Daniel Orr The Highs and Lows Thyroid Problems in the ICU.

Daniel Orr

The Highs and Lows

Thyroid Problems in the ICU

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– Altered mental state

– Hypothermia

– Other organ failure

– Typically triggered by underlying illness or event


– Incidence• Rare

– F>M (80%)– Elderly, > 60 years– 90% cases during winter months– Mortality ~ 30%


– 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


– 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


• 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


• 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


• 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


• 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


• 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


• Pathogenesis– Trigger

• Intercurrent illness– LRTI, UTI

– AMI, GIH, CVA

– Should be investigated for and excluded


• 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)


• 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


• 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


• 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



• 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



• Empiric broad spectrum antibiotics– Take cultures first


• Complications• Hypoglycaemia

– iv glucose may be required

• Arrhythmia– Cardiac monitoring required

• Ileus/Megacolon• LRTI• Hyponatraemia• Intubation

– May be difficult as a consequence of myxomatous change


• Considerations• Drug clearance

• Other endocrine disorders

Thyroid - Hyperthyroidism

• Definition• Excessive levels of circulating thyroid hormone

• Results in generalised acceleration of metabolic processes

• Aetiology– Graves

– Toxic Adenoma/MNG

– Iodine induced

– TSH mediated

– Germ cell tumours

– Surgical

– Cause has implications for treatment


• Incidence/Prevalence/Prognosis– F>M 5:1– Prevalence 1.3%

• Clinical Features– CNS

– Anxiety, emotional lability– Weakness– Tremor


• Clinical Features– Eyes/Skin

– Lid Lag

– Exophthalmos

– Sweating

– CVS– Tachycardia, palpitations and AF

– Increased cardiac output, increased contractility

– Widening pulse pressure, decreased SVR

– Heart failure

– SOB


• Clinical Features– Resp

– Dyspnoea

– Increased O2 consumption and CO2 production

– Potential hypoxaemia and hypercapnia

– GIT– Increased motility with diarrhoea and malabsorption


• 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

Daniel Orr The Highs and Lows Thyroid Problems in the ICU.

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