2016 SPRING: Heart of Texas CE | Canine Hip Dysplasia | Food Bloat | Catheter Size | Lymphoma | Marijuana | ACVIM Forum 2015 | Feline Anemia Trial
Heart of Texas CE
Join us for our third annual Heart of Texas continuing education day for veterinarians, Sunday, April 17, 2016. We’re offering 7 hours of CE from 8:00am – 6:00pm at The Woodlands Resort and Conference Center – 2301 N Millbend Drive. View the agenda or click below to register.
Canine Hip Dysplasia
Hip dysplasia is a complex disease with both genetic and environmental factors that affect expression in our patients. The actual incidence of canine hip dysplasia (CHD) is unknown, but the frequency of disease is much higher in our large and giant breed populations, with the exception of our sighthounds such as the greyhounds and Borzois. Male and female dogs are affected with equal frequency, which differs from the disease in humans where 80% of people affected are female. Puppies that are genetically predisposed to hip dysplasia, unlike humans, are normal at birth. Though the true cause of hip dysplasia is still unclear, stretching of the joint capsule and ligament of the femoral head is observed as early as two weeks of age. Joint effusion and progressive stretching of these structures are associated with increasing joint laxity. This allows the femoral head to subluxate when bearing weight and changes the forces acting on the plastic, immature skeleton. These abnormal forces lead to degenerative changes and bone remodeling. The rate and degree of disease progression vary with the individual. Direct cause and effect between instability and osteoarthritis has not been established. While dogs affected with osteoarthritis due to hip dysplasia show laxity, not all dogs that show laxity develop osteoarthritis.
Patients may initially present between 5-12 months of age with an acute unilateral or bilateral lameness; however, signs may be more subtle such as “bunny hopping,” difficulty rising, reluctance to run, jump, play or use the stairs. Owners may also present their pet at varying stages of chronic disease.
Observation and physical examination such as pain on hip manipulation and evidence of hip laxity “Ortolani sign” can arouse suspicion of hip dysplasia. However, the diagnosis is established by radiographic examination of the dog while under general anesthesia, or deep sedation, to ensure proper positioning. Currently Penn Hip radiographic evaluation offers the most objective evaluation of hip laxity particularly when compared to the OFA technique.
Dogs that have joint instability with minimal or no radiographic evidence of osteoarthrosis are usually immature or young adult animals. These dogs may not show any signs of hip pain, or they may exhibit a sudden onset of unilateral or bilateral hind limb lameness. In many cases, surgical treatment is the best option. Options for surgical treatment that we recommend are a triple pelvic osteotomy for patients under 6 months of age with subluxated hips and otherwise good joint confirmation. In patients with degenerative changes, the recommended surgical procedure would be a total hip replacement or in some cases femoral head and neck excision – but only if finances are an issue. Although chronic pain management may be effective in dysplastic dogs with mild to moderate osteoarthritis, the degree of coxofemoral incongruence and severity of osteoarthritis changes in some dogs may preclude alleviation of pain by conservative means. Conservative management consists of the administration of analgesics and/or chondro-protective agents, weight reduction and controlled exercise. As with many other musculoskeletal abnormalities, surgical intervention often carries the best results when performed earlier in the course of disease.
Total hip replacement is the best option if a pain-free joint with normal biomechanical function is desired. Multiple remarkable technology advances in hip replacement implants and the surgical procedure have been made during the last 12 years for dogs, and for humans. Dogs receiving a hip replacement ideally have reached skeletal maturity which is at about 10 months of age. The implants used in total hip replacements do not “wear out” in a dog’s lifetime so it is now commonplace to do the surgery before their first birthday. It is not necessary to wait until the osteoarthritis has reached end-stage disease. In fact, waiting too long until the osteoarthritis is advanced slightly increases the risk factors of doing the surgery, and in worst case scenarios, chronic changes present can preclude the surgery completely.
When They Can’t Eat Another Bite
It’s not uncommon for us to overeat during the holidays. Our bellies get a little distended, and we feel over full. We recognize our mistake and swear not to eat as much next year. But what if the food we ate at the holiday meal kept on increasing in volume as it sat in your stomach? That could be a problem.
