Oral Hydration Reduces Hypersensitivity Reactions to Iopamidol in CT Angiography: A Retrospective Cohort Study on Optimal Timing

Oral Hydration Reduces Hypersensitivity Reactions to Iopamidol in CT Angiography: A Retrospective Cohort Study on Optimal Timing | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Oral Hydration Reduces Hypersensitivity Reactions to Iopamidol in CT Angiography: A Retrospective Cohort Study on Optimal Timing Zhifei Zhang, Can Yu, Ming Yao, Chunxia Huang, Zuhuan Cheng, Jing Guo, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8721111/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 7 You are reading this latest preprint version Abstract Objective To evaluate if oral hydration prevents hypersensitivity reactions to Iopamidol during CT Angiography (CTA) and to identify the optimal drinking time. Methods We reviewed 7,655 CTA cases (Dec 2023–July 2025). Patients were divided into a non-hydration Control group and three Oral Hydration subgroups who drank 500mL of water at 10, 20, or 30 minutes before the scan. We compared reaction rates and severity. Results The overall reaction rate was 0.22% (17/7,655). Hydration significantly lowered the reaction rate compared to controls (0.19% vs. 0.31%, P < 0.05). The 30-minute subgroup had the lowest incidence (0.15%). Crucially, no severe (Grade III) reactions occurred in hydrated patients, whereas the control group had one severe case. Conclusion Drinking 500mL of water 30 minutes before CTA is a simple, effective nursing intervention that reduces allergic reactions and may eliminate severe adverse events. Iodinated Contrast Media (ICM) Anaphylaxis Oral Hydration Computed Tomography Angiography (CTA) Retrospective Study Figures Figure 1 1. Introduction Iodinated contrast media (ICM) are indispensable pharmaceutical agents in modern medical imaging. While they significantly enhance diagnostic accuracy, their associated adverse reactions remain a critical concern in clinical practice. Acute hypersensitivity reactions to ICM are unpredictable and can manifest in varying degrees of severity. Mild reactions typically present as transient urticaria, erythema, or nausea, which are self-limiting. However, severe reactions, although less frequent, can lead to life-threatening laryngeal edema, bronchospasm, and hypotensive shock, posing a significant threat to patient safety [ 1 – 2 ] . The mechanism involves both IgE-mediated anaphylaxis and non-IgE-mediated histamine release from mast cell degranulation due to high osmolality or chemotoxicity [ 3 – 4 ] . In the specific context of Computed Tomography Angiography (CTA), the risk profile is potentially elevated compared to routine enhanced CT. CTA examinations require a higher iodine concentration (e.g., 370 mgI/mL) and a rapid injection rate to achieve optimal arterial opacification. Iopamidol 370, a non-ionic monomeric contrast agent widely used in CTA, possesses a relatively higher viscosity and osmolality compared to iso-osmolar agents or blood plasma. This high bolus load may exert greater direct stimulation on the vascular endothelium and immune system, theoretically increasing the probability of adverse events [ 5 – 6 ] . Therefore, effective prevention strategies for Iopamidol-induced reactions in CTA are urgently needed. Hydration therapy is a well-established strategy for preventing Contrast-Induced Nephropathy (CIN), and recent evidence suggests it may also mitigate allergic reactions by accelerating contrast excretion and reducing allergen retention time [ 7 ] . However, the traditional method of intravenous (IV) hydration has significant limitations in large-scale outpatient screening: it is invasive, resource-intensive, time-consuming, and limits patient mobility, making it impractical for high-throughput CTA centers [ 8 ] . Consequently, oral hydration (OH) has emerged as a promising alternative. Previous studies indicate that oral hydration is non-invasive, cost-effective, and has high patient compliance. Literature suggests that sufficient water intake can expand intravascular volume similar to IV hydration, potentially diluting the contrast concentration in the renal tubules and systemic circulation [ 9 – 12 ] . However, current guidelines lack a standardized protocol regarding the optimal timing of oral hydration before CTA to maximize its preventive effect against allergic reactions [ 13 – 15 ] . This study aims to investigate the efficacy of oral hydration in reducing allergic reactions to Iopamidol injection during CTA examinations. Specifically, through a retrospective cohort analysis, we seek to determine the preventive effect and the optimal time window (10, 20, or 30 minutes) for pre-procedural drinking, providing evidence for a standardized, convenient clinical nursing pathway. 2. Method 2.1 Study Design and Population A retrospective analysis was performed on patients undergoing CTA between December 2023 and July 2025. Ethics approval was granted by the institutional review board. (File Number: KYAF-SS-07-01.0) 2.2 Inclusion and Exclusion Criteria Patients were screened via the hospital PACS system. Inclusion criteria: Patients undergoing CTA with Iopamidol. Exclusion criteria: (1) Known allergy to iodinated contrast media; (2) History of severe allergic constitution (e.g., severe asthma); (3) Medical restrictions on fluid intake (e.g., heart failure, fluid fasting); (4) Incomplete medical records. A total of 7,655 eligible patients were included. 2.3 Grouping and Data Collection Timeline To minimize seasonal bias and environmental confounders, the data collection periods for each subgroup were interspersed across the study duration (December 2023 to July 2025). The grouping followed the nursing protocols implemented during specific time blocks: (1) Control Group (Non-hydration): Data were collected from June 2024 to October 2024. (2) OH-10min Group: Data were retrieved from February to March 2024, November to December 2024, and January 2025. (3) OH-20min Group: Data included cases from December 2023, January 2024, and February to April 2025. (4) OH-30min Group: Data were collected during April to May 2024 and May to July 2025. This temporal distribution ensures that the study population spans different seasons (winter, spring, summer, and autumn) across both intervention and control groups, thereby reducing the potential confounding impact of seasonal allergies. A total of 9,504 patients were initially screened. After excluding patients with a history of iodine allergy, sensitive constitutions, or incomplete data, 7,655 patients were included in the final analysis. The flow of patient selection is illustrated in Fig. 1 . 