Radiology Review Manual (Dahnert, Radiology Review Manual)

Authors: Dahnert, Wolfgang

Title: Radiology Review Manual, 6th Edition

Copyright 2007 Lippincott Williams & Wilkins

> Table of Contents > Water-Soluble Contrast Media

Water-Soluble Contrast Media

• Ionic = dissociation in water

• Nonionic = soluble in water (hydrophilic); no dissociation in solution

• Iodine-to-particle ratio:

  • = quotient of iodine atoms (attenuation of rays) and number of particles (osmotoxic effect)

  • ratio 1.5 agents = high-osmolar contrast media (HOCM)

  • ratio 3.0 agents = low-osmolar contrast media (LOCM)

  • ratio 6.0 agents = isotonic contrast media (IOCM)

Ionic Monomers

• = monoacidic salts composed of benzoic acid derivatives, with 3 hydrogen atoms replaced by iodine atoms + 3 hydrogen atoms replaced by simple amide chains

• in solution: strong organic acid completely dissociated (ionized) into negatively charged ions / anions

• Conjugated cations:

  • sodium

  • methylglucamine (meglumine)

  • combination of above

• Iodine concentration: up to 400 mg/mL

• Iodine-to-particle ratio: 3:2 or 1.5:1

• Osmolality: 1,400-2,100 mOsm/kg = HOCM

Ionic Dimers

• Construction:

  • 2 iodinated benzene rings containing 6 iodine atoms, one of which contains an ionizing carboxyl group; benzene rings are connected by a common amide side chain

The parent triiodinated contrast medium in first clinical use; the benzene ring is attached to a carboxyl (COO-) group at the 1-carbon position and conjugated with sodium / meglumine

The unsubstituted hydrogen of acetrizoate has been exchanged for another acetamido unit leading to higher biologic tolerance through higher degree of protein binding Iodine concentration: up to 350 mg/mL Iodine-to-particle ratio: 3:1 Compounds: iohexol, iopamidol, ioversol, iopental,

Sodium + meglumine are conjugated with the carboxyl group

• Conjugation with: sodium + meglumine

• Compound: ioxaglate (the only available)

• Iodine concentration: 320 mg/mL

• Iodine-to-particle ratio: 6:2 or 3:1

• Osmolality: 600 mOsm/kg = LOCM

Nonionic Monomers

• Construction:

• benzoic acid carboxyl group replaced by amide; side chains have been modi.ed by adding 4-6 hydroxyl (OH) groups, which allows solubility in water

The first compound with 4 hydroxyl groups positioned at one end of the molecule on the glucosamide moiety

contains 6 hydroxyl (OH) groups more evenly distributed around the molecule improving subarachnoid toxicity

This nonionic monomer contains 5 hydroxyl (OH) groups

This nonionic monomer contains 6 hydroxyl (OH) groups

P.1131

• Iodine concentration: up to 350 mg/mL

• Iodine-to-particle ratio: 3:1

• Compounds: iohexol, iopamidol, ioversol, iopental, iopromide (Ultravist ), iobitridol (Xenetix ), ioxilan (Oxilan )

• Osmolality: 616-796 mOsm/kg

Nonionic Dimers

• Construction:

  • contain up to 12 hydroxyl groups to eliminate ionicity, increase hydrophilicity, lower osmotoxicity, and increase iodine atoms per molecule

  • Iodecol, iotrolan (Isovist ), iodixanol (Visipaque )

  • Iodine-to-particle ratio: 6:1

  • Osmolality: hypo- / isoosmolar

Excretory Urography

• Clearance:>99% of contrast material eliminated through kidney (<1% through liver, bile, small and large intestines, sweat, tears, saliva); vicarious excretion with renal insult / failure (may be unilateral as in obstructive uropathy)

This noniomic dimer contains 12 hydroxyl (OH) groups

Physicochemical Properties of Commonly Used Radiographic Contrast Media

P.1132

• Halftime: 1-2 hours (doubled in dialysis patients)

• Concentration: 60% by weight

  • Sodium-containing HOCM

    • less distension of collecting system

  • Meglumine-only HOCM

    • improved distension of collecting system (due to decreased tubular resorption of water)

  • LOCM

    • denser nephrogram + slightly denser pyelogram than HOCM (due to higher tubular concentration)

Angiography

• Burning sensation:

  • intense with concentration of 60-76% HOCM

  • reduced with concentration of 30% HOCM / LOCM

    • Overall incidence of adverse allergic-type reactions is (for unknown reasons) much less with intra-arterial than with intravenous use of contrast media!

