By K. Rasarus. The Ohio State University. 2019.
The rate of tapering of the arteries is assessed by measuring the length of a segment over which the lumen diameter narrows from 2 20 mg aciphex sale. More abrupt arterial tapering is suggestive of more severe changes in the intra- acinar arteries purchase 20 mg aciphex, assessed both morphometrically and by the Heath–Edwards classification (Table 65 order 20 mg aciphex overnight delivery. Quantitative structural analysis of the pulmonary vascular bed in congenital heart defects. Pulmonary stenosis or previous placement of a pulmonary artery band, owing to poststenotic dilation, will give the impression of rapid tapering. With advanced vascular disease, there is sometimes such extensive intimal hyperplasia that the vessel appears narrowed all the way from the hilum so that abrupt tapering is no longer apparent. In this situation, however, the background haze is absent and the pulmonary circulation time is usually prolonged. If the injection of contrast fails to fill the vessels all the way out to the pleura, the background will appear dark, and if the balloon does not completely occlude the vessel, the false impression of a dense background will be created owing to filling of capillaries and veins. Assessment of the circulation time depends on the exclusion of pulmonary vein stenosis and intrapulmonary shunting. Intravascular ultrasound could be investigated to estimate the severity of pulmonary vascular disease at least in proximal vessels. Optical coherence tomography is a new technique that can resolve neointimal lesions in very small arteries and may hold greater promise, but has just recently been applied clinically to assess coronary stent stenosis (13). Early studies of optical coherence tomography in the pulmonary vasculature studies have shown correlation in pulmonary artery remodeling with changes in histology (14). Reactive Pulmonary Circulation A major challenge in pediatric cardiology is to understand and control the reactive pulmonary circulation, which can be particularly problematic in the early postoperative period. The pulmonary hypertensive crisis, as it has been called, is thought to result from interaction of a hypertrophied and perhaps hypercontractile circulation with an injured vascular endothelium, with platelets and leukocytes that were exposed to postcardiopulmonary bypass and hypothermia and may more easily degranulate and release potent vasoconstrictor agents, particularly thromboxanes and leukotrienes. In recent studies, increased density of neuroepithelial bodies has been observed in the airways of patients at risk for this complication (15). The neuroendocrine cells, which are also oxygen sensors, contain bombesin and serotonin, agents known to be potent vasoconstrictors. There is also an increase in vasoconstrictor neuropeptide-containing nerves (16) (Fig. Because most of the pulmonary hypertensive crises occur while weaning from the ventilator, it is tempting to speculate that swings in airway pressure might lead to degranulation of the neuroepithelial cells and release of the vasoconstrictor substances. Moreover, there is a striking decrease in lung compliance accompanying the pulmonary hypertensive crisis. In ultrastructural lung biopsy studies from patients with congenital heart defects and pulmonary hypertension, alterations in endothelial cells support endothelial dysfunction as a cause of heightened pulmonary vascular reactivity and also relate endothelial dysfunction to the pathogenesis of progressive pulmonary vascular disease. On scanning electron microscopy, the endothelial surface of normal thin-walled pulmonary arteries has a “corduroy-like” appearance in that the cells form narrow, even ridges. In contrast, the endothelial surface of hypertensive thick-walled pulmonary arteries has a “cable-like” texture in that the cells form deep, twisted ridges. The hypertensive endothelium may be predisposed to interact abnormally with marginating blood elements, such as platelets and leukocytes. This might result in the release of pulmonary vasoconstrictor substances and smooth muscle mitogens (17). On transmission electron microscopy, the endothelium appeared to show heightened metabolic activity with an increased rough endoplasmic reticulum. The subendothelium of the muscular arteries is also abnormal in that there appears to be degradation and neosynthesis of the internal elastic lamina. This observation provided an important clue related to the discovery of heightened elastolytic activity in the vessel wall associated with the initiation and progression of pulmonary vascular disease. This could indeed account for the development of platelet fibrin