988 q 2001 Blackwell Science Ltd

FORUM

A survey of pre-operative optimisation of high-risk surgical

patients undergoing major elective surgery

S. Singh1 and M. Manji2

1 Specialist Registrar in Anaesthesia, and 2 Consultant in Anaesthesia and Intensive Care, Department of Anaesthesia,

Selly Oak Hospital, University Hospital NHS Trust, Birmingham B29 6JD, UK

Summary

Pre-operative optimisation of high-risk patients undergoing major elective surgery has been shown

to decrease peri-operative morbidity and mortality. It is also cost effective because of the resulting

decrease in postoperative complications. A questionnaire was sent to 170 intensive care and high

dependency units in Britain in order to quantify the number of units practising pre-operative

optimisation. There was a 91% response rate. Of the respondents familiar with the evidence

advocating pre-operative optimisation, 91% believe pre-operative optimisation improves outcome

but only 62% admit patients for such preparation. Moreover, only eight units (6%) admit more than

25% of eligible patients. The reasons given for not admitting such patients pre-operatively are a lack

of manpower, beds or both. This survey demonstrates the need for greater investment of resources

into intensive care and high dependency units, so that clinicians can deliver high-quality evidence-

based healthcare in accordance with the principles of clinical governance.

Keywords Pre-operative care: pre-operative optimisation; elective surgery.

.................................................................................................

Correspondence to: Dr S. Singh.

E-mail: sukbinder.singh@virgin.net

Accepted: 6 January 2001

In England, more than 8000 patients a year die within

30 days of non-emergency surgical procedures [1]. Pre-

operative optimisation of high-risk surgical patients can

substantially reduce postoperative morbidity and mortality

[2]. In light of such evidence, we conducted a postal

survey of intensive care and high dependency units in

Britain to determine how many units practise pre-

operative optimisation of high-risk patients undergoing

major elective surgery.

Methods

Questionnaires (Appendix A) were addressed to director or

lead clinician of 170 randomly selected intensive care and

high dependency units in Britain. Specialist units, such as

cardiac and neurosurgical units, were not surveyed. The

primary aim was to quantify the number of intensive care

and high dependency units practising pre-operative opti-

misation in high-risk patients undergoing major elective

surgery. Where pre-operative optimisation was not prac-

tised, the questionnaire was designed to identify the reasons

why. The number of clinicians familiar with the evidence

advocating pre-operative optimisation and whether they

agreed with the evidence was also recorded.

Results

One hundred and fifty-five (91%) of the 170 question-

naires sent were returned fully completed. Responses

were from consultant staff (85%), trainee medical staff

(10%) and nurses (5%).

One hundred and forty (90%) of the respondents were

familiar with the clinical publications regarding pre-

operative optimisation for high-risk major elective

surgical patients (Table 1). Of these 140, 127 (91%)

respondents believe that pre-operative optimisation for

high-risk major elective surgery can improve outcome.

Only 79 of 127 (62%) intensive care and high dependency

Anaesthesia, 2001, 56, pages 988±1002................................................................................................................................................................................................................................................

units admit patients for pre-operative optimisation, of

which only eight (representing only 6% of 127 units)

admit more than 25% of all patients who may benefit

from such intervention. The reasons cited for not

admitting such patients pre-operatively were lack of

manpower (3%), lack of beds (23%) or a combination of

both (74%).

Fifteen (10%) of the respondents had not read any

publications regarding pre-operative optimisation. Four

were consultants (representing 3% of consultant respon-

dents), five were trainee medical staff and six were nursing

staff.

Discussion

In the era of clinical effectiveness and the drive for quality

improvement in the NHS, clinicians are expected to apply

the most efficacious treatment based on the best available

evidence [3]. In order to justify a change in established

practice, evidence from well-designed, large prospective

randomised control trials is required. For high-risk

patients undergoing major elective surgery, at least four

prospective randomised trials [4±7] have been published

since 1988, including a recent meta-analysis [8]; all

demonstrated the value of pre-operative optimisation in

this patient group. In these studies, mortality in the

control group was as high as 28% whilst the treatment

group's mortalities ranged from 1.5 to 6%. In addition,

there was a significant decrease in morbidity and length of

hospital stay [5]. Moreover, a recent retrospective cost

analysis showed an overall reduction of costs in the pre-

optimisation group, due mainly to a decrease in the cost

of treating postoperative complications and a shorter

hospital stay [9].

Although evidence-based information regarding pre-

operative optimisation is available and criteria defining

these high-risk patients are well known [4], our survey

shows that 10% of respondents had not heard of any

publications and interventions relating to these groups of

patients. In a highly specialised field such as intensive care

medicine, this is a cause for concern but may reflect the

number of questionnaires answered by non-consultant

staff. This emphasises the importance of developing

reliable systems that ensure the effective dissemination

of evidence-based information [10].

In our survey, the majority of clinicians are familiar

with the published evidence and agree that pre-operative

optimisation improves postoperative morbidity and mor-

tality. However, only 6% of critical care units admit more

than 25% of eligible patients and no unit admits more than

50% of patients that may benefit from such intervention.

Inadequate bed space and/or manpower were identified as

the reasons for the majority of units not practising pre-

operative optimisation. Some of those who are unable to

admit high-risk patients to an intensive care or high

dependency unit for pre-operative optimisation feel that

this can be achieved immediately pre-operatively in the

anaesthetic room. Whilst this remains an attractive option,

especially in terms of cost implications, the evidence to

support the proposal is lacking.

If the drive to practise medicine on the best available

evidence is to advance, then health care planners must

practise evidence-based health budgeting [11]. Individual

patient episode cost should not be used as the sole

measure of health efficiency and quality. The benefits in

terms of survival, reduced morbidity, shorter hospital stay

and lower costs are sufficient to justify the initial

investment required to enable pre-operative optimisation

of high-risk patients for major elective surgery. Govern-

ment and health authorities need to allocate these specific

resources to intensive care and high dependency units to

enable clinicians to deliver high-quality evidence-based

healthcare in accordance with the principles of clinical

governance.

References

1 Department of Health. Quality and performance in the NHS;

NHS Performance Indicators: July 2000. London: Department

of Health, 2000.

