Vol.3, No.3, 162-165 (2011) Health
doi:10.4236/health.2011.33031
Copyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/HEALTH/
Is routine blood test of value for evaluating health
effects among midwives working with nitrous oxide for
pain relief in delivery unit
Gudrun Abascall1, Maud Johansson1, Jan Jakobsson2
1BB Stockholm, Stockholm, Sweden;
2Department of Anaesthesia & Intensive Care Institution for Physiology and Pharmacology, Karolinska Institutet, Stockholm, SWE-
DEN; *Corresponding Author:
Received 2 January 2011; revised 20 January 2011; accepted 25 February 2011.
ABSTRACT
Chronic workplace exposure to high nitrous ox-
ide concentrations has been suggested to po-
tentially be associa ted to nega tiv e health eff ects
caused by the interference with the vitamin B12,
methionine synthase pathway. The objective of
the present study was to determine if delivery
unit work place ambient air nitrous oxide ex-
posure results in detectable hyperhomocysteine-
mia or signs of macrocytocis in personnel. Blood
samples from thirty healthy female fulltime em-
ployees, midwives, aged 43 (range 25-62) years
were studied. Routine blood test analysed for
plasma homocysteine and blood status; hae-
moglobin, mean corpuscular volume, mean cor-
puscular haemoglobin concentration, blood sta-
tus was analysed once before going on vacati on
and repeated after at least 10 days’ leave, ni-
trous oxide free period. Median time weighted
average w as 41 [10 - 547] ppm; 3 out of 11 TWA
measurements were above recommended100
ppm limit. Median homocysteine concentrations
were 10.7 [5.6 - 16] micromol/L with reference
limits of 5.0 – 15 micromol/L. Megaloblastic ery-
throcytes was not detected in any personnel and
no changes in blood st atus could be detected be-
tween before and after a nitrous oxide-free pe-
riod. Conclusions: One of 3 delivery units’ am-
bient air qualit y measures exceed recommended
ranges. No signs of routi ne blood test pathology
could be seen in the personnel studied.
Keywords: Nitrous oxide; ambient air quality; TWA;
homocysteine; megaloblastic anaemia.
1. INTRODUCTION
Chronic working day exposure to nitrous oxide in
healthcare workers is associated with alterations of vi-
tamin B12 metabolic status, the extent of which depends
on the level of exposure [1]. Air conditioning and an
efficient pressure/exhaust ventilation (above 12 air ex-
changes/h) together with efficient active scavenging
systems are sufficient to sustain N(2)O exposure in oper-
ating theatres at levels below or within th e OE L val ue of
180 mg/m(3) [2]. Ventilation and scavenging is not al-
ways optimal in maternity wards and work place expo-
sure has been shown to be not uncommonly exceeding
set national recommendation, occupational exposure lim-
its [3,4]. The use of scavenging equipment is not always
easily adopted in the delivery situation with mothers
experiencing painful contractions [5].
The inhibitory effects of nitrous oxide on the vitamin
B12 dependent methionine synthase pathway have been
suggested to be one of major factors for the develop-
ments of negative health effects [6]. Homocysteine and
megaloblastic erythrocytes and anaemia are early signs
from prolonged nitrous oxide exposure triggered me-
thionine synthase inhibition [7,8].
The aim of this study was to explore if any changes
could be seen in routin e blood testing as signs of nitrous
oxide inhibition on the methionine synthase pathway in
full-time delivery room personnel.
2. METHODS
The study was conducted in delivery unit of Stockholm
BB. Annual numbers of deliveries is about 2 800 in the
unit. Nitrous oxide is the most commonly used an algesic
technique used, 73% of mothers uses nitrous oxide as
some point during the delivery. Nitrous oxide is admin-
istered via an on-demand valve from a dedicated nitrous
oxide oxygen mixture Ventyo (Linde Healthcare, AGA
AB, Lidingö, Sweden). The system use includes a basic
waste gas scavenging system but no “double-mask scav-
enging” is available. Time Weighted Average (TWA) for

G Abascall et al. / Health 3 (2011) 162-165
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163
nitrous oxide was measured on eleven random 8-hour
workdays using nitrous oxide diffusion samplers (Dräger
Safety AG & Co. KGaA, Lubeck, Ge rmany).
After informed consent, venous blood samples for
analysis of plasma homocysteine and blood status were
taken in 30 healthy full-time female personnel, aged 43
(range 25-62) years. A second blood status was analysed
after vacation a nitrous oxide-free period in all 30 sub-
jects, each subject serving as its own control. All blood
samples were immediately frozen. Standard hospital
laboratory techniques were use to analyse all samples for
plasma homocysteine, haemoglobin value (Hb), hemato-
crit, erythrocytes, mean corpuscular haemoglobin (MCH),
mean corpuscular volume (MCV), mean corpuscular
haemoglobin concentration (MCHC) and leucocytes.
Statistics: All data are given as mean and standard de-
viation or median and range.
3. RESULTS
Work place nitrous oxide concentration TWA varied
considerably with a median of eleven measured TWA of
41 [10 - 547] ppm. Three of the 11 TWA measurements
were above the recommended Swedish maximum TWA
of 100 ppm. Median homocysteine concentrations were
10.7 [5.6 - 16] micromol/L with reference limits of 5.0 –
15 micromol/L. Concentrations of 16 micromol/L, just
above the upper reference limit, were found in 2 mid-
wives. The plasma levels of homocysteine for these two
nurses did not change after a vacation period of at least
14 days free from exposure to nitrous oxide. Haemato-
logical test results are shown in Table 1. Four personnel
had mild anaemia that showed a tendency to improve
following a vacation period; haemoglobin before/after
vacation; 116/120, 103/108, 111/118, 118/123 respec-
tively. No signs of megaloblastic erythrocytes of mega-
loblastic anaemia were seen in any of these or any other
of the midwives. All MCH, MCV or MCHC values were
within reference ranges and there were no systematic
changes in any variable when compared before versus
after vacation Table 1. The mean duration of vacation
was 23 [10-44] days. Mean change in MCHC before ver-
sus after vacation was -0.4 [-17 to + 15]. Individual
changes in MCHC concentrations are shown in Figure 1.