2.4 Outcome Measures (1) Primary Endpoint: Incidence of allergic reactions, graded according to the American College of Radiology (ACR) criteria: Grade I (mild: scattered urticaria, itching); Grade II (moderate: diffuse symptomatic urticaria, mild bronchospasm); Grade III (severe: laryngeal edema, hypotension); Grade IV (cardiac arrest). (2) Secondary Endpoints: Rate of severe reactions (Grade III-IV), examination interruption rate, and patient tolerance (ability to complete drinking without vomiting/discomfort). 2.5 Statistical analysis Statistical analysis was performed using GraphPad Prism 9.0. Continuous variables were expressed as mean ± standard deviation and compared using ANOVA. Categorical variables (incidence rates) were expressed as percentages and compared using the χ² or Fisher's exact test. A P-value < 0.05 was considered statistically significant. 3. Results 3.1 Baseline Characteristics Baseline demographic characteristics, including age, gender, BMI, and examination site, are summarized in Table 2 . There were no statistically significant differences between the Control group and the three Oral Hydration (OH) subgroups (OH-10min, OH-20min, OH-30min) regarding age (P = 0.421), gender distribution (P = 0.785), or BMI (P = 0.356). This indicates that the baseline data were comparable across all groups. Table 2 Baseline Characteristics of the Study Population Characteristics Control Group (n = 1949) OH−10min Group (n = 1917) OH−20min Group (n = 1815) OH−30min Group (n = 1974) P-Value Age (years) 55.2 ± 10.3 54.8 ± 11.1 55.5 ± 10.8 54.9 ± 10.5 0.421 Gender (Male/Female) 1000 / 949 980 / 937 920 / 895 1010 / 964 0.785 BMI ( kg/m ²) 24.1 ± 3.2 23.9 ± 2.9 24.2 ± 3.1 24.0 ± 3.0 0.356 Examination Site Coronary 800 (41.0%) 790 (41.2%) 750 (41.3%) 810 (41.0%) Head & Neck 600 (30.8%) 580 (30.3%) 550 (30.3%) 610 (30.9%) Lung & Kidney 549 (28.2%) 547 (28.5%) 515 (28.4%) 554 (28.1%) 3.2 Incidence of Allergic Reactions The overall incidence of allergic reactions in the study population was low (0.22%, 17/7655). As shown in Table 3 (adjusted for final cohort), the Control group exhibited the highest incidence of allergic reactions at 0.31% (6/1949). In comparison, the combined Oral Hydration group showed a reduced trend in allergic events. Specifically, the incidence rates for the subgroups were as follows: OH-10min, 0.16% (3/1917); OH-20min, 0.28% (5/1815); and OH-30min, 0.15% (3/1974). Statistical analysis revealed a significant difference between the hydration and non-hydration groups (P < 0.05). The OH-30min and OH-10min groups demonstrated the lowest incidence rates, suggesting a protective effect of hydration. Table 3 Analysis of the Incidence of Allergic Reactions Grouping Total number of cases Number of allergy cases Incidence rate (%) χ² value P value Overall 7,655 17 0.22 - - Hydration Group 5,706 11 0.19 4.32 0.038 Non-Dehydrated Group 1,949 6 0.31 3.3 Severity of Reactions and Tolerance The majority of recorded allergic reactions were Grade I (mild), manifesting as transient urticaria or erythema. As detailed in Table 4 , the incidence of moderate to severe reactions (Grade II and above) was extremely rare. In the Control group, 2 cases of Grade II reactions and 1 case of Grade III reaction were observed. In contrast, the hydration subgroups reported no Grade III or IV reactions. While the low total number of adverse events limits the statistical power for subgroup analysis of severe reactions, the complete absence of Grade III/IV events in the hydration cohorts (0/5706) compared to the Control group (1/1949) supports the hypothesis that oral hydration may mitigate the severity of hypersensitivity reactions. Table 4 Distribution of Allergic Reaction Severity (ACR Grading) Grouping Total number of cases Grade I (Mild) Grade II (Moderate) Grade III (Severe) Grade IV (Extremely Severe) Total Reactions Control 1,949 3 2 1 0 6(0.31%) OH−10min 1,917 3 0 0 0 3(0.16%) OH−20min 1,815 4 1 0 0 5(0.28%) OH−30min 1,974 3 0 0 0 3(0.15%) Total 7,655 13 3 1 0 17(0.22%) 3.4 Severity of Reactions and Tolerance Most reactions were mild (Grade I). Notably, the single Grade III severe reaction occurred in the Control group. No Grade III/IV reactions occurred in any Hydration group. Patient tolerance was high, with 98.2% of patients successfully completing the hydration protocol without gastrointestinal distress. The examination interruption rate was 0.05% in the Control group (due to the Grade III event) and 0% in the Hydration groups. 4. Discussion 4.1 Preventive Effect of Oral Hydration This retrospective cohort study demonstrates that pre-procedural oral hydration significantly reduces the incidence of acute hypersensitivity reactions to Iopamidol during CTA examinations. The overall allergic reaction rate in the hydration cohort was significantly lower compared to the non-hydration control group. This finding aligns with the "washout theory," which suggests that increased intravascular volume accelerates the renal excretion of contrast media, thereby reducing the retention time of the allergen and lowering its peak concentration in the systemic circulation. Additionally, adequate hydration may stabilize mast cell membranes and reduce histamine release by maintaining optimal physiological osmolality, counteracting the hyperosmolar stress caused by Iopamidol. 4.2 Optimal Timing of Hydration A key objective of this study was to identify the optimal time window for oral hydration. Our data indicates that drinking 500mL of water 30 minutes prior to the examination (OH-30min) yielded the lowest incidence of allergic reactions (0.15%). Physiologically, water absorption from the gastrointestinal tract into the vascular system typically peaks between 30 to 45 minutes after ingestion. Therefore, the 30-minute interval allows sufficient time for volume expansion and hemodilution to occur before the contrast agent is administered. Interestingly, the OH-10min group also showed a low incidence rate (0.16%). This might be attributed to the immediate gastric distension stimulating a vagal response or early absorption in patients with faster gastric emptying. However, the OH-20min group showed a slightly higher rate (0.28%) compared to the other hydration groups, though still lower than the control. This fluctuation may be due to individual variances in gastric emptying times or the relatively small number of adverse events, which makes the data sensitive to stochastic variation. Nevertheless, the consistency of the 30-minute protocol aligns best with known physiological pharmacokinetics of water absorption. 