Circulatory and metabolic changes in the brain during induced hypotension--comparison among trimetaphan, glycerin trinitrate and prostaglandin E1

Human middle cerebral artery flow velocity during controlled hypotension combined with hemodilution—transcranial Doppler study

STUDY OBJECTIVE

To evaluate the effects of controlled hypotension combined with hemodilution on human middle cerebral artery flow velocity (Vmca) by transcranial Doppler ultrasonography.

DESIGN

Randomized prospective study.

SETTING

Inpatient surgery at Nagasaki Rosai Hospital.

PATIENTS

Thirty American Society of Anesthesiologists physical status I and II patients scheduled for total hip arthroplasty.

INTERVENTIONS

Anesthesia was maintained with nitrous oxide-oxygen (N(2)O-O(2)) and sevoflurane during normocapnia. Hemodilution was carried out after induction of anesthesia, in which blood was withdrawn then replaced with the same amount of hydroxyethyl starch to achieve a final hematocrit level of 32% (group A = mild hemodilution group, N = 15) or 24% (group B = moderate hemodilution group, N = 15). In both groups, controlled hypotension was induced with prostaglandin E(1) to maintain mean arterial pressure at approximately 55 mm Hg for 80 minutes.

MEASUREMENTS AND MAIN RESULTS

Vmca and blood gas were measured before hemodilution, after hemodilution, 80 minutes after starting hypotension, and 60 minutes after recovery from hypotension. Vmca significantly increased in group A (+122%) and group B (+156%) after each hemodilution. In group B, Vmca was significantly greater than baseline values at 80 minutes after starting hypotension (+135%) and 60 minutes after recovery from hypotension (+140%).

CONCLUSION

The combination of moderate hemodilution, such as hematocrit value of 24%, and prostaglandin E(1)-induced hypotension would not impair middle cerebral artery flow during sevoflurane-N(2)O-O(2) anesthesia during normocapnia.