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Air versus saline in the loss of resistance technique for identification of the epidural space

  1. Pedro L Antibas1,
  2. Paulo do Nascimento Junior2,
  3. Leandro G Braz2,
  4. João Vitor Pereira Doles3,
  5. Norma SP Módolo2,
  6. Regina El Dib2,*

Editorial Group: Cochrane Anaesthesia, Critical and Emergency Care Group

Published Online: 18 JUL 2014

Assessed as up-to-date: 7 SEP 2013

DOI: 10.1002/14651858.CD008938.pub2


How to Cite

Antibas PL, do Nascimento Junior P, Braz LG, Vitor Pereira Doles J, Módolo NSP, El Dib R. Air versus saline in the loss of resistance technique for identification of the epidural space. Cochrane Database of Systematic Reviews 2014, Issue 7. Art. No.: CD008938. DOI: 10.1002/14651858.CD008938.pub2.

Author Information

  1. 1

    Hospital Sírio Libanês, Department of Anaesthesiology, São Paulo, São Paulo, Brazil

  2. 2

    Botucatu Medical School, Universidade Estadual Paulista (UNESP), Department of Anaesthesiology, Botucatu, São Paulo, Brazil

  3. 3

    Botucatu Medical School, UNESP–Universidade Estadual Paulista, Botucatu, São Paulo, Brazil

*Regina El Dib, Department of Anaesthesiology, Botucatu Medical School, Universidade Estadual Paulista (UNESP), Distrito de Rubião Júnior, s/n, Botucatu, São Paulo, 18603-970, Brazil. eldib@fmb.unesp.br. re.lucci@terra.com.br.

Publication History

  1. Publication Status: New
  2. Published Online: 18 JUL 2014

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Characteristics of included studies [ordered by study ID]
Beilin 2000

MethodsDesign: RCT

Multi-centre or single-centre: not reported

Period of recruitment: not reported

Sample size: justified (71 in each group is sufficient to provide 80% power to detect a difference between the 2 groups if 1 of the groups has a 10% incidence of inadequate analgesia and the other group has a 30% incidence. This is based on a 2-tailed test at the 5% level of significance)

Follow-up: 15 minutes after the last dose of local anaesthetic had been administered with reassessment considered


ParticipantsN = 160

Sex (male/female): 0/160

Age (mean), years: air group, 33; saline group, 32

Setting: not reported

Inclusion criteria: patients in active labour with contractions at least once every 5 minutes, who requested epidural analgesia

Exclusion criteria: spinal column disorders, including scoliosis and herniated discs, and previous spine surgery


InterventionsAir 2 mL (n = 80) versus 2 mL of 0.9% saline (n = 80)


OutcomesIncidence of paraesthesia; failed epidural; and analgesia requiring additional medication, as well as pain scores and catheter replacement


NotesWe contacted the first study author on 16 October 2013 to clarify whether researchers had evaluated any other outcomes predefined in our protocol and not described in their paper


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Low riskComputer-generated restricted random number programme

Allocation concealment (selection bias)Low riskSealed in opaque envelopes and opened sequentially by the anaesthesiologist after the participant requested labour analgesia

Blinding of participants and personnel (performance bias)
All outcomes
Unclear riskParticipants: not reported. Personnel: not applicable

Blinding of outcome assessment (detection bias)
All outcomes
Unclear riskNot reported

Incomplete outcome data (attrition bias)
All outcomes
Low riskNo withdrawals and no dropouts were reported. However, the study authors did not consider an intention-to-treat analysis because participants for whom the catheter could not be threaded into the epidural space, or for whom the catheter was threaded into the intravascular space, were excluded from the analysis of adequate analgesia

Selective reporting (reporting bias)Low riskNot detectable

Other biasLow riskNot detectable

Grondin 2009

MethodsDesign: RCT

Multi-centre

Period of recruitment: not reported

Sample size: justified (160 per group was needed to demonstrate the stated difference (90% vs 98%) between groups in the primary outcome variable to achieve a power of 0.8 and an alpha of 0.05. An estimated total of 360 participants was planned for enrolment, with the goal to obtain at least 320 participants)

Follow-up: 4 hours of analgesia initiation


ParticipantsN = 360 randomly assigned but only 345 analysed

Sex (male/female): 0/360

Age (mean),years: air group, 28; saline group, 27

Setting: not reported

Inclusion criteria: patients in active labour and requesting neuraxial labour analgesia; those with cervical dilation of no more than 8 cm, verbal rating score for pain of at least 6 of 10 maximum, vertex singleton pregnancy and no medical/obstetrical contraindications for CSE placement

Exclusion criteria: American Society of Anesthesiologists physical status greater than 2, or weight greater than 114 kg


InterventionsAir (n = 173) versus saline (n = 172)


