Description of the condition
Airway management is a task performed by anaesthesiologists, intensivists and emergency physicians every day, both in hospital and out of hospital: Patients undergoing surgery need airway management during general anaesthesia; airway management is mandatory in critically ill patients with a non-patent airway; and in emergency or trauma patients, airway management can be necessary if the airway is obstructed or threatened or if the respiration fails and controlled ventilation is needed. Because airway control can be life-saving, it is mandatory that physicians who manage the airway are able to recognize a failing airway and perform an emergency airway if all other techniques are unsuccessful.
Airway control is the first priority according to the ‘ABCDE‘ (airway breathing circulation disability exposure) algorithm (ACS COT 2008; Nolan 2010; Thim 2012). A critical airway must always be managed before other problems are addressed because an obstructed airway quickly leads to hypoxia, which can cause brain damage, cardiac arrest and death (ACS COT 2008; Nolan 2010; Thim 2012). Different methods are known to gain and maintain control of the airway, and these methods are organized and prioritized in the guidelines (ACS COT 2008; Apfelbaum 2013; Henderson 2004; Nolan 2010).
According to these guidelines, the first step in management of the unanticipated difficult airway is to attempt initial tracheal intubation with direct laryngoscopy. If the view is poor, an alternative laryngoscope can be used (e.g. a video laryngoscope). If these techniques fail, ventilation and oxygenation are maintained through supraglottic airway devices: the laryngeal mask airway (LMA) and the intubating laryngeal mask (ILMA). Secondary tracheal intubation can be attempted by fibreoptic tracheal intubation through the LMA/ILMA or by blind technique through the ILMA. If oxygenation cannot be maintained via LMA/ILMA, or if intubation through these devices fails, it is recommended to return to bag-mask ventilation. During general anaesthesia, postponing the surgery and waking the patient should be considered (Apfelbaum 2013; Henderson 2004). In critically ill patients and trauma patients, however, this opportunity does not exist (ACS COT 2008; Lim 2003). In situations in which intubation has failed, bag-mask ventilation cannot maintain oxygenation and hypoxia increases, the ‘can't intubate, can't ventilate’ (CICV) situation exists. This is the final, and most severe, step in the difficult airway algorithm and requires a quick rescue technique such as a cricothyroidotomy (Apfelbaum 2013; Henderson 2004).
Patients with a difficult airway are at higher risk of needing an emergency cricothyroidotomy, hence predictors of a difficult airway outline the characteristics of patients in this risk group. Predictors of a difficult airway include high Mallampati classification, short thyromental distance, short sternomental distance, slight mouth opening, obesity, limited head and neck movement, beard, history of snoring and advanced age (Henderson 2004; Kheterpal 2006; Langeron 2000; Shiga 2005). It has been shown that the prevalence of patients with difficult mask ventilation is 5% in the general population (Langeron 2000), and the prevalence of difficult intubation is 5.8% (Shiga 2005). One study found the need for a surgical airway to be as little as 0.0044% (Kheterpal 2006), and another reports the incidence of CICV to be 0.0001% to 0.02% (Heard 2009).
Description of the intervention
Cricothyroidotomy is an intervention intended to gain control of the airway by creating an artificial airway through the skin, connective tissues and cricothyroid membrane into the trachea (Fikkers 2004; Henderson 2004). Cricothyridotomy is the method of choice for establishing an airway in an emergency setting when noninvasive techniques such as intubation and supraglottic devices have failed, hypoxaemia is increasing and bag-mask ventilation is difficult. It is the rescue technique for the CICV situation and is the final step in the difficult airway algorithm of the American Society of Anesthesiologists (ASA) (Fikkers 2004; Henderson 2004).
Overall, two strategies exist for performing a cricothyroidotomy: the surgical cricothyroidotomy and the percutaneous dilatation or wire-guided cricothyroidotomy. With the first method, a scalpel is used to make an incision through the skin and cricoid membrane, then a tracheal hook is placed to make a cephalad retraction, thereby making room for an airway tube or a tracheal cannula to pass into the trachea (Schaumann 2005). The latter method is performed using the Seldinger technique. With this technique, a hollow needle is used to locate the lumen of the trachea through the skin and the cricothyroid membrane; a guidewire is then advanced through the lumen of the needle, and the needle is withdrawn; a combined dilator and airway tube is then inserted over the guidewire, and the guidewire and the dilator can be removed, leaving the airway tube in place (Schaumann 2005). Both methods allow oxygenation and ventilation to take place (ACS COT 2008; Apfelbaum 2013; Henderson 2004). Each of the two cricothyroidotomy methods has it advantages and disadvantages; different equipment and premade cricothyroidotomy sets exist, but no universal consensus has been established as to which method is safest or quickest to perform (Davis 2000; Fikkers 2004; Henderson 2004; Holmes 1998; Keane 2004).
