Thyroid Storm

Definition:

➧ Acute life-threatening exacerbation of thyrotoxicosis

Precipitating factors:

➧ Withdrawal of antithyroid drugs

➧ Severe infection

➧ Diabetic ketoacidosis (DKA)

➧ Cerebro-vascular accident (CVA)

➧ Cardiac failure

➧ Surgery

➧ Trauma 

➧ Radioiodine

➧ Drug reaction

➧ Iodinated contrast medium

Clinical picture:

➧ Patient with Graves disease who has discontinued antithyroid medication OR is previously undiagnosed

➧ Hyperpyrexia (40ºC)

➧ Sweating

➧ Tachycardia with or without AF

➧ Nausea, vomiting, and diarrhea

➧ Tremulousness and delirium, occasionally apathetic

Diagnosis:

➧ Free T4, free T3 elevated

➧ TSH suppressed

➧ Note that findings are not different than those of hyperthyroidism, but the difference is in the setting

Management of Thyroid Storm:

1-Inhibition of hormone production:

➤ Antithyroid agents:

➧ Thionamides (1st line therapy):

➧ Carbimazole/Methimazole 20-25 mg/6 h. orally or rectally (although once stable, the frequency of dosing can be decreased to once or twice daily).

-Carbimazole is metabolized to methimazole after ingestion.

-Halt synthesis of thyroid hormone by interfering with thyroid peroxidase.

➧ Propylthiouracil (PTU): 200 mg or 300 mg/6 h.

-Blocks peripheral conversion of T4 to T3 through inhibition of type 1 deiodinase.

2-Inhibition of thyroid hormone release:

➤ Iodine: (high concentration) 0.2-2 g/ d.

-Blocks release a stored hormone (Wolff-Chaikoff effect).

-Decreases iodide transport.

-Prevents oxidation in follicular cells.

-Iodine is given 1 hr after PTU to prevent incorporation into a new hormone.

-Above effects are only transient (48 h.).

-Lower concentration accelerates thyroid metabolism.

➧ Lugol’s solution: (assuming 20 drops/mL, 8 mg iodine/drop) 4-8 drops/6-8 h. oral.

➧ Potassium iodide: (with 20 drops/mL, 38 mg iodide/ drop) 5 drops/6 h.

➧ Oral iodinated contrast agents: 

-Competitively inhibit Types 1 and 2 50-mono-deiodinase in the liver, brain, and thyroid, blocking the conversion of T4 to T3, resulting in a rapid decrease in T3 and an increase in reverse T3. 

-Inhibit binding of T3 and T4 to cellular receptors. 

➧ Sodium ipodate: (308 mg iodine/500mg capsule) 1-3 g/ d.

➧ Iopanoic acid: 1g/8 h. for the first 24 hours, followed by 500 mg/12 h.

3-Controlling of cardiovascular manifestations:

➤ β-blockers:

-Control cardiovascular and hyperadrenergic manifestations.

-Decrease T4-T3 conversion.

➧ Propranolol: 60 to 80 mg/4 h., or 80 to 120 mg/4 h.

-The onset of action after oral dosing takes place within 1 hour. 

➧ For a more rapid effect, propranolol can also be administered parenterally, with a bolus of 0.5-1 mg over 10 min. followed by 1-3 mg over 10 min., every few hours, depending on the clinical context.

-Relatively large doses of propranolol are required in the setting of thyrotoxicosis because of the faster metabolism of the drug, and possibly because of a greater quantity of cardiac beta-adrenergic receptors.

➧ Esmolol: 50-100 µg/kg/min. IV.

➧ Longer-acting cardioselective β-adrenergic receptor antagonists: such as ➧ Atenolol and Metoprolol may be used also.

➤ Anticoagulation of AF:

➧ One of the significant cardiovascular complications of thyrotoxicosis is atrial fibrillation, occurring in 10% to 35% of cases. In the largest retrospective study, it appears that thyrotoxic patients who have atrial fibrillation are not at greater risk for embolic events, compared with age-matched patients who have atrial fibrillation due to other causes.

➧ Standard therapy with warfarin or aspirin is indicated, according to standard guidelines for atrial fibrillation.

➧ Thyrotoxic patients may require a lower maintenance dose of warfarin than euthyroid patients because of increased clearance of vitamin K-dependent clotting factors.