So it is with dogs who get into a bag of dry food. Every dog will eat until they are full; that’s not the problem. It has been reported that the normal canine stomach can accommodate 7-8 % of the dog’s body weight in food. The problem starts when the dry food starts to absorb fluid from the stomach, or the dog drinks. The dry food swells as it absorbs the fluid overdistending the stomach. This condition is known as food bloat.
Signs of food bloat are usually acute in onset. Patients frequently present similar to those with GDV. Dogs demonstrate abdominal discomfort and anxiety. Attempts at vomiting are frequently non-productive, and pressure on the diaphragm from the gastric distention can cause increased respiratory effort. Occasionally, the stomach is distended enough to interfere with blood return by the vena cava causing signs of poor cardiac output.
Food bloat is diagnosed with radiographs. The food-filled stomach, unlike a GDV, is normally positioned.
Treatment recommendations for patients with food bloat vary:
- Some clinicians attempt to induce vomiting; however, this is frequently ineffective. Overdistention of the stomach interferes with its ability to contract and expel its contents. We don’t recommended emesis.
- The administration of IV fluids is recommended. Dogs risk dehydration as the dry stomach contents draw in fluid. Furthermore, the stomach contents need to be moist enough to be broken down and passed through the pyloris. Those dogs demonstrating compromise in perfusion from dehydration, or reduced cardiac return from the excessive gastric dilation, could also benefit from fluid therapy.
- Providing frequent walks has been suggested as it appears to help stimulate gastric emptying.
- Administering pro-motility medications such as metoclopramide may also be helpful.
- Analgesics are indicated in painful dogs. It has been suggested that NSAIDs be avoided so as not to further irritate the stomach.
- Finally, the resolution of food bloat takes time. Most dogs improve within 12 hours of presentation.
- Surgery is not recommended to treat food bloat unless the stomach is torsed.
How about lavaging the food out of the stomach?
Lavage is typically not necessary and would likely prove difficult to perform because of the density and dryness of the stomach contents. The risk of inducing aspiration pneumonia in many cases outweighs any potential benefit you might gain. Lavage might be considered if the stomach is distended to the point where perfusion is compromised.
Note: The occurrence of food bloat has not been associated with an increased risk of developing GDV.
For further questions about food bloat, please contact any of our three Houston hospitals.
Gauging Your Catheter Size
It’s rare that a day goes by that we don’t place an IV catheter in one of our patients. But what size catheter is correct? Unfortunately, no clear guidelines exist in the veterinary or human medical fields when it comes to choosing what gauge and length of catheter to place.
Before picking a catheter size, consider Poiseuille’s law, which states
|Flow =||π(radius)4(pressure drop)|
In general terms, it states that the narrower the lumen or the longer the tube, the greater the resistance to fluid flow. A short, wider diameter catheter will have much greater flow than a long narrow one. In addition, the greater the viscosity of the fluid, the slower the fluid will flow.
Taking this law into consideration, if the desire is to be able to administer large volumes of fluids quickly or to administer more viscous fluids such as plasma, blood or parenteral nutrition, a shorter wider diameter catheter is preferred. Patients presenting in shock, at risk for requiring rapid fluid resuscitation or undergoing surgical procedures would therefore benefit from a lower gauge, i.e. larger diameter catheter, to facilitate rapid or viscous fluid flow. In addition, larger diameter catheters are less likely to kink or become plugged by a blood clot and are less likely to induce hemolysis or thrombosis when used for blood transfusions. A disadvantage to larger diameter catheters is the discomfort that occurs both during catheter placement and while the catheter is in place.
The size and fragility of the vein to be catheterized are also important factors when it comes to choosing a catheter gauge. It is obviously easier to place a narrower (higher gauge) catheter in the smaller veins found more peripherally in the body and in small patients. In addition, if the catheter is too large you risk directly damaging the vein from the catheter rubbing on the vessel walls. Fragile vessels, such as those found in patients with vasculitidies (think kidney failure or immune conditions) are also susceptible to injury from larger diameter catheters. A disadvantage to narrow lumen catheters is their tendency to kink and to become plugged.
How about the length of the catheter?