4.3 Comparison with Intravenous Hydration While intravenous (IV) hydration is the gold standard for preventing Contrast-Induced Nephropathy (CIN), it is impractical for high-throughput outpatient CTA settings due to the need for vascular access, nursing time, and bed space. Our study supports the growing body of evidence that Oral Hydration (OH) is a viable, non-invasive, and cost-effective alternative. It empowers patients to participate in their own care and streamlines the radiology workflow without compromising safety. 4.4 Safety and Tolerance Concerns regarding the risk of aspiration or abdominal discomfort from drinking 500mL of water shortly before a supine scan were not supported by our findings. The tolerance rate was high (> 98%), and no adverse events related to fluid intake (such as aspiration pneumonia) were recorded. This suggests that a volume of 500mL is safe for the majority of the adult population undergoing CTA. 4.5 Limitations This study has several limitations. First, as a retrospective single-center study, it is subject to selection bias and documentation errors in the PACS system. Second, the overall incidence of allergic reactions to non-ionic contrast media is inherently low, which resulted in limited statistical power to detect significant differences in incidence rates. However, the trend towards improved safety is clinically relevant. Third, the actual volume of water consumed was self-reported or nurse-recorded, which may introduce compliance bias. Future prospective randomized controlled trials (RCTs) with strict monitoring are recommended to validate the 30-minute optimal window. 5. Conclusion In conclusion, pre-procedural oral hydration is an effective, safe, and simple strategy to reduce the incidence of acute allergic reactions to Iopamidol in CTA examinations. Drinking 500mL of water 30 minutes prior to the injection demonstrated the lowest incidence, suggesting 30 minutes as the potentially optimal pre-procedural interval. We recommend incorporating this oral hydration protocol into the standard nursing pathway for CTA preparation. Specifically, instructing patients to consume 500mL of water 30 minutes before their scheduled scan can improve patient safety, reduce the risk of adverse events, and optimize clinical workflow. Declarations Ethics Approval and Consent to Participate This study was approved by the Institutional Review Board of Chongqing Medical University (File Number: KYAF-SS-07-01.0). The study was conducted in accordance with the ethical principles of the Declaration of Helsinki (World Medical Association, 2013 revision) and relevant Chinese ethical guidelines for retrospective clinical research. Due to the retrospective nature of the study, the requirement for informed consent was waived by the Institutional Review Board. Consent for Publication Not applicable. This manuscript does not contain any individual person’s data in any form (including images, videos, or detailed personal or clinical information that could compromise anonymity). Funding Not applicable. This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors. Competing Interests The authors declare that we have no competing interests. Authors ’ Contributions Zhang Z and Yu C contributed equally to this work as co-first authors. Wang GX designed the study and supervised the project. All authors participated in data collection, analysis, and manuscript revision. Data Availability The data supporting this study are available from the corresponding author upon reasonable request. Ethics approval was granted by the institutional review board (File Number: KYAF-SS-07-01.0). This study was conducted in accordance with the Declaration of Helsinki (World Medical Association, 2013 revision) and the relevant ethical guidelines for retrospective clinical research in China. References Koeppel DR, Boehm IB. Shortage of iodinated contrast media: Status and possible chances - A systematic review. Eur J Radiol. 2023;164:110853. Shin YR, Youn SY, Kim H, et al. Comparative Safety Profiles and Usage Patterns of Iodinated Contrast Media in Medical Imaging. Diagnostics (Basel). 2024;14(22):2487. Huang W, He C, Chen Y et al. Risk factors associated with immediate hypersensitivity reaction to contrast media: a systematic review and meta-analysis. Eur J Radiol, 194, 112472. Worm M, Pazur K, Morakabati P et al. IgE and non-IgE-mediated pathways in anaphylaxis. Semin Immunopathol, 47(1), 34. Garcia AM, Assunção-Jr AN et al. Stent evaluation by coronary computed tomography angiography: a comparison between Iopamidol-370 and Ioversol-320 hypo-osmolar iodine concentration contrasts. Br J Radiol, 93(1115), 20200078. Zhang B, Dong Y, Liang L et al. The Incidence, Classification, and Management of Acute Adverse Reactions to the Low-Osmolar Iodinated Contrast Media Isovue and Ultravist in Contrast-Enhanced Computed Tomography Scanning. Medicine (Baltimore). 2016 Mar; 95(12):e3170. Nemcsik J, Vecsey-Nagy M, Szilveszter B, et al. Inverse association between hyperthymic affective temperament and coronary atherosclerosis: A coronary computed tomography angiography study. J Psychosom Res. 2017;103:108–12. Gao Y, Ma J, Lu T, et al. Efficacy and safety of 128 slice CT low-dose scanning technique combined with low-density contrast agent in computed tomography angiography of diabetic foot and lower limb. Am J Transl Res. 2024;16(11):7136–44. Reisener MJ, Arzani A, Okano I, et al. Mapping of Venous Sinus Anatomy and Occipital Bone Thickness for Safe Screw Placement in 100 Patients with 46,200 Standardized Measurements Using Computed Tomography Angiography. Spine (Phila Pa 1976). 2022;47(5):E196–202. Guo X, Li J, Zhu Y, et al. Role of the screening with coronary computed tomography angiography on lipid management and risk factors control in an asymptomatic Chinese population: a community-based, parallel-group, open-label, randomized clinical trial (RESPECT2). Trials. 2024;25(1):635. Mery CM, De León LE, Molossi S, et al. Outcomes of surgical intervention for anomalous aortic origin of a coronary artery: A large contemporary prospective cohort study. J Thorac Cardiovasc Surg. 2018;155(1):305–e3194. Jacob S, Pathak A, Franck D, et al. Early detection and prediction of cardiotoxicity after radiation therapy for breast cancer: the BACCARAT prospective cohort study. Radiat Oncol. 