Key messages
Devices called laryngoscopes are used to help medical staff to insert a plastic breathing tube into someone’s windpipe because they need help with their breathing. A video camera can be attached to the device. We found that videolaryngoscopes generally improve the success of inserting a breathing tube compared with conventional laryngoscopes.
What is intubation?
People who are very ill or having surgery under general anaesthesia may need help to breathe. Trained medical staff may need to place a flexible plastic tube into a person’s windpipe. This is called intubation. It will keep the airway open so that the person can be given help to breathe.
What are laryngoscopes?
During intubation, the medical staff need to move the tongue and soft tissues of the mouth so that they can see the vocal cords before inserting the tube. To achieve this they use a laryngoscope. However, seeing the vocal cords may be difficult, for example when the person has restricted neck movement. Difficulties in intubation may lead to complications, including low oxygen levels and in extreme cases death.
In this review, we looked at two types of laryngoscopes: Macintosh direct laryngoscopes and videolaryngoscopes. A Macintosh direct laryngoscope is a curved piece of metal or plastic with a handle designed to hold down the tongue and soft tissues. A videolaryngoscope uses video technology and allows medical staff to see the position of the tube on a video screen while it is being inserted. There are three main designs of videolaryngoscopes: Macintosh-style (with a similar shape to the traditional laryngoscope), hyperangulated (more curved than other laryngoscopes), and channelled (with a groove to guide the breathing tube).
What is laryngoscopy?
Laryngoscopy is a medical procedure in which a device called a laryngoscope is used to examine the voice box and help with insertion of a breathing tube into the windpipe to protect the airways during anaesthesia or when patients have breathing difficulties. 'Direct laryngoscopes' rely on a direct line of sight to the voice box to achieve this. A 'videolaryngoscope' incorporates video technology that allows the voice box to be viewed on a screen during the procedure.
What did we want to find out?
We wanted to find out which type of laryngoscope works best for intubation for medical staff and patients. Which type of laryngoscope works best for certain groups of patients: for example, those with neck restrictions or obesity, different medical staff (experienced or less experienced) and in different settings (in or out of hospital). We also wanted to find out if any of the laryngoscopes cause unwanted effects.
What did we do?
We searched for studies that compared Macintosh laryngoscopes against each of the three different types of videolaryngoscopes. We compared and summarized their results, and rated our confidence in the evidence, based on factors such as study design, methods and numbers of participants.
What did we find?
We found 222 studies with 26,149 adults who were intubated using a laryngoscope. Most people were undergoing surgery and the intubation was planned or expected, but some intubations happened in emergency situations. Most studies included a mix of people. Some studies were in selected groups, such as people who were obese or when medical staff expected that intubation may be difficult. The studies were conducted in countries from around the world. Manufacturers of laryngoscopes were involved in 14 of the studies.
Main results
Compared to the traditional Macintosh laryngoscope, all three types of videolaryngoscope probably reduce the number of failed intubations. Hyperangulated videolaryngoscopes may lead to fewer failed intubations particularly in people with an airway that is difficult to intubate (or an expected difficult airway). All videolaryngoscopes may also increase the chances of being successfully intubated on the first attempt and improve the view of the vocal cords.
Macintosh-style and channelled videolaryngoscopes probably reduce the risk of the person experiencing a low oxygen level, but there may be little or no difference when a hyperangulated videolaryngoscope is used. Using a hyperangulated videolaryngoscope may reduce the risk of the breathing tube being accidentally inserted into the food pipe instead of the windpipe. The other videolaryngoscopes may or may not reduce this risk.
No type of laryngoscope increased or reduced accidental damage to the teeth, but we are very uncertain about this finding. We were unable to tell if any of the laryngoscopes reduced the time taken for intubation.
What are the limitations of the evidence?
We were moderately confident that videolaryngoscopes reduce failed intubations. We had moderate to very low confidence in our other findings. It was not possible for researchers to conceal what type of laryngoscope the medical staff used and this might have affected how they carried out intubations. The studies included different types of people, and some findings included the possibility of benefits or harms for both types of laryngoscope.
How up to date is this evidence?
This review updates our previous review. The evidence is up-to-date to March 2021.
VLs of all designs likely reduce rates of failed intubation and result in higher rates of successful intubation on the first attempt with improved glottic views. Macintosh-style and channelled VLs likely reduce rates of hypoxaemic events, while hyperangulated VLs probably reduce rates of oesophageal intubation. We conclude that videolaryngoscopy likely provides a safer risk profile compared to direct laryngoscopy for all adults undergoing tracheal intubation.
Tracheal intubation is a common procedure performed to secure the airway in adults undergoing surgery or those who are critically ill. Intubation is sometimes associated with difficulties and complications that may result in patient harm. While it is traditionally achieved by performing direct laryngoscopy, the past three decades have seen the advent of rigid indirect videolaryngoscopes (VLs). A mounting body of evidence comparing the two approaches to tracheal intubation has been acquired over this period of time. This is an update of a Cochrane Review first published in 2016.
To assess whether use of different designs of VLs in adults requiring tracheal intubation reduces the failure rate compared with direct laryngoscopy, and assess the benefits and risks of these devices in selected population groups, users and settings.
