This document discusses contrast media used for medical imaging. It begins by explaining that most contrast media contain iodine, which provides high contrast due to its high atomic number and low toxicity. It then describes conventional, high osmolar contrast media that are salts consisting of iodinated benzoate anions bound to sodium or meglumine cations. The document discusses various contrast agents and notes their advantages and disadvantages, ideal properties of contrast media, risks of toxicity from hyperosmolarity, and treatments for adverse reactions.

1. Contrast Media
DR. MAHENDAR REDDY

4. IODINE
Most of the I.V. Contrast media contain Iodine
which has an atomic number of 53 and atomic
weight 127.
It’s preferred because
1) High contrast density due to high atomic
number. 2) Allows
firm binding to highly variable benzene ring
3) Low Toxicity

5. Conventional contrast Media/ High Osmolar
contrast media/ Ionic Monomers
 These are salts consisting of a sodium or meglumine cation and a
triodinated benzoate anion.
 Anions consisting of a benzoic acid molecule with three atoms of
iodine firmly attached at C2, C4 and C6.
 The C3 and C5 are connected to radicals CR3 and R5, which are
amines E-NH2 , and greatly reduce toxicity and increase solubility of
the molecules.
 Iodine particle ratio 3:2
 Sodium or meglumine acts as Cations
 Ex : Diatrizoic Acid ,Iothalamic Acid

6. Diatrizoic Acid
 The two side chains R3 and R5 in Diatrizoic acid
are replaced by ( NHCOCH3) . This
 Increases solubility
 Decreases plasma protein binding thereby
increasing its ability to be filtered in
glomerulus.
 Improves patient tolerance.

7. Disadvantages of conventional contrast
media
 Osmolar concentration(osmolality) is extremely
high up to 8times the physiological level of 300m
Osm/kg water.
 Osmolar challenge to every cell , tissue and fluid
in the body is responsible for their adverse
effects.

8. Useful facts to remember
 Osmolality is dependent on number of particles of
solute in solution.
 Radiopacity is dependent on the iodine concentration
of the solution and is therefore dependent on the
number of iodine atoms in each molecule of the
contrast media.
 High radiopacity and low osmolality are desirable
requirements.

9.  The ratio of the number of iodine atoms per
molecule to the number of particles per
molecule of solute in solution is therefore a
fundamental criterion.
 Iodine particle ratio for all is 3:2.
 Non- ionicity is essential for myelography and
reduces the reactions to I.V injection.

10. Additives used in contrast media
Stabilizer - Ca or Na EDTA.
BUFFERS – stabilizes pH during storage –
Na acid phosphates.
Preservatives: Generally not disclosed by
manufacturers.

11. Ideal contrast media should have
 High water solubility.
 Heat and chemical stability (shelf life). Ideally 3-5
years.
 Biological inertness ( non antigenic).
 Low viscosity.
 Low or iso-osmolar to plasma.
 Selective excretion, like excretion by kidney is
favourable.

12. Safety : LD50( lethal dose) should be
high.
Reasonable cost.

13. Points to remember
Contrast media used for myelography are
non- ionic contrast media.
 Contrast media used for cerebral angiography
are contrast media containing only meglumine
cation.
 Meglumine salts cause bronchospasm, so contra-
indicated in bronchial asthma.

14. Points to remember
Incidence of thrombo embolic
phenomenon is fairly high when
contrast media is mixed with blood.
So, meticulous heparinization is
required during angiography.

15. Toxicity
 Reactions unrelated to contrast media. 1)
Pyrogenic ( unsterile injection).
 2) vasovagal especially in anxious or
psychosomatic patient.
 3)Hypertensive attacks in patient with
pheochromocytoma.
 Excessive dehydration, hypoglycemia.

16. Toxicity: Hyper osmolarity
 This is due to high osmolarity of contrast media than
plasma. More with conventional contrast media. These
reactions include:
ERYTHROCYTE DAMAGE: Injection of
hyperosmolar contrast media > Loss of H20
from RBC > Dehydrated shrunken RBC >
Increased internal viscosity with loss of ability
of RBC to deform to traverse capillaries >
Obstruction of important capillary beds
(cerebral, coronary, renal, pulmonary).

