Gastrointestinal function in critical illness-a complex interplay between the nervous and enteroendocrine systems

Abstract

Gastrointestinal (GI) dysfunction affects 40-80% of critically ill children and is associated with morbidity and mortality. GI function, specifically GI motility, is dependent on a complex interplay between the extrinsic and intrinsic nervous systems and the endocrine system. During critical illness the coordinated actions of these systems are disrupted resulting in GI dysmotility. The extrinsic parasympathetic nervous system is inhibited, thereby directly and indirectly contributing to GI dysmotility, whereas the sympathetic nervous system is upregulated. The enteric nervous system (ENS) is altered by local inflammatory and altered extrinsic nervous system signaling and the enteroendocrine system is dysregulated with variable up- and down-regulation of different GI hormones. Current approaches to diagnose GI motility at the bedside are primarily based on clinical assessments, which can be unreliable. Application of modalities such as ultrasound or serum biomarkers are promising diagnostic tools and may provide real-time guidance on GI motility for critically ill patients. Treatments for GI dysmotility remain limited, though research on the pathophysiology of GI dysmotility is guiding the development of novel therapies such as targeted GI hormone therapeutics to treat GI dysmotility. In this review, we present an overview of the physiology of GI motility during health and critical illness, the currently available modalities to diagnose GI motility in critical illness and available therapies. Understanding the role of the nervous and endocrine systems on GI dysmotility in critical illness will guide innovations in clinical practice and research, thereby advancing the diagnostic and therapeutic alternatives for this condition.