Non-invasive blood haemoglobin and plethysmographic variability index during brachial plexus block

Br J Anaesth. 2015 May;114(5):812-7. doi: 10.1093/bja/aeu484. Epub 2015 Jan 20.


Background: Plethysmographic measurement of haemoglobin concentration ([Formula: see text]), pleth variability index (PVI), and perfusion index (PI) with the Radical-7 apparatus is growing in popularity. Previous studies have indicated that [Formula: see text] has poor precision, particularly when PI is low. We wanted to study the effects of a sympathetic block on these measurements.

Methods: Twenty patients underwent hand surgery under brachial plexus block with one Radical-7 applied to each arm. Measurements were taken up to 20 min after the block had been initiated. Venous blood samples were also drawn from the non-blocked arm.

Results: During the last 10 min of the study, [Formula: see text] had increased by 8.6%. The PVI decreased by 54%, and PI increased by 188% in the blocked arm (median values). All these changes were statistically significant. In the non-blocked arm, these parameters did not change significantly.

Conclusions: Brachial plexus block significantly altered [Formula: see text], PVI, and PI, which indicates that regional nervous control of the arm greatly affects plethysmographic measurements obtained by the Radical-7. After the brachial plexus block, [Formula: see text] increased and PVI decreased.

Keywords: haemoglobinometry; nerve blockade; perfusion; photoplethysmography; vasodilation.

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Aged, 80 and over
  • Anesthetics, Local / administration & dosage
  • Brachial Plexus Block / methods*
  • Female
  • Hand / blood supply
  • Hemoglobins / metabolism*
  • Humans
  • Male
  • Mepivacaine / administration & dosage
  • Middle Aged
  • Oximetry / methods
  • Oximetry / statistics & numerical data
  • Plethysmography / methods
  • Plethysmography / statistics & numerical data
  • Young Adult


  • Anesthetics, Local
  • Hemoglobins
  • Mepivacaine