17. Hyperosmolar Contrast media >
Shrinkage of endothelial cells >
Widening of intercellular gaps >
Capillary permeability.
Toxicity: Capillary endothelial damage

18. Toxicity: Vasodilation
 Vasodilatation of arteriolar beds, is a direct result of
perfusion with any hyperosmolar solution.
 Clinically, this is evident by marked vasodilatation
produced on peripheral arteriography.
 This produces a sensation of heat, which may be
uncomfortable and often accompanied by pain,
especially in hand and external carotid artery
territory.

19. Toxicity: Hypervolemia
 This is due to diffusion of extracellular fluid through capillary
walls into blood which occurs whenever large volumes of
hyperosmolar fluid are injected intravascularly.
 The extravascular fluid is drawn in so much that the blood
volume may increase by 10% within a few seconds.
 The increased capillary permeability due to endothelial
damage, permits intravascular fluid to escape from the
capillaries and soon reduces the blood volume towards its
original level.

20. Toxicity: Cardiovascular effects
 Peripheral vasodilatation.
 Decreased systemic blood pressure.
 Tachycardia.
 Cardiovascular insufficiency.
 Acute hypervolemia > Left ventricular stress.
 Selective arteriography induces bradycardia and moderate reduction in
cardiac output.
 Na edetate and Na citrate which are used as preservatives in the
contrast media chelate Ca2+, therefore leading to transient
hypocalcaemia. This causes negative ionotropic effect on heart.

21. Nephrotoxicity is due to:
 Decreased renal perfusion. (low B.P., peripheral
vasodilatation).
 Glomerular injury - manifest as proteinuria.
 Tubular injury - due to osmolarity, chemotoxicity,
ischaemia.
 Contrast media precipitation of Tamm Horsfall proteins
that block tubules.
 Swelling of renal tubular cells causing obstruction.

22. Immunological ( allergic)
Toxicity:Mechanisms
 Deactivation of angiotensin converting enzyme
 Incidence of adverse contrast media reactions to intra-arterial
injection is about l/3rd of incidence following intravenous
injection because the latter stimulate release of vasoactive
substances from mast cells or deactivates ACE in lung.
 ACE deactivates bradykinin, the concentration of which rises
with IV injection of Contrast media.
 Due to damage to the endothelium which initiates the activation
system which inturn may be responsible for many adverse
anaphylactoid reactions.

23.  Activation of complement, kinins, coagulation
and fibrinolytic systems.
 Inhibition of cholinesterase with consequent
vagal over stimulation > acetylcholine release
> collapse, bradycardia, bronchospasm.
 Release of vasoactive substances like
histamine, bradykinin,serotonin.

24. High risk group people
 Prior reactions to contrast media - 11 times more prone.
 History of allergy - 4 times more prone.
 Cardiac disease - 4 times more prone.
 Asthma - 5 times more prone.
 Diabetes - 4 times more prone.
 Old age - 4 times more prone.
 Neonates - 4 times more prone.
 Myelomatosis, polycythemia.
 Sickle cell anaemia, pheochromocytoma, homocystinuria.

25. Severity of Reactions
 Minor : 1 in 20 cases - 5% -Nausea, vomiting, mild rash, light
headache and mild dyspnoea. Needs no treatment, but requires
assurance.
 Intermediate l in 100 - 1% - Extensive urticaria, facial edema,
bronchospasm, laryngeal oedema, dyspnoea, mild chest pain or
hypotension. Requires treatment but generally there is no need
for hospitalization.
 Severe reactions (l in 2000 - 0.05%) - Circulatory collapse,
pulmonary oedema, severe angina, myocardial infarction,
convulsions, coma, cardiac or respiratory arrest. Requires
hospitalization and intensive care.
 Mortality - (l in 40,000 - 0.0025%).

26. Treatment if needed:
 No patient will have serious reaction after 60 mins of contrast
administration, so for first 60mins we need to monitor and
watch out for adverse reactions.
 Oxygen : Current recommendation for use of high dose
oxygen is at the rate of 10-12 L/min via face mask.•
 02 can be provided at up to 100% concentration.
 Currently it is recommended that high concentration of 02
shouldbe administered to any patient in respiratory distress,
regardless of his or her pre-existing condition.

27. Treatment
 Epinephrine: The most important medication
needed for Anaphylactoid reaction.

28. Thank you