2 Treasure T, Bennett D. Reducing the risk of major elective

surgery. Optimising oxygen delivery before surgery does

work; now we have to implement it. British Medical Journal

1999; 318: 1087±8.

3 Scally G, Donaldson J. Clinical governance and the drive for

quality improvement in the new NHS in England. British

Medical Journal 1998; 317: 61±5.

4 Boyd O, Grounds RM, Bennett ED. A randomised clinical

trial of the effect of deliberate peri-operative increase of

oxygen delivery on mortality in high risk surgical patients.

Journal of American Medical Association 1993; 270: 2699±707.

5 Wilson J, Woods I, Fawcett J, et al. Reducing the risk of

major elective surgery: randomised controlled trial of pre-

operative optimisation of oxygen delivery. British Medical

Journal 1999; 318: 1099±103.

6 Shoemaker WC, Appel PL, Kram HB, Waxman K, Lee TS.

Prospective trial of supranormal values of survivors as

Table 1 Results of questionnaire.

No. of units surveyed 170Completed questionnaires returned (%) 155 (91)Respondents familiar with evidence for pre-operativeoptimisation (%)

140 (90)

Respondents who agree with published evidence (%) 127 (91)Units that admit patients for pre-operative optimisation (%) 79 (62)Units that admit more than 25% of eligible patients (%) 8 (6)

Anaesthesia, 2001, 56, pages 988±1002 Forum................................................................................................................................................................................................................................................

q 2001 Blackwell Science Ltd 989

therapeutic goals in high risk surgical patients. Chest 1988;

94: 1176±86.

7 Berlauk JF, Abrams JH, Gilmour IJ, O'Conner SR, King-

hton DR, Cerra FB. Pre-operative optimisation of cardio-

vascular haemodynamics improves outcome after peripheral

vascular surgery. A prospective randomised clinical trial.

Annals of Surgery 1991; 214: 289±97.

8 Boyd O. Peri-operative cardiovascular optimisation. BaillieÁre's

Clinical Anaesthesiology 1999; 13: 267±77.

9 Guest JF, Boyd O, Hart WM, Grounds RM, Bennett ED. A

cost analysis of a treatment policy of a deliberate

peri-operative increase in oxygen delivery in high risk

surgical patients. Intensive Care Medicine 1997; 23: 85±90.

10 Glanville J, Haines M, Auston I. Finding information on

clinical effectiveness. British Medical Journal 1998; 317:

200±3.

11 Massel D. Evidence based budgeting is now necessary. British

Medical Journal 1999; 319: 384.

Appendix A

Questionnaire on pre-operative optimisation of

high-risk patients undergoing major elective

surgery

Status (please circle one)

Consultant/SpR/SHO

Other (please specify)

1. Have you read any papers on ICU/HDU

pre-operative optimisation of high-risk patients

undergoing major elective surgery?

Yes No

2. Can you remember approximately how many papers

you have read?

Number

3. Do you believe that pre-operative optimisation

(on ICU/HDU) of such patients improves outcome?

Yes No

4. On your unit do you admit such patients for

pre-operative optimisation?

Yes No

5. Approximately what percentage of such patients are

optimised in ICU/HDU?

0% 1±25% 26±50% 51±75% 76±100%

If less than 100%, the reasons are because you do not

have the resources due to lack of:

X Bed space

X Manpower

X Both

X Other, please specify

FORUM

Oral midazolam premedication for day case breast surgery,

a randomised prospective double-blind placebo-controlled

study

M. S. Abdul-Latif,1 A. J. Putland,2 A. McCluskey,3 D. P. Meadows3 andS. A. M. Remington3

1 Specialist Registrar, and 3 Consultant Anaesthetists, Department of Anaesthesia, Stepping Hill Hospital,

Stockport SK2 7JE, UK

2 Consultant Anaesthetist, Department of Anaesthesia, The Royal Bolton Hospital, Bolton BL4 0JR, UK

Summary

We conducted a randomised prospective double-blind placebo-controlled study to assess the efficacy

of oral midazolam premedication in 50 ASA I and II female patients scheduled to undergo day case

breast surgery. Anxiety was assessed using 100-mm visual analogue scales (VAS) and The State-Trait

Anxiety Inventory (STAI) psychometric questionnaire. Midazolam premedication did not

significantly reduce either VAS or STAI score, although heart rate and systolic arterial pressure

immediately before induction of anaesthesia were significantly lower in patients who received

midazolam (p � 0.006 and 0.039, respectively). Induction of anaesthesia was achieved with a lower

dose of propofol (p � 0.0009) and excellent (Grade I) conditions for insertion of a laryngeal mask

Forum Anaesthesia, 2001, 56, pages 988±1002................................................................................................................................................................................................................................................

990 q 2001 Blackwell Science Ltd

airway were achieved more often after midazolam premedication (p � 0.038). Arterial desaturation

during induction of anaesthesia and insertion of a laryngeal mask airway occurred more often in

patients who received placebo (p � 0.022). There was a good correlation between VAS and STAI

used to assess the anxiolytic effects of premedication. (Spearman coefficient 0.58, p , 0.0001).

Keywords Anaesthesia: day case. Premedication: oral midazolam.

.................................................................................................

Correspondence to: Dr A. McCluskey

E-mail: amccluskey@mcmail.com

Accepted: 25 April 2001

Anxiolytic premedication is not usually prescribed for

day surgery because of concerns that postoperative

sedation may delay recovery from anaesthesia and

discharge from the day surgery unit. Midazolam has a

rapid onset after oral administration and a short

duration of action with an elimination half-life of

approximately 2 h [1±4]. This pharmacokinetic profile

suggests that oral midazolam should be a suitable

premedicant for day surgery. Oral midazolam has been

studied widely outside the UK and a recent survey

indicated that it is the most commonly used oral

premedicant in Germany [5]. Although midazolam is

often given intravenously as a co-induction agent, its

use as a premedicant has received comparatively little

attention in the UK. This is probably due to the fact

that oral midazolam does not have a product licence

and a tablet formulation is currently not available in

the UK. Therefore, the aim of this study was to

determine the effects of oral midazolam premedication

on anxiolysis, co-induction of anaesthesia with

propofol and recovery in patients scheduled for day

case breast surgery. We were also interested in

comparing the simple and commonly used visual

analogue scale (VAS) with the more complex State-

Trait Anxiety Inventory (STAI) psychometric ques-

tionnaire as clinical tools for measuring the anxiolytic

effects of premedication.