4-Steroids:

➤ Hydrocortisone: 100mg /8 h. IV with tapering as the signs of thyroid storm improve.

- Decreases T4-T3 conversion.

5-Alternative therapies:

-Several therapeutic agents used in the treatment of thyrotoxicosis are only considered when the first-line therapies of thionamides, iodide, beta-blockers, and glucocorticoids fail or cannot be used owing to toxicity.

➤ Potassium perchlorate: 1g qid oral

-Amiodarone induced thyrotoxicosis

-Inhibits iodide uptake by the gland.

➤ Lithium: 300 mg/8 h. 

-When thionamide is contraindicated.

-Inhibits new hormone synthesis.

-Decreases hormone secretion.

-To avoid lithium toxicity, lithium levels should be monitored regularly (perhaps even daily) to maintain a concentration of about 0.6-1.0 mEq/L.

➤ Guanethidine: 30-40 mg/6 h. orally

➤ Reserpine: 2.5-5 mg/4 h. IM

- Before β-adrenergic receptor antagonists were used to counteract the peripheral effects of thyroid hormone, the antiadrenergic agents, reserpine and guanethidine, were often used.

-Reserpine is an alkaloid agent that depletes catecholamine stores in sympathetic nerve terminals and the central nervous system.

- Guanethidine also inhibits the release of catecholamines.

-Side effects of these medications include hypotension and diarrhea. Reserpine can also have central nervous system depressant effects.

-These agents are indicated only in rare situations where β-adrenergic receptor antagonists are contraindicated, and when there is no hypotension or evidence of central nervous system-associated mental status changes

➤ Cholestyramine: 4 g four times a day oral.

-Decreases enterohepatic reabsorption of thyroid hormone.

➤ Plasmapheresis:

-When clinical deterioration occurs in thyroid storm, despite the use of all of these medications, removal of thyroid hormone from circulation would be a therapeutic consideration. Plasmapheresis, charcoal hemoperfusion, resin hemoperfusion, and plasma exchange are effective in rapidly reducing thyroid hormone levels in thyroid storms.

6-Supportive care:

➤ Supportive care is an important part of the multisystem therapeutic approach to thyroid storm.

➤ Antipyretics should be used; paracetamol is the preferable choice. Salicylates should be avoided in thyrotoxicosis because salicylates can decrease thyroid protein binding, causing an increase in free thyroid hormone levels. External cooling measures can also be used.

➤ Fluid loss and dehydration are also common in severe thyrotoxicosis. The fluid loss could result from the combination of fever, diaphoresis, vomiting, and diarrhea.

➤ Intravenous fluids with dextrose: (isotonic saline with 5% or 10% dextrose) should be given to replenish glycogen stores.

➤ Multivitamins, particularly thiamine, to prevent Wernicke's encephalopathy, which could result from the administration of intravenous fluids with dextrose in the presence of thiamine deficiency.

➤ If indicated digoxin for congestive heart failure.

➤ Treating the precipitating cause of thyrotoxicosis is particularly important, considering that the most common precipitant is thought to be an infection.

Prognosis:

➧ Mortality dropped since the 1920s from 100% to 20 – 30%

➧ Mortality is most frequently associated with serious underlying medical conditions 

Read more ☛ Myxedema Coma

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Myxedema Coma

Definition:

➧ The end-stage of untreated or insufficiently treated hypothyroidism.

Pathogenesis of Myxedema: (Figure 1)

Figure 1: Pathogenesis of Myxedema Coma

Precipitating factors:

➧ CVA

➧ Myocardial infarction

➧ Infection (UTI, Pneumonia)

➧ Gastrointestinal hemorrhage

➧ Acute trauma

➧ Administration of sedative, narcotic, or potent diuretics

Typical clinical picture:

➧ Elderly obese female

➧ Becoming increasingly withdrawn, lethargic, sleepy, and confused

➧ Slips into a coma

History:

➧ Previous thyroid surgery

➧ Radioiodine

➧ Default thyroid hormone therapy

Physical findings:

➧ Comatose or semi comatose

➧ Dry coarse skin

➧ Hoarse voice

➧ Thin dry hair

➧ Delayed reflex relaxation time

➧ Hypothermia

➧ Pericardial, pleural effusions, ascites

Laboratory tests:

➧ Free T4 low and TSH high

➧ If the T4 is low and TSH low normal consider pituitary hypothyroidism

➧ Blood gases

➧ Electrolytes and creatinine 

➧ Distinguish from the euthyroid sick syndrome

➧ Low T3, Normal or low TSH, normal free T4

ECG in a patient with Myxedema Coma: (Figure 2)

Figure 2: ECG in Myxedema Coma

Management of Myxedema:

➧ ICU admission: may be required for ventilatory support and IV medications.

