Cerebrovascular CO 2 reactivity during isoflurane-nitrous oxide anesthesia in patients with chronic renal failure.

PURPOSE: We assessed the cerebrovascular CO2 reactivity (CO2 R) in chronic renal failure (CRF) patients without diabetes mellitus (DM), uncontrolled hypertension, peripheral vascular disease, or neurological disease under isoflurane-nitrous oxide anesthesia.

METHODS: Forty-nine patients undergoing surgery, including 36 CRF patients (30 receiving dialysis and six pre-dialysis patients) and 13 patients without CRF (controls). Middle cerebral artery flow velocity (VMCA) was measured by transcranial Doppler ultrasonography at an end-tidal CO2 of 35 to 45 mmHg. CO2 R was calculated as an absolute value (change in VMCA per mmHg PaCO2 ) and a relative value (absolute CO2 R/baseline VMCA × 100). Factors associated with CO2 R were evaluated simultaneously.

RESULTS: Despite no significant differences in the absolute and relative values of CO2 R between the CRF (mean 2.5 cm/s/mmHg; median 5.0%/mmHg) and control (2.4 cm/s/mmHg; 5.0%/mmHg) groups, blood urea nitrogen (BUN) concentrations in the CRF group correlated inversely with both absolute and relative CO2 R. BUN concentration was higher (mean 72 versus 53 mg/dl, p = 0.006) and relative CO2 R was lower (mean 2.6 versus 5.7%/mmHg, p = 0.011) in patients with pre-dialysis CRF (n = 6) versus CRF patients receiving dialysis (n = 30).

CONCLUSIONS: CO2 R in CRF patients was not significantly different from that in controls. However, in CRF patients with high BUN concentrations, CO2 R might be impaired, leading to reduced cerebrovascular reserve capacity. Because DM is a major cause of CRF and we excluded DM patients, our results might not be applicable to patients with DM-induced CRF.