Rapid fluid infusion therapy decreases the plasma concentration of continuously infused propofol

Rapid fluid infusion therapy to treat hypovolemia in anesthetized patients is a common practical regimen in daily clinical settings. This study investigated the effect of large volume loading on the plasma concentration of propofol (Cp), hemodynamic parameters, hemoglobin concentration (Hb), hematocrit value (Ht) and the bispectral index (BIS).

Sixty patients were administered propofol using a target-controlled infusion technique. We studied two independent groups. Half of the patients (group F, n = 30) were administered fentanyl, and the other half (group E, n = 30) epidural administration of mepivacaine for analgesia. After achieving a pseudo-steady state of propofol anesthesia, baseline values of blood pressure, heart rate, Hb, Ht, cardiac output, Cp and BIS were measured, and 10 ml/kg Ringer's solution was infused over 15 min.

In group F, Cp was significantly decreased from 2.24 (0.69) [mean (SD)] to 2.07 (0.61) microg/ml and in group E from 2.02 (0.98) to 1.75 (0.51) microg/ml immediately after infusion (P < 0.05). The significant reduction lasted until 30 min in group F, whereas, Cp quickly recovered in group E. Cardiac output was increased only in group F. The dilution ratio demonstrated the prolonged diluting effect in group E and the significant correlation with the rate of decrease in Cp (P < 0.0003, R = 0.21). The BIS value showed no significant change immediately after infusion.

Large volume loading decreased Cp without a significant change in BIS values. The effect of infusion therapy on the depth of anesthesia might be small and usually negligible during propofol anesthesia.