OutcomesSuccess of spinal labour analgesia as defined by verbal pain score of no more than 3 at 15 minutes after spinal dose administration; spontaneous fluid return and fluid return upon preinjection and postinjection aspiration; epidural catheter replacement rate; and average hourly total quantities of epidural medications required within 4 hours of initial epidural catheter insertion


Notes
  • Anaesthesia residents with more than 2 months of successful obstetrical anaesthesia training experiences, obstetrical anaesthesia fellows and attending obstetrical anaesthesiologists, all of whom are comfortable with the CSE procedure using air or saline LORT, participated in placing the blocks. All trainees were supervised by an attending obstetrical anaesthesiologist
  • We contacted the first study author on 16 October 2013 to clarify whether investigators had evaluated any other outcomes predefined in our protocol and not described in their paper


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Low riskComputer-generated randomization

Allocation concealment (selection bias)Low riskWithout knowledge of previous or future participant group assignment

Blinding of participants and personnel (performance bias)
All outcomes
Low riskParticipants: blinded. Personnel: not applicable

Blinding of outcome assessment (detection bias)
All outcomes
Low riskData collector and interpreters were blinded to group assignment

Incomplete outcome data (attrition bias)
All outcomes
Low risk15 excluded patients (less than 20%)

Selective reporting (reporting bias)Low riskNot detectable

Other biasLow riskNot detectable

Norman 2006

MethodsDesign: RCT

Single-centre

Period of recruitment: not reported

Sample size: justified but inadequate (power for analysis with VAS scores was calculated at 0.85 for this study)

Follow-up: 30 minutes after epidural placement. For epidural-related adverse events, follow-up involved removal of the epidural catheters and care provided several hours post partum and on the following day


ParticipantsN = 50

Sex (male/female): 0/50

Age (mean), years: air group, 24.9; saline group, 24.2

Setting: US military medical centre in the mid-Atlantic region

Inclusion criteria: parturient individuals admitted for active labour, of any age, planning to have a vaginal birth and wanting epidural analgesia

Exclusion criteria: conditions that contraindicate epidural analgesia or make it a poor choice for pain relief; coagulopathies associated with severe pre-eclampsia; previous lumbar spine surgery; severe scoliosis; receipt of magnesium sulfate; or any condition likely to require rapid preparation for a cesarean section


InterventionsAir 3 mL (n = 25) versus 3 mL of saline (n = 25)


OutcomesPain relief by VAS; dermatome (vertebral level of anaesthesia); adverse events; and patchy blocks


NotesWe contacted the first study author on 16 October 2013 to clarify whether researchers had evaluated any other outcomes predefined in our protocol and not described in their paper


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Low riskComputerized table of random numbers

Allocation concealment (selection bias)Unclear riskNot reported

Blinding of participants and personnel (performance bias)
All outcomes
High riskParticipants: not blinded (information was not shared with participants unless they requested the information). Personnel: not applicable

Blinding of outcome assessment (detection bias)
All outcomes
Unclear riskNot reported.

Incomplete outcome data (attrition bias)
All outcomes
Low riskOnly one participant was unable to complete the study and was not included in the analysis

Selective reporting (reporting bias)Low riskNot detectable

Other biasLow riskNot detectable

Sarna 1990

MethodsDesign: RCT

Multi-centre or single-centre: not reported

Period of recruitment: not reported

Sample size: not reported

Follow-up: 24 hours after delivery


ParticipantsN = 67

Sex (male/female): 0/67

Age (mean), years: air group, 25.2; saline group, 23.4

Setting: not reported

Inclusion criteria: women who required insertion of a lumbar epidural catheter for relief of pain in labour, caesarean section or other obstetrical procedure

Exclusion criteria: not reported


InterventionsAir 10 mL (n = 32) versus 10 mL saline (n = 35)


OutcomesParaesthesia; complications such as vascular puncture; difficulty in passing the epidural catheter; quality of pain relief; occurrence of unblocked segment


NotesWe contacted the first study author on 16 October 2013 to clarify whether investigators had evaluated any other outcomes predefined in our protocol and not described in their paper


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Unclear riskNot reported

Allocation concealment (selection bias)Unclear riskNot reported

Blinding of participants and personnel (performance bias)
All outcomes
Low riskParticipants: blinded. Personnel: not applicable

Blinding of outcome assessment (detection bias)
All outcomes
Low riskThe midwife, who was blind to the technique, ensured that the anaesthetist did not influence the participant's assessment

Incomplete outcome data (attrition bias)
All outcomes
Unclear riskNot reported

Selective reporting (reporting bias)Low riskNot detectable

Other biasLow riskNot detectable

Valentine 1991

MethodsDesign: RCT

Multi-centre or single-centre: not reported

Period of recruitment: not reported

Sample size: not reported

Follow-up: 30-minute duration of the study


ParticipantsN = 50

Sex (male/female): 0/50

Age (mean), years: air group, 25.3; saline group, 24.7

Setting: not reported

Inclusion criteria: primiparous individuals in early labour who had requested extradural analgesia