Methods

Following approval by the local ethics committee and

written informed consent, 50 ASA I and II female

patients aged 18±70 years, were allocated to receive a

tablet of either oral midazolam 7.5 mg (Dormicumw;

Roche Nederland B.V., Holland) or placebo 1 h prior to

the anticipated start of surgery. The tablets were ordered

directly from the manufacturer and prior authorisation to

use an unlicensed product was obtained from The

Medicines Control Agency. Anxiety was assessed by a

blinded investigator using both 100-mm VAS and STAI

[6] before premedication and again in the anaesthetic

room. The premedication time interval was recorded.

The electrocardiogram, non-invasive arterial blood

pressure and peripheral oxygen saturation were recorded

before induction of anaesthesia and monitored through-

out the study period. All patients received fentanyl

1 mg.kg21 and were pre-oxygenated for 2 min. Anaes-

thesia was then induced with propofol at a constant rate of

10 mg per 5 s until conditions were judged satisfactory

for insertion of a laryngeal mask airway by one of the

investigators (D.P.M. or S.A.M.R.) who was blinded to

the study medication given. Conditions for insertion of

the laryngeal mask airway were then graded using a four-

point scale (Table 1). If the attempt to insert the laryngeal

mask airway was unsuccessful, further boluses of propofol

were given at the same rate as before at the discretion of

the anaesthetist and the number of attempts at insertion

recorded. Ventilation was assisted if arterial oxygen

saturation fell below 95%. The time from the start of

induction of anaesthesia to satisfactory insertion of the

laryngeal mask airway and the minimum arterial oxygen

saturation observed during this period were also recorded.

As all our patients were pre-oxygenated, a value below

95% was considered to indicate significant arterial

desaturation.

Anaesthesia was maintained using 67% nitrous oxide in

oxygen and isoflurane adjusted according to clinical

response. Further doses of fentanyl were given at the

discretion of the anaesthetist. At the end of surgery, the

duration of anaesthesia and times to early recovery and

discharge from the day surgery unit were recorded.

Recovery was further assessed using p-deletion psycho-

motor tests comparing patient performance 90 min after

the end of anaesthesia with a control measurement

obtained before premedication.

Data from a preliminary pilot study of 28 patients with

a mean (SD) VAS anxiety score 53 (26) mm were used to

determine that a sample size of 22 patients per study

Anaesthesia, 2001, 56, pages 988±1002 Forum................................................................................................................................................................................................................................................

q 2001 Blackwell Science Ltd 991

group was required to detect a reduction in VAS anxiety

score > 20 mm with 80% power. Statistical analyses were

performed using SPSS on an IBM PC. Continuous

normative data were analysed by Student's unpaired t-test.

Anxiety scores were analysed using the Mann±Whitney

U-test for between-group comparisons and the Wilcoxon

Matched Pairs test for within-group comparisons. The

Fisher Exact test was used for categorical data. A value of

p , 0.05 was considered significant.

Results

Both study groups were comparable with respect to age,

weight, pre-operative anxiety, premedication time inter-

val and duration of anaesthesia (Table 2). Midazolam

premedication did not significantly reduce either VAS or

STAI anxiety scores although pre-induction heart rate and

systolic arterial pressure were significantly lower

(p � 0.006 and p � 0.039) in patients who received

midazolam premedication (Table 3). Satisfactory induc-

tion of anaesthesia was achieved using a lower dose of

propofol (p � 0.0009) and insertion of the laryngeal mask

airway was achieved in a shorter time (p � 0.043)

following midazolam premedication. Five patients in the

placebo group experienced a decrease in peripheral

oxygen saturation below 95% (range 87±92%) despite

pre-oxygenation due to severe coughing or gagging

occurring either during the attempt to insert the laryngeal

mask airway or immediately after insertion compared

with none in the midazolam group (p � 0.022). One of

the patients in the placebo group in whom the oxygen

saturation decreased to 72% was excluded from this

analysis as the period of pre-oxygenation had been

unintentionally omitted. The grades of insertion of the

laryngeal mask airway are summarised in Table 4.

Excellent (Grade I) conditions for insertion of the

laryngeal mask airway were achieved more often in the

midazolam group (p � 0.038). Three patients in the

midazolam group and five patients in the placebo group

required more than one attempt at insertion of the LMA.

There was a trend towards delayed early recovery

following midazolam premedication (p � 0.057)

although psychomotor performance after 90 min and

time to hospital discharge were unaffected. A good

correlation was observed between the use of VAS and

STAI to assess the anxiolytic effects of premedication.

(Spearman coefficient 0.58, p , 0.0001).

Discussion

A significant proportion of day surgery patients experi-

ence peri-operative anxiety [7]. This is particularly true of

patients scheduled for breast surgery where fear of cancer

and organ disfigurement is a major concern [8]. Despite

this, the use of anxiolytic premedication in day surgery

remains controversial. In the UK, it is not usually given to

day surgery patients [9] whereas in Germany day surgery

patients are routinely premedicated [5]. Factors support-

ing UK practice include the lack of a suitably long

premedication time interval between hospital admission

and surgery and concern that postoperative sedation may

reduce patient turnover in busy day surgery units or delay

hospital discharge.

Table 1. Grading scheme used for insertion of laryngeal maskairway.

Grade Description

I Excellent - Satisfactory insertion of laryngeal maskairway at first attempt.

II Fair - laryngeal mask airway inserted at first attemptassociated with good jaw relaxation but with minorcoughing, gagging, laryngospasm or limb movement.

III Poor - laryngeal mask airway inserted at first attemptassociated with poor jaw relaxation, severe coughing,gagging, laryngospasm, limb movement or unsatisfactorycontrol of the airway with SpO2 ,95%.

IV Impossible - Failure to insert the laryngeal mask airwayat first attempt.

