Rapid sequence induction (RSI) is a technique used by critical care clinicians, mainly anaesthetists, intensive care physicians and emergency physicians, when setting out to secure a clear airway for a general anaesthetic and the patient is thought to be at risk of vomiting their stomach contents into their airway and down into their lungs. Stomach contents in the lungs can cause infection of the lung and, in severe cases, death. Cricoid pressure is a technique where pressure is placed on an area of bone-like tissue in the neck to flatten the oesophagus (tube that connects the mouth to the stomach). This is intended to prevent vomiting up of the stomach contents. The application of cricoid pressure for this purpose is very common. It is, however, a controversial practice as some clinicians and researchers believe it to be ineffective. It may also interfere with the clinician's view of the patient's airway.
Our search strategy was designed to identify randomized controlled trials (RCTs) where RSI was undertaken to secure an artificial airway for a general anaesthetic with or without the application of cricoid pressure. Vomiting or regurgitation of stomach contents during anaesthesia was to be assessed either by looking directly down the airway or by various laboratory and imaging (radiological) methods. We also set out to determine whether applying cricoid pressure caused any harm.
We searched the databases until May 2015. Only one RCT met our inclusion criteria but unfortunately this trial did not report on any clinically relevant results. We classified one other trial as ongoing. The researchers have reported on their planned protocol for the clinical trial, where cricoid pressure applied using a measured force will be compared with cricoid pressure without measuring the force applied. The number of patients who vomit is to be monitored.
Quality of evidence
This systematic review shows an absence of evidence regarding the effectiveness and risks of cricoid pressure during RSI for intubation. Little can be said therefore about whether this technique should be continued in clinical practice. One current ongoing study shows promise that it will provide useful information in the future.
There is currently no information available from published RCTs on clinically relevant outcome measures with respect to the application of cricoid pressure during RSI in the context of endotracheal intubation. On the basis of the findings of non-RCT literature, however, cricoid pressure may not be necessary to undertake RSI safely, and therefore well-designed and conducted RCTs should nonetheless be encouraged to properly assess the safety and effectiveness of cricoid pressure.
Rapid sequence induction (RSI) for endotracheal intubation is a technique widely used in anaesthesia, emergency and intensive care medicine to secure an airway in patients deemed at risk of pulmonary aspiration. Cricoid pressure is conceptually used to reduce the risk of aspiration by compressing the oesophagus.
To identify and evaluate all randomized controlled trials (RCTs) involving participants undergoing elective or emergency airway management via RSI and compare participants who have cricoid pressure administered with participants who do not have cricoid pressure administered.
We searched the Cochrane Central Register of Controlled Trials (CENTRAL 2015, Issue 4), MEDLINE via OvidSP (1946 to May 2015), EMBASE via OvidSP (1980 to May 2015), ISI Web of Science (from 1940 to May 2015) and CINAHL via EBSCOhost (1982 to May 2015).
We included all RCTs comparing people undergoing RSI who have cricoid pressure applied, either intermittently or continuously, with people undergoing RSI who do not have cricoid pressure applied in the context of endotracheal intubation using a direct laryngoscopic technique. We included both elective and emergency cases. We included studies of blinded and unblinded participants. Participants (male or female) were involved in any type of procedure where general anaesthetic utilizing RSI or emergency airway management utilizing RSI and endotracheal intubation was undertaken. We expected the control arm to be the absence of cricoid pressure at any stage during RSI. The primary outcome of interest was the reported event rate or prevalence of aspiration determined by a) documented gastric aspiration determined by visual inspection of aspirated stomach contents on laryngoscopy; b) pepsin detection in tracheal aspirate using the Ufberg method; c) post-anaesthetic radiographic changes suggestive of aspiration pneumonitis or d) any combination of a to c. Secondary outcomes of interest included documented impaired visualization of the airway by a treating laryngoscopist, force applied during cricoid pressure, the direction of application of force of applied cricoid pressure, independent risk factors for aspiration and whether the person applying cricoid pressure had previously done so in an emergency airway context.
Two review authors independently screened the titles and abstracts of all the studies obtained from the search using recognition of words such as 'cricoid pressure', 'rapid sequence intubation', 'emergency airway management' and 'aspiration'. Two authors independently determined the study inclusion by using a study eligibility form that we developed for the purpose of this review. We also reported the decisions regarding inclusion and exclusion in accordance with the preferred reporting items for systematic reviews and meta-analyses (PRISMA) statement. We assumed that studies that did not describe the use of RSI in their title, abstract or methodology used an alternative method of anaesthetic induction or emergency airway management and thus we excluded them. Data extracted from included studies comprised study characteristics, participant demographics, intervention and comparison details plus outcome measures and results. We contacted primary authors of studies with missing or unreported but potentially relevant data to obtain missing data.
Of 493 records that we identified from databases as a result of the search (excluding duplicates), we regarded 70 abstracts/titles as potentially relevant studies. Independent scrutiny of these 70 titles and abstracts identified 29 potentially relevant studies. Of the 29 potentially relevant studies, one study met the criteria for inclusion. This study was a RCT that compared participants undergoing RSI and endotracheal intubation in the context of elective surgery requiring a general anaesthetic. Forty participants were recruited, 20 of whom had cricoid pressure applied and 20 of whom had cricoid pressure simulated. The main outcomes reported were systolic arterial pressure and heart rate after laryngoscopy and tracheal intubation. We did not consider these outcomes relevant for the purposes of this systematic review. The search also identified one study that could potentially be included in an updated systematic review in the future, but was at the time of the search a proposal for a trial only and had no reported outcomes at this time.