IMPACT OF RESPIRATORY ACID-BASE STATUS IN PATIENTS WITH PULMONARY-HYPERTENSION

Background. The perioperative management of patients undergoing mitral valve replacement (MVR) with pulmonary hypertension from mitral steno sis may be complicated by increased pulmonary vascular resistance. The purpose of this study was to examine the influence of respiratory aci d-base status on the pulmonary hemodynamic indices of patients with pu lmonary hypertension before and after MVR. Methods. Ten patients with pulmonary hypertension from mitral stenosis (mean preoperative systoli c pulmonary artery pressure, 73 +/- 8 mm Hg) undergoing MVR were studi ed in the operating room before and after MVR. Arterial partial pressu re of carbon dioxide was manipulated by the addition of 5% carbon diox ide to the breathing circuit. Hemodynamic data were collected as the p artial pressure of carbon dioxide rose from 30 mm Hg to 50 mm Hg and d ecreased back to 30 mm Hg. Results. There were no differences in mean pulmonary artery pressure or pulmonary vascular resistance before and after MVR. Before MVR, mean pulmonary artery pressure increased from 3 2 +/- 1 mm Hg to 48 +/- 1 mm Hg as the partial pressure of carbon diox ide rose from 30 mm Hg to 50 mm Hg (p < 0.05), and pulmonary vascular resistance rose from 379 +/- 30 to 735 +/- 40 dynes . second . cm(-5) (p < 0.05). These effects on mean pulmonary artery pressure and pulmon ary vascular resistance were not different after MVR. Conclusion. Resp iratory acid-base status has a profound impact upon pulmonary vascular resistance in patients with pulmonary hypertension from mitral stenos is undergoing MVR. This impact persists in the immediate postoperative period. We conclude that respiratory acidemia should be avoided in th ese patients, whereas respiratory alkalemia may be used to help minimi ze pulmonary vascular resistance.