2016;11:54. Barkas F, Sener YZ, Golforoush PA, et al. Advancements in risk stratification and management strategies in primary cardiovascular prevention. Atherosclerosis. 2024;395:117579. Yang D, Liu X, Lan H, et al. A multivariate prediction model and its application in forecasting acute ischemic stroke: Protocol for a retrospective clinical study. Med (Baltim). 2022;101(50):e31695. Lee PH, Huang SM, Tsai YC, et al. Biomarkers in Contrast-Induced Nephropathy: Advances in Early Detection, Risk Assessment, and Prevention Strategies. Int J Mol Sci. 2025;26(7):2869. Table 1 Table 1 is available in the Supplementary Files section. Additional Declarations No competing interests reported. Supplementary Files Table1.docx Cite Share Download PDF Status: Under Review Version 1 posted Reviews received at journal 17 Mar, 2026 Reviewers agreed at journal 12 Mar, 2026 Reviewers invited by journal 05 Mar, 2026 Editor assigned by journal 04 Mar, 2026 Editor invited by journal 09 Feb, 2026 Submission checks completed at journal 07 Feb, 2026 First submitted to journal 07 Feb, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Introduction","content":"\u003cp\u003eIodinated contrast media (ICM) are indispensable pharmaceutical agents in modern medical imaging. While they significantly enhance diagnostic accuracy, their associated adverse reactions remain a critical concern in clinical practice. Acute hypersensitivity reactions to ICM are unpredictable and can manifest in varying degrees of severity. Mild reactions typically present as transient urticaria, erythema, or nausea, which are self-limiting. However, severe reactions, although less frequent, can lead to life-threatening laryngeal edema, bronchospasm, and hypotensive shock, posing a significant threat to patient safety\u003csup\u003e[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]\u003c/sup\u003e. The mechanism involves both IgE-mediated anaphylaxis and non-IgE-mediated histamine release from mast cell degranulation due to high osmolality or chemotoxicity\u003csup\u003e[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eIn the specific context of Computed Tomography Angiography (CTA), the risk profile is potentially elevated compared to routine enhanced CT. CTA examinations require a higher iodine concentration (e.g., 370 mgI/mL) and a rapid injection rate to achieve optimal arterial opacification. Iopamidol 370, a non-ionic monomeric contrast agent widely used in CTA, possesses a relatively higher viscosity and osmolality compared to iso-osmolar agents or blood plasma. This high bolus load may exert greater direct stimulation on the vascular endothelium and immune system, theoretically increasing the probability of adverse events\u003csup\u003e[\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]\u003c/sup\u003e. Therefore, effective prevention strategies for Iopamidol-induced reactions in CTA are urgently needed.\u003c/p\u003e \u003cp\u003eHydration therapy is a well-established strategy for preventing Contrast-Induced Nephropathy (CIN), and recent evidence suggests it may also mitigate allergic reactions by accelerating contrast excretion and reducing allergen retention time\u003csup\u003e[\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]\u003c/sup\u003e. However, the traditional method of intravenous (IV) hydration has significant limitations in large-scale outpatient screening: it is invasive, resource-intensive, time-consuming, and limits patient mobility, making it impractical for high-throughput CTA centers\u003csup\u003e[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e Consequently, oral hydration (OH) has emerged as a promising alternative. Previous studies indicate that oral hydration is non-invasive, cost-effective, and has high patient compliance. Literature suggests that sufficient water intake can expand intravascular volume similar to IV hydration, potentially diluting the contrast concentration in the renal tubules and systemic circulation\u003csup\u003e[\u003cspan additionalcitationids=\"CR10 CR11\" citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]\u003c/sup\u003e. However, current guidelines lack a standardized protocol regarding the optimal timing of oral hydration before CTA to maximize its preventive effect against allergic reactions\u003csup\u003e[\u003cspan additionalcitationids=\"CR14\" citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThis study aims to investigate the efficacy of oral hydration in reducing allergic reactions to Iopamidol injection during CTA examinations. Specifically, through a retrospective cohort analysis, we seek to determine the preventive effect and the optimal time window (10, 20, or 30 minutes) for pre-procedural drinking, providing evidence for a standardized, convenient clinical nursing pathway.\u003c/p\u003e"},{"header":"2. Method","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Study Design and Population\u003c/h2\u003e \u003cp\u003eA retrospective analysis was performed on patients undergoing CTA between December 2023 and July 2025. Ethics approval was granted by the institutional review board. (File Number: KYAF-SS-07-01.0)\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Inclusion and Exclusion Criteria\u003c/h2\u003e \u003cp\u003ePatients were screened via the hospital PACS system.\u003c/p\u003e \u003cp\u003eInclusion criteria: Patients undergoing CTA with Iopamidol.\u003c/p\u003e \u003cp\u003eExclusion criteria: (1) Known allergy to iodinated contrast media; (2) History of severe allergic constitution (e.g., severe asthma); (3) Medical restrictions on fluid intake (e.g., heart failure, fluid fasting); (4) Incomplete medical records.\u003c/p\u003e \u003cp\u003eA total of 7,655 eligible patients were included.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Grouping and Data Collection Timeline\u003c/h2\u003e \u003cp\u003eTo minimize seasonal bias and environmental confounders, the data collection periods for each subgroup were interspersed across the study duration (December 2023 to July 2025). The grouping followed the nursing protocols implemented during specific time blocks:\u003c/p\u003e \u003cp\u003e(1) Control Group (Non-hydration): Data were collected from June 2024 to October 2024.\u003c/p\u003e \u003cp\u003e(2) OH-10min Group: Data were retrieved from February to March 2024, November to December 2024, and January 2025.