Effect of Extrinsic Warming of Low-Osmolality CT Contrast Media (Iohexol 350) on Extravasations and Patient Reaction Rates: A Retrospective Study.

Background: Extrinsic warming of iodinated CT contrast media to body temperature reduces viscosity and injection pressures. However, studies examining the effect of extrinsic warming on clinical adverse events are limited in number and provide conflicting results. Therefore, consensus practice recommendations have been sparse. Objective: To compare rates of extravasation, allergic/allergic-like reactions, and physiologic reactions between iohexol 350 warmed to body temperature (37°C) and maintained at room temperature. Methods: This retrospective study compared adult patients who received CT examinations using IV iohexol 350 that had either been warmed to body temperature or maintained at room temperature. At our institution, contrast media had historically been warmed to body temperature prior to a protocol change unrelated to this investigation. Patient and CT examination characteristics were extracted from the electronic medical record. Adverse events, including extravasations, allergic/allergic-like reactions, and physiologic reactions, were compared between groups. Results: A total of 3939 patients received contrast media warmed to body temperature before the protocol change; 3933 patients received contrast media at room temperature after the protocol change. The body temperature group experienced 11 (0.28%; 95% CI 0.14%, 0.50%) adverse events, all extravasations; allergic/allergic-reaction rate was 0.00% (97.5% CI 0.00%, 0.09%). The room temperature group experienced 17 (0.43%; 95% CI 0.25%, 0.69%) adverse events [13 (0.33%; 95% CI 0.17%, 0.56%) extravasations; 4 (0.10%; 95% CI 0.03%, 0.26%) allergic/allergic-like reactions]. No physiologic reaction occurred in either group. The two groups were not different in terms of overall reaction rate (p=.19), extravasation rate (p=.69), allergic/allergic-like reaction rate (p=.06), or physiologic reaction rate (p>.99). Logistic regression adjusting for patient and CT characteristics (age, sex, conventional CT vs CTA, contrast media volume, injection location, needle gauge) showed no significant association of patient group and adverse reaction rate (odds ratio=2.19, 95% CI 0.68-7.00). Multivariable regression modeling demonstrated an excess of 0.27 adverse events per 100 patients within the room temperature group, below a 0.6% non-inferiority margin. Conclusion: The data suggest that maintaining iohexol 350 at room temperature is non-inferior to warming the agent to body temperature before injection. Clinical Impact: The resources involved to prewarm iohexol 350 before injection may not be warranted.