Cerebrovascular CO2 reactivity during anesthesia in patients with diabetes mellitus and peripheral vascular disease

Diabetes mellitus (DM) and systemic atherosclerosis are risk factors for stroke. Although the origins of increased risk are complex, one possibility is that cerebrovascular reactivity is impaired and does not allow the brain to compensate for aberrations in physiology. The current study tested this issue by evaluating mean blood flow velocity of the middle cerebral artery (Vmca) and carbon dioxide reactivity during anesthesia in patients with DM and peripheral vascular disease (PVD).

Fifty-two patients were observed: 20 patients with DM (the DM group), 12 patients with PVD (the PVD group), and 20 patients classified as American Society of Anesthesiologists physical status 1 or 2 (the control group). The Vmca was measured using transcranial Doppler ultrasonography during isoflurane-nitrous oxide anesthesia. After measuring baseline Vmca at a partial pressure of carbon dioxide in arterial blood (PaCO2) of 37.7 +/- 4.5 mmHg (mean +/- SD), measurements were repeated at a PaCO of 44.2 +/- 3.8 mmHg, and the carbon dioxide reactivity (absolute value: cm x s(-1) x mmHg(-1); relative value: percentage of baseline Vmca/mmHg) was calculated.

The baseline Vmca of the DM group (51 +/- 12 cm/s) was significantly greater than those of the control group (42 +/- 6 cm/s) and the PVD group (42 +/- 13 cm/s). The absolute and relative values of carbon dioxide reactivity in the DM group (3.1 +/- 1.3 cm x s(-1) x mmHg(-1); 6.3 +/- 2.4%/mmHg) were significantly greater than or equivalent to those of the control group (2.3 +/- 0.8 cm x s(-1) x mmHg(-1); 5.3 +/- 1.7%/mmHg), respectively. In the PVD group, the baseline Vmca was equivalent to the control group, but the carbon dioxide reactivity (1.1 +/- 0.5 cm x s(-1) x mmHg(-1) 2.8 +/- 1.2%/mmHg) was significantly less.

The patients with DM have increased baseline cerebral blood flow velocity and normal carbon dioxide reactivity during anesthesia. The patients with PVD have decreased carbon dioxide reactivity, but baseline flow velocity is maintained.