Gastric Ultrasound

Introduction

Perioperative aspiration of gastric contents is a serious complication of anesthesia associated with high morbidity and mortality. Mortality after aspiration pneumonia can be as high as 5% and it accounts for up to 9% of all anesthesia-related deaths. Prevention of perioperative pulmonary aspiration is part of the process of preoperative evaluation and preparation of the patient. The preoperative fasting guidelines were developed to lower the risk of pulmonary aspiration in patients undergoing surgery. They assist health care providers and patients in knowing when to stop eating and drinking. They are considered to be the standard of clinical care and evidence-based practice. 
 
These guidelines however are only intended to a patient population of all ages undergoing elective procedures. The guidelines do not apply to patients who undergo procedures with no anesthesia or only local anesthesia when upper airway protective reflexes are not impaired and when no risk factors for pulmonary aspiration are apparent. The guidelines are also limited in that they may not apply to or may need to be modified for patients with coexisting diseases or conditions that can affect gastric emptying or fluid volume (e.g., pregnancy, obesity, diabetes, hiatal hernia, gastroesophageal reflux disease, ileus or bowel obstruction, emergency care, or enteral tube feeding) and patients in whom airway management might be difficult. These conditions severely limit the applicability to all patients. Finally, the use of cricoid pressure is has been debated since in up to 50% of the population the esophagus is not behind the trachea and thus ineffective when performed. Enter the era of gastric ultrasound.
 
Gastric ultrasound is a point-of-care tool for aspiration risk assessment. It can determine the nature of the content (empty, clear fluid, thick fluid / solid) and when clear fluid is present, its volume can be estimated. POCUS  can be used to measure the gastric antrum at this time since it is the easiest to interrogate. The gastric antrum expands from a baseline empty state as fluid enters the stomach in a linear relation to that of the rest of the body of the stomach up to 300ml. Volumes in excess of 300 ml result in only modest further increases in antral size, with excess volumes being accommodated by more proximal areas of the stomach.