Gastrointestinal ultrasound in the critically ill: A narrative review and a proposal for a protocol

Critically ill patients are at risk of presenting with gastrointestinal dysfunction at intensive care unit admission or during their stay. However, identifying gastrointestinal dysfunction is difficult because clinical evaluation is frequently nonspecific and validated biomarkers are lacking. In this context, ultrasound of the digestive tract may help to identify gastrointestinal dysfunction. In this narrative review, we summarize available evidence and propose a protocol for assessment of the gastrointestinal tract with ultrasound. First, we report available evidence from use of four available protocols: the gastrointestinal and urinary tract sonography protocol, the acute gastrointestinal injury ultrasound score, the transabdominal gastrointestinal ultrasound protocol, and the Lai protocol, each addressing somewhat different aspects. Outputs from these protocols have been associated with clinical scores of gastrointestinal failure, feeding intolerance, and 28-day mortality. Second, we describe the potential pitfalls of using ultrasound in the critically ill, such as obesity, abdominal dressings, or the presence of intraluminal gas. Third, we suggest perspectives of ultrasound in monitoring the response to enteral nutrition and for early identification of nonocclusive mesenteric ischemia. Fourth, we propose a structured protocol for gastrointestinal ultrasound describing all the different structures that should be evaluated and provide detailed guidance for a clockwise abdominal examination. In conclusion, the use of a specific and structured protocol might help to identify patients presenting with gastrointestinal dysfunction, guide nutrition, and allow the proposal of pathophysiological hypotheses (complications of enteral nutrition, intra-abdominal infection, bowel ischemia, etc.). The benefit of using a structured protocol requires further investigation.