A distinct advantage to longer catheters is that they are less likely to become dislodged. This would be important in active patients where excessive movement of the catheter site is a concern or if administering medications that irritate surrounding tissues when leaked out of the vessel. The primary disadvantage to longer catheters is the additional resistance to fluid flow. This applies to even those catheters placed in larger central veins. It’s not the size of the vessel that affects the rate of potential fluid flow but the length of the catheter.
So before choosing a catheter gauge and length, consider the purpose and potential need of the catheter, the condition and size of the vessel to be catheterized, the status of the patient (underlying illness, activity level, potential complications), the medications and fluid types to be administered, and the fluid flow rates that might be required.
- Smaller diameter (higher gauge: 24 ga/22 ga) catheters are probably best reserved for patients who have very small or fragile veins or require short-term fluid or IV medical treatments.
- Medium diameter (20 ga/18 ga) catheters are useful in medium-sized to larger patients with healthy veins who may require moderate fluid rates or blood transfusions.
- Larger patients and those who may require rapid or high volume resuscitative fluid loads or viscous fluids (lipids/parenteral nutrition) would benefit from the largest catheter diameters (18 ga/16 ga).
Longer catheters are preferred if a prolonged duration of catheter use is expected, there is excessive mobility at the site which could dislodge the catheter, or to ensure the medication and/or fluids being administered is done so safely into the vessel lumen.
Note: Studies suggest that the length of the catheter probably has no effect on the risk of developing thrombophlebitis in the vein. The composition of the catheter, such as silicone or polyurethane, and the character of the fluid being infused (caustic medications and those with low pH or high viscosity) are more likely to play a role.
For any questions about catheter placement, please call and ask to speak to a member of our emergency medicine team.
Is it Lymphoma?
We have all had patients in whom we suspect lymphoma, based on our exam and clinical assessment, only to have the cytology or biopsy results come back inconclusive or suggesting inflammation. This may be the result of poor sampling on our part, the presence of concurrent lymph node abnormalities such as inflammation or necrosis, or even a reflection of a less advanced stage or grade of disease. What now? We could pull out our old trusty corticosteroid, but if the patient actually has lymphoma, we might be doing more harm than good. Studies and clinical experience have suggested that treatment of lymphoma with corticosteroids alone will induce changes in the lymphoma cells making them less responsive to other chemotherapeutic agents when the final diagnosis of lymphoma becomes apparent.
So what other options do we have when cytology or biopsy samples are inconclusive?
If the cytology or biopsy results are inconclusive despite the suspicion for lymphoma, then the pathologist may suggest you perform a PARR, or PCR for antigen receptor rearrangement, or flow cytometry. These are the most cost effective and can more quickly obtain a diagnosis. Immunohistochemistry is an additional test that might be useful for both supporting the presence of lymphoma as well as determining the lineage of lymphoma; however, this requires a surgical procedure to remove the lymph node and then special stains. PARR and flow cytometry require fine needle aspirate (cytology) of the lymph node only.
How does PARR work?
PARR can be useful for differentiating neoplastic lymphocytes from normal lymphocytes whether they are retrieved from pleural effusion, a lymphoid organ or an enlarged lymph node. Cancer cells are clones of a single cell. PCR amplification of the cellular DNA (responsible for encoding for the antigen receptors on the cell surface) within the lymphocytes is performed to determine if the DNA is derived from a single clone (same gene length and sequence) or is derived from multiple cell lines (variable and multiple gene lengths and sequences typical of normal immune responses). PARR testing can be performed on both cytology and biopsy samples.
Varying with the lab, PARR is reported to have a sensitivity of up to 90% in dogs, i.e. 90% of dogs with lymphoma will be correctly identified. PARR is less useful in cats where it is reported to have a sensitivity of only 65%. PARR is reported to have a specificity in both dogs and cats of approximate 92%, i.e. 8% of pets without lymphoma will be falsely positive. Much like any testing, the results of the PARR test should be used in conjunction with your other test results when formulating a final diagnosis.
What is flow cytometry?
Studies indicate that lymphoma cells, due to their clonal expansion, typically demonstrate identical antigen receptors. By comparison, normal lymphocytes demonstrate a huge variety of antigen receptors. To perform flow cytometry, live cells, such as those retrieved from lymph node aspirates, are gently injected into a vial of the patient’s serum combined with saline. Fluorescent-labeled antibodies which bind to proteins present on the cell surface of the lymphocytes are then added to the fluid. The labeled lymphocytes are run through the laser light of a flow cytometer producing a ‘scattergram’ which is used to determine whether the cells are homogeneous (typical of lymphoma) or heterogeneous. Because B- and T-cell type lymphomas express different surface antigens, the test is also useful for differentiating B- and T-cell types of lymphoma.