Midazolamn�25

Placebon�25

Age; years 41.5 (11.1) 39.1 (10.2)Weight; kg 64.7 (9.4) 63.2 (10.7)Premedication time interval; min 60.5 (16.5) 61.0 (17.8)Duration of anaesthesia; min 24.5 (9.8) 20.1 (5.2)Baseline VAS anxiety score; mm 35.4 (19.8) 42.6 (19.6)Baseline STAI anxiety score 43.4 (12.1) 48.2 (10.0)Reduction in VAS following premedication; mm 7.0 (20.2) 2.4 (18.8)Reduction in STAI following premedication 2.4 (7.3) 1.7 (8.5)Time to early recovery; min 9.7 (5.2) 7.3 (3.5)Time to hospital discharge; min 120 (24) 124 (13)

Table 2 Demographic, pre-operativeand postoperative data. Values are mean(SD). No significant differences betweengroups or within groups for paired data.

Forum Anaesthesia, 2001, 56, pages 988±1002................................................................................................................................................................................................................................................

992 q 2001 Blackwell Science Ltd

In the present study, administration of oral midazolam

7.5 mg did not significantly reduce subjective anxiety

measured using either VAS or STAI scores. However, we

did observe a number of benefits of premedication with

midazolam. The reduction in heart rate and systolic

arterial pressure observed in the anaesthetic room suggest

that activation of the autonomic nervous system due to

anxiety was reduced in these patients. We also observed a

beneficial effect on co-induction of anaesthesia that has

not been reported previously. Patients who received

midazolam were induced with a lower dose of propofol,

had a shorter time to insertion of the laryngeal mask

airway and were more likely to achieve excellent

conditions for insertion of the laryngeal mask airway.

They were also less likely to have a stormy induction of

anaesthesia associated with arterial desaturation. Our

study design included pre-oxygenation of all patients

and we believe that, in the absence of this, arterial

desaturation would have occurred more often and to a

greater degree in patients receiving placebo.

Although it is possible that a larger dose of midazolam

would have been more effective, previous studies suggest

that midazolam 7.5 mg is an appropriate oral dose for

adults undergoing day surgery. Thus, satisfactory anxio-

lysis has been reported following oral midazolam 7.5 mg

[10, 11] and 10 mg [12], although in another study

midazolam 7.5 mg was found to be ineffective when

compared with placebo [13]. When doses of oral

midazolam ranging from 3.75 to 15 mg were compared,

the authors concluded that midazolam 7.5 mg produced

the best compromise between desirable and undesirable

effects [14]. Whilst larger doses have been shown to

produce effective anxiolysis, this has often been at the

expense of unacceptably delayed recovery from anaes-

thesia [13, 15±17]. Our data similarly suggest that a larger

dose of midazolam may have caused a significant delay in

early recovery that would have had an adverse impact on

turnover of the operating list.

Oral midazolam has been used successfully at a higher

dose (0.5 mg.kg21) for paediatric day surgery [18±21].

However, different criteria are used to assess `street fitness'

in this group of patients and children who receive oral

midazolam may experience delayed recovery from

anaesthesia [22±24].

Peri-operative anxiety is a subjective judgement and

therefore difficult to measure in absolute units. Visual

analogue scales are commonly used to measure patient

anxiety in premedication studies. They are quick and

simple to perform and easily explained to patients who

readily understand the concept. However, the VAS is

subject to bias with a tendency for patients to avoid

extreme values [25, 26]. This is partly because patients

are required to express complex emotional and physical

behaviour in unfamiliar units of measure. Psychometric

questionnaires have been designed to give a quasi-

objective measure of patient anxiety. The STAI

comprises a series of 20 statements in everyday simple

language to which patients are required to answer how

they are presently feeling. VAS and STAI have not been

compared previously in a study of premedication. We

obtained a good correlation between VAS and STAI in

measuring the change in anxiety score following

premedication. Our data therefore suggest that the

simple VAS is a valid tool for measurement of anxiety

in studies of premedication. In conclusion, we have

found oral midazolam 7.5 mg to be an acceptable

Table 3 Anaesthetic induction data. Values are mean (SD) or proportions.

Midazolamn�25

Placebon�25 p value

Pre-induction heart rate; min21 74 (12) 88 (20) 0.006Pre-induction systolic arterial pressure; mmHg 121 (20) 134 (21) 0.039Pre-induction diastolic arterial pressure; mmHg 73 (12) 76 (12) 0.282Induction dose propofol; mg.kg21 2.5 (0.5) 3.4 (0.9) 0.0009Excellent (Grade I) conditions for insertion of laryngeal mask airway 20/25 12/25 0.038Time to insert laryngeal mask airway; s 107 (60) 150 (82) 0.043SpO2 ,95% 0/25 5/24* 0.022

*Excludes one patient because of omission of pre-oxygenation.

Table 4 Grade of insertion of laryngeal mask airway. p � 0.038for the difference between the proportion of patients with GradeI conditions.

GradeMidazolamn�25

Placebon�25

I - Excellent 20 12II - Fair 2 5III - Poor 0 3IV - Impossible 3 5

Anaesthesia, 2001, 56, pages 988±1002 Forum................................................................................................................................................................................................................................................

q 2001 Blackwell Science Ltd 993

premedicant for use in day care patients undergoing

breast surgery.

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3 Jochemsen R, van Rijn PA, Hazelzet TG, van Boxtel CJ,

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5 Tolksdorf W, Schou J, Brenneisen A. Survey of premedica-

tion in Germany 1998. Anasthesiologie und Intensivmedizin

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6 Spielberger CD, Grouch URL, Lushness RE, Vague PR,

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7 Mackenzie JW. Day case anaesthesia and anxiety. A study of

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8 Millar K, Jelicic B, Bonke B, Asbury AJ. Assessment of

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9 Millar JM. Premedication in adult day surgery. In: Millar JM,

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10 Short TG, Galletly DC. Double-blind comparison of

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11 Ahmed N, Khan FA. Evaluation of oral midazolam as pre-

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12 Turner GA, Paech M. A comparison of oral midazolam

solution with temazepam as a day case premedicant.

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13 Raybould D, Bradshaw EG. Premedication for day case

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14 Biro P, Weidmann G, Pietzsch S, Alon E, Brugger P. The

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15 Hargreaves J. Benzodiazepine premedication in minor day-

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with placebo. British Journal of Anaesthesia 1988; 61: 611±16.

16 Forrest P, Galletly DC, Yee P. Placebo controlled comparison

of midazolam, triazolam and diazepam as oral premedicants

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1987; 15: 296±304.

