Primary Pulmonary Hypertension (PPH)

Primary Pulmonary Hypertension (PPH) is a progressive disease characterized by raised pulmonary vascular resistance, which results in impaired right-heart function as a consequence of the increased right ventricular afterload and occurring in the absence of an identifiable cause.

Idiopathic Pulmonary Hypertension (IPAH); pulmonary hypertension (PHT). It is also termed precapillary pulmonary hypertension.

First described clinically and hemodynamically in 1951 by D.T. Dresdale and colleagues.

Approximately 1-3:1,000,000 population per year in the United States and internationally.

Autosomal dominant inheritance with incomplete penetrance and a 2.5:1 female predilection. The PPH1 gene was mapped to chromosome 2q31-q32. A worsening of the disease occurs in successive generations.

Current theories on pathogenesis focus on abnormalities in interaction between endothelial and smooth-muscle cells. Endothelial-cell injury may result in an imbalance in endothelium-derived mediators, favoring vasoconstriction. Defects in ion-channel activity in smooth-muscle cells in the pulmonary artery may contribute to vasoconstriction and vascular proliferation. Inflammatory oxidant mechanisms and deficiency in nitric oxide (NO) have also been implicated in the pathogenesis of pulmonary hypertension. In addition, the findings of frequent monoclonal endothelial cell proliferation in PPH also suggest that a somatic genetic alteration similar to that present in neoplastic processes might be responsible for the pathogenesis of PPH.

On chest radiography, the width of the pulmonary arteries is increased and the peripheral lung fields are clear. The electrocardiogram demonstrates right ventricular hypertrophy, as does echocardiography. Cardiac catheterization with measurement of pulmonary artery pressures demonstrates elevation of systolic pulmonary artery pressure >35 mmHg or mean pulmonary artery pressure >25 mmHg. Histology shows extension of muscle layers into small pulmonary arteries that are normally nonmuscular. The cross-sectional area of the pulmonary vascular bed is also decreased. Histopathology shows plexiform lesions composed of proliferating endothelial cells present in 20 to 80% of cases of primary pulmonary hypertension. Other diagnostic testing primarily excludes secondary causes.

Neonatal pulmonary hypertension results in right-to-left shunting via the foramen ovale, or ductus arteriosus, or both. Right-heart failure is inevitably present. It is usually lethal. In older children or adults, the predominant symptoms include exertional dyspnea and fatigue, which result from fixed cardiac output in response to exertion. PPH occurs most commonly in young and middle-age women; mean survival from onset of symptoms is 2 to 3 years. Primary pulmonary hypertension is progressive, and there is no specific treatment. The terminal event may be related to right-heart failure and is often sudden, possibly related to arrhythmias.

Catheterization is necessary to assess hemodynamics and to evaluate vasoreactivity during acute drug challenge. Decrease in pulmonary vascular resistance in response to acute vasodilator challenge (intravenous epoprostenol or inhaled NO) occurs in approximately 30% of patients, and predicts a good response to chronic therapy with oral calcium-channel blockers (nifedipine, diltiazem, amlodipine). Determination of the presence of cor pulmonale. Prophylaxis of infective endocarditis.

The principal consideration is to prevent increases in pulmonary hypertension that may result in right-heart failure. Continuous monitoring of arterial and central venous pressure, electrocardiography, and pulse oximetry are recommended for every anesthetic procedure. The use of a pulmonary artery catheter is controversial. Transesophageal echocardiography is useful. The choice of anesthetic technique and drugs per se is of secondary importance and should be governed by individual preferences. Avoid known factors that may exacerbate pulmonary hypertension—hypoxemia, hypercarbia, acidosis, high airway pressures, positive end-expiratory pressure, stress, and pain. Tracheal intubation increases positive airway pressure and causes right-heart strain. A “stress-free” anesthetic with controlled ventilation, gentle intubation, and continuous hemodynamic monitoring would provide ideal conditions. An appropriate regional anesthetic technique performed with care to avoid any hemodynamic disturbances, and with deafferentation of all noxious input is equally satisfactory.

Nitrous oxide causes considerable increases in pulmonary vascular resistance patients with pulmonary hypertension. Ketamine may increase vascular resistance and should be avoided. A continuous intravenous infusion of epoprostenol (prostacyclin [PGI2]) may be used to improve hemodynamics. Inhaled nitric oxide (iNO) has been used as a selective pulmonary vasodilator with variable success in the treatment of persistent pulmonary hypertension.