FASTING IN CONTRAST ENHANCED CT STUDIES: MANDATORY OR MYTH?

Abstract

Contrasts enhanced computerized tomogram (CECT) is the most common worldwide cross sectional imaging used in radiology services. In USA, about 40 million CECT studies are performed each year.[i] Over the last many decades, pre-procedural fasting for CT prior to intravenous administration of iodinated contrast medium (ICM) has been considered a common medical practice.[ii] The prime reason of fasting prior to CECT is to protect the supine patient from pulmonary aspiration of gastrointestinal contents during delivery of intravenous, high-osmolar ionic contrast agent which has been associated with significant emetic responses.[iii] Another reason for fasting prior to CECT was understanding that contrast related nausea and vomiting would occur more often with full-stomach.[iv] It was also believed that a full stomach would interfere with transit of oral contrast and also gastric food content could mimic intraluminal lesions posing diagnostic challenge.[v] In current radiology practice, low-osmolar non-ionic contrast has essentially replaced high osmolar ionic contrast agents. Sentinel reason for this switch is significantly lower incidence of adverse emetic responses with non-ionic agents.[vi] Studies have also shown that fasting in patients who had CT with non-ionic  agents has increased the incidence of nausea and vomiting.[vii] Another study has shown that fasting longer than 3 h lowers gastric pH level which increased the risk for aspiration pneumonitis.[viii] However, despite of these evidences, many diagnostic services worldwide continue the practice of fasting (4h to overnight) prior to contrast-enhanced CT. In 2012, a multinational survey reported highly variable fasting policies between countries and even between hospitals within the same country, ranging from no fasting to overnight fasting.[ix]