17 Nightingale JJ, Norman J. A comparison of midazolam and

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18 Kain ZN, Mayes LC, Wang SM, Caramico LA, Hofstadter

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19 McCluskey A, Meakin G. Oral administration of midazolam

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20 Patel D, Meakin G. Oral midazolam compared with

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21 Gillerman RG, Hinkle AJ, Green HM, Cornell L, Dodge

CP. Parental presence plus oral midazolam decreases

frequency of 5% halothane inductions in children. Journal of

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FORUM

Tracking the early acquisition of skills by trainees

M. J. Harrison

Specialist Anaesthetist, Department of Anaesthesia, Auckland Hospital, and Associate Professor of Anaesthesia, University

of Auckland, Auckland 1, New Zealand

Summary

A form of sequential analysis has been developed to track performance of tracheal intubation by

novice intubators. One hundred and nineteen trainees completed logbooks during their attachment

to the Departments of Anaesthesia and these data were used to produce rates of success for sequential

attempts at the procedure. A grid was created from this on which future trainees could report their

performance. A boundary drawn on the grid can be used as a trigger to indicate the need for more

basic instruction.

Keywords Education: medical students. Intubation, tracheal: training.

.................................................................................................

Correspondence to: Dr M. J. Harrison

E-mail: mikehar@adhb.govt.nz

Accepted: 15 May 2001

CUSUM, a cumulative summation of scores, has been

used as a way of tracking performance at complex skills [1,

2]. For statistical confidence, many sequential attempts at

the task are required to ensure that the rate of success

required has been achieved. Parry's study [1] involved 334

colonoscopies and Kestin's study [2] of obstetric extra-

dural anaesthesia required between 29 and 185 attempts to

demonstrate the required competency. It is possible to use

the conventional CUSUM technique for the tracking of

early training but it requires mathematical functions that

are not easily handled by a paper logbook, which is the

method used by many trainees to record their experience.

Another technique is to generate a learning curve with

confidence limits [3]. This may be used to assess an

individual or a group. Once again, it is not easily

applicable to a logbook.

This report describes an alternative method of

sequential analysis that has been used for tracking student

performance and is applicable to paper records.

Methodology

Over a period of 1 year, 100 fourth year medical students

and 19 trainee interns at the Auckland Medical School

were attached to four departments of anaesthesia, Auck-

land Hospital, Greenlane Hospital, Middlemore Hospital

and Waikato Hospital. None had previous experience of

tracheal intubation. All the students attended a 1-day

`introduction' course on anaesthesia, intravenous cannu-

lation and airway management techniques before starting

work in the anaesthetic departments. The airway

management tuition involved a practice session on

tracheal intubation using mannequins. Logbooks were

kept during their 2-week attachment and they were

required to record their success or failure at tracheal

intubation. At the end of the 2 weeks, the data from the

logbooks were collated.

A grid was produced that on its x-axis reflected

sequential successes and on the y-axis sequential failures.

The data were processed so that the value in each cell in

the grid represented the percentage of students that passed

through that cell. These values were used to create a

boundary beyond which more basic tuition was thought

desirable.

Results

Table 1 displays the number of trainees who attempted

tracheal intubation. Of the 119 trainees, 117 attempted at

least one intubation. As can be seen, the numbers decrease

so that only 16% manage 10 attempts.

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q 2001 Blackwell Science Ltd 995

Figure 1 displays the rate of successful tracheal intuba-

tion amongst the novice intubators. It should be noted

that n decreases with an increasing number of attempts, as

detailed in Table 1.

A sequential analysis grid has been constructed (Fig. 2).

The second cell on the x-axis from the left-hand lower

corner indicates the percentage of students who would

have succeeded on the first attempt. The third cell on this

axis would indicate the percentage of trainees who

succeeded on both first and second attempts. Similarly

with the y-axis, but these cells represent failure. Cells not

on the margin of the x and y axes represent combinations

of success and failure. For example, a trainee who has two

successes followed by two failures and then another two

successes would follow the path of cells that are labelled

52, 28, 41, 36, 34 and 31 in Fig. 2. These numbers are the

percentages of students that are, on average, likely to pass

through the cells.

The percentages were determined using the linear

regression equation (as displayed in Fig. 1) as outlined in

the appendix.

Figure 3 is a sequential analysis grid that could be used

in a logbook. The figures that represent the proportion of

students passing through the cell have been removed. The

shaded cells are occupied by less than 10% of trainees at

each attempt.

Figures 2 and 3 are based on the average performance

of the trainee group. A trainee who succeeds on the first

attempt may have a higher than average likelihood of

success on the second attempt. To investigate this

possibility, the raw data were sorted to produce results

for specific combinations of success and failure. These are

presented in Fig. 4. The numbers of trainees in these

specific combinations fall quite rapidly and so only the

first four attempts have been processed. Occupancy rates

of the cells using this method (Fig. 4) can be compared

with the `average performance' technique (Fig. 2). The

allocation of the 4th cell on the y-axis to a shaded or

unshaded format does not change.

Discussion

The traditional CUSUM analysis has been used to

determine when a certain degree of competence has

been reached. It has the drawback that large numbers of

attempts at a task are required for statistical certainty. In

many training situations, what is required is some

indication that the trainee's progress is satisfactory.

Because of curriculum constraints, the amount of time

that many trainees spend in a specialty is short, and

therefore the number of procedures that they are likely to

perform are few.

The data collected in this study have several potential

deficiencies; the trainees collected them, they were

collected from four different institutions over which the

author had no `quality control' and the students were

attached to the departments in six batches over the

year. The first batch had no previous clinical experience

at all, whereas the final batch had 10 months of other

clinical experiences, which would have made them

perhaps more confident in the clinical setting. The

completion of the logbook was a requirement of the

Medical School and therefore the data collection was

compulsory. There was, however, no requirement for

any individual to perform a certain number of

procedures and therefore no pressure to `over report'.

Neither was there a requirement for a particular level of

success. All students were supervised at all times but it

is impossible to know the quality of the tuition and

support given. However, the routine anonymous

reporting of students to the Medical School about

their attachments showed great satisfaction with their

time in anaesthesia.