How about immunochemistry?
Immunocytochemistry utilizes special stains applied to histopathology slides to identify cell markers that are typical for various types of cancers. The testing is useful for differentiating B- and T-cell lymphomas, mast cell tumors, melanomas, carcinomas and sarcomas. Further studies may find immunohistochemistry, as well as flow cytometry, useful for identifying the presence of specific proteins or other cell markers which may be associated with multidrug resistance, rate of cell division or other factors useful for predicting prognosis or the best treatment protocol.
For any questions concerning lymphoma and treatments, please contact our oncologist in Spring, Dr. Melissa Parsons at 832.616.5000.
A Growing Toxicity
Marijuana is believed to be the most commonly used illicit drug in the United States. With its legalization for medical use in humans and its recent decriminalization in Colorado and Washington, the frequency with which pets are being exposed to marijuana or one of its derivatives is increasing.
The toxic chemical in marijuana is delta 9-tetrahydrocannabinol or THC. Dried leaves and flowers of the hemp plant Cannabis sativa contain 1-8% THC. Hashish, compressed resin produced from the flowering tops of the plants, contains 10% THC. Hash oil or butter, a concentrated form of hashish or marijuana in which the cannabinoids are extracted into the fat of oil or butter, can have a THC concentration exceeding 50%.
The most common means by which dogs and, uncommonly, cats are exposed to marijuana is by ingestion of home cooked or commercial products containing THC. THC is stored in the tissues of the brain, liver and kidneys. Being highly lipid soluble the chemical is also stored in fat deposits where it can remain for days. The majority of the THC is excreted via the biliary system and eliminated via the feces.
Signs of marijuana intoxication typically occur within 60 minutes of exposure and can last several days. The THC binds to cannabinoid receptors in the brain where it interacts with the neurotransmitters norepinephrine, dopamine, serotonin and gamma-aminobutyric acid inducing varying stimulatory and inhibitory signs involving the GI, cardiovascular and neurologic systems.
Signs of marijuana intoxication:
- Depression or dysphoria
- Hyperstartle response
- Urine dribbling
Is it marijuana?
The challenge in diagnosing marijuana toxicity is getting the pet owner to confirm the pet’s potential exposure. Routine blood testing and imaging typically fail to demonstrate significant abnormalities. Furthermore, over-the-counter drug tests as well as laboratory tests for THC have not yet been proven effective in pets. Luckily the signs of THC toxicity, i.e. dysphoria, drowsiness, a hyperstartle response and especially urine dribbling are pretty recognizable.
What’s the best treatment?
Treatment after immediate exposure to marijuana could include induction of emesis and the administration of activated charcoal. Both would be contraindicated if the clinician feels the patient’s mental state predisposes the pet to the possibility of aspiration pneumonia. Interestingly, induction of emesis may not be effective as one of the marijuana’s medical uses is to inhibit nausea and vomiting in human cancer patients. The repeat administration of activated charcoal 6-8 hours after an initial administration should be considered to reduce GI absorption of the THC as it goes through enterohepatic circulation.
Symptomatic supportive care should be individualized to the patient and would typically include IV fluids to ensure hydration and perfusion, external heating or cooling as indicated, and anti-anxiety therapy. More severely affected patients may require cardiovascular medications, oxygen supplementation or even ventilation. Intralipid therapy should be considered in more severely affected patients and those with prolonged duration of signs. Because THC is lipid soluble, it can be leached from the body with intralipid therapy. Close monitoring of these patients is important. Luckily THC has a high safety margin. To be lethal most dogs must be exposed to greater than 3 g/kg.
Could marijuana be beneficial for treating ill pets?
