James L. Whiteside, MD

• Assistant Professor, Dartmouth-Hitchcock Medical Center, Dartmouth Medical
• School, Lebanon, New Hampshire

Detrimental effects of catecholamine release during anesthesia in patients with hypertrophic obstructive cardiomyopathy and in patients experiencing hypercyanotic spells associated with tetralogy of Fallot may be blunted by administration of esmolol treatment 5th metatarsal shaft fracture purchase generic cytoxan. Administration of esmolol to patients chronically treated with badrenergic antagonists has not been observed to produce additional negative inotropic effects medicine bottle purchase discount cytoxan. Likewise, esmolol infused during cardiopulmonary bypass is not associated with adverse effects after discontinuation of cardiopulmonary bypass medications used to treat fibromyalgia generic 50 mg cytoxan with visa. The elimination half-time of esmolol is about 9 minutes, reflecting its rapid hydrolysis in the blood by plasma esterases that is independent of renal and hepatic function medications not to take before surgery best 50mg cytoxan. Clinically insignificant amounts of methanol also occur from the hydrolysis of esmolol treatment statistics buy discount cytoxan 50 mg on-line. Plasma esterases responsible for the hydrolysis of esmolol are distinct from plasma cholinesterase, and the duration of action of succinylcholine is not predictably prolonged in patients treated with esmolol medicine to prevent cold discount cytoxan 50 mg on line. Indeed, plasma concentrations of esmolol are usually not detectable 15 minutes after discontinuing the drug. Which drug prevents tachycardia and hypertension associated with tracheal intubation: lidocaine, fentanyl, or esmolol Fever, rash, myopathy, alopecia, and thrombocytopenia have been associated with chronic b-adrenergic antagonist treatment. The principal contraindication to administration of b-adrenergic antagonists is preexisting atrioventricular heart block or cardiac failure not caused by tachycardia. Administration of b-adrenergic antagonists to hypovolemic patients with compensatory tachycardia may produce profound hypotension. In patients with diabetes mellitus, there is the risk that b-adrenergic blockade may mask the signs of hyperglycemia and thus delay its clinical recognition. Cardiovascular System b-Adrenergic antagonists produce negative inotropic and chronotropic effects. In addition, the conduction speed of cardiac impulses through the atrioventricular node is slowed and the rate of spontaneous phase 4 d epolarization is decreased. Preexisting atrioventricular heart block due to any cause may be accentuated by b-adrenergic antagonists. The cardiovascular effects of b-adrenergic blockade reflect removal of sympathetic nervous system innervation to the heart (b1 blockade) and not membrane stabilization, which occurs only at high plasma concentrations of the antagonist drug. The magnitude of cardiovascular effects produced by b-adrenergic antagonists is greatest when preexisting sympathetic nervous system activity is increased, as during exercise or in patients in cardiac failure. Indeed, the tachycardia of exercise is consistently attenuated by b-adrenergic antagonists. Resting bradycardia is minimized and cardiac failure is less likely to occur when a partial b-adrenergic antagonist with intrinsic sympathomimetic activity is administered. Acute cardiac failure is rare with oral administration of b-adrenergic antagonists. Classically, b-adrenergic antagonists prevent inotropic and chronotropic effects of isoproterenol as well as baroreceptor-mediated increases in heart rate evoked by decreases in systemic blood pressure in response to peripheral vasodilator drugs. Conversely, the influence of badrenergic antagonists on the cardiac-stimulating effects of calcium, glucagon, and digitalis preparations is not detectable. Likewise, b-adrenergic antagonists do not alter the response to a-adrenergic agonists such as epinephrine or phenylephrine. Indeed, the pressor effect of epinephrine is enhanced because the nonselective b antagonists prevent the b2 vasodilating effect of epinephrine and leave unopposed its a-adrenergic effect. Unexpected hypertension has occurred in patients receiving clonidine who subsequently receive a nonselective b-adrenergic antagonist. Patients with peripheral vascular disease do not tolerate well the peripheral vasoconstriction associated with b2 receptor blockade produced by nonselective b-adrenergic antagonists. Indeed, the development of cold hands and feet is a common side effect of b blockade. The principal antidysrhythmic effect of b-adrenergic blockade is to prevent the dysrhythmogenic effect of endogenous or exogenous catecholamines or sympathomimetics. Membrane stabilization is probably of little importance in the antidysrhythmic effects produced by usual doses of b-adrenergic antagonists. Treatment of Excess Myocardial Depression the usual clinical manifestations of excessive myocardial depression produced by b-adrenergic blockade include bradycardia, low cardiac output, hypotension, and cardiogenic shock. Seizures and prolonged intraventricular conduction of cardiac impulses are thought to be the result of local anesthetic properties of certain badrenergic antagonists (see Table 19-1). If atropine is ineffective, drugs to produce direct positive chronotropic and inotropic effects are indicated. Glucagon appears to be particularly effective in the presence of life-threatening bradycardia and has been described as the drug of choice to treat massive badrenergic antagonist overdose. Hemodialysis should be reserved to remove minimally protein-bound, renally excreted b-adrenergic antagonists in patients refractory to pharmacologic therapy. Airway Resistance Nonselective b-adrenergic antagonists such as propranolol consistently increase airway resistance as a manifestation of bronchoconstriction due to blockade of b2 receptors. These airway resistance effects are exaggerated in patients with preexisting obstructive airway disease. Because bronchodilation is a b2-adrenergic agonist response, selective b1adrenergic antagonists such as metoprolol and esmolol are less likely than propranolol to increase airway resistance. For example, nonselective b-adrenergic antagonists such as propranolol interfere with glycogenolysis that ordinarily occurs in response to release of epinephrine during hypoglycemia. Furthermore, tachycardia, which is an important warning sign of hypoglycemia in insulin-treated diabetics, is blunted by b-adrenergic antagonists. For this reason, nonselective b-adrenergic antagonists are not recommended for administration to patients with diabetes mellitus who may be at risk for developing hypoglycemia because of treatment with insulin or oral hypoglycemics. Altered fat metabolism is evidenced by failure of sympathomimetics or sympathetic nervous system stimulation to increase plasma concentrations of fatty-free acids in the presence of b-adrenergic blockade. Distribution of Extracellular Potassium Distribution of potassium across cell membranes is influenced by sympathetic nervous system activity as well as insulin. Specifically, stimulation of b2-adrenergic receptors seems to facilitate movement of potassium intracellularly. As a result, b-adrenergic blockade inhibits uptake of potassium into skeletal muscles, and the plasma concentration of potassium may be increased. Indeed, increases in the plasma concentration of potassium associated