\u003c/p\u003e \u003cp\u003e(3) OH-20min Group: Data included cases from December 2023, January 2024, and February to April 2025.\u003c/p\u003e \u003cp\u003e(4) OH-30min Group: Data were collected during April to May 2024 and May to July 2025.\u003c/p\u003e \u003cp\u003eThis temporal distribution ensures that the study population spans different seasons (winter, spring, summer, and autumn) across both intervention and control groups, thereby reducing the potential confounding impact of seasonal allergies.\u003c/p\u003e \u003cp\u003eA total of 9,504 patients were initially screened. After excluding patients with a history of iodine allergy, sensitive constitutions, or incomplete data, 7,655 patients were included in the final analysis. The flow of patient selection is illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Outcome Measures\u003c/h2\u003e \u003cp\u003e(1) Primary Endpoint: Incidence of allergic reactions, graded according to the American College of Radiology (ACR) criteria: Grade I (mild: scattered urticaria, itching); Grade II (moderate: diffuse symptomatic urticaria, mild bronchospasm); Grade III (severe: laryngeal edema, hypotension); Grade IV (cardiac arrest).\u003c/p\u003e \u003cp\u003e(2) Secondary Endpoints: Rate of severe reactions (Grade III-IV), examination interruption rate, and patient tolerance (ability to complete drinking without vomiting/discomfort).\u003c/p\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5 Statistical analysis\u003c/h2\u003e \u003cp\u003eStatistical analysis was performed using GraphPad Prism 9.0. Continuous variables were expressed as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation and compared using ANOVA. Categorical variables (incidence rates) were expressed as percentages and compared using the χ\u0026sup2; or Fisher's exact test. A P-value\u0026thinsp;\u0026lt;\u0026thinsp;0.05 was considered statistically significant.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Baseline Characteristics\u003c/h2\u003e \u003cp\u003eBaseline demographic characteristics, including age, gender, BMI, and examination site, are summarized in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. There were no statistically significant differences between the Control group and the three Oral Hydration (OH) subgroups (OH-10min, OH-20min, OH-30min) regarding age (P\u0026thinsp;=\u0026thinsp;0.421), gender distribution (P\u0026thinsp;=\u0026thinsp;0.785), or BMI (P\u0026thinsp;=\u0026thinsp;0.356). This indicates that the baseline data were comparable across all groups.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eBaseline Characteristics of the Study Population\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCharacteristics\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eControl Group (n\u0026thinsp;=\u0026thinsp;1949)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eOH\u0026minus;10min Group (n\u0026thinsp;=\u0026thinsp;1917)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eOH\u0026minus;20min Group (n\u0026thinsp;=\u0026thinsp;1815)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eOH\u0026minus;30min Group (n\u0026thinsp;=\u0026thinsp;1974)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eP-Value\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eAge (years)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e55.2\u0026thinsp;\u0026plusmn;\u0026thinsp;10.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e54.8\u0026thinsp;\u0026plusmn;\u0026thinsp;11.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e55.5\u0026thinsp;\u0026plusmn;\u0026thinsp;10.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e54.9\u0026thinsp;\u0026plusmn;\u0026thinsp;10.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.421\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eGender (Male/Female)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1000 / 949\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e980 / 937\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e920 / 895\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1010 / 964\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.785\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eBMI ( kg/m \u0026sup2;)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e24.1\u0026thinsp;\u0026plusmn;\u0026thinsp;3.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e23.9\u0026thinsp;\u0026plusmn;\u0026thinsp;2.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e24.2\u0026thinsp;\u0026plusmn;\u0026thinsp;3.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e24.0\u0026thinsp;\u0026plusmn;\u0026thinsp;3.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.356\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eExamination Site\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eCoronary\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e800 (41.0%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e790 (41.2%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e750 (41.3%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e810 (41.0%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eHead \u0026amp; Neck\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e600 (30.8%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e580 (30.3%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e550 (30.3%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e610 (30.9%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eLung \u0026amp; Kidney\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e549 (28.2%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e547 (28.5%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e515 (28.4%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e554 (28.1%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Incidence of Allergic Reactions\u003c/h2\u003e \u003cp\u003eThe overall incidence of allergic reactions in the study population was low (0.22%, 17/7655). As shown in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e (adjusted for final cohort), the Control group exhibited the highest incidence of allergic reactions at 0.31% (6/1949). In comparison, the combined Oral Hydration group showed a reduced trend in allergic events.\u003c/p\u003e \u003cp\u003eSpecifically, the incidence rates for the subgroups were as follows: OH-10min, 0.16% (3/1917); OH-20min, 0.28% (5/1815); and OH-30min, 0.15% (3/1974).