Influence of Isoflurane General Anesthesia or Anesthesia and Surgery on Thyroid Function Tests in Dogs

Background: Anesthesia and surgery affect thyroid function tests in humans but have not been studied in dogs. Hypothesis: Anesthesia and anesthesia with surgery will affect thyroid function tests in dogs. Animals: Fifteen euthyroid dogs. Methods: Prospective, controlled, interventional study. Dogs were assigned to one of 3 groups: control, general anesthesia, and general anesthesia plus abdominal exploratory surgery. Dogs in the anesthesia and surgery groups were premedicated with acepromazine and morphine, induced with propofol, and maintained on isoflurane. Samples for measurement of serum thyroxine (T₄), free T₄ (fT₄) by equilibrium dialysis, triiodothyronine (T₃), reverse T₃ (rT₃), and thyroid‐stimulating hormone concentrations were collected from each dog immediately before premedication, at multiple times during anesthesia, surgery, 4, 8, 12, 24, 36, and 48 hours after anesthesia, once daily for an additional 5 days, and once 14 days after anesthesia. Sampling was performed at identical times in the control group. Results: Serum T₄ decreased significantly from baseline in the surgery and anesthesia groups compared with the control group at 0.33 (P= 0.043) and 1 hour (P= 0.018), and 2 (P= 0.031) and 4 hours (P= 0.037), respectively, then increased significantly in the surgery group compared with the control group at 24 hours (P= 0.005). Serum T₃ decreased significantly from baseline in the anesthesia group compared with the control group at 1 hour (P= 0.034). Serum rT₃ increased significantly from baseline in the surgery group compared with the control and anesthesia groups at 8 (P= 0.026) and 24 hours (P= 0.0001) and anesthesia group at 8, 12, 24, and 36 hours (P= 0.004, P= 0.016, P= 0.004, and P= 0.014, respectively). Serum fT₄ increased significantly from baseline in the surgery group compared to the control at 24 hours (P= 0.006) and at day 7 (P= 0.037) and anesthesia group at 48 hours (P= 0.023). Conclusions and Clinical Importance: Surgery and anesthesia have a significant effect on thyroid function tests in dogs.     

Euthyroid sick syndrome in dogs with idiopathic epilepsy before treatment with anticonvulsant drugs

Euthyroid sick syndrome is a common finding in dogs and is attributable to nonthyroidal illness or treatment with any of a variety of drugs such as phenobarbital. In dogs with epilepsy, treatment with anticonvulsant drugs can lead to subnormal plasma thyroid hormone concentrations despite normal thyroid function. One-hundred thirteen dogs with seizure activity were retrospectively evaluated to determine the influence of idiopathic epilepsy (IE) on thyroid hormone concentrations. Blood samples were taken from 60 dogs with IE before initiation of anticonvulsant therapy. Control groups consisted of 34 dogs with IE and receiving anticonvulsants and 19 dogs with secondary epilepsy. Thyroid concentrations consistent with euthyroid sick syndrome were diagnosed in 38% of dogs with untreated IE without clinical signs of hypothyroidism or concomitant diseases. There was a significant correlation (r = 0.363, P = .01) between seizure frequency and plasma thyroid hormone concentrations: the longer the interval between 2 seizure events, the higher the serum total thyroxine concentration. There was no correlation between the degree of alteration of thyroid hormone concentrations and the time span between the most recent seizure event and blood collection, the type of the most recent seizure event, the duration of the complete seizure history, or the predominant seizure type. These results suggest that IE can be a reason for euthyroid sick syndrome in dogs. The effect of phenobarbital on plasma thyroid hormone concentrations must be investigated in future studies, as it might be less pronounced than expected.     

Plasma vasopressin concentrations in healthy foals from birth to 3 months of age

Background: Arginine vasopressin (AVP) has received increased attention in equine critical care but there is minimal information of AVP concentration in foals. The clinical usefulness of measuring AVP in ill foals depends on knowledge of age-related changes in AVP concentrations in healthy foals.
Hypothesis: Plasma AVP concentrations will be significantly different when measured from birth to 3 months of age in healthy foals.
Animals: Thirteen healthy university-owned foals.
Methods: Prospective, observational study. Blood was collected from healthy foals at birth and 3, 5, 7, 10, 14, 21, 28, 42, 56, and 84 days of age. Plasma was harvested and plasma AVP concentrations were determined by radioimmunoassay.
Results: No statistically significant differences were detected in plasma AVP concentrations over the study period. Plasma AVP concentrations over the entire study period was 6.2 ± 2.5 pg/mL.
Conclusions and Clinical Importance: There was no age-related variation in plasma AVP concentrations detected in healthy foals from birth to 3 months of age suggesting that AVP concentrations are similar across foals of these ages.