Measurements of hindlimb blood flow recorded using Doppler ultrasound during administration of vasoactive agents in halothane-anesthetized horses

The purpose of the study was to determine the ability of Doppler ultrasound to detect changes in femoral blood flow during pharmacologic manipulation of arterial blood pressure. Doppler ultrasonography was performed in the fe moral vessels of six halothane-anesthetized horses before and during admini stration of phenylephrine HCl and sodium nitroprusside. The time-averaged m ean velocity and volumetric flow were calculated. The contour of the veloci ty waveform was assessed, and the early diastolic deceleration slope (EDDS) and pulsatility index (PI) were calculated. Administration of phenylephrin e HCl resulted in increased mean aortic blood pressure (MABP) by 40% (29.3- 53.0%). This caused significant decrease in cardiac output (26.8 to 13.5 l/ min), femoral arterial velocity (left artery 7.20 to 4.00 cm/s; right arter y 5.01 to 3.39 cm/s) and volumetric flow (left artery 556 to 221 ml/min; ri ght artery 397 to 193 ml/min) in the femoral vessels and significant increa se in systemic vascular resistance (163 to 433 dyn-s/cm(5)), EDDS (la: 285 to 468: ra: 250 to 481) and PI (la: 9.38 to 20.4; ra 17.1 to 29.1), Adminis tration of sodium nitroprusside resulted in a decreased MABP of 27.2% (22.5 -33%), This increased cardiac output (20.8 to 32.4 L/min), however, no sign ificant changes were observed in femoral blood flow. Despite obvious change s in the waveform contour, no significant change occurred in EDDS or PI. Th ese results suggest that Doppler ultrasound may be useful for measuring fem oral blood flow in anesthetized horses. However, waveform analysis appears to be limited when multiple changes occur in central and peripheral haemody namics.