with infusion of this ion are greater in the presence of b-adrenergic blockade produced by propranolol. Interaction with Anesthetics Myocardial depression produced by inhaled or injected anesthetics could be additive with depression produced by b-adrenergic antagonists. Additive cardiovascular effects with inhaled anesthetics and b-adrenergic antagonists seem to be greatest with enflurane and least with isoflurane. Cardiac output and systemic blood pressure are similar with or without b-adrenergic blockade in the presence of one or two minimum alveolar concentration isoflurane. In the presence of anesthetic drugs that increase sympathetic nervous system activity (ketamine), or when excessive sympathetic nervous system activity is present because of hypercarbia, the acute administration of a b-adrenergic antagonist may unmask direct negative inotropic effects of concomitantly administered anesthetics, with resulting decreases in systemic blood pressure and cardiac output. For example, fatigue and lethargy are commonly associated with chronic propranolol therapy. Memory loss and mental depression have been alleged to occur, although b-adrenergic antagonist therapy has not been shown to produce these effects. Fetus b-Adrenergic antagonists can cross the placenta and cause bradycardia, hypotension, and hypoglycemia in newborn infants of mothers who are receiving the drug. Breast milk is also likely to contain b-adrenergic antagonists administered to the mother. Withdrawal Hypersensitivity Acute discontinuation of b-adrenergic antagonist therapy can result in excess sympathetic nervous system activity that manifests in 24 to 48 hours. Presumably, this enhanced activity reflects an increase in the number of b-adrenergic receptors (upregulation) during chronic therapy with badrenergic antagonists. It is accepted that patients being treated with b-adrenergic receptor antagonists should have their medication continued uninterrupted through the perioperative period. It is also recommended that patients at high risk for myocardial ischemia and presenting for major surgery should be treated with b-adrenergic receptor antagonists beginning preoperatively and continuing into the postoperative period. Treatment of Essential Hypertension Chronic therapy with b-adrenergic antagonists results in gradual decreases in systemic blood pressure. The antihypertensive eff ct of b-adrenergic blockade is largely dependent on decreases in cardiac output due to decreased heart rate. Large doses of b-adrenergic antagonists may decrease myocardial contractility as well. An important advantage in the use of b-adrenergic antagonists for the treatment of essential hypertension is the absence of orthostatic hypotension. All orally administered b-adrenergic antagonists appear to be equally effective antihypertensive drugs. Release of renin from the juxtaglomerular apparatus that occurs in response to stimulation of b2 receptors is prevented by nonselective b-adrenergic antagonists such as propranolol. This may account for a portion of the antihypertensive effect of propranolol, especially in patients with high circulating plasma concentrations of renin. Management of Angina Pectoris Orally administered b-adrenergic antagonists are equally effective in decreasing the likelihood of myocardial ischemia manifesting as angina pectoris. Th s desirable response reflects drug-induced decreases in myocardial oxygen requirements secondary to decreased heart rate and myocardial contractility. The effective dose usually decreases resting heart rate to less than 60 beats per minute. A more important measure is the heart rate during exercise, which should not exceed 75% of the heart rate at which myocardial ischemia occurs. The concept that b-adrenergic antagonists and calcium channel blockers act on different determinants of the myocardial oxygen supply-to-demand ratio suggests combined uses of these drugs would be beneficial in the management of patients with coronary artery disease. Nevertheless, the evidence from clinical studies suggests that patients managed with combined therapy do not experience greater beneficial therapeutic effects but may experience more adverse effects than if they had received optimal treatment with a single drug. Treatment with b-adrenergic antagonists is contraindicated in the presence of severe bradycardia, unstable left ventricular failure, and atrioventricular heart block. Relative contraindications to treatment with b-adrenergic antagonists include asthma or reactive airway disease, mental depression, and peripheral vascular disease. Diabetes mellitus is not a contraindication to treatment with b-adrenergic antagonists recognizing that signs of hypoglycemia may be masked. Whether b-adrenergic antagonists can decrease mortality in patients with angina pectoris who have not yet experienced a myocardial infarction is unknown. The cardioprotective effect of b-adrenergic antagonists is present with both cardioselective and nonselective drugs (see Tables 19-1 and 19-2). The mechanism of the cardioprotective effect is uncertain, but antidysrhythmic actions may be important. A nonselective b-adrenergic antagonist that prevents epinephrine-induced decreases in plasma potassium concentrations (a b2-mediated response) may be useful in decreasing the incidence of ventricular dysrhythmias. Perioperative b-Adrenergic Receptor Blockade Perioperative b-adrenergic receptor blockade is recommended for patients considered at risk for myocardial ischemia (known coronary artery disease, positive preoperative stress tests, diabetes mellitus treated with insulin, left ventricular hypertrophy) during high-risk surgery (vascular surgery, thoracic surgery, intraperitoneal surgery, anticipated large blood loss). Perioperative myocardial ischemia is the single most important potentially reversible risk factor for mortality and cardiovascular complications after noncardiac surgery. Administration of atenolol for 7 days before and after noncardiac surgery in patients at risk for coronary artery disease may decrease mortality and the incidence of cardiovascular complications for as long as 2 years after surgery. The incidence of bronchospasm, hypotension, bradycardia, and cardiac dysrhythmias was not increased in treated patients. The mechanism for the beneficial effects of perioperative b-adrenergic receptor blockade is not known but is most likely multifactorial (Table 19-4). It is not known if patients with cardiac risk factors but no signs of underlying coronary artery disease will benefit from perioperative administration of a b-adrenergic antagonist. Acebutolol, metoprolol, atenolol, propranolol, and timolol are approved for prevention of sudden death following acute myocardial infarction. Management of Congestive Heart Failure Controlled studies have demonstrated that metoprolol, carvedilol, and bisoprolol improve ejection fraction and increase survival in patients in chronic heart failure (see Table 19-2). Prevention of Excessive Sympathetic Nervous System Activity b-Adrenergic blockade is associated with attenuated heart rate and blood pressure changes in response to direct laryngoscopy and tracheal intubation. Tachycardia and cardiac dysrhythmias associated with pheochromocytoma and hyperthyroidism are effectively suppressed by propranolol. The likelihood of cyanotic episodes in patients with tetralogy of Fallot is minimized by b blockade. Even anxiety states as caused by public speaking have been