The Million Anesthesia Cases Study (MACS) - a Cohort Study of Preoperative Fasting and Perioperative Outcomes

Perioperative fasting has historically been viewed as a low-risk intervention. However, preliminary data indicate that perioperative loss of nutrition and fluids is likely harmful. This study intends to characterize perioperative fasting practices and their potential effects on clinical outcomes through possible effects on patient well-being (anxiety, hunger, thirst), physiology (hypovolemia, hypotension), perioperative aspiration, etc. The research team hypothesized that in addition to known adverse effects on patients' well-being, prolonged preoperative fasting adversely affects circulating blood volume-related (hypotension, decreased urine output etc.) and glucose metabolism-related (e.g., hypo/hyperglycemia) perioperative physiology. The investigators will also test for an association between the duration of preoperative fasting and the risk of perioperative pulmonary aspiration. Additional knowledge on the potential adverse effects of preoperative fasting will inform preoperative fasting policies and research interventions that are relevant to hundreds of millions of patients subjected to preoperative/preprocedural fasting worldwide each year.

NCT Number	NCT07022951
Lead Sponsor	Massachusetts General Hospital Collaborators: Anesthesia Patient Safety Foundation (APSF)
Conditions	Anesthesia, Sedation, Monitored Anesthesia Care, Procedure, Surgery, Day, Surgery, Surgery Scheduled, Fasting Before Operation +1 more
Enrollment	1,200,000 participants
Start Date	2016-01-01
Primary Completion	2028-12-31 (estimated)
Study Completion	2030-12-31 (estimated)
Updated on ClinicalTrials.gov	2026-04-08