Exclusion criteria: patients who had previously experienced an extradural or spinal procedure, patients in whom urgent delivery was anticipated and those who had a contraindication to extradural analgesia


Interventions4 mL of air (n = 25) versus 4 mL of 0.9% saline (n = 25)


OutcomesUnblocked segments and participant satisfaction with insertion


Notes
  • The blocks were undertaken by a group of 5 anaesthetists, including investigators, all of whom had more than 3 years of experience with the extradural technique
  • We contacted the first study author on 16 October 2013 to clarify whether researchers had evaluated any other outcomes predefined in our protocol and not described in their paper


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Unclear riskNot reported

Allocation concealment (selection bias)Unclear riskNot reported

Blinding of participants and personnel (performance bias)
All outcomes
Unclear riskParticipants: not reported. Personnel: not applicable

Blinding of outcome assessment (detection bias)
All outcomes
Low riskAn investigator who had no knowledge of the medium used to identify the extradural space assessed onset of sensory loss and dermatomal spread, using sterile 21-gauge needles to test pinprick at 5-minute intervals up to 30 minutes

Incomplete outcome data (attrition bias)
All outcomes
Low riskNo withdrawals

Selective reporting (reporting bias)Low riskNot detectable

Other biasLow riskNot detectable

van den Berg 2010

MethodsDesign: RCT

Multi-centre or single-centre: not reported

Period of recruitment: not reported

Sample size: justified (25 participants per group using the formula for a 2-sided comparison, with confidence limits of 95% and 80% power, on the basis that a 40% difference in incidence of any subjective or objective response would be a significant outcome)

Follow-up: not reported


ParticipantsN = 55

Sex (male/female): 0/55

Age (mean), years: air group, 26.3; saline group, 24.4

Setting: not reported

Inclusion criteria: patients requesting and those submitted for epidural labour analgesia

Exclusion criteria: contraindication to neuraxial block or pertinent drug allergy


InterventionsAir (n = 27) versus saline (n = 28)


OutcomesSubjective and objective responses to dural puncture; grimacing and involuntary movement; occurrence of paraesthesia, dysaesthesia and/or neurological deficit


Notes
  • One participant was excluded because of present combined spinal epidural failure, and another participant was enrolled. However, we considered the excluded participant in the air group for the outcome of combined spinal epidural failure (i.e. n = 28 for air group)
  • We contacted the first study author on 16 October 2013 to clarify whether researchers had evaluated any other outcomes predefined in our protocol and not described in their paper


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Low riskPre-prepared block randomization list (sequential groups of 5 participants)

Allocation concealment (selection bias)Unclear riskNot reported

Blinding of participants and personnel (performance bias)
All outcomes
Unclear riskParticipants: not reported. Personnel: not applicable

Blinding of outcome assessment (detection bias)
All outcomes
Unclear riskNot reported

Incomplete outcome data (attrition bias)
All outcomes
Low riskNo withdrawals and no dropouts were reported

Selective reporting (reporting bias)Low riskNot detectable

Other biasLow riskNot detectable

Vigfússon 1995

MethodsDesign: RCT

Multi-centre or single-centre: not reported

Period of recruitment: not reported

Sample size: not reported

Follow-up: not reported


ParticipantsN = 110

Sex (male/female): not reported

Age (mean), years: not reported

Setting: not reported

Inclusion criteria: not reported

Exclusion criteria: not reported


InterventionsAir (n = 60) versus saline (n = 50)


OutcomesAbility to locate the epidural space: easy, relatively easy, difficult or impossible


Notes
  • Study available only in abstract
  • We contacted the first study author on 16 October 2013 to clarify whether researchers had evaluated any other outcomes predefined in our protocol and not described in their paper, as well as to ask for a possible full-text article. The study author replied on 16 November 2013 with information related to outcomes data


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Unclear riskNot reported

Allocation concealment (selection bias)Unclear riskNot reported

Blinding of participants and personnel (performance bias)
All outcomes
Unclear riskParticipants: not reported. Personnel: not applicable

Blinding of outcome assessment (detection bias)
All outcomes
Unclear riskNot reported

Incomplete outcome data (attrition bias)
All outcomes
Unclear riskNot reported

Selective reporting (reporting bias)Low riskNot detectable

Other biasLow riskNot detectable

 
Characteristics of excluded studies [ordered by study ID]

StudyReason for exclusion

Evron 2004Randomized controlled trial (RCT), however evaluated air versus lidocaine

