Comparison of the effect of hypertonic hydroxyethyl starch and mannitol on the intraocular pressure in healthy normotensive dogs and the effect of hypertonic hydroxyethyl starch on the intraocular pressure in dogs with primary glaucoma

PURPOSE: The purpose of this study was to determine if intravenous hypertonic hydroxyethyl starch (7.5%/6%) (HES) could decrease the intraocular pressure (IOP) in healthy normotensive dogs, and compare its effect with that of mannitol (20%) (experimental study). In addition, the potential IOP-lowering effect of hypertonic HES was evaluated in six dogs with primary glaucoma (clinical study). MATERIAL AND METHODS: Experimental study: eight male ophthalmoscopically and clinically healthy Beagles were included in this study. The IOP of each dog was measured by applanation tonometry in both eyes to obtain control values at 10:00, 10:15, 10:30, 10:45, 11:00 a.m., and then every hour until 6:00 p.m. prior to the first treatment (control period). Each dog received, with at least 2-week intervals and in a random order, an intravenous (IV) infusion of 4 mL/kg hypertonic HES (1.2 g/kg NaCl; 0.96 g/kg HES) and 4 mL/kg mannitol 20% (1 g/kg) over a period of 15 min starting at 10:00 a.m. IOP was measured oculus uterque (OU) at the same time intervals as in the control study. The differences in IOP between the treatment groups and the baseline IOP (before the start of infusion), between oculus sinister (OS) and oculus dexter (OD) and between the same time points of all groups were determined with a Student's t-test for paired samples (P = 0.05). Clinical study: six dogs with primary glaucoma (representing seven eyes) received an IV infusion of 4 mL/kg hypertonic HES over a period of 15 min. IOP was measured before and 15 and 30 min after starting the infusion. RESULTS: Experimental study: no significant difference between IOP of both eyes was found. A significant decrease in IOP from baseline value was recorded at 15, 30, 45, and 60 min after the start of mannitol infusion (mean amplitude in IOP decrease 3.21 mmHg; P < 0.05) and at 15 and 30 min in dogs treated with HES (mean amplitude in IOP decrease 2.43 mmHg; P < 0.05). At 120 and 180 min there was a significantly higher IOP (P < 0.05) in HES treatment group compared to the values of the control group. Clinical study: in 5/7 eyes diagnosed with primary glaucoma a maximum decrease in IOP of an average of 24% from the baseline value (IOP before start of the infusion) was observed (range of decrease 2-21 mmHg). In three of these five cases the maximum decrease was reached at 15 min and in two cases at 30 min. In one case an increase in IOP of 35% (+ 18 mmHg) was seen after 15 min and 26% (+ 13 mmHg) after 30 min. Case 4 showed an increase in IOP of 5% (+ 3 mmHg) after 15 min and a decrease of 6% (- 4 mmHg) after 30 min. CONCLUSIONS: Intravenous hypertonic HES is comparable to intravenous mannitol 20% in lowering the intraocular pressure in healthy normotensive dogs. But this effect lasted half an hour longer after mannitol. In 6/7 eyes with primary glaucoma, hypertonic HES decreased IOP.     

Colloid Oncotic Pressure and the Clinical Use of Colloidal Solutions

The synthetic colloids, dextran and hydroxyethyl starch, have only recently enjoyed widespread use in critically ill veterinary patients. Plasma proteins normally provide colloid oncotic pressure and, thereby, are the primary force responsible for retaining fluid within the vasculature. Abnormally low plasma protein concentrations, common in the critically ill patient, are associated with excessive fluid loss from capillaries and development of peripheral or pulmonary edema. Infusion of colloid solutions decreases the potential for and severity of edema in hypooncotic states. Dextran and hydroxyethyl starch solutions also provide other positive hemodynamic benefits and are a preferable alternative to crystalloid usage in the resuscitation of selected patients from hypotensive and hypovolemic states. Potential side effects of synthetic colloid infusion include anaphylactoid reactions, increased risk of bleeding, interference with cross matching, and acute renal failure. Knowledge of the mechanisms responsible for these adverse effects minimizes their occurrence.     