treated with propranolol. This has prompted many practitioners to only start low-dose b-blocker regimens in the preoperative period or to hold initiation until postoperatively. Treatment of Intraoperative Myocardial Ischemia Appearance of evidence of myocardial ischemia on the electrocardiogram or as wall motion abnormalities on the transesophageal echocardiogram may benefit from treatment with a b-adrenergic receptor blocking drug, assuming the absence of contraindications (severe reactive airway disease, shock, left ventricular failure) and the presence of an adequate concentration of inhaled anesthetic drugs. Suppression of Cardiac Dysrhythmias b-Adrenergic receptor blocking drugs are effective in the treatment of cardiac dysrhythmias as a result of enhanced sympathetic nervous system stimulation (thyrotoxicosis, pheochromocytoma, perioperative stress). Esmolol and propranolol are eff ctive for controlling the ventricular response rate to atrial fibrillation and atrial flutter. These drugs are also effective for controlling atrial dysrhythmias Combined a- and b-Adrenergic Receptor Antagonists Labetalol Labetalol is a unique parenteral and oral antihypertensive drug that exhibits selective a1- and nonselective b1- and b2-adrenergic antagonist effects. Pharmacokinetics Metabolism of labetalol is by conjugation of glucuronic acid, with 5% of the drug recovered unchanged in urine. The elimination half-time is 5 to 8 hours and is prolonged in the presence of liver disease and unchanged by renal dysfunction.

Comparison of brachial and radial arterial pressure monitoring in patients undergoing coronary artery bypass surgery symptoms zoloft order cytoxan master card. Short-term cardiovascular oscillations in man: measuring and modeling the physiologies medicine reaction cheap cytoxan 50 mg. Pulmonary artery blood temperature and the measurement of cardiac output by thermodilution symptoms gallbladder problems cheap cytoxan 50mg on line. Bench to bedside: electrophysiologic and clinical principles of noninvasive hemodynamic monitoring using impedance cardiography medications valium buy cytoxan 50mg with amex. Endothelial and smooth muscle cell conduction in arterioles controlling blood fl w treatment hpv buy cytoxan 50 mg low price. Ventilation-perfusion and gas exchange effects of sodium nitroprusside in dogs with normal and edematous lungs medicine 44390 discount cytoxan 50mg fast delivery. Halothane and isoflurane do not decrease Pao2 during one-lung ventilation in intravenously anesthetized patients. Hypoxia-induced pulmonary vasoconstriction in the human lung: the effect of isoflurane anesthesia. Gravity is an important but secondary determinant of regional pulmonary blood flow in upright primates. Shanewise the heart has four chambers and can be characterized as two pumps connected in series, each composed of an atrium and a ventricle. The atria function primarily as conduits to the ventricles, but they also contract weakly to facilitate movement of blood into the ventricles during the filling phase, diastole. The ventricles serve as pumps during systole to supply the main force that propels blood through the systemic and pulmonary circulations. Because the heart is coupled to two circulations in series, its function is influenced by the characteristics of both. The right atrium is divided into three regions, the posteriorly located smooth-walled venous component, the anteriorly located vestibule of the tricuspid valve, and the right auricle. The venous component, or the sinus venosum, receives the vena cavae and the coronary sinus. The venous part of the atrium is separated from atrium proper and the auricle by a ridge of muscle called the crista terminalis. The pectinate muscles are muscular trabeculae that extend anterolaterally from crista terminals into the auricle. Anterior to the orifice of inferior vena cava is the eustachian valve, which in the fetal circulation directs oxygen-rich blood from placenta into left atrium through the foramen ovale of atrial septum. The fossa ovalis is the thin part of the atrial septum, above and to the left of the orifice of inferior vena cava. The vestibule of the tricuspid valve is the anteroinferior portion of right atrium. The tricuspid valve is so named as it has three leaflets, one each located anterosuperiorly, septally, and inferiorly. True chordae arise usually Cardiac Anatomy Pericardium the pericardium is a fibrous sac that contains the heart and the proximal portions of great vessels. The fibrous layer is fibrocollagenous and is continuous superiorly with the adventitia of the great vessels and the pretracheal fascia and inferiorly with the diaphragm. Anteriorly, the fibrous layer attaches to the sternum through the sternopericardial ligaments. The aorta, pulmonary arteries, and pulmonary veins also receive extensions from the fibrous pericardium. The serosal layer of the pericardium is enclosed within the fibrous pericardium and consists of a single, continuous membrane that is divided into two parts, the visceral and the parietal pericardium. The visceral layer surrounds the heart and the great vessels and is reflected on to the parietal layer that lines the inner surface of the fibrous pericardium. The inelastic nature of the pericardium limits acute dilation of the heart and enhances the resulting mechanical interaction of the four cardiac chambers. There are three papillary muscles in the right ventricle: two larger, located in the anterior and posterior positions of the right ventricle, and a smaller muscle arising from the ventricular septum. The inlet and outlet components are separated by a transverse ridge of muscle called the supraventricular crest or the crista supraventricularis. The many muscular ridges and protrusions into the inner surface of the inlet and apex are known as trabeculae carneae. The septal band or the septomarginal trabecula reinforces the septal surface; at the apex, it supports the anterior papillary muscle, from where it crosses to the parietal wall of the ventricle as the moderator band. The pulmonic valve is located at the distal end of the infundibulum and consists of three semilunar cusps, an anterior, a right, and a left cusp. The right and the left atrium are separated by the obliquely positioned atrial septum. The superior posterior aspect of the left atrium receives the pulmonary veins and forms the anatomic base of the heart. The left auricle is longer and narrower than the right auricle and is the only portion of the left atrium that is trabeculated. The anterior and posterior leaflets converge at the anterolateral and posteromedial commissures, each of which is associated with a papillary muscle. The anterior leaflet is semicircular and occupies one-third of the circumference, whereas the posterior leaflet is elongated and narrow and is attached to the remaining two-thirds of the annulus. The posterior leaflet is divided into three parts based on the presence of two indentations: a lateral P1, a central P2, and a medial P3 scallop. The segments of anterior leaflet opposing the posterior leaflet are similarly designated as A1, A2, and A3 scallop. The chordae tendineae attach to the edges of mitral leaflets or to its ventricular surface. The left ventricle has two papillary muscles: the anterolateral papillary muscle and the posteromedial papillary muscle. The chordae tendineae arise from the papillary muscle and attach to the ipsilateral half of anterior and posterior mitral