Principles of diathermy relevant to gastrointestinal endoscopy

Electrosurgery, commonly referred to as diathermy, underpins most therapeutic gastrointestinal (GI) endoscopic procedures, including polypectomy, endoscopic mucosal resection, endoscopic submucosal dissection, endoscopic sphincterotomy and third-space endoscopy. Despite its widespread use, many endoscopists rely on empirically selected generator settings without a clear understanding of the physical principles that govern tissue effects and safety. This narrative review explains the core concepts of diathermy most relevant to GI endoscopy, translating electrophysical principles into clinically meaningful guidance. Key determinants of tissue effect including voltage, impedance, current density, waveform modulation, electrode design, application time and procedural environment are discussed in practical terms. Particular emphasis is placed on understanding why identical electrosurgical settings may produce markedly different outcomes depending on tissue contact, technique and whether procedures are performed in air or saline immersion. Commonly used electrosurgical modes are reviewed with reference to their dominant tissue effects and typical endoscopic applications, highlighting frequent pitfalls and misconceptions. The influence of monopolar versus bipolar configurations, as well as environment-dependent behaviour of electrosurgical currents, is addressed to support safer and more predictable practice. This review aims to equip trainees and general gastroenterologists with a conceptual understanding of diathermy that can be applied across devices, procedures and clinical contexts.