Venography

• Foot / calf discomfort or pressure or burning

  • ~24% with 60% HOCM

  • ~5% with 40% HOCM / 300 mg iodine/mL LOCM

    • The addition of 10-40 mg lidocaine/50 mL of contrast media decreases patient discomfort!

• Postphlebography deep vein thrombosis

  • 26-48% with 60% HOCM

  • 0-9% with dilute HOCM / LOCM

    • Infusion of 150-200 mL of 5% dextrose in water / 5% dextrose in 0.45% saline / heparinized saline through injection site immediately after examination reduces likelihood of DVT!

Contrast Material in Pediatrics

• Conventional dose: 1 mL / pound up to 150 mL

• Maximum dose: 280-300 mg I/mL

Adverse Contrast Reactions

• Nonidiosyncratic (= dose-related) reactions

  • Cause: direct chemotoxic / hyperosmolar effect

    • nausea, vomiting

    • cardiac arrhythmia

    • renal failure

    • pulmonary edema

    • cardiovascular collapse

• Idiosyncratic (= anaphylactoid) reactions

  • = reactions occurring unpredictably + independently of dose / concentration = not a true antigen-IgE antibody-mediated reaction nor a reaction to iodine / iodide

  • Cause: unknown

    • hives, itching

    • facial / laryngeal edema

    • bronchospasm, respiratory collapse

    • circulatory collapse

• Delayed reactions

  • erythematous rashes, pruritus

  • fever, chills, ulike symptoms

  • joint pain

  • loss of appetite, taste disturbance

  • headache, fatigue, depression

    Prevalence of Adverse Contrast reactions

    	High-osmolar Ionic	Low-osmolar Nonionic
    Non-life-threatening reaction	1-2%	0.2-0.4%
    Life-threatening reaction	0.2%	0.04%
    Mortality	1:100,000	1:100,000
    Late reaction		6%

  • abdominal pain, constipation, diarrhea

Signi.cant underlying medical conditions:

• renal disease

• cardiac disease

• blood dyscrasias

• pheochromocytoma

• increased symptoms with COPD plus pulmonary hypertension

• increased sickling in patients with sickle-cell disease

  • Approximately 20-40% of population are at increased risk for adverse reaction to contrast media!

  • In patients with adverse reactions to HOCM repeated reactions will be lowered to 5% by using LOCM

  • No direct correlation / association to povidone-iodine skin cleansing solution (Betadine )

Nephrotoxicity

Nonoliguric Transient Renal Dysfunction

• = transient decline of renal function

  • serum creatinine level peaks on days 3-5

  • serum creatinine returns to baseline values within 14-21 days

  • fractional excretion of sodium < 0.01 (DISTINCTIVE CHARACTERISTIC compared with other causes)

Acute Renal Failure

• = sudden + rapid deterioration of renal function

• = increase in serum creatinine of > 25% or to > 2 mg/dL within 2 days of receiving contrast material

Risk Factors and Incidence of Adverse reactions for High- and Low-Osmolality Contrast Media

P.1133

• Frequency:1-30%; 3rd most common cause of in-hospital renal failure after hypotension and surgery

• Risk factors:

  • Preexisting renal insuf.ciency (serum creatinine <1.5 mg/dL)

  • Diabetes mellitus with renal insuf. ciency (possibly related to dehydration / hyperuricemia)

    • Ratio 3 nonionic LOCM appear to be 50% less nephrotoxic than ratio 1.5 ionic HOCM

    • Diabetics with normal renal function are not at increased risk!

  • Dehydration

  • Cardiovascular disease

  • Use of diuretics

  • Advanced age <70 years

  • Multiple myeloma (in dehydrated patients)

  • Hypertension

  • Hyperuricemia / uricosuria

  • High dose of contrast material

• CAVE:

  • Small decreases in renal function may greatly exacerbate the mortality caused by the underlying condition!