The average success rate, reported above, for the

subset of trainees who completed 12 tracheal intubations

was 85%. This is perfectly comparable with Mulcaster et

al.'s figures [4]; their failure rate was 15%. However,

there is a large discrepancy between the success rate in

the Auckland figures above and their figures for attempts

Table 1 Number of trainees attempting tracheal intubation

nth attempt 1 2 3 4 5 6 7 8 9 10 11 12No. of trainees 117 107 92 74 56 41 34 31 26 19 15 12

Figure 1 The group success rate for tracheal intubation at each

attempt. The number of trainees at each attempt decreases as

seen in Table 1. First attempt n � 117, 10th attempt n � 19.

Forum Anaesthesia, 2001, 56, pages 988±1002................................................................................................................................................................................................................................................

996 q 2001 Blackwell Science Ltd

1±5. Their failure rate for intubation in this early group

was 14.7%; the Auckland figures are 50% for the first

attempt and 38% for the fifth attempt. It is difficult to

understand why Mulcaster's figures for the first five

attempts should have a similar failure rate to the second

batch of five.

This technique, as described, is a norm-referenced

method in that it compares performance against that of a

peer group. In contrast, the major strength of the

CUSUM method is that performance is usually measured

against external standards. The grid could be constructed

to reflect an external standard but it could be argued that

for the early stage of learning a peer referenced learning

rate is more acceptable than pushing trainees to achieve

unattainable goals.

Another limitation of this analysis of performance is

that a trainee may arrive at a particular cell by a number of

routes and the `path' by which the student arrives at a

given cell may be important. The route is very dependent

on the `easiness' of the intubations as well as the aptitude

of the trainee. No statistical certainty can be determined

about whether the student has achieved adequate

performance, is improving or deteriorating.

The keeping of logbooks is now commonplace and

it would be helpful if the completion of the logbook

also provided information as to performance, auto-

matically.

The grid presented here could be used with or without

the figures in the cells. The boundary line drawn on the

grid, if touched by the student's success/fail sequence,

could be used as an indicator for further detailed tuition in

the basic tenets of tracheal intubation. The placement of

the boundary is an arbitrary choice but only less than 10%

of students transgress this boundary. It is important that

patients' management is not compromised by recurrent

ineptitude and it is also important that the trainees'

confidence is not damaged by lack of interventional

tuition when they repeatedly fail at a particular practical

skill.

This type of grid could be used for any procedure.

Figure 2 A sequential analysis grid

indicating the number of trainees that, on

average, would enter each cell. Each cell

being the result of a combination of

successful and unsuccessful attempts.

Figure 3 A simplified sequential analysis

grid for the first 10 attempts at tracheal

intubation. The shaded area on the

`unsuccessful' axis indicates where less

than 10% of trainees will go.

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q 2001 Blackwell Science Ltd 997

References

1 Parry BR, Williams SM. Competency and the colonoscopist:

a learning curve. Australian and New Zealand Journal of Surgery

1991; 61: 419±22.

2 Kestin IG. A statistical approach to measuring competence of

anaesthetic trainees at practical procedures. British Journal of

Anaesthesia 1995; 75: 805±9.

3 Schuepfer G, Konrad C, Schmeck J, Poortmans G, Staffelbach

JM. Generating a learning curve for pediatric caudal epidural

blocks: An empirical evaluation of technical skills in novice

and experienced anesthetists. Regional Anesthesia and Pain

Medicine 2000; 25: 385±8.

4 Mulcaster JT, Hung OR, Law A, Pytka S, Alexiadis P.

Evaluation of proficiency of laryngoscopic intubation by

novice intubators. Anesthesiology 1998; 89: A77.

Appendix

1 The linear regression equation for the success rate at

tracheal intubation was: Success rate � 2.6 � nth

attempt 1 50.3 (Fig. 1). The success rate for the first

attempt was therefore (2.6 � 1) 1 50.3 � 52.9%.

2 The average success/failure rates for the first 10

attempts were:

3 Using the success and failure rates at each attempt

the occupancy of the cells of the sequential analysis grid

can be determined.

Figure 4 A sequential analysis grid with

figures for cell occupancy superimposed.

The figures were determined using

specific combinations of `success' and

`failure' from the raw data.

nth attempt 1 2 3 4 5 6 7 8 9 10Success rate percentage 53 55 58 61 63 66 68 71 73 76Failure rate percentage 47 45 42 39 37 34 32 29 27 24

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998 q 2001 Blackwell Science Ltd

FORUM

Effect of nitrous oxide on the bispectral index and the 95%

spectral edge frequency of the electroencephalogram

during surgery

P. Hans,1 V. Bonhomme,2 H. Benmansour,3 P. Y. Dewandre,2 J. F. Brichant4 andM. Lamy5

1 Chef de Service Adjoint, 2 Chef de Clinique Adjoint, 3 Resident in Anaesthesia, 4 Chef de Clinique and

5 Chef de Service and President, University Department of Anaesthesia and Intensive Care Medicine, CHR de la

Citadelle, Liege University Hospital, 4000 Liege, Belgium

Summary

We studied the effect of nitrous oxide on the bispectral index and 95% spectral edge frequency of the

electroencephalogram in 20 patients undergoing lumbar surgery under general anaesthesia combined

with epidural administration of 5 mg morphine. Anaesthesia was induced with propofol and

sufentanil, and maintained with sevoflurane in air/oxygen adjusted to keep the bispectral index

between 40 and 60. One and a half hours after the start of surgery, nitrous oxide was administered in

a randomised sequence of concentrations (20, 40 and 60% end-expired). Under steady-state

conditions, mean (SD) bispectral index and spectral edge frequency decreased as end-tidal

concentration of nitrous oxide increased, from 47.7 (4.3) and 15.6 (1.3) at 0% nitrous oxide to 39.8

(6.3) and 14.3 (1.8) at 60% nitrous oxide. A negative correlation was found between nitrous oxide

concentration and bispectral index (r � 20.48; p , 0.01) and spectral edge frequency (r � 20.39;

p , 0.05). We conclude that this dose-dependent decrease in bispectral index and spectral edge

frequency induced by nitrous oxide may reflect the level of analgesia associated with the anaesthetic

regimen.

Keywords Monitoring: bispectral index; electroencephalogram. Anaesthetic agents: nitrous oxide.

.................................................................................................