leaflets. In the long axis, it descends forward and to the left from its base at the atrioventricular groove to form the cardiac apex. It consists of the inlet region, the apical trabecular component, and the smooth-walled outflow tract. At rest, the myocardium extracts about 75% of the oxygen delivered by coronary blood flow more than any other tissue in the body. So whenever myocardial oxygen demand increases, as with exercise, the coronary arteries must dilate to increase blood flow and oxygen delivery to meet the demand, or ischemia results. This coronary artery dilation is mediated through the local release of vasodilator substances within the myocardium. The right ventricular branches are the right conus artery or the infundibular artery and the acute marginal arteries. The atrial branch in majority of the population is the artery to the sinoatrial node. The right diagonal branches are small and rare; the left diagonal arteries can vary in number anywhere from two to nine and cross the anterior surface of the left ventricle. The first septal branch is usually targeted for ablation in interventional treatment for hypertrophic cardiomyopathy. The CxA curves left in atrioventricular groove giving rise to obtuse marginal branches extending over the posterolateral wall toward the apex. The bundle of His and bundle branches are insulated from the myocardium by a fibrous sheath, thus forming specialized network of conduction tissue. This functional organization results in a coordinated, synchronized contraction of the atria and ventricles, improving the efficiency of the heart. It is an essential tool for detecting myocardial ischemia, arrhythmias, and conduction system abnormalities. Electrocardiogram Leads the cardiac electrical activity is usually measured by electrodes placed on the skin. Unipolar leads consist of one positive electrode (exploring) and a composite pole that averages electrical activity from a number of other leads to zero potential, referred to as the indifferent electrode. When the depolarization wave is perpendicular to the lead, a biphasic deflection is recorded. The standard limb leads and the augmented limb leads record electrical impulses that flow in the frontal plane, whereas the precordial leads record impulses in the horizontal plane. Electrocardiographic Axis of the Heart the axis represents the overall direction of the electric impulse in the heart and is created by averaging all the action potentials. It is biased toward the left because of the larger muscle mass of the left ventricle compared to the right. The standard limb leads combined with the augmented limb leads form the hexaxial diagram, which is used to calculate the electrical axis of the heart on the frontal plane. Hypertrophy of the left ventricle shifts the axis to the left, and hypertrophy of the right shifts it to the right. Left axis deviation is defined as an axis less than 230 degrees and right axis deviation as more than 90 degrees. Two electrodes are used to form the selected lead and the third becomes the ground. In the modified three-lead bipolar standard limb lead system, the electrodes are placed in different locations on the chest wall. This allows for improved detection of arrhythmias (taller P waves) and monitoring for ischemia of the heart surface closer to each exploring pole. Augmented Limb Leads Augmented leads are similar to the standard limb leads but are unipolar. The central terminal presents a stable reference potential point that is used to measure the varying potential at the exploring electrode. Precordial Leads the precordial (V1 to V6) are unipolar leads that are placed on the chest wall, with the exploring electrode over one of six separate points (Table 15-1). The five-lead system uses five electrodes placed on the right arm, right leg, left arm, left leg, and one on the chest wall in any one position from V1 to V6. The electrodes are placed on the right arm and leg, left arm and leg, and on the anterior and anterolateral chest wall. London and colleagues11 examined lead sensitivity for detecting intraoperative myocardial ischemia. They concluded that using single-lead monitoring, V5 had the greatest sensitivity, 75%, whereas V4 had 61%. This allows detection of the site of a conduction delay, important for prognosis and treatment. The heart rate in beats per minute can be calculated by dividing 300 by the number of large boxes (or 1,500 by the number of small boxes) counted between two beats. Another method of calculating heart rate in beats per minute is to divide 60 by the number of seconds (5 0. The electrical activity that activates the cardiac contraction is observed on a monitor display as a graph of voltage change through time. Repolarization happens in the reverse direction, from the epicardium to the endocardium. P Wave the P wave represents the atrial depolarization and has a normal duration and amplitude of 0. P-R Interval the P-R interval corresponds to the time from the beginning of the atrial depolarization to the beginning of the ventricular depolarization. Therefore, the direction of the sum of the action potentials in the specific plane changes and is recorded accordingly. It is normally isoelectric and elevation or depression more than 1 mm from the baseline may indicate myocardial ischemia. T Wave the T wave is caused by the repolarization of the ventricles, and its normal amplitude is less than 10 mm in the precordial leads and 6 mm in the limb leads. Inverted T waves in V1 to V3 in children (juvenile T waves) and occasionally in women can be a normal variant. U Wave the U wave, when present, follows the T wave and it probably represents part of the ventricular repolarization. Cardiac Physiology Myocardium the myocardium is the involuntary, striated muscle tissue in the heart between the epicardium and the endocardium; its cells are called cardiomyocytes. The primary structural proteins of the cardiac muscle are actin and myosin filaments, which interdigitate and slide along each other during contraction in a manner similar to skeletal muscle. But unlike the skeletal muscle in which the actin and myosin filaments are linear and longitudinal, in cardiomyocytes, they are branched. Cardiac muscle T tubules form diads with the sarcoplasmic reticulum intercalated discs with permeable junctions that allow rapid diffusion of ions so that action potentials travel easily from cell to cell. Thus, cardiomyocytes are functionally interconnected in a syncytium, so that activation of one cell results in the spread to all connected cells. This plateau causes the contraction of a cardiomyocyte to last much longer than a skeletal muscle cell and is due to the slow calcium channels, which open after the sodium channels and remain open several tenths of a second. Depolarization of the cardiomyocyte is also prolonged by a decrease in permeability of the potassium channels after initiation of the action potential, another difference from skeletal muscle. Depolarization of the T tubule causes influx of calcium into the sarcoplasm, which binds to troponin activating the contraction of actin and myosin filaments. In the cardiomyocyte, however, the initial influx of calcium ions is just a small fraction of the amount needed for contraction, and it triggers an additional release of calcium from the sarcoplasmic reticulum into the sarcoplasm. The structural differences between cardiac and skeletal muscle reflect the difference in coupling mechanism.

