Autoregulation and vasodilator responses by isoflurane and desflurane in the feline renal vascular bed.

BACKGROUND

Inhalational anesthetics have agent-specific effects on the renal circulation. This study investigated renal vasodilator responses produced by either autoregulation, 0.8% isoflurane (ISO) or 3.5% desflurane (DES).

METHODS

We measured systemic mean arterial pressure (MAP-SYST; axillary artery), renal blood flow (QREN; perivascular ultrasound) and central venous pressure (CVP) in normoventilated cats (n = 8) during basal chloralose anesthesia (control) and after the addition of ISO and DES. Renal mean arterial pressure (MAPREN) was controlled by an aortic clamp. QREN was measured at pre-set-MAPREN levels of 50, 70 and 90 mmHg. Renal vascular resistance (RREN) was derived.

RESULTS

When MAPREN was artificially restrained from 133 +/- 5 mmHg to 90 mmHg during control, RREN decreased by 35% and no significant change in QREN was observed, reflecting an intact autoregulation. RREN levels during ISO or DES at stages with unrestrained MAPREN (95 +/- 6 and 102 +/- 9 mmHg, respectively), were not significantly different from RREN at 90 mmHg during control. When MAPREN was artificially decreased below 90 mmHg, QREN decreased in a similar fashion among control and ISO/DES sequences. The autoregulatory capacity was not significantly different among these sequences. Between 90-70 mmHg, the autoregulatory capacity was reduced and not demonstrable below 70 mmHg.

CONCLUSION

The renal autoregulatory capacity was not attenuated by either ISO or DES. These agents produced equipotent renal vasodilation, which was not more powerful than that produced by autoregulation alone. The renal vasorelaxant effects of ISO and DES may therefore to a substantial extent be attributable to autoregulation.