Difficult airway management has been identified as the main cause of death and severe morbidity related to anaesthesia (Braz 2009; Lim 2003). Therefore, it is paramount that anaesthesiologists, but also emergency physicians and intensivists, are able to manage a difficult airway, including the performance of a cricothyroidotomy.
We wish to compare the surgical cricothyroidotomy and the percutaneous dilatation cricothyroidotomy. Terms used for the percutaneous dilatation cricothyroidotomy include wire-guided, Seldinger technique and Seldinger method.
How the intervention might work
The cricothyroidotomy provides oxygenation to the patient through the cricothyroid membrane to avoid or reverse hypoxia. The cricothyroidotomy is a technique for emergency airway management, hence it is a temporary measure, and definitive airway management must often follow. This might be a formal tracheostomy, but tracheal intubation will be possible in some patients (Apfelbaum 2013; Henderson 2004).
The need to convert an emergency cricothyroidotomy to a tracheotomy has been debated. Conversion to tracheotomy to decrease the complication of subglottic stenosis is advocated by some (Esses 1987), whereas others question the need for conversion because tracheotomy does not guarantee the prevention of long-term complications (DeLaurier 1990; Graham 2011). To summarize, the need for routine conversion of a cricothyroidotomy to a tracheotomy cannot be supported by all studies; however, most investigators agree that conversion to a tracheotomy should be considered for patients who require operative exploration for haemorrhage or other complications of the cricothyroidotomy and for patients who will require long-term airway maintenance or mechanical ventilation (Gillespie 1999). In situations in which the patient has regained a patent airway and spontaneous ventilation after an emergency cricothyroidotomy, maintaining the cricothyroidotomy for a short time with subsequent extubation must be considered (Graham 2011).
Why it is important to do this review
Currently, many different techniques and devices are available for the performance of an emergency cricothyroidotomy; this applies to both the surgical technique and the percutaneous dilatation technique. Furthermore, different devices are accessible at different locations. Cricothyroidotomy is not performed very often; therefore, it is important for the physician to know the available techniques and the different devices that can be used to increase the success rate and safety and familiarity with the equipment, as well as to minimize complications, performance time and stress in the emergency situation (Davis 2000; Holmes 1998; Keane 2004).
At present, no overview has summarized the different techniques and devices, and it is currently unclear whether one technique or one device is superior to the others. It is possible that some techniques and devices have a higher success rate and are safer, faster and easier to use than others. This review is needed to determine whether one of the two cricothyroidotomy methods—the surgical cricothyroidotomy and the percutaneous dilatation cricothyroidotomy—is superior to the other. Furthermore, this review is needed to outline the different devices available for cricothyroidotomy and to determine their advantages and disadvantages to establish which technique and device are recommendable.
To determine in the CICV situation which emergency cricothyroidotomy technique is superior—the surgical cricothyroidotomy or the percutaneous dilatation cricothyroidotomy—in adult patients aged 16 years or older in any emergency setting (including intensive care unit (ICU), emergency room (ER), operating room (OR) and prehospital care). Furthermore, to describe the techniques and devices that are available for emergency cricothyroidotomy, and to assess the advantages and disadvantages of the different techniques and devices in terms of success rate, performance time, complication rate and preferences among physicians performing the procedure.
Criteria for considering studies for this review
Types of studies
We will include randomized controlled trials (RCTs) irrespective of publication status, date of publication, blinding status or language.
We do not expect to find many RCTs, if any, because emergency cricothyroidotomy is performed in acute situations in which time is limited, thereby making the procedure difficult to randomize. Therefore, we plan to include quasi-randomized studies as well.
If RCTs and/or quasi-randomized studies are found to be unavailable, or if the quality of evidence in the RCTs is low, we will include non-randomized studies (NRSs). Evidence from RCTs and NRSs will not be combined. If RCTs become available as the review is updated, NRSs will be excluded.