➧ Parenteral thyroxine: Loading dose of 300-500 μg IV, then 50-100 μg/d. IV or 100-200 μg/d. oral

➧ Glucocorticoids: Hydrocortisone: 100 mg/8 h. for 1 week, then taper.

-Controversial but necessary in hypopituitarism or multiple endocrine failures.

➧ Electrolytes:

-Water restriction for hyponatremia 

-Avoid fluid overload

➧ Avoid sedation

Prognosis:

➧ Mortality is 20% and is mostly due to underlying and precipitating diseases.

Read more ☛ Thyroid Storm

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Acute Adrenal Insufficiency

Causes:

➧ Usually presents as an acute process in a patient with underlying chronic adrenal insufficiency

➧ Causes of Primary adrenal insufficiency:

   - Auto-immune

   - TB of adrenals

   - Metastatic malignancy to adrenals

➧ Causes of Secondary or Tertiary adrenal insufficiency

   - Pituitary or hypothalamic disease

➧ Acute destruction of the adrenals can occur with bleeding in the adrenals:

   - Sepsis

   - Disseminated intravascular coagulopathy (DIC)

   - Complication of anticoagulant therapy

Precipitating factors:

➧ Omission of medication

➧ Precipitating illness:

   - Severe infection

   - Myocardial infarction

   - Cerebro-vascular accident (CVA)

   - Surgery without adrenal support

   - Severe trauma

➧ Withdrawal of steroid therapy in a patient on long-term steroid therapy (Adrenal atrophy)

➧ Administration of drugs impairing adrenal hormone synthesis e.g. Ketoconazole

➧ Using drugs that increase steroid metabolism e.g. Phenytoin and Rifampicin

Clinical picture:

➧ Nausea and vomiting

➧ Hyperpyrexia

➧ Abdominal pain

➧ Dehydration

➧ Hypotension and shock

Clues to underlying Chronic Adrenal Insufficiency:

➧ Pigmentation in unexposed areas of the skin:

   - Creases of hands

   - Buccal mucosa

   - Scars

➧ Consider adrenal insufficiency if hypotension does not respond to pressors

Laboratory diagnosis:

➧ Hyponatremia and hyperkalemia (Hyponatremia might be obscured by dehydration).

➧ Random cortisol is not helpful unless it is very low (less than 5 mg/L) during a period of great stress.

➧ ACTH (Cosyntropin) stimulation test:

- Failure of cortisol to rise above 552 nmol/L 30 min after administration of 0.25 mg of synthetic ACTH IV

➧ Basal ACTH will be raised in primary adrenal insufficiency but not in secondary.

➧ CT of the abdomen will reveal enlargement of adrenals in patients with adrenal hemorrhage, active TB, or metastatic malignancy.

Management of Acute Adrenal Insufficiency:

➧ Hydrocortisone: 200 mg IV stat then 100 mg/8 h. for 24 h

-Taper slowly over the next 72 h.

-When oral feeds are tolerated change to oral replacement therapy.

-Overlap the first oral and last IV doses.

➧ Dexamethasone: 10 mg/6 h. IV

➧ Fludrocortisone: 0.05-0.3 mg/d. (if hydrocortisone less than 100 mg/d).

-Patients with primary adrenal insufficiency may require mineralocorticoid therapy (fludrocortisone) when shifted to oral therapy.

➧ 5% dextrose: IV for hypoglycemia

➧ Normal saline: IV for volume expansion

➧ Treat precipitating diseases

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Pituitary Apoplexy

Clinical Setting:

➧ Hemorrhagic infarction of a pituitary adenoma/tumor.

➧ Sudden crisis in a patient with a known or previously unknown pituitary tumor.

➧ It may occur in a normal gland during and after childbirth, with head trauma, or in a patient on anticoagulation therapy. 

