Self-administered isoflurane in labour

Entonox (50% nitrous oxide in oxygen) and isoflurane (0.75% in oxygen) were compared as analgesics in the first stage of labour in 32 consenting women. The drugs were self-administered and given in random sequence, each during five consecutive uterine contractions. Each patient acted as her own control. Linear analogue pain scores were significantly lower (p less than 0.001) with isoflurane than with Entonox, but scores for drowsiness were higher for isoflurane. Further study is needed to assess the effects of more prolonged use of isoflurane in labour.     

Maternal hypoxaemia associated with the use of Entonox in labour

We report the occurrence of severe hypoxaemic episodes associated with the use of Entonox in labour, in an otherwise healthy woman. These did not occur when the parturient breathed room air during contractions and did not recur when epidural analgesia was established. Possible mechanisms of arterial desaturation associated with the use of Entonox in labour are discussed.     

Analgesia with sevoflurane during labour: ii. Sevoflurane compared with Entonox for labour analgesia

Background. We determined the optimal inspired sevoflurane concentrationfor use during labour as 0.8% in our previous study. This studycompared sevoflurane at a concentration of 0.8% and Entonox^®(nitrous oxide 50%: oxygen 50%) for analgesia during labourin 32 healthy parturients. Methods. Each mother underwent two open-label, three-part sequencesin random order, Entonox-sevoflurane-Entonox or sevoflurane-Entonox-sevoflurane.In each part the agent was self-administered during 10 contractions.A 100 mm visual analogue scores for pain relief and sedationwas completed immediately after each contraction. Results. Two patients withdrew during administration of sevoflurane(because of its odour) and five during Entonox (requesting epiduralanalgesia). Of the remaining women, data were available foranalysis from 29 participants: median (IQR [range]) pain reliefscores were significantly higher for sevoflurane 67 (55–74[33–100]) mm than for Entonox 51 (40–69.5 [13–100])mm (P<0.037). Nausea and vomiting were more common in theEntonox group [relative risk 2.7 (95% CI 1.3–5.7); P=0.004].No other adverse effects were observed in the mothers or babies.There was significantly more sedation with sevoflurane thanwith Entonox {74 (66.5–81 [32.5–100]) and 51 (41–69.5[13–100]) mm, respectively; P<0.001}. Twenty-nine patientspreferred sevoflurane to Entonox and found its sedative effectshelpful. Conclusions. We conclude that self-administered sevofluraneat subanaesthetic concentration (0.8%) can provide useful painrelief during the first stage of labour, and to a greater extentthan Entonox. Although greater sedative effects were experiencedwith sevoflurane, it was preferred to Entonox.      

The effects of Entonox and epidural analgesia on arterial oxygen saturation of women in labour

The arterial oxygen saturation of 40 mothers in the first stage of labour was monitored using pulse oximetry. Half the mothers received epidural analgesia and the rest inhaled Entonox for pain relief. Eight mothers in the Entonox group and six in the epidural group had at least one episode of significant hypoxia (saturation < 90%). There was little difference in the number of hypoxic episodes experienced by either group (29 in the Entonox and 21 in the epidural) although their mean duration and severity was greater in the Entonox group. Women in labour who inhale Entonox have an appreciable incidence of arterial desaturation. Epidural analgesia reduces the severity of hypoxic episodes although it does not eliminate them.     

Entonox in the emergency department

The use of Entonox (BOC Medishield) was examined in a large accident and emergency department and was found to give satisfactory relief from pain in 92 per cent of cases. This compares favourably with reports of its results in other applications.     

Self-administered nalbuphine, morphine and pethidine

In a double-blind clinical trial of 48 patients, nalbuphine, morphine, and pethidine were compared by on-demand intravenous analgesia during the first 24 hours after cholecystectomy. Overall pain relief (visual analogue score) was recorded by the patients as 50 (SEM 4) for nalbuphine, 44 (SEM 4) for morphine and 53 (SEM 5) for pethidine. These scores were not significantly different. The mean demand for each drug over the 24-hour period was 70 (SEM 12) mg for nalbuphine, 46 (SEM 6) mg for morphine and 614 (SEM 49) mg for pethidine. Pain on movement, either during deep breathing or turning, was found to be less well controlled after nalbuphine (70, SEM 2), and pethidine (67 SEM 7) than after morphine (52, SEM 5; p less than 0.01). The incidence of side effects was similar with each drug. Nalbuphine is a useful postoperative analgesic, as effective as pethidine. Nalbuphine 15 mg is apparently equipotent with morphine 10 mg or pethidine 120 mg by this mode of administration.     

The use of 0.25% isoflurane premixed in 50% nitrous oxide and oxygen for pain relief in labour

The addition of 0.25% isoflurane to 50% nitrous oxide in oxygen provides more effective pain relief in labour than 50% nitrous oxide alone. This study was carried out to determine whether self-administration by demand valve of 0.25% isoflurane in 50% nitrous oxide in oxygen premixed in cylinders at 13.7 MPa (IN2O) was practical and safe during labour. Two hundred and twenty-one mothers used IN2O in labour after 50% nitrous oxide had become inadequate for pain relief. Data on IN2O use was recorded during labour and details of the course of labour and opioid usage were taken from the clinical notes. The duration of IN2O use was 0.1-12.35 h (median 2.3). Thirty-two mothers (14.5%) required an epidural and intolerance to IN2O was seen in a maximum of 17 cases (7.7%). One hundred and twenty-six cases were primiparous and 93 parous with 151 deliveries being spontaneous and 70 interventional, of which 12 were by Caesarean section. Maternal blood loss was 20-1500 ml (median 200 ml). Apgar scores at 1 and 5 min were unaffected by IN2O use although a positive correlation was found between the use of opioids and the number of neonates with a 1-min score below 8 and the number requiring resuscitation. Six neonates had an Apgar score below 8 at 5 min, but their condition was adequately explained by factors other than the sedative technique used. Self-administered IN2O was found to be a safe and practical technique for sedation in labour when 50% nitrous oxide alone had become inadequate.     

Entonox equipment as a potential source of cross-infection

A survey of the hospitals with obstetric units within the Anglia and Oxford Region was performed to assess current practices regarding the cleaning of, and use of filters with, Entonox apparatus. The survey revealed that there was no consensus regarding the cleaning of the equipment and, in contrast to anaesthetic machines in which microbiological filters are recommended and in widespread use, only 10% of the hospitals surveyed were using such filters with the Entonox apparatus in their units. Cleaning procedures were changed in 75% of hospitals when dealing with known 'high-risk' patients, the remaining hospitals treating all patients as 'high-risk' or denied caring for such patients. All patients should be protected from potential cross-infection, and the recommendation that a microbiological filter should be placed between patients and the breathing system should be extended to Entonox equipment.     

Anti-infective measures and Entonox equipment: a survey

We surveyed 102 maternity suites to investigate whether the guidelines of the Association of Anaesthetists of Great Britain and Ireland, for the use of anti-infective filters or fully disposable anaesthetic breathing systems for each patient, were being followed with regard to Entonox equipment on labour wards. Of 100 units giving information (98%), only seven used filters and only two replaced tubing between cases. Our survey shows that the recommended policy is not being applied to Entonox apparatus in delivery suites.