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

Abstract

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 (T 4 ), free T 4 (fT 4 ) by equilibrium dialysis, triiodothyronine (T 3 ), reverse T 3 (rT 3 ), 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 T 4 decreased significantly from baseline in the surgery and anesthesia groups compared with the control group at 0.33 (P 5 0.043) and 1 hour (P 5 0.018), and 2 (P 5 0.031) and 4 hours (P 5 0.037), respectively, then increased significantly in the surgery group compared with the control group at 24 hours (P 5 0.005). Serum T 3 decreased significantly from baseline in the anesthesia group compared with the control group at 1 hour (P 5 0.034). Serum rT 3 increased significantly from baseline in the surgery group compared with the control and anesthesia groups at 8 (P 5 0.026) and 24 hours (P 5 0.0001) and anesthesia group at 8, 12, 24, and 36 hours (P 5 0.004, P 5 0.016, P 5 0.004, and P 5 0.014, respectively). Serum fT 4 increased significantly from baseline in the surgery group compared to the control at 24 hours (P 5 0.006) and at day 7 (P 5 0.037) and anesthesia group at 48 hours (P 5 0.023).Conclusions and Clinical Importance: Surgery and anesthesia have a significant effect on thyroid function tests in dogs.

Retrospective evaluation of circulating thyroid hormones in critically ill dogs with systemic inflammatory response syndrome

“…An increase in serum rT3 has been reported during NTI in humans [ 27 ]. A similar increase has been reported in healthy euthyroid dogs during general anesthesia and surgery [ 28 ], and in a small population of healthy dogs following endotoxin administration [ 18 ]; however, no similar results in canine species during spontaneous SIRS have been reported. In the present study, the median concentration of rT3 was not significantly different between SIRS and control dogs.…”

“…Derangement of the thyroid axis was documented in chronic inflammatory conditions and during heterogeneous non-thyroidal diseases [ 13 15 23 ]. Finally, significant abnormalities in thyroid function test results have been reported in healthy euthyroid dogs during anesthesia or surgical procedures [ 28 ].…”

Thyroid function tests during nonthyroidal illness syndrome and recovery in acutely ill dogs

“…Two studies in dogs have demonstrated that anesthesia and surgery alter serum TT4, TT3, and fT4 concentrations, but any significant change from baseline occurred within 8 to 12 hours after implementation of these interventions. 52 , 53 To minimize the impact of anesthesia and surgery on thyroid function tests, dogs had initial blood sampling performed before these interventions and subsequent blood samples were obtained a minimum of 12 hours afterward. Moreover, when serum thyroid hormone concentrations were compared between the dogs managed medically and those undergoing anesthesia and surgery, no significant differences were found except for the serum TT3 concentration at 2 weeks.…”

Optimal Testing for Thyroid Hormone Concentration after Treatment with Methimazole in Healthy and Hyperthyroid Cats

“…Cats used in the study were acclimated to blood collection and were sampled only once daily, randomly over 6 days, eliminating the need for an IV catheter or anesthesia for blood collection. This design helped to minimize any potential effect of additional drugs or procedures on thyroid hormone concentrations; surgery and anesthesia have been shown to suppress thyroid hormone concentrations in dogs and humans 15 and similar effects are also likely in cats.…”