microthrombi in the postoperative period and for abnormal release of vasoactive compounds causing increased vascular reactivity. B: Tyrosine hydroxylase immunoreactive perivascular nerve fibers at the advential–medial border of an alveolar duct artery in a child aged 2 1/2. A study of nerves containing peptides in the pulmonary vasculature of healthy infants and children and of those with pulmonary hypertension. There also is evidence that production of the vasoconstrictor endothelin also might be increased in patients with pulmonary hypertension and congenital heart defects (21). Many patients with high-flow congenital heart defects that are operated upon in a timely fashion show a fall in pulmonary artery pressure and return to normal resting hemodynamics, indicating resolution and regression of pulmonary hypertensive structural changes. This is supported by experimental studies and by anecdotal reports of resolution of severe pulmonary vascular disease in the remaining lung after single lung transplant. There are, however, some patients who maintain a high level of pulmonary vascular resistance and are refractory to vasodilator therapy despite what appear to be mild vascular changes on light microscopy (medial hypertrophy), P. For these patients, the prognosis may be not much better than those with unexplained pulmonary hypertension (22). A recent study of outcomes of patients with congenital heart disease (systemic-to-pulmonary shunt lesions) and pulmonary hypertension in the current treatment era demonstrated significantly decreased 20- year survival in patients with residual pulmonary vascular disease following defect closure (36%) relative to patients with Eisenmenger syndrome (87%) or those patients with an unrepaired systemic-to-pulmonary shunt without Eisenmenger syndrome (86%). While preoperative hemodynamics are unknown for the surgically repaired group, the late average age at operation may suggest advanced pulmonary vascular disease at the time of operation and inability of the right ventricle to adapt to the increased workload (23). Therapies for the patient with Eisenmenger syndrome have included chronic oxygen, anticoagulants, and palliative surgical procedures, including atrial septal defect creation and intravenous as well as, more recently, subcutaneous, inhaled, or oral prostacyclin analogs. In some cases, these measures have improved the quality of life and in others they have acted as a bridge to a heart–lung transplant or surgical correction along with lung transplant. More recent addition of phosphodiesterase inhibitors and endothelin receptor antagonists in this group of patients awaits the results of clinical trials, but is discussed later in this chapter, and in the subsequent chapter, with regard to patients with idiopathic pulmonary hypertension. Pathophysiology Based Upon Further Pathologic Assessments Recent immunohistochemical studies have been carried out in lung biopsy tissue from patients with congenital heart defects to elucidate mechanisms that are directly related to enhanced proliferation and migration of cells in the neointima with characteristics of smooth muscle cells. There is a progressive increase in the deposition of two matrix glycoproteins, tenascin and fibronectin, in the media and neointima (Fig. We previously related the increased expression of tenascin to vascular smooth muscle cells P. Fibronectin has been related to increased migration of smooth muscle-like cells in the context of neointimal formation. It is also proposed that endothelial cell proliferation and a form of angiogenesis is observed with plexiform lesions. The plexiform lesions in pulmonary hypertension associated with congenital heart disease appear to be derived from different clonal populations of endothelial cells compared with those observed in unexplained pulmonary hypertension where a single clone is usually found (25). Tenascin-C, proliferation and subendothelial fibronectin in progressive pulmonary vascular disease. Creation of large aortopulmonary shunts in dogs, particularly into a single pulmonary artery, resulted in more rapidly progressive pulmonary vascular changes. There are several other experimental models of high-flow congenital heart defects such as sheep or calves after an aortopulmonary lobar anastomosis. In utero placement of an aortopulmonary shunt most faithfully reproduces the changes that might be expected to occur in the newborn with a left-to-right shunt when the pulmonary vascular resistance falls.
