Effects of anaesthesia on thyroxine and thyroid-stimulating hormone levels in dogs

Summary

Objective: Although hypothyroidism is a common endocrinopathy in dogs, the diagnosis is not always straightforward. Several factors, including systemic disease or administration of drugs, can affect thyroid function and may lead to erroneous test results. The aim of this study was to evaluate if anaesthesia has an effect on total thyroxin (TT₄) or thyroid-stimulating hormone (cTSH) levels in dogs. Material and methods: Twenty-four dogs presented for various primary problems underwent anaesthesia for endoscopy. Four different anaesthetic protocols using a combination of propofol and isoflurane, propofol and halothane, thiopental and isoflurane or thiopental and halothane (each n = 6) were randomly chosen for each dog. TT₄ and cTSH levels were measured before and 24 hours after anaesthesia. Results: Post-anaesthetic TT₄ levels were significantly lower than pre-anaesthetic levels (p = 0.0002). There was no significant difference between the four anaesthetic groups (p = 0.17). The post-anaesthetic cTSH values were not significantly (p = 0.73) different compared to the pre-anaesthetic values. Conclusions: Results indicate that TT₄ values may significantly decrease for at least 24 hours post recovery from anaesthesia irrelevant of the anaesthetic agent used. Clinical relevance: The study has highlighted that thyroid testing in dogs should always be viewed in light of the clinical situation. General anaesthesia can lower TT₄ levels to a point where hypothyroidism may be wrongly diagnosed.

Zusammenfassung:

Gegenstand und Ziel: Die Diagnosestellung der Hypothyreose, eine häufige endokrinologische Erkrankung des Hundes, ist nicht immer einfach. Verschiedene Faktoren, wie die Verabreichung von Medikamenten oder aber auch Systemerkrankungen, können die Schilddrüsenfunktion und damit auch Resultate beeinflussen. Ziel dieser Studie war, den Einfluss einer Anästhesie auf die Serumkonzentration von Thyroxin (TT₄) und thyroideastimulierendem Hormon (cTSH) zu evaluieren. Material und Methoden: Vierundzwanzig Hunde mit unterschiedlichen Primärerkrankungen wurden zur Durchführung einer Endoskopie narkotisiert. Anhand der verwendeten Narkosewirkstoffe erfolgte eine Einteilung der Tiere in vier Gruppen (je n = 6): Propofol plus Halothan; Propofol plus Isofluran; Thiopental plus Halothan; Thiopental plus Isofluran. Die Serumkonzentration von TT₄ und cTSH wurde jeweils vor und 24 Stunden nach der Narkose bestimmt. Ergebnisse: Die Serumkonzentration von TT₄ nach der Narkose lag signifikant niedriger als die Konzentration vor der Narkose (p = 0,0002). Zwischen den vier Gruppen gab es keinen signifikanten Unterschied (p = 0,17). Die präund postanästhetischen Serumkonzentrationen von cTSH differierten nicht signifikant (p = 0,73). Schlussfolgerungen: Die Ergebnisse machen deutlich, dass die TT₄-Serumkonzentration unter dem Einfluss einer Narkose signifikant erniedrigt sein kann. Diese Absenkung bleibt mindestens 24 Stunden bestehen und war unabhängig von der Art des Narkoseprotokolls. Klinische Relevanz: Die Studie verdeutlicht, dass die Untersuchung auf eine Hypothyreose immer im Zusammenhang mit der klinischen Verdachtsdiagnose erfolgen muss. Eine vorangegangene Narkose kann die TT₄-Serumkonzentration so stark erniedrigen, dass fälschlicherweise eine Hypothyreose diagnostiziert würde.

Key words

Hypothyroidism - endocrine disease - euthyroid sick syndrome - endoscopy

Schlüsselwörter

Hypothyreose - Euthyroid Sick Syndrome - Endoskopie

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