Key words
perinatal - nitrous oxide - inhaled analgesia - pain management - satisfaction - labour
Schlüsselwörter
perinatal - Lachgas - inhalative Analgetika - Schmerzmanagement - Zufriedenheit -
Wehen - Geburt
Introduction
The pain suffered during birth has a significant impact on the experience and perception
of the birth, making pain management an important aspect for women in labour [1], [2], [3].
A number of different medicinal and non-medicinal methods are available for pain management.
According to the perinatal statistics of the Bavarian Study Group for Quality Assurance
in In-patient Care (BAQ), epidural analgesia (EPA) is the most common analgesia in
labour and it is used in around 44 % of births [4], [5]. However, for various reasons (e.g. clotting disorders) it is sometimes not possible
to use EPA, making it difficult to provide adequate pain relief. Moreover, a number
of pregnant women refuse EPA, even though it
is an established method with sufficient evidence-based studies showing that it is
safe [5].
In this situation, obstetricians and midwives in Germany can use LIVOPAN® (Linde AG,
München), an inhaled analgesia [6]. This air-gas mixture consists of 50 % oxygen and 50 % N2O (nitrous oxide); it has a slightly sleep-inducing and a moderately powerful analgesic
effect [7]. From a medical point of view, the chief advantages of this form of pain management
are its rapid onset and its fast elimination and clearance within minutes. The effectiveness
and safety of inhaled analgesia for the management of pain during
labour are well documented [8]. In addition to its good analgesic effect, nitrous oxide and oxygen offers additional
advantages during labour: it has no effect on muscle tone and allows the patient to
control the intensity of pain reduction. It is easy to use and can be administered
by trained, non-medical staff [7]; side effects include dizziness, nausea, vomiting and sleepiness [5], [7], [8], [9].
The use of nitrous oxide is an established method for pain management, although up
to now it has not been generally used in Germany. In Scandinavia, the UK and Australia
there is a long tradition of using nitrous oxide mixtures – and in some countries
it is even the most common form of pain relief during labour [10]. The satisfaction of patients and their midwives with this form of pain management
has been sufficiently documented in international studies [11], [12], [13], [14]; however, data on the experience and satisfaction of patients and midwives with
this type of analgesia in Germany are limited or non-existent.
The aim of this study was therefore to investigate the acceptance of inhaled nitrous
oxide and oxygen by women in labour and their midwives.
Material and Methods
After the inhaled nitrous oxide and oxygen was introduced in the Gynaecological Department
of the University Hospital Erlangen, all pregnant women expecting singleton term pregnancies
between April and September 2013 who used inhaled nitrous oxide and oxygen during
labour were included in the study. Women who were ineligible for EPA due to an underlying
condition or who refused EPA despite extensive information about the evidence-based
efficacy of EPA were offered the option of receiving inhaled nitrous oxide and oxygen.
Women were excluded from the study if a breech
presentation was present. Additional exclusion criteria were primary caesarean section,
intrauterine foetal death, structural or chromosomal anomalies and contraindications
for nitrous oxide administration.
Gestational age was determined based on the date of the last menstruation and corrected,
where necessary, using crown-rump length measurements.
The study was approved by the Ethics Commission of Friedrich-Alexander University
of Erlangen-Nuremberg.
The study did not require any changes to normal clinical routine. If inhaled nitrous
oxide and oxygen was administered by the midwife, the midwife completed a questionnaire
after the birth ([Fig. 1]). Only fully trained midwives recorded the indications for inhaled analgesia, the
stages of labour in which the inhaled analgesia was administered, and their own satisfaction
with this method of analgesia. The satisfaction of patients was documented based on
the patientʼs subjective statements on tolerance, side effects and whether she would
chose this
method of analgesia again. The pain intensity before and after receiving inhaled nitrous
oxide and oxygen was assessed using a numerical rating scale (NRS, 1 = lowest pain,
10 = worst pain).
Fig. 1 Questionnaire.