Correspondence to: Dr P. Hans

E-mail: pol.hans@chu.ulg.ac.be

Accepted: 7 June 2001

The aim of monitoring depth of anaesthesia is to avoid an

excessive degree of hypnosis and prevent awareness

during surgery. The bispectral index (BIS) is a neurophy-

siological variable extracted from the processed electro-

encephalogram (EEG). It has been shown to correlate

with the hypnotic component of anaesthesia and is

commonly used as a guide to the administration of

intravenous and volatile anaesthetics [1±3]. In clinical

practice, changes in BIS have also been observed during

painful stimulation under general anaesthesia, depending

on the analgesic regimen [4±6]. The 95% spectral edge

frequency (SEF) is another processed EEG parameter

indicating the frequency below which 95% of the spectral

power of the EEG is detectable. It has also been proposed

as a monitor of depth of anaesthesia but, according to

recent studies, it appears to be less powerful than the BIS

[7±9].

Nitrous oxide is commonly used as an adjunct to

anaesthetic agents because of its capacity to spare

hypnotics, its potent analgesic properties and its low

incidence of side-effects. No effect of nitrous oxide alone

has been demonstrated on BIS and SEF in the absence of

noxious stimulation [10, 11]. The purpose of this

prospective study was to investigate the effect of nitrous

oxide on BIS and SEF during conditions of painful

stimulation at a steady state of general anaesthesia,

Anaesthesia, 2001, 56, pages 988±1002 Forum................................................................................................................................................................................................................................................

q 2001 Blackwell Science Ltd 999

analgesia being provided mostly by pre-operative epidural

morphine.

Patients and methods

After approval from the hospital ethics committee and

informed consent, we studied 20 patients scheduled for

major lumbar surgery under general anaesthesia combined

with pre-operative epidural administration of morphine.

Selection criteria for eligibility included the absence of

any neurological and psychiatric disease, and complete

abstinence from illicit drugs and alcohol.

Premedication consisted of alprazolam 0.5 mg and

atropine 0.5 mg orally 1 h before surgery. Upon arrival in

the operating theatre, a peripheral venous cannula was

sited and non-invasive blood pressure monitoring,

electrocardiography and pulse oximetry instituted

(Datex AS3, Helsinki, Finland). The ASPECT A-1000

monitor (version 3.3, Aspect Medical Systems, Natick,

MA, USA) was used to collect EEG data. After mild

abrasion of the skin, Zipprep electrodes (Aspect Medical

Systems) were applied to the patient's forehead according

to the classical bifrontal montage. Contact impedance was

verified to be , 5 kV. In all patients, an epidural catheter

was sited at the L122 interspace and positioned 4 cm

within the epidural space in the cephalic direction. After a

test dose of 3 ml lidocaine 1% with epinephrine

1 : 200 000, 5 mg morphine in 10 ml normal saline

was injected epidurally before induction of anaesthesia.

General anaesthesia was induced with 1.5 mg.kg21

propofol and 0.15 mg.kg21 sufentanil. Tracheal intuba-

tion was facilitated with 0.5 mg.kg21 rocuronium.

Anaesthesia was maintained with sevoflurane in oxygen/

air adjusted to keep the BIS between 40 and 60 in all

patients. Mechanical ventilation was adjusted to keep the

end-expired concentration of carbon dioxide between 4.0

and 4.7 kPa. Body temperature was monitored using an

Figure 1 Bispectral Index (BIS; W) and 95% spectral edge frequency (SEF; X) at different end-expired concentrations of nitrous oxide

(%). Linear regression lines are shown for BIS (- - -) and SEF (Ð). *p , 0.05 compared with values at 0% N2O; **p , 0.05

compared with values at 0, 20 and 40% N2O.

Table 1 Systolic, mean and diastolic arterial pressure (SAP, MAP and DAP, respectively) and heart rate at different end-expiredconcentrations of nitrous oxide. Values are mean (SD).

0% nitrous oxide 20% nitrous oxide 40% nitrous oxide 60% nitrous oxide

SAP; mmHg 102.0 (13.7) 99.5 (13.0) 96.5 (13.6)* 94.9 (12.9)*MAP; mmHg 77.7 (11.0) 76.3 (9.7) 73.3 (9.9) 73.8 (10.1)DAP; mmHg 64.7 (11.3) 64.2 (9.9) 61.5 (9.3) 62.4 (10.1)Heart rate; beat.min21 66.1 (12.1) 62.9 (12.4)* 61.9 (11.9)* 63.4 (13.5)

*p , 0.05 compared with 0% nitrous oxide.

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1000 q 2001 Blackwell Science Ltd

oesophageal probe and normothermia was maintained

with a forced warm air device (Bair Hugger model 200,

Augustine Medical, Eden Prairie, MN, USA) placed on

the upper part of the body. A bladder catheter was also

inserted. Under steady-state anaesthesia 1.5 h after the

start of surgery, nitrous oxide was administered in a

randomised sequence of concentrations (20, 40 and 60%

end-expired) while maintaining the sevoflurane concen-

tration at its previous level. The BIS, SEF, heart rate, and

systolic, diastolic and mean blood pressures were recorded

three times at 2-min intervals before administration of

nitrous oxide and, following a 10-min equilibration

period, at each end-tidal nitrous oxide concentration

(20, 40 and 60%).

Analysis of the recorded BIS values by inspection and

construction of normal quartile plots revealed a normal

distribution. Statistical analysis was therefore performed

using one-way within-subjects anova with Tukey's test

for post hoc comparisons. Least-squares regression was

used to define the relationship between nitrous oxide

concentration and BIS or SEF values. A p value of , 0.05

was considered statistically significant.

Results

Ten males and 10 females were studied, aged 30±77 years

[mean (SD) 50.8 (14.2) years]. Both BIS and SEF decreased

with increasing nitrous oxide concentration (Fig. 1).

Haemodynamic values decreased with increasing nitrous

oxide concentration (Table 1). Upon wakening, all patients

were comfortable and did not complain of any pain.

Discussion

The results of this study demonstrate that during lumbar

surgery and at a steady state of sevoflurane anaesthesia

combined with epidural administration of 5 mg mor-

phine just before induction, nitrous oxide produced a

significant dose-dependent decrease in BIS and SEF, and a

clinically insignificant decrease in arterial blood pressure

and heart rate. The correlation between nitrous oxide and

SEF was less significant than that observed between BIS

and nitrous oxide. Therefore, the results of this study are

in agreement with the results of other studies showing

that SEF is probably less powerful than the BIS for

monitoring the depth of anaesthesia [7±9].

