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TECHNOLOGY ASSESSMENT STATUS EVALUATION
T E C H N O L O G Y ASSESSMENT STATUS E V A L U A T I O N R A D I O G R A P H I C C O N T R A S T M E D I A USED IN E R C P MAY, 1995
INTRODUCTION In order to promote the appropriate use of new or emerging endoscopic technologies and those technologies which impact on endoscopic practice, the ASGE Technology Assessment Committee has developed a series of Status Evaluation papers. By this process, relevant information about these technologies may be presented to practicing physicians for the education and care of their patients. In many cases, data from randomized controlled trials is lacking and only preliminary clinical studies are available. Practitioners should continue to monitor the medical literature for subsequent data about the efficacy, safety and socioeconomic aspects of these technologies.
BACKGROUND Since the introduction of ERCP there have been significant developments in water-soluble low osmolar contrast media (LOCM) with clinical and financial implications for vascular and other radiologic applications. This report reviews the use of contrast media (CM) in ERCP with respect to image quality, complications and cost. TECHNICAL CONSIDERATIONS All CM currently available can be classified into one of four groups: ionic monomer, ionic dirner, nonionic monomer and nonionic dimer (Table). All are benzoic acid derivatives with molecular weights less than 2000. They possess one or two benzene rings a n d are therefore monomers or dimers. They are hydrophilic, with low lipid solubility and a low binding affinity for proteins. They move freely in the extracellular space. The osmolality of these media is determined by the number of particles into which they dissociate in solution. The number of iodine atoms in the parent VOLUME 43, NO. 6, 1996
molecule determines the density of the CM and therefore the degree of attenuation of x-ray photons. Ionic monomers dissociate in solution into cations (e.g. sodium or methylglucamine) and anions (the iodine containing benzene ring component such as iothalamate or diatrizoate). These compounds carry the highest osmolality [high osmolality contrast media (HOCM)]. Nonionic CM do not dissociate and have the lowest osmolality [low osmolality contrast media (LOCM)] (see Table). Ionic dimers dissociate into two particles but carry six iodine atoms so that the osmolality remains low for the degree of x-ray attenuation achieved. Contrast media also have an inherent viscosity that increases geometrically with concentration and is greater for larger molecules. Viscosity is substantially affected by the temperature of the CM. For example, the viscosity of the nonionic monomer iohexol is 50% greater at 25°C than it is at 37°C. EFFICACY & EASE OF USE The effect of CM on image quality during ERCP is the resultant interaction of density, viscosity and osmolality. Although no optimal iodine concentration has been defined for ERCP, most commonly used CM (diluted and undiluted) provide between 150 and 300 nag iodine/ml (see Table). Such concentrations are derived from vascular and urographic experience where, in general, equivalent iodine concentrations produce equivalent images for the same radiographic conditions. Dilution of HOCM directly affects radiographic quality. Many believe this enhances detection of some bile duct stones and routinely use diluted HOCM for cholangiography. The quality of fluoroscopy and the technique of injection are also important. The need for increased volumes and the GASTROINTESTINAL ENDOSCOPY
647
INTRODUCTION In order to promote the appropriate use of new or emerging endoscopic technologies and those technologies which impact on endoscopic practice, the ASGE Technology Assessment Committee has developed a series of Status Evaluation papers. By this process, relevant information about these technologies may be presented to practicing physicians for the education and care of their patients. In many cases, data from randomized controlled trials is lacking and only preliminary clinical studies are available. Practitioners should continue to monitor the medical literature for subsequent data about the efficacy, safety and socioeconomic aspects of these technologies.
BACKGROUND Since the introduction of ERCP there have been significant developments in water-soluble low osmolar contrast media (LOCM) with clinical and financial implications for vascular and other radiologic applications. This report reviews the use of contrast media (CM) in ERCP with respect to image quality, complications and cost. TECHNICAL CONSIDERATIONS All CM currently available can be classified into one of four groups: ionic monomer, ionic dirner, nonionic monomer and nonionic dimer (Table). All are benzoic acid derivatives with molecular weights less than 2000. They possess one or two benzene rings a n d are therefore monomers or dimers. They are hydrophilic, with low lipid solubility and a low binding affinity for proteins. They move freely in the extracellular space. The osmolality of these media is determined by the number of particles into which they dissociate in solution. The number of iodine atoms in the parent VOLUME 43, NO. 6, 1996
molecule determines the density of the CM and therefore the degree of attenuation of x-ray photons. Ionic monomers dissociate in solution into cations (e.g. sodium or methylglucamine) and anions (the iodine containing benzene ring component such as iothalamate or diatrizoate). These compounds carry the highest osmolality [high osmolality contrast media (HOCM)]. Nonionic CM do not dissociate and have the lowest osmolality [low osmolality contrast media (LOCM)] (see Table). Ionic dimers dissociate into two particles but carry six iodine atoms so that the osmolality remains low for the degree of x-ray attenuation achieved. Contrast media also have an inherent viscosity that increases geometrically with concentration and is greater for larger molecules. Viscosity is substantially affected by the temperature of the CM. For example, the viscosity of the nonionic monomer iohexol is 50% greater at 25°C than it is at 37°C. EFFICACY & EASE OF USE The effect of CM on image quality during ERCP is the resultant interaction of density, viscosity and osmolality. Although no optimal iodine concentration has been defined for ERCP, most commonly used CM (diluted and undiluted) provide between 150 and 300 nag iodine/ml (see Table). Such concentrations are derived from vascular and urographic experience where, in general, equivalent iodine concentrations produce equivalent images for the same radiographic conditions. Dilution of HOCM directly affects radiographic quality. Many believe this enhances detection of some bile duct stones and routinely use diluted HOCM for cholangiography. The quality of fluoroscopy and the technique of injection are also important. The need for increased volumes and the GASTROINTESTINAL ENDOSCOPY
647