Methemoglobin concentrations in three salmonid species following exposure to benzocaine or tricaine methanesulfonate.

Methemoglobin is hemoglobin containing ferric iron rather than ferrous iron which renders it incapable of binding to oxygen. Blood sampling of fish is done under sedation or general anesthesia. Tricaine methanesulfonate (TMS) or benzocaine is commonly used but both can cause oxidation of hemoglobin to methemoglobin. Our objective was to determine if methemoglobin concentrations in healthy rainbow trout (Oncorhynchus mykiss), brook trout (Salvelinus fontinalis), or Atlantic salmon (Salmo salar) increase during sedation with 25 mg/L of a 10% benzocaine solution or with repeated short anesthetizations by 65 mg/L of 10% benzocaine solution or 65 mg/L of TMS. Sedation by benzocaine caused a significant increase in methemoglobin in all species over time (P < 0.05). The methemoglobin percentage in brook trout increased by 129%, rainbow trout by 42%, and Atlantic salmon by 49%. The methemoglobin in brook trout was significantly greater than the other species at multiple time points. Repeated brief anesthetizing by benzocaine and TMS caused significant methemoglobin by 60 (P < 0.05), 90 (P < 0.01), and 120 min (P < 0.001) in brook trout but no significant change in methemoglobin in rainbow trout or Atlantic salmon except at 120 min in Atlantic salmon (P < 0.05) repeatedly anesthetized with benzocaine. For example, following multiple anesthetizations with benzocaine, the methemoglobin percentage in brook trout increased by 140%, whereas the rise in methemoglobin in rainbow trout and Atlantic salmon was more modest (37% increase in Rainbow trout and 53% increase in Atlantic salmon). Following multiple anesthetizations with TMS, the methemoglobin increased by 90%, 5%, and 1% in brook trout, rainbow trout, and Atlantic salmon, respectively. Methemoglobin may increase significantly over time in fish immersed in a sedating dose of benzocaine or repeatedly anesthetized with benzocaine or TMS. The susceptibility varies with the individual and species with brook trout being more susceptible than Atlantic salmon or rainbow trout.

Comparison of NADH-dependent cytochrome b5 reductase activity and in vitro methemoglobin induction by sodium nitrite in Oncorhynchus mykiss, Salmo salar, and Salvelinus fontinalis.

Methemoglobin is hemoglobin containing ferric iron. Methemoglobin cannot bind to oxygen and at high concentrations causes tissue hypoxia. Brook trout (Salvelinus fontinalis) develop significantly greater methemoglobinemia than Atlantic salmon (Salmo salar) or rainbow trout (Oncorhynchus mykiss) following general anesthesia with benzocaine or tricaine methanesulfonate. The objective of this study was to compare the activity of the major methemoglobin reducing enzyme, NADH-dependent cytochrome b5 reductase (CB5R), in brook trout erythrocytes to the activity of CB5R in Atlantic salmon and rainbow trout erythrocytes. Methemoglobin levels were compared using co-oximetry following in vitro incubation of erythrocytes with sodium nitrite (NaNO(2)). The CB5R activity was measured using a ferricyanide assay. There was significantly greater methemoglobin at time 0 in brook trout erythrocytes than in rainbow trout or Atlantic salmon erythrocytes (2.79 ± 0.29 %, 2.19 ± 0.23 %, 2.08 ± 0.14 %), (P < 0.001). There was significantly greater methemoglobin induction by NaNO(2) in brook trout erythrocytes (33.14 ± 3.32 %) than in rainbow trout or Atlantic salmon erythrocytes (28.73 ± 2.92 % and 24.85 ± 1.40 %, respectively), (P < 0.001). The CB5R activity was significantly less in brook trout erythrocytes (median of 3.05 µmol/min/µl) than in rainbow trout erythrocytes (median of 6.73 µmol/min/µl). The CB5R activity in Atlantic salmon erythrocytes (median 4.09 µmol/min/µl) was not significantly different than in brook or rainbow trout erythrocytes. Total methemoglobin at any one time is a balance between induction by oxidants and reduction by antioxidants. Lower CB5R activity in brook trout erythrocytes may contribute to a species-specific sensitivity to methemoglobin induction; however, there are likely additional factors.

Compounding errors in 2 dogs receiving anticonvulsants.