Recent progress in monitoring depth of anaesthesia has

principally involved two techniques, namely the BIS and

the middle latency auditory evoked response. The BIS is

recognised as a useful trend monitor of the depth of the

hypnotic component of general anaesthesia in clinical

practice. The decrease in BIS with increasing nitrous

oxide concentrations may reflect either a direct increase in

the hypnotic depth or an improvement of analgesia that

may secondarily affect the hypnotic component of

anaesthesia. In the absence of painful stimulations,

previous studies have shown that the BIS is not affected

by nitrous oxide. In healthy young adult volunteers, 10±

50% nitrous oxide has no major sedative effect and does

not affect either the BIS or SEF [10]. Inhalation of 70%

nitrous oxide in volunteers results in loss of consciousness

without any change in BIS [11]. It has also been reported

that the BIS is not altered by addition of nitrous oxide

during general anaesthesia with propofol and remifentanil

[12]. During noxious stimulation under general anaes-

thesia, changes in BIS may reflect the analgesic compo-

nent of anaesthesia. Noxious stimulation induces

autonomic reactions, somatic reactions and arousal. It

has been demonstrated in a recent study that noxious

stimulation affects the level of cortical electrical activity

measured by SEF 95, median power frequency and the

BIS [13]. The correlation between electroencephalo-

graphic parameters and the level of sedation or uncon-

sciousness implies that noxious stimulation may decrease

the level of sedation. Indeed when compared with the

unstimulated state, surgery leads to a rightward shift of the

concentration2response curve [13]. When drugs such as

propofol or isoflurane are used as the primary anaesthetic,

changes in BIS correlate with the probability of the

patient's response to skin incision but this correlation

becomes less significant when opioid analgesics are added

[5]. In a previous study comparing the effects of two

calculated plasma sufentanil concentrations on the BIS

response to head pinning, we suggested that BIS changes

recorded during noxious stimulation could be related to

the analgesic regimen [6]. Recently, it has been shown

that addition of remifentanil to propofol affected BIS only

when a painful stimulus was applied, and that the increase

in BIS associated with laryngoscopy and tracheal intuba-

tion reflected a deficit in the analgesic component of

anaesthesia [14]. In another study, a dose-related reduc-

tion in BIS by remifentanil was reported during

administration of propofol in the absence of painful

stimuli [15]. In that study, propofol infusion was targeted

at 2 mg.ml21 to ensure sedation in spontaneously

breathing patients [15]. Therefore, if the effect of the

combination of opiates and hypnotics on BIS is not yet

completely clarified, a body of data suggests that BIS

changes during noxious stimulation under general

anaesthesia are correlated with the appropriateness of

analgesia.

Few studies have investigated the effect of nitrous oxide

on BIS during noxious stimulation. During coronary

artery bypass surgery in patients receiving midazolam and

fentanyl infusions, nitrous oxide caused no change in BIS

after sternotomy [11]. In this study, patients were

premedicated with 7.5±12.5 mg morphine, and received

high-dose fentanyl at induction as well as during surgery.

Anaesthesia, 2001, 56, pages 988±1002 Forum................................................................................................................................................................................................................................................

q 2001 Blackwell Science Ltd 1001

During orotracheal intubation under target-controlled

anaesthesia using propofol and remifentanil at effect-site

concentrations of 3 mg.ml21 and 4 ng.ml21, respectively,

addition of nitrous oxide prevented movement without

affecting BIS [12]. In these two studies, one can

reasonably assume that the analgesic regimen was

appropriate to the degree of noxious stimulation. In our

study, nitrous oxide caused a decrease in BIS and SEF

during surgery. The effect of nitrous oxide was studied at

the same time during the surgical procedure in all

patients. In fact, our patients received 5 mg epidural

morphine prior to surgery and an iv bolus of

0.15 mg.kg21 sufentanil at induction of anaesthesia. In

those conditions, analgesia provided by epidural mor-

phine could have been insufficient with respect to the

intensity of noxious stimulation 1.5 h after the start of

surgery, and administration of 40 or 60% nitrous oxide

might have improved analgesia, resulting in a slight but

significant decrease in BIS. Indeed, 5 mg epidural

morphine is a quite low dose compared with the 5±

10 mg commonly used to ensure analgesia for such surgical

procedures [16]. The absence of pain at emergence from

anaesthesia does not rule out insufficient analgesia during

surgery as the intensity of painful stimulation is not the

same during and after surgery. The haemodynamic changes

associated with the addition of nitrous oxide could also be

explained by a more appropriate analgesic state provided by

the nitrous oxide. Hence during surgery, BIS reflects the

depth of anaesthesia that is affected by the balance between

noxious stimulation and the degree of analgesia. The depth

of anaesthesia, reflected by the BIS, is primarily dependent

on hypnotics and sedatives but is also indirectly affected by

noxious stimulation and hence by the level of analgesia.

Therefore, the statement of Coste and colleagues, that the

algorithm that computes BIS does not detect the effect of

nitrous oxide on the central nervous system, should be

reviewed [12]. Nitrous oxide does not modify BIS in the

absence of noxious stimulation, even when administered at

sufficient concentration to induce loss of consciousness. In

contrast, nitrous oxide does modify BIS in case of noxious

stimulations that affect arousal.

References

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Manberg P. Bispectral analysis measures sedation and memory

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2 Gan TJ, Glass PS, Windsor A, et al. Bispectral index

monitoring allows faster emergence and improved recovery

from propofol, alfentanil, and nitrous oxide anesthesia.

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3 Song D, Joshi GP, White PF. Titration of volatile anesthetics

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7 Schraag S, Mohl U, Bothner U, Georgieff M. Clinical utility

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8 Struys M, Versichelen L, Mortier E, et al. Comparison of

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9 Sleigh JW, Donovan J. Comparison of bispectral index, 95%

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10 Rampil IJ, Kim JS, Lenhardt R, Negishi C, Sessler DI.

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Anesthesiology 1998; 89: 671±7.

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13 RoÈpcke H, Rehberg B, Koenen-Bergmann M, Bouillon T,

Bruhn J, Hoeft A. Surgical stimulation shifts EEG

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