The Specialist Forum Volume 13 No 11 November 2013 | Page 28

ADVERTORIAL

Effectiveness of N2O for
postpartum perineal repair

D

espite the fact that the episiotomy rate has declined in developed
countries over the past few years, the overall rates of genital
tract trauma after vaginal delivery are still high. Studies have also
shown an increase in childbirth-related trauma.
According to the authors of a new study, only a few trials have investigated the anaesthesiological management of maternal postpartum
trauma to the genital tract. The majority of studies to date have focused
on using material and methods of perineal repair.
The objective of the new study was to compare the effectiveness of
self-administered 50% nitrous oxide (N2O) and conventional infiltrative anaesthesia with 1% prilocaine hydrochloride in postpartum perineal repair.

Study design
Between November 2012 and February 2013, 100 women with childbirthrelated injuries, independent of the duration of pregnancy, were included
in this prospective study done by the Department of Obstetrics based at
the University Medical Centre Mannheim (Germany).
Exclusion criteria were epidural anaesthesia, maternal age below 18
years, multiple pregnancy, fourth degree perineal tear, insufficient knowledge of the German language preventing adequate consent, and previous adverse reaction to local anaesthetics or N2O.
The 100 participants were randomised to use self-administered (n=48)
50% N2O for pain management (study group), and a control group who
were given a local infiltrative anaesthesia with up to 20ml prilocaine hydrochloride (n=52).
Women in the study group started inhaling N2O five to ten minutes
before perineal suturing was started. If necessary, patients in both groups
received additional anaesthesia with prilocaine hydrochloride 1% on
request.
For women in the study group, additional infiltrative anaesthesia was
applied in the event of insufficient analgesia or non-toleration of the mask.
In the control group, additional infiltrative anaesthesia was given in the
event of insufficient analgesia.
Vaginal, vulval and perineal lacerations were categorised according
to Williams Obstetrics and suturing was accomplished with subcuticular
continuous stitches using an absorbable 3–0 vicryl suture.

Data
The researchers documented information about the anaesthesia used as
well as the characteristics of the patients and labour. Maternal parameters
included age, type of delivery and birth injury, body mass index (BMI),
duration of suturing, gravity and parity.
Information noted about the neonates included head circumference,
birth weight and gestational age. In the study group the womens’ tolerance of the inhalation mask, side effects of N2O and necessity for additional local anaesthesia were analysed. In the control group the need for
more than 20ml prilocaine hydrochlo-ride was also documented.
Additionally, time of surgery was recorded, and immediately after surgery patients filled in a standardised pain questionnaire concerning the
pain experienced during perineal suturing. Comparisons between study
and control groups were made using univariate tests. A p-value below
0.05 was considered statistically significant.

Results
Only the parametric results were reported. Both groups showed no

statistically significant differences concerning maternal age (p-value =
0.5072), BMI (p-value = 0.3032), duration of pregnancy (p-value = 0.8903),
suturing time (p-value = 0.7091), birth weight (p-value = 0.1981) or neonatal head circumference (p-value = 0.4695).
Vacuum extraction was performed in 10 patients in the study group and
14 in the control group [21% versus 27%; p-value = 0.476]. Thirty-eight
patients in each group had a spontaneous delivery [38/48, 79% versus
73%; p-value = 0.476].
In the study group 23 [48%], and in the control group 26 [50%] women
had had a previous vaginal delivery. In terms of pain scoring, no statistically significant differences were recorded. Thirty-seven patients of the
study group and 47 patients of the control group were satisfied with
anaesthesia during perineal repair and would recommend it to other parturients [77% versus 90%; p-value = 0.0699].
In the study group tolerance of the inhalation mask and N2O side effects were documented. The mask was used and never tolerated in two
participants [4%), initially tolerated and then removed without replacement
in two women [4%), occasionally removed due to anxiousness and then
replaced after calming in one case [2%], occasionally removed and then
replaced without occurrence of fear or necessity of calming in 14 women
[29%], and in 29 participants [60%] there was neither necessity for mask
removal nor other difficulties.
N2Oside effects included nausea (4%), vertigo in (35%), euphoria (31%)
and dizziness (40%). Almost half the women experienced no side effects.

Conclusion
Investigations concerning perineal suturing throughout the past decades
concentrated mainly on material and methods of surgical repair, which
unequivocally are of high importance. Sufficient analgesia also constitutes
a significant factor in order to achieve optimal surgical results and to minimise postpartum discomfort.
The most common anaesthesiological method for perineal repair after
childbirth is infiltrative anaesthesia. The reasons for this are small costs,
good availability, easy handling and the fact that it is a safe method for
achieving sufficient analgesia. Nevertheless there are also major disadvantages to this approach, such as pain provoked by skin infiltration
and injection of the anaesthetic, the risk of intravascular application and
impairment of surgical procedures due to iatrogenic oedema.
These major drawbacks of infiltrative anaesthesia are avoided using
N2O, possibly generating other side effects which are described to be
uncommon, such as nausea, headache, drowsiness and dizziness.
Although there is a theoretical risk of diffusion hypoxia, various investigations failed to demonstrate this severe event after use of 50% N2O.
According to the researchers, no severe N2O side effects occurred and
compared to conventional medication or placebo, patients treated with
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