The laryngeal mask airway (LMA) is a new supraglottic ventilation device invented and first advocated by Brain in 1981. The LMA is placed into the pharynx through the mouth, and after inflation, it forms a sealed annular space around the larynx, which can preserve spontaneous breathing and perform positive pressure ventilation, and is a ventilation tool between tracheal intubation and mask.
For more than 20 years, LMA has been widely used in emergency resuscitation and clinical anesthesia for the advantages of simple placement and easy maintenance of ventilation, so far, LMA has been used in general anesthesia for more than 150 million times, and there has not been any death directly related to the laryngeal mask.
I. Definition and classification of difficult airway.
There are many clinical situations, such as surgery and critical care process, are required for airway management. According to statistics, the incidence of difficult airway in general surgical patients is between 1% and 5%. However, in some cases, such as oral and maxillofacial and plastic surgery patients, the incidence of a difficult airway can be as high as 15%.
When a difficult airway occurs, effective artificial ventilation cannot be performed and the patient can suffer cardiac arrest, brain damage or even death within a short period of time due to hypoxia. A study of anesthesia-related deaths found [3] that 70% of anesthesia deaths were due to airway problems, with the main causes being airway obstruction, difficult intubation, and inadvertent intubation of the tracheal tube into the esophagus.
The possibility of difficult endotracheal intubation in patients is an important element to be noted in the preanesthesia examination. If difficult intubation can be accurately predicted preoperatively, the rate of misdiagnosis and danger of difficult intubation can be avoided, which is always the goal of anesthesiologists.
(A) Definition of difficult airway
A difficult airway is usually considered to occur when a patient is unable to maintain adequate voluntary ventilation and the surgeon is unable to maintain effective assisted ventilation with conventional instruments and techniques. Perioperatively, difficult ventilation or difficult tracheal intubation with laryngoscopic exposure occurs most commonly after induction of anesthesia. However, many factors can influence the accuracy of this determination due to the uncertainty of the measures, such as the pathophysiological changes in the patient, the technical experience of the operator, the psychological quality, the number of attempts, the degree of injury and the condition of the clinical equipment.
ASA definition of difficult airway: In 1993, ASA had recommended the development of a definition of difficult airway.
1, difficult airway (difficult airway): refers to the difficulty of patient mask ventilation and/or tracheal intubation under the management of a routinely trained anesthesiologist;
2.Difficulty in mask ventilation: It refers to insufficient ventilation during mask administration of pure oxygen and positive pressure ventilation, resulting in patients with SpO2>90% before anesthesia, unable to maintain SpO2 above 90%;
3.Difficulty in laryngoscopic exposure: refers to the inability to see any part of the voice box under conventional laryngoscopic exposure;
4.difficult tracheal intubation (difficult tracheal intubation): refers to the conventional laryngoscopic intubation time greater than 10 minutes or more than 3 attempts to intubate failed.
In 2003, the ASA followed the evidence-based medical model and reworked the airway management strategy, arguing that the scope of airway management should be expanded from being limited to difficult airways to all airways that need to be managed. It also called for safer strategies to avoid emergencies due to unexpected difficult intubation whenever possible. At the same time, the status of laryngeal mask ventilation was raised, shifting it from the emergency route to the routine route, and it was considered that a laryngeal mask could be routinely used for ventilation in non-emergency situations. Therefore, when laryngoscopic exposure fails, a difficult airway can be considered to have occurred only when both laryngeal mask and mask ventilation are difficult.
(B) Difficult airway grading
For a long time, there is no uniform grading standard for difficult airway, and there is a big difference in the clinical understanding of difficult airway. Difficult airway grading methods that originate from different sources have their own strengths and weaknesses, but each has its own problems. Commonly used clinical methods for assessing airway patency (modern anesthesiology) include.
① Difficulty in opening the mouth.
(ii) Restriction of cervical spine movement.
③Maxillofacial deformity.
④Pharyngeal diseases.
⑤ morbidly obese short neck and neck scar contracture causing chin-thorax adhesions.