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Meanwhile, the number of cardiac myocytes is decreased due to necrosis and apoptosis medications used to treat adhd effective cytoxan 50mg. Despite these changes, resting systolic function tends to be well preserved in healthy individuals translational medicine 50 mg cytoxan mastercard. As a result, increases in cardiac output in response to severe exertion are attenuated by approximately 20% to 30% symptoms celiac disease buy cheap cytoxan 50mg on line. Cardiac dysfunction in aging is largely related to impaired diastolic left ventricle function with increased prevalence of diastolic heart failure treatment 247 cheap 50 mg cytoxan otc. Ventricular filling in the elderly is especially dependent on active diastolic relaxation medicine rock generic cytoxan 50mg amex. In this process, calcium is removed from troponin C binding sites, triggering the dissociation of actin and myosin, thus facilitating isometric relaxation symptoms multiple sclerosis cytoxan 50 mg on-line. Active diastolic relaxation uses approximately 15% o f the energy consumed during the cardiac cycle. This process is significantly impaired in the elderly and exacerbates the adverse effects of ventricular hypertrophy on diastolic filling. As such, the elderly heart is markedly dependent on the atrial "kick" for adequate ventricular preload. It is estimated that atrial contraction contributes approximately 30% of ventricular filling in the elderly versus 10% in younger individuals. Because of the importance of atrial contraction, Aging and the Cardiovascular System Increasing age is associated with increasing cardiac morbidity. Aging is associated with an increasing prevalence of cardiovascular disease and decreasing cardiovascular functional reserve. However, it is important to separate the cardiovascular effects of aging from those of common diseases with increased prevalence in the elderly, such as atherosclerosis, hypertension, and diabetes mellitus. The decline in cardiac function that occurs with aging in the healthy individual appears to be related, in part, to decreasing functional demand. Indeed, when exercise and low-calorie diet are maintained into the later decades, the decline in cardiovascular function is markedly attenuated. Important functional changes include arterial hypertrophy resulting in increased afterload, ventricular hypertrophy resulting in elevated systolic blood pressure, loss of cells in the electrical conduction system predisposing to arrhythmia, and loss of sensitivity to catecholamines resulting in reduced maximal heart rate and heart rate variability. Tachycardia and shortened diastolic intervals are associated with marked decreases in ventricular preload in the elderly. Loss of the atrial kick is particularly poorly tolerated by elderly patients because of decreased capacitance of the left ventricle from the previously noted changes. Perioperative events that reduce venous return, such as hypovolemia, positive pressure ventilation, and increased venous capacitance, may be accompanied by signifi ant decreases in cardiac output. Conversely, excessive perioperative increases in blood volume or decreases in contractility can precipitate congestive cardiac failure. Diastolic dysfunction is now recognized as a major contributor to cardiovascular disease in the elderly population and is exacerbated by several coexisting diseases8,9 (Table 46-1). It is difficult to distinguish systolic dysfunction from diastolic dysfunction during routine clinical evaluation. Furthermore, routine preoperative echocardiographic indices of function such as left ventricular ejection fraction will fail to identify diastolic dysfunction. However, diastolic filling can be evaluated by comparing Doppler echocardiographic measurements of mitral valve inflow velocities during the early and late (atrial contraction) phases of diastole. Dyspnea in the elderly may indicate congestive cardiac failure and/ or pulmonary disease. Large Vessels Structural changes in the large vessels are an important element of the aging process and contribute significantly to the age-related changes in the heart described earlier. The sinoatrial node, atrioventricular node, and conduction bundles also become infiltrated with fibrous and fatty tissue. These changes are responsible for the increased incidence of first- and second-degree heart block, sick sinus syndrome, and atrial fibrillation in the elderly. The development of atrial fibrillation is also facilitated by left atrial enlargement, which typically accompanies aging in otherwise healthy individuals. Otherwise, healthy elderly men also experience an age-related increase in the prevalence, frequency, and complexity of ventricular ectopy. Their intima and media are thickened, causing these vessels to be less distensible. The normal cushioning function of the large vessels is impaired; causing accelerated and enhanced pulse wave propagation. In young adults, the reflected pulse wave generally has lower amplitude and its return from the peripheral circulation is delayed such that diastolic rather than systolic pressure is augmented. Thus, in the elderly, both systolic pressure and pulse pressure are increased and left ventricular afterload is elevated. All of the aforementioned age-related vascular structural changes are accelerated in the presence of hypertension or atherosclerosis. Autonomic and Integrated Cardiovascular Responses Aging is associated with increased norepinephrine entry into the circulation and deficient catecholamine reuptake at nerve endings. Therefore, elevated circulating concentrations of norepinephrine are usual, generating chronically increased adrenergic receptor occupancy. However, the cardiovascular response to increased adrenergic stimulation is attenuated by downregulation of postreceptor signaling and reduced contractile response of the myocardium. The response to exogenously administered b agonists, such as isoproterenol, is similarly attenuated. Receptor downregulation is responsible for the age-related decline in maximum heart rate during exercise. Indeed, receptor downregulation in the elderly makes their cardiovascular function similar to that of a younger individual who has received b-adrenergic antagonists. Impaired baroreceptor reflexes and attenuated peripheral vasoconstriction are partially responsible. Hypovolemia and salt depletion also contribute and are the result of iatrogenic diuretic administration or increased atrial natriuretic peptide release. Orthostatic hypotension is more common in patients who are hypertensive at baseline. It is difficult to separate the effects of aging per se from those of age-related chronic increases in systolic pressure. The normal baroreceptor response to this maneuver includes an increase in heart rate and peripheral Endothelial Function the vascular endothelium is an important regulator of vasomotor response, coagulation, fibrinolysis, immunomodulation, and vascular growth and proliferation. Endothelial dysfunction is an important element in the early pathogenesis of atherosclerosis, diabetes mellitus, and systemic hypertension. Reactive oxygen species, such as superoxide anions, have been implicated in age-related endothelial dysfunction. Endothelial dysfunction is accelerated by smoking, diabetes, hypertension, and hyperlipidemia. In the