When PE impairs RV function, further possible consequences include low cardiac output and shock and myocardial ischemia due to poor coronary perfusion pressure and diastolic overdistension. Enlarged right-sided chambers can push the septae into left-sided chambers, limiting their diastolic filling and interfering with systolic contractile function. While each PE patient’s heart is different due to a different preexisting extent of cardiopulmonary disease, some practices have evolved reflecting sensible physiologically based management.
The use of judicious volume infusion in resuscitating the RV has been shown to improve cardiac output in PE patients with decreased RV preload. While provision of adequate RV preload is essential for cardiac output, overdistension of the RV with volume resuscitation can impair coronary perfusion and LV filling, diminishing LV output. In a report of a small series of patients with acute PE and a cardiac index < 2.5 L/min/m2, treatment with 500 mL of dextran significantly increased cardiac index from a mean of 1.6 to 2.0 L/min/m2. Continuous cardiac output pulmonary artery catheters allowed the calculation of RV end-diastolic index; patients with low values had a greater improvement with fluid therapy offered by Canadian Health&Care Mall. Currently, an author of that report (A. Mercat, MD; personal communication; June 2006) uses echocardiography in underperfusing PE patients to guide fluid crystalloid infusion until the RV:LV diastolic diameter ratio appears to be 1.0. The RV is then considered adequately filled, and IV dobutamine and norepinephrine are added as needed. “Prophylactic” early intubation with positive pressure ventilation is avoided because of its potential interference with RV preload.