The purpose of this study was to compare tissue response and insulin bolus spread using straight and angled insulin infusion sets (IIS).
IIS with different cannula insertion angles (30° or 90°) were inserted subcutaneously every other day for 2 weeks in 11 swine and connected to an insulin pump (basal/bolus pattern). After 2 weeks, an insulin/contrast agent bolus was delivered while recording a pressure profile, evaluating maximum tubing pressure (pmax) and area under the pressure curve (AUC). The tissue-cannula specimen was excised and imaged using micro‑CT to measure bolus surface area (SA) and volume (V). Histopathological analysis of area of inflammation (AI) and thickness of inflammatory layer (LT) surrounding the cannula was carried out. Data were analyzed using ANOVA GLM, Kruskal Wallis, and post-hoc Bonferroni correction.
Insulin infusion through a straight cannula caused significantly higher pmax (p=0.005) and AUC (p=0.014). Bolus SA (30°: 314.0±84.2 mm2 vs 90°: 228.7±99.7 mm2, p<0.001) and V (30°: 198.7±66.9 mm3 vs 90°: 145.0±65.9 mm3, p=0.001) were larger using an angled IIS. Bolus SA and V decreased significantly over infusion set wear time independent of insertion angle (p<0.05). Straight cannulas caused a greater mean AI (30°: 9.1±4.0 mm2 vs 90°: 14.3±8.6 mm2, p<0.001) and LT (30°: 0.7±0.4 vs 90°: 1.2±0.7 mm, p<0.001). As the LT increased, pmax increased and bolus volume decreased.
Although a straight IIS is clinically preferred due to easier insertion, our data suggest that angled cannulas elicit less inflammation, and deliver an insulin bolus with lower tubing pressure and greater SA and V.