2026 FSA Podium and Poster Abstracts

Introduction: Obesity affects approximately 42% of adults in the United States and presents unique perioperative challenges related to altered respiratory mechanics, difficult airway management, and anesthetic pharmacology. Minimum alveolar concentration (MAC) is defined as the alveolar concentration of volatile anesthetic required to prevent movement in 50% of patients in response to surgical stimulus and serves as a population-based measure of anesthetic potency. MAC is known to vary with age, body temperature, thyroid function, pregnancy, and concomitant medications. However, whether obesity independently alters MAC remains uncertain. In contemporary anesthetic practice, neuromuscular blockade frequently eliminates movement as a clinical endpoint, despite movement forming the basis of MAC determination. Anesthesiologists must therefore rely on end-tidal concentrations to ensure adequate depth while minimizing postoperative respiratory compromise. If obesity alters MAC, failure to recognize this could increase the risk of intraoperative awareness in paralyzed patients. Clarifying this relationship is therefore clinically significant.

Methods: A structured literature review was conducted using PubMed to identify studies evaluating volatile anesthetic use in adults with obesity. Search terms included combinations of “minimum alveolar concentration,” “MAC-awake,” “end-tidal,” “desflurane,” “sevoflurane,” “isoflurane,” and obesity-related terms. Studies were included if they investigated volatile anesthetic potency, MAC-related outcomes, pharmacodynamics, or recovery characteristics in adults. Pediatric studies and those exclusively examining intravenous anesthetics were excluded. Titles and abstracts were screened, followed by full-text review. Data were extracted regarding study design, patient population, anesthetic agent, MAC outcomes, and recovery measures. Due to heterogeneity in study design and endpoints, quantitative meta-analysis was not performed.

Results: Across available studies, no consistent evidence demonstrated that increasing body mass index independently increases MAC requirements. Age consistently emerged as the dominant determinant of anesthetic potency, with MAC declining predictably across the lifespan. Most clinical studies in obese populations emphasized recovery characteristics rather than direct MAC measurement. Lower blood gas solubility agents, particularly desflurane, were frequently associated with faster emergence profiles. These differences appear attributable to uptake and elimination kinetics rather than altered intrinsic potency. Interventions that enhance anesthetic washout, such as increased minute ventilation with maintenance of normocapnia, shortened time to extubation without requiring higher MAC targets. In extreme obesity, higher rates of early respiratory complications were observed, reflecting physiologic vulnerability rather than increased anesthetic potency requirements.

Discussion: Current evidence does not support increasing MAC targets solely based on body mass index. Although anesthesiologists often select less soluble volatile agents in patients with obesity, this practice likely reflects concerns regarding respiratory safety, delayed drug accumulation, and postoperative recovery rather than differences in intrinsic potency. Because neuromuscular blockade removes movement as a clinical endpoint, accurate understanding of MAC in obesity is essential to ensure adequate depth and prevent awareness while avoiding unnecessary escalation of volatile dosing. Age-adjusted MAC values remain appropriate for titration in adults with obesity. Clinical strategies should emphasize physiologic optimization, structured ventilation, and deliberate washout rather than BMI-based increases in anesthetic concentration.

Figure

Tables