Hypothyroidism/hyperthyroidism Flashcards
Hypothyroidism effects dogs multi systemically and is associated with a number of clinical signs resulting from a reduced overall metabolism; what are some?
Weight gain, hair loss, dry skin, pyoderma, lethargy, otitis, seizures, facial paralysis, laryngeal paralysis, megaoesophagus.
In what ways can hypothyroidism impact anaesthesia?
A decreased ventilatory response to hypercapnia and hypoxaemia, reduced FRC, longer recoveries, hypothermia, decreased myocardial contractility, hypotension, hypoglycaemia, mild to moderate anaemia.
What systemic support may be required when anaesthetising patients with hypothyroidism?
Positive inotropes, vasopressors, fluid therapy, ventilation
What kind of anaesthesia drugs should be used for hypothyroid patients?
Drugs of shorter duration and that can be antagonised. L&J suggest opioids and benzodiazepines.
What is a hypothyroid crisis and how is it treated?
Myxoedema coma is a rare condition due to severe, untreated hypothyroidism. Excess mucin accumulates in the skin causing oedema, particularly on the face. Also characterised by dull mentation, hypothermia and weakness. Treated with levothyroxine.
Hyperthyroidism is due to excessive circulating thyroid hormone concentration and consequently increases overall metabolism. It (like hypothyroidism) has multi systemic effects. What are the clinical signs?
Hypertension, often concurrent heart dz (HCM), gallop rhythm, chronic cellular malnutrition, hepato-cellular stress, decreased GI transit time, increased GFR, weight loss, polyphagia, PU/PD, hyperactivity.
What are the anaesthetic considerations for hyperthyroidism?
Concurrent HCM is common, tachycardia, hypertension, increased myocardial workload - avoid increasing myocardial O2 demand, fluid overload, gallop rhythm, arrhythmias (Vtach), check renal parameters and BP prior to GA, stress prior to GA, increased metabolism = increased O2 and glucose demands. Know what medication they are on for their condition.
What drugs can/should not be used in patients with hyperthyroidism?
Avoid ketamine, desflurane & nitrous as they increase sympathetic stimulation. Ketamine also increases myocardial O2 demand.
ACP can be used (if no heart dz!) - reduces myocardial sensitivity to catecholamines & blocks alpha adrenergic receptors (i.e. vasodilation).
Opioids can be used - generally reduce HR & myocardial O2 consumption.
Alpha 2 agonists can be used as part of premed.
How is feline hyperthyroidism treated?
Methimazole blocks production of T3 & T4 hormones.
Carbimazole (Vetmedin) is metabolised into methimazole.
Atenolol is a beta blocker and used to treat hypertension.
ACE inhibitors are used to treat hypertension.
What is a thyrotoxic storm?
It is a rare risk in hyperthyroid cats post op and is characterised by tachycardia, hypertension, arrhythmias, fever and shock.
