REACTION TO INTRAARTERIAL IONIC IODINATED CONTRAST MEDIUM ADMINISTRATION IN ANESTHETIZED HORSES
Abstract
The purpose of this report was to evaluate the frequency and type of reactions to intraarterial iodinated contrast medium injection in horses. Ninety-seven received an intraarterial injection of ionic, iodinated contrast medium for computed tomographic assessment of the distal limb. Nine (9.0%) horses developed a reaction attributable to the contrast medium administration. Of those, 4/97 (4.0%) developed a skin response (three with urticaria, one with facial edema) within 20 min. Five (5.0%) developed elevation of heart rate and/or blood pressure immediately upon administration of the contrast medium. No horse developed a severe reaction such as shock, cardiac, or respiratory arrest. No treatment was necessary in any horse.
Introduction
In people, side effects associated with the administration of intravenous iodinated contrast media occur 3–15% of the time, depending on the contrast medium.1–3 Acute reactions are the most common with 70% occurring in the first 5 min.4 Acute reactions can be subdivided into mild, intermediate, and severe types.3 Mild reactions include arm pain, urticaria, edema, and pruritis and do not typically require intervention. Intermediate reactions such as tachycardia, hypotension, nausea, vomiting, and diarrhea are measurable but not life-threatening. Severe reactions include bronchospasm, shock, cardiac or respiratory arrest, and require medication and/or hemodynamic support. Certain people with preexisting conditions such as food allergies, asthma, and atopy are predisposed to contrast media reactions.1,3,5,6
Iodinated contrast media are administered intravenously to dogs and cats for excretory urography, angiography, and computed tomography (CT). Three to six percent of dogs and 2–25% of cats undergoing CT develop substantial changes in heart rate or blood pressure attributable to contrast medium administration.5,6 Indications for systemic iodinated contrast medium administration to horses are limited and dosing is expensive. Hypoxemia and hypotension were reported in a horse receiving intravenous ionic iodinated contrast medium.7 We have used intra-arterial iodinated contrast media in the distal limb of horses as a method for assessment of regional soft tissues.8 The contrast medium dose is relatively small because it is injected regionally, obviating the cost of a systemic dose. Our perception is that intraarterial contrast medium administration results in infrequent cardiovascular and skin responses. The purpose of this brief report was to evaluate the frequency and type of reactions in anesthetized horses receiving intraarterial iodinated contrast medium.
Materials and Methods
Ninety-seven horses that received intraarterial ionic iodinated contrast medium* for CT of the distal extremity between March 2004 and April 2007 were identified. The mean (±standard deviation) age was 10.0±3.8 years. There were 34 Warmbloods, 17 Quarterhorses, 15 Thoroughbreds, six Hanoverians, three each American Paint horses, and Arabians with the remaining 19 horses being single representatives of their breed or being of mixed breeding. There were 27 mares, 64 geldings, and six stallions.
Ultrasound guidance was used in all horses to place an 18 G 1.88 in. catheter† into the median or medial palmar artery. Ionic-iodinated contrast medium‡ was diluted 50:50 with normal saline and injected using a pressure injector§ at a rate of 1.5–2 ml/s over 30–60 s.
All horses had measurement of heart rate and mean arterial or peak systolic blood pressure, as determined by Doppler, oscillometric or direct techniques, at 5-min interval throughout the procedure. Medical records were reviewed for evidence of urticaria, skin redness, surface edema, shock, cardiac, or respiratory arrest as well as the temporal relation to contrast medium administration. The magnitude and temporal relationship of changes in heart rate or mean arterial blood pressure attributed to contrast medium administration were recorded. Any intervention performed as a result of the response to contrast medium injection was also noted.
Results
Nine of the 97 (9.0%) horses developed reactions attributable to contrast medium administration. Four (4.0%) developed a skin response within 20 min. Of those, three developed generalized urticaria (one each 12-year-old Warmblood mare, 3-year-old Andalusian stallion, 11-year-old Warmblood gelding) and one developed facial edema (8-year-old Warmblood gelding). The Andalusion stallion first developed urticaria on the limb into which contrast medium had been injected; this spread to the remainder of the body and neck over the ensuing 15 min.
Five (5.0%) horses developed elevation of heart rate or blood pressure immediately upon administration of contrast medium. Heart rate and blood pressure increased immediately after injection and then returned to baseline over the next 5–10 min (Tables 1 and 2).
| Prior | Immediate | 5 min | 10 min | 15 min | |
|---|---|---|---|---|---|
| Horse 5 | 78 | 108 | 78 | NA | NA |
| Horse 6 | 78 | 88 | 84 | 80 | 70 |
| Horse 7 | 85 | 105 | 90 | 85 | 83 |
| Horse 8* | 110 | 180 | 170 | 130 | NA |
| Horse 9 | 80 | 200 | NA | NA | NA |
- * Values indicate systolic arterial blood pressure . NA, not available.
| Prior | Immediate | 5 min | 10 min | 15 min | |
|---|---|---|---|---|---|
| Horse 6 | 40 | 53 | 50 | 48 | 50 |
| Horse 7 | 33 | 60 | 40 | 40 | 40 |
| Horse 8 | 33 | 50 | 48 | 36 | NA |
| Horse 9 | 40 | 80 | NA | NA | NA |
- NA, not available.
No horse developed erythema, shock, or cardiac or respiratory arrest. No treatment of any contrast medium reaction was necessary.
Discussion
Based on our results, the incidence of a reaction to intraarterial ionic iodinated contrast medium injection is 9.0%. This approximates the incidence seen in other species including people, dogs and cats. All reactions were mild based on criteria applied to people. No horse required treatment of the contrast medium interaction. It is important to note that the incidence of severe reactions in people receiving ionic iodinated contrast medium is low (0.04–0.22%)4,9 so that the absence of severe reactions in our population of horses may be a reflection of the sample size. Moreover, some horses that developed a reaction did not have data past 5 or 10 min after contrast medium administration which suggests a reaction to contrast medium but may represent a different and less transient physiologic process.
Most immediate contrast medium reactions fall in to the category of anaphylactoid responses.3 Anaphylactoid reactions are similar to anaphylactic reactions but are not mediated by IgE. Rather, they are the direct result of systemic mast cell and basophil degranulation and therefore do not require previous exposure to the antigen.3 The release of histamine from mast cells and basophils results in vascular permeability alterations that manifest in the skin as urticaria, itchiness, or edema.10 Approximately one-half of the reactions in the horses in this study involved urticaria or edema, likely as a result of a mild anaphylactoid response. Anaphylactoid reactions are not dose related so that the relatively lower dose of contrast medium administered in horses undergoing distal limb arteriography are not protective.3
In people that develop moderate or severe anaphylactiod reactions to contrast medium administration, heart rate becomes elevated but blood pressure drops as a result of permeability changes and fluid shift out of the vasculature.4 No horse in this study developed this type of reaction. However, 5/9 horses that had a reaction to contrast medium experienced a change in heart rate and/or blood pressure. Arm pain associated with contrast medium injection is reported frequently as a mild and transient reaction in people. Moreover, there is evidence that contrast medium can exert a direct effect on the vasculature, including vasospasm and constriction.11 Because the horses that developed a transient change in heart rate and blood pressure experienced tachycardia and hypertension, we suspect that this was related to peripheral vasoconstriction and a systemic response to localized pain in the limb where contrast injection occurred.
In conclusion, urticaria, facial edema, transient tachycardia, and hypertension predominated as the most commonly observed reaction to ionic, iodinated contrast medium injection in this study. Reactions were self-limiting and did not require intervention. Breed, gender, and age predilections were not identified.