The role of albumin replacement in the critically ill veterinary patient

Objective: To review the human and veterinary literature on the physiological role and effects of therapeutic albumin supplementation. Data sources: Data from human and veterinary literature was reviewed. Human data synthesis: Hypoalbuminemia often occurs in a variety of critical illnesses, and contributes to the development of life‐threatening complications, including pulmonary edema, delayed wound healing, feeding intolerance, hypercoaguability, and multiple organ dysfunction. Serum albumin concentration has been used as a prognostic indicator in cases of chronic hypoalbuminemia. The use of albumin replacement therapy in humans is sometimes controversial, but may be associated with improved morbidity and decreased mortality. Veterinary data synthesis: Unlike human literature, there is a paucity of controlled clinical studies in the literature regarding albumin supplementation in veterinary patients. Rather, the majority of published studies were performed in experimental animals or via retrospective analyses. One recent study evaluated the use of plasma to improve albumin concentration in dogs with hypoalbuminemia. Other older studies investigated wound healing in dogs with experimentally induced hypoalbuminemia. As in human medicine, serum albumin concentration may be helpful as a prognostic indicator in critically ill dogs. Conclusion: Albumin is one of the most important proteins in the body because of its role in maintenance of colloid oncotic pressure, substrate transport, buffering capacity, as a mediator of coagulation and wound healing, and free‐radical scavenging. Albumin replacement in veterinary medicine is difficult, but until prospective clinical trials determine the efficacy of albumin replacement are conducted, a suggested clinical guideline would be to maintain albumin concentration at or above 2.0 g/dl utilizing fresh frozen plasma.     

Changes in colloid osmotic pressure as a function of anesthesia and surgery in the presence and absence of isotonic fluid administration in dogs

Objective  To determine how a combination of anesthetic drugs; including pre-medication, induction agents and inhalational agents; affect colloid osmotic pressure (COP) in the presence and absence of isotonic fluid administration. Secondarily, to determine if changes in total plasma protein (TPP) correlate with COP in anesthetized patients.
Study Design  Prospective, randomized clinical study.
Animals  Ten female dogs, 4 months to 4 years of age and >8 kg undergoing elective ovariohysterectomy.
Methods  All dogs were anesthetized in a similar fashion. After induction, five dogs received lactated ringer's solution (LRS) at 10 mL kg⁻¹ hour⁻¹ and five dogs received no fluid therapy during anesthesia. Blood samples were collected prior to pre-medication, prior to induction, immediately post-induction/prior to the inhalational agent, 30 minutes post-induction, at the time of recovery and 45 minutes post-discontinuation of inhalant. TPP and COP were measured from each sample.
Results  Administration of fluids resulted in a decrease in COP and TPP over time that did not return to baseline by 45 minutes after recovery. Anesthesia without the administration of fluids also resulted in a significant decrease in COP over time, that was rebounding by recovery (but still significantly less than baseline). TPP had variable correlation with COP at different time points with or without fluid administration.
Conclusions and clinical relevance  Anesthetic drugs alter COP similarly in the presence and absence of isotonic fluids. These changes in COP did not have a simple relationship to TPP and so the latter could not be used to predict COP in this patient population.     

Mechanisms of aquatic therapy and its potential use in managing equine osteoarthritis

Aquatic therapy has become increasingly popular in its use for rehabilitation of equine musculoskeletal injuries. Unfortunately, there has been no scientific evaluation of its clinical application for the treatment of osteoarthritis (OA) or associated musculoskeletal injuries in horses. The purpose of this review is to describe mechanisms of action of aquatic therapy and its potential use in the clinical management of equine OA.     

