Respiratory variations in right atrial pressure predict the response to fluid challenge

Abstract

We tested the hypothesis that the respiratory pattern of the right atrial pressure (Pra) can be used to predict the response to a fluid challenge. We used a case series in medical and postcardiovascular surgery intensive care units at a university teaching hospital. The sample included 33 patients with Swan-Ganz catheters (Spectramed Inc, Oxnard, CA) in place for clinical indications. The fluid challenge was prescribed by the treating physician and consisted of a rapid infusion of normal saline until Pre increased by ≥2 mm Hg. The volume infused to achieve this ranged from 100 to 950 mL. Right atrial pressure, pulmonary capillary wedge pressure (Pcw), and arterial pressure (Pa) were measured. Capillary wedge pressure had to fall by ≥2 mm Hg to indicate an adequate inspiratory effort. Patients were classified as having a positive respiratory response if Pre decreased by ≥1 mm Hg and negative respiratory response of Pre decreased by less than 1 mm Hg. An increase in cardiac output of ≥250 mL/min was considered a significant response to the fluid challenge. Cardiac output increased in only one of 14 patients with negative respiratory response but increased in 16 of 19 patients with positive respiratory response. The initial Pra, Pcw, cardiac output, and Pa did not predict the response to the fluid infusion. In conclusion, it is very unlikely that volume loading will increase the cardiac output in a patient who does not have an inspiratory fall in Pra, whereas volume loading will usually increase the cardiac output of patients who have an inspiratory fall in Pra.