The primary outcome measure was the likelihood that the patient would use inhaled
analgesia again. Additional outcome measures were satisfaction of the midwife with
its use, pain reduction after receiving nitrous oxide and oxygen, and its tolerance
by patients.
The following parameters were investigated to assess their potential effects on the
birth and neonatal outcome: mode of birth, umbilical cord arterial blood pH, umbilical
cord arterial blood base excess (BE), Apgar score, pathological CTG, foetal blood
analysis, meconium-stained amniotic fluid, and transfer to the neonatal intensive
care unit.
Statistical analysis
All statistical calculations were done using the statistical programme SAS, Release
9.3 (SAS Institute Inc., Cary, NC, USA). The median value, standard deviation and
minimum and maximum sample values were calculated for quantitative analysis. Ordinal
scaled variables (e.g. pain intensity) are described using median values and range.
Absolute and relative frequencies are given for nominal scaled variables. Medians
of normally distributed variables were compared using t-test for two independent samples.
Ordinal scaled variables were compared using the Cochran-Armitage trend
test. Analysis of nominal scaled variables was done using χ2-test or, if the criteria for this were not met, using Fisherʼs exact test. The values
for pain intensity before and after administration of nitrous oxide were evaluated
using Wilcoxon test for two related samples. Multiple logistic regression analysis
was done for the primary dependent variables to analyse several potential influencing
variables at the same time. Results were considered significant if p < 0.05.
Results
A total of 66 pregnant women were included in the study. The demographic data and
birth parameters are given in [Table 1].
Table 1 Demographic data for the study cohort and their birth parameters.
|
|
Study cohort (range) (n = 66)
|
|
Age
|
30.6 ± 4.9 (22–43)
|
|
Body Mass Index
|
23.7 ± 4.8 (18.0–39.6)
|
|
Pregnancy
|
median: 2.0 (1–6)
|
|
Parity (excluding the birth in this study)
|
median: 0 (0–3)
|
|
Gestational age (in days)
|
279.5 ± 9.5 (238–291)
|
|
Birth weight
|
3 473.2 ± 523.7 (2 980–4 950)
|
|
Type of birth, n (%)
|
|
|
Spontaneous delivery
|
53 (80 %)
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|
Surgical vaginal delivery
|
7 (11 %)
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Caesarean section
|
6 (9 %)
|
|
pH, arterial cord blood
|
7.27 ± 0.08 (7.12–7.51)
|
|
pH < 7.10 (n, %)
|
0
|
|
BE, arterial cord blood
|
− 5.13 ± 2.95 (− 12.9 – + 0.1)
|
|
BE < − 12 (n, %)
|
1 (2 %)
|
|
5-minute Apgar score
|
median: 10 (7–10)
|
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5-minute Apgar score < 7 (n, %)
|
0
|
|
Pathological CTG (n, %)
|
14 (21 %)
|
|
Foetal blood analysis (n, %)
|
3 (5 %)
|
|
Meconium-stained amniotic fluid (n, %)
|
4 (6 %)
|
|
Transfer to a neonatal intensive care unit (n, %)
|
9 (14 %)
|
Why and when was inhaled analgesia used?
Inhaled nitrous oxide and oxygen was usually administered because the patient refused
an EPA (n = 39, 59 %). In 15 cases (23 %), it was not possible to place the epidural,
and in 5 cases (8 %) the existing epidural analgesia was insufficient. There were
various other reasons for the remaining 7 women (11 %) or reasons were not specified.
Inhaled analgesia most commonly used during the dilation stage (n = 51, 77 %), followed
by the expulsion stage (n = 34, 52 %) and the bearing-down stage (n = 33, 33 %). Some
of the women only used inhaled nitrous oxide and oxygen during the 1st stage (n = 39,
59 %), while others used it in the 2nd stage (n = 13, 20 %) or in all 3 stages (n = 14,
21 %); none of the stages were skipped.
Pain reduction with inhaled nitrous oxide and oxygen
The pain intensity prior to receiving inhaled analgesia was reported as between 5–10
on the NRS (median 9). There was a significant reduction in the intensity of the pain
after administration of the nitrous oxide ([Table 2]).
