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 IS0 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 13325 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 IS0 or DES at stages with unrestrained MAPREN (9526 and 10229 mmHg, respectively), were not significantly different from RREN at 90 mmHg during control. When MAPREN was artificially decreased below 90 mmHg, QMN 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 IS0 or DES. These agents produced equipotent renal vasodilation, which was not more powerful than that produced by autoregulation alone. The renal vasorelaxant effects of IS0 and DES may therefore to a substantial extent be attributable to autoregulation.