Anesthesia for Thyroidectomy

SAAD A. SHETAMBCh B, MA, MD

Associate Professor,Consultant AnesthesiologistKSU

THYROID Anatomy

THYROID Pathophysiology

SIMPLE GOITER(↓ I )SIMPLE GOITER(↓ I ) HYPERTHYROIDISMHYPERTHYROIDISM AUTO IMMUNE THYOIDITIS AUTO IMMUNE THYOIDITIS (HASHIMOTO’S)(HASHIMOTO’S) CANCERCANCER VIRAL DE QUERVANS THYOIDITISVIRAL DE QUERVANS THYOIDITIS

THYROID Physiology

Thyroid hormones

controls metabolic processes

follicular cells synthesize/secrete thyroid hormones (T4, T3) when stimulated by TSH, low iodide levels, iodide TSH, low iodide levels, iodide uptakeuptake

Regulated by negative feedback loop of hypothalamus-anterior pituitary-thyroid initiated by TRH causing TSH release

Thyroid hormones

T4 thyroxine Th

yro

nin

e 5

’deio

din

ase

Thyroglobin (iodinated by peroxidase) back to cell

TRH (Hypothalamus)

TSH (Ant. Pituitary)

THYROID Anesthetic consideration

HYPERTHYROIDISM MULTI NODULAR DIFFUSE ENLARGEMENT

PREGNANCYPREGNANCY THYOIDITISTHYOIDITIS THYROID ADENOMATHYROID ADENOMA CHORIOCARCINOMACHORIOCARCINOMA TSH SECRETING TUMOURSTSH SECRETING TUMOURS

Diagnostics : Thyroid Function Tests

TestPurposeTotal plasma Thyroxine (T4) level

Detect > 90% hyperthyroidismInfluenced by T4- binding protein (TBG)

Resin Triiodothyroxine Uptake (RT3U)

▲T4 levelThyroid dysfunction Vs ▲ T4 binding globulin (TBG)

total Triiodothyroxine (T3) level

↑ in hyperthyroidism ↓ in hypothyroidism (or cirrhosis & nutrition)

Thyroid Stimulating Hormone (TSH) level

Primary Hypothyroidism↑ in hypothyroidism (beforeT4 level ↓)

Thyroid ScanIodide Concentrating CapacityFunctioning thyroid rarely malignant

UltrsonographyCystic (rarely malignant)

Antibodies to TG components

Hashimoto’s thyoiditis

Diagnostics: Differential Diagnosis

ConditionConditionTT44RTRT33UUTT33TSHTSH

HyperHyperthyroidismthyroidism↑↑↑↑↑↑normal or ↓normal or ↓

Primary Primary HypothyroidismHypothyroidism

↓↓↓↓↓↓↑↑

Secondary Secondary HypothyroidismHypothyroidism

↓↓↓↓↓↓↓↓

PregnancyPregnancy↑↑↓ ↓ or or normalnormalnormalnormalnormalnormal

Hyperthyroidism: Medical Treatment

*PropylthiouracilInhibit thyroid hormone synthesis Inhibit peroxidase *inhibit peripheral conversion of T3 to T4

Potassium or sodium iodidePrevent hormone release

propranalol

(quicker 7-14 days vs. 2 -6 weeks)

Decrease heart rate

IV propranalol (0.2 – 10 mg )IV esmolol (50 – 500 ug)

Emergency Surgery

Hyperthyroidism : Surgical Treatment

SUBTOTAL OR PARTIAL THYROIDECTOMYSUBTOTAL OR PARTIAL THYROIDECTOMY

removal of about 5/6’s of thyroid gland to treat hyperthyroidism

enlarged glands affecting breathing or swallowing problems; tracheal or esophageal obstruction

ANESTHETIC CONSIDERATIONS ANESTHETIC CONSIDERATIONS ““PROBLEMSPROBLEMS””

FROM MAJOR MANIFESTATIONSFROM MAJOR MANIFESTATIONS

Weight loss Heat Intolerance Muscle weakness (Large muscle group)

Diarrhea - DehydrationDehydration

Menstrual Abnormalities - AnemiaAnemia

Hyperactive reflexes and Nervousness Exophthalmos – Exposure keratitisExposure keratitis

Hypercalcaemia Bone loss (↑alkaline phosphatase) Thrombocytopenia

ANESTHETIC CONSIDERATIONS ANESTHETIC CONSIDERATIONS ““PROBLEMSPROBLEMS””

CARDIOVASCULAR SYSTEMCARDIOVASCULAR SYSTEM

Tachycardia / palpitation Tachycardia / palpitation

Cardiac Arrhythmias AFCardiac Arrhythmias AF

Hyperdynamic circulation Hyperdynamic circulation

↑ ↑ myocardial contractilitymyocardial contractility

↑ ↑ CO CO

CardiomegallyCardiomegally

High output HFHigh output HF

Mitral valve prolapse Mitral valve prolapse (papillary muscles dysfunction)(papillary muscles dysfunction)

ANESTHETIC CONSIDERATIONS “ANESTHETIC CONSIDERATIONS “PROBLEMSPROBLEMS””

Enlargement of the gland Retrosternal Enlargement of the gland Retrosternal Lower tracheal compression SVC obstruction Respiratory obstruction Tracheomalasia (after removal)