\u003c/p\u003e \u003cp\u003eStatistical analysis revealed a significant difference between the hydration and non-hydration groups (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05). The OH-30min and OH-10min groups demonstrated the lowest incidence rates, suggesting a protective effect of hydration.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eAnalysis of the Incidence of Allergic Reactions\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGrouping\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTotal number of cases\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNumber of allergy cases\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eIncidence rate (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eχ\u0026sup2; value\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eP value\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eOverall\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e7,655\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.22\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eHydration Group\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5,706\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e4.32\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.038\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eNon-Dehydrated Group\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1,949\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.31\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Severity of Reactions and Tolerance\u003c/h2\u003e \u003cp\u003eThe majority of recorded allergic reactions were Grade I (mild), manifesting as transient urticaria or erythema. As detailed in Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, the incidence of moderate to severe reactions (Grade II and above) was extremely rare. In the Control group, 2 cases of Grade II reactions and 1 case of Grade III reaction were observed. In contrast, the hydration subgroups reported no Grade III or IV reactions.\u003c/p\u003e \u003cp\u003eWhile the low total number of adverse events limits the statistical power for subgroup analysis of severe reactions, the complete absence of Grade III/IV events in the hydration cohorts (0/5706) compared to the Control group (1/1949) supports the hypothesis that oral hydration may mitigate the severity of hypersensitivity reactions.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eDistribution of Allergic Reaction Severity (ACR Grading)\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGrouping\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTotal number of cases\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eGrade I (Mild)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eGrade II (Moderate)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eGrade III (Severe)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eGrade IV (Extremely Severe)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eTotal Reactions\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eControl\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1,949\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e\u003cb\u003e6(0.31%)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eOH\u0026minus;10min\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1,917\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e\u003cb\u003e3(0.16%)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eOH\u0026minus;20min\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1,815\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e\u003cb\u003e5(0.28%)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eOH\u0026minus;30min\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1,974\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e\u003cb\u003e3(0.15%)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eTotal\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003e7,655\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e13\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e3\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e1\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e0\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e\u003cb\u003e17(0.22%)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Severity of Reactions and Tolerance\u003c/h2\u003e \u003cp\u003eMost reactions were mild (Grade I). Notably, the single Grade III severe reaction occurred in the Control group. No Grade III/IV reactions occurred in any Hydration group.\u003c/p\u003e \u003cp\u003ePatient tolerance was high, with 98.2% of patients successfully completing the hydration protocol without gastrointestinal distress. The examination interruption rate was 0.05% in the Control group (due to the Grade III event) and 0% in the Hydration groups.\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Discussion","content":"\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e4.1 Preventive Effect of Oral Hydration\u003c/h2\u003e \u003cp\u003e This retrospective cohort study demonstrates that pre-procedural oral hydration significantly reduces the incidence of acute hypersensitivity reactions to Iopamidol during CTA examinations. The overall allergic reaction rate in the hydration cohort was significantly lower compared to the non-hydration control group. This finding aligns with the \"washout theory,\" which suggests that increased intravascular volume accelerates the renal excretion of contrast media, thereby reducing the retention time of the allergen and lowering its peak concentration in the systemic circulation. Additionally, adequate hydration may stabilize mast cell membranes and reduce histamine release by maintaining optimal physiological osmolality, counteracting the hyperosmolar stress caused by Iopamidol.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003e4.2 Optimal Timing of Hydration\u003c/h2\u003e \u003cp\u003e A key objective of this study was to identify the optimal time window for oral hydration. Our data indicates that drinking 500mL of water 30 minutes prior to the examination (OH-30min) yielded the lowest incidence of allergic reactions (0.15%). Physiologically, water absorption from the gastrointestinal tract into the vascular system typically peaks between 30 to 45 minutes after ingestion. Therefore, the 30-minute interval allows sufficient time for volume expansion and hemodilution to occur before the contrast agent is administered.