The effect of Hetastarch (670/0.75) in vivo on platelet closure time in the dog

Objective – To evaluate the effect of 6% hydroxyethyl starch (HES) solution in vivo, with an average molecular weight of 670 kDa and degree of substitution of 0.75, on canine platelet function.
Design – Prospective, controlled-experimental study.
Setting – University of California, Davis, Veterinary Medical Teaching Hospital.
Animals – Seven healthy employee-owned dogs.
Interventions – Seven dogs were included in the treatment group. Four of these dogs also served as the control group. Platelet closure time (CT) was measured using a platelet function analyzer and collagen/ADP cartridges. Dogs were given 20 mL/kg of either sodium chloride 0.9% (control group, n =4) or HES (treatment group, n =7) IV over 1 hour. CT was measured before the infusion, and at 1, 3, 5, and 24 hours after the start of the infusion.
Measurements and Main Results – There was a significant change over time from 0 to 24 hours ( P <0.001), a significant difference between groups across time ( P <0.001), and a significant group-by-time interaction ( P =0.007). At 3 hours, mean CT for the treatment group was 122.3±18.1 seconds, which was significantly different ( P <0.001) from the control group (71.0±3.5 s). At 5 hours, mean CT for the treatment group was 142.7±33.9 seconds, which was significantly different ( P =0.001) from the control group (75.0±8.6 s). Mean CT at 24 hours was within the reference interval for both the control and treatment group (66.0±2.9 and 81.8±11.9 s, respectively); however, CT in 3 individual dogs in the treatment group at this time point remained prolonged.
Conclusions – A clinically relevant dose of HES 670/0.75 prolongs CT in dogs for up to 24 hours. This may be due to platelet dysfunction in addition to the effects of hemodilution, and therefore, may increase the risk of bleeding.     

Current controversies in equine antimicrobial therapy

Controversies exist regarding the use, misuse and potential overuse of antimicrobial treatments in foals and adults. When antimicrobials are required for treatment of infectious diseases, veterinarians should follow a logical approach and not simply reach for the newest drug. Targeted, single drug therapy is probably best, and culture and sensitivity testing should be undertaken. The most likely infectious agent, potential drug toxicities, and age‐appropriate dose and route should be considered. The development of an increasing number of different multiple drug resistant pathogens requires that veterinarians use antimicrobial drugs responsibly to protect veterinary patients and the public at large.     

Glucocorticoid therapy and the risk of equine laminitis

Although glucocorticoids have been used successfully for the treatment of noninfectious inflammatory diseases of horses for more than 35 years, their use has been attended by a fear of the induction of laminitis. This paper reviews the evidence for this fear and the possible mechanisms whereby glucocorticoids could participate in laminitis induction. Although the association of laminitis with elevated serum cortisol in pituitary pars intermedia dysfunction suggests that chronic exposure to glucocorticoids may be part of laminitis pathogenesis, review of published reports and databases suggests that glucocorticoid‐induced laminitis is a relatively rare occurrence. However, several of the actions of glucocorticoids are similar to those known to be involved in laminitis pathogenesis. Glucocorticoid administration can induce insulin resistance, lead to vascular dysfunction that potentiates vasoconstriction, and interfere with keratinocyte proliferation and differentiation as well as matrix integrity, all mechanisms that could possibly induce laminitis. Drug formulation, dose and route of administration, and the systemic and hoof disease history of the horse must all be considered when assessing laminitis risk during glucocorticoid treatment. Generally, local glucocorticoid administration presents little risk as does systemic treatment of recurrent airway obstruction without concurrent disease. Caution should be used however in horses that are overweight and/or insulin resistant, or have had a recent bout of acute laminitis of alimentary or endotoxic origin. Overall, however, the risk of laminitis after glucocorticoid treatment, especially local use, is acceptable compared to the many benefits of these drugs.     

Septic peritonitis in a Percheron mare associated with Clostridium haemolyticum

This report describes an 11‐year‐old Percheron mare that presented with signs of colic and was ultimately diagnosed with bacterial peritonitis of unknown origin. Bacterial culture of a peritoneal fluid sample isolated 2 Clostridial species, one of which was strongly suspected to be Clostridium haemolyticum. The horse was markedly hypoalbuminaemic at presentation, leading to the development of low oncotic pressure and ventral oedema. The mare was administered a low molecular weight/low molar substitution hydroxyethyl starch solution in conjunction with other therapies that resulted in marked improvement of clinical signs. The purpose of this report is to describe the clinical findings associated with equine peritonitis associated with C. haemolyticum, a rarely identified pathogen in the horse. Secondly, this report serves to describe the beneficial effects of tetrastarch administration in a clinical case with severe hypoalbuminaemia and ventral oedema.     

The current status of antibiotic use in equine reproduction

Antibiotics are infused into the uterine lumen, added to semen extenders and given systemically for infections of the reproductive tract of the mare and stallion. Evidence‐based guidelines for determining treatment length and route of administration are limited and use is frequently based on convenience or tradition. Current recommended antibiotic use for the treatment of bacterial and fungal endometritis, placentitis and metritis in the mare and genital infections of the stallion are presented. Antibiotic classes used for reproductive problems are also reviewed.