The dynamic nature of pulmonary vascular resistance (PVR) in the neonate makes it difficult to maintain a Qp/Qs approximating 1. The reactive pulmonary vasculature is unpredictable and may result in poor systemic perfusion with pulmonary edema or inadequate oxygenation and elimination of carbon dioxide. The increase of pulmonary blood flow is at the expense of perfusion of the body and perfusion of the body at the expense of oxygenation and removal of carbon dioxide. The mortality is high if PVR is not managed properly and, therefore, an understanding of the physiology and treatment options is important to lowering the morbidity and mortality of unequal Qp/Qs. This article reviews the normal changes in PVR at birth, discusses various dynamic parameters of PVR, outlines accepted treatment options to maintain a Qp/Qs close to 1 in patients with reactive pulmonary vasculature, and discusses a new therapy for pulmonary hypertension that is being evaluated in the basic science laboratory.

Key words: pulmonary vascular resistance; nitric oxide; prostacyclin; milrinone; prostaglandin E1; eiconasoids