Patients who require general anaesthesia or ventilation to help them breathe while in intensive care, need a clear airway. This is usually achieved by inserting a tube to help air reach their lungs and a new Cochrane Review from May 2018 examines the evidence for different tests to help doctors assess how difficult this might be for patients with no immediately obvious problems with their breathing. We asked one of the authors, Jasmin Arrich from the Medical University of Vienna in Austria, to tell us what they found.
"Placing a tube into the patient’s airway, or tracheal intubation, is the best way to ensure that their airway stays clear and that air can get into their lungs during general anaesthesia, or when they need ventilation or oxygenation for other reasons. Before intubation, it’s common practice to determine if the patient has a difficult airway, which is a potentially life-threatening situation because they will not be able to breathe, and will quickly die.
There are several bedside airway examination tests to help doctors to anticipate possible difficulties before intubation and such tests are used every day by clinicians all across the world. However, there is little information about which test is most useful and we have investigated this further by reviewing the validity of different tests for detecting a difficult airway in patients with no apparent airway abnormalities.
We found no less than 133 eligible studies involving more than 840,000 patients on four continents. Most of the studies included patients undergoing elective surgery, and, overall, the evidence was of moderate to high quality. All studies focused on the assessment of predictors that would indicate if a patient was likely to have difficult face mask ventilation, laryngoscopy or intubation.
When we pooled the results, we found high variability among the tests. The upper lip bite test for diagnosing difficult laryngoscopy provided a summary sensitivity of 67%, which was higher than any of the other tests. However, this suggests that even this, the most sensitive test in the studies we reviewed, correctly identifies the presence of a problem only two-thirds of the time. The modified Mallampati test had the highest sensitivity for detecting difficult tracheal intubation, but its summary sensitivity of 51% means that it fails to identify the problem in nearly half the patients for whom it will be difficult to insert the tube.
In summary, bedside airway examination tests for detecting a difficult airway are intended as screening tests and are expected to miss only very few patients with a potential problem. They are recommended in airway management guidelines around the world, but we have found that they often fail to meet their goal and that most are little better than simply flipping a coin to decide if the patient has a difficult airway. On the other hand, the tests were consistently better at showing that a patient did not have a difficult airway when there really did not have one, but this is of little relevance in this context. In conclusion, therefore, standard bedside airway examination tests for difficult airways in patients with no apparent airway abnormalities do not appear to be good screening tests, and we urge great caution in their use and interpretation."