The Highs and Lows
Thyroid Problems in the ICU
Daniel Orr
Thyroid - Hypothyroidism
– Definition
– Defect within the hypothalamic-pituitary-thyroid axis,
with the net result of inadequate thyroid hormone
production
• Majority are primary - affecting thyroid gland itself
– Causes include
» Hashimoto’s thyroiditis
» Thyroidectomy
» Radioiodine & Deficiency/excess
» Drugs
» Intentional - carbimazole/propylthiouracil
» Side effect - lithium, amiodarone
Thyroid - Myxoedema Coma
– Definition
• Misnomer
• Severe Hypothyroidism with
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Altered mental state
Hypothermia
Other organ failure
Typically triggered by underlying illness or event
Thyroid - Myxoedema Coma
– Incidence
• Rare
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F>M (80%)
Elderly, > 60 years
90% cases during winter months
Mortality ~ 30%
Thyroid - Myxoedema Coma
– Clinical Findings
• Preexisting hypothyroid symptoms (collateral from
relatives)
– General
» Fatigue, weight gain, cold intolerance, constipation
» Anaemia
– Specific
» Myxoedema, skin, hair, face, tongue, hoarseness
» Eye signs
Thyroid - Myxoedema Coma
– Clinical Findings - All organ systems affected
• CNS
– Altered state of consciousness typical
» Lethargy, obtunded
» Seizures possible
• Thermoregulation
– Depression of hypothalamic function
– Patients typically cool, temperatures 24oC reported!
– Normothermia/hypothermia may represent sepsis
Thyroid - Myxoedema Coma
• CVS
– Overall reduction in metabolic requirements, therefore
reduction in cardiac output
– Bradycardia, decreased myocardial contractility
– Reduced pulse pressure with diastolic hypertension, or
hypotension
– Cardiac failure rarely seen owing to reduced cardiac
demands
Thyroid - Myxoedema Coma
• Resp
– Hypoventilation typical
– Results in respiratory acidosis and hypoxaemia
– Owing to
» central depression of respiratory drive, and
responsiveness to O2 and CO2
» Pump failure
» Sleep apnoea
Thyroid - Myxoedema Coma
• Metabolic & Renal
– Hyponatraemia
» Secondary to decreased renal perfusion (increased
creatinine) and impaired free water clearance
(SIADH)
» May be significant enough to contribute to alteration
in mental state
» Other electrolyte disturbance may occur by similar
mechanisms
– Hypoglycaemia
» Occurs concomitantly with hypothyroidism, even in
the absence of adrenal insufficiency or hypo-pituitary
disease
Thyroid - Myxoedema Coma
• Pathogenesis
– Overall decrease in oxygen and substrate usage
by all organ systems
– CVS
• Myocardium
– Alteration in gene expression
– Both systolic and diastolic function depressed
» Failure of contraction, compliance and filling
– Rhythm disturbance
» PVCs
» Torsade
Thyroid - Myxoedema Coma
• Pathogenesis
– CVS
• Vasculature
– Decreased release of nitric oxide, promoting increased
vascular resistance
• Perfusion
– Overall reduction, but tissue oxygenation reduced also, so
A-V O2 difference preserved
Thyroid - Myxoedema Coma
• Pathogenesis
– Trigger
• Intercurrent illness
– LRTI, UTI
– AMI, GIH, CVA
– Should be investigated for and excluded
Thyroid - Myxoedema Coma
• Diagnosis
• Based initially on history, examination and
exclusion of other forms of coma
• High TSH and low T4 useful in confirming
diagnosis, but clouded somewhat in secondary
hypothyroidism (Low TSH and T4)
• Other findings include
– Anaemia (normochromic, normocytic)
– Normal WCC
– Raised CK (skeletal muscle source)
Thyroid - Myxoedema Coma
• Management
– Specific
• Replacement of thyroxine mainstay of treatment
• Exact means of replacement controversial
– Bolus dose of T3/T4 to commence followed by
‘intermediate’ dosing
– Both high and low doses associated with increased
mortality
Thyroid - Myxoedema Coma
• Management
– Considerations
– Availability of intravenous preparations (owing to ileus)
– T3 v T4 v Combination
– Precipitation of AMI, arrhythmia
• Corticosteroids
– Use of corticosteroids recommended until coexisting
adrenal insufficiency is excluded
Thyroid - Myxoedema Coma
• Management
– Supportive
• Intubation & Ventilation
– Often required for decreased conscious state and
correction of respiratory acidosis and hypoxia
– Ongoing hypoxia may persist secondary to intrapulmonary
shunting
• Vascular tone