ABNORMAL GLUCOSE TOLERANCEABNORMAL GLUCOSE TOLERANCE

EXOPHTHALMOSEXOPHTHALMOS

THYROTOXIC MYOPATHIESTHYROTOXIC MYOPATHIES

ANESTHETIC CONSIDERATIONS “ANESTHETIC CONSIDERATIONS “PROBLEMSPROBLEMS””

Thyroid CrisisThyroid Crisis

THYROID STORM IS A LIFE THREATENING EXACERBATION OF HYPERTHYROIDISM PRECIPITATED BY (INJURY, INFECTION, SURGERY )

MOST OFTEN POPO IN UNTREATED OR INADEQUATE TREATED PATIENT IN EMERGENCY SURGERY

Mimics Malignant Hyperthermia Pheochromocytoma, Inadequate anesthesiaMimics Malignant Hyperthermia Pheochromocytoma, Inadequate anesthesia

Clinical Manifestation

ANXIETY, CONFUSION, RESTLESSNESS , DELIRIUM PYREXIA, FLUSHING, SWEATING, ABDOMINAL PAIN TACHYCARDIA, AF, HIGH OUTPUT CHF DEHYDRATION

ANESTHETIC CONSIDERATIONS “ANESTHETIC CONSIDERATIONS “PROBLEMSPROBLEMS””

MANAGEMENT Treat the precipitating cause (infection) Sedation, ETT, O2, IPPV (mat be required) Hydration (glucose containing IV fluids )

Propranalol 0.5 mg, repeat till HR is < 100 Propyl thiouracil 250 mg 6 hourly (Orally or via ETT) Sodium iodide 1 mg, IV, 12 hourly

Digoxin (CHF with AF & rapid VR) Dexamethazone or hydrocortisone Circulatory Shock (vasopressor) Cooling (Blanket, Pethedine)

ANESTHETIC CONSIDERATIONS “ANESTHETIC CONSIDERATIONS “PREOPERATIVEPREOPERATIVE””

Careful assessment of upper airway & tracheal deviation Thoracic inlet X-ray, CT scan

Patient must be rendered EUTHYROID Use anti-thyroid drugs and B - blockers Resting pulse rate 85/min

Benzodiazepines premedication

In Emergency Surgery (before Euthyroid)

Iv propranalol (0.2 – 10 mg) Iv Esmolol (50 – 500 ug) Caution with CHF

However , ↑Pump function by control fast V. rate)

Consider PCWP

ANESTHETIC CONSIDERATIONS “ANESTHETIC CONSIDERATIONS “INTRAOPERATIVEINTRAOPERATIVE””

Closely monitor temperature & CVS Protect eyes (lacerations) Use armored tracheal tube Raise head 10-15 degrees (▼air embolism)

Blunt the response to laryngoscopy Normal MAC (prevent Exaggerated SNS to Surgical Stimulation) Avoid Drugs that stimulate SNS (Ketamine)

Liver susceptible to damage due to Enflurane Use muscle relaxants carefully (myopathies)

Epinephrine free local anesthetics

ANESTHETIC CONSIDERATIONS “ANESTHETIC CONSIDERATIONS “POSTOPERATIVEPOSTOPERATIVE””

Extubation Light Anesthesia Inspection of the cord Under optimal circumstances for intubation

Injury to recurrent laryngeal nerve Bilateral stridor & laryngeal obstruction (re-intubation ) Unilateral : hoarseness Selective injury of both RLNs

(adductive fibers , leave abductors relatively unopposed Caution: → Aspiration )

Stridor Bleeding / Haematoma Dyspnoea Pneumothorax Air embolism Hypo parathyroidism in 24 – 48 hrs (Hypocalcaemia → Laryngeal Spasm,

Tetany)

Parathyroid glands parathyroid hormone (PTH)

control calcium levels (with calcitonin)

Vitamin D : facilitate absorption of ca ++, ph++, mg ++from the gut

facilitate bone reabsorption by parathormone

Parathyroid glands parathyroid hormone (PTH)

Plasma half life 2-5 minutes

mobilize ca++ to extracellular fluid

Active absorption of ca ++ from the small intestine

vitamin D dependent

Increase bone resorption of ca ++

Increase renal tubular resorption of ca++

INCREASE Ca ++

Calcium

Hypercalcaemia > 10.5 mg/dlNormal calcium 8.6 – 10.4 mg/dlHypocalcaemia < 8.5 mg/dl

serum calcium 40% clinically relevant fraction)

50 % bound to albumin 10 % bound to chelating

agents

decrease in serum albumin 1 gm → decrease in serum calcium 0.8 mg/dl

Effects of Hypoparathyroidism

ORGAN SYSTEM

CLINICAL MANIFESTATIONS

Cardiovascular Hypotension, CHF, ECG changes

Musculoskeletal Muscle cramps, weakness,

Neurological Neuromuscular irritability, laryngeospasm, Inspiratory stridor, Tetany, peripheral paresthesia, mental status changes

Hypocalcaemia : Medical Treatment

Ca gluconate IV: 10 – 20 ml of (10 %) Infusion: 10 ml (10%) / 500 ml for 6hrs

oral

maintain Ca ++ level to lower normal

Vitamin D

Monitor

Ca ++

Ph++

Mg++