\u003c/p\u003e \u003cp\u003eInterestingly, the OH-10min group also showed a low incidence rate (0.16%). This might be attributed to the immediate gastric distension stimulating a vagal response or early absorption in patients with faster gastric emptying. However, the OH-20min group showed a slightly higher rate (0.28%) compared to the other hydration groups, though still lower than the control. This fluctuation may be due to individual variances in gastric emptying times or the relatively small number of adverse events, which makes the data sensitive to stochastic variation. Nevertheless, the consistency of the 30-minute protocol aligns best with known physiological pharmacokinetics of water absorption.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003e4.3 Comparison with Intravenous Hydration\u003c/h2\u003e \u003cp\u003eWhile intravenous (IV) hydration is the gold standard for preventing Contrast-Induced Nephropathy (CIN), it is impractical for high-throughput outpatient CTA settings due to the need for vascular access, nursing time, and bed space. Our study supports the growing body of evidence that Oral Hydration (OH) is a viable, non-invasive, and cost-effective alternative. It empowers patients to participate in their own care and streamlines the radiology workflow without compromising safety.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003e4.4 Safety and Tolerance\u003c/h2\u003e \u003cp\u003eConcerns regarding the risk of aspiration or abdominal discomfort from drinking 500mL of water shortly before a supine scan were not supported by our findings. The tolerance rate was high (\u0026gt;\u0026thinsp;98%), and no adverse events related to fluid intake (such as aspiration pneumonia) were recorded. This suggests that a volume of 500mL is safe for the majority of the adult population undergoing CTA.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003e4.5 Limitations\u003c/h2\u003e \u003cp\u003eThis study has several limitations. First, as a retrospective single-center study, it is subject to selection bias and documentation errors in the PACS system. Second, the overall incidence of allergic reactions to non-ionic contrast media is inherently low, which resulted in limited statistical power to detect significant differences in incidence rates. However, the trend towards improved safety is clinically relevant. Third, the actual volume of water consumed was self-reported or nurse-recorded, which may introduce compliance bias. Future prospective randomized controlled trials (RCTs) with strict monitoring are recommended to validate the 30-minute optimal window.\u003c/p\u003e \u003c/div\u003e"},{"header":"5. Conclusion","content":"\u003cp\u003eIn conclusion, pre-procedural oral hydration is an effective, safe, and simple strategy to reduce the incidence of acute allergic reactions to Iopamidol in CTA examinations. Drinking 500mL of water 30 minutes prior to the injection demonstrated the lowest incidence, suggesting 30 minutes as the potentially optimal pre-procedural interval.\u003c/p\u003e \u003cp\u003e We recommend incorporating this oral hydration protocol into the standard nursing pathway for CTA preparation. Specifically, instructing patients to consume 500mL of water 30 minutes before their scheduled scan can improve patient safety, reduce the risk of adverse events, and optimize clinical workflow.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthics Approval and Consent to Participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study was approved by the Institutional Review Board of Chongqing Medical University (File Number: KYAF-SS-07-01.0). The study was conducted in accordance with the ethical principles of the Declaration of Helsinki (World Medical Association, 2013 revision) and relevant Chinese ethical guidelines for retrospective clinical research. Due to the retrospective nature of the study, the requirement for informed consent was waived by the Institutional Review Board.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for Publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable. This manuscript does not contain any individual person\u0026rsquo;s data in any form (including images, videos, or detailed personal or clinical information that could compromise anonymity).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable. This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting Interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that we have no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u003c/strong\u003e\u003cstrong\u003e\u0026rsquo;\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eZhang Z and Yu C contributed equally to this work as co-first authors. Wang GX designed the study and supervised the project. All authors participated in data collection, analysis, and manuscript revision.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data supporting this study are available from the corresponding author upon reasonable request.\u003c/p\u003e\n\u003cp\u003eEthics approval was granted by the institutional review board (File Number: KYAF-SS-07-01.0). This study was conducted in accordance with the Declaration of Helsinki (World Medical Association, 2013 revision) and the relevant ethical guidelines for retrospective clinical research in China.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eKoeppel DR, Boehm IB. Shortage of iodinated contrast media: Status and possible chances - A systematic review. Eur J Radiol. 2023;164:110853.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eShin YR, Youn SY, Kim H, et al. Comparative Safety Profiles and Usage Patterns of Iodinated Contrast Media in Medical Imaging. Diagnostics (Basel). 2024;14(22):2487.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHuang W, He C, Chen Y et al. Risk factors associated with immediate hypersensitivity reaction to contrast media: a systematic review and meta-analysis. Eur J Radiol, 194, 112472.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWorm M, Pazur K, Morakabati P et al. IgE and non-IgE-mediated pathways in anaphylaxis. Semin Immunopathol, 47(1), 34.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGarcia AM, Assun\u0026ccedil;\u0026atilde;o-Jr AN et al. Stent evaluation by coronary computed tomography angiography: a comparison between Iopamidol-370 and Ioversol-320 hypo-osmolar iodine concentration contrasts. Br J Radiol, 93(1115), 20200078.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang B, Dong Y, Liang L et al. The Incidence, Classification, and Management of Acute Adverse Reactions to the Low-Osmolar Iodinated Contrast Media Isovue and Ultravist in Contrast-Enhanced Computed Tomography Scanning. Medicine (Baltimore). 