Okutomi 1999Randomized controlled trial (RCT), however evaluated 1, 5 or 10 mL of saline solution

Siddik-Sayyid 2006Randomized controlled trial (RCT), however evaluated 2 versus 10 mL of saline solution

Wantman 2006Systematic survey to assess method preferred (air vs saline) by anaesthesiologists

 
Comparison 1. Air versus saline

Outcome or subgroup titleNo. of studiesNo. of participantsStatistical methodEffect size

 1 Inability to locate the epidural space3619Risk Ratio (M-H, Random, 95% CI)0.88 [0.33, 2.31]

 2 Accidental intravascular catheter placement2223Risk Ratio (M-H, Random, 95% CI)0.90 [0.33, 2.45]

 3 Accidental subarachnoid catheter placement4682Risk Ratio (M-H, Random, 95% CI)2.95 [0.12, 71.90]

 4 Combined spinal epidural failure2400Risk Ratio (M-H, Random, 95% CI)0.98 [0.44, 2.18]

 5 Unblocked segments5423Risk Ratio (M-H, Random, 95% CI)1.66 [0.72, 3.85]

 6 Adverse events4Risk Ratio (M-H, Random, 95% CI)Subtotals only

    6.1 Paraesthesias
3572Risk Ratio (M-H, Random, 95% CI)0.89 [0.69, 1.15]

    6.2 Difficulty in advancing the catheter
2227Risk Ratio (M-H, Random, 95% CI)0.91 [0.32, 2.56]

    6.3 Catheter replacement and/or reposition
2501Risk Ratio (M-H, Random, 95% CI)0.69 [0.26, 1.83]

    6.4 Postdural puncture headache
1110Risk Ratio (M-H, Random, 95% CI)0.83 [0.12, 5.71]

 7 Pain relief2395Mean Difference (IV, Random, 95% CI)-0.09 [-0.37, 0.18]

 
Summary of findings for the main comparison.

Air versus saline in the loss of resistance technique for identification of the epidural space

Patient or population: adults classified as ASA grades 1 to 3 undergoing surgical procedures, pregnant women in obstetrical labour and patients receiving postoperative analgesia

Intervention: air

Comparison: saline

OutcomesAssumed risk

(air)
Corresponding risk

(saline)
Relative effect
(95% CI)
No. of participants
(studies)
Quality of the evidence
(GRADE)

Inability to locate the epidural space

Follow-up: 15 minutes after last dose of local anaesthetic (Beilin 2000); 4 hours of analgesia initiation (Grondin 2009); and not reported (Vigfússon 1995)a
27%26%RR 0.88 (0.33 to 2.31)619 (3)⊕⊕⊝⊝
lowb ,d

Accidental intravascular catheter placement

Follow-up: 15 minutes after last dose of local anaesthetic (Beilin 2000) and 24 hours after delivery (Sarna 1990)a
6%7%RR 0.90 (0.33 to 2.45)223 (2)⊕⊕⊝⊝
lowb ,d

Accidental subarachnoid catheter placement

Follow-up: 15 minutes after last dose of local anaesthetic (Beilin 2000); 4 hours of analgesia initiation (Grondin 2009); and 24 hours after delivery (Sarna 1990)e
0.2%0%RR 2.95 (0.12 to 71,90)682 (4)⊕⊕⊝⊝
lowb ,c,d

Unsuccessful combined spinal epidural

Follow-up: 4 hours of analgesia initiation (Grondin 2009) and not reported (van den Berg 2010)e
5%5%RR 0.98 (0.44 to 2.18)400 (2)⊕⊕⊝⊝
lowb ,d

*The basis for the assumed risk (e.g. median control group risk across studies) is provided in footnotes. The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI).
CI: Confidence interval; RR: Risk ratio.

GRADE Working Group grades of evidence.
High quality: Further research is very unlikely to change our confidence in the estimate of effect.
Moderate quality: Further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate.
Low quality: Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate.
Very low quality: We are very uncertain about the estimate.

 aParturient individuals (with the exception of Vigfússon 1995, which did not report the inclusion criteria; van den Berg 2010, which considered any patients requesting or submitted for epidural labour analgesia and Sarna 1990, which also considered other obstetrical procedures), so the applicability of findings might be compromised.
bAll studies presented an overall low risk of bias; no inconsistency was noted across studies (i.e. I2 = 0%), and a reasonable overlap in confidence intervals was seen, as well as small sample sizes and small numbers of events with small (but not very narrow) confidence intervals.
cThe latter is an exception for the outcome of accidental subarachnoid catheter placement, which presents a wider CI.
dIt was not possible to verify publication bias, as fewer than 10 studies were included in the meta-analysis; however, the search strategy was comprehensive, and no language restriction was applied.
eParturient individuals, so the applicability of findings might be compromised.