Contrast Media are agents which are used to image organs or body structures after their introduction into body cavities or through vessels.
Side effects and reactions
Adverse reaction to contrast media may be considered under three main conditions of clinical usage:
(1) Reactions following use of a very large dose of contrast media e.g. in angiocardiography and high dose pyrography.
(2) Reactions were due to delivery of a concentrated bolus of contrast medium to some critical area such as myocardium, brain, spinal cord, or kidneys.
(3) Reactions were due to idiosyncrasy.
About 5-8% of all intravascular contrast media injections are associated with side effects, most of which are fortunately mild or moderate.
Classifications of reactions of contrast media
1. Mild: Side effects considered physiological. No treatment e.g. nausea, vomiting.
2. Moderate: Transient, non-life-threatening: (intermediate) Occasionally treated, maybe prodromal.
3. Severe: Life-threatening; treatment and hospitalization required.
4. Death.
Those primarily involving the respiratory system are accompanied by minor reactions while those primarily involving CVS have more serious reactions. Pretesting has been found to be no value in determining which patient will have an adverse reaction.
Major and Minor Risk factors of contrast media
Major Risk factors
1. Age < 1 yr, > 50-60 yrs.
2. Previous reaction to contrast media
3. Allergy/asthma
4. Cardiovascular disease
Minor Risk factors
1. Azotemia
2. Diabetes mellitus
3. Dehydration
4. Dysproteinemia
5. Sickle cell disease
6. Anxiety
Delayed contrast media reactions occur in 30% of cases:
1. Delayed rashes in 5% of cases.
2. Delayed arm pain in 14% of cases.
3. Iodism: 9% by iodine or related compounds.
4. Steriods gave 24 hrs. before have been found useful.
5. The treating doctor should remain calm and should not arouse anxiety or fear.
General guidelines Treatment of contrast reactions
In any severe reaction release compassion and administer 100% oxygen by face mask and bag. Further treatment depends on the type of reaction.
1. Anaphylactic type: While mild cases may have just urticaria, severe cases may develop oedema of glottis or pulmonary edema. They are treated by chlorpheniramine maleate.
(a) Piriton 10 mg intravenously.
(b) Adrenaline 0.5 ml ( 1 : 1000 ) subcutaneously.
(c) Methylprednisolone or hydrocortisone succinate in doses of 40 mg or 100 mg I/V respectively.
(d) Tracheostomy or cricothyroid membrane puncture.
2. In case there are generalized convulsions in. diazepam 10 mg I/V slow.
3. Hypotensive with peripheral circulatory failure.
(a) Elevate feet 18 in.
(b) Vasoxine 5 mg I/V every 3 minutes.
(c) Hydrocortisone succinate 100 mg I/V.
4. Cardiac arrest
(a) Thumb precordium external cardiac massage, elevate foot 18 inches.
(b) Mouth-to-mouth respiration.
(c) Intubation.
(d) Put the patient on cardiac monitoring ECG and defibrillators.
(e) Clear the airways, constantly extend the head and push the lower jaw forward.
Intravascular contrast media
The first reports of opacification of the urinary tract by renal excretion rather than by retrograde introduction of a contrast agent appeared in 1923 with the use of 10% sodium iodide. In 1950 modern water-soluble contrast media were introduced into clinical radiology.
There are all derivatives of triiodobenzoic acid, the first being sodium acetrizoate was reported. This had an acetamido group at the previously unsubstituted position 5 and unlike acetrizoate was fully saturated benzoic acid derivative. Isomerization of diatrizoate and substitution at position 5 of methyl carbamyl produced the iothalamate molecule in 1962.
The majority of modern conventional water-soluble contrast agents are distinguished by differences at position 5 of the anion and by the cations sodium and meglumine. Iodine with atomic weight 127 is the only element that has proved satisfactory for general use as an intravascular radiological contrast agent. The iodine provides the radio-opacity, the other elements in the molecule act as carriers of the iodine, increasing the solubility and reducing the toxicity of the molecule.
Very large amounts of iodine are necessary because of the low sensitivity inherent in conventional photographic film radiography screens. Alternative non-photographic radiographic recording systems such as photon detectors are much more contrast sensitive, CT, for example, will detect a vascular blush in 90-97% of intrarenal tumors on IV injection of contrast agent compared to probably less than 50% after selective intracarotid arterial injection recorded by conventional radiographic photography.
All conventional ionic agents are salts, consisting of a sodium or meglumine cation and a triiodinated substituted benzoate anion. All of these anions are based on a common format consisting of a benzoic acid molecule with 3 atoms of iodine firmly attached to C2, C4, and C6. The remaining 2 carbon atoms (C3 and CS) are connected to small side chains or radicals which are substituted amines that greatly reduce the toxicity and the solubility of the molecule.
Proprietary brands differ only in a minor modification of the radicals but do not provide any superiority over the other. Meglumine salts are less toxic than sodium salts, but meglumine is a strong diuretic and its salts are more viscous in solution.
The major disadvantage of all conventional ionic contrast media is that their molar concentration is extremely high i.e. up to 8 times the physiological level of 300 mmol/kg water. This high osmolarity is responsible for any adverse effects. The very high osmolarity is due to the fact that the non-radiopaque cations i.e. Na or Me exert just as great an osmolar load as the radiopaque iodinated anion. The cation is merely a carrier and serves no radiographic function. It would be much more advantageous to have a contrast medium with
fewer or no radiopaque cations. The iodine: particle ratio for all conventional high osmolar monomeric contrast medium salts is 3: 2.
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