Identification of Risk Factors Causing Difficulty in Laryngeal Mask Insertion

Backgrounds Since its introduction into clinical practice in 1983, the laryngeal mask (LM) has found a role in the daily practice of anesthesiologists, including its use as a primary device in the airway management in both elective and emergency and as an emergency approach to the management of difficult airways.

Moreover, the insertion of the LM has become a common technique in the management of the airway, in particular outpatient surgery, where it is associated with a shorter recovery time, faster discharge and thus with a reduction of costs.

Even if the LM is considered a device very safe with a low incidence of complications, there may be situations where it is difficult to insert.

Aim of the study Some studies have concerned the causes that determine the difficulty in the insertion of an LM. They are retrospective studies and/or focused on the analysis of a single type of device.

Therefore, it seems appropriate to carry out a prospective observational study that will identify and weight the risk factors relating to the positioning of LM for the purpose of identification and prediction of them.

Methods From reading the literature and from the opinion of the experts with extensive practice in airway management (part of the Working Group "Management of Airway" of the Italian Society of Anaesthesia, Analgesia, Resuscitation and Intensive Care SIAARTI) some possible causes of difficulty in the insertion of laryngeal mask have been identified; these possible causes were listed in a report that will be distributed to the centers enrolled in the conduction of the study.

The centers will be selected based on the fact that between the researchers is including an anesthesiologist part of the Working Group "Airway management" of SIAARTI to act as supervisor.

Statistic Descriptive: for each quantitative variable will be reported mean, standard deviation, first and third quartiles, median, minimum and maximum. For each qualitative variable will be reported frequency and percentage of each category.

Explorative: The association between each risk factor and the proportion of incorrect insertion will be evaluated only in a univariate analysis, using the relative risk and its confidence interval.

Sample size: For a hypothesis test on the relative risk so specified H0: RR ≤ 1 H1: RR> 1 and considering an expected relative risk of 2, a proportion of 2.9% of the failures in the group of experts and a first type error equal to 5%, 832 patients per group are needed to ensure a power equal to 90%.

The limit of significance is set at 5%.

Expected results To calculate the relative risk of each of the factors analyzed in order to identify those that, in view of the LM positioning, can be modified to reduce the risk of failure and, secondly, to identify the risk factors whose presence may contraindicate the use of the device and indicate the use of alternative methods for airway management.

Inclusion criteria

• ASA classification I-II
• Age between 18 and 65 years
• Airway management with laryngeal mask
• Signed informed consent to the study in the medical record

Exclusion criteria

• Diseases of the upper airways
• Risk of inhalation of gastric contents (previous gastric surgery, hiatal hernia, gastroesophageal reflux, peptic ulcer, stomach full, pregnancy)
• Large obese (BMI> 40)
• Sore throat, voice alteration
• A history of difficult intubation
• Intervention lasting more than 4 hours