CT with IV contrast in low renal function
Author:
Mikael Häggström [notes 1]
In CT with IV contrast, decreased renal function and several other conditions increase the risk of contrast-induced nephropathy, which is a potentially lethal renal injury to the kidney following intravenous radiocontrast.[1]
Contents
When it matters
According to European guidelines, the main risk factors of contrast-induced nephropathy:[2]
- Estimated glomerular filtration rate (eGFR) of less than 30 ml/min/1.73 m2 before intra-venous or intra-arterial radiocontrast administration with second-pass renal exposure (passing lungs or other tissues before the kidneys).
- eGFR of less than 45 ml/min/1.73 m2 before intra-arterial administration with first-pass renal exposure or in ICU patients
- Known or suspected acute renal failure
- Large doses of radiocontrast given IA with first-pass renal exposure
- Multiple radiocontrast injections within 48-72 h
Other risk factors
Look in the medical records (or ask the patient) for other risk factors of contrast-induced nephropathy.
The Roxana Mehran score predictor applies the following ten variables:[3]
- Age (4 points if older than 75 years old)
- Anemia (3 points)
- Use of an intra-aortic balloon pump (5 points)
- Decreased real function. In terms of estimated glomerular filtration rate in ml/min:
- eGFR 60 to 40 (2 points)
- eGFR 40 to 20 (4 points)
- eGFR less than 20 (6 points)
- Hypotension (5 points, if systolic BP less than 80 mmHg for at least one hour requiring inotropic support)
- Contrast media volume (1 point per 100 ml)
- Congestive heart failure (5 points)
- Diabetes (3 points).
A risk score of less than 6 carries a risk of 7.5% to score more than 16 carries up to 57% risk.[3]
In addition to those in the Roxana Mehran score, the following are also risk factors of contrast-induced nephropathy:[2]
- Hypoxia
- Cirrhosis
- NSAIDs or (other) nephrotoxic drugs
- Persons in dialysis with residual renal function of at least 400 ml urine / 24h
- Individuals who have undergone kidney transplantation
Adjustment of dose
If and how to adjust the dose depends on supply and demand:
How much contrast can be given?
In some emergent conditions such as CT of aortic aneurysm with suspected rupture, the need for contrast is greater than the risk of contrast-induced nephropathy.
For the rest of the investigations, evidence suggests that contrast doses should be limited to a ratio of grams of iodine to glomerular filtration rate (Igram / GFRml/min) of a maximum of 1 g/(ml/min).[4] According to European guidelines, the ratio should be less than 1.1 g/(ml/min) for intra-arterial contrast medium administration with first-pass renal exposure (not passing lungs or peripheral tissue before reaching the kidneys).[2] Swedish guidelines are more restrictive, recommending a ratio of less than 0.5 g/(ml/min) in patients with risk factors and irrespective of route of administration, and even more caution in first-pass renal exposure.[2]
| Igram / GFRml/min ratio |
240 mg/ml | 350 mg/ml | 370 mg/ml |
|---|---|---|---|
| 0.5 | 2.1 ml *GFRml/min | 1.4 ml *GFRml/min | 1.4 ml *GFRml/min |
| 1 | 4.2 ml *GFRml/min | 2.9 ml *GFRml/min | 2.7 ml *GFRml/min |
| 1.1 | 4.6 ml *GFRml/min | 3.1 ml *GFRml/min | 3.0 ml *GFRml/min |
How much contrast is needed
| Exam | Iodine concentration | Comments | |||
|---|---|---|---|---|---|
| 300 mg/ml | 350 mg/ml | 370 mg/ml | |||
| CT of brain | 95ml[5] | 80 ml[5] | 75 ml[5] | ||
| CT of thorax | Overall | 70 - 95 ml[notes 2] | 60 - 80 ml[notes 2] | 55 - 75 ml[notes 2] | Parenchymal changes of the lung can often be evaluated adequately without the use of intravenous contrast. |
| CT pulmonary angiogram | 20 ml[notes 3] | 17 ml[notes 3] | 15 ml[notes 3] | Minimal amount when using specific low-contrast protocol.[notes 3] | |
| CT of abdomen | Overall | 70 ml[5] | 60 ml[5] | 55 ml[5] | |
| Liver | 55 ml[notes 4] | 45 ml[notes 4] | 40-45 ml[notes 4] | Minimal required amount.[notes 4] | |
| CT angiography | 25 ml[notes 5] | 20 ml[notes 5] | When using specific low-contrast protocol.[notes 5] | ||
Departments often have formulas that give the amount of contrast needed for various investigations, using patient sex and weight as main parameters. These may include creatitine levels as well, and in such cases it can help to get a value of of much contrast would hypothetically have been given if the creatinine level was normal, such as for example 80 μmol/L or 0.9 mg/dL. This value can be compared to how much can actually be given in order to determine if it is worth doing the exam with contrast.
Treating risk factors
Risk factors can sometimes be treated or at least mitigated, especially if having suddenly appeared, such as a decreased renal function when it was previously normal. In such cases a common easily treated cause is dehydration.
Hydration by drinking or intravenous volume expander, either before or after contract administration, decreases the risk of contrast-induced nephropathy.[6]
Notes
- ↑ For a full list of contributors, see article history. Creators of images are attributed at the image description pages, seen by clicking on the images. See Radlines:Authorship for details.
- ↑ 2.0 2.1 2.2 0.3–0.4 gI/kg in a 70kg individual, according to:
- Iezzi, Roberto; Larici, Anna Rita; Franchi, Paola; Marano, Riccardo; Magarelli, Nicola; Posa, Alessandro; Merlino, Biagio; Manfredi, Riccardo; et al. (2017). "Tailoring protocols for chest CT applications: when and how?
- ↑ 3.0 3.1 3.2 3.3 Using dual energy CTA (such as 90/150SnkVp), according to:
- Leroyer, Christophe; Meier, Andreas; Higashigaito, Kai; Martini, Katharina; Wurnig, Moritz; Seifert, Burkhardt; Keller, Dagmar; Frauenfelder, Thomas; et al. (2016). "Dual Energy CT Pulmonary Angiography with 6g Iodine—A Propensity Score-Matched Study
- ↑ 4.0 4.1 4.2 4.3 The liver generally needs an enhancement of at least 30 HU for proper evaluation according to:
- Multislice CT
- Bae, Kyongtae T. (2010). "Intravenous Contrast Medium Administration and Scan Timing at CT: Considerations and Approaches
- ↑ 5.0 5.1 5.2 CT-angiography in a 70kg person, with 100-150 mg I/kg by using 80 kVp, mAs-compensation for constant CNR, fixed injection duration adapted to scan time, automatic bolus tracking and a saline chaser, according to:
- Nyman, Ulf (2012). Contrast Medium-Induced Nephropathy (CIN) Gram-Iodine/GFR Ratio to Predict CIN and Strategies to Reduce Contrast Medium Doses
References
- ↑ Rudnick, M.; Feldman, H. (2008). "Contrast-Induced Nephropathy: What Are the True Clinical Consequences? ". Clinical Journal of the American Society of Nephrology 3 (1): 263–272. doi:. ISSN 1555-9041.
- ↑ 2.0 2.1 2.2 2.3 Nyman, Ulf; Ahlkvist, Joanna; Aspelin, Peter; Brismar, Torkel; Frid, Anders; Hellström, Mikael; Liss, Per; Sterner, Gunnar; et al. (2018). "Preventing contrast medium-induced acute kidney injury ". European Radiology. doi:. ISSN 0938-7994.
- ↑ 3.0 3.1 Kalgi Modi, Scott C. Dulebohn (2017). Contrast-Induced Nephropathy. StatPearls Publishing. CC-BY-4.0
- ↑ Keaney, J. J.; Hannon, C. M.; Murray, P. T. (2013). "Contrast-induced acute kidney injury: how much contrast is safe? ". Nephrology Dialysis Transplantation 28 (6): 1376–1383. doi:. ISSN 0931-0509.
- ↑ 5.0 5.1 5.2 5.3 5.4 5.5 . New Zealand Datasheet. New Zealand Medicines and Medical Devices Safety Authority. Retrieved on 2018-10-16.
- ↑ Yang, Xiaoming; Hiremath, Swapnil; Akbari, Ayub; Shabana, Wael; Fergusson, Dean A.; Knoll, Greg A. (2013). "Prevention of Contrast-Induced Acute Kidney Injury: Is Simple Oral Hydration Similar To Intravenous? A Systematic Review of the Evidence ". PLoS ONE 8 (3): e60009. doi:. ISSN 1932-6203.
