Airway Changes in Patients Undergoing Elective Surgical Procedures in the Prone and Trendelenburg Positions

Background: One of the primary methods to assess airway dimension changes is the Modified Mallampati Score (MMS). MMS has been a valuable tool in assessing difficulty of intubation in previous studies as it is a simple, reproducible, and reliable preoperative and preanesthetic assessment of oral volume. MMS is evaluated by asking the patient to open their mouth and protrude their tongue without phonation. A score on a scale of 1-4 is assigned based on identifiable intraoral anatomic structures. MMS scores of 3 and 4 are strongly associated with difficult laryngoscopy and intubation.

Extensive observational research in the obstetric population has demonstrated that airway changes, including increasing MMS and decreasing oropharyngeal volume, occur during labor. It has been found that 63% of parturients experienced an increase in MMS over the course of their labor, with the fraction of patients scoring 3 or 4 peaking at 51.7%, compared with only 10.3% early in labor. Notably, of those patients that reached a class 4, 21% remained at that classification 48 hours postpartum. It has been found that 18% of patients whose airway class worsened during labor had not returned to their prelabor class 36-48 hours after delivery.

These obstetric findings have prompted a limited number of studies investigating airway changes in patients undergoing surgical procedures. This study will focus on surgeries in the prone and Trendelenburg positions, as they would intuitively predispose patients to edema and fluid retention in the head and neck. MMS increased in 78% of patients, with 29% increasing by two or more classes in patients undergoing lumbar spine surgery in the prone position. Furthermore, although laparoscopic surgery has been shown to increase lung and chest wall mechanical impedance, which leads to increases in abdominal and intrathoracic pressure, as well as an increase in central venous pressure with subsequent increases in intraocular pressure, no studies have been performed to specifically track resultant airway changes. Lastly, to investigators' knowledge no studies have investigated the postoperative resolution of airway changes after either type of procedure.

Rationale: There is evidence, both investigational and anecdotal, that airway changes may occur during certain surgeries or procedures, and that patient positioning may play a large role in precipitating them. However, research on this phenomenon in the surgical population, unlike the obstetric population, is sparse. Similarly, investigations into the time required for airway changes to regress back to baseline has been included in a number of obstetric airway studies, but not in any surgical ones. Lastly, it has been suggested that other surgical factors, such as fluid balance or procedure duration, may alter the degree of airway changes, but results from the few recent studies on the topic have been unclear. Thus, this study seeks to further investigate the influence of prone and Trendelenburg positioning, as well as surgical variables, on perioperative airway changes, and quantify the time required for patients' airways to return to their preoperative state.

Based on clinical observation, the primary hypothesis is that there will be a significant difference between mean scoring class change between 2 study groups from preoperative baseline to initial postoperative assessment. Investigators hypothesize that T-burg surgery patients will have a mean change of 2 classes compared to a mean change of only one class for prone spine surgery patients.

The secondary hypothesis is that airway changes occurring in patients undergoing prone procedures will resolve significantly sooner than (3 - 4 hours) than those of patients undergoing Trendelenburg surgeries (> 4 hours).

Thirdly investigators will investigate the effects of demographic, physiological, and surgical \& anesthetic variables on postoperative MMS changes and their resolution.