Combined spinal‐epidural versus spinal anaesthesia for caesarean section
Abstract
This is a protocol for a Cochrane Review (Intervention). The objectives are as follows:
To compare the effectiveness and adverse effects of combined spinal‐epidural anaesthesia to single shot spinal anaesthesia for caesarean section.
Background
Caesarean section is a common form of child birth reported at rates of 20% to 25% in higher‐income countries (Hofmeyr 2008). Regional anaesthesia is often employed during caesarean section. The methods which have been commonly used for the regional anaesthesia are either an epidural block, or a spinal block which is given as a single injection, i.e. a single shot spinal (SSS). The relative benefits and side‐effects of these established techniques has been the subject of a systematic review (Ng 2004). A combination of these two techniques, a combined spinal‐epidural (CSE) has gained popularity and been in clinical use for more than a decade (Shibli 2000). It is therefore appropriate to evaluate the possible benefits and relative adverse effects of CSE for anaesthesia relative to these other techniques. This review will focus specifically on SSS versus CSE for caesarean section anaesthesia.
Spinal anaesthesia for caesarean section involves a single injection which is relatively easily performed and with a rapid onset. However, when a single injection is done there is no capacity to extend the block after initial administration. It may also be associated with adverse effects such as hypotension related to the rapid onset of extensive sympathetic blockade especially when more traditional higher doses of local anaesthetic are used (Cyna 2006). Epidural anaesthesia involves the insertion of a larger needle but with a technique endpoint that is sometimes less obvious than for a SSS and the rate of onset of the block is also considerably slower. However, the epidural technique typically includes insertion of a fine catheter and with this there is the opportunity for further administration of drugs after the initial injection. This feature may avoid the need for a general anaesthetic during longer operations and also may be used for delivery of pain relieving medication after the operation (Rawal 2003).
The combination of spinal anaesthesia with an epidural creates the opportunity to have the potential benefits of having an epidural catheter in place and retain the speed of onset of the spinal. The CSE technique however, involves the insertion of two needles and there has been some debate as to whether the spinal needle should be placed through the epidural needle or inserted at a separate site so as to improve effectiveness or reduce side‐effects (Puolakka 2001). The commonly employed needle‐through‐needle technique may facilitate epidural catheter placement, but this may be significantly influenced by needle design (Browne 2005). There are also at least theoretical concerns of the increasing complexity of CSE versus SSS adding to technical difficulty and the time taken to perform the block, as well as its effectiveness (Kinsella 2008) and side‐effects such as infection (Sandkovsky 2009) or post dural puncture headache (PDPH). As most of these outcomes are of low incidence, results from single randomised controlled trials generally do not have sufficient numbers to be informative and case series or audits are subject to the limitations of these methods. The most common of these problems is PDPH either as a result of an accidental dural puncture with the epidural needle or following the intentional piercing of the dura with a spinal needle. The reported incidence of accidental dural puncture with an epidural needle is approximately 1.5%, with half of these women developing a PDPH (Choi 2003). The incidence of PDPH after a SSS is dependent on the needle gauge and the needle tip design. Commonly used smaller gauge needles with an atraumatic design have a similar incidence of PDPH to that of epidural needles (Choi 2003). The CSE technique also has a similar reported incidence of PDPH to these other alternatives (Van de Velde 2008).
There are several variants of the CSE technique. In its simplest form a spinal is performed and an epidural catheter is merely inserted at the same time as a backup for the spinal anaesthesia or to provide for postoperative pain relief. Another form makes use of an epidural injection, typically of saline, coincident with the spinal anaesthetic to extend the spinal effect through mechanical compression of the dura (Blumgart 1992); this is referred to as epidural volume extension. In yet another variant, small doses of spinal anaesthetic are administered in conjunction with epidural drugs. These alternatives are potentially sufficiently different from each other that it is appropriate they be considered as separate subgroups. These techniques may have particular benefits related to the lower doses of local anaesthetic used including quicker return of motor function, enabling earlier discharge from the postanaesthesia care unit, and less effect on the cardiovascular system (McNaught 2007), leading to a reduced need for interventions secondary to a fall in blood pressure. In the light of these possible benefits, there have been increasing reports of ever diminishing doses of local anaesthetic in SSS as well (Langesaeter 2008). It may be informative therefore to subgroup the SSS studies into the more traditional high dose and also low‐dose techniques.
Objectives
To compare the effectiveness and adverse effects of combined spinal‐epidural anaesthesia to single shot spinal anaesthesia for caesarean section.
Methods
Criteria for considering studies for this review
Types of studies
Types of studies to be considered for review will be all published randomised controlled trials involving a comparison of combined spinal‐epidural (CSE) anaesthesia with single shot spinal anaesthesia for caesarean section; studies reported only as abstracts will also be included.
