Impact of knife size and saline-optimized electrosurgical modes on tissue effects in saline-immersion third-space...

Saline-immersion therapeutic endoscopy (SITE) enhances visualization and haemostasis, but it alters electrosurgical behavior due to the high conductivity of saline which reduces tissue impedance and peak voltage. These effects may vary depending on the knife size, as electrode diameter influences current density. An ex vivo porcine gastric mucosa model was used to compare three electrosurgical knives with different sizes, namely one with a thick electrode (HybridKnife^® T-Type, 1.5 mm) and two with thin electrodes (HYBRIDKnife^® flex I-Type, 0.5 mm; DualKnife J-Type, 0.4 mm) - in air and under saline across seven electrosurgical modes (2 cutting, 3 coagulation and 2 dissection modes). Electrical parameters (impedance, peak voltage, power output), cutting success, and lateral thermal spread were measured during 252 standardized incisions. Statistical analysis was performed using both univariate and multivariate methods. The average decrease in impedance when passing from air to saline immersion was higher for thick as compared with thin knives (92% vs. 55%, p < 0.001) across multiple modes. Corresponding increase in power was also higher for thick (up to 19-fold) than for thin (up to 5-fold, p < 0.001) knives, while peak voltage decreased by 30% for thick knives and increased by approximately 2% for thin knives (p < 0.001). Across cutting and dissection modes, both thin knives sustained 100% cutting success in air and under saline, whereas the thick knife declined from 100% to 75% under saline. Lateral thermal spread increased from < 1 mm in CO₂ to 1.35 mm (256%) in saline for the thick knife, while it was ≤ 0.8 mm (71%) for thin knives (p < 0.001, between thin and thick knives), irrespective of the setting. Electrode diameter and saline immersion were the strongest independent predictors of lateral spread. The effect of saline immersion on impedance and voltage is dramatically higher when using thicker than thinner knives This may contribute to the differing tissue effects observed with varying electrode sizes in third-space endoscopy.