Cleaton-Jones, P.

Moyes, D.

Shaw, R.

English

Wits Institutional Repository on DSPACE

120 S A M r: d i n s i- T y d s k r i  r 19 Julie 1980
Early and Late Scavenging of Anaesthetic Gases
P CLEATON-JONES, D. MOYES, R. SHAW, J. AUSTIN, L. BONNER, H. FAIN,
R. CRICHTON
SUMMARY
The effectiveness of two waste gas scavenger devices, 
the Carstens box and the Ventex apparatus, with regard 
to nitrous oxide pollution was studied under comparable 
conditions in an operating theatre. The scavengers were 
brought into use in the early and late stages of induction 
of anaesthesia, and nitrous oxide concentrations in the 
breathing zone and theatre peripheral air were measured. 
Both scavengers reduced nitrous oxide pollution at the 
sampling points. Similar reductions in nitrous oxide pol­
lution in the breathing zone were obtained with both 
scavengers, but the Carstens box was more effective in 
reducing nitrous oxide pollution in the peripheral air.
5. Afr. nwi/. J.. 58, 120 (1980).
The harmful effects of long-term exposure of operating- 
theatre staff to air polluted with anaesthetic gases are 
under scrutiny. This is not a new phenomenon, since 
Hirsch and Rappers suggested in 1929 that inhalation of 
anaesthetic agents present in the air of operating rooms 
might have an injurious effect on the health of surgeons 
and those who assist them.1 It is, however, a controversial 
matter. National surveys of anaesthetists in the UK" and in 
the USA1' have shown an increase in the frequency of spon­
taneous abortion in women who work in operating theatres, 
but other authors have not confirmed this. Congenital ano­
malies may also be present in higher than expected num­
bers in the offspring of anaesthetists. This has been shown 
in the children of female anaesthetists in some studies' "' 
and among children of both male and female anaesthetists 
in another study."
Although the effects of anaesthetic gas pollution are at 
present uncertain, health authorities in both the UK and 
the USA suggest the use of scavenging systems to lessen 
pollution.1 This study was undertaken to examine the
Dental Research Institute of the South African Medical 
Research Council, Johannesburg
I’. CLEATON-JONES. n . n . s . .  m  u . ii.c i i .. i>i i . i>.. i>..\.
I. AUSTIN, ii.v.sr-.
It. CRICHTON
Departm ent of Anaesthesia, Karagwanath Hospital and Uni­
versity of the YVitwatersrand, Johannesburg
D. MOYES. m . h .c . s ., i. .« .c . i 1., m . h . rai.ii.. r . r .A .
R. SHAW, ii.so.
Departm ent of Anaesthesia, Johannesburg Hospital and Uni­
versity of the W itwatersrand, Johannesburg
L. BONNER, M.n. ii.c i i .
Departm ent of Maxillofacial and Oral Surgery, University of 
the W itwatersrand, Johannesburg
II. EAIN, m .h . ii.c i i ., i).a .
D ale received: IK O ctober 197‘J.
effects of two scavenging systems, connected to the anaes­
thetic circuit during the early and late stages of induction, 
on nitrous oxide pollution of air in an operating theatre.
MATERIALS AND METHODS
The operating theatre at the Oral and Dental Hospital of 
the University of the Witwatersrand, Johannesburg, was 
the venue for the study. This is a room of 138 m1 capacity 
ventilated by means of two window-mounted air-cooling 
units (12 660 kJ/h), producing approximately two air 
changes per hour.
Sampling
Snatch air samples were collected by twice aspirating 
and expelling 20 ml of air in disposable polypropylene 
syringes, followed by aspiration of a final 20 ml sample 
which was injected into a gas-tight nylon storage bag. The 
samples were collected at two sites, initially before com­
mencing the day’s operating and thereafter at 10-minute 
intervals following the beginning of the first anaesthetic.
The sites sampled were: (/') in the breathing zone at the 
Heidbrink valve, and (ii) in the peripheral air at the air 
conditioner intake.
Each final air sample was collected within 1 second and 
the sampling was completed at both sites within 1 minute. 
The samples were then transferred to a laboratory for 
analysis in a gas chromatograph.
Gas Chromatographic Technique
The concentration of N.O was determined in all the 
samples with a Pye Unicam model GCV gas chromato­
graph. N.O was separated using a 2 m x 4 mm borosilicate 
glass column packed with 80- 100 mesh Poropak type Q 
(Waters Associates, Milford, Mass., USA) at a column tem­
perature of 80°C. Helium was used as the carrier gas at a 