In addition 10 mg aciphex with mastercard, there are balanced with benzodiazepines to insure amnesia and adequate operative scenarios in which monitoring both proximal and depth of anesthesia discount aciphex 20mg mastercard. Volatile anesthetics order aciphex, such as isofurane or distal arterial pressures is quite helpful in detecting residual sevofurane, help to modulate systemic vascular resistance in coarctation or aortic arch obstruction. It is important to maintain an adequate depth Use of the posterior tibial and dorsalis pedis arteries for of anesthesia and neuromuscular blockade in order to limit intraoperative arterial blood pressure monitoring should be systemic oxygen consumption. These locations yield pressure measurements that shivering can manifest as low venous oxygen saturation. In addition, use of brachial Standard American Society of Anesthesiologists monitors and axillary arteries is also not commonly employed due to are utilized for every cardiac surgical procedure. This is because physiologic Invasive Arterial Blood Pressure dead space in this heterogeneous patient population varies Noninvasive blood pressure is monitored until invasive arte- tremendously and will be increased due to any reduction in rial access is achieved. Successful cannulation is usu- fow can be an acute phenomenon due to cardiac dysfunc- ally achieved via a sterile percutaneous procedure employ- tion, pulmonary embolus, dynamic increases in pulmonary ing the Seldinger technique. However, gaining arterial access vascular resistance, increased intracardiac right to left shunt- with the assistance of ultrasonography has become a popular ing, or worsening right ventricular outfow tract obstruction approach, especially when cannulation is anticipated to be as with a cyanotic spell in patients with tetralogy of Fallot, 26 Comprehensive Surgical Management of Congenital Heart Disease, Second Edition for example. Alternatively, reduced pulmonary blood fow catheters provide a mechanism for rapid volume delivery. For example, the child with hypoplastic left heart rax, hematoma, inadvertent arterial puncture, central vein syndrome who is status post bidirectional Glenn-type cavo- thrombosis, and infection. Thrombosis in the single-ventricle pulmonary anastomosis will, by defnition, have a pulmonary cohort is of signifcant concern. Thus, institutions and practitioners must be well versed in Temperature and comfortable with their use. Monitoring patient temperature in at least two different sites is the standard of care when using controlled hypothermia Near Infrared Spectroscopy in the operative setting. Continuously monitoring tempera- Near infrared spectroscopy is a noninvasive method to mea- ture from both the body shell and core allows for assessment sure regional tissue oxygenation. Using between two and of the regional distribution of cooling and depth of hypo- four wavelengths of near infrared light, tissue oxygenation thermia, and provides an index of the adequacy of cooling is determined via the Beer–Lambert equation based on the and somatic protection. The common sites used for such absorption spectra of oxyhemoglobin, deoxyhemoglobin, and monitoring include the esophagus, rectum, tympanic region, oxidized cytochrome aa. Tympanic, nasopharyngeal, and esopha- 75% of the blood contributing to the signal is in the venous geal values are thought to approximate brain temperature. Although successful insertion of incidence of acute postoperative neurologic events in infants such catheters is readily achievable in the majority of patients and children from 26% to 7%. This can be achieved with supplemental narcotics with signal by bilirubin, excessive ambient light, and deep or with volatile anesthetic agents, such as isofurane, deliv- hypothermia. Thus, regional tissue ing during hypothermia (which can dramatically increase oxygenation may not refect global cerebral perfusion and oxygen consumption). Benzodiazepines, such as midazolam, may not detect all areas of brain that are at risk. The goal of the rewarming result in transient reductions in preload and output leading processes is to achieve a core temperature of 35–37°C. Use of an under- ventricular fbrillation, can occur especially in cases involv- body thermal water blanket and forced air warmer can help ing repeat sternotomy and in patients with arrhythmogenic to prevent such cooling and maintain normothermia once the myocardium. The During the rewarming phase, it is possible for patients to anesthesiologist must be able to recognize the transient and experience intraoperative awareness, especially during peri- often unavoidable nature of the benign effects of surgical ods of light anesthetic depth. The sole use of volatile anesthet- manipulation on cardiovascular status and be able to differ- ics should not be relied upon for amnesia during this phase entiate them from more severe, sustained