Methods of incorporating NRSs
A strong possibility exists that NRSs will be incorporated into this review to provide evidence of the effects of interventions that are unlikely to be randomized. NRSs will be evaluated in accordance with Cochrane guidance on including NRSs (Higgins 2011). NRSs will be included if the evidence ‘matches’ the population, interventions and comparators defined in this protocol. Therefore, studies must include at least two comparison groups consisting of adult participants (aged minimum 16 years) who are having cricothyroidotomy performed. NRSs are included only if studies provide a description of how the comparison groups are formed (e.g. time differences, location differences, healthcare decision makers). For NRSs to be included, key steps in the studies must be described, including identification of participants, assessment before intervention, actions leading to an individual becoming a member of a group and assessment of outcomes. Furthermore, comparability between groups must be assessed according to potential confounders (Higgins 2013; Norris 2013; Reeves 2013; Schünemann 2013; Valentine 2013; Wells 2013). Both prospective and retrospective NRSs will be included.
Types of participants
We will include adult patients aged ≥ 16 years in the CICV situation in which emergency cricothyroidotomy is performed.
Types of interventions
Performance of surgical cricothyroidotomy versus percutaneous dilatation cricothyroidotomy in the CICV situation.
We expect that the groups can be divided into subgroups according to commercially available devices, thereby making it possible to compare the outcomes in different subgroups against each other.
Types of outcome measures
- Overall mortality. We will use the maximal follow-up data from each trial.
- Success rate. We will use the percentage of successfully performed cricothyroidotomies for each technique and type of equipment as the success rate.
- Performance time.
- Overall complication rate.
- Bleeding (in cc).
- Preference among physicians performing the procedure by using more than one method.
Search methods for identification of studies
We will search the latest issue of the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE (Ovid, 1950 to date), EMBASE (Ovid, 1980 to date) and ISI Web of Science (1956 to date).
We will utilize a systematic search strategy to identify relevant studies. Our search strategies for CENTRAL, MEDLINE, EMBASE and ISI Web of Science will be found in Appendix 1, Appendix 2, Appendix 3 and Appendix 4.
We will impose no language restrictions in the search strategy.
Searching other resources
We will search for ongoing clinical trials and unpublished studies on the following Internet sites: Current Controlled Trials; ClinicalTrials.gov; and www.centerwatch.com.
We will screen the reference lists of all eligible trials and reviews. We will contact authors of studies and experts in the field to ask about unreported or ongoing studies. We will contact relevant manufacturers of airway devices.
Data collection and analysis
Selection of studies
The above described search will be assessed, and obviously irrelevant reports excluded. Two review authors (MLA and AMM) will independently examine studies for eligibility without blinding of study authors, institutions, journal of publication and results. We will retrieve the full text of potentially relevant studies and will contact the investigators and the study authors to retrieve relevant non-published data. Two review authors (MLA and AMM) will decide which studies to include. We will resolve disagreements by discussion, and if no agreement is found, we will consult a third review author (NLP).
Data extraction and management
Using a data extraction sheet (Appendix 5), we will evaluate each study and will enter the data in RevMan 5.2; data entry will be checked for accuracy. If data in the identified reports are somewhat unclear, we will make attempts to contact the authors of the original study to request further details.
If NRSs are included, we will furthermore apply the checklist provided by Wells et al: 'Checklists of methodological issues for
review authors to consider when including non-randomized studies in systematic reviews' (Wells 2013).
Assessment of risk of bias in included studies
Two review authors (MLA and AMM) will independently and without blinding assess the risk of bias, using the criteria outlined in the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011). We will resolve disagreements by discussion, and if no agreement is found, we will consult a third review author (NLP) .
We will assess the risk of bias by using the risk of bias table and by answering the following questions, as described in the Cochrane Handbook for Systematic Reviews of Interventions, Section 8.5 (Higgins 2011).
Random sequence generation
Assessment of randomization: the sufficiency of the method in producing two comparable groups before intervention.
- Low risk of bias: description of a truly random process in the sequence generation (e.g. random number table, random computer number generator, coin tossing, shuffling of cards/envelopes, throwing of dice).
- High risk of bias: description of any non-random process in the sequence generation (e.g. date of birth, date of admission, hospital or clinic record number, judgement of clinician, preference of participant, results of series of tests, availability of the intervention).
- Unclear risk of bias: insufficient information about the sequence generation process.
Allocation method prevented investigators or participants from foreseeing the assignment.
- Low risk of bias: adequately concealed allocation (e.g. central allocation, sealed envelopes, serially numbered or otherwise convincing concealment of allocation).
- High risk of bias: inadequately concealed allocation (e.g. open allocation schedule, unsealed envelopes, alternation of rotation, date of birth, case record number, other unconcealed procedure).
- Unclear risk of bias: no information on allocation method or no clear distinction of the method.
Blinding of participants and personnel, blinding of outcome assessment
Knowledge of the allocated intervention was adequately prevented during the study.
