Clinical Usefulness of Respiratory Variations in Arterial Pressure

There is increasing interest in the use of respiratory variations in arterial pulse pressure to predict the Q response to a fluid challenge (1–4). This has likely evolved because of the appreciation that excess fluid infusion is harmful, as well as concerns over invasive monitoring (5). Thus, techniques that provide noninvasive assessment of volume status hold great promise. The major impetus for these tests came from the work of Perel and coworkers (6) who followed-up on a preliminary report by Coyle and coworkers (7). They defined the difference between maximum and minimum arterial systolic pressure during a respiratory cycle as systolic pressure variation (SPV) (6). The inspiratory increase in pressure relative to the value at end-expiration was called dUp, and the fall in pressure relative to the end-expiratory value was called dDown (Figures 1 and E1). The larger the dDown and SPV, the larger the predicted increase in Q with volume loading.