perturbations in because anesthetic concentrations can vary and be unpredict- physiology. As the patient is warmed, the cardiac anesthesiologist Impaired venous drainage can result in venous engorgement, must systematically gauge several parameters. As an inodilator and lusitropic agent, order to prevent pulmonary vein desaturation and maximize milrinone provides inotropic support and afterload reduc- alveolar expansion, the cardiac anesthesiologist should gen- tion via systemic vasodilation, modulates pulmonary vas- tly suction the airway with an appropriately sized catheter cular resistance, and improves diastolic relaxation. Aggressive suc- is ideal in the setting of ventricular dysfunction and poor tioning should be avoided due to the risk of bleeding during compliance, valvular regurgitation, pulmonary hyperten- full heparinization. Following a loading After coordination and communication with the cardiac dose of 50–100 μg/kg, a continuous infusion (0. Although milrinone is usually well tolerated, the most thesiologist must directly visualize both lungs during this common deleterious effect is hypotension due to profound process to insure full expansion. Following removal of the aortic cross-clamp, coronary artery perfusion is permitted and reperfusion of the heart com- hemostasis mences. Initially, asynchronous pacing modes are administers protamine only at the direction of the cardiac preferred to limit interference from electrocautery. However, surgeon and that the perfusionist is made aware of its admin- if the need for pacing persists, transition to demand modes istration. Prior to separation from bypass, the operating table should communication with the perfusionist permits timely discon- be placed in the neutral position and all invasive lines zeroed tinuation of the cardiotomy suction in order to maintain an at heart level. Careful observation during this phase will emergent or unexpected extracorporeal support is required provide information about systolic function and ventricular for hemodynamic decompensation. Benefts of commonly used vasoactive agents include positive inotropic and chronotropic effects. Based on the more recent evidence, contribute to impaired factor synthesis in these patients. Platelet counts have been shown to be inversely proportional to hematocrit, and chil- Autologous Fresh Whole Blood dren with cyanotic heart disease are commonly thrombocy- Autologous donation of fresh whole blood is a method that topenic. Whole blood collected within 6 hours from donation does not require refrigeration and contains fully functioning plate- Component Therapy lets. Thus, antifbrinolytic therapy has been used as an signifcant hemolysis and hyperkalemia, posing further risks adjunct approach targeting improved hemostasis following to the neonate. The three antifbrinolytic agents used Bacterial contamination of banked blood products can lead in congenital heart surgery are aprotinin, ε-aminocaproic to life-threatening infection and sepsis in recipients. Its the incidence of contamination is very low, transfusion- procoagulant effects are thought to be due to prevention related bacterial infection is a potential life-threatening risk. Since stored platelets are suspended rates of renal injury with aprotinin use versus lysine analog. Plasmin is a ser- treatment and prevention of hemorrhage and bleeding asso- ine protease responsible for fbrinolysis. Patients with Blalock–Taussig shunts and coronary genital heart disease following cardiac surgery. The pre- dynamic, monitoring during transport is usually less robust, handover process is streamlined and systematically designed and accessibility to supportive resources is limited en route. In addition, suction must be applied to the chest tubes resuscitation medications should be available during trans- and thermoregulation initiated (if necessary). In order to port, and blood products and volume sources must be trans- ensure effciency and safety, it is ideal to establish a specifc ported with the patient in a readily deliverable modality (i. For example, at the previously checked, warmed [if necessary], drawn up into Children’s National Medical Center, after the ventilator set- syringes, and clearly labeled). This hypoxemia, which can elevate pulmonary vascular resistance process should take no more than 5 minutes. In is confrmed, samples for point-of-care testing are drawn by addition, the anesthesiologist must decide whether to venti- an assisting nurse and transition to the information handover late the patient with a Jackson–Rees system and an FiO2 of phase commences. Cardiopulm onary bypass:Bypass: 97 minutes, Cross clamp: 57 minutes, Circ arrest: 10 minutes.