cialist at UCLA Medical Center and assistant clinical professor at the UCLA School of Nursing in Los Angeles, Calif. A variety of backrest positions may be used that do not compromise the accuracy of measurements of pulmonary artery pressure. Backrest elevations of 0°, 30°, 45°, and 60° with the patient supine (back flat against bed surface) do not affect the accuracy of measurements of pulmonary artery pressure if the hemodynamic monitoring system has been properly referenced and zeroed. As the patient moves from flat to higher levels of backrest elevation, the reference level must remain horizontal to the phlebostatic axis in order for measurements of pulmonary artery pressure to remain accurate (Figure 2).