flow rate of 25 ml/min. A katharometer was used to detect 
(he N.O, the filament temperature being 180°C and the 
detector temperature being 100°C. At the injection port the 
temperature was 150°C. Peak areas were integrated with 
a Pye DP 88 integrating computer and compared with 
those of commercially prepared 100 ppm and 1 000 ppm 
(v/v) in N: standard mixtures (Altec Associates Calibra­
tion Gas, Arlington Heights, III., USA).
Scavenging Devices
Two scavenging devices were used, both of which have 
been described in detail elsewhere.’' The first, developed at 
Baragwanath Hospital by Carstens, consists of a Perspex 
box containing a 2 1 reservoir bag. This bag is open at the 
base opposite an outlet attached to the main room suction. 
The outflow from the patient was attached to the bag inlet.
I‘) July 1080 S A M i: n I c a i . J o u k n a i 12!
An adjustable inlet/outlet valve on the upper surface of 
the box completes the apparatus (Fig. 1).
Fig. 2. Ventex scavenger. The device comprises a metal 
tube with negative (N) and positive (!’) relief valves 
and suction (arrowed) controlled bv a needle valve (V).
A 2 I reservoir bag is attached to the device.
In late scavenging, the patients were intubated and con­
nected to the circuit, gas How was begun, and the pack was 
inserted. A scavenger was then attached to the circuit.
Control samples were collected during operations when 
no scavenger was attached to the anaesthetic circuit. The 
order of use of the scavenging devices was randomized 
using a table of random numbers, and each technique was 
used on 4 days.
Before the start of the investigation, the effect of the
The second device, the Ventex scavenger (Allan Cornish 
(Pty) Ltd, Johannesburg), consists of a metal tube with an 
attached reservoir bag, gravity-operated non-sprung inlet 
and outflow valves and a suction attachment adjustable 
through a needle valve (Fig. 2).
Piped suction (equivalent to a gas flow of 24 I/min) was 
adjusted to allow similar inflation of the reservoir bags on 
each scavenging device and in the Magill circuit.
Anaesthetic Technique
Anaesthesia was induced in patients in the operating 
theatre by intravenous thiopentone or alphaxalone and the 
gas flows set at CL 3 I and N=0 5 l/min. Halothane supply 
was adjusted as required. All patients were intubated via 
the nasal route with Portex non-cuffed endotracheal tubes
(Portex, Hythe, Kent. England) and throat packs, either 
moistened gauze or vaginal tampons, were used.
The scavengers were used either early or late in the in­
duction of anaesthesia. If used in the early stage they were 
attached to a hooded valve (F. H. Gardner Co., Oxford, 
England) in the Magill circuit before any anaesthetic gases 
were switched on. The patients were intubated, the cir­
cuitry connected to the endotracheal tube, and the gas flow 
begun. The throat pack was then inserted.
Fig. I. Carstens box scavenger. This consists of a Perspex 
box surrounding a 2 I reservoir bag, into which waste 
gases How, open at the distal end above a suction outlet 
(arrowed). An adjustable pressure relief valve is situated 
on the upper surface of the box.
122 S A M t: n i i; s i: T y n s k i m  p I1) Julie 1980
operating theatre ventilation on the concentration of N O 
in the air was observed in the following manner. A Magill 
circuit with attached catheter mount was placed on the 
operating table so that the Weidbrink valve was in the 
position at which it would lie during an anaesthetic. The 
minute volume gas flow was set at X l/min (O.- 3 l/min, 
N.O 5 l/min) for 20 minutes. Samples of air were collected 
as described above at the Heidbrink valve and air condi­
tioner intake prior to commencing gas How anti then at 
10-minute intervals for 140 minutes.
Statistical Analysis
The concentrations of N.O measured in parts per million 
(v/v) were tabulated and means and standard deviations 
calculated. The statistical tests used were the one-way 
analysis of variance and Schelfe’s multiple comparison 
test. A probability value of less than 0,05 was selected as 
the level of statistical significance.
RESULTS
The pattern of the rise and fall of nitrous oxide concen­
tration in the operating-theatre air is shown in Fig. 3.
There was a rapid increase in N O concentration after gas 
How commenced. On the cessation of gas llow. the N-O 
