The Difficult Airway: Incidence and Predictors in Lean vs. Obese Patients in a Large Public Teaching Hospital

The study will enroll 4500 ASA physical status 1-4 patients who are scheduled to undergo surgery under general endotracheal anesthesia (GETA) at Parkland Hospital. A research assistant will identify eligible patients using the electronic medical record. After it is deemed that the patient satisfies all inclusion and exclusion criteria, the anesthesia provider or research assistant will approach the patient in the preoperative surgery holding area to ask for their permission to enroll in the study. Only study team personnel will ask potential patients for participation in the study; anesthesia providers who are not study team personnel will not be allowed to consent patients for the study. All relevant information to the study will be provided and the patient will be asked to sign an informed consent. After consent is obtained, measurements of the patient's anatomical features including thyromental distance, sternomental distance, neck circumference, interincisor distance, mandibular protrusion, and Mallampati score will be taken and recorded by the research assistant or anesthesia provider.

In the operating room, patients will have standard ASA monitors (NIBP, SpO2, EKG, ETCO2, temperature) placed. Lean patients will be placed in the standard "sniffing" position while obese patients will be placed in the "ramped" position as previously described. All patients will undergo pre-oxygenation for at least 3 minutes prior to induction of anesthesia. Patients will undergo induction of general anesthesia according to a standardized protocol that does not differ from the usual standard of care. The initial blade used for laryngoscopy will be selected by the anesthesia provider according to the characteristics of the patient as has been recommended by previous authors. After induction of general anesthesia, a research assistant will ask the anesthesia provider the degree of difficulty of mask ventilation and laryngoscopy using a standardized questionnaire modified from the intubation difficulty score. For mask ventilation, any adjunct use of equipment such as an oral airway or nasopharyngeal airway will be recorded. If two-handed ventilation is used, it will be recorded as well. The type of laryngoscope blade and Cormack-Lehane grade during laryngoscopy will be recorded. The level of training of the laryngoscopist (resident vs CRNAs vs faculty) and how many years they have been in that role will be recorded. The time from induction to intubation will also be recorded, based on the time those events are marked in the electronic medical record, as well as the lowest SpO2 that occurred between induction to intubation.

The intubation difficulty scale (IDS), which has previously been validated, will be used to score the intubation. This scale has been used in comparing difficult tracheal intubation in lean vs. obese patients.

The IDS will be comprised of 7 questions with numerical values for each question, resulting in a cumulative score. Those with an IDS score <5 will be considered "not difficult" and those with an IDS score ≥5 will be considered "difficult." A "failed intubation" will be defined as that in which the airway cannot be secured in a non-invasive fashion (e.g., cricothyrotomy) or the patient has to be awakened. The 7 questioned used to determine the IDS score will be the same as those used by Adnet et al:

1. Number of additional intubation attempts
2. Number of additional operators
3. Number of alternative intubation techniques used
4. Laryngoscopic view (Grade 1 = 0, Grade 2 = 1, Grade 3 = 2, Grade 4 = 3)