Patient Safety Issues in Radiology

Key Clinical Questions

How can cumulative radiation dose be estimated?
What commonly ordered CT scan delivers the highest dose of ionizing radiation?
What are the risk factors for contrast-related allergic reactions?
How can the potential for contrast-induced nephropathy be minimized?

Introduction

For an acutely ill patient whose illness is one snapshot in time, one must not lose sight of the cumulative risks of short- and long-term adverse effects of modern imaging. These may be due to contrast administration, ionizing radiation, and the possibility of incidental findings generating additional studies.

Contrast Materials

Oral Contrast

Contrast materials may be administered intravenously, orally, rectally, and for problem solving, through a variety of support lines and tubes. The selection of a specific oral contrast agent is based on the risk for aspiration versus the risk for extravasation of the contrast material. Catastrophic aspiration requiring ICU admission can occur when oral contrast material is administered to a patient with achalasia or other significant risk factor for aspiration, especially when contrast material is administered while the patient is supine. Although inert, when aspirated into the lungs, barium is permanent. Barium becomes concentrated as it passes through the GI tract and can contribute to constipation and obstipation, particularly at the concentrations administered for X-ray and fluoroscopic examinations. Gastrografin is more commonly used when there is concern for extravasation into mediastinum or peritoneal cavity. It is important to remember that although gastrografin will be reabsorbed, it can cause pulmonary edema due to its hypertonicity. Gastrografin contains iodine, and should not be used in patients with a known iodine allergy, as a small amount is absorbed in the GI tract. Specialized contrast agents may also be used for purposes such as distending the bowel without obscuring mucosal enhancement.

Iodinated Intravenous Contrast

Low osmolar nonionic contrast agents are almost universally used in current practice due to their reduced risk of fluid shifts and allergic reaction. In a labile patient, these risks may not be warranted for the increase in diagnostic information provided by the contrast enhancement. This is best determined in consultation with the radiologist, to explore how crucial the intravenous contrast is for the clinical question at hand (Tables 106-1 and 106-2).

Table 106-1 Conditions Associated with Adverse Reactions to Contrast Material

Risk factors for contrast-acquired renal failure

Preexisting renal insufficiency
Diabetes alone, and diabetic nephropathy, especially > Cr 1.5 mg/dL, or 60 ml/minute/1.73 m2
Acutely rising Cr
Concurrent use of vasoconstrictive (nonsteroidal anti-inflammatory medications), nephrotoxic medications (aminoglycosides), and volume-depleting agents such as diuretics
States of reduced perfusion such as hypotension, hypovolemia, cirrhosis, and congestive heart failure
Age > 70, hypertension, anemia, female gender, multiple comorbidities
Urgent procedures
Large volume contrast load

Risk factors for contrast-related allergy reactions

Previous anaphylaxis to contrast material
Asthma
Multiple medication allergies, including food or medication

Table 106-2 Patient Safety Measures for All Patients About to Receive Contrast

Is the study necessary? How important is the study? If contrast is not administered, will you obtain the information you need to make a clinical decision?
Does the patient have risk factors for contrast-induced nephropathy?
Does the patient have allergy to contrast and if so, which type?
Is there an alternative study that does not involve contrast?
Are there any modifiable risk factors?
- Discontinue NSAIDS at least 24 hours prior to the administration of contrast, particularly in patients at increased risk.
- Discontinue metformin for 48 hours prior to the administration of contrast if the creatinine is abnormal; if normal, discontinue and perform the study, if required, without delay.
- Consider holding oral hypoglycemics on the day of the study as most patients will be npo, and prescribe replacement insulin as needed.
- Hold diuretics on the day of the study.
- Regarding ACE inhibitors, the data is mixed because there is increased risk as well as protective effects. Do not start ACE inhibitors on the day of the procedure.
- Optimize volume status prior to the procedure.
Will the patient require another contrast study within 72 hours?
If the patient is at increased risk for an ADE, has a discussion occurred with radiology to either reduce the risk or to consider an alternative study?