  • Metformin (Glucophage ) should be discontinued for 48 hours after contrast medium administration (accumulation of metformin may result in lactic acidosis, which is fatal in 50%)!

    • It is not necessary to stop metformin after gadolinium administration because gadolinium is not nephrotoxic!

  • Avoid concomitant use of nephrotoxic drugs (eg, gentamycin, NSAIDs)

• Proposed mechanisms:

  • contrast agents are concentrated in nephrons + collecting tubules

    • Vasoconstriction

      • increase in intrarenal pressure induced by hypertonicity

      • intrarenal smooth muscle contraction in response to hypertonic substances

    • RBC aggregation in medullary circulation

    • Direct tubular cell injury

• Potential antidotes:

  • Hydration (0.9% saline at 100 mL/h) 12 hours before + 12 hours after angiography

  • Extracellular volume expansion is the most effective + widely recommended measure!

  • immediate dense nephrogram persisting for up to 24 hours (in 75%) gradually increasing dense nephrogram resembling bilateral acute ureteral obstruction (in 25%):

  • bilaterally enlarged smooth kidneys

  • poor opaci.cation of urine-conducting structures

  • effacement of collecting system (interstitial edema)

Cx: 34% mortality (0.4% of all patients)

Rx: 0.1% require renal replacement therapy

Assessment of Patients before Contrast Injection

• General status

  • Assess hemodynamic, neurologic, general nutritional, anxiety status

• History of signi. cant allergies

  • Prior anaphylactic response to any allergen

  • Asthma

• Renal disease

  • Renal dysfunction: obtain baseline BUN + creatinine

  • Diabetes mellitus

  • Multiple myeloma

    • Hydrate patients and limit contrast dose!

• Cardiac disease

  • Angina

  • CHF with minimal exertion

  • Severe aortic stenosis

  • Primary pulmonary hypertension

  • Severe cardiomyopathy

    • Limit contrast dose!

Treatment of Contrast Reactions

• 94-100% of severe + fatal anaphylactoid reactions occur within 20 minutes of contrast medium injection

  • use a plastic cannula for IV access

  • maintain IV access for 30 minutes

  • have emergency drugs close to the room where contrast injections are done

  • post a listing of available medications + their common doses in the room

Oral Steroid Premedication Protocol

• 32 mg methylprednisolone (Medrol ) PO 12 and 2 hours prior to contrast injection

• 50 mg prednisone PO 13 + 7 + 1 hour prior to contrast injection, plus

  • 50 mg diphenhydramine (Benadryl ) IV / IM / PO 1 hour prior to contrast injection

• nonionic low-osmolality contrast agent

  • Indication: previous respiratory adverse contrast reaction, history of signi.cant allergies / severe asthma

  • Caution in patients with: active tuberculosis, diabetes mellitus, peptic ulcer disease

• Antihistamines alone have not proved to be effective!

Treatment of Premedicated Patients

• Patient on -blocker

  • if response to epinephrine inadequate

  • 1-5 mg glucagon IV + subsequent slow drip of 5 mg glucagon over 60 min

• Patient on calcium channel blocker (eg, nifedipine, nicardipine)

  • calcium IV

• Excessive vasoconstriction on epinephrine IV

  • infusion of 0.5-10 g/kg/min of reconstituted sodium nitroprusside (Nipride ) (50 mg in 500-1000 mL of 5% dextrose wrapped in metal foil during use to protect solution from light)

• Metformin (Glucophage )

  • Stop metformin medication at time of contrast injection + for subsequent 48 hours

  • Reinstate medication if renal function remains normal

  • Contrast material is contraindicated if patient is in renal failure because of risk of lactic acidosis!

