The use of contrast agents

Use of contrast preparations inside

With computed tomography of the abdominal cavity and pelvic organs, it is very important to clearly differentiate the intestinal loops from adjacent muscles and other organs. This problem will help to resolve the contrast of the intestinal lumen after oral administration of contrast medium. For example, without a contrast preparation it is difficult to distinguish the duodenum from the head of the pancreas.

The remaining parts of the gastrointestinal tract are also very similar to nearby structures. After taking an oral contrast medium, the duodenum and pancreas become clearly distinguishable. To obtain an image of optimal quality, the contrast drug is taken orally on an empty stomach.

Choosing the right contrast preparation

Better enveloping of the mucous membrane is achieved with the use of barium sulfate, but it is insoluble in water. Therefore, this contrast agent for oral administration can not be used if surgery is planned to open the intestinal lumen, for example, partial resection with anastomosis or if there is a risk of damage to the intestine. Also, the barium suspension can not be used for suspected puff or perforation of the intestinal loops. In these situations, it is necessary to use a water-soluble contrast drug, such as gastrografine, because when it enters the abdominal cavity it easily resolves.

For a better evaluation of the walls of the stomach, regular water is often used as a hypodense contrast preparation, while the buskapan is injected with a view to relaxing the smooth musculature. If the bladder is removed and a reservoir is created from the ileum, the abdominal cavity is first examined with intravenous administration of contrast medium. Which is excreted in the urine into the reservoir and does not enter other parts of the intestine. If you need to study other parts of the gastrointestinal tract, an additional scan is performed after taking the contrast drug inside.

Time factor

To fill the proximal parts of the gastrointestinal tract, 20 to 30 minutes is enough. The patient drinks the contrast preparation on an empty stomach in small portions in several doses. If you need to fill with barium sulphate thick and, especially, the rectum, you may need a minimum of 45 to 60 minutes. A water-soluble contrast agent (for example, gastrografen) advances through the intestines somewhat faster. When examining the pelvic organs (bladder, cervix, ovaries), the rectal administration of 100-200 ml of contrast preparation ensures their clear delimitation from the rectum.

Dosage

To contrast the entire gastrointestinal tract, 250 - 300 ml of barium sulfate suspension must be thoroughly mixed with water, bringing the volume to 1000 ml. If it is necessary to use a water-soluble drug, 10 to 20 ml of gastrografine (in 1000 ml of water) is sufficient for a complete gastrointestinal examination. If it is necessary to contrast only the upper gastrointestinal tract, 500 ml of any oral contrast preparation

Intravenous application of contrast agents

Increasing the density of blood vessels not only makes it possible to differentiate them better from surrounding structures, but also helps to evaluate perfusion (accumulation of contrast medium) of pathologically altered tissues. This is important for the violation of the blood-brain barrier, the evaluation of the abscess boundaries, or the non-homogeneous accumulation of a contrast agent in tumor-like formations. This phenomenon is called contrast enhancement. In this case, the amplification of the signal occurs due to the accumulation of a contrast agent in the tissues and the associated increase in their density.

Depending on the clinical task, before the / in the introduction of a contrast agent, the scanning of the area of interest without contrast enhancement is usually done-native scanning. When comparing the usual and enhanced images, the evaluation of vascular grafts, inflammatory changes in the bones, and capsule of the abscess is simplified. The same technique is used in the traditional CT scan of focal liver formations. If spiral CT of the liver is used, the venous phase of perfusion of the contrast agent can be used as an analogue of the image without amplification for comparison with the early arterial phase. This makes it possible to detect even small focal formations.

