CONTRAST AGENTS

Contrast agents 

Introduction :- 
•    Contrast agents are required in the cardiac catheterization  procedures.
•    Can cause fatal allergic reactions.
•    It is important to know the history of any previous contrast exposure and allergy..
•    “Iodine”  gives it “radioopaque” and causes allergy too.
•    Patients with seafood allergy as some “shellfish” have iodine are prone for adverse reactions.

Ideal Contrast Media in Angiography:-
•    Water soluble 
•    Chemical and heat stable
•    Biologically inert (no antigen)
•    Low viscosity 
•    Low or Iso-osmolar,
•    excreted Selectively through the kidneys 
•    Safe
•    Inexpensive 

Mechanism of action of Contrast Media:-
•    Iodine has atomic number, increases the attenuation by increasing the linear coefficient of radiation.

Classification:-2 major classes
  Ionic - Dissociate into ionic particle in solution and Non-ionic - do not dissociate 

High osmolar Ionic = Diatrizoate (Hypaque)
Low osmolar Ionic = Ioxaglate 
Low osmolar Non Ionic = Iohexol (omnipaque)
Iso osmolar Non Ionic= Iodixanol ( visipaque)
All agents are derivatives of “Benzoic acid”,only number of iodine molecules , ionic and osmolar composition vary.
Low osmolar, non ionic are safer, produce less side effects.

Volume of CM :- 
 Ionics = 2-3ml/kg    

Non-ionics = 5ml/kg

Also calculated as = 5.weight / Sr Creatinine (mg/dl)

Side effects:-
                             1. Nausea vomiting 
                             2. Flushing (due to vasodilatation) 
                             3. Pain and burning sensation at the site of injection.
                             4. Anaphylaxis 
                             5. Urine output –may increase due to hypertonicity diuresis occur initially  it increases circulatory

                                blood volume by osmotically shifting fluid into vascular space.

Classification of contrast- induced anaphylactoid reactions :-

Minor  - urticaria(limited)/pruritus /erythema 
Moderate – urticaria (diffuse)/ angioedema /lanyxngeal edema/bronchospasm 
Severe - cardiovascular shock/ respiratory arrest /cardiac arrest.

Different diagnosis for severe reactions :- 
    Cardiac                                                          Non-cardiac
1. Vasovagal reaction,                                      1. Hypovolumia 
2. Cardiogenic shock                                        2. Dehydration 
3. RV infection                                                 3. Blood loss
4. Cardiac tamponade                                      4. Sepsis
5. Cardiac rupture                                            5.Drug related-Narcotics, benzodiazepines,protamine

Ionic contrast agents produce hypotension by-

-Vasodilatation 
-Transient myocardial dysfunction  
-Decreasing circulating volume after osmotic diuresis .

Indications  for low osmolar non-ionic agents – 

Unstable ischaemic syndrome 
CCF
DM
Renal insufficiency 
Hypotension
Severe bradycardia 
H/O contrast allergy 
Severe valvular  heart disease ( severe AS)
IMA  and peripheral vascular injections 
 Anticipated use of large volume of contrast agents 
EF < 30>

Both  ionic and nonionic agents are Anticoagulant  & Antiplatelet.
Trans placental / milk passage can cause iodine mumps or hypothyroidism in child.

- by Dr Amarja