Article Review: Ocular lesions associated with systemic hypertension in dogs: 65 cases (2005–2007)

The first of a bunch of articles I recently picked out of JAVMA was interesting because while I never got any readings without some form of anesthesia, I imagine that hypertension was extremely common in many of the dogs I saw at Lapaw Animal Hospital. Whether it’s a result of obesity, illness, or hospital stress, systemic hypertension is usually an indicator of some other problem, and therefore important in the analysis of the patient.

Image from Conrad Weiser Animal Hospital

The article is a bit confusing, because it goes into great detail the different potential causes of both hypertension and ocular lesions, and the significance of the data based on which was diagnosed first with each case. I began to lose track when on one hand they would mention that the data may be too biased to determine a cause and effect relationship between the two symptoms due to a preexisting condition, but then also said that those preexisting conditions had such a relationship.  It does seem clear that ocular lesions are promoted by the presence of hypertension in both dogs and cats, while the disagreements in the literature are mainly in how much one is indicative of the other. The relationship of hypertension correlating with ocular lesions in cats has varied from 50-100%, which tallied with the frequency of 62% in this case review. While these frequencies don’t prove any sort of direct relationship, they do support the evidence we do have that hypertension can lead to ocular lesions, and that if one is discovered in a patient, it’s worth looking for the other.

This is the first case study I’ve looked at in detail, and I’ll certainly be reading more as I move into veterinary medicine. It was really interesting to me how they selected cases, and how thoroughly they reviewed the significance of possible bias in each case. I absolutely understand why it’s so important, and the way each patient is presented changes how each symptom is portrayed in relation to the others, which makes the range of values for this specific correlation so understandable. Owners are much more likely to bring their dog into the clinic when seeing a clouded or irritated eye

Image from Bass Lake Pet Hospital

than hypertension would be found during a routine exam. Then you have to examine old clinic notes to see if other conditions led to either event, or to see if the veterinarian made the assumption that they were related, and though the situation was resolved, no lab work supports their theory. Some of the limitations  mentioned in the study were the fact that they lad a low sample of normotensive dogs with ocular lesions, and that diagnosis of hypertension is difficult due to situational stress interpretation in the face of blood pressure values and varied measurements within the “grey area” of test results. They also did significant analysis within the cases that took into account patients that were taking anti-hypertensive drugs for other conditions, but mention that those patients might have skewed the data, because there is no way to ensure that there was owner compliance in administration.

An interesting note is that all 5 dogs in the study that were currently taking Phenylpropanolamine either acutely or chronically were all hypertensive, supporting anecdotal evidence that it can promote hypertension. This makes sense to me, as PPA is controlled due to its potential use in creating amphetamine, and its inclusion in many prescription stimulants (Adderall, etc.).

All in all, a good article, and a good look at the relationship between ocular findings and hypertension. Though a large part of me does feel for those research assistants at the University of Wisconsin School of Veterinary Medicine who combed through thousands of patient files to find these 65 cases.

ResearchBlogging.orgLeblanc NL, Stepien RL, & Bentley E (2011). Ocular lesions associated with systemic hypertension in dogs: 65 cases (2005-2007). Journal of the American Veterinary Medical Association, 238 (7), 915-21 PMID: 21453181

Article Review: Effects of intravenous administration of Lactated Ringer’s solution on hematologic, serum biochemical, rheological, hemodynamic, and renal measurements in healthy isoflurane-anesthetized dogs

Well, it’s about time I mentioned an article I didn’t particularly enjoy on here. It’s not like I think it’s a waste of paper, it’s an important topic, but it does nothing creative and does little to contribute to the understanding of the subject. The article looks at the effects of different rates of Lactated Ringers Solution administered while under isoflurane anesthesia. It uses healthy animals, discusses well documented effects in humans, and just reinforces common practice.

Lactated Ringers is the most frequently prescribed fluid for maintenance of homeostasis in surgery and pretty much any other health stress event. I know when any patient wasn’t feeling well from any situation at my clinic, we always administered LRS either through a catheter or subcutaneously for outpatients, the dosage based on weight and severity of condition. We know how to use it, and it’s gotten a proven history of effectiveness in both humans and animals. The article justifies itself by saying that fluid therapy in dogs is largely based on human evidence, and that the formulas we use to determine rates have not been thoroughly investigated. Yet throughout the article they repeatedly compare their results to similar studies, and make no conclusions that aren’t already accepted in human and animal medicine. Additionally, the gaps in the literature they identify can’t even be answered using the methods and results of this study, so you can’t use them to justify its existence.

So the big conclusions they determined were that providing LRS increased plasma volume and cardiac output, didn’t increase urine production, and appears to leave the blood volume and remain in extracellular space. These are important points, but they were accepted unanimously without the presence of this study. Further, if their goal was to confirm these assumptions, their results are pretty much irrelevant with a sample size of only 8 animals, all in perfect health, similar size (26-41 lbs isn’t a lot of variance in the world of dogs), and undergoing no medical stress other than common anesthesia and mechanical ventilation.

My impression after finishing the paper was that the people at QTest labs (associated with Ohio State University College of Veterinary Medicine) needed a study to do, needed to get a grant proposal ready, and did enough research on the subject to sell this trial. It’s well written and the authors do a great job of placing their results in context of the literature, mostly because it all agrees. But it can’t hide the fact that it does nothing revolutionary other than providing history on the subject, and giving an excellent account of the methods used in the study. With such great, specific, and controlled procedures, this facility could be solidifying other theories that have conflicting data, if they’d use a sample size large enough.  I’m sure that they don’t always do milk run trials such as this one, and I look forward to seeing their name again in future articles.

ResearchBlogging.orgWilliam W. Muir III, Anusak Kijtawornrat, Yukie Ueyama, Steven V. Radecki, & Robert L. Hamlin (2011). Effects of intravenous administration of lactated Ringer’s solution on hematologic, serum biochemical, rheological, hemodynamic, and renal measurements in healthy isoflurane-anesthetized dogs JAVMA, 239 (5), 630-637