related to the therapeutic efficacy
of ECT (Scott, 1989), but if
the shorter seizures observed with propofol were associated with a rise in
seizure threshold this might be a cause for concern. The extent to which the
electrical dose exceeds the seizure threshold has been shown to be related to
the therapeutic efficacy of ECT in the treatment of depressive illness
(American Psychiatric Association,
2001). No study of the initial seizure threshold in ECT has ever
compared induction with methohexitone and propofol. A prospective study is now
impossible, and this prompted the study reported here.
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Method
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The index card records at the ECT clinic at the Royal Edinburgh Hospital
contain information on treatments from January 1991 onwards. These were
searched by hand up to and including the records for December 2000 to identify
patients who had undergone both induction with methohexitone and induction
with propofol in separate courses of ECT. Methohexitone became unavailable in
July 1999. The further inclusion criterion was the initial prescription of a
bilateral electrode placement. Exclusion criteria were the intake of an
anti-epileptic or mood stabilising drug (excluding lithium carbonate) and ECT
in the previous 6 months. Twenty patients satisfied the initial inclusion and
exclusion criteria.
Treatment was always given using a machine from the Ectron 5A series and
therefore the characteristics of electrical stimulation were standard
throughout the study. Empirical measurement of the initial seizure threshold
was carried out routinely at the clinic, and the treatment protocol has been
described before (Special Committee on ECT,
1995). Four patients had to be excluded from the study because the
treatment protocol was not followed sufficiently closely to give an accurate
measurement of initial seizure threshold at one of the courses. Two other
patients had to be excluded because they were subsequently prescribed an
anti-epileptic or mood stabilising drug. One patient had to be excluded
because she was switched to a unilateral electrode placement. Seizure duration
was recorded routinely and measured from the end of electrical stimulation to
the end of generalised convulsive muscular activity.
Neither initial seizure threshold nor initial seizure duration was normally
distributed, and non-parametric statistics have been used throughout.
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Results
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The sample consisted of 13 patients, 6 men with a median age of 38 (range
27-67) years, and 7 women with a median age of 51 (range 30-79) years. About
half of the people in the sample (n=6) suffered from recurrent
depressive disorder in which the treated episodes were severe. Five of the
patients suffered from a manic—depressive psychosis and the treatments
were prescribed for severe depressive episodes; one patient who suffered from
a manic—depressive psychosis was treated each time for mania. One
patient suffered from a depressive episode in a schizoaffective disorder. The
median length of time between treatment courses was 25 (range 10-71) months.
Table 1 shows that the median
initial seizure thresholds were identical, 75 mC (Wilcoxon matched-pairs
signed ranks test, n=9, t=19, critical value 6, not
significant). The median initial seizure duration with threshold stimulation
was 25% shorter when propofol was used (n=12, t=8, critical
value 10, two-tailed P=0.02).
Two patients decided to stop one of the courses of ECT prematurely; one man
with hypomania withdrew consent and one woman with depression went on holiday.
The total number of treatments was therefore based on the 11 patients who
completed the prescribed courses of treatment. The median total numbers of
treatments in the course were also identical (n=8, t=14,
critical value 4, not significant).
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Discussion
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This was not the first study to confirm the impressions of practitioners
that seizure duration is shorter when propofol is used as the induction agent
(see Martin et al,
1998). The novel finding from this study was that this can occur
without any commensurate increase in the initial seizure threshold in
bilateral ECT. The median initial seizure threshold with propofol induction
was identical to the median value found in an earlier study of 100 depressed
patients treated with the same ECT machine in whom methohexitone was the
induction agent (Dykes & Scott,
1998). The findings add to the evidence that seizure duration and
seizure threshold are only modestly correlated in ECT
(Scott & Boddy, 2000). That
the shorter seizures were not associated with a higher seizure threshold makes
it less likely that propofol compromises the therapeutic efficacy of ECT. The
lack of a difference in the total number of prescribed treatments lends
support to this.
Methohexitone is still not available in our clinic and a retrospective
comparison is all that is feasible. The strengths of this study are that it
was conducted on a representative sample from one clinic over a defined
period, and had a within-subject design. Its major limitation is that it
lacked the statistical power to conclude confidently that the two induction
agents were equivalent in their effect on the seizure threshold. The study
would have been strengthened if cerebral seizure activity had been measured
directly by electroencephalography, but this was not available routinely in
the clinic. There are other reasons to be cautious in the interpretation of
the findings. It was beyond the scope of the study to assess the effects of
concurrent psychotropic drug treatment, or the effect of increasing age over
the period of the study (age is positively correlated with the initial seizure
threshold). Measures of clinical outcome normally seen in treatment studies
were not available.
The clinical implication is that the study has added to the evidence that
the shorter seizures observed after induction with propofol need not
compromise the therapeutic efficacy of ECT.
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Acknowledgments
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We thank Staff Nurse Rena Good of the ECT clinic at the Royal Edinburgh
Hospital for her help with the study. We also thank Alex Celini, Research
Assistant for the Royal College of Psychiatrists' Special Committee on ECT,
for preparing the manuscript.
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References
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AMERICAN PSYCHIATRIC ASSOCIATION (2001) The
Practice of Electroconvulsive Therapy: Recommendations for Treatment,
Training, and Privileging (2nd edn). Washington, DC:
APA.
DYKES, S. & SCOTT, A. I. F. (1998) Seizure
threshold in bilateral electroconvulsive therapy. Psychiatric
Bulletin, 22,
298-299.[Abstract/Free Full Text]
MARTIN, B. A., COOPER, R. N. & PARIKH, S. V.
(1998) Propofol anaesthesia, seizure duration and ECT: a case
report and literature review. Journal of ECT,
14, 99-108.[Medline]
SCOTT, A. I. F. (1989) Which depressed patients will
respond to electroconvulsive therapy? British Journal of
Psychiatry, 154,
8-17.[Abstract/Free Full Text]
SCOTT, A. I. F. & BODDY, H. (2000) The effect of
repeated bilateral ECT on the seizure threshold. Journal of
ECT, 16,
244-251.[Medline]
SPECIAL COMMITTEE ON ECT (1995) The ECT
Handbook. London: Gaskell.
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Abstract
Introduction
