Conjunctival oxygen tension monitoring during a controlled phlebotomy.

A decrease in the conjunctival oxygen tension (Pcjo2) and conjunctival index (Pcjo2/Pao2) has been shown to be an early marker of acute blood loss. We sequentially measured Pcjo2, Pcjo2/Pao2, blood pressure, and pulse rate in five healthy adults after controlled phlebotomy of 450 mL and after intravenous fluid repletion. No significant changes occurred in either the Pcjo2 or Pcjo2/Pao2 after phlebotomy or after fluid replacement. We conclude that a blood loss of 450 mL in healthy, euvolemic adults is insufficient to perturb the conjunctival index. The lower limits of sensitivity of changes in Pcjo2 and Pcjo/Pao2 in response to acute blood loss remain to be established.