الفهرس 
Anatomical, Physiological and Pharmacological Considerations During PregnancyOnly 14 pages are availabe for public view
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Abstract
Over a 30 year period, the incidence of heart disease dur¬ing pregnancy has declined from 3.5% to approximately 1.6%. Rheumatic heart disease, despite declining incidence, still accounts for most cases with mitral stenosis the most prevalent resulting lesion. Maternal mortality during pregnancy with rheumatic heart disease varies from less than 1% in asymp¬tomatic patients to 17% in patients with mitral stenosis com¬plicated by atrial fibrillation.
Classification of cardiac diseases in pregnancy is done according to etiology, incidence of occurrence, mortality and morbidity risk, time relation to pregnancy or according to the functional cardiac state of the patient as recommended by the NYHA.
Pregnancy normally results in dramatic changes in the cardiovascular system. Four principal changes that present unique problems to the patient with cardiac disease have been well delineated and have special anesthetic implications. First, there is a 50% increase in intravascular volume that generally peaks by the early-to-middle third trimester. This relative volume overload may be poorly tolerated in patients whose cardiac output is limited by myocardial dysfunction from ischemia or intrinsic or valvular lesions.
Second, there is a progressive decrease in SVR throughout pregnancy, so that mean arterial pressure is preserved at normal values despite a 30%-40% increase in cardiac output. Systolic blood pressure is decreased. This may be of importance in those patients at risk for right-to-left shunting as well as for patients with some types of valvular disease (e.g., aortic stenosis).
Third, the compromised cardiovascular system is further stressed by the marked fluctuations in cardiac output observed during labor. Pain and apprehension may precipitate an increase in cardiac output to as much as 45%-50% over those levels seen in the late second stage of labor. Further, each uterine contraction serves, in effect, as an autotransfusion to the central blood volume, resulting in an increase in cardiac output of 10%-5%. The Valsalva maneuver results in wide swings in both venous and arterial pressures, which have been associated with acute cardiac decompensation. The increases in cardiac output reach a maximum of 80% higher than antepartum levels immediately following delivery secondary to a relief of inferior vena cava obstruction and a final autotransfusion of approximately 500 ml from uterine contraction.
The fourth consideration is the hypercoagulability associated with pregnancy and the possible need for appropriate anticoagulation, especially in those patients at increased risk for arterial thrombosis and embolization (prosthetic heart valve or chronic atrial fibrillation). Therapeutic anticoagulation affects the options for anesthetic management, perhaps the use of invasive monitors, and increases the risk of postpartum hemorrhage.
Most cardiovascular diagnostic studies are noninvasive and can be conducted safely in pregnant women. In most cases, conventional testing including electrocardiography, echocardiography, and chest radiography will provide necessary data. Echocardiography is a safe, noninvasive test underused in pregnancy. The diagnosis made should consider all four levels, if appropriate, namely aetiological, anatomical, patho-physiological, and functional. The New York Heart Association (NYHA) functional classification has been widely used and is largely based on limitation of physical activities and associated symptoms. It should be used together with other levels of diagnosis for management planning and prognostication and remains useful for comparing performance of individuals with similar aetiological and anatomical diagnoses.
The anesthetic considerations for the pregnant patient with cardiac disease naturally vary according to the nature of the disease and its progression. However, some general guidelines can be offered. Cardiac medications should be continued throughout pregnancy, labor, and delivery.
For most cardiac diseases, no one anesthetic approach is ex¬clusively indicated or contraindicated. Most patients can be divided into one of two groups. Patients in the first group include those with mitral valve disease, aortic insufficiency, or congenital lesions with left-to-right shunting. These patients benefit from regional techniques, particularly continuous epidural anesthesia. The induced sympathectomy reduces both preload and afterload, relieves pulmonary congestion, and in some cases increases forward flow (COP). Patients in the second group are gathered in the acronym CAT PIE, namely coarctation, aortic stenosis, tetralogy of Fallot, pulmonary hypertension, Idiopathic Hypertophic Obstructive Cardiomyopathy (IHOC) and Eisenmenger syndrome. Regional anesthesia is generally detrimental in this group. Reductions in venous return (preload) or afterload are usually poorly tolerated. These patients are better managed with intra-thecal opioids alone, systemic medications, pudendal nerve blocks and if necessary general anesthesia.
Radial and pulmonary artery monitoring are applied in almost all par¬turients with symptomatic cardiac disease, and monitoring of central venous pres¬sure where appropriate, e.g., in patients with pulmonic stenosis.