➧ Sheehan’s Syndrome:

-Refers to pituitary apoplexy of the non-tumorous gland. It is due to the postpartum arterial spasm of arterioles supplying the anterior pituitary and its stalk.

Clinical Picture:

➧ Severe headache and visual disturbance

➧ Bitemporal hemianopia (Figure 1)

➧ CN III palsy

➧ Meningeal symptoms with neck stiffness

➧ Symptoms of secondary acute adrenal insufficiency:

-Nausea, vomiting, hypotension, and collapse

Figure 1: Bitemporal Hemianopia

Diagnosis:

➧ CT/MRI scan of head and pituitary

➧ Hormonal studies only of academic interest

➧ Assessment of pituitary function after the acute stage has settled

Management:

a) Hormonal:

➧ Dexamethasone: 4 mg/12 h.

-Glucocorticoid support and relief of cerebral edema.

b) Neurosurgical:

➧ Transsphenoidal pituitary decompression

-After the acute episode the patient must be evaluated for multiple pituitary deficiencies.

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Pheochromocytoma Crisis

Causes:

➧ The action of unopposed high circulating levels of catecholamines

- α - receptors: Pressor response

- β - receptors: positive ino- and chrono-topic

Precipitating factors:

➧ Spontaneous

➧ Hemorrhage into pheochromocytoma

➧ Exercise

➧ Pressure on the abdomen

➧ Urination

➧ Drugs: glucagon, naloxone, metoclopramide, ACTH, cytotoxics, tricyclic antidepressants

Clinical picture:

➧ History of poorly controlled Hypertension or accelerated Hypertension.

➧ Hypertension, palpitations, sweating, pallor, pounding headache, anxiety, tremulousness, pulmonary edema, feeling of impending death, hyperhidrosis, nausea and vomiting, abdominal pain, paralytic ileus, hyperglycemia, hypertensive encephalopathy, myocardial infarction, and stroke.

➧ Attacks build up over a few minutes and fade gradually over 15 min or can be more sustained (60 min).

➧ Signs of end-organ damage (Figure 1)

Figure 1: Hypertensive Retinopathy - Grade IV

Biochemical Diagnosis:

➧ 24 h. urine collection for free catecholamines and metanephrines.

Management of Pheochromocytoma Crisis:

-Do not wait for biochemical confirmation of the diagnosis.

-Be aware of postural hypotension.

-Avoid histamine-releasing drugs.

-Surgical resection treatment of choice.

α-adrenergic blockers:

-Treatment with a-antagonists should precede β-antagonist treatment with 48 h. to avoid exacerbation of the crisis.

➧ Phentolamine: (short-acting) 2-5 mg IV repeated/5 min.

➧ Phenoxybenzamine: 1st choice because it’s irreversible and long-acting

10 mg/12h., then 20-40 mg/8 h.

➧ Prazosin, Terazosin & Doxazosin: are selective α1-blockers. Preferable for long term Rx due to favorable S/E

β-blockers:

-Control tachycardia.

-After adequate α-adrenergic blockage to prevent unopposed hypertension.

➧ Non selective b- antagonist: Propranolol: 1-2 mg/5-10 min. 30-60 mg/d. oral.

➧ Esmolol: 500 µg/kg/min. for 1 min., then 100-300 µg/kg/min.

➧ Metoprolol

➧ Labetalol: α and β blocker.

Catecholamine synthesis inhibitors:

➧ Metyrosine

-Inhibit catecholamine synthesis.

-Used when alpha &beta blockers are ineffective or poorly tolerated.

-Combined for difficult resections.

Calcium channel blockers:

-Inhibit norepinephrine mediated calcium transport.

Acute hypertensive crisis (pre/intra-op):

➧ Nitroprusside

➧ Phentolamine

➧ Nicardipine

Surgery and Post-operative care:

➧ Experienced surgeon/anesthetist team.

➧ Last α & β doses on the day of surgery.

➧ Avoid fentanyl, ketamine, morphine, atropine, halothane, and desflurane during surgery.

➧ Treat hypotension post resection with fluids and intermittent doses of vasopressors.

➧ 24 h. urine metanephrine & catecholamine level 1-2 wks post-surgery and annually for life.