Types of participants
Women having an elective caesarean section.
Types of interventions
CSE anaesthesia compared with single shot spinal anaesthesia for caesarean section. CSE techniques involving epidural volume extension and low‐dose sequential CSE will be analysed as subgroups of CSE. Single shot spinals will be subgrouped as either low dose or high dose.
Types of outcome measures
The outcome measures to be included will be as follows.
Primary outcomes
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Number of women requiring an additional intervention for anaesthesia at any time after CSE or spinal anaesthetic insertion
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Number of women requiring conversion to general anaesthesia
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Number of women satisfied with their anaesthesia
Secondary outcomes
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Mean time and standard deviation from commencement of the regional anaesthetic to effective anaesthesia for surgery
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Number of women with an intra‐operative complication requiring treatment or intervention specifically identified: pruritus, nausea and/or vomiting, hypotension, respiratory depression/arrest, sedation, high block
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Mean time and standard deviation from admission to discharge from the postanaesthesia recovery unit
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Number of women fully breastfeeding at hospital discharge
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Number of women with a post dural puncture headache
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Number of women requiring follow up for an adverse outcome present at one month or more after the procedure and specifically identified: meningitis, neuropraxia, paralysis, backache, footdrop, unresolved post dural puncture headache
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Mean pH and standard deviation in the neonate for umbilical artery, umbilical vein, umbilical cord
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Number of neonates with Apgar scores less than seven at five minutes
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Number of neonates admitted to the neonatal unit
Search methods for identification of studies
Electronic searches
We will contact the Trials Search Co‐ordinator to search the Cochrane Pregnancy and Childbirth Group’s Trials Register.
The Cochrane Pregnancy and Childbirth Group’s Trials Register is maintained by the Trials Search Co‐ordinator and contains trials identified from:
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quarterly searches of the Cochrane Central Register of Controlled Trials (CENTRAL);
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weekly searches of MEDLINE;
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handsearches of 30 journals and the proceedings of major conferences;
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weekly current awareness alerts for a further 44 journals plus monthly BioMed Central email alerts.
Details of the search strategies for CENTRAL and MEDLINE, the list of handsearched journals and conference proceedings, and the list of journals reviewed via the current awareness service can be found in the ‘Specialized Register’ section within the editorial information about the Cochrane Pregnancy and Childbirth Group.
Trials identified through the searching activities described above are each assigned to a review topic (or topics). The Trials Search Co‐ordinator searches the register for each review using the topic list rather than keywords.
We will not apply any language restrictions.
Data collection and analysis
Selection of studies
Three review authors will independently assess for inclusion all potential studies we identify as a result of the search strategy. We will resolve any disagreement through discussion or, if required, we will consult a fourth person.
Data extraction and management
We will design a form to extract data. At least two review authors will extract the data using the agreed form. We will resolve discrepancies through discussion or, if required, we will consult a third person. Data will be entered into Review Manager software (RevMan 2008) and checked for accuracy.
When information regarding any of the above is unclear, we will attempt to contact authors of the original reports to provide further details.
Assessment of risk of bias in included studies
Two review authors will independently assess risk of bias for each study using the criteria outlined in the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2008). Any disagreement will be resolved by discussion or by involving a third assessor.
(1) Sequence generation (checking for possible selection bias)
We will describe for each included study the method used to generate the allocation sequence in sufficient detail to allow an assessment of whether it should produce comparable groups.We will assess the method as:
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adequate (any truly random process, e.g. random number table; computer random number generator);
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inadequate (any non random process, e.g. odd or even date of birth; hospital or clinic record number); or
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unclear.
(2) Allocation concealment (checking for possible selection bias)
We will describe for each included study the method used to conceal the allocation sequence in sufficient detail and determine whether intervention allocation could have been foreseen in advance of, or during recruitment, or changed after assignment.We will assess the methods as:
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adequate (e.g. telephone or central randomisation; consecutively numbered sealed opaque envelopes);
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inadequate (open random allocation; unsealed or non‐opaque envelopes, alternation; date of birth);
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unclear.
(3) Blinding (checking for possible performance bias)
We will describe for each included study the methods used, if any, to blind study participants and personnel from knowledge of which intervention a participant received. Studies will be judged at low risk of bias if they were blinded, or if we judge that the lack of blinding could not have affected the results. Blinding will be assessed separately for different outcomes or classes of outcomes.We will assess the methods as:
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adequate, inadequate or unclear for participants;
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adequate, inadequate or unclear for personnel;
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adequate, inadequate or unclear for outcome assessors.