Intravenous administration of contrast medium

Contrast preparations are administered iv in such a way that the bolus (high concentration) in the vessels remains as long as possible until it is diluted in a small circle of circulation. Therefore, to achieve a sufficient degree of vasoconstriction, the administration of contrast preparations should be carried out quickly (2-6 ml / s). Intravenous cannulae with an external diameter of at least 1.0 mm (20G), but better - 1.2 - 1.4 mm (18G, 17G) are used. It is very important to make sure that the cannula is correctly installed in the lumen of the vessel. Before the introduction of a contrast agent, an intravenous injection of sterile saline at the same rate is performed. The absence of subcutaneous swelling at the puncture site confirms the correct placement of the cannula. It also confirms the possibility of passing the required amount of contrast medication through the punctured vein.

Dosage

Calculation of the dose of contrast preparation is carried out based on the patient's body weight and the diagnostic task. For example, the concentration of contrast medium in the study of the neck or aortic aneurysm (to exclude its dissection) should be higher than in the CT scan of the head. In most cases, a good contrast quality is obtained by administering 1.2 ml of the drug per kg of body weight of the patient with a concentration of 0.623 g / ml of yopromide. In this case, it is possible to achieve a combination of optimal vascular contrast and good tolerability of the contrast medium.

Influence phenomenon

In the image of the lumen of the superior vena cava, reinforced and unresponsive areas can be identified due to the simultaneous occurrence of contrasted and uncontracted blood in the vein. A similar phenomenon occurs because of the short time between the onset of contrast agent administration and the onset of scanning. Contrast preparation is introduced from one side and through the axillary, subclavian and brachiocephalic veins enters the upper vena cava, inside which lumen the filling defect is determined. If you do not know about the inflow phenomenon, you can mistakenly diagnose vein thrombosis. Such an artifact occurs more often when too high concentrations of contrast medium are used, especially with spiral CT. On the following pages, the inflow phenomenon will be analyzed in more detail.

Effects of the initial phase of contrasting

In the inferior vena cava at the level of the renal veins, one can see the phenomenon of the tide. A similar phenomenon occurs due to simultaneous visualization of uncompacted blood in the lumen of the vena cava, flowing from the pelvic organs and lower extremities, and blood from the renal veins containing a sufficiently high concentration of the contrast agent. In the initial phase of contrasting, the lower hollow vein is lower (caudal) than the renal veins, in comparison with the descending aorta.

Immediately above the level of renal veins, the lumen of the inferior vena cava in the central part still remains without amplification, and the enhancement is determined near-walled from both sides by contrasting blood flowing from the kidneys. If the kidney is removed or the renal veins flow into the lower vena cava at different levels, contrast enhancement is determined only on one side. Such differences in density should not be mistaken for thrombosis of the inferior vena cava.

The phenomenon of tide

If we follow the lumen of the lower hollow foam towards the right atrium, then after the entry into it of other veins with contrasted blood, an additional tidal phenomenon appears. In the lumen of a hollow thing, regions of non-uniform density are determined, which arise as a result of turbulent flow and mixing of blood with and without contrast medium. This phenomenon does not last long, and after a short time the density of the lumen of the inferior vena cava aorta is equalized.

Specific features of spiral CT

If spiral scanning begins immediately after intravenous injection of contrast medium. And the concentration of the drug in the axillary, subclavian and brachiocephalic veins will be very high, then in the area of the upper aperture of the chest of the corresponding side inevitably there will be significant artifacts in the image. Therefore, with a spiral CT of the chest, the examination starts from the bottom and continues upward (from the caudal to the cranial part). Scanning starts from the diaphragm with the surrounding structures and, when it reaches the cranial part, the contrast drug is already sufficiently diluted in a small circle of blood circulation. This method of research avoids artifacts.

Adverse reactions to the administration of contrast agents

Adverse reactions to the administration of contrast agents are rare. Most of them appear within 30 minutes after the injection, and in 70% of cases - in the first 5 minutes. The need to monitor a patient for more than 30 minutes arises only if he has risk factors. Usually information about the possible occurrence of adverse reactions is present in patients in the medical history, and before the study they receive appropriate premedication.

