Safety and effectiveness of inhaled analgesia for labour pain

Labour pain is one of the most sever pains in the life of women. It is multifactorial and affected by both psychological, many biochemical and physiological factors. Many methods are used to manage labour pain which are divided into pharmacological and non-pharmacological methods. Inhaled analgesia, as part of the pharmacological methods, involves the inhalation of smaller dose of the inhaled anaesthetic agents while maintaining awareness of the mother. Drugs used for inhaled analgesia for relief of labour pain include nitrous oxide, isoflurane, sevoflurane, trichloroethylene, methoxyflurane and cyclopropane. It is important to do this review because all women should have a relatively effective and safe analgesia during labour. Therefore, this review objective was to explore the efficacy and safety of inhaled analgesia as pain relief for women in labour planning a vaginal delivery. We included randomised controlled and cross-over trials. A total of 74 reports of studies were identified from the search strategy. A total of 26 studies reporting data on 2959 women (31 reports) were included and 27 studies (43 reports) were excluded. We studied effect of inhaled analgesia on pain intensity, pain relief and satisfaction with pain relief. For the safety of inhaled analgesia, we studied the effect of inhaled analgesia on assisted vaginal birth, caesarean section, nausea, vomiting, drowsiness, amnesia, Apgar score less than seven at five minutes. This review concluded that inhaled analgesia may be beneficial for labour pain relief, with minimal to no effect on Apgar score of the newborn. There is a need for adequately powered randomised controlled trials which include relevant clinical outcomes. Background Labour pain is one of the most sever pains in the life of women. It is multifactorial and affected by both psychological, many biochemical and physiological factors [1, 2]. Recognition of labour pain varies. Occasionally women feel no pain in labour, while in the other hand, labour pain has been described as the most severe pain that a woman experiences in her lifetime [3, 4]. Therefore, reliving labour pain is one of the main concerns for pregnant women, healthcare attendants and the general public [5]. These methods to relief labour pain have implications on the course of labour, quality of mother and baby outcomes and the cost of obstetric care.During labour pain originates from different sites during each stage of the labour and delivery process. In the first stage of labour (defined as the period from the onset of labour to the complete dilatation of the cervix) [6], pain occurs during contractions. It is cramp-like pain. It is originated in the uterus and cervix by distension of uterine tissues and dilation of the cervix. This pain is transmitted via spinal nerves T10-L1. Because of that, this pain can be referred to the abdominal wall, lumbosacral region, iliac crests, gluteal areas, and thighs. Usually, primiparas experience greater pain than multiparous women, typically during early labour before 5 cm dilatation [1]. The chosen positions by woman during labour may affect her feeling of pain [7, 8],[9]. It was found that women using upright or lateral position report less severe pain than women lying on their back during labour. In the other hand, Women may experience less pain during spontaneous labour than induced labour [10]. Psychosocially, many factors influence women's experience of labour pain including previous delivery experiences, culture, ethnicity and education [1]. Now a day, general public has a negative belief of pain, that it is barbaric and should not be suffered by any one.A wide range of pain management methods are used by women during childbirth [5]. These are either, non-pharmacological methods and pharmacolog ica l methods. Non-pharmacological methods help women cope with pain in labour and includes hypnosis, biofeedback, subcutaneous sterile water injection, immersion in water, aromatherapy, relaxation techniques (yoga, music, audio), acupuncture, manual methods (massage, reflexology), and transcutaneous electrical nerve stimulation (TENS). On the other hand, pharmacological methods relieve the pain of labour and includes inhaled analgesia, opioids, non-opioid drugs, local anaesthetic nerve blocks, epidural and intrathecal injections of local anaesthetics or opioids, or both [11]. From the above, we recognize that pain in labour is multifactorial and with some overlap between factors. Added to that, some pain relief methods are explained and exercised in antenatal classes then it is used before to the onset of labour, for example, hypnosis and use of TENS. On the contrary, other pain relief methods are administered only during labour, for example, inhaled analgesia.Inhaled analgesia during labour defined as the inhalation of sub-anaesthetic concentrations of agents while the WebmedCentral > Systematic Review Page 2 of 5 WMC004971 Downloaded from http://www.webmedcentral.com on 08-Sep-2015, 04:45:12 AM mother remains awake. Historically, inhaled analgesics was used for the first time for relief of labour pain in 1847 by James Simpson [12]. While, Stanislaw Klikovich was the first to use nitrous oxide 80% in oxygen in 1881 on women in labour [13]. However, Minnitt was the first to introduce an apparatus for the self-administration of nitrous oxide In 1934 [14].Drugs used as inhaled analgesia for pain relief in labour are nitrous oxide, isoflurane, sevoflurane, trichloroethylene, methoxyflurane and cyclopropane. Trichloroethylene and cyclopropane are not used anymore in the developed world because the first is flammable, while the second is explosive. On the other spectrum, sevoflurane is not used because it has no analgesic activity at sub-anaesthetic concentrations. This leaves us with, nitrous oxide, enflurane, isoflurane and methoxyflurane. These medications do not decrease uterine contractions and that's why they are preferred. However, nitrous oxide use is widespread in modern obstetric wards because it is easy to administer, lack flammability, lack odour, has no effect on uterine contractions, has minimal toxicity and minimal depression of the cardio-vascular system [15, 16]. Inhaled analgesics are characterized by their low blood/gas solubility ratio, which is due to their rapid uptake/washout rate. Therefore, at 37 Co the blood/gas solubility ratio for nitrous oxide is 0.47; for Isoflurane is 1.4; for Sevoflurane is 0.69; for Enflurane is 1.64 and for Methoxuyflurane is 13.Methoxyflurane is more potent than all the other inhaled analgesic drugs in spite of its low solubility, therefore, it is still used in some obstetrics wards. On the other hand, nitrous oxide maximal effect can be obtained in 30 to 60 seconds and wash-out in three or four exhalations [17]. However, there is argument about the use of nitrous oxide because of few safety concerns for female care givers [18-24]. Nitrous oxide characteristically inactivate methionine synthase in the cells which can affect female care givers fertility [25]. This cel lularlevel damage starts during a maternity-care worker's shift, but it will happen only in a poorly ventilated hospital where nitrous oxide is used without cleaning of the gas. Furthermore, the damage produced stops when the care worker leaves the hospital by the process of restitution, but, as she returns to work in the same environment before restitution is complete, the damage-producing process resumes and over time, the damage may accumulate enough to produce pathology [23]. This pathology may decrease the fertility of female care givers or increase their risk of spontaneous abortion, but this risk can be stamped out in well ventilated modern hospitals [23, 26].Inhaled analgesia, in general if used too long or extensively may cause maternal drowsiness, nausea and vomiting. It is uncertain how inhaled analgesia relief pain, otherwise, the suggestion that these drugs induces the release of endogenous opioids in the midbrain, which, could balance labour pain stimuli through the descending spinal cord nerves [27].It is important to do this review because all women should have a relatively effective and safe analgesia during labour [26]. Added to that, it is important to have other options for pain relief during labour in view of the side effects of the invasive options.