➧ Lifelong glucocorticoid and mineralocorticoid therapy for bilateral adrenalectomy.

➧ Radiotherapy, cryoablation, and combination chemotherapy should be considered for malignant pheochromocytoma.

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Burn Fluid Resuscitation Formulas

1-Harkins formula (1942)

Initial 24 hours:

➧ 1000 ml plasma/10% burn Used in patients with ≥ 10% burn.

2-Body weight burn budget (1947)

Initial 24 hours:

➧ Ringer's lactate (RL) solution 1-4 L + 1200ml NS + 7.5% body weight colloid + 1.5-5 L D5W.

Next 24 hours: 

➧ RL 1-4 L + 1200ml NS + 2.5%body weight colloid + 1.5-5 L D5W.

3-Evans formula (1952)

Initial 24 hours:

➧ 0.9% saline at 1 ml/kg/% burn + colloids at 1 ml/kg/% burn + 2000 ml G5W.

Next 24 hours:

➧ 0.9% saline at 0.5 ml/kg/% burn + colloids at 0.5 ml/kg/% burn + 2000 ml G5W.

4-Brooke formula (1953)

Initial 24 hours:

➧ RL solution 1.5 ml/kg/% burn + Colloids 0.5 ml/kg/% burn + 2000 ml G5W.

Next 24 hours:

➧ RL 0.5 ml/kg/% burn + Colloids 0.25 ml/kg/% burn + 2000 ml G5W.

5-Modified Brooke formula (1979)

Initial 24 hours:

➧ RL solution 2 ml/kg/% burn (for adults).

➧ RL solution 3 ml/kg/% burn (for children).

Next 24 hours:

➧ Colloids at 0.3-0.5 ml/kg/% burn.

➧ G5W to maintain good urinary output.

N.B. Pediatric supplementation for children less than 20 kg: RL at calculated maintenance.

6-Parkland formula (Baxter and Shires) (1974)

Initial 24 hours:

➧ RL solution 4 ml/kg/% burn (for adults).

➧ RL solution 3 ml/kg/% burn (for children).

Next 24 hours:

➧ Colloids are given as 20-60% of calculated plasma volume. 

➧ G5W is added in amounts required to maintain a urinary output of 0.5-1 ml/kg/h (in adults) & 1 ml/kg/h (in children).

7-Modified Parkland formula

Initial 24 hours:

➧ RL 4 ml/kg/% burn (for adults).

Next 24 hours:

➧ 5% albumin 0.3-1 ml/kg/% burn/16 per h.

8-Consensus (by the American Burn Association)

Initial 24 hours:

➧ RL solution 2-4 ml/kg/% burn.

Next 24 hours:

➧ Colloids at 0.3-0.5 ml/kg/% burn. 

➧ G5W is added in the amounts required to maintain good urinary output.

9-Mount Vernon (Muir and Barclay) formula

➧ Used in >15% burn (in adults) or >10% burn (in children).

➧ 1 ml/kg/% burn, Type of fluid: 50% crystalloids + 50% colloids (5% albumin).

➧ This volume is given in each of the following 6 periods: (0-4, 4-8, 8-12, 12-18, 18-24, 24-36h.)

10-Hypertonic saline formula

➧ NS containing: 250 mEq Na⁺ (0.6 ml/kg/% burn) + 1/3 isotonic salt solution orally up to 3500 ml.

11-Monafo (Hypertonic saline) formula (1984)

Initial 24 hours:

➧ NS containing: 250 mEq Na⁺ + 150 mEq lactate⁻ + 100 mEq Cl⁻. The amount is adjusted to maintain a urine output of 30 ml/h.

Next 24 hours:

➧ 1/3 normal saline according to urinary output.

12-Modified hypertonic formula (Metro Health Medical Center)

Initial 24 hours:

➧ RL + 50 mEq NaHCO₃ (180 mEq Na/L) RL 4 ml/kg/% burn titrated to urine output.

Next 24 hours:

➧ ½ NS + One unit FFP/L ½ NS + G5W to prevent hypoglycemia.

13-Slater formula

➧ (RL 2000ml + FFP 75 ml/kg)/24 h.

Formulas developed for children:

1-Shriner's Cincinnati formula

Initial 24 hours:

For older children:

➧ RL solution 4 ml/kg/% of burned tissue (burn-related losses) + 1500 ml/m² total BSA (maintenance fluid) (1/2 of total volume over 8 h, rest of the total volume during the following 16 h).