We searched MEDLINE, Embase, CENTRAL and Web of Science on 27 February 2021. We also searched clinical trials databases, conference proceedings and conducted forward and backward citation searches.
We included randomized controlled trials (RCTs) and quasi‐RCTs with adults undergoing laryngoscopy performed with either a VL or a Macintosh direct laryngoscope (DL) in any clinical setting. We included parallel and cross-over study designs.
We used standard methodological procedures expected by Cochrane. We collected data for the following outcomes: failed intubation, hypoxaemia, successful first attempt at tracheal intubation, oesophageal intubation, dental trauma, Cormack-Lehane grade, and time for tracheal intubation.
We included 222 studies (219 RCTs, three quasi-RCTs) with 26,149 participants undergoing tracheal intubation. Most studies recruited adults undergoing elective surgery requiring tracheal intubation. Twenty-one studies recruited participants with a known or predicted difficult airway, and an additional 25 studies simulated a difficult airway. Twenty-one studies were conducted outside the operating theatre environment; of these, six were in the prehospital setting, seven in the emergency department and eight in the intensive care unit.
We report here the findings of the three main comparisons according to videolaryngoscopy device type.
We downgraded the certainty of the outcomes for imprecision, study limitations (e.g. high or unclear risks of bias), inconsistency when we noted substantial levels of statistical heterogeneity and publication bias.
Macintosh-style videolaryngoscopy versus direct laryngoscopy (61 studies, 9883 participants)
We found moderate-certainty evidence that a Macintosh-style VL probably reduces rates of failed intubation (risk ratio (RR) 0.41, 95% confidence interval (CI) 0.26 to 0.65; 41 studies, 4615 participants) and hypoxaemia (RR 0.72, 95% CI 0.52 to 0.99; 16 studies, 2127 participants). These devices may also increase rates of success on the first intubation attempt (RR 1.05, 95% CI 1.02 to 1.09; 42 studies, 7311 participants; low-certainty evidence) and probably improve glottic view when assessed as Cormack-Lehane grade 3 and 4 (RR 0.38, 95% CI 0.29 to 0.48; 38 studies, 4368 participants; moderate-certainty evidence). We found little or no clear difference in rates of oesophageal intubation (RR 0.51, 95% CI 0.22 to 1.21; 14 studies, 2404 participants) but this finding was supported by low-certainty evidence. We were unsure of the findings for dental trauma because the certainty of this evidence was very low (RR 0.68, 95% CI 0.16 to 2.89; 18 studies, 2297 participants). We were not able to pool data for time required for tracheal intubation owing to considerable heterogeneity (I2 = 96%).
Hyperangulated videolaryngoscopy versus direct laryngoscopy (96 studies, 11,438 participants)
We found moderate-certainty evidence that hyperangulated VLs probably reduce rates of failed intubation (RR 0.51, 95% CI 0.34 to 0.76; 63 studies, 7146 participants) and oesophageal intubation (RR 0.39, 95% CI 0.18 to 0.81; 14 studies, 1968 participants). In subgroup analysis, we noted that hyperangulated VLs were more likely to reduce failed intubation when used on known or predicted difficult airways (RR 0.29, 95% CI 0.17 to 0.48; P = 0.03 for subgroup differences; 15 studies, 1520 participants). We also found that these devices may increase rates of success on the first intubation attempt (RR 1.03, 95% CI 1.00 to 1.05; 66 studies, 8086 participants; low-certainty evidence) and the glottic view is probably also improved (RR 0.15, 95% CI 0.10 to 0.24; 54 studies, 6058 participants; data for Cormack-Lehane grade 3/4 views; moderate-certainty evidence). However, we found low-certainty evidence of little or no clear difference in rates of hypoxaemia (RR 0.49, 95% CI 0.22 to 1.11; 15 studies, 1691 participants), and the findings for dental trauma were unclear because the certainty of this evidence was very low (RR 0.51, 95% CI 0.16 to 1.59; 30 studies, 3497 participants). We were not able to pool data for time required for tracheal intubation owing to considerable heterogeneity (I2 = 99%).
Channelled videolaryngoscopy versus direct laryngoscopy (73 studies, 7165 participants)
We found moderate-certainty evidence that channelled VLs probably reduce rates of failed intubation (RR 0.43, 95% CI 0.30 to 0.61; 53 studies, 5367 participants) and hypoxaemia (RR 0.25, 95% CI 0.12 to 0.50; 15 studies, 1966 participants). They may also increase rates of success on the first intubation attempt (RR 1.10, 95% CI 1.05 to 1.15; 47 studies, 5210 participants; very low-certainty evidence) and probably improve glottic view (RR 0.14, 95% CI 0.09 to 0.21; 40 studies, 3955 participants; data for Cormack-Lehane grade 3/4 views; moderate-certainty evidence). We found little or no clear difference in rates of oesophageal intubation (RR 0.54, 95% CI 0.17 to 1.75; 16 studies, 1756 participants) but this was supported by low-certainty evidence. We were unsure of the findings for dental trauma because the certainty of the evidence was very low (RR 0.52, 95% CI 0.13 to 2.12; 29 studies, 2375 participants). We were not able to pool data for time required for tracheal intubation owing to considerable heterogeneity (I2 = 98%).