If, in spite of all the precautions, after the IV management of the contrast medium, the patient develop erythema, urticaria, itching, nausea, vomiting or, in severe cases, a drop in blood pressure, shock, loss of consciousness, shown tables. It should be remembered that the effect of antihistamines after IV introduction does not occur immediately, but after a certain latent period. Severe reactions (pulmonary edema, convulsions, anaphylactic shock) with the use of modern X-ray contrast preparations are very rare and, in case of occurrence, require urgent intensive care.

All possible reactions to contrast agents observed in the patient should be recorded in his medical history. Thus, the radiologist, planning future studies, will be warned in advance about the patient's increased sensitivity to contrast drugs.

Treatment of adverse reactions to the introduction of radiocontrast preparations

Hives

1. Immediately stop the injection of contrast medium.
2. In most cases, there is no need for treatment.
3. Take inside or enter the / m or / in the antihistamine: diphenhydramine (dimedrol) in an amount of 25 - 50 mg.

With severe urticaria and propensity to spread the lesion, adrenomimetic is injected subcutaneously: adrenaline (1: 1,000) in an amount of 0.1-0.3 ml (= 0.1-0.3 mg) in the absence of contraindications from the heart.

Quincke's edema and laryngeal edema

1. Enter adenalinemine (1: 1,000) adrenaline (1: 1,000) in the amount of 0.1-0.3 ml (= 0.1-0.3 mg) or, if the blood pressure falls, adrenaline (1: 10,000) I / in slowly 1 ml (= 0.1 mg). If necessary, the injection can be repeated, but the total dose of the injected drug should not exceed 1 mg.
2. Inhalation of oxygen through the mask (6 - 8 liters per minute). If after this therapy the symptoms of swelling do not pass or continue to grow, you should immediately call a team of resuscitators.

Bronchospasm

1. Inhalation of oxygen through the mask (6 - 8 liters per minute). Configure patient monitoring: ECG, oxygen saturation (pulse oximeter), blood pressure level.
2. 2 - 3 inhalations of the aerosol of betaadrenomimetics: metaproterenol (alupent), terbutaline (brethaire, bricanil) or albuterol (proventil, ventolin, salbutamol). If necessary, inhalation can be repeated. If inhalations are ineffective, adrenaline should be used.
3. Introduce sc or adrenaline: adrenaline (1: 1,000) in an amount of 0.1-0.3 ml (= 0.1-0.3) mg or, if the blood pressure drops, epinephrine (1: 10,000) I / in slowly 1 ml (= 0.1 mg). If necessary, the injection can be repeated, but the total dose of the injected drug should not exceed 1 mg.

Alternative therapy:

Enter i / drip aminophylline (euphyllin) 6 mg / kg body weight in a solution of 5% glucose for 10-20 minutes (shock dose), then 0.4-1 mg / kg / h (if necessary). It is necessary to control blood pressure, because it is possible to significantly reduce it.

If the bronchoconstriction was not able to stop or the blood oxygen saturation is lower than 88%, the brigade of resuscitators should be immediately called.

A drop in blood pressure with tachycardia

1. Raise the legs of the lying patient by 60 ° or higher, or place it in the Trendelenburg position.
2. Monitor: ECG, oxygen saturation of blood (pulse oximeter), patient's blood pressure level.
3. Inhalation of oxygen through the mask (6 - 8 liters per minute).
4. Quickly provide intravenous fluids (physiological or ringerovogo solution)

If therapy is ineffective:

I / in slowly inject adrenaline (1: 10,000) in a volume of 1 ml (= 0.1 mg), if there are no contraindications from the heart). If necessary, the injection can be repeated, but the total dose of the injected drug should not exceed 1 mg. If pressure could not be raised, a brigade of resuscitators should be called in.