For younger children:

➧ 4 ml/kg/% of burned tissue (burn-related losses) + 1500 ml/m² total BSA (maintenance fluid).

➧ RL solution + 50 mEq NaHCO₃ in the first 8 h.

➧ RL solution in the second 8 h.

➧ 5% albumin in RL solution in the third 8 h.

2-Galveston formula

➧ Every 1000 ml of the solution consists of 50 ml of 25% albumin added to 950 ml of 5% D5W in the RL solution.

Initial 24 hours:

➧ 5000 ml/m² of burned tissue (burn-related losses) + 2000 ml/m² total BSA (maintenance fluid) (1/2 of total volume over 8 h, rest of the total volume during the following 16 h).

Next 24 hours:

➧ 3750 ml/m² of burned tissue (burn-related losses) + 1500 ml/m² total BSA (maintenance fluid). 

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Ropivacaine (Naropin®)

➧ Ropivacaine is a long-acting amide local anesthetic (LA) drug. The name ropivacaine refers to both the racemic mixture and the marketed S-enantiomer.

➧ It produces effects similar to other LAs via reversible inhibition of sodium ion influx in nerve fibers.

Advantages:

➧ Ropivacaine is less lipophilic than bupivacaine and is less likely to penetrate large myelinated motor fibers, resulting in a relatively reduced motor blockade. Thus, ropivacaine has a greater degree of motor-sensory differentiation, which could be useful when the motor blockade is undesirable. 

➧ The reduced lipophilicity is also associated with decreased potential for central nervous system toxicity and cardiotoxicity.

Uses:

1-Epidural anesthesia 

2-Peripheral nerve block 

3-Postoperative pain management 

4-Intrathecal hyperbaric solution of ropivacaine was tried and found to be less potent than bupivacaine and resulted in a faster onset and recovery from the blocks. Hyperbaric ropivacaine solutions are not commercially available.

Contraindications:

1-Intravenous regional anesthesia (IVRA): However, recent data suggested that ropivacaine (1.2-1.8 mg/kg in 40 ml) can be used, because it has less cardiovascular and central nervous system toxicity than racemic bupivacaine. 

2-Intra-articular infusion: Ropivacaine is toxic to cartilage and its intra-articular infusion can lead to Postarthroscopic glenohumeral chondrolysis.

Adverse effects:

a) CNS effects: occur at lower blood plasma concentrations; CNS excitation followed by depression. 

-CNS excitation: nervousness, tingling around the mouth, tinnitus, tremor, dizziness, blurred vision, seizures. 

-CNS depression: drowsiness, loss of consciousness, respiratory depression, and apnea. 

b) Cardiovascular effects: occurs at higher blood plasma concentrations. 

-Hypotension, bradycardia, arrhythmias, and/or cardiac arrest – some of which may be due to hypoxemia secondary to respiratory depression.

Treatment of overdose:

➧ As for bupivacaine, Intralipid, a commonly available intravenous lipid emulsion, can be effective in treating severe cardiotoxicity secondary to local anesthetic overdose in animal experiments and in humans in a process called lipid rescue.

Read more ☛ LA Toxicity

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Down's Syndrome

Anesthetic Management of Down's Syndrome

➧ This well-known syndrome, with characteristic morphological features and mental retardation, results from the chromosomal abnormality, trisomy 21.

➧ Anesthetic risk is increased in these children. Indeed, the mortality is increased at any stage of life, but improved medical and nursing care means that many more individuals are surviving into adulthood and may present for surgery.

➧ Between 60 and 70% of patients now survive beyond 10 years of age.

Preoperative abnormalities:

1. Cardiac abnormalities: occur in 50–60% of patients and are usually responsible for the initial mortality in infancy. The commonest lesions are septal defects, Fallot’s tetralogy, and patent ductus arteriosus. In adults, there is an increased risk of mitral valve prolapse and mitral and aortic valve regurgitation.

2. Immune system defect: results in an increased incidence of infection. Granulocyte abnormalities decreased adrenal responses, and defects in cell-mediated immunity have all been identified. There is an increased incidence of lymphomas and leukemias.

