The upper lip bite test is a simple, non-invasive assessment used in medical settings. It evaluates anatomical characteristics of a patient’s airway. This assessment helps healthcare providers understand potential challenges related to airway management and prepare for procedures involving a breathing tube.
What is the Upper Lip Bite Test
The upper lip bite test (ULBT) serves as a bedside tool to predict a difficult endotracheal intubation, a procedure where a tube is placed into the windpipe to help a patient breathe. This assessment is often conducted during pre-anesthetic evaluations, allowing medical teams to anticipate and prepare for challenges before surgery or other procedures requiring intubation. Patient safety during anesthesia is a primary concern, and identifying potential intubation difficulties beforehand can prevent complications like brain damage or death if an airway cannot be secured.
The test assesses the mobility of the patient’s jaw and the alignment of their teeth, factors influencing how easily a breathing tube can be inserted. It evaluates mandibular movement, which can reveal anatomical features such as lower jaw anomalies, chin protrusion, or limited jaw movement that contribute to a difficult intubation. The ULBT helps identify these features.
How the Test is Performed and Scored
Performing the upper lip bite test is a simple, quick procedure that does not require special equipment. The patient sits upright in a neutral position and is instructed to bite their upper lip with their lower incisors. The examiner observes how much of the upper lip the lower teeth can cover. This observation relates to jaw mobility and teeth alignment, offering insights into potential airway access.
The test is scored into three classes based on how much the lower incisors can bite the upper lip. In Class I, the lower incisors can bite the upper lip completely, extending beyond its vermilion border, making the mucosa of the upper lip entirely invisible. Class II indicates that the lower incisors can bite the upper lip, but they cannot extend above the vermilion border, meaning the mucosa is partially visible. Class III is assigned when the lower incisors are unable to bite the upper lip at all. Class II and III results are considered indicative of a potentially difficult intubation.
Why This Test Matters
The upper lip bite test offers clinical utility in anesthesia planning, influencing medical decisions by providing an early warning of potential airway difficulties. When a patient scores in Class II or III, it suggests a higher likelihood of a challenging intubation, prompting the medical team to prepare for alternative airway management strategies. This proactive approach contributes to patient safety by allowing for the readiness of specialized equipment or techniques, such as a video laryngoscope or fiber optic bronchoscopy, which can aid in securing the airway.
While useful, the ULBT is not a standalone definitive test and is considered one of several tools used in airway assessment. Its predictive value varies, with studies showing a range of sensitivities and specificities. For instance, an abnormal ULBT (Class III) can increase the probability of a difficult intubation from approximately 10% to over 60%. However, its diagnostic accuracy can differ between populations, and some patients, such as those who are edentulous or have altered mental status, may not be able to perform the test.