Table 2 Pain experienced before and after administration of inhaled nitrous oxide and oxygen
(n = 66).
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|
Before
|
After
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p-value
|
|
Pain
|
median: 9 (5–10)
|
median: 5 (1–10)
|
p < 0.0 001
|
Tolerance of inhaled nitrous oxide and oxygen
Overall, inhaled analgesia was well tolerated: 54 (82 %) women reported that they
had tolerated the air-gas mixture “well to very well”; only 12 (18 %) women described
their tolerance as “poor to moderate”.
Reported side effects included dizziness (n = 8), nausea (n = 5), raspy/dry throat
(n = 3), vomiting and “feeling woozy” (2 women, respectively) as well as feelings
of euphoria and powerlessness; one of the women did not provide any details. The majority
of women reported no side effects (n = 43, 65 %).
Likelihood of using inhaled nitrous oxide and oxygen again
Most of the women reported that it was “quite to very” likely that they would use
inhaled analgesia again (n = 45, 68 %).
To analyse the factors which could affect the probability of the patient using inhaled
analgesia again, the group of pregnant women who had assessed their likelihood of
using it again as “absolutely not to moderately likely” was compared to the other
group (“quite to very” likely) ([Table 3]). The probability that they would use nitrous oxide and oxygen again was higher
if the patient had tolerated the drug well (p = 0.0129). Women who used inhaled analgesia
in the expulsion stage or the bearing-down stage were also very likely to use the
drug
again (p = 0.0003 and p = 0.0008, respectively). The incidence of side effects was
approximately the same in both groups (p = 0.7053). The midwivesʼ satisfaction depended
on how inhaled analgesia was accepted by the women; 96 % of midwives were satisfied
with its administration if their patients considered it “quite to very” likely that
they would use inhaled nitrous oxide and oxygen again. Women who were likely to use
the drug again were older on average (31.6 ± 5.0 years vs. 28.7 ± 4.3 years; p = 0.0253).
Table 3 Results of the survey depending on whether the patients would be prepared to use
inhaled nitrous oxide and oxygen again. The percentages refer to the size of the respective
groups, n = 21 and n = 45.
|
|
“absolutely not to moderately likely” to use inhaled analgesia again
n = 21 (32 %)
|
“quite likely to very likely” to use inhaled analgesia again
n = 45 (68 %)
|
p-value
|
|
The possible answers “poorly”, “ a little”, “moderately”, “well” and “very well” were
summarised as “poorly to moderately” and “well to very well”.
|
|
Inhaled nitrous oxide and oxygen was tolerated by the patient (n, %)
|
13 (62 %)
|
41 (91 %)
|
p = 0.0129
|
|
Midwife was “quite to very” satisfied with use of inhaled analgesia (n, %)
|
3 (14 %)
|
43 (96 %)
|
p < 0.0001
|
|
No side effects (n, %)
|
8 (38 %)
|
15 (33 %)
|
p = 0.7053
|
|
When was used inhaled nitrous oxide and oxygen
|
|
|
|
|
|
19 (90 %)
|
32 (71 %)
|
p = 0.1166
|
|
|
4 (19 %)
|
30 (67 %)
|
p = 0.0003
|
|
|
1 (5 %)
|
21 (47 %)
|
p = 0.0008
|
|
Why was used inhaled nitrous oxide and oxygen
|
|
|
|
|
|
3 (14 %)
|
12 (27 %)
|
p = 0.6475
|
|
|
13 (62 %)
|
26 (58 %)
|
|
|
|
2 (10 %)
|
3 (7 %)
|
|
|
|
3 (14 %)
|
4 (9 %)
|
|
|
Age (mean ± standard deviation; minimum – maximum)
|
31.6 ± 5.0 (22–43)
|
28.7 ± 4.3 (22–38)
|
p = 0.0253
|
Logistic regression analysis (which took account of patient-specific variables) showed
that the variable “Use of inhaled nitrous oxide and oxygen in the bearing-down stage”
(p = 0.0140), how well the patient tolerated the drug (p = 0.0241) and womenʼs age
(p = 0.0289) were the most important factors which influenced the likelihood that
they would use inhaled analgesia again.