3. Skeletal abnormalities: atlantoaxial instability was recognized as being a problem, at a time when these children were encouraged to participate in gymnastics. Down’s children may have C1–C2 articulation abnormalities, subluxation, and odontoid peg abnormalities. It may occur in association with either medical procedures or physical activity. The cause of instability may be due to: poor muscle tone, ligamentous laxity, and abnormal development of the odontoid peg.

4. Biochemical abnormalities: involve the metabolism of serotonin, catecholamines, and amino acids.

5. Thyroid hypofunction: is common in both adults and children, although hyperthyroidism can sometimes occur. A child with Down’s syndrome had a thyrotoxic crisis that mimicked malignant hyperthermia.

6. Sleep-induced ventilatory dysfunction: has been reported.

7. Institutionalized Down’s patients have an increased incidence of hepatitis B antigen.

8. Autonomic dysfunction: in particular increased sympathetic function and decreased vagal activity, result from brainstem abnormalities.

Anesthetic problems:

1. Cervical spine abnormalities: increase the risk of dislocation of certain cervical vertebrae on intubation, or when the patient is paralyzed with muscle relaxants with risk of atlantoaxial subluxation and spinal cord compression. Cervical spine screening has to be carried out, and precautions taken during intubation. 

2. The larynx is often underdeveloped and smaller tracheal tube size is required than would be anticipated for the age of the patient. The adult larynx may only accept a size 6-mm tube.

3. Airway and intubation difficulties sometimes occur, from a combination of anatomical features. These include a large tongue, a small mandible and maxilla, a narrow nasopharynx, and irregular teeth. Even in the absence of teeth, intubation is made more difficult by excessive pharyngeal tissue.

4. Postoperative stridor after prolonged nasal intubation. Congenital subglottic stenosis occurs occasionally.

5. Obstructive sleep apnea is common in Down’s syndrome. Compared with normal children they had an increased incidence of stridor and chest wall recession, lower baseline oxygen saturations, and a greater number of episodes of desaturation to 90% or less. Chronic episodes of hypoxia and hypercarbia may lead to pulmonary hypertension and congestive heart failure. Airway patency depends upon both the anatomical structure of the upper respiratory tract and the normal functioning of the pharyngeal muscles. Abnormalities of either or both may occur.

6. Upper airway obstruction, because it has multiple causes, is not necessarily resolved with surgical treatment. Young patients with more severe symptoms often had multiple sites of obstruction and a high incidence of cardiac disease.

7. Problems of the associated cardiac disease, which in later life may lead to pulmonary hypertension.

8. A high incidence of atelectasis and pulmonary edema after surgery for congenital heart disease. Those with Down’s syndrome and ventricular septal defects were predisposed to pulmonary vascular obstruction.

9. Posterior arthrodesis of the upper cervical spine carries a high complication rate. Problems included infection and wound dehiscence, instability at a lower level, neurological sequelae, and postoperative death.

Management:

1. Lateral cervical X-rays are required, in full flexion and extension positions, to detect atlantoaxial instability. This may show as an increase in the distance between the posterior surface of the anterior arch of the atlas, and the anterior surface of the odontoid process. Patients with an atlanto-odontoid interval of 4.5–6.0 mm were asymptomatic, but those in whom the distance exceeded 7 mm had neurological signs. If instability is present, great care should be taken to immobilize the neck during intubation and muscle relaxation. These changes do not appear to progress with time. 

2. If a significant cardiac disease is present, management must be appropriate to the lesion, and endocarditis prophylaxis is given as recommended.

3. A tracheal tube should be used that is 1–2 sizes smaller than would be expected from the patient’s age.

4. If prolonged nasotracheal intubation is required, steroids should be given before extubation. The child should receive humidification and be observed carefully for signs of stridor.

5. Close observation is required in the perioperative period, to detect episodes of obstructive apnea. A pulse oximeter is useful.

6. Loss of locomotor skills or disturbances of gait after surgery or acute trauma should alert staff to the possibility of subluxation and cord compression. In the event of this, an urgent neurological opinion should be sought. However, in the absence of neurological signs, non-operative management has been advised, because of the high complication rate after surgery.

7. In patients with adenotonsillar hypertrophy, surgery may improve obstruction. However, close monitoring and oxygen therapy are important for the first postoperative night.

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