(4) Incomplete outcome data (checking for possible attrition bias through withdrawals, dropouts, protocol deviations)
We will describe for each included study, and for each outcome or class of outcomes, the completeness of data including attrition and exclusions from the analysis. We will state whether attrition and exclusions were reported, the numbers included in the analysis at each stage (compared with the total randomised participants), reasons for attrition or exclusion where reported, and whether missing data were balanced across groups or were related to outcomes. Where sufficient information is reported, or can be supplied by the trial authors, we will re‐include missing data in the analyses which we undertake. We will assess methods as:
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adequate;
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inadequate;
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unclear.
Outcomes with 20% or more loss of participants will be excluded.
(5) Selective reporting bias
We will describe for each included study how we investigated the possibility of selective outcome reporting bias and what we found. We will assess the methods as:
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adequate (where it is clear that all of the study’s prespecified outcomes and all expected outcomes of interest to the review have been reported);
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inadequate (where not all the study’s prespecified outcomes have been reported; one or more reported primary outcomes were not prespecified; outcomes of interest are reported incompletely and so cannot be used; study fails to include results of a key outcome that would have been expected to have been reported);
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unclear.
(6) Other sources of bias
We will describe for each included study any important concerns we have about other possible sources of bias. We will assess whether each study was free of other problems that could put it at risk of bias:
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yes;
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no;
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unclear.
(7) Overall risk of bias
We will make explicit judgements about whether studies are at high risk of bias, according to the criteria given in the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2008). With reference to (1) to (6) above, we will assess the likely magnitude and direction of the bias and whether we consider it is likely to impact on the findings. We will explore the impact of the level of bias through undertaking Sensitivity analysis.
Measures of treatment effect
Dichotomous data
For dichotomous data, we will present results as summary risk ratio with 95% confidence intervals.
Continuous data
For continuous data, we will use the mean difference if outcomes are measured in the same way between trials. We will use the standardised mean difference to combine trials that measure the same outcome, but use different methods.
Unit of analysis issues
We will not be including cluster‐randomised trials or studies with crossover designs in this review.
Dealing with missing data
For included studies, levels of attrition will be noted. The impact of including studies with high levels of missing data in the overall assessment of treatment effect will be explored by using sensitivity analysis. For all outcomes analyses will be carried out, as far as possible, on an intention‐to‐treat basis, i.e. we will attempt to include all participants randomised to each group in the analyses. The denominator for each outcome in each trial will be the number randomised minus any participants whose outcomes are known to be missing.
Assessment of heterogeneity
We will use the I² statistic to measure heterogeneity among the trials in each analysis. If we identify substantial heterogeneity we will explore it by prespecified subgroup analysis. We will regard a level of 50% or above as substantial.
Assessment of reporting biases
Where we suspect reporting bias (see 'Selective reporting bias' above), we will attempt to contact study authors asking them to provide missing outcome data. Where this is not possible, and the missing data are thought to introduce serious bias, the impact of including such studies in the overall assessment of results will be explored by a Sensitivity analysis. Funnel plots will be used with visual testing of asymmetry where there are 10 or more studies.
Data synthesis
We will carry out statistical analysis using the Review Manager software (RevMan 2008). We will use fixed‐effect inverse variance meta‐analysis for combining data where trials are examining the same intervention, and the trials’ populations and methods are judged sufficiently similar. Where we suspect clinical or methodological heterogeneity between studies sufficient to suggest that treatment effects may differ between trials we will use random‐effects meta‐analysis. If substantial heterogeneity is identified in a fixed‐effect meta‐analysis this will be noted and the analysis repeated using a random‐effects method.
Subgroup analysis and investigation of heterogeneity
We will conduct planned subgroup analyses classifying whole trials by interaction tests as described by Deeks 2001.
We plan to do the following subgroup analyses.
1. CSE group:
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epidural volume extension versus low‐dose sequential versus spinal plus epidural catheter placement alone subgroups;
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needle‐through‐needle versus two level insertion subgroups.
2. Single shot spinal group:
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low‐dose versus high‐dose local anaesthetic subgroups defined as less than or greater than 10 mg of bupivacaine (or equivalent) respectively.
For fixed‐effect meta‐analyses we will conduct planned subgroup analyses classifying whole trials by interaction tests as described by Deeks 2001. For random‐effects meta‐analyses we will assess differences between subgroups by inspection of the subgroups’ confidence intervals; non‐overlapping confidence intervals indicate a statistically significant difference in treatment effect between the subgroups.
Sensitivity analysis
Sensitivity analyses will be performed where there is risk of bias associated with the quality of some of the included trials and to explore the effects of fixed‐ or random‐effects analyses for outcomes with statistical heterogeneity.