– Vasopressors often required in early stages
Thyroid - Myxoedema Coma
• Management
– Supportive
• Fluid management
– Balance
– Volume resuscitation required, but risk of precipitating
cardiac failure
– Appropriate fluids considered to allow for slow correction
of Sodium (fluid restriction often advocated),
consideration of HTS
• Thermoregulation
– Passive warming only, as active warming will precipitate
shock as a result of vasodilitation
Thyroid - Myxoedema Coma
• Management
– Supportive
• Empiric broad spectrum antibiotics
– Take cultures first
Thyroid - Myxoedema Coma
• Complications
• Hypoglycaemia
– iv glucose may be required
• Arrhythmia
– Cardiac monitoring required
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Ileus/Megacolon
LRTI
Hyponatraemia
Intubation
– May be difficult as a consequence of myxomatous change
Thyroid - Myxoedema Coma
• Considerations
• Drug clearance
• Other endocrine disorders
Thyroid - Hyperthyroidism
• Definition
• Excessive levels of circulating thyroid hormone
• Results in generalised acceleration of metabolic
processes
• Aetiology
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Graves
Toxic Adenoma/MNG
Iodine induced
TSH mediated
Germ cell tumours
Surgical
Cause has implications for treatment
Thyroid - Hyperthyroidism
• Incidence/Prevalence/Prognosis
– F>M 5:1
– Prevalence 1.3%
• Clinical Features
– CNS
– Anxiety, emotional lability
– Weakness
– Tremor
Thyroid - Hyperthyroidism
• Clinical Features
– Eyes/Skin
– Lid Lag
– Exophthalmos
– Sweating
– CVS
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Tachycardia, palpitations and AF
Increased cardiac output, increased contractility
Widening pulse pressure, decreased SVR
Heart failure
SOB
Thyroid - Hyperthyroidism
• Clinical Features
– Resp
– Dyspnoea
– Increased O2 consumption and CO2 production
– Potential hypoxaemia and hypercapnia
– GIT
– Increased motility with diarrhoea and malabsorption
Thyroid - Hyperthyroidism
• Pathogenesis
– T3 binds nuclear receptors upregulating genes responsible
for calcium cycling in the cardiac myocyte
• Myocardium
– Increased heart rate, contractility, cardiac output, and
myocardial oxygen consumption, AF a precipitant for
heart failure
• Vasculature
– Reduction in SVR and diastolic pressure
– Pulmonary hypertension
Thyroid - Storm
– Life threatening thyrotoxicosis, often with a
precipitant history
– Mortality > 10%
– Burch and Wartofsky scoring system designed
to clarify the diagnosis
Thyroid - Storm
– CVS
• Tachycardia, rate related
• Shock worst case scenario
• Heart failure, oedema, bibasal creps, pulmonary
oedema
– Thermoregulation
• >40 degrees common
– CNS
• Agitation, delirium, or degree obtundation
considered essential to diagnosis
Thyroid - Storm
– GIT
• NVD, hepatic failure with jaundice
– Pathogenesis
• Typically a trigger
– Acute infection/Stress response - AMI/Trauma
– Both Thyroidal and non-thryoidal surgery
– Radioiodine treatment
• Occurs on a background (usually) of those with
know hyperthyroidism
Thyroid - Storm
– Genesis thought to be related to
• Decreased levels of thyroid binding globulin in
above conditions, rather than raised total level of
thyroid hormones, resulting in increased unbound
fraction of T3 & 4
• Increased number of adrenergic binding sites,
resulting in increased sensitivity to catecholamines
Thyroid - Storm
• Diagnosis
– Raised T4 (& 3) and TSH depending upon
disorder
– Radioiodine uptake scan to differentiate
Thyroid - Storm
• Management
• Management of Thyroid storm is the same as for
uncomplicated hyperthyroidism, but the patient
should be managed in an intensive care environment
– Specific
• Beta Blockade
– Multiple forms
– Consideration of verapamil, if contraindicated
• Thionamide therapy
– Propylthiouracil, dual effect
Thyroid - Storm
• Iodine solutions
– Sodium ipodate
– Potassium iodide
– Lugol’s solution
• Corticosteroids
• Plasmapheresis/PD may be effective in removing
excess thyroid hormone
Thyroid - Storm
– Supportive
• Active cooling, paracetamol
– Avoid aspirin due to PPB
• Antiarrhythmics
• Volume resuscitation/Diuresis
• Antibiotics
• Sedation/Intubation/Ventilation
Thyroid - Storm
• Complications
– Airway complications as a result of goitre
• Considerations
– Anticoagulation for AF