Tissue hypoxia distal to a Peñaz finger blood pressure cuff.

The Peñaz finger method to measure blood pressure uses a finger cuff in which the pressure level fluctuates in the vicinity of the mean arterial pressure level and thereby interferes with the circulation of blood to and from the fingertip. We measured capillary blood gases and saturation of hemoglobin in the finger during Peñaz finger blood pressure (PFBP) monitoring to assess the degree to which it impairs circulation in the fingertip. Within 2.5 minutes after initiating PFBP monitoring, capillary oxygen tension (PO2) had decreased significantly, from about 71 mm Hg to between 49 and 58 mm Hg for up to 50 minutes. These changes were quite different from those occurring when an occlusive tourniquet was applied around the finger. Within 10 minutes of tourniquet application, acidosis (pH 7.25), hypercapnia (carbon dioxide tension, 59.0 mm Hg), and hypoxemia (PO2, 29 mm Hg) resulted. Within 30 seconds of releasing the PFBP cuff, capillary blood gas values were back to normal. Interspersing 30-second rest periods every 5 minutes during 35 minutes of PFBP monitoring actually decreased capillary oxygen values compared with monitoring without such rest periods. A finger pulse oximeter distal to the PFBP cuff showed desaturation from an average of 97% to 93.7%, with much variability. However, desaturation was statistically significant within 1 minute of application of the PFBP cuff. Within 1 minute the finger volume increased an average of 0.05 ml. After 1 minute the volumes varied widely and, on the average, returned to normal despite continued PFBP monitoring.