Treatment of adverse reactions to the introduction of radiocontrast preparations

Falling blood pressure with bradycardia (vagal reaction)

1. Monitor: ECG, oxygen saturation of blood (pulse oximeter), patient's blood pressure level.
2. Raise the legs of the lying patient by 60 ° or higher or place it in the Trendelenburg position.
3. Inhalation of oxygen through the mask (6 - 8 liters per minute).
4. Quickly provide intravenous fluids (physiological or ringerovogo solution).
5. In / in slowly enter 0.6 mg of atropine. If the patient does not improve, return to points 2 to 4.
6. Atropine can be re-administered, but the total dose should not exceed 0.04 mg / kg of adult body weight (2 - 3 mg).
7. The patient leaves the room only after normalizing the pressure and heart rate.

Increased blood pressure

1. Inhalation of oxygen through the mask (6 - 10 liters per minute)
2. Monitor: ECG, oxygen saturation of blood (pulse oximeter), patient's blood pressure level.
3. Nitroglycerin: 0.4 mg tablet under the tongue (can be repeated 3 times) or in the form of ointment (squeeze out a 1-inch-long strip from the tube and rub into the skin).
4. Transfer the patient to the intensive care unit.
5. If the patient has a pheochromocytoma, 5 mg of phentolamine should be administered iv.

Epileptic seizure or convulsions

1. Inhalation of oxygen through the mask (6 - 10 liters per minute)
2. It is necessary iv to enter 5 mg of diazepam (valium) (the dose can be increased) or midazolam (versed) 0,5 - 1 mg.
3. If a longer effect is required, specialists should be consulted (usually a dropwise injection of phenytoin (dilantin) 15-18 mg / kg at a rate of 50 mg / min is used).
4. Monitoring of the patient, especially should monitor the oxygen saturation of blood in connection with possible respiratory depression due to the use of benzodiazepines.
5. If there is a need for intubation of the patient, you should call a team of resuscitators.

Pulmonary edema

1. Raise the trunk, apply venous strands.
2. Inhalation of oxygen through the mask (6 - 10 liters per minute)
3. In / in slowly enter diuretic: furosemide (lasix) 20 - 40 mg.
4. You can inject iv into the morphine (1 - 3 mg).
5. Transfer the patient to the intensive care unit.
6. If necessary, use corticosteroids.

Thyrotoxic crisis

Fortunately, with the use of modern non-ionic iodine-containing drugs, this complication is very rare. Patients who have a history of hyperthyroidism before the IV administration of KB should block thyroid function with a thyreostatic drug, for example, perchlorate. Also, to reduce the synthesis of thyroxine, Mercazolilum is used. In both cases, the effect of taking the drugs comes about a week later. It is necessary to verify the effectiveness of antithyroid therapy, for which it is necessary to repeat the study of the level of thyroid hormones.

If the patient has hyperthyroidism with an erased clinical picture and is in time unrecognized, the introduction of iodine-containing contrast agents may exacerbate the disease and provoke a vivid thyrotoxicosis clinic. In this case, the patient develops diarrhea, muscle weakness, fever, increased sweating, signs of dehydration, unmotivated fear and anxiety, and necessarily tachycardia. The main problem in this situation is a long latent period before the bright manifestation of the thyrotoxic crisis.

Delayed iodine-induced hyperthyroidism develops in some patients with latent hyperthyroidism or suffering from other pathology of the thyroid gland (especially those living in an area depleted of iodine) 4 to 6 weeks after intravenous administration of contrast medium, regardless of the ionicity and osmolarity of the contrast agent. Special treatment is not required, and the symptoms go away after a certain period of time.

To patients with thyroid cancer, if necessary, intravascular or oral administration of an iodine-containing contrast agent (ionic or non-ionic) should be treated particularly carefully. This is due to the fact that a week after the introduction of iodine-containing contrast agent, thyroid absorption I-131 decreases by an average of 50% and recovers after a few weeks. Therefore, if treatment with radioactive iodine is planned, the introduction of iodine-containing contrast preparations (intravenously or intravenously) with a diagnostic purpose may be contraindicated. In this case, an additional consultation with the doctor in charge, who has appointed a study using a contrast agent, will be required.