Table 6Effectiveness of inhalational anesthetic gases

Author
Year
Study Type
N
InterventionsOther Labor Pain Management Method(s)Findings
Yeo et al.,38
2007
Crossover RCT
N = 32
Entonox (nitrous oxide 50%)None
  • Women used both gases.
  • Visual analogue scales with 100 mm rulers were used to assess pain relief, pain intensity, and sedation.
  • Pain relief significantly better with sevoflurane than Entonox in the first (p = 0.01) and second (p < 0.001) crossovers.
  • Pain intensity significantly higher with Entonox than sevoflurane in the first crossover (p = 0.04) but not different in the second crossover.
  • Sedation significantly greater with sevoflurane than Entonox in both crossovers (p < 0.001). 97% of participants preferred sevoflurane over nitrous oxide (p < 0.001).
Sevoflurane 0.8%
Abboud et al.,40
1995
RCT
N = 80
Nitrous oxide 30% to 60%, usually 46%Not reported
  • Satisfactory analgesia scores were comparable among women, anesthesiologists, and obstetricians.
Desflurane 1% to 4.5%, usually 2%
Abboud et al.,45
1989
RCT
N = 60
Nitrous oxide 30%-60%, usually 33%Local infiltration, pudendal block, epidural
  • Proportion of satisfactory pain scores did not differ significantly between groups among mothers (87% for nitrous oxide, 83% for isoflurane), anesthesiologists (97% for nitrous oxide, 90% for isoflurane), and obstetricians (83% for nitrous oxide, 87% for isoflurane).
Isoflurane 0.2%-0.7%, usually 0.4%
McLeod et al.,47
1985
Crossover RCT
N = 32
Entonox (nitrous oxide 50%)None
  • Pain was assessed with a linear analogue scale (0-100). Mean pain scores were 63.0 (range 24-92) with Entonox and 46.6 (range 19-86) with isoflurane (p < 0.001).
  • Drowsiness scores were higher with isoflurane than nitrous oxide.
  • When women asked which agent they preferred at the end of the study, 69% chose isoflurane, 25% chose Entonox, and 6% were undecided.
Isoflurane 0.75%
McGuinness et al.,48
1984
Crossover RCT
N = 20
Nitrous oxide 50%Pethidine
  • Women used both gases.
  • Pain assessed with linear analogue scores (0-100). Scores with enflurane (median 50, range 13-79) were significantly lower than the scores with nitrous oxide use (median 52, range 29-79, p < 0.02).
  • Drowsiness scores for enflurane were significantly higher that the scores for nitrous oxide (p < 0.02).
Enflurane 1%
Abboud et al.,49
1981
RCT
N = 105
Nitrous oxide 30% to 60%, usually 40%Narcotic analgesia, local infiltration, pudendal block
  • Most women had satisfactory analgesia according to scores from the women, anesthesiologists, and obstetricians.
  • The difference in satisfactory analgesia scores for the two gases was significant only for the obstetricians (p < 0.05).
Enflurane 0.25% to 1.25%, usually 0.5%
Bergsjo et al.,51
1971
Crossover RCT
N = 63
Nitrous oxide 50%None
  • After using both, a higher proportion of mothers chose nitrous oxide (63%) than methoxyflurane (35%) with 2% undecided (p < 0.05).
  • Analgesic effect of nitrous oxide (rated by physician): excellent for 8%, good for 82%, moderate for 4%, and poor for none.
  • Analgesic effect of methoxyflurane (rated by physician): good for 95% and moderate for 5%.
Methoxyflurane 0.8%
Jones et al.,54
1969
RCT
N = 48
Nitrous oxide calibrated in 5% steps from 20% to 100% oxygenPethidine
  • Mean proportion of time the anesthetists assessed the women's reactions to contractions as satisfactory did not differ significantly between groups.
  • Most midwives and women reported pain relief was complete or considerable.
Methoxyflurane with 40% oxygen
Jones et al.,53
1969
RCT
N = 50
Nitrous oxide 50%Pethidine
  • Mean proportion of time the anesthetists assessed the women's reactions to contractions as satisfactory was significantly (p < 0.05) higher for methoxyflurane (79.3 ± 20%) than nitrous oxide (62.3 ± 30%).
  • Most midwives and women reported pain relief was complete or considerable.
Methoxyflurane 0.35%
Rosen et al.,66
1969
Prospective cohort
N = 1257
Nitrous oxide 50%Pethidine, morphine
  • No significant difference between groups in the women's assessment of their pain relief in interviews immediately after the birth and two days later.
  • Midwives rated pain relief good or excellent more frequently with methoxyflurane (53%, p < 0.01) and trichloroethylene (49%, p < 0.02) than nitrous oxide (42%).
Trichloroethylene 0.35% or 0.5%
Methoxyflurane 0.35%
Smith et al.,68
1968
Prospective cohort
N = 1616
Nitrous oxide 25% to 40%Local or pudendal nerve block
  • Participants and physician pain ratings did not differ significantly across groups.
Methoxyflurane 0.2% to 0.5%
Cyclopropane 1% to 5%

From: Results

Cover of Nitrous Oxide for the Management of Labor Pain
Nitrous Oxide for the Management of Labor Pain [Internet].
Comparative Effectiveness Reviews, No. 67.
Likis FE, Andrews JC, Collins MR, et al.

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