Discussion
The safety of mother and child is the highest priority in obstetrics – and this includes
an optimal birth experience. In addition to other factors, adequate pain management
has a significant impact on the birth experience. Nitrous oxide is used all over the
world in many different settings because it can be controlled extremely well and is
easy to use, also in paediatrics [7]. In many countries nitrous oxide is part of clinical routine in obstetrics; however,
in Germany it has not yet gained widespread acceptance. Inhaled nitrous oxide and
oxygen was
introduced as an analgesia on our labour wards; this observational study shows that
the nitrous oxide mixture was accepted very well both by the midwives and the women
in labour. The drug was tolerated well and its side effects were tolerable. We recorded
no serious complications.
While the satisfaction of patients and their midwives with pain relief during nitrous
oxide and oxygen administration has been proven in international studies [11], [12], [13], [14], there is currently no data available on this for Germany. This is the first German
study which has prospectively investigated the satisfaction of patients and their
midwives with inhaled analgesia. The case numbers in this study are not very high,
and this should prompt obstetricians to
include nitrous oxide in their repertoire as an additional option for analgesia and
to carry out further studies. Nevertheless, we could show that the willingness to
use inhaled nitrous oxide and oxygen again was correlated with how well the patient
tolerated the drug, the satisfaction of the patientʼs midwife and the stages of labour
in which it was administered.
Epidural anaesthesia continues to be the gold standard, but often it is not possible
to use this method [15]; this can sometimes result in a bad birth experience and even the necessity to convert
a vaginal delivery to a caesarean section. In addition, some women are critical of
EPA; in our study a significant number of pregnant women refused spinal analgesia.
Fear of complications is the primary reason why pregnant women refuse EPA [16].
The use of nitrous oxide is an effective alternative option [5], [8]. The pain relief obtained during delivery with nitrous oxide was confirmed in a
Cochrane analysis carried out in 2012 [8]. Our study also showed that the perception of pain was significantly lower after
the administration of inhaled nitrous oxide and oxygen.
Analgesia with nitrous oxide is considered safe [8], [17] and can be safely administered by non-medical staff [17]. The most common side effects are of a neurological (e.g. dizziness) and gastrointestinal
nature (e.g. nausea and vomiting). In accordance with the literature, the most common
side effects found in our study cohort were dizziness, nausea and vomiting [5], [7], [8], [9], [17]. But these acute side effects are reversible. The potential sequelae are controversially
discussed, but high-dose administration of inhaled nitrous oxide and oxygen for less
than six hours is harmless [18], [19].
There were no suspicious outcome parameters in our study (rate of secondary caesarean
sections 9 %; no arterial cord blood pH < 7.10; no 5-minute Apgar score < 7). This
is in accordance with the results of the most recent literature, where nitrous oxide
was not found to affect the course of the birth [8].
Valid information on the satisfaction with nitrous oxide are limited. In particular,
the impact on the experience of the birth has not been investigated much [8]. Our study showed that patients tolerated inhaled nitrous oxide and oxygen well
and would be prepared to use it again in a subsequent pregnancy. The midwives were
also satisfied with the effect of the nitrous oxide.
Use of a nitrous oxide mixture represents an additional asset for pain management.
Inhaled nitrous oxide and oxygen was very effective, particularly in the expulsion
and bearing-down stages. Nitrous oxide can therefore be considered as an additional
option to supplement existing methods such as EPA. In addition to using nitrous oxide
for analgesia during labour, it can also be used successfully when treating birth-related
injuries [17], [19], [20] – and in this context it offers additional scope for
treatment in clinical practice.
Conclusion
Inhaled nitrous oxide and oxygen is an effective method for pain relief during delivery;
it is accepted very well by both women in labour and their midwives. This method is
easy to use and is considered safe. Nitrous oxide is an important addition to other
well-known methods for pain management in obstetrics and can also be used postpartum
during the treatment of birth-related injuries.
