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.


OBJECTIVE
Anesthesia and anesthesia with surgery will affect thyroid function tests in dogs.


METHODS
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
Surgery and anesthesia have a significant effect on thyroid function tests in dogs.
Wood
M A
MA
Department of Small Animal Clinical Sciences, Virginia-Maryland Regional College of Veterinary Medicine, Virginia Polytechnic Institute and State University, Blacksburg, VA, USA.
Panciera
D L
DL
Berry
S H
SH
Monroe
W E
WE
Refsal
K R
KR
D000768:Anesthesia, General / Q000662:veterinary*; D018685:Anesthetics, Inhalation / Q000494:pharmacology; D000818:Animals; D004283:Dog Diseases / Q000139:chemically induced*; D004285:Dogs; D005260:Female; D007530:Isoflurane / Q000494:pharmacology*; D008297:Male; D013514:Surgical Procedures, Operative / Q000662:veterinary*; D013959:Thyroid Diseases / Q000139:chemically induced / Q000662:veterinary*; D013960:Thyroid Function Tests / Q000662:veterinary*; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000097:blood; D013997:Time Factors; D014284:Triiodothyronine / Q000097:blood
D018685:Anesthetics, Inhalation; D014284:Triiodothyronine; D013972:Thyrotropin; D007530:Isoflurane; D013974:Thyroxine