4. DISCUSSION
Our results are mixed, the ambient air quality measures
showed that further efforts have to be taken in order to
apply to national recommendations. We could, however,
no see any clear signs of blood pathology attributable to
a potential more profound inhibition of the methionine
synthase pathway. Most countries provide clear guide-
lines as to work place ambient air concentrations for
Table 1. Blood status in 30 midwifes before and after vacation
(mean and range).
Before vacation After vacation
Haemoglobin (g/L) 129.1 [103-154] 130.9 [108-146]
Erythrocyte volume fraction 37.9 [32-45] 38.5 [34-43]
Mean corpuscular volume
(× 10-15L) 87.4 [74-96] 88.2 [74-98]
Mean corpuscular
haemoglobin (10-9 g) 29.7 [24-33] 29.9 [24-33]
Mean corpuscular
haemoglobin
concentration (g/L) 340.2 [325-352] 339.1 [320-352]
Platelets (× 109/L) 246 [171-418] 254 [168-398]
Leucocytes (× 109/L) 6.0 [4.4-9.5] 6.3 [4.4-9.6]
Figure 1. Individual mean corpuscular haemoglobin concen-
trations (g/L) for 30 personnel exposed to nitrous oxide, before
and after vacation. Bold lines show normal limits.
gases possessing potential health risk. In the US as well
as in most European nations nitrous oxide have well-
established time- weighted averag e limits that shou ld not
be exceeded in order to assure personnel safety and
health [9]. These limits are in parts per million range
varying in the magnitude of 25 – 100 parts per million
(ppm). Gas concentrations in parts per million are diffi-
cult to measure and today there is no easily available
technique to on every day basis monito r and secure good
work place air quality. We found that ambient nitrous
oxide concentration varied considerably and almost a
third of measured TWA values were above national
recommended limits for Sweden.
Operating room with forced basic ventilation in com-
bination with commonly adopted routines in order to
minimise work-place pollutions by means of avoidance
of mask ventilation use of laryngeal mask airway and

G Abascall et al. / Health 3 (2011) 162-165
Copyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/HEALTH/
164
intubation and low-fresh gas flows have made incidence
of personnel exposure to nitrous oxide above set rec-
ommendation infrequent (10). The large variation in
nitrous oxide work place exposure detected in our unit is
similar with what has been found elsewhere. Recent re-
port both from UK and Sweden have shown high inci-
dences of TWA above set national recommendations in
delivery units [3,4]. It is obvious that further efforts to
improve ambient workplace air quality are warranted in
the delivery unit studied. The importance of adequate
ventilation and scavenging is well acknowledged [4]. In
our centre the nitrous oxide is administered from an
on-demand valve attached to a standard a scavenging
system. The problem with adequate scavenging of ex-
haled air associated with the use of nitrous oxide during
childbirth, in association to painful contractions is well-
known [5].
Homocysteine increase has been suggested to be a
sensitive marker for the inhibitory effect of nitrous oxide
on this enzyme complex [11]. We found, however, no
signs of nitrous oxide associated hyperhomocysteinae-
mia. In the two midwifes exhibiting borderline values
during a period of consistent work, no change could be
noticed after a period of 10 days without any nitrous
oxide exposure. Furthermore neither of these two per-
sonnel showed any signs of blood status abnormalities.
Megaloblastocis and megaloblastic anaemia are signs of
vitamin B12 deficiency and such changes have been
shown in patient following nitrous oxide anaesthesia [12,
13]. No signs of megaloblastocis and no changes in
mean corpuscular volume or mean corpuscular haemo-
globin concentrations were found in any of the subjects
studied. All individual values were within normal ranges
and no signs of chang e in any erythrocyte variable could
be found when each subject acted as its own control and
values following a longer period of work were compared
with values after at least 10 days of vacation.
Personnel health is an important topic and all efforts
should be taken to secure good work environment. It is
hard to help personnel to check their workplace compli-
ance to set guidelines as the recommended trace concen-
trations limits are extremely low. Furth ermore, the abso-
lute safe exposure limits is not known. Blood status and
homocysteine analyses are easy to perform and have
well verified normal ranges. The literature on screening
of health aspects in personnel working in risk environ-
ments is sparse. Salo et al studied peripheral blood in
operating room personnel and found similar to us no
signs of B12-nitrous oxide in teraction [14].
This is an entirely explorative pilot study. No inter-
ventions were made, we studied every day clinical prac-
tice and had blood samples from personnel without con-
trol of concomitant diseases, nutritional status etc. We
had the intention to see if any signs or signals of adverse
effects of work place nitrous oxide exposure could be
detected from routine blood tests having the midwifes as
their own control, before and after at least a week with-
out any nitrous oxide exposure.
In conclusion, high ambient nitrous oxide concentra-
tions above set national occupational exposure limits
were seen in about 1/3 of measures and further efforts in
order to reduce personnel exposure has been initiated.
We could see no signs of hyperhomocysteine or blood
status pathological influences of nitrous oxide. Further
studies are warranted to determine whether routine blood
test could be of value to discriminate potential health
effects.
Conflicts of interest statement: Jan Jakobsson is con-
sultant doing safety review for Linde Healthcare,
Gudrun Abascall is Chief-midwife for the unit, and no
other of the authors has any actual or potential personal
or financial conflicts of interest.
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