The Effects of Hypercapnia and High Flow on Cerebral Metabolism During Cardiopulmonary Bypass

Kang, Do Kyun; Choi, Seok Cheol; Yoon, Young Chul; Choi, Kook Lyeol; Jung, Shin Hyun; Hwang, Yoon Ho; Cho, Kwang Hyun

Abstract

BACKGROUND: Recent studies have demonstrated that cerebral desaturation during rewarming period of CPB was associated with postoperative neurologic dysfunction. The prevention of cerebral desaturation during CPB may reduce the incidences of neurologic and neuropsychological complications. The present study was prospectively undertaken to compare the clinical effects between two strategies (hypercapnic CPB and high flow CPB) to prevent cerebral desaturation for establishing a proper CPB technique. MATERIAL AND METHOD: Thirty-six adult patients scheduled for elective cardiac surgery were randomized into either hypercapnic (PaCO2 45~50 mmHg, n=18) or high flow group (flow rate 2.75 L/m2/min and PaCO2 35~40 mmHg, n=18) during rewarming period of CPB. In each patient, middle cerebral artery blood flow velocity (VMCA), cerebral arteriovenous oxygen content difference (C(a-v)O2), modified cerebral metabolic rate for oxygen (MCMRO2), cerebral oxygen transport rate (TEO2), incidence of cerebral desaturation (internal jugular bulb blood oxygen saturation < or =50%), increased rate of S-100 beta concentration, and arterial and internal jugular bulb blood gas were measured during the five phases of the operation; Pre-CPB, CPB-10 min (steady-state CPB, nasopharyngeal temperature 29~30 degrees C), Rewarm-1 (rewarming phase, nasopharyngeal temperature 33 degrees C), Rewarm-2 (nasopharyngeal temperature 37 degrees C), and CPB-off. Incidence of postoperative delirium and duration were assessed in all patients. All variables were compared between the two groups. RESULT: VMCA (157.88+/-10.87 vs 120.00+/-6.18%, p=0.006), internal jugular bulb O2 saturation (68.01+/-2.75 vs 61.28+/-2.87%, p=0.03) and O2 tension (41.01+/-2.25 vs 32.02+/-1.67 mmHg, p=0.03), and TEO2 (110.84+/-7.41 vs 81.15+/-8.11%, p=0.003) at rewarming periods were higher in the hypercapnic group than in the high flow group. C(a-v)O2 (4.0+/-0.30 vs 4.84+/-0.38 mg/dL, p=0.04), COE (0.36+/-0.03 vs 0.42+/-0.03, p=0.04), increased rate of S-100 beta(391.67+/-23.40 vs 940.0+/-17.02%, p=0.003), and incidence of cerebral desaturation (2 vs 4 patients, p= 0.04) at rewarming periods, and duration of postoperative delirium (18 vs 34 hr, p=0.02) were low in the hypercapnic group compared to the high flow group.
CONCLUSION
These results indicate that hypercapnic CPB may provide relatively diminished cerebral injury and beneficial effects for cerebral metabolism relatively compared to high flow CPB.