concentration diminished rapidly for the First 10 minutes, 
alter which the fall in concentration was slower. The initial 
level was reached after 140 minutes. The N.O concentra­
tion at the position of the Heidbrink valve was greater 
than in the peripheral air for the first SO minutes anil 
thereafter the two were almost identical.
On the sampling days the numbers of general anaes­
thetics administered varied from 1 to 4 per day and the 
total perioil of N.O gas llow from 50 to 100 minutes per 
day. The mean gas llow times per patient during the sam­
pling perioil in each group were similar, however, ranging 
from 22 to 27 minutes, and the total gas flow in each 
group varied from 290 minutes (no scavenging) through 
300 (Venlex, early; C'arstens, late), 310 (C'arstens, early) to 
350 minutes (Ventex, late).
The percentage frequency distribution of the concentra­
tions of N.O measured in the breathing zone during the 
limes that the gas was flowing is shown in Table I. This 
shows a wide variation in the concentrations with a trend 
towards lower concentrations when the scavengers were 
used. The N O concentrations in the peripheral air were
1000
• breathing zone 
. peripheral air
750
500
250
o
on
i
oft
60
minutes
120
Fig. 3. Concentrations of N.O in ppm (v/v) in the 
breathing zone and peripheral air after a 20-minutc flow 
of N O  <<).- 3 I and N O  5 l/m in) into the operating 
theatre.
ventex carstens
control early late early late
19 July 1980 S A M i: I) I (' A I. J O U R N A  L 123
TABLE I. PERCENTAGE FREQUENCY DISTRIBUTION OF N20 POLLUTION BREATHING ZONE
n 2o Control Ventex Ventex Carstens Carstens
concentration (no scavenger) early late early late
(ppm (v/v) (N =  29) [N =  30) (N =  35) (.N =  31) (N =  30)
> 1 0 0  000 34 10 11 3 0
10 001 - 100 000 38 27 26 29 13
1 001 - 10 000 21 23 43 32 23
101 - 1 000 7 30 20 32 47
0 - 100 0 10 0 3 17
TABLE II. DETAILS OF N20  CONCENTRATIONS IN PPM
Ventex
Control early
No. of samples 29 30
Breathing zone
Range 469 - 221 007 86 - 245 897
Mean 71 663 29 565
SD 70,999 54 426
%  reduction in pollution — 59
Peripheral air
Range 146 - 1462 29 - 710
Mean 519 307
SD 287 181
%  reduction in pollution — 41
lower, were spread over a narrower range, and are shown 
in scattergram form in Fig. 4. The trend towards lower 
concentrations when the scavengers were used can be 
clearly seen. Details of the ranges of NT) concentrations, 
means and standard deviations are listed in Table II. Also 
indicated are the percentage reductions in pollution. These 
were calculated by subtracting the mean NT) concentra­
tion when each scavenger was used from the mean con­
trol concentration and expressing this difference as a per­
centage of the control.
Table II reveals a wide variation in N=0 concentrations, 
especially in the breathing zone, exemplified by wide ranges 
and high standard deviations. Use of the C'arstens box in 
the late stage was associated with the greatest reduction. 
Statistical analysis of differences in mean NT) concentra­
tions using Scheffe’s multiple comparison test showed the 
following:
In the breathing zone all the scavenging devices signifi­
cantly reduced NT) pollution below the level noted when 
no scavenger was used. There were no significant differ­
ences between the mean NT) concentrations noted when 
each of the methods of scavenging were used.
All the scavenging methods produced statistically signi­
ficant lower concentrations of N^O in peripheral air. Some 
significant differences were seen between the methods. Late 
use of the Carstens box produced significantly lower NT) 
concentrations than either early or late use of the Ventex 
device. Also, early use of the Carstens box was associated 
with significantly less pollution than late use of the Ventex 
device. Comparisons between early and late use of the 
Ventex device and also between early and late use of the 
Carstens box showed no statistically significant differences.
(V /V )  DURING THE PERIODS THAT GAS W AS FLOWING
Ventex Carstens Carstens
late early late
35 31 30
263 - 116 389 6 5 -2 5 5  421 49 - 18 265
25 316 19 715 5 096
38 059 47 805 15 610
65 72 93
2 - 648 8 0 -3 4 7 41 - 365
377 241 145
156 84 89
27 54 72
DISCUSSION
The choice of sampling sites in pollution studies is diffi­
cult and always represents a compromise between the 
desirable and the feasible.'1 Our choice of one site in the 