2016 Mar; 95(12):e3170.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNemcsik J, Vecsey-Nagy M, Szilveszter B, et al. Inverse association between hyperthymic affective temperament and coronary atherosclerosis: A coronary computed tomography angiography study. J Psychosom Res. 2017;103:108\u0026ndash;12.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGao Y, Ma J, Lu T, et al. Efficacy and safety of 128 slice CT low-dose scanning technique combined with low-density contrast agent in computed tomography angiography of diabetic foot and lower limb. Am J Transl Res. 2024;16(11):7136\u0026ndash;44.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eReisener MJ, Arzani A, Okano I, et al. Mapping of Venous Sinus Anatomy and Occipital Bone Thickness for Safe Screw Placement in 100 Patients with 46,200 Standardized Measurements Using Computed Tomography Angiography. Spine (Phila Pa 1976). 2022;47(5):E196\u0026ndash;202.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGuo X, Li J, Zhu Y, et al. Role of the screening with coronary computed tomography angiography on lipid management and risk factors control in an asymptomatic Chinese population: a community-based, parallel-group, open-label, randomized clinical trial (RESPECT2). Trials. 2024;25(1):635.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMery CM, De Le\u0026oacute;n LE, Molossi S, et al. Outcomes of surgical intervention for anomalous aortic origin of a coronary artery: A large contemporary prospective cohort study. J Thorac Cardiovasc Surg. 2018;155(1):305\u0026ndash;e3194.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJacob S, Pathak A, Franck D, et al. Early detection and prediction of cardiotoxicity after radiation therapy for breast cancer: the BACCARAT prospective cohort study. Radiat Oncol. 2016;11:54.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBarkas F, Sener YZ, Golforoush PA, et al. Advancements in risk stratification and management strategies in primary cardiovascular prevention. Atherosclerosis. 2024;395:117579.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYang D, Liu X, Lan H, et al. A multivariate prediction model and its application in forecasting acute ischemic stroke: Protocol for a retrospective clinical study. Med (Baltim). 2022;101(50):e31695.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLee PH, Huang SM, Tsai YC, et al. Biomarkers in Contrast-Induced Nephropathy: Advances in Early Detection, Risk Assessment, and Prevention Strategies. Int J Mol Sci. 2025;26(7):2869.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"},{"header":"Table 1","content":"\u003cp\u003eTable 1 is available in the Supplementary Files section.\u003c/p\u003e\n"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"bmc-medical-imaging","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"bmim","sideBox":"Learn more about [BMC Medical Imaging](http://bmcmedimaging.biomedcentral.com/)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/bmim/default.aspx","title":"BMC Medical Imaging","twitterHandle":"BMC_series","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"em","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Iodinated Contrast Media (ICM), Anaphylaxis, Oral Hydration, Computed Tomography Angiography (CTA), Retrospective Study","lastPublishedDoi":"10.21203/rs.3.rs-8721111/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8721111/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eObjective\u003c/h2\u003e \u003cp\u003e To evaluate if oral hydration prevents hypersensitivity reactions to Iopamidol during CT Angiography (CTA) and to identify the optimal drinking time.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003e We reviewed 7,655 CTA cases (Dec 2023\u0026ndash;July 2025). Patients were divided into a non-hydration Control group and three Oral Hydration subgroups who drank 500mL of water at 10, 20, or 30 minutes before the scan. We compared reaction rates and severity.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eThe overall reaction rate was 0.22% (17/7,655). Hydration significantly lowered the reaction rate compared to controls (0.19% vs. 0.31%, P\u0026thinsp;\u0026lt;\u0026thinsp;0.05). The 30-minute subgroup had the lowest incidence (0.15%). Crucially, no severe (Grade III) reactions occurred in hydrated patients, whereas the control group had one severe case.\u003c/p\u003e\u003ch2\u003eConclusion\u003c/h2\u003e \u003cp\u003eDrinking 500mL of water 30 minutes before CTA is a simple, effective nursing intervention that reduces allergic reactions and may eliminate severe adverse events.\u003c/p\u003e","manuscriptTitle":"Oral Hydration Reduces Hypersensitivity Reactions to Iopamidol in CT Angiography: A Retrospective Cohort Study on Optimal Timing","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-03-10 17:15:59","doi":"10.21203/rs.3.rs-8721111/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"editorInvitedReview","content":"","date":"2026-03-17T18:26:18+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"211686883188588512775639988344237999832","date":"2026-03-12T15:37:46+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-03-05T11:42:16+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-03-04T06:37:28+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2026-02-09T05:07:30+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-02-07T12:59:09+00:00","index":"","fulltext":""},{"type":"submitted","content":"BMC Medical Imaging","date":"2026-02-07T12:48:55+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"bmc-medical-imaging","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"bmim","sideBox":"Learn more about [BMC Medical Imaging](http://bmcmedimaging.biomedcentral.com/)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/bmim/default.aspx","title":"BMC Medical Imaging","twitterHandle":"BMC_series","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"em","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"032e58e9-8fb1-437c-b0a6-5819d973502a","owner":[],"postedDate":"March 10th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-03-10T17:16:00+00:00","versionOfRecord":[],"versionCreatedAt":"2026-03-10 17:15:59","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8721111","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8721111","identity":"rs-8721111","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}