Two cases that involve drug compounding errors are described. One dog exhibited increased seizure activity due to a compounded, flavored phenobarbital solution that deteriorated before the expiration date provided by the compounder. The other dog developed clinical signs of hyperkalemia and bromine toxicity following a 5-fold compounding error in the concentration of potassium bromide (KBr).

Evaluation of co-oximetry for the measurement of methemoglobin in rainbow trout (Oncorhynchus mykiss) and values in 3 salmonid species.

BACKGROUND: Methemoglobin (metHb) is oxidized hemoglobin that cannot reversibly bind oxygen, and concentrations in healthy fish have been reported to be 0.6-24.8% compared with 0-3% in healthy mammals. In fish, metHb has been measured using spectrophotometric methods using potassium cyanide (KCN), but not using co-oximetry, which is the preferred method for human samples. OBJECTIVES: The aims of this study were to evaluate co-oximetry as a method for measuring metHb in Oncorhynchus mykiss, compare co-oximetry with a KCN spectrophotometric method, and establish reference values for metHb concentrations as measured using co-oximetry in O mykiss, Salmo salar, and Salvelinus fontinalis. METHODS: Blood samples from healthy female O mykiss, female S salar, and female and male S fontinalis were prepared by separation and washing of erythrocytes in Tris/NaCl/EDTA buffer followed by lysis in Tris/EDTA buffer. MetHb concentrations were measured using an IL-682 co-oximeter. Moderate and high metHb concentrations were produced in vitro using NaNO(2). RESULTS: At low concentrations of methemoglobin, CVs for intraday precision were 10.3% and 53.9% using co-oximetry and the KCN spectrophotometric method, respectively. The CV for interday precision using co-oximetry was 11.9%. MetHb concentrations were stable in whole blood stored at 4°C for 7 days. MetHb concentrations were linear up to 58.2% (r = .99) using co-oximetry and 27.5% (r = .94) using the KCN method. The lower limit of detection for metHb was 0.02 g/dL using co-oximetry. Reference values for metHb concentrations using co-oximetry in O mykiss, S salar, and S fontinalis (n = 40 of each species) were 0.6-1.8%, 1.1-1.9%, and 1.1-4.0%, respectively. CONCLUSIONS: Co-oximetry can be used to measure methemoglobin in blood from fish, in particular in O mykiss, and is better than the KCN spectrophotometric method. Reference values for methemoglobin concentrations in O mykiss, S salar, and S fontinalis are similar to those in mammals.

Survey of euthanasia practices in animal shelters in Canada.

Questionnaires on methods of euthanasia used in Canadian animal shelters were sent to 196 Canadian animal shelters yielding 67 responses. Sodium pentobarbital injection was the only method of euthanasia used by 61% of establishments that euthanized dogs and 53% of the establishments that euthanized cats. Many of these establishments used pre-medication. Sodium pentobarbital was mostly administered intravenously but some establishments also used intracardiac and intraperitoneal routes, and some only used intracardiac administration for cats. T-61 injection was the only method of euthanasia used by 23% of the establishments that euthanized dogs and 35% of the establishments that euthanized cats. All of these establishments used pre-medication, but the percentages of establishments that only used the intravenous route for administration of T-61 in dogs and cats were 45% and 7%, respectively. Further studies on the use of T-61, and the training and provision of counselling services for staff are recommended.

Malignant adrenal neuroblastoma in a young dog.

A 1.5-year-old dog was evaluated for abnormal mentation, collapse, and weight loss. Radiographs and ultrasonographs revealed soft tissue masses in the mid abdomen. Ultrasound-guided fine-needle aspirates provided a diagnosis of malignant epithelial or round cell neoplasia. Histopathologic and immunohistochemical findings on the tumors were consistent with a primitive neuroblastoma.

Leishmanial polyarthritis in a dog.

A dog adopted as a stray in Spain and then brought to Canada 4 years prior to presentation was evaluated for polyarthritis. An electrophoresis showed a marked polyclonal gammopathy and synovial smears contained leishmanial organisms within macrophages.

Peritoneal fluid values and collection technique in young, normal calves.

Peritoneal fluid from 10 healthy young male Holstein calves was analyzed three times (2 to 3 days, 12 to 15 days and 27 to 30 days) during the first month of life. A new technique for collection of peritoneal fluid from calves positioned in left lateral recumbency was developed. The technique was found to be reliable and without noticeable complications. Mean peritoneal fluid nucleated cell counts, red blood cell counts, and absolute counts for mononuclear cells, lymphocytes and eosinophils did not change significantly (P