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[The effects of hemodilution on cerebral hemodynamics and oxygen consumption during nonpulsatile hypothermic
Insights
Mild hemodilution (15% hematocrit) during cardiopulmonary bypass (CPB) safely maintains cerebral blood flow and oxygenation. Increased cerebral blood flow compensates for reduced oxygen-carrying capacity in patients undergoing open heart surgery.
Area of Science:
- Cardiovascular Surgery
- Neuroanesthesia
- Physiology
Context:
- Cardiopulmonary bypass (CPB) is frequently used in open heart surgery.
- Hemodilution is a common practice during CPB, potentially affecting cerebral hemodynamics.
- Understanding the impact of hemodilution on the brain is crucial for patient safety.
Purpose:
- To investigate the effects of hemodilution on cerebral blood flow and oxygen consumption during hypothermic CPB.
- To compare cerebral hemodynamics between high (25%) and low (15%) hematocrit groups during CPB.
Summary:
- 16 patients undergoing elective open heart surgery were divided into high (25%) and low (15%) hematocrit groups during CPB.
- Cerebral blood flow velocity in the middle cerebral artery (VMCA) and jugular venous oxygen tension (PjvbO2) were measured.
- Despite lower hematocrit, the low hematocrit group showed increased VMCA, compensating for oxygen content, with no significant differences in PjvbO2 compared to the high hematocrit group.
Impact:
- Profound hemodilution to 15% hematocrit appears safe during CPB.
- Increased cerebral blood flow can compensate for reduced oxygen content due to hemodilution.
- Findings support the safety of mild hemodilution techniques in cardiac surgery patients.
Abstract:
The effects of hemodilution on cerebral hemodynamics and oxygen consumption during nonpulsatile hypothermic cardiopulmonary bypass (CPB) were investigated in 16 patients undergoing elective open heart surgery under CPB. They were divided into 2 groups; high (25%) (H) and low hematocrit (15%) (L) groups according to the hematocrit values during CPB. Simultaneous measurements of blood flow velocity in the middle cerebral artery (VMCA) and oxygen tension in the jugular venous bulb (PjvbO2) were performed at prebypass, bypass, and post bypass periods. There were no significant differences in nasopharyngeal temperature (NPT), cerebral perfusion pressure, pump flow rate, and PaCO2 between the two groups at any period. VMCA changed in correlation with NPT in both groups, and VMCA in the L group was faster than that in the H group at any period. PjvbO2 increased during aortic cross clamp, and decreased on rewarming in both groups. However, there were no significant differences in VMCA and PjvbO2 between the two groups at any period. These findings suggest that increased cerebral blood flow may compensate the decreased oxygen content due to the hemodilution during CPB. Therefore, the profound hemodilution up to 15% of hematocrit is considered to be a safe technique during CPB.