elderly, endothelial nitric oxide release is decreased in all vascular beds, including the coronary circulation. Vasodilator responses to b2 agonists and vasoconstrictor responses to a-adrenergic stimulation are similarly attenuated in the elderly. Thus, agerelated endothelial dysfunction can be characterized as a decrease in the ability of the endothelium to dilate or contract blood vessels in response to physiologic and pharmacologic stimuli. Agerelated impairment of baroreceptor responses makes hypotension more likely after the initiation of positive pressure ventilation, particularly in the presence of hypovolemia. In the Irish Longitudinal Aging Study, antidepressants and b blockers were associated with orthostatic hypotension, and hypnotics and sedatives worsened preexisting orthostatic intolerance. These findings should be considered in the mobilization of elderly patients who may have received these drugs in the perioperative period. Table 46-2 Intrinsic and Extrinsic Events that Influence the Respiratory System during Aging Intrinsic to the Aging Process Decreased bronchiolar caliber Decreased alveolar surface area Increased lung collagen content Decreased lung elastin content Kyphoscoliosis Increased thoracic cage rigidity Decreased diaphragmatic strength Environmental, Behavioral, and Disease Related Industrial and environmental pollution Smoking General deconditioning Coexisting disease Anesthetic and Ischemic Preconditioning in the Aging Heart It is now recognized that, under certain circumstances, exposure to volatile anesthetics (anesthetic preconditioning) or several brief periods of ischemia (ischemic preconditioning) may enhance tolerance to subsequent ischemia, enhance cardiac function, and reduce infarction size. However, both anesthetic and ischemic preconditioning may be markedly attenuated in the elderly, potentially explaining the difficulty of translating promising preclinical results to treatment. Respiratory System Mechanics and Architecture the chest wall becomes less compliant with aging, presumably related to changes in the thoracic skeleton and a decline in costovertebral joint mobility. Therefore, the diaphragm and abdominal muscles assume a greater role in tidal breathing. However, diaphragmatic function declines with age, predisposing the elderly to respiratory fatigue when required to significantly increase minute ventilation. Although the diaphragm does not appear to undergo significant atrophy or change in muscle fiber type with aging, it does occupy a flatter position and therefore has a less favorable mechanical advantage. These changes predispose the elderly to respiratory insufficiency in the setting of high regional anesthesia. Aging and the Respiratory System the respiratory system undergoes a multifactorial decline in functional reserve with aging (Tables 46-2 and 46-3). However, decreased respiratory reserve may be unmasked by illness, surgery, anesthesia, and other perioperative events. Common respiratory diseases and the effects of smoking and environmental pollution frequently exacerbate the decline in respiratory function with aging. The anticipation and amelioration of their effects is critically important to anesthetic management in the elderly, as postoperative respiratory complications result in 40% of perioperative deaths in patient older than 65 years. Changes in surfactant function may also contribute to age-related changes in lung compliance. The net result of these changes in the elastic properties of the lung and chest wall is an increase in intrapleural pressure that significantly impacts on respiratory function. Increased intrapleural pressures increase the tendency for small airway collapse to occur, thus causing gas trapping and/or expiratory airflow limitation. The opposing recoil forces of the lung and chest wall generate the subatmospheric intrapleural pressure. This is because the increased stiffness of the chest wall counteracts the increase in lung volume. Closing Capacity Airway closure may occur in small airways (,1 mm) whose caliber is determined by their transmural pressure. Airway closure typically occurs in dependent areas of the lung where the surrounding intrapleural pressure is likely to be greater. However, as intrapleural pressure increases with age, airway closure occurs at progressively greater lung volumes. Thus, gas exchange impairment due to shunting in regions of airway closure is typical in the elderly during normal tidal breathing. In this regard, the supine position makes airway closure during normal tidal breathing more likely. Indeed, airway closure may occur during tidal breathing as early as the mid-40s in the supine position. Age-related loss of lung elastic recoil predisposes to dynamic airway collapse during forced expiratory maneuvers. Diffusing Capacity and Alveolar-toArterial Oxygen Gradient Gas exchange efficiency declines with aging as a result of increasing intrapulmonary shunting and decreasing lung diffusing capacity. Residual Volume the residual volume is the volume remaining in the lungs after a maximal expiration. In young individuals, the residual volume is determined primarily by ability of the expiratory muscles to overcome the elastic recoil properties of the lung and chest wall. Therefore, aging is associated with a progressive increase in residual volume of up to 10% per decade. A: the change in alveolar/arterial oxygen tension with age (shunt fraction or percent shunt). Influence of aging on lung function-clinical significance of changes from age 20 years. Physiologic shunt (%) 100 60 10 20 30 40 50 60 70 80 Age (yr) supine Pao 2 between early adulthood and 65 years of age. Cardiac output is often decreased in the elderly to the extent that mixed venous oxygen tension is decreased. Thus, even modest amounts of shunting may produce a significant decrease in Pao 2 because of the contribution of desaturated venous blood. The diameter of the alveolar ducts is increased and their respective alveoli are wider and shallower. As a result, diffusing capacity for carbon monoxide may decline by up to 50% between early adulthood and 80 years of age. Upper Airway Protective Reflexes Cough effectiveness is reduced in the elderly because of diminished refle sensitivity and impaired muscle function. Cough reflex attenuation is associated with an increased incidence of aspiration pneumonia. The mechanisms of cough refle impairment include desensitization of airway epithelial irritant receptors and impaired swallowing. General anesthetics inhibit the cough refle through inhibition of central respiratory neurons. The increases in heart rate and minute ventilation in response to elevations in Paco 2 or decreases in Pao 2 are markedly attenuated in the elderly. The attenuated ventilatory response is multifactorial and reflects decreased peripheral chemoreceptor sensitivity, reduced respiratory muscle activity, decreased respiratory mechanical efficiency, and general respiratory deconditioning. These important protective reflexes are further attenuated by the administration of opioids and sedative/hypnotic drugs. Thus, the elderly are at particular risk from life-threatening respiratory depression in the perioperative period. In a recent report, investigators found that the risk of opioidinduced ventilatory depression increased with increasing age, with patients 61 to 70 years of age having 2.