For the intervention in question, blinding will be very difficult to achieve. However, we will still grade the papers according to the following.
- Low risk of bias: adequate blinding in which participants and personnel were unaware of intervention allocations after inclusion of participants in the study; or no blinding that is unlikely to introduce bias.
- High risk of bias: inadequate or no blinding (e.g. not double-blinded, open-label study, no use of placebo or an intervention disguised in the same manner as placebo).
- Unclear risk of bias: insufficient description of the blinding procedure.
Incomplete outcome data
The completeness of outcome data for each main outcome, including attrition and exclusions from the analysis.
- Low risk of bias: The numbers and the reasons for dropouts and withdrawals in the intervention groups are described, or it is specified that no dropouts or withdrawals occurred.
- High risk of bias: No description of dropouts and withdrawals is provided.
- Unclear risk of bias: The report gives the impression that no dropouts or withdrawals occurred, but this is not specifically stated.
The possibility of selective outcome reporting.
- Low risk of bias: The reported outcomes are those prespecified in an available study protocol, or, if this is not available, the published report includes all expected outcomes.
- High risk of bias: Not all prespecified outcomes have been reported, or they have been reported using subscales that were not prespecified, or they were reported incompletely or failed to include a key outcome that would be expected to have been reported for such a study.
- Unclear risk of bias: It is not clear whether all predefined or clinically relevant and reasonably expected outcomes are reported or are not reported fully, or it is unclear whether data on these outcomes are recorded.
The assessment of any possible sources of bias is not addressed in any of the other domains.
- Low risk of bias: The report appears to be free of such.
- High risk of bias: At least one important bias is present that is related to study design, such as early stopping due to some data-dependent process, extreme baseline imbalance, claimed fraudulence or other problems.
- Unclear risk of bias: Insufficient information or evidence suggests that an identified problem will introduce bias.
Measures of treatment effect
We will calculate the risk ratios (RRs) with 95% confidence intervals (CIs) for dichotomous data (binary outcomes).
We will use the mean difference (MD) with 95% CI if data are continuous and are measured in the same way between trials. The standardized mean difference (SMD) will be used to combine trials that measure the same outcome but use different metrics of measurement.
Unit of analysis issues
We will include studies with non-standard designs, such as cluster-randomized trials and studies with multiple treatment groups if appropriate, as well as interventions grouped according to the interventions in question. We will use appropriate adjustments for clustering.
Dealing with missing data
We will contact the first authors of studies and will contact persons from trials with missing data to try to retrieve the relevant data.
If it is impossible to retrieve the missing data, we will impute the missing data with replacement values according to best case/worst case, and we will treat these as if they were observed.
Assessment of heterogeneity
Clinical and methodological diversity always occurs between different studies, making heterogeneity inevitable (Higgins 2003).
We aim to meta-analyse trial results only in the case of low to moderate clinical heterogeneity.
Statistical variability due to heterogeneity will be investigated via calculation of the inconsistency factor (I
Assessment of reporting biases
Reporting bias occurs when the dissemination of research findings is influenced by the nature and direction of results (Higgins 2011).
To detect reporting biases, we will construct funnel plots if 10 or more studies are included. We will also conduct tests for funnel plot asymmetry.
We will attempt to minimize reporting biases by searching multiple sources to identify relevant studies. Furthermore, we will search online trial registries to identify unpublished trials.
We will use Review Manager software (RevMan 5.2) as our statistical software. We will calculate RRs with 95% CIs for dichotomous variables (binary outcomes). We will also calculate the risk difference, but if the results are similar, we will report only the RR. Additionally, we will calculate the MD (measure of absolute change) or the SMD with 95% CI for continuous outcomes. We will assume a random-effects model for all data syntheses. We will use an inverse variance weighting for summary statistics. We will report summary statistics as point estimates with 95% CIs; summary statistics will be declared statistically significant if P < 0.05 and if 95% CIs do not cross the line of identity.
We will use the I
We plan to do a narrative synthesis of the included studies to describe the different emergency cricothyroidotomy techniques and devices, as well as the advantages and disadvantages of the different techniques and devices.
Subgroup analysis and investigation of heterogeneity
We expect to be able to split the intervention group into subgroups according to cricothyroidotomy techniques and devices used. If this is possible, we wish to perform a subgroup analysis to compare outcomes between these subgroups.
We will perform sensitivity analysis according to trial quality (allocation concealment, blinding of outcome assessment, completeness of follow-up) to assess the robustness of estimates of treatment effect.
We will look into the costs of the interventions in question. We will evaluate costs narratively.