breathing zone and another (termed peripheral air) at the 
air conditioning intake is based on the suggestion of 
Whitcher.'" Within each of the zones chosen, the con­
centrations of nitrous oxide will vary with time because of 
the three factors that determine gas movement within a 
room, namely variations in air flow into the room, varia­
tion in temperature and the presence of moving bodies. 
These were not controlled in our study which was con­
ducted during routine operating sessions. The order of use 
of the scavenging device was randomized to reduce pos­
sible bias over choice of operating day.
Four possible types of nitrous oxide monitoring are pos­
sible. These consist of sampling of the air in operating 
theatres with snatch samples, such as was used in this study, 
with continuous sampling," or with the use of continuous 
monitoring devices such as the Miran infrared absorption 
analyser (Wilks Scientific Corp., South Norwalk, Conn., 
USA). It is also possible to use integrated personal sam­
pling of occupational exposure of staff." Snatch samples 
collected in nylon bags have proved convenient and reli­
able in our hands15 and have produced values similar to 
continuous monitoring.15
The slow reduction in nitrous oxide concentration ob­
tained when no operation was in progress confirmed the 
poor ventilation in the operating theatre. Although the 
scavengers reduced pollution, this was much higher than 
the 30 ppm (v/v) upper limit suggested by Whitcher ct al."
124 S A M i: t) i i: s i! T y i j s k r i f 19 Julie 1980
This study has not revealed a marked superiority of 
either of these devices over the other, nor does there ap­
pear to be strong justification for the early use of these 
scavengers.
We wish to thank our operating-theatre colleagues who co­
operated in the study, Mr Allan Cornish for having donated 
the Ventex device, and Mrs J. l.ong lor secretarial assistance.
REFERENCES
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237. L eiden: U niversity  o f  Leiden Press.
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7. Spence, A. A. and K nill-Jones, R. P. (1979): Ib id ., I , 1144.
8. M oyes, D. G ., C lea ton -Jones , P. and  F oster, P. A. (1979): S. Afr. med. 
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Offlce.
Lorazepam as a Premedicant in Dental Surgery
J. RUBIN, I. SCHWLGGMANN. P. UYS
SUMMARY
In a double-blind study, 100 young, healthy (American 
Society of Anesthesiologists physical status I) patients 
received lorazepam (Ativan; Wyeth) 2,5 mg or placebo 
orally as premedication before general anaesthesia for 
extraction of wisdom teeth.
Lorazepam produced a significant reduction in the in­
cidence of pre-operative anxiety and post-anaesthetic 
headache compared with placebo (P < 0 ,0 1 ). Anterograde 
amnesia was also more frequent in the patients who had 
received lorazepam (P < 0 ,001 ).
The medicolegal implications of using lorazepam as a 
premedicant in dental surgery at a day clinic are discussed.
S. Afr.  med. J.. 58, 124 (1980).
Most patients presenting for dental surgery under general 
anaesthesia are naturally apprehensive, and may prefer to
Departm ents of Anaesthesia and Surgery, University of Natal, 
Durban
J. RUBIN, B.SC ., M .li. C ll .n ., f . f . a . ,  Principal Anaesthetist and 
Senior Lecturer 
I. SCHWEC.GMANN, s . k .n .
P . UYS, n .D .S ., D .M .F .O .S .
D ate  received: 12 M arch  1980.
be unaware of the period immediately preceding the 
operation. The unpredictable length of the surgical pro­
cedure poses problems in the timing of administration of 
premedicant drugs. An oral premedicant with a short 
latency of onset and reasonable duration of action which 
relieves anxiety and produces anterograde amnesia there­
fore appears highly desirable.
Lorazepam (Ativan; Wyeth) is the ortho-chloro-phcnyl 
derivative of oxazepam, the main metabolite of diazepam 
(Fig. 1). In animals, lorazepam is 20 times as potent as 
chlordiazepoxide.’ It is non-toxic to man,’ doses of up to 
7,5 mg being well tolerated, although electro-cncephalo- 
graphic changes characteristic of hypnotic agents have
DIAZEPAM LORAZEPAM
Fig. 1. M olecular formulae of diazepam and lorazepam.


Early and late scavenging of anaesthetic gases

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Early and late scavenging of anaesthetic gases

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