Some animal studies have shown an endothelium-independent vasodilatory response to ketamine in the pulmonary bed medicine in the civil war order cytoxan uk. The hemodynamic effects of a bolus of ketamine can be attenuated or abolished with premedicants such as droperidol, dexmedetomidine, or benzodiazepines treatment vertigo buy cytoxan 50mg amex. They have poor cardiorespiratory reserve and are at risk of having perioperative complications including pulmonary hypertensive crises with resultant heart failure, respiratory failure, and dysrhythmias symptoms torn meniscus purchase 50mg cytoxan fast delivery. Reducing the consequences of an elevated pulmonary vascular resistance and the resulting right ventricular dysfunction should be considered as the primary goal of therapy with pulmonary vasodilators symptoms definition buy cheap cytoxan 50mg online. Owing to the contractile properties of the naive right ventricle, attempts at improving its contractility are generally not effective symptoms menopause order cytoxan 50mg free shipping. Other case reports highlight the value of the relative cardiostability of the drug in patients with minimal cardiorespiratory reserve treatment laryngomalacia infant generic 50 mg cytoxan mastercard. The advantages, in particular maintenance of stable hemodynamics and coronary perfusion pressure, seem to outweigh the potential disadvantages. It is frequently used to maintain anesthesia during and after lung transplantation. In regard to direct effects on the pulmonary vasculature, animal studies have shown that during increased tone conditions in the pulmonary vasculature, propofol may act as a pulmonary vasoconstrictor. As mentioned earlier, it appears to have vasorelaxant properties in isolated pulmonary arteries. Clinical experience would echo the cardiostability of judicious narcotic administration in hemodynamically fragile patients. Volatile Anesthetics At clinically relevant concentrations, modern volatile anesthetics likely have little to no direct vasodilating effect on the pulmonary vasculature. It would appear to be an important cofactor for endothelial-dependent pulmonary vasodilation. Opioids Opioids seem to have little to no deleterious effects on the pulmonary vascular system. In anesthetized cats, administration of morphine, fentanyl, remifentanil, and sufentanil caused a vasodilatory response under elevated tone conditions in isolated lobar artery. In general, the potential benefits of regional anesthesia in thoracoabdominal surgery typically outweigh the risks of hypotension and right ventricular dysfunction. A few reports illustrate successful use of epidural analgesia in this patient population. In general, parenteral and oral vasodilators are hampered by their relatively nonselective actions in the pulmonary vascular bed. In addition to their hypotensive systemic hemodynamic effects, their use may also lead to perfusion of underventilated alveoli, worsen intrapulmonary shunt and, in turn, worsen oxygenation. The ideal pulmonary vasodilator should have a ra pid onset of action, a s hort half-life, and produce regional pulmonary vasodilation. Th s would avoid systemic hypotension and the potential adverse effects on ventilationperfusion matching that limit the use of systemic agents in critically ill patients. In this regard, inhaled vasodilators are attractive as they preferentially dilate ventilated alveoli and have less systemic effects. Vasopressors and Inotropes Vasopressors and inotropes are commonly required during anesthesia to counteract the effects of cardiodepressant and vasodilating drugs. Treatment of hypotension in these patients can be difficult to manage given the typical cautious fluid administration most patient populations. Neurotransmitter receptors in this system include those from the adrenergic, cholinergic, and dopaminergic families as well as histamine, serotonin, adenosine, purines, and peptides. In human pulmonary artery, administration of acetylcholine induces pulmonary relaxation. Heart and lung transplantation represent two distinct areas where acute pulmonary vasodilation has strong theoretic benefit as it relates to improving acute right ventricular failure and attenuating reperfusion injury, respectively. The acute right ventricular failure complicating heart transplantation may be attenuated with the use of a pulmonary vasodilator. Prostaglandins Prostanoids induce relaxation of vascular smooth muscle, inhibit growth of smooth muscle cells and are powerful inhibitors of platelet aggregation. Owing to the short half-life of epoprostenol, the drug must also be continuously nebulized. The synthetic prostanoids, treprostinil and iloprost, hold promise as inhaled vasodilators in that they may only require intermittent administration. In this acute hemodynamic study, there was no significant difference in hemodynamics or oxygenation between agents. This could theoretically contribute to perioperative bleeding during large surgeries such as lung transplantation and is a concern in regard to neuraxial analgesia. The clinical relevance of platelet inhibition with these inhaled agents is unknown. In cardiac surgery patients, laboratory confirmation of platelet dysfunction with inhaled prostacyclin did not correlate with chest tube losses. In general, vasodilators can be expected to cause some deterioration in Pao 2 during anesthesia. When milrinone is combined with inhaled prostacyclin, there appears to be a potentiation and prolongation of the pulmonary vasodilatory effect. A direct effect on the right ventricle has been postulated; however, the clinical relevance of this fi ding is uncertain. Thus, there is ample blood-endothelial interface for surface enzyme activity as well as uptake and secretion. Consistent with high metabolic activity, endothelial cells typically have both extensive cytoplasmic vesicles and prominent caveolae. The caveolae are tiny membrane invaginations and near-membrane vesicles similar to those found elsewhere in the body, measuring 50 t o 100 n m, associated with caveolin proteins, and derived from lipid rafts within the membrane. The predominant activities of these caveolae, thought to include endocytosis and signal transduction, have not been fully delineated, and may be pleiotropic. Metabolism by the endothelial cell occurs either on the surface of the cell via enzymes associated with the membrane ("ectoenzymes") or by cytosolic processing after substances are taken up by the cell. Some surface enzymes are distributed along the luminal membrane, whereas others are associated exclusively with the caveolae. Metabolism may be further divided into exogenous versus endogenous substances as well as