P.1134

Useful Medications

• Alpha- and -adrenergic agents:

  • Action: vasoconstriction, increased cardiac output

  • Epinephrine

    • 1 mL glass vials of epinephrine 1:1,000

      • Adult dose: 0.1-0.2 mL epinephrine (1:1,000) (= 0.1-0.2 mg) SQ

      • Pediatric dose: 0.01 mL/kg up to 0.3 mL/dose

      • Repeat in 15-30 minutes if needed

      • Indications: bronchospasm, facial edema, severe urticaria, laryngospasm

    • prepackaged 10-mL syringes of epinephrine 1:10,000

      • Adult dose: 1-3 mL epinephrine (1:10,000) (= 0.1 mg) slowly IV

      • Pediatric dose: 0.1 mL/kg slowly IV

      • Repeat every 5-15 minutes if needed

      • Indications: bronchospasm / laryngospasm with peripheral vascular collapse

      • Maximum dose: 1.0 mg

  • Dopamine (Inotropin )

    • Adult dose: 2-5 pg/kg/min IV; rarely need to exceed 20 pg/kg/min

    • Indications: hypotension

    • Cx: arrhythmia, myocardial ischemia, nausea, vomiting, tremulousness, headache

• Atropine sulfate

  • Adult dose: 0.6-1.0 mg slowly IV

  • Pediatric dose: 0.02 mg/kg slowly IV (0.2 mg/kg of the 0.1 mg/mL solution); min dose of 0.1 mg (children) + 1.0 mg (adolescents)

  • Repeat after 5 min

  • Maximum dose: 0.04 mg/kg (2-3 mg) in adults

  • Indications: bradycardia, hypotension

  • Cx: angina, myocardial infarction

• Metered-dose inhalers of -adrenergic bronchodilators

  • Metaproteranol (Alupent )

  • Terbutaline (Brethaire )

  • Albuterol (Proventil , Ventolin )

  • Dose: 2 puffs every 20-30 minutes, as needed

• H1 antagonists = antihistamines

  • Diphenhydramine (Benadryl )

    • Adult dose: 25-50 mg PO/IM/IV

    • Pediatric dose: 1-2 mg/kg IV, up to 50 mg

  • Hydroxyzine (Vistaril )

    • Dose: 25-50 mg PO/IM/IV

    • Indications: hives, rash, itching

    • Cx: hypotension, sedation

• H2 receptor blockers

  • Cimetidine (Tagamet )

    • Dose: 300 mg PO / slowly IV (diluted in 10 mL D5W solution)

  • Ranitidine (Zantac )

    • Dose: 50 mg PO / slowly IV (diluted in 10 mL D5W solution)

    • Indications: hypotension; bronchospasm

• Aminophylline

  • 250 mg in 250 mL of 5% dextrose

    • Dose: 6 mg/kg IV in D5W over 15-20 minutes (loading dose); then 0.4-1.0 mg/kg/hour

    • Indications: bronchospasm, pulmonary edema

    • Cx: hypotension, cardiac arrhythmia

• Terbutaline

  • 0.25-0.50 mg IM/SQ

• Sedatives

  • Midazolam (Versed )

    • Dose: 0.5-1.0 mg IV; short acting

    • Indications: sedation

  • Diazepam (Valium )

    • Dose: 2-10 mg IV

    • Indications: seizures

  • Pentobarbital (Nembutal )

    • Dose: <50 mg/min IV; 150-200 mg IM

    • Indications: toxic convulsions

    • Cx: respiratory depression, apnea, laryngospasm, hypotension

• Pain

  • Fentanyl

    • Dose: 25-50 mg IV; short acting

  • Morphine

    • Dose: 1-3 mg IV Indications: pain; pulmonary edema

  • Demerol

    • Cx: respiratory depression

• Volume expander

  • Crystalloid solution as 0.9% saline

  • Hydroxylethyl starch (high-molecular-weight colloid)

• Furosemide (Lasix )

  • Adult dose: 20-40 mg IV slow push / PO

  • Pediatric dose: 1 mg/kg/dose IV up to 40 mg

  • Effect: 5-15 minutes after IV; 60 minutes after PO

  • Indications: acute pulmonary edema, CHF, hypertensive emergency

• Corticosteroids

  • Methylprednisolone (Solu-Medrol )

    • Dose: (a) 32 mg PO; 12 & 2 hours prior

    • (b) 100-1,000 mg (anaphylaxis with shock)