Methods for further updates
We will update this review within three years from its publication date. If important new evidence is published, we will update the review as soon hereafter as possible.
Summary of findings
We will use in our review the principles of the GRADE system (Guyatt 2008) to assess the quality of the body of evidence associated with specific outcomes (overall mortality, success rate, performance time, overall complication rate, preference among physicians performing the procedure using more than one method) and will construct a summary of findings (SoF) table using the GRADE software. The GRADE approach appraises the quality of a body of evidence based on the extent to which one can be confident that an estimate of effect or association reflects the item being assessed. Assessment of the quality of a body of evidence takes into consideration within-study risk of bias (methodological quality), directness of the evidence, heterogeneity of the data, precision of effect estimates and risk of publication bias.
We would like to thank Rodrigo Cavallazzi (content editor); Cathal Walsh (statistical editor); and Melissa Giraldo-Duque, Davide Cattano, Javier Eslava-Schmalbach, Joshua Atkins and Christopher Rassekh (peer reviewers) for their help and editorial advice during the preparation of this protocol for the systematic review.
Appendix 1. Search strategy for CENTRAL
#1 cricothyroidotom* OR cricothyrotom*
Appendix 2. Search strategy for MEDLINE (Ovid SP)
1. (cricothyrotom* or cricothyroidotom*).af.
2. ((randomized controlled trial or controlled clinical trial).pt. or randomized.ab. or placebo.ab. or drug therapy.fs. or randomly.ab. or trial.ab. or groups.ab.) not (animals not (humans and animals)).sh.
3. 1 and 2
Appendix 3. Search strategy for EMBASE (Ovid SP)
1. (cricothyrotom* or cricothyroidotom*).af.
2. (randomized-controlled-trial/ or randomization/ or controlled-study/ or multicenter-study/ or phase-3-clinical-trial/ or phase-4-clinical-trial/ or double-blind-procedure/ or single-blind-procedure/ or (random* or cross?over* or multicenter* or factorial* or placebo* or volunteer*).mp. or ((singl* or doubl* or trebl* or tripl*) adj3 (blind* or mask*)).ti,ab. or (latin adj square).mp.) not (animals not (humans and animals)).sh.
3. 1 and 2
Appendix 4. Search strategy for ISI Web of Science
#1 Topic=(cricothyrotom* or cricothyroidotom*)
#2 TS=(random* or placebo* or multicenter* or prospective or (trial* SAME (controlled or clinical))) or TS=((blind* or mask*) SAME (single or double or triple or treble))
#3 #2 AND #1
Appendix 5. Data extraction form
Study ID (surname year: as it will appear in RevMan)
Name of review author completing this form
Notes (unpublished—for own use)
Do not proceed if answers to 1., 2. and 3. are 'No' or 'Unclear' and/or answers to 4. through 6. are 'No'. If so, the study should be registered in 'excluded studies'. If the study is classified as NRS, address as many of the following subjects as possible, and apply the 'Checklists of methodological issues for review authors to consider when including non-randomized studies in systematic reviews' (Wells 2013).
Intervention and control groups
Details of study
Risk of bias
Contributions of authors
Mette Legaard Andersson (MLA), Ann Merete Møller (AMM), Nathan Leon Pace (NLP)
Conceiving of the review: MLA, AMM
Designing the review: MLA, AMM
Co-ordinating the review: MLA
Undertaking manual searches: MLA
Screening search results: MLA
Organizing retrieval of papers: MLA
Screening retrieved papers against inclusion criteria: MLA, AMM
Appraising quality of papers: MLA, AMM, NLP
Abstracting data from papers: MLA
Writing to authors of papers to ask for additional information: MLA
Providing additional data about papers: MLA
Obtaining and screening data on unpublished studies: MLA
Providing data management for the review: MLA, AMM
Entering data into Review Manager (RevMan 5.2): MLA, AMM
Managing RevMan statistical data: MLA, NLP
Performing other statistical analyses not using RevMan: NLP, MLA
Interpreting data: MLA, AMM, NLP
Making statistical inferences: NLP
Writing the review: MLA
Providing guidance on the review: AMM
Securing funding for the review: AMM, MLA
Performing previous work that provided the foundation for the present study: MLA, AMM, NLP
Serving as guarantor for the review (one review author): AMM
Taking responsibility for reading and checking the review before submission: AMM
Declarations of interest
Mette Legaard Andersson: none known.
Ann Merete Møller: none known.
Nathan Leon Pace: none known.
Sources of support
- Cochrane Anaesthesia Review Group (CARG), Denmark.
- No sources of support supplied