Mejora Continua

LEI WANG, MD

overview

■ Definition: heterogeneous left ventricular hypertrophy w/o other cardiac or systemic causes

➣

Septum is usually disproportionately affected.

➣

Left ventricular outflow tract (LVOT) is obstructed during systole by anterior motion of the anterior leaflet of mitral valve against the hypertrophied septum.

➣

The obstruction is dynamic & peaks at mid to late systole.

■ Risk: rare. Inherited as autosomal dominant w/ variable penetrance, or occurs sporadically.

■ About 25% of affected pts present w/ LVOT obstruction.

■ Usual Rx: medical therapy w/ beta blockers, calcium blockers

➣

Less commonly, more invasive therapy such as cardiac myomec-tomy

preop

Issues/Evaluation

■ Most pts are asymptomatic, but symptomatic pts usually complain

➣

of Dyspnea on exertion

➣

^Fatigue

➣

Syncope, near syncope

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^Angina

➣

Sudden death is often the first manifestation in young pts.

■ Key clinical features

➣

Severe diastolic dysfunction

➣

Increased risk for myocardial ischemia

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Supraventricular & ventricular arrhythmia common

➣

Pts w/ obstruction present w/ harsh systolic murmur, which is increased w/ Valsalva & decreased w/ squatting or handgrip

➣

EKG shows LVH.

➣

Echocardiography or cardiac catheterization confirms the diagnosis

Hypertrophic Cardiomyopathy 133 What To Do

■ Place pt on beta blocker or calcium channel blocker preop to decrease contractility.

■ Replace preop fluid deficit.

■ Adequate sedation to avoid anxiety-induced sympathetic discharge.

■ Amiodarone is generally effective in controlling arrhythmias.

■ Avoid diuretics, digoxin, or nitrates.

intraop

■ Potential issues

➣

Profound hypotension due to worsening obstruction w/

increases in sympathetic discharge, or decrease in preload or afterload

➣

Myocardial ischemia

➣

^Arrhythmia

Management

■ Consider arterial line, CVP, PAC; TEE when large fluid shift is antici-pated.

■ Take efforts to blunt sympathetic stimulation during induction.

➣

Avoid prolonged laryngoscopy.

■ Use volatile anesthetics that decrease ventricular contractility, such as halothane.

■ Avoid tachycardia.

➣

Give beta blocker or calcium channel blocker to treat worsening obstruction.

➣

Avoid agents that can increase heart rate or contractility, such as ephedrine, pancuronium, or epinephrine.

■ Avoid decreases in preload or afterload.

➣

Provide adequate fluid replacement from the very start of proce-dure.

➣

Avoid agents that decrease preload or afterload, such as nitro-glycerin or nitroprusside.

■ Treat hypotension w/ volume expansion & phenylephrine.

postop

■ Aggressive pain control to avoid sympathetic stimulation.

■ Maintain adequate preload & afterload.

■ Continue medical therapy (usually beta blockers, calcium blockers).

134 Hypocalcemia

HYPOCALCEMIA

LUDWIG H. LIN, MD

overview

■ Definition: serum calcium<8 mg/dL, or ionized calcium <1 mmol/L

■ Causes: acute hypocalcemia

➣

Blood transfusions: owing to citrate in banked blood

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Critically ill pts: associated w/ sepsis, burns, ARF, pancreatitis

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Hypoalbuminemia: reduced total calcium concentration (but normal ionized calcium concentration)

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Metabolic alkalosis: increases calcium’s binding to protein, so will decrease ionized calcium concentration

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Postop pts following parathyroidectomy or thyroidectomy

■ Causes: chronic hypocalcemia due to parathyroid hormone (PTH) abnormalities

➣

Hypoparathyroidism r Congenital r Hypomagnesemia

r Surgical removal of parathyroids

➣

Ineffective PTH (eg, pseudohypoparathyroidism, vitamin D defi-ciency)

➣

Overwhelmed PTH (eg, hyperphosphatemia from tumor lysis or rhabdomyolysis)

■ Usual Rx

➣

Hypoparathyroidism: vitamin D or calcitriol; calcium supple-ment

➣

Hypomagnesemia: IV magnesium administration

preop

Issues/Evaluation

■ Look for systemic effects of hypocalcemia.

➣

CNS: numbness & circumoral paresthesia, confusion, seizures

➣

Hypotension, increased left ventricular filling pressures

➣

Prolonged QT interval

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Weakness & fatigue, skeletal muscle spasm, laryngospasm r Chvostek & Trousseau signs indicate neuromuscular

irritability.

r Chvostek sign: tapping on facial nerve anterior to ear results in ipsilateral facial muscle twitching

Hypocalcemia Hypoparathyroidism 135 r Trousseau sign: inflating BP cuff above systolic pressure for

several minutes results in muscular contraction of the hand

What To Do

■ Confirm hypocalcemia w/ an ionized calcium measurement (to exclude the contribution of the albumin level to the total calcium level).

■ Obtain ECG.

intraop

■ Administer 500 mg to 1 g calcium chloride or calcium gluconate IV, check ionized calcium, & repeat IV calcium administration as needed to correct hypocalcemia.

■ Avoid hyperventilation, as respiratory alkalosis can increase calcium binding to serum proteins.

■ Consider checking phosphate & magnesium levels.

postop

■ Continue to follow serum & ionized calcium levels; continue replace-ment as necessary.

HYPOPARATHYROIDISM

BETTY LEE-HOANG, MD

overview

■ Definition: lack of parathyroid hormone (PTH).

■ Usual Rx: calcium supplement.

■ Hypoparathyroidism usually follows parathyroidectomy or occurs inadvertently after thyroidectomy; idiopathic forms are rare & will not be considered here.

preop

Issues/Evaluation

■ Presents as hypocalcemia: (total serum calcium)<4.5 mEq/L, or ionized calcium<1 mmol/L

■ Chvostek sign is painful facial twitching after tapping on the facial nerve.

■ Trousseau sign is carpal spasm after inflation of a tourniquet.

136 Hypoparathyroidism Hypothyroidism

intraop

■ Treatment is w/ calcium IV in the form of calcium gluconate or cal-cium chloride.

■ Intraop anesthetic agents that depress the myocardium may cause hypotension.

■ Laryngospasm is more likely w/ hypocalcemia.

■ Consider avoiding products that may lower Ca even further if possi-ble, such as citrate-containing blood products & 5% albumin.

postop

■ Continue to follow Ca levels & treat appropriately.

■ After parathyroidectomy, signs of hypocalcemia do not typically appear until after 24–72 h.

HYPOTHYROIDISM

JEREMY NUSSBAUMER, MD BETTY LEE-HOANG, MD

overview

■ Definition: inadequate levels of circulating T3 & T4 hormone

■ Primary hypothyroidism (95% of all cases) may be caused by

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Hashimoto’s thyroiditis (autoimmune)

➣

Thyroidectomy

➣

Radioactive iodine treatment

➣

Iodine deficiency

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Antithyroid medication

➣

Neck irradiation

■ Diagnosis of primary hypothyroidism: low levels of free thyroxine &

increased TSH

■ Secondary hypothyroidism is caused by failure of the hypothalamic-pituitary axis.

■ Signs/symptoms of hypothyroidism may include

➣

Fatigue, weakness

➣

Weight gain despite poor appetite

➣

Cold intolerance

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