The rise in referrals of older patients for diagnostic and interventional procedures that use contrast media includes many people aged over 60 who also suffer renal impairment - a group at significant risk of developing CIN. The risks factors, contrast media safety, wider issues surrounding CIN and how to avoid CIN, were the subject of a refresher course session at the ECR in March.
Taking part was radiologist Dr Remy Geenen a private practitioner who works at Medisch Centrum, a large, non-university teaching hospital in Alkmaar, the Netherlands. Dr Geenen focuses on abdominal and cardiac radiology, and has a specific interest in contrast media.
At the ECR session he discussed the pharmacology of contrast media, the pathogenesis of CIN, iso- vs. low osmolar CM and hydration with NCL vs. NaHCO3.n ‘The pathophysiology of CIN is complex and not well understood,’ he explained. ‘Basically, an imbalance between vasodilatation and vasoconstriction takes place inside the kidney after intra-arterial or intravenous CM administration.
‘Furthermore, increased oxygen demand of tubular cells due to increased re-absorption of sodium and water is a second mechanism, leading to transient medullar ischaemia. Patients who develop CIN have a significantly higher chance of serious or adverse events such as stroke or myocardial infarction. There is also a higher risk of death, especially in the short-term.’
A key first step toward prevention is to identify patients at risk and they are primarily those with kidney problems, or older patients.
Dr Geenen explained that the CIN incidence in healthy patients with normally functioning kidneys is as low as 1-2%. For those with any severe kidney disease this increases up to 50%. ‘Knowledge of the patient’s medical record and recent basic kidney function is mandatory. High-risk patients should receive prevention. Two major questions in CIN prevention are whether iso-osmolar CM causes significantly less CIN than low-osmolar CM and whether hydration schedules with NaHCO3 give significantly less CIN than hydration schedules with NaCl 0.9%.’
Evidence for the standard use of iso-osmolar contrast media for CIN prevention in radiological procedures is limited, he said. Five randomised, controlled trials regarding intravenous administration showed conflicting results - three showed no significant difference in CIN incidence; one favoured comparing low-osmolar agent and one favoured the iso-osmolar agent.
For NaHCO3 versus NaCl, Dr Geenen said, of the 12 RCTs performed, seven favoured NaHCO3, with five showing no significant difference in CIN incidence. ‘Pre- and post-hydration with NaHCO3 is therefore at least equal to NaCl.’
Radiologists can take certain steps to avoid or reduce the CIN risk, he advised. Calculating the patient’s estimated Glomerular Filtration Rate (eGFR) is important -- if less than 60, the radiologist should act promptly with pre- and post-hydration.
However, whilst Dr Geenen remains content that contrast agents are as safe as radiologists wish them to be, and usually only 10-15% of patients are at increased CIN risk, he said it is crucial that preventive measures be taken in high-risk patients.