deactivated versus activated products. The terminology of pulmonary metabolism can be confusing and sometimes inconsistent. In general, "pulmonary uptake" (or "extraction") is simply used to describe transfer from blood to lung. It does not indicate whether the substance of interest is subsequently metabolized or returned back into the blood (with or without alteration). The lung has a pronounced impact on the blood concentration of substances even when it does not ultimately break them down or secrete them. This is because of simple uptake and retention of substances, often followed by release back into the blood. Exogenous Substances Drugs the cytochrome P450 m onooxygenase enzyme systems are the most studied metabolic pathways for medications. While P450 a nd other enzyme systems have long been known to exist in the human lung, the actual activity of lung enzymes ranges from negligible to 33% o f that of the liver. The uptake of fentanyl is higher than expected even for this basic and lipophilic drug. Under extremes of metabolic acidosis and alkalosis, lidocaine demonstrates increased uptake with higher blood pH. It is postulated that this fi ding is the consequence of increased drug lipophilicity because, in a less acidic environment, more of the drug is in its nonionized form. Bupivacaine has been investigated less extensively than lidocaine and with less consistent results. In most animal species, peak extraction has been reported as high with variable first-pass retention. In humans, however, the effective first-pass extraction appears to be lower when studied by epidural dosing. The first is the relative safety of levobupivacaine and ropivacaine in comparison to bupivacaine. However, a r eview of the pharmacodynamics and pharmacokinetics of local anesthetics145 describes the challenges of comparing toxicities in clinical practice. A second area of interest is the treatment of local anesthetic toxicity with lipid emulsion. The issue of pulmonary uptake and delayed release of local anesthetics must be considered in the treatment of suspected local anesthetic toxicity with emulsified lipid. When the kidney responds to changes in physiologic parameters such as vascular volume, blood pressure, and adrenergic stimulation by the cleaving of prorenin, the resultant renin catalyzes the formation of angiotensin I from angiotensinogen. In response to sodium, potassium, and renal perfusion changes, renin is secreted by the kidneys. Mast cells and neuroendocrine cells in the lung are also capable of producing serotonin by uptake of tryptophan along the same enzymatic pathway. This is thought to be the reason that the right heart shows the greatest myocardial and valvular injury in this syndrome. When an intracardiac right-to-left shunt is present in the carcinoid patient with a partial bypass of the pulmonary circulation, the left heart demonstrates valvular injury similar to that of the right heart. The mass effect of embolism does not, in itself, account for the typical cardiopulmonary consequences. Just as the lung has the enzymes to metabolize both histamine and serotonin but the ability to take up only serotonin, its uptake of catecholamines also demonstrates marked selectivity. Arachidonic Acid Metabolites Extensive production and metabolism of arachidonic acid derivatives occurs in the lung. The term eicosanoids refers to the 20-carbon carboxylic acids derived from the metabolism of the lipid membrane component icosatetraenoic acid, more commonly known as arachidonic acid. The action of phospholipase A2 converts the esterified form, as found in the membrane, and releases arachidonic acid from structural glycerol. They are responsible for bronchoconstriction and increased pulmonary vascular permeability, are chemotactic and chemokinetic for neutrophils, and facilitate eosinophil degranulation. The lipoxins have become identified as critical factors in the resolution of inflammation throughout the body. They are endotheliumdependent vasodilators of both pulmonary and systemic vasculature. The final products of these pathways typically have opposed or balancing effects locally and regionally. They are further known to have general antiinflammatory effects, to modulate reperfusion injury, and to inhibit platelet aggregation. Autonomic nervous system control of the cardiovascular and respiratory systems in asthma. Use of regularly scheduled albuterol treatment in asthma: genotype-stratified, randomised, placebo-controlled cross-over trial. The effect of polymorphisms of the beta(2)-adrenergic receptor on the response to regular use of albuterol in asthma. National Asthma Education and Prevention Program Coordinating Committee, National Heart, Lung, and Blood Institute, U. Differential effects of maintenance long-acting beta-agonist and inhaled corticosteroid on asthma control and asthma exacerbations. Assessment of tachyphylaxis following prolonged therapy of asthma with inhaled albuterol aerosol. Tolerance to beta 2-agonists in patients with chronic obstructive pulmonary disease. The Salmeterol Multicenter Asthma Research Trial: a c omparison of usual pharmacotherapy for asthma or usual pharmacotherapy plus salmeterol. Subcutaneous adrenaline versus terbutaline in the treatment of acute severe asthma. A comparison of ipratropium and albuterol vs albuterol alone for the treatment of acute asthma. Glycopyrrolate and atropine inhalation: comparative effects on normal airway function. Pharmacological assessment of the duration of action of glycopyrrolate vs tiotropium and ipratropium in guinea-pig and human airways. Absence of bronchodilation during desflurane anesthesia: a c omparison to sevoflurane and thiopental. Direct inhibitory mechanisms of halothane on canine tracheal smooth muscle contraction. Different inhibitory effects of volatile anesthetics on T- and L-type voltage-dependent Ca21 channels in porcine tracheal and bronchial smooth muscles. Procaine, lidocaine, and ketamine inhibit histamine-induced contracture of guinea pig tracheal muscle in vitro. Mechanisms underlying the inhibitory effect of propofol on the contraction of canine airway smooth muscle. Mechanisms of bronchoprotection by anesthetic induction agents: propofol versus ketamine. Intravenous lidocaine as a suppressant of coughing during tracheal intubation in elderly patients. A multicenter, randomized trial of noninvasive ventilation with helium-oxygen mixture in exacerbations of chronic obstructive lung disease. Effect of azelastine, montelukast, and their combination on allergen-induced bronchoconstriction in asthma. Pharmacological characterization of the muscarinic receptor antagonist, glycopyrrolate, in human and guinea-pig airways.