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.

Bilateral femoral capital physeal fractures in an adult cat with suspected congenital primary hypothyroidism

“…In addition, it may be argued that in the present case blood for thyroid hormone tests was collected 4 days after surgery and that surgery under general anesthesia could have affected thyroid hormone measurements. However, a study on euthyroid dogs receiving abdominal surgery under general anaesthesia revealed no significant differences between the surgery and the control group regarding T4, fT4, T3, and TSH concentrations on days 1-6 post surgery [39]. Although these results cannot be directly transferred to cats and the situation in an orthopedic surgery may differ from that in soft tissue surgeries, the cited study indicates that the preceding surgical procedure may have had only limited influence on initial hormone values.…”

Influence of Isoflurane Anesthesia on Plasma Thyroxine Concentrations in Black-tailed Prairie Dogs (Cynomys ludovicianus)

“…In veterinary medicine, the only 2 species previously tested are dogs and laboratory rats, and in both, the measured thyroid hormones serum concentration was decreased after isoflurane anesthesia. 6,27 The rats under brief anesthesia were compared with control animals, 6 and the dogs were tested over multiple time points until 338 h after procedures. 27 The prairie dogs in our study were tested at 3 time points during brief (60 min) isoflurane-only anesthesia, to assess the effect on the thyroid as a potential risk factor for this type of anesthesia.…”

“…6,27 The rats under brief anesthesia were compared with control animals, 6 and the dogs were tested over multiple time points until 338 h after procedures. 27 The prairie dogs in our study were tested at 3 time points during brief (60 min) isoflurane-only anesthesia, to assess the effect on the thyroid as a potential risk factor for this type of anesthesia. Future studies should include a prolonged testing period and unanesthetized control animals.…”

“…3,5,12,19,23,24,26 In dogs, halothane has been suggested to reduce serum concentrations of T4, triiodothyronine (T3), and reverse triiodothyronine, and isoflurane reportedly decreases serum T4 and T3 concentrations. 9,27 In rats, ether increased measured serum T4 concentrations. 22 However, a more recent study in rats showed that ether, CO 2 /O 2 , methoxyflurane, and isoflurane decreased serum T4 and T3 concentrations.…”

“…4 Changes in T4 concentration (and other thyroid hormones) can lead to unstable anesthesia and increase the associated risks. 3,5,12,19,23,24,26,27 To our knowledge, the potential effect of anesthesia on thyroid function has not been explored in prairie dogs.…”