Risk of Contrast-Induced Renal Failure

It is best to avoid ordering multiple contrast studies in rapid succession and seek alternative imaging modalities whenever possible because contrast-induced renal failure is associated with higher morbidity and mortality as well as longer length of hospitalization. Based on a generally accepted definition of contrast-induced renal failure, administration of contrast material causes renal failure in 0.1% to 13% of patients who receive it and it is responsible for 12% of cases of hospital-acquired renal failure. How contrast materials cause renal failure is unclear, but it is likely due to direct cellular toxicity and intrarenal vasoconstriction. If a patient has an estimated glomerular filtration rate < 60 ml/minute/1.73 m2, the patient is at increased risk; the risk is much higher if there are other contrast-induced nephropathy risk factors, or if the patient has an acutely rising creatinine, even if below 1.5 mg/dL.

The risk of renal failure following contrast administration is dose dependent and occurs most frequently in patients with already diminished renal function, particularly diabetic nephropathy. A patient with preexisting renal insufficiency is 5 to 10 times more likely to develop contrast-induced renal failure than the general population. The risk of further renal injury may be decreased by hydration. Radiologists typically avoid administering iodine contrast agents to patients with multiple myeloma, especially if they are dehydrated, but it can be used when absolutely necessary. The risk of renal failure in patients with multiple myeloma is caused by an interaction of light chains and contrast material. Due to the decline of renal function with age, elderly patients are at increased risk of developing renal insufficiency from contrast. Institutional guidelines may include renal function testing prior to contrast administration based on patient age.

Patients treated with nephrotoxic medications (eg, aminoglycosides and nonsteroidal anti-inflammatory agents) and those who have recently received iodinated contrast material are at greater risk for acquiring renal failure. Metformin (Glucophage), frequently used to treat type II diabetes may cause severe lactic acidosis following administration of intravenous contrast media. Metformin therapy may be suspended for at least 48 hours following the administration of iodine contrast material and resumed after the patient’s renal function has returned to baseline serum creatinine level. Adjustment of medications that are excreted by the kidneys may also be helpful.

Patients with eGFR >60 are considered by radiologists to have normal renal function for routine prescription of IV contrast. For eGFR between 30 and 60, the dose of contrast material may be reduced if the diagnostic quality of the scan may be preserved at lower contrast doses. If not, alternative diagnostic strategies should be pursued. When eGFR is less than 30, IV contrast material should be avoided. Patients with end stage renal failure on dialysis may receive IV contrast material when necessary if prior discussion with their nephrologists has taken place.

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Case 106-1

WEIGHING THE RISK OF CONTRAST

A 61-year-old female mentioned transient right-sided pleuritic chest pain to her nephrologist. When a CXR revealed a new moderate right-sided pleural effusion, he recommended a V/Q scan. Her glomerular filtration rate (eGFR) estimated at 32 ml/minute might not preclude a contrast study according to hospital protocols but she had only one functioning kidney. Extensive changes of intersitital lung disease were also reported on CXR. Lower extremity ultrasound did not reveal deep venous thrombosis.

Key question:

Would a V/Q scan provide any meaningful information given her extensive interstitial lung disease, bronchiectasis, and bullous emphysema?

This patient would most likely have an indeterminate or, perhaps, an intermediate probability scan. In a landmark PIOPED study, more than half of individuals with intermediate probability and indeterminate studies were found to actually have PE (pulmonary embolism).
Would hydration and mucomist provide suitable protection for PE protocol imaging?

Although hydration is definitely helpful, it may not provide adequate protection in patients with markedly compromised renal function. It is debatable whether mucomist would provide any additive benefit.
Should such a patient receive hemodialysis following administration of IV contrast for CT if required for adequate diagnosis or selection of treatment?

Hemodialysis will not adequately remove contrast material to conserve renal function.
What are the risks of gadolinium in patients with compromised renal function?

Gadolinium can no longer be recommended due to high risk of NSF.
Would there be any utility to performing MR without gadolinium?

MRI is infrequently used to address PE, and then almost always with gadolinium enhancement of vessels. MRI does not offer a practical solution for obtaining a diagnostic quality examination of pulmonary vessels in an acutely ill, dyspneic patient.
What if this patient had pleuritic chest pain from active SLE?

If the patient has active SLE, it is possible that her renal insufficiency might become unstable, thereby further increasing her risk. This patient also had light chains in her urine consistent with multiple myeloma.