In humans, marijuana and its derivatives have been shown or suggested to have many potential medical uses including:
- Stimulating appetite and reducing nausea in cancer patients
- Treatment of glaucoma
- Increasing lung capacity
- Controlling epilepsy
- Reducing cancer spread
- Slowing the progression of Alzheimer’s disease
- Reducing the pain of multiple sclerosis
- Relieving arthritis discomfort
- Treating inflammatory bowel disease
Reports of marijuana’s effectiveness for treating ill pets are very limited and at best anecdotal. Marijuana is a Schedule I narcotic. Even if you live in a state where medical marijuana is sanctioned, as a veterinarian it remains illegal for you to prescribe or recommend it to treat a patient.
If you feel you may be dealing with a pet who has a potential toxicity or desire closer 24 hours or after-hours monitoring of your patient, please don’t hesitate to give us a call. Our emergency and critical care services have loads of experience dealing with all types of toxicities.
Pearls from the ACVIM Forum 2015
Can you trust the urine SG (USG) in dogs with glucosuria?
A recent study evaluated the effect of adding increasing concentrations of glucose to urine samples with varying starting USGs. Predictably they found that the lower the starting nonglucosuric USG, the greater the effect adding glucose had on the subsequent USG. Furthermore, the higher the concentration of glucose added to the urine sample, the greater the change in the subsequent USG. However, the addition of even higher concentrations of glucose to urine samples with low USG failed to cause clinically significant changes in the final USG. Researchers concluded that the presence of glucosuria did not interfere with the assessment of renal concentrating ability. (Behrend et al)
Are all antiemetic medications the same?
Well that depends on your goal. Gastric antral motility (contractions per minute) was measured before, during and hourly after the feeding of a meal in normal dogs given metoclopramide, maropitant, dolasetron or saline 1 hour prior to feeding. Researchers found that all three medications increased gastric motility prior to feeding and then intermittently during hourly measurements performed for 7 hours after feeding. Only metoclopramide increased motility at all time measurements. If the goal is only to inhibit nausea then all three medications can be effective. However, if increasing gastric emptying is also the goal, then metoclopramide may be your drug of choice. (Bogard et al)
So how do the new anti-seizure medications add up?
Phenobarbital still appears to be one of the most effective medications for treating seizures in dogs. Alternative medications continue to be evaluated with the goal of avoiding the short-term side effect of sedation and long-term side effect of potential liver disease. A review of records of dogs receiving zonisamide (40), levetiracetum (16) or phenobarbital (65) as first line therapy for control of seizures found that phenobarbital was more likely to be associated with adverse effects but was also most effective as monotherapy to control seizures. Dogs receiving zonisamide or levetiracetum were ultimately more likely to require additional therapy to reduce seizure frequency. (Waldron et al) In another study evaluating zonisamide alone, approximately 75% of 53 dogs demonstrated a 50% reduction in seizure frequency. (Nomura et al)
Feline Anemia Trial
BluePearl Veterinary Partners in Spring is currently recruiting patients for a fully-funded trial to evaluate the safety and efficacy of an oral medication to manage anemia associated with chronic kidney disease in cats. The study consists of two phases: the efficacy phase (28 days) and the maintenance phase (8 weeks).
- Cats, > 1 year old, male or female, > 2.0 kg
- Not pregnant, lactating or intended for breeding
- Diagnosis of chronic kidney disease
- Non-regenerative anemia with PCV < 27% at study days -7 and 0
- Stable concurrent medical conditions
- Cats may be receiving SQ fluids
- Fractious cats
- Positive urine culture on study day -7
- Systolic blood pressure > 165 mmHg on study days -7 or 0
- Previous treatment with erythrocyte stimulating agents (ESA), including erythropoietin (EPO)
- Previous blood transfusion since being diagnosed with CKD
- Severe clinical signs of inflammation not attributed to CKD
- Other significant uncontrolled medical issues
- FeLV+ or FIV+ (if not vaccinated, sponsor will cover the cost to test)
- Obvious signs of GI bleeding
The study medication, diagnostic lab work and examinations will be provided at no cost to owners. Owners will be expected to administer the study medication at home, keep an owner diary and comply with study protocols.
*Note that this study is not funded for diagnostic or treatment costs associated with the underlying renal disease. Those costs must still be assumed by the owner.
For more information, or if you have a patient who may meet the above requirements, please contact Dr. Richard Stone